tag:blogger.com,1999:blog-1706822422194259832024-03-13T08:15:22.142-06:00Flow Science BlogFollow the Flow Science blog to receive the latest news and developments for our state-of-the-art CFD products: FLOW-3D, FLOW-3D Cast and FLOW-3D/MP.Anonymoushttp://www.blogger.com/profile/16812132416403361030noreply@blogger.comBlogger22125tag:blogger.com,1999:blog-170682242219425983.post-28426788592272175982016-05-18T10:12:00.002-06:002016-05-19T08:47:11.278-06:00Non-Inertial Reference Frame Visualization<div class="MsoNormal">
Adapting non-inertial reference frame model results to
enable visualization from a stationary frame of reference is a nifty new
feature coming in the upcoming releases of FlowSight<sup><span style="font-size: xx-small;">TM</span></sup> for<b> <i>FLOW-3D
</i>Cast</b> v4.2 (next month) and <i><b>FLOW-3D</b></i> v11.2 (late 2016). This brief note describes
this feature and gives a couple examples. <o:p></o:p></div>
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Many real-world processes happen
in accelerating or non-inertial reference frames. Examples of such processes
include sloshing of fuel in satellite tanks and centrifugal casting. <i><b>FLOW-3D</b></i>
has long incorporated in its solver the ability to model fluid and solid motion
using a non-inertial reference frame model (NIRF), but lacked the ability to
visualize the motion depicted from a stationary frame of reference. After the
introduction of the General Moving Objects (GMO) model, users could have their cake
and eat it, too: modeling the coupled fluid-solid motion and visualizing the
resulting motion in a realistic way. Unfortunately, the GMO model comes with a
price in terms of computational time. While the NIRF may be more computationally
convenient for solving large problems, the inability to analyze the solution
from a stationary frame of reference frustrated many users. FlowSight’s
recent development makes it easy to apply the NIRF feature to all parts of a
case, such as iso-surfaces, clips and streamlines, allowing the user to view
the rigid body motion and the fluid flow from a stationary reference frame. <o:p></o:p></div>
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NIRF motion can be captured in
animations that are created by FlowSight. The user can activate only one or
both of the possible motions – rotation and translation. The scale of the translational
motion can be adjusted for better visualization in cases where the translations
are huge, like aerospace applications where the moving body can translate for
miles.<o:p></o:p></div>
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Below are the two animations with
NIRF motions for tilt pour and centrifugal casting.<o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/vvBdedoXG58/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/vvBdedoXG58?feature=player_embedded" width="320"></iframe></div>
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<a href="https://www.youtube.com/watch?v=vvBdedoXG58&feature=youtu.be" target="_blank">Watch YouTube video here</a></div>
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Tilt pour casting with NIRF
motion on the left and stationary motion on the right<o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/hvjz4AUJeQI/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/hvjz4AUJeQI?feature=player_embedded" width="320"></iframe></div>
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<a href="https://www.youtube.com/watch?v=hvjz4AUJeQI&feature=youtu.be" target="_blank">Watch YouTube video here</a></div>
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Centrifugal casting with NIRF
motion on the top and stationary motion on the bottom left<o:p></o:p></div>
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In the upcoming few blogs, I will
discuss the featured developments of <b><i>FLOW-3D</i> Cast</b> v4.2.<o:p></o:p></div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1tag:blogger.com,1999:blog-170682242219425983.post-31142591461998900232016-04-26T11:12:00.002-06:002016-04-26T11:12:44.658-06:00Microfluidic Circuit - Pneumatic Latching Valve<div class="MsoNormal">
In this final post in the series of Flow Science’s 35th
anniversary simulation contest, I will talk about a case study simulating a
part of a microfluidic circuit – pneumatic latching valve. These devices are a relatively
new industry application that Flow Science is exploring, in the context of a
broader exploration of the use of CFD in microfluidics applications, and
results have been very encouraging.<o:p></o:p></div>
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There have been recent developments in the field of
microfluidic circuit devices, also called <i>Lab-on-a chip</i>. These circuits are
used in biological sciences to transport matter from one place to another, or to
perform hundreds of assays in parallel, based on certain logic. Hence these
circuits are also known as microfluidic logic circuits. Analogous to an
electronic circuit, the fluid runs through channels and is driven by pressure
differentials (as opposed to the traditional potential/voltage differentials in
an electronic circuit). Combinations of valves and the application of correct pressures
forms logic gates like AND, OR, XNOR, etc. Eventually the combination of these
logic gates forms a microprocessor chip that can be used as a positive edge
detector, toggle, clock, demultiplexer, etc. One such example of a 4-bit
microfluidic <a href="https://en.wikipedia.org/wiki/Multiplexer" target="_blank">demultiplexer</a> is shown in Figure 1. The demultiplexer has 16
(4-bit implies 16 possible combinations or outputs) pneumatic valves that work in parallel to
attain a desired output. Therefore, understanding these latching valves is
central to the correct operation of the circuit. CFD simulations can play a
vital role in reducing costs by testing the design of these types of circuits
before fabrication.<br />
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<a href="https://1.bp.blogspot.com/-eRbOpEmwXSo/Vx9_WxhpD7I/AAAAAAAAARw/r_JQ7ine0po543v8ZxX221GDcDIf8Y-lwCLcB/s1600/fig1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="329" src="https://1.bp.blogspot.com/-eRbOpEmwXSo/Vx9_WxhpD7I/AAAAAAAAARw/r_JQ7ine0po543v8ZxX221GDcDIf8Y-lwCLcB/s640/fig1.png" width="640" /></a></div>
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Figure 1. A microfluidic 4-bit demultiplexer for routing
pressures and vacuum pulses. Inside the red box is a single latching valve that
will be simulated in <i><b>FLOW-3D</b></i>.<o:p></o:p></div>
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<span style="font-size: large;">Pneumatic Latching valve</span><o:p></o:p></div>
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A latching valve, as the name indicates, holds (latches) a
valve in open/closed position without continuous application of external
pressure. Latching valves are used for energy efficiency and are analogous to
electrical solenoid valves. Details of the working of a latching valve system
are shown in Figure 2. Stages 1-7 show how the system changes from a closed
state to a latched open state, and then back to a closed state again. An open
state is one where the fluid can flow through the valve, and in a closed state
fluid cannot flow through the valve.<o:p></o:p></div>
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<a href="https://3.bp.blogspot.com/-oh9HDoMd_AA/Vx9_401TesI/AAAAAAAAAR4/y5-vI3GoZUMm36P5KeFSUy4311K_WUDQACLcB/s1600/fig2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="190" src="https://3.bp.blogspot.com/-oh9HDoMd_AA/Vx9_401TesI/AAAAAAAAAR4/y5-vI3GoZUMm36P5KeFSUy4311K_WUDQACLcB/s640/fig2.png" width="640" /></a></div>
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Figure 2. The 7 stages of latching valve system as it
evolves from closed to latched open to closed again. NC means not connected*<o:p></o:p></div>
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<span style="font-size: large;">Latching valve setup in <b><i>FLOW-3D</i></b></span><o:p></o:p></div>
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The latching system primarily comprises of 3 types of
features – valves, inlet channels and control channels. Valves and inlet
channels are made from solid components in <b><i>FLOW-3D</i></b>, while the control channels
are directly represented through meshes (seen in black in the figure below). Each
valve has an inlet channel and a control channel except for valve 3. Valve 3
has an inlet channel and two output channels. The inlet channel brings in fluid and the control
channel allows the pressure to be manually controlled externally by the
user/designer. Setup of the entire latching valve system in <b><i>FLOW-3D</i></b> is shown in
Figure 3. <o:p></o:p></div>
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<a href="https://1.bp.blogspot.com/-297kTqud4Wo/Vx-AKEuxWYI/AAAAAAAAAR8/YH3wuvDyf_EdQHnO_GFAXplDsmpoqSRMwCLcB/s1600/fig3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="346" src="https://1.bp.blogspot.com/-297kTqud4Wo/Vx-AKEuxWYI/AAAAAAAAAR8/YH3wuvDyf_EdQHnO_GFAXplDsmpoqSRMwCLcB/s400/fig3.png" width="400" /></a></div>
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Figure 3. Setup of the latching valve system (currently in
stage-7) in <b><i>FLOW-3D</i></b>. <o:p></o:p></div>
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<span style="font-size: large;">Time dependent pressure boundary conditions</span><o:p></o:p></div>
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Being pneumatic valves, the functioning of the latching
system is totally dependent on the application of pressures at the boundaries
of the system. The inlet boundary condition is a time-varying pressure boundary
condition with vacuum (below atmospheric pressure) and pressure pulses (Figure 4).
The control channel for valve 1 has a pressure pulse twice the atmospheric
pressure (Figure 5). The control channel for valve 2 is maintained at
atmospheric pressure. The outlet channel is at atmospheric pressure. Notice
that eventually all the pressures fall back to atmospheric pressure, which means
that no additional external pressure is required by the latching system to stay
in its state (closed in this case).<o:p></o:p></div>
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<a href="https://1.bp.blogspot.com/-hZF-tIlaJwk/Vx-BD3ZU0dI/AAAAAAAAASM/nVPAR5jqu6M8c3OKFhusZNPdFq1ypgl8QCLcB/s1600/fig4.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="205" src="https://1.bp.blogspot.com/-hZF-tIlaJwk/Vx-BD3ZU0dI/AAAAAAAAASM/nVPAR5jqu6M8c3OKFhusZNPdFq1ypgl8QCLcB/s400/fig4.png" width="400" /></a></div>
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Figure 4. Time-varying<span style="font-family: inherit;"> pressur</span>e boundary condition for the inlet
channel to Valve 1.<o:p></o:p></div>
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<a href="https://2.bp.blogspot.com/-1VkQDDEe4No/Vx-BD0fznmI/AAAAAAAAASI/RcHZ0C078a0KANDlVfLG3r1R5gxfgeWpwCKgB/s1600/fig5.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="233" src="https://2.bp.blogspot.com/-1VkQDDEe4No/Vx-BD0fznmI/AAAAAAAAASI/RcHZ0C078a0KANDlVfLG3r1R5gxfgeWpwCKgB/s400/fig5.png" width="400" /></a></div>
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<span style="line-height: 115%;"><span style="font-family: inherit;">Figure
5. Time-varying pressure boundary condition for the control channel of Valve 1.</span></span></div>
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<span style="font-size: large;">Simulation results</span><o:p></o:p></div>
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Stages 3-7 were simulated using <b><i>FLOW-3D</i></b> and the results post-processed in <a href="https://www.flow3d.com/flowsight" target="_blank">FlowSight</a>. The latching mechanism has been accurately
simulated, as shown in the reference paper, by starting at the open stage
(stage 3) and ending at the closed (stage 7) stage. Pressure pulses in the inlet
channel are 500 Pa, positive or negative and the pulses span over 50
milliseconds. Water is used as the fluid, and compressibility of water is used
to allow some propagation time for the pressures in the system. Opening and
closing of the individual valves can be seen in top three viewports of the
animation below. The simulation below shows the evolution of the system from
stages 3-7.<o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/585FBk6rAjU/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/585FBk6rAjU?feature=player_embedded" width="320"></iframe></div>
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<a href="https://www.youtube.com/watch?v=585FBk6rAjU&feature=youtu.be" target="_blank">Watch on YouTube</a></div>
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Simulation of a pneumatic latching valve used in
microfluidic demultiplexer. The animation starts at stage 3 – the open
stage, and finally evolves to stage 7 – the closed stage.<o:p></o:p></div>
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An accurate simulation of the working of the pneumatic latching
valve can help designers reduce the cost of trials and errors in the design
phase, ensuring that the best design goes to the fabrication stage. Notice that
in the final stage, the valves are in a closed state and would remain so for a
certain period of time, in spite of the absence of external pressures through control channels.<o:p></o:p></div>
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In the upcoming post I will talk about our new optimization and parametric study capabilities using <a href="https://www.caeses.com/" target="_blank">CAESES</a>, an optimization software by Friendship Systems.<o:p></o:p></div>
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<i>*Reference: William H. Grover, Robin H. C. Ivester, Eric C.
Jensen, Richard A. Mathies, Development and multiplexed control of latching
pneumatic valves using microfluidic logical structures, 2006</i><o:p></o:p></div>
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Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0Santa Fe, NM, USA35.6869752 -105.9377989999999835.4806132 -106.26052249999998 35.8933372 -105.61507549999999tag:blogger.com,1999:blog-170682242219425983.post-38172504521350361502016-04-05T09:18:00.001-06:002016-04-15T10:51:40.111-06:00Simulating Pelton Turbines<div class="MsoNormal">
In this third post of the Flow Science simulations contest blog series, I will be talking about the simulation of a Pelton turbine using <i><b>FLOW-3D</b></i>. This work was done by our associate in Italy, <a href="http://www.xceng.com/en/">XC Engineering</a>.<o:p></o:p></div>
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Pelton turbines are used for electricity generation in hydraulic power plants. They are suitable for operation when water energy is available at high head and low flow rate. In a Pelton turbine, the energy extracted from the kinetic energy of the water is used for the rotation of the impeller. Water, coming from an upper basin, is accelerated and ejected from the surface of the Pelton paddles. Paddle geometry is designed to absorb as much kinetic energy of the fluid as possible for the rotation of the paddle. The rotational speed of the turbine is then converted to electric power using an electricity generator with a rotor and a stator. The aim of this study is to analyze the initial transient of the turbine, where water impacts the Pelton’s paddle at around 120 m/s, providing torque and angular acceleration.</div>
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<span style="font-size: large;">Modelling a Pelton turbine in <b><i>FLOW-3D</i></b></span><o:p></o:p></div>
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The geometry used in the simulation is shown below. All geometries and data used in the simulation are rea<span style="font-family: inherit;">listic and in line with the real phenomena: the wheel geometry has a real shape and mass property, the fluid is water with a reasonable speed, and the nozzle contains a Doble valve (not visible here), used in real turbines to adjust the flow rate of the water.</span></div>
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<a href="https://3.bp.blogspot.com/-KTYGezR0YOM/VwLAS5ptRwI/AAAAAAAAAQ8/iUbkyjwVFFkZKKRgOGeALbfo_j_On1IWQ/s1600/geometry.png" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="360" src="https://3.bp.blogspot.com/-KTYGezR0YOM/VwLAS5ptRwI/AAAAAAAAAQ8/iUbkyjwVFFkZKKRgOGeALbfo_j_On1IWQ/s640/geometry.png" width="640" /></a></div>
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<span style="line-height: 115%;"><span style="font-family: inherit;">Pelton turbine (red), inlet (blue), inner casing (yellow), outer casing (pink) and probes (grey spheres)</span></span></div>
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<span style="font-family: inherit; font-size: large;"><span style="line-height: 16.8667px;">Moving <span style="font-family: inherit;">o</span>bjects</span></span></div>
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Many kinematics are involved in this simulation, which makes <i><b>FLOW-3D</b></i> a very good choice for this study. The motion of an object can have all six degrees of freedom (3 rotational + 3 translational), or it can be constrained in a prescribed way. For this simulation, the Pelton turbine is allowed to have only fixed x-axis coupled rotation while staying constrained in every other direction (both rotational and translational). The other components do not move.<o:p></o:p></div>
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<span style="font-size: large;">Gravity and non-inertial reference frame</span><o:p></o:p></div>
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The figure below shows that the acceleration due to gravity is not inclined to any of the axes. This is because in the original CAD geometry, the axes are defined relative to the inlet such that inlet is parallel to the y-axis and perpendicular to the z-axis. However, for this simulation, gravity has to be in the direction shown below (pink vector) and not along any of the axes. <i><b>FLOW-3D</b></i>’s gravity and non-inertial reference frame model allows users to overcome such difficulties. Instead of defining a value of gravity (G) along one axis, the user can define multiple values of accelerations along multiple axes such that the net resultant is equal to G and is along the desired direction. The figure below highlights how this was done in <i><b>FLOW-3D</b></i>. Acceleration in the –y direction was set to 3.35 m<sup>2</sup>/s and in the –z direction to 9.209 m<sup>2</sup>/s such that the resultant is 9.8 m<sup>2</sup>/s in the desired direction.<o:p></o:p></div>
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<a href="https://2.bp.blogspot.com/-bBn2UBZ2QC8/VwLA_fDySMI/AAAAAAAAARE/GskgxSGlqEAbWnFokq4504c_jY84sqwxg/s1600/fig2.png" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="352" src="https://2.bp.blogspot.com/-bBn2UBZ2QC8/VwLA_fDySMI/AAAAAAAAARE/GskgxSGlqEAbWnFokq4504c_jY84sqwxg/s640/fig2.png" width="640" /></a></div>
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Net resultant gravity with correct magnitude and desired direction based on prescribed acceleration vectors in –y and –z directions. <i>(Vectors are not to scale. Directions of vectors, however, are exact)</i><o:p></o:p></div>
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<span style="font-size: large;">Results</span></div>
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For Pelton turbines, it is known that the top efficiency is reached when the peripheral speed of the wheel is about half the speed of the water at the nozzle. For this purpose, a probe was located at the center of the nozzle to monitor the fluid speed, while another probe was attached to a paddle’s wheel, to track the peripheral speed. The two quantities are shown in the animation below. <o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/zwiFp3uQb5g/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/zwiFp3uQb5g?feature=player_embedded" width="320"></iframe></div>
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<a href="https://www.youtube.com/watch?v=zwiFp3uQb5g&feature=youtu.be" target="_blank">Watch YouTube video here</a></div>
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Pelton turbine simulation showing the fluid velocity (blue) plot and the corresponding peripheral velocity (red). Also shown is the sectional view highlighting the coupled motion of paddles and water.<o:p></o:p></div>
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The plots above show that by the end of the simulation, the peripheral speed is asymptotically becoming steady at more than half the velocity of the impacting fluid. Half of the impacting fluid velocity is 60m/s, but the peripheral speed reaches 75m/s by the end of the simulation. This difference (which is desirable) arises because currently the turbine is not receiving any rotational resistance from a rotor. A higher peripheral speed ensures higher kinetic energy to overcome losses in case a rotor was connected to the turbine. The final goal is to adjust, for each water velocity exiting from the nozzle, the resistance from a rotor in order to reduce the rotational speed at its maximum efficiency point and extract the energy.<o:p></o:p></div>
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Understanding the results of this study was made significantly easier by the advanced post-processing features of <a href="https://www.flow3d.com/flowsight" target="_blank">FlowSight</a><sup>TM</sup>, such as alpha transparency based on variable value, moving camera, fine tuning of light and reflections, multi-plots and multi-viewport visualization. One of the many such post-processed results is shown below to highlight the moving camera and slow motion recording of FlowSight.<o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/bCpZ737mOWE/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/bCpZ737mOWE?feature=player_embedded" width="320"></iframe></div>
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<a href="https://www.youtube.com/watch?v=bCpZ737mOWE&feature=youtu.be" target="_blank">Watch YouTube video here</a></div>
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Pelton turbine simulation showing slow motion and moving camera animation<o:p></o:p></div>
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<i><b>FLOW-3D</b></i>’s robust moving objects model backed by multi-directional acceleration prescription and state-of-the-art post-processor, FlowSight, yields good results for this case study. In the upcoming post, I will be talking about another Flow Science contest entry based on a relatively new field of research, microfluidic circuits.</div>
<o:p></o:p>Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1Santa Fe, NM, USA35.6869752 -105.9377989999999835.4806132 -106.26052249999998 35.8933372 -105.61507549999999tag:blogger.com,1999:blog-170682242219425983.post-15200737933914451722016-03-22T11:43:00.000-06:002016-03-22T11:43:23.174-06:00Turbulent Dispersion of Environmental Discharges<div class="separator" style="clear: both; text-align: left;">
<span style="font-family: inherit;">Continuing the blog series on Flow Science’s 35</span><sup style="font-family: inherit;">th</sup><span style="font-family: inherit;">
anniversary contest, I will cover the case study from the winner
of the contest, Daniel Valero Huerta from </span><a href="http://www.hes.fh-aachen.de/" style="font-family: inherit;">FH
Aachen University of Applied Sciences</a><span style="font-family: inherit;"> in Germany. His research focuses on
understanding the dispersion of contaminants/discharges in rivers and
estuaries. In this research, </span><b style="font-family: inherit;"><i>FLOW-3D</i></b><span style="font-family: inherit;"> has been extensively used as
the computational model for studying the turbulent dispersion of the
discharges.</span></div>
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Environmental discharges and outfall structures have been
traditionally designed by means of complex, cost-intensive and time-consuming
experimental studies. Models based on an integral approach are commonly
employed despite their limitations, but contaminant re-entrainment or
strong adverse discharges fall outside the hypothesis of such models. Thus,
using a full 3D model for contaminant dispersion may improve knowledge on the real
contaminant dispersion in rivers and estuaries. Similarly, bounded jets can be
modeled and different diffusor locations can be tested in order to improve the
overall environmental water quality and biotic conditions.<o:p></o:p></div>
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<span style="font-size: large;">Relevant
physics and the case study</span><b><o:p></o:p></b></div>
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In this study, a jet discharge was modeled both
experimentally and numerically. Then, an estimation of the turbulent dispersion
in the shear region was obtained. For the turbulence modeling, the Renormalized
Group (RNG) model was employed together with the TruVOF method for tracking the
free surface. A monotonicity-preserving, second-order scheme was employed for
contaminant advection ensuring proper modeling of turbulent transport. <i><b>FLOW-3D</b></i>
is a very good choice for the numerical modeling of such engineering problems
because it offers a comprehensive turbulence modeling suite and accurately
estimates the free surface. Another advantage of <i><b>FLOW-3D</b></i> is the ability
to use a one-fluid approach because modeling air (a two-fluid problem) is not important
for river contaminant transport problems for practical applications. One-fluid
modeling is a more natural, and efficient approach for hydraulic problems. Figure
1 shows a snapshot of the simulation results.<o:p></o:p></div>
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<a href="https://1.bp.blogspot.com/-nfWLM-P7P0k/VvFo9nFF_MI/AAAAAAAAAQc/9Fzzl8oMN2YOj99kfdayo6gc0rRBQBFxA/s1600/Compound%2Bview%2BII.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="432" src="https://1.bp.blogspot.com/-nfWLM-P7P0k/VvFo9nFF_MI/AAAAAAAAAQc/9Fzzl8oMN2YOj99kfdayo6gc0rRBQBFxA/s640/Compound%2Bview%2BII.png" width="640" /></a></div>
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Figure 1. Top view (top) and side view (bottom) showing the
discharge ejected from an outfall. Complex flow patterns are seen along with
circulation zones between groins (pink blocks). </div>
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<o:p></o:p></div>
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<u>Turbulence modeling</u><o:p></o:p></div>
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<i><b>FLOW-3D</b></i> offers a comprehensive set of turbulence models.
They can be broadly divided into two categories – Reynold’s Averaged Navier
Stokes (RANS) models and Large Eddy Simulation (LES) models. As the name
suggests, RANS models average out the fluctuating quantities in the governing
equations. LES models, on the other hand, solve for the turbulent motions at
scales resolved by the mesh. RANS models are good for understanding the average
behavior of a flow over a period of time, while LES models are used to describe
individual experiments or significant transient behavior. For this study, the RNG
model, which falls into the category of RANS type models, was used. RNG is an
improved k-ԑ model, with coefficients determined through rigorous statistical
analysis. Other options that could have been used as RANS models are the classical
k-ԑ model or the Wilcox k-ω model. RNG was chosen because it is typically good
for transitional flows.</div>
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<u>Free surface tracking<o:p></o:p></u></div>
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<b><i>FLOW-3D<span class="apple-converted-space"> </span></i></b>uses an enhanced variant of Volume-of-Fluid (VOF) technique called
<b>TruVOF</b>®. <b>TruVOF</b> provides a natural way to capture free surfaces and their
evolution with great efficiency. More details on the free surface fluid flow
can be found<span class="apple-converted-space"> </span><a href="https://www.flow3d.com/home/resources/cfd-101/free-surface-fluid-flow">here</a>.<o:p></o:p></div>
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<u>Momentum advection<o:p></o:p></u></div>
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<b><i>FLOW-3D</i></b> offers three options for momentum advection based on
the order of accuracy desired. The first order is the simplest and fastest
method. The second order is preferred for minimizing numerical dissipation. The
third option is called second order monotonicity preserving. This method is
second order accurate in space and first order accurate in time. It was used
for this study to properly model the turbulent transport of the contaminant. Preservation
of monotonicity ensures that the quantity gradients are limited to avoid
non-physical oscillations. <o:p></o:p></div>
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<span style="font-size: large;">Simulation results</span><b><o:p></o:p></b></div>
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The animation below shows that the upstream channel flow
deforms the jet, pushing it to the side groin fields where re-circulation takes
place.<br />
<o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/6mYWLrJaP5M/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/6mYWLrJaP5M?feature=player_embedded" width="320"></iframe></div>
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Simulation showing the deformation of the jet and circulation zones in two different views.</div>
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<a href="https://www.youtube.com/watch?v=6mYWLrJaP5M" target="_blank">Watch the YouTube video</a></div>
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This bounded jet shows unsteady behavior even for the
statistically steady final solution. For ease of visualization, two
iso-concentration surfaces are shown: <!--[if gte msEquation 12]><m:oMath><i
style='mso-bidi-font-style:normal'><span style='font-family:"Cambria Math","serif"'><m:r>C</m:r><m:r>=0.01</m:r></span></i></m:oMath><![endif]--><!--[if !msEquation]--><span style="font-family: "calibri" , "sans-serif"; font-size: 11.0pt; line-height: 115%; position: relative; top: 4.5pt;"><!--[if gte vml 1]><v:shapetype
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<v:imagedata src="file:///C:\Users\adwaith\AppData\Local\Temp\msohtmlclip1\01\clip_image001.png"
o:title="" chromakey="white"/>
</v:shape><![endif]--><!--[if !vml]--><!--[endif]--></span><!--[endif]--> <i>C=0.01 </i>(red) and <!--[if gte msEquation 12]><m:oMath><i
style='mso-bidi-font-style:normal'><span style='font-family:"Cambria Math","serif"'><m:r>C</m:r><m:r>=0.001</m:r></span></i></m:oMath><![endif]--><!--[if !msEquation]--><span style="font-family: "calibri" , "sans-serif"; font-size: 11.0pt; line-height: 115%; position: relative; top: 4.5pt;"><!--[if gte vml 1]><v:shape
id="_x0000_i1025" type="#_x0000_t75" style='width:48pt;height:15pt'>
<v:imagedata src="file:///C:\Users\adwaith\AppData\Local\Temp\msohtmlclip1\01\clip_image003.png"
o:title="" chromakey="white"/>
</v:shape><![endif]--><!--[if !vml]--><!--[endif]--></span><!--[endif]--> <i>C=0.001 </i>(grey), which act as a representative envelope
of the contaminant reach. The grid space was set to 5 cm for visual comparison
with the experimental results (see animations below).<o:p></o:p></div>
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<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/86zQDYjeR08/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/86zQDYjeR08?feature=player_embedded" width="320"></iframe></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.youtube.com/watch?v=86zQDYjeR08" target="_blank">Watch the YouTube video</a></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/nS21Ni4tQOs/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/nS21Ni4tQOs?feature=player_embedded" width="320"></iframe><br />
<a href="https://www.youtube.com/watch?v=nS21Ni4tQOs" target="_blank">Watch the YouTube video</a></div>
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Animations showing a visual comparison of experimental results (top) and numerical results (bottom)</div>
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We see that <i><b>FLOW-3D</b></i> captured all the relevant physics
important in modeling turbulent dispersion of environmental discharges. The
results match the experiment to a good degree of accuracy both visually and
numerically.</div>
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In my next blog, I will be talking about another entry from
our 35th anniversary simulation contest, which focuses on modeling Pelton turbines.<o:p></o:p></div>
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Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1Santa Fe, NM, USA35.6869752 -105.9377989999999835.4806132 -106.26052249999998 35.8933372 -105.61507549999999tag:blogger.com,1999:blog-170682242219425983.post-60626198039220106712016-03-08T08:41:00.000-07:002016-03-08T08:41:58.043-07:00Dynamic Response of a Constrained Floating Structure<div class="MsoNormal" style="text-align: center;">
<i>This is the first in a series of blog posts in which I feature some of the entries for Flow Science's 35th anniversary contest.</i></div>
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Floating structures on an ocean surface, restrained by mooring ropes, are a common sight in the oil and gas industry. Understanding the dynamic response of these structures in the presence of ocean waves is crucial for their structural design. Additionally, each structure is typically made of multiple elements (sub-structures) that interact with each other and the waves. The problem of understanding the dynamic response of a floating structure becomes challenging due to the complex dynamics of the system. A good CFD model should be able to accurately calculate the dynamic response of the floating structure with all of its complex variables in place. In this article, I will talk about the dynamic response of a floating structure made of 3 elements hinged together, followed by a presentation of <b><i>FLOW-3D</i></b> simulation results. <b><i>FLOW-3D </i></b>can simulate moving objects, generate desired wave types, calculate very accurate free surfaces, and has a robust mooring lines model. All these features make <b><i>FLOW-3D </i></b>an excellent tool for estimating the dynamic response of constrained floating structures.</div>
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<span style="font-size: large;">Details of the floating structure</span><b><o:p></o:p></b></div>
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Figure 1 (a) shows the details of the floating structure with its 3 elements. The blue and the yellow elements float on the ocean surface, while the red element is submerged. The 3 elements are connected via axial hinge support. The relative motion of the elements is governed by the motion constraints from the axial hinge support, which allows rotational motion along the longitudinal axis of the hinge.<o:p></o:p></div>
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<a href="https://3.bp.blogspot.com/-Z91QJwzUGeQ/Vt3AuexcD0I/AAAAAAAAAPg/m-6iwWYItuw/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="305" src="https://3.bp.blogspot.com/-Z91QJwzUGeQ/Vt3AuexcD0I/AAAAAAAAAPg/m-6iwWYItuw/s400/fig1.jpg" width="400" /></a></div>
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Figure 1 (a) Details of the floating structure with its 3 elements colored in blue, yellow and red. </div>
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<a href="https://1.bp.blogspot.com/-YxeGRmmIpuM/Vt3AuRg8DnI/AAAAAAAAAPc/YgzUYetQsrg/s1600/fig-b.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="270" src="https://1.bp.blogspot.com/-YxeGRmmIpuM/Vt3AuRg8DnI/AAAAAAAAAPc/YgzUYetQsrg/s400/fig-b.jpg" width="400" /></a></div>
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<span style="text-align: center;"> Figure 1 </span><span style="text-align: center;">(b) Floating structure relative to the ocean floor and connected to the ocean bottom with a mooring/catenary rope.</span></div>
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The model setup of the system is shown in Figure 1 (b). The floating structure is shown in the context of the ocean surface. Also, the red element is tied to the bottom floor using a mooring rope. A wave train is applied at the left boundary.<o:p></o:p></div>
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<span style="font-size: large;">Physics and Simulation</span><b><o:p></o:p></b></div>
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As discussed earlier, <b><i>FLOW-3D </i></b>is a natural choice to model such scenarios. In the following sections, I will discuss the details of the important physics involved and <b><i>FLOW-3D</i></b>‘s ability to simulate them.</div>
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<u>Moving objects</u></div>
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<b><i>FLOW-3D</i></b>’s moving and simple deforming objects<i> </i>model allows the user to prescribe a type of motion to the elements in a structure. Users can constrain the motion of elements in a certain direction or let the system evolve in a completely coupled way. In this example, motion is constrained in the direction perpendicular to the plane of paper. However, in every other direction, rotations and translations are set to evolve per coupled forces from other elements and the fluid.</div>
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<u>Waves </u></div>
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Users can set a particular type of wave train in <b><i>FLOW-3D </i></b>as a boundary condition. Available wave types are <i>Linear, Stokes, Stokes and Cnoidal, Solitary and Random </i>waves. Each of these wave types can be fully defined by specifying wave height, mean fluid depth, wavelength/wave period, and current velocities. <i>Random </i>waves, however, are defined based on a power/energy spectrum and can be allowed to evolve based on the wind speed. In this example, <i>Stokes and Cnoidal </i>waves were used with a wave height of 6m, mean fluid depth of 50m and wave period of 6s. The current velocity is unidirectional from left to right and is set to 0.25m/s. Figure 2 shows the definition of a <i>Stokes and Cnoidal </i>wave.<br />
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<o:p></o:p></div>
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<a href="https://1.bp.blogspot.com/-1zj2LCRKMUQ/Vt3AuTDpcEI/AAAAAAAAAPY/ZKx76ZFooSw/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="297" src="https://1.bp.blogspot.com/-1zj2LCRKMUQ/Vt3AuTDpcEI/AAAAAAAAAPY/ZKx76ZFooSw/s400/fig2.jpg" width="400" /></a></div>
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Figure 2. <i>Stokes and Cnoidal </i>wave definition from <b><i>FLOW-3D</i></b>.</div>
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<u>Free Surface estimation</u></div>
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<b><i>FLOW-3D </i></b>uses an enhanced variant of Volume-of-Fluid (VOF) technique called TruVOF®. TruVOF provides a natural way to capture free surfaces and their evolution with great efficiency. More details on the free surface fluid flow can be found <a href="https://www.flow3d.com/home/resources/cfd-101/free-surface-fluid-flow">here</a>.</div>
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<u>Mooring lines</u></div>
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<b><i>FLOW-3D</i></b>’s <i>Mooring Lines</i> model provides an effective, flexible and robust implementation to accurately simulate the transient dynamic response of floating structures in moored configurations. In addition to basic parameters like free length, linear density, material density and diameter, advanced options such as drag coefficients in normal and tangential directions, and deep water behavior of mooring lines can be set. In this example, a mooring line with a free length of 28m, diameter of 0.2m and a tangential drag coefficient of 0.3 is used. A spring coefficient of 10 <sup>6</sup> N/m is provided to imitate the slacking and extension behavior of a rope.</div>
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<span style="font-size: large;">Simulation results</span><b><o:p></o:p></b></div>
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The animation below shows the simulation results from <b><i>FLOW-3D</i></b>, post-processed in <a href="https://www.flow3d.com/flowsight">FlowSight<sup>TM</sup></a>. The animation captures all the complex physics involved in the process. The top right frame shows the evolution of the velocity of waves. Notice the complex fluid velocity fields around the hinge and at the bottom of the red element. The left frame shows streamlines colored by their relative magnitude. Also, a plot of catenary extension from its free state is shown as the entire structure sways to and fro, causing mooring rope to stretch and slacken. After 20 seconds the catenary extension starts following a steady oscillatory motion.<o:p></o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/SQ6mR9uMIA0/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/SQ6mR9uMIA0?feature=player_embedded" width="320"></iframe></div>
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Dynamic hinged motion of three structural elements using <b><i>FLOW-3D</i></b> and the oscillating behavior of the constraining catenary extension from the free state.<br />
<a href="https://youtu.be/SQ6mR9uMIA0" target="_blank">Watch the YouTube video > </a><br />
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Simulating floating structures involves complex physics and requires a CFD solution that is capable of capturing these physics easily and accurately. <b><i>FLOW-3D </i></b>not only gives good results in this case, but the ease with which the entire process can be set up is amazing. <o:p></o:p></div>
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In my next post, I will be talking about another 35<sup>th</sup> anniversary contest entry, applying <b><i>FLOW-3D</i></b> to the dispersion of environmental discharges.<o:p></o:p></div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1tag:blogger.com,1999:blog-170682242219425983.post-40643372214936972772016-02-23T09:42:00.000-07:002016-02-23T09:42:09.918-07:00FlowSight Key Improvements, Part III<div class="MsoNormal">
In this third and final blog post about the latest
improvements to FlowSight™, I will discuss the key features of the new Preferences Dialog
followed by the new calculation options on history data and extra menu options
for sampling volumes. Finally, I will give a brief overview of existing
and new features to demonstrate the advanced post-processing capabilities of
FlowSight.<o:p></o:p></div>
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<span style="font-size: large;">Reducing Redundancy using the Preferences Dialog</span><o:p></o:p></div>
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An important part of a CFD study is post-processing the
simulations. A strong CFD software can generate high-quality data, but it needs
to be coupled with a good post-processor that will let the user easily extract
useful and compelling information from that data in an efficient manner. In this section, I will talk about reducing, or eliminating
altogether, the repetition of tasks using the Preferences Dialog in FlowSight.</div>
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The goal of the new Preferences Dialog is to allow the user
to set preferences in FlowSight so that they do not need to be reset for future
simulations. A preference can be a timeline, viewport background color, color
scale setting, text font, etc. Users have the following Preferences options:<o:p></o:p></div>
<div class="MsoNormal">
</div>
<ul>
<li>Load Preferences: Includes timeline preferences, geometry preference,
and iso-surface preferences.</li>
<li>Legend/Color Preferences: Includes legend text font, color
and number of levels. Allows setting a preference to a particular variable.</li>
<li>Image Saving Preference: Allows images to be saved in the
same format (resolution and file type) every time.</li>
<li>Viewport Preference: Includes preferences for viewport background
color, border visibility, height and width.</li>
</ul>
<br />
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
Other preferences include Views, Mouse Actions and
Annotations. An example of a Legend/Color Preferences Dialog is shown below.<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="MsoNormal">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-HeDjNDk4lMs/VstZBCrDjUI/AAAAAAAAAOw/-hg5n9rKfW8/s1600/fig1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="194" src="https://1.bp.blogspot.com/-HeDjNDk4lMs/VstZBCrDjUI/AAAAAAAAAOw/-hg5n9rKfW8/s640/fig1.jpg" width="640" /></a></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal" style="text-align: center;">
A Legend/Color Preferences Dialog box (left) and the applied
preferences to a simulation (right)<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Calculations on History Data</span><o:p></o:p></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In addition to visualization capabilities, FlowSight has
numerous ways to perform calculations on History data. The History data
calculated by the solver includes important time-dependent quantities such as
fluid volume, fill fraction and solid fraction. Also included is the output
from cooling channels, sampling volumes, history probes, flux surfaces, moving
object data, and the pressure and shear force output on the geometry components.
Users can perform mathematical calculations on the history data to extract even
more information, such as scaling, integration, derivation,
summation, multiplication, division, combination, equation specification and fast
Fourier transform. An example of the “Sum” query on cooling channels is shown
below.</div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://2.bp.blogspot.com/-3Q2S6g-6S4E/VstZNx_RLZI/AAAAAAAAAO0/3GkM9cLonKw/s1600/fig2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" height="400" src="https://2.bp.blogspot.com/-3Q2S6g-6S4E/VstZNx_RLZI/AAAAAAAAAO0/3GkM9cLonKw/s400/fig2.jpg" width="365" /></a></div>
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</div>
<div class="MsoNormal" style="text-align: center;">
Sum query of total heat flow rate from cooling channels<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Extra Menu Options on Sampling Volumes</span><o:p></o:p></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In addition to the existing sampling volume options like
Transparency, Shading, Fill pattern, etc., users now have two new features – Plot
and Display of the history queries associated with the sampling volume. Users
can plot fluid forces, moments, volume, etc. and then display them on the
FlowSight window as shown in the example below.<br />
<br />
<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://4.bp.blogspot.com/-2oX7hXcVuC8/VstZ3u9obAI/AAAAAAAAAO4/YvDzptQJ4b4/s1600/fig3.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="330" src="https://4.bp.blogspot.com/-2oX7hXcVuC8/VstZ3u9obAI/AAAAAAAAAO4/YvDzptQJ4b4/s640/fig3.jpg" width="640" /></a></div>
<div class="MsoNormal" style="text-align: center;">
<br /></div>
<div class="MsoNormal" style="text-align: center;">
Example showing the options in a Sampling Volume drop down
menu (left) and the plotted query of fluid force in X-direction (right)<o:p></o:p></div>
<div class="MsoNormal" style="text-align: left;">
<span style="font-size: large;">FlowSight Recap</span></div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In the last few posts, we have seen how FlowSight enhances
the user experience during the post-processing phase. In addition to its core
capabilities of volume rendering, CFD calculators, animated streamlines and
pathlines, 2D and 3D slicing, animated time-dependent plots and vortex core
generation, these latest improvements have taken FlowSight to another level. With
improvements to the visualization of baffles, sampling volumes, probes, open
volumes and iso-surfaces; reducing the computational burden during volume
rendering using Stencils; stitching multiple simulations into one seamless
simulation; or, simply being able to set preferences to reduce redundancy and
speed up workflows; FlowSight continues to provide increased flexibility and
ease of use. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
Readers who are interested in seeing more of FlowSight and
its capabilities can go to our <a href="mailto:https://www.flow3d.com/flowsight" target="_blank">website</a>
or <a href="mailto:sales@flow3d.com" target="_blank">contact our </a><a href="mailto:sales@flow3d.com">sales team</a>. And, as a reminder,
FlowSight is available in all <b><i>FLOW-3D</i></b> products: <b><i>FLOW-3D</i></b>, <b><i>FLOW-3D</i></b> <b>Cast</b>, and
<b><i>FLOW-3D</i>/MP</b> for no additional cost. </div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0tag:blogger.com,1999:blog-170682242219425983.post-54206396173871401292016-02-02T11:29:00.000-07:002016-02-02T11:29:30.052-07:00FlowSight Key Improvements, Part II<div class="MsoNormal">
In my last post, I talked about the new developments in <a href="https://www.flow3d.com/flowsight" target="_blank">FlowSight</a><sup>TM</sup> that provide a better connection between simulation setup and post-processing in relation to visualizing geometry features. Continuing the theme, I will discuss the improvements to volume rendering and the new case linking features in FlowSight.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Volume rendering improvements </span><o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Volume rendering is a very powerful way of looking at simulation results. However, it is computationally intensive as it directly displays 3D volume data as a pixel map instead of drawing a surface by creating polygons or triangles. This computational burden can be reduced in FlowSight using a new feature called Stencil. Another improvement, Filters, provide the ability to create a volume render that only shows a specified region. I will explain more about how you can use these features to improve your workflow in the following sections.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
<span style="font-size: large;">Stencils</span><o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Stencils control the resolution of a volume render. The default value of the stencil is 1 in all the directions, which means that all mesh cells will be used. Increasing the stencil size coarsens the volume rendering, reducing the time to create the rendering and providing comparable visualization depending on the original mesh resolution. Stencils can only be set during their creation and cannot be modified later. A comparison of two volume renderings with different stencil sizes is shown below followed by a table that shows performance improvements as the stencil size varies.<br />
<br />
<o:p></o:p></div>
<div class="MsoNormal">
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<a href="http://4.bp.blogspot.com/-nf5NAospmtU/VrDaKrLzu8I/AAAAAAAAAMU/2Tm1XKw_27o/s1600/fig1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="370" src="http://4.bp.blogspot.com/-nf5NAospmtU/VrDaKrLzu8I/AAAAAAAAAMU/2Tm1XKw_27o/s640/fig1.png" width="640" /></a></div>
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Volume render stencil 1:1:1 (finer) vs. 2:2:1 (coarser)<o:p></o:p><br />
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<a href="http://1.bp.blogspot.com/-XLZ9FNxl5m8/VrDhiaVdQ7I/AAAAAAAAAOA/JZJWa3Y6CRo/s1600/stencil-size-table.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="143" src="http://1.bp.blogspot.com/-XLZ9FNxl5m8/VrDhiaVdQ7I/AAAAAAAAAOA/JZJWa3Y6CRo/s400/stencil-size-table.png" width="400" /></a></div>
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Volume render time comparison showing performance improvement with increasing stencil size. Comparison has been done for mesh cell count of 15 million.</div>
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<span style="font-size: large;">Filters</span><o:p></o:p></div>
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The Filters option allows the user to define the region where a volume render should be created. Using Filters, the user can specify to create a volume render only in Fluid 1 or only in the Solid region. There are seven predefined filter options shown below. The options include 6 surfaces: fluid 1, void, solid volume, open volume, liquid fluid, solidified fluid and auto. This last is the default option, and it selects the filter based on color by variable. <o:p></o:p><br />
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<a href="http://2.bp.blogspot.com/-c8QLtbU2sTY/VrDbykdD8RI/AAAAAAAAAMk/G9LP-jlAqws/s1600/fig3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="155" src="http://2.bp.blogspot.com/-c8QLtbU2sTY/VrDbykdD8RI/AAAAAAAAAMk/G9LP-jlAqws/s400/fig3.png" width="400" /></a></div>
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Volume render - predefined filters<o:p></o:p></div>
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In addition, FlowSight allows the user to create up to five custom filters (shown below) that work in combination of and /or logical operators. <o:p></o:p><br />
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<a href="http://2.bp.blogspot.com/-S9nRep0ijq0/VrDcDAb2QYI/AAAAAAAAAMs/1FpwwfuXZ20/s1600/fig4.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="246" src="http://2.bp.blogspot.com/-S9nRep0ijq0/VrDcDAb2QYI/AAAAAAAAAMs/1FpwwfuXZ20/s400/fig4.png" width="400" /></a></div>
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Volume render - custom filters<br />
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Volume render comparison with(right) and without (left) filter. Fluid-1 has been chosen for filtering.</div>
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</span> <span style="font-size: large;">Case linking</span><o:p></o:p></div>
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Sometimes a simulation is intentionally (or unintentionally, for example, due to a computer crash), broken into a series of restart simulations. But, the user may still want to see several data sets in one continuous timeline/animation. The user can use Case Linking feature to create a single animation from a simulation and associated restart simulations so that the entire timeline/process can be seen from the start of the first simulation to the end of the last restart simulation.<o:p></o:p><br />
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The Case Linking feature controls the overall visibility of a case. Based on the link times, only the case valid at a current time will have its parts available in the display. The user needs to correctly set the Viewport visibility. So, in the example below, we want to a create a single animation from three cases with the left viewport showing fluid isosurface colored by the velocity and the right viewport showing fluid isosurface colored by the temperature. So, to achieve this, “Isosurface-1” for all the three cases must be made visible only in the left viewport and similarly “Isosurface-2” for all the cases must be made visible only in the right viewport.<o:p></o:p><br />
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For new FlowSight users, I would like to briefly explain how viewports work. The FlowSight window can be divided into multiple sub-sections or viewports. Each viewport can have a different view, different iso-surface, etc. Multiple viewports provide flexibility to the user to study and perform an action on the same simulation in different ways while visualizing them simultaneously. For example, a velocity isosurface can be seen in one viewport, a temperature isosurface can be seen in another viewport, a volume render can be seen in the third viewport, and so on.<o:p></o:p></div>
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<a href="http://4.bp.blogspot.com/-r3Qr8F8_gJA/VrDddZ5kzAI/AAAAAAAAANA/unlOdk7VEYo/s1600/fig7.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" src="http://4.bp.blogspot.com/-r3Qr8F8_gJA/VrDddZ5kzAI/AAAAAAAAANA/unlOdk7VEYo/s1600/fig7.png" /></a></div>
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<a href="http://4.bp.blogspot.com/-na5pTl2VGnU/VrDddSqc0EI/AAAAAAAAANE/tBHZKnzxmUM/s1600/fig8.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="396" src="http://4.bp.blogspot.com/-na5pTl2VGnU/VrDddSqc0EI/AAAAAAAAANE/tBHZKnzxmUM/s640/fig8.png" width="640" /></a></div>
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Setting part viewport visibility:<br />
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<li>Isosurface-1 colored by velocity visible in the Left viewport</li>
<li>Isosurface-2 colored by temperature visible in the Right viewport</li>
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<o:p>Once the viewport visibility is set correctly, an animation can be captured from the Create animation dialog. One such animation is shown below that uses the Case Linking feature. </o:p></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/MDkhEovsHq0/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/MDkhEovsHq0?feature=player_embedded" width="320"></iframe></div>
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<a href="https://www.youtube.com/watch?v=MDkhEovsHq0&feature=youtu.be" target="_blank">Watch it on YouTube</a></div>
Video highlighting the new <i>Case Linking </i>feature of FlowSight where multiple simulations were sewn together to generate one seamless animation<o:p></o:p></div>
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This post focused on reducing the computational burden while creating volume renders and linking multiple simulations to create a single seamless animation. In my next post, I will talk about the improved Preferences option in FlowSight.</div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0tag:blogger.com,1999:blog-170682242219425983.post-44313156600774191692016-01-19T14:43:00.001-07:002016-01-19T14:43:39.190-07:00FlowSight Key Improvements, Part I<div class="MsoNormal">
FlowSight™ is an advanced visualization and analysis tool powered
by the world-leading EnSight® post-processor from CEI. FlowSight is included
with all <b><i>FLOW-3D</i></b> products without any additional cost. FlowSight is a robust
post-processor that provides enormous flexibility to the user for analyzing and
presenting the simulation data generated from <b><i>FLOW-3D</i></b> products. Some of FlowSight’s
key capabilities include volume rendering, volume/surface/point queries, case
comparison, CFD calculators, and animated streamlines. Just as new developments
are added to <b><i>FLOW-3D</i></b> products, FlowSight also continues to be extended and
improved. With the release of <b><i>FLOW-3D</i></b> v11.1 and <b><i>FLOW-3D</i></b> <b>Cast</b> v4.1, FlowSight’s
feature and functionality list has grown further. <o:p></o:p></div>
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<br /></div>
<div class="MsoNormal">
In this series of upcoming blog posts, I will be talking
about the key improvements to the latest version of FlowSight. I will start
with geometry list improvements, open volume and void isosurface visualization
developments, and new 3D-clipping features.<o:p></o:p></div>
<div class="MsoNormal">
<span style="font-size: large;"><br /></span></div>
<div class="MsoNormal">
<span style="font-size: large;">Geometry List Improvements </span><o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In addition to geometry components, geometry types like
baffles, sampling volumes, and probes form an important part of many simulations.
FlowSight can now display more geometry types allowing the user a more clear
connection between geometry setup and results analysis. This connection is
important as it helps the user understand how a certain geometry type, for
instance a solid baffle, has affected the overall results in the simulation.
Another example is a probe, which is passive in the sense that it does not the
change the simulation results, and only collects data. But, it is informative
to visualize a probe during post-processing to give the user a thorough insight
about the location of the probe in the simulation.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
The Geometry list now includes the following subtypes: <o:p></o:p></div>
<div class="MsoNormal">
</div>
<ul>
<li>Isosurface of open volume with and without cooling channels</li>
<li>Isosurface of all components</li>
<li>Geometry components (Isosurface and STL)</li>
<li>TSE - solidified fluid</li>
<li>FSI - deformable components</li>
<li>Marker particles / probes / mass momentum sources</li>
<li>Sampling volumes</li>
<li>Mooring lines</li>
<li>Cooling channels (STLs only)</li>
</ul>
<div>
</div>
<br />
<div class="MsoNormal">
A geometry subtype is only shown in the li<span style="font-family: inherit;">st, if geometry
belonging to this subtype exists in the simulation. The screenshot below shows
a geome</span>try list of possible geometry types for an example case. Notice that
baffles can be seen at the bottom of the list.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://4.bp.blogspot.com/-0wqEtUAVIPs/Vp6YCjfVHyI/AAAAAAAAALU/m_apCN1dNgc/s1600/fig1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="396" src="http://4.bp.blogspot.com/-0wqEtUAVIPs/Vp6YCjfVHyI/AAAAAAAAALU/m_apCN1dNgc/s400/fig1.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
Geometry list of an example simulation in FlowSight</div>
<div class="separator" style="clear: both; text-align: center;">
<span style="font-size: large;"><br /></span></div>
<div class="MsoNormal">
<span style="font-size: large;">Open Volume and void isosurface without cooling channels </span><o:p></o:p></div>
<div class="MsoNormal">
<span style="font-family: "calibri" , "sans-serif"; font-size: 11.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="line-height: 115%;"><span style="font-family: inherit;">For
the benefit of our die casting customers, FlowSight now allows users to hide
cooling channels with an option to draw Open volume without Cooling Channels. Open
volume is basically any region in the computational domain without solid. This feature
enables the user to view the casting geometry without having cooling channels
in the way. </span></span></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://1.bp.blogspot.com/-PbEq3DHTcuk/Vp6Yi8OcjsI/AAAAAAAAALc/eEWl9w9xvwA/s1600/fig2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="326" src="http://1.bp.blogspot.com/-PbEq3DHTcuk/Vp6Yi8OcjsI/AAAAAAAAALc/eEWl9w9xvwA/s640/fig2.png" width="640" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="MsoNormal" style="text-align: center;">
Void isosurface with cooling channels Vs w/o cooling
channels<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">3D clipping </span><o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
The 3D clipping tool allows users to slice an isosurface in
all six directions simultaneously. This is very useful for finding areas of interest,
such as porosity-related defects, or visualizing output such as temperature,
pressure, or velocity profiles inside the domain.<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://1.bp.blogspot.com/-Oqi8xa1le2M/Vp6ZRRxfZFI/AAAAAAAAALk/rnbZALwrBzs/s1600/fig3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="395" src="http://1.bp.blogspot.com/-Oqi8xa1le2M/Vp6ZRRxfZFI/AAAAAAAAALk/rnbZALwrBzs/s640/fig3.png" width="640" /></a></div>
<div class="MsoNormal" style="text-align: center;">
3D clip showing temperature profile<o:p></o:p></div>
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<br /></div>
<div class="MsoNormal">
3D clipping is currently allowed with a Cartesian mesh only.
The image above shows a high pressure die casting (HPDC) simulation. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
A 3D clip can be animated between the given extents in a
particular direction. The user can swap 3D clips in one of the X, Y or Z
directions at a time. Animations can be played forward/backward once or in a
loop mode. These options can be accessed from the loop control combo box. <o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://1.bp.blogspot.com/-QsN-h3L4dzo/Vp6Z9_h1sWI/AAAAAAAAALs/wxRkVkrxiXQ/s1600/fig4.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="95" src="http://1.bp.blogspot.com/-QsN-h3L4dzo/Vp6Z9_h1sWI/AAAAAAAAALs/wxRkVkrxiXQ/s400/fig4.png" width="400" /></a></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
A saved 3D clip animation is shown in the video below. The left
half of the animation plots temperature isosurface and the right half plots
entrained air fraction isosurface. The rates of animation in the two halves
have been set differently, causing the left half animation to take longer to go
through the geometry, compared to the right half. The rate is governed by the number
of steps shown in the loop control combo box above. <o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/ojqXS-2_eaE/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/ojqXS-2_eaE?feature=player_embedded" width="320"></iframe></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.youtube.com/watch?v=ojqXS-2_eaE" target="_blank">Watch it on YouTube</a></div>
<div class="MsoNormal" style="text-align: center;">
3D clip animation for a sample simulation of HPDC</div>
<div class="MsoNormal" style="text-align: center;">
<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="MsoNormal">
The new developments in FlowSight described here provide
users with a better connection between the simulation and post-processing,
particularly in relation to visualizing the geometry features such as baffles,
probes, and sampling volumes. In the upcoming blog posts, more new features of
the latest version of FlowSight will be discussed. </div>
<div class="MsoNormal">
<o:p></o:p></div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com2tag:blogger.com,1999:blog-170682242219425983.post-27155553886020463172015-12-22T11:23:00.000-07:002015-12-22T11:23:47.952-07:00Cavitation model improvements<div class="MsoNormal">
Cavitation is the evolution of vapor and/or gas bubbles
within liquid in the regions of low pressure in the flow, or due to heating
that raises the vapor saturation pressure. The sudden appearance and subsequent
collapse of bubbles may cause large oscillations of pressure within
incompressible fluid that in turn result in severe mechanical damage to the
surrounding structures. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Advantages and disadvantages</span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Cavitation can cause damage to turbines and pipes, erode
concrete from the dam spillways, <i>etc</i>.
Figure 1 shows the erosion of concrete near the bottom of the spillway in a
dam. Concrete used in dams is typically high strength but cavitation can still
erode it.</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://1.bp.blogspot.com/-RbhXHa1t4sk/Vnh2ADLiooI/AAAAAAAAAKg/Edpg3JPjGEI/s1600/fig%2B1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="310" src="http://1.bp.blogspot.com/-RbhXHa1t4sk/Vnh2ADLiooI/AAAAAAAAAKg/Edpg3JPjGEI/s400/fig%2B1.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
Figure 1. Eroded concrete due to cavitation on the spillway of a dam</div>
<div class="separator" style="clear: both; text-align: left;">
<br /></div>
<div class="MsoNormal">
In high pressure dies casting, die erosion can occur where
fast movement of the molten alloy through constrictions and curves in the die
results in rapid pressure drops and lead to cavitation. The resulting vapor
bubbles can lead to porosity in the final casting, or worse, lead to damage of
the die, contaminating the casting and leading to early die failure. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="separator" style="clear: both;">
</div>
<div class="MsoNormal">
Cavitation is sometimes intentionally induced for certain
industrial applications like water purification by breaking down the pollutants
and organic molecules, joining hydrophobic chemicals, destroying kidney stones
through shock waves created due to implosion of cavitation bubbles, increasing
turbulence for mixing, <i>etc</i>.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Therefore, it is critical to understand where cavitation is
likely to occur, and how intense it is likely to become. Since initiating and
visualizing cavitation experimentally is difficult and can be potentially
damaging, it is important to be able to simulate the process.<o:p></o:p></div>
<div class="MsoNormal">
<span style="font-size: large;"><br /></span></div>
<div class="MsoNormal">
<span style="font-size: large;">Modeling cavitation
in <i>FLOW-3D</i> v11.1 and <i>FLOW-3D </i>Cast v4.1</span><b><o:p></o:p></b></div>
<div class="MsoNormal">
<b><i><br /></i></b></div>
<div class="MsoNormal">
The Cavitation<b> </b>model has been successfully used to simulate cavitation in thermal
bubble jets and MEMS devices. In the new version, the model has been upgraded
for even better accuracy. <b><i>FLOW-3D</i></b> v11.1 and <b><i>FLOW-3D</i>
Cast v4.1 </b>provide a better estimate of the location and amount of cavitation
in the computational domain.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<o:p></o:p></div>
<div class="MsoNormal">
Users have the choice to choose between <i>Simplified model</i> and <i>Empirical
model</i>. The former is controlled by a user-defined characteristic time for
nucleation of bubbles, while in the latter the nucleation of bubble is
controlled by the by local turbulence. Opening of the actual cavitation voids
can be controlled by selecting <i>Passive
model</i> (voids are not opened) or <i>Active
model</i> (voids are opened). Passive model is best for simulations where the
brief appearance of small bubbles is expected, while the active model is best
for cases where larger cavitation regions are expected that will significantly affect
the flow field.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
A new variable called <i>Cavitation
gas volume fraction</i> has been added to the model and can be used to
visualize cavitation.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Sample simulations</span><b><o:p></o:p></b></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Simulation 1 shows a constricting nozzle. The animation shows
the evolution of cavitation bubbles demonstrating a highly transient,
oscillatory behavior. The cavitation volume fraction is plotted to visualize the
onset of cavitation in the initially continuous liquid.<br />
<br />
<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/jDGH3TNqpIc/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/jDGH3TNqpIc?feature=player_embedded" width="320"></iframe></div>
<br /></div>
<div align="center" class="MsoNormal" style="text-align: center;">
Simulation 1.
Cavitation in a constricting nozzle<br />
<br />
<o:p></o:p></div>
<div class="MsoNormal">
Simulation 2 shows cavitation within a <i>venturi</i> with an entry velocity of 8m/s, a convergent slope of 18°,
and a divergent slope of 8°. Again, the transient behavior of cavitation is
well modeled, with the model predicting a cavitation cycle period of 17.4ms
compared with the experimental result of 22ms.<br />
<br />
<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/L35vtvFrOiE/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/L35vtvFrOiE?feature=player_embedded" width="320"></iframe></div>
<br /></div>
<div class="MsoNormal">
</div>
<div align="center" class="MsoNormal" style="text-align: center;">
Simulation 2.
Cavitation in <i>a venturi</i><o:p></o:p></div>
<o:p></o:p>Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1tag:blogger.com,1999:blog-170682242219425983.post-10756695541504293222015-11-24T08:48:00.000-07:002015-11-24T08:54:57.402-07:00New Boundary Conditions for Water and Environmental Applications<div class="MsoNormal">
For numerical modeling of river flows, typically water
elevation is required at the upstream boundary. Yet water elevation in natural
environmental systems is often unknown and has to be estimated. Improper
elevation estimation, however, can generate nonphysical results. In <a href="http://www.flow3d.com/home/products/flow-3d/flow-3d-v11-1"><b><i>FLOW-3D</i></b>
v11.1</a>, which has just been released, users now have the option of having
boundary water elevations dynamically adapt to the conditions inside the domain.
This can be achieved through the use of rating curves provided by the user, or
in the absence of rating curves; the solver can dynamically adjust the elevation
to vary smoothly with the conditions inside the fluid domain. These variations
may be further constrained to certain Froude regimes or absolute elevation
bounds.<br />
<o:p></o:p></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-DFFpJU5dVRU/VlM8O05r2lI/AAAAAAAAAJM/TupZIXfxU-E/s1600/Picture1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="297" src="http://2.bp.blogspot.com/-DFFpJU5dVRU/VlM8O05r2lI/AAAAAAAAAJM/TupZIXfxU-E/s640/Picture1.png" width="640" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
Figure 1. Rating curve for John Creek at Sycamore from USGS</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Rating curves</span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Rating curves define elevation variations at a given
location in a river reach according to inflow rates at that location. A
relationship between elevation and volume flow rate is established by physical
measurements at a particular cross section of the river. Rating curves for
rivers in the United States are available from the <a href="http://www.usgs.gov/">USGS</a> (U. S. Geological Survey). A typical
rating curve will have volume flow rate on the X-axis and elevation on the Y-axis
(Figure 1).<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Natural inlets</span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
In a case where inflow rate is known but a rating curve is
unavailable, a natural boundary condition can be selected in the <b><i>FLOW-3D</i></b>
model setup interface. At a given cross-section, for a certain specific energy,
there can be two possible depths. This arises from the quadratic relationship
between specific energy and the depth (see the equation below). The two mathematical
depths manifest into supercritical and subcritical depths in reality. In the
case of a perfect unique solution to the quadratic equation, the flow is
critical. <o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-JsH0JDpeke8/VlM85DzvOHI/AAAAAAAAAJU/4IJInvJ3Jj8/s1600/equation.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://2.bp.blogspot.com/-JsH0JDpeke8/VlM85DzvOHI/AAAAAAAAAJU/4IJInvJ3Jj8/s1600/equation.png" /></a></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Here, E is the specific energy, q is the unit discharge, g
is acceleration due to gravity and y is the height of fluid. Graphically, the
specific energy and depth relationship can be seen in Figures 2-4. </div>
<div class="separator" style="clear: both; text-align: center;">
</div>
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-L3GCsQKRxkU/VlM9CcfEyaI/AAAAAAAAAJY/VDLtOXla694/s1600/EYDiagram-General.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="240" src="http://2.bp.blogspot.com/-L3GCsQKRxkU/VlM9CcfEyaI/AAAAAAAAAJY/VDLtOXla694/s400/EYDiagram-General.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
Figure 2. Changes to E-y curve, changing q</div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://2.bp.blogspot.com/-ILNKOz3kpOA/VlM9CRdJPII/AAAAAAAAAJc/C7AdNGNEx54/s1600/EYDiagram-AltDepths.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="237" src="http://2.bp.blogspot.com/-ILNKOz3kpOA/VlM9CRdJPII/AAAAAAAAAJc/C7AdNGNEx54/s400/EYDiagram-AltDepths.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
Figure 3. Possibility of two flow depths (supercritical and subcritical) for the same value of specific energy</div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="separator" style="clear: both; text-align: center;">
<a href="http://3.bp.blogspot.com/-Nxb4rKjX2nU/VlM9CQJPUuI/AAAAAAAAAJk/hKdDq-7rmzA/s1600/EYDiagram-SSCritical.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="240" src="http://3.bp.blogspot.com/-Nxb4rKjX2nU/VlM9CQJPUuI/AAAAAAAAAJk/hKdDq-7rmzA/s400/EYDiagram-SSCritical.png" width="400" /></a></div>
<div class="separator" style="clear: both; text-align: center;">
Figure 4. Flow depth can be critical (yc) for a unique value of depth and specific energy. In this case, flow is neither subcritical nor supercritical.</div>
<div class="separator" style="clear: both; text-align: center;">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Applying new boundary conditions</span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
A rating curve can only be defined for volume flow rate and pressure
boundary conditions in <b><i>FLOW-3D</i></b> v11.1. For volume flow rate
type boundary conditions, instantaneous elevations are calculated using the rating
curve to find the elevation corresponding to the flow rate. For a pressure type
boundary condition, the volume flow rate is calculated by the solver and
elevation is calculated using the rating curve. Rating curves can be applied at
both upstream and downstream boundaries. It is important to note that an incorrect
rating curve can result in nonphysical flow fluctuations.<o:p></o:p></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Natural boundary conditions can only be defined at the
inlet. Flow categories can be defined from one of the following:<o:p></o:p></div>
<div class="MsoNormal">
</div>
<ol>
<li>Supercritical flow (y<yc)</li>
<li>Subcritical flow (y>yc)</li>
<li>Critical flow (y=yc)</li>
<li>Automatic flow regime (calculated by the solver)</li>
</ol>
<div>
</div>
<br />
<div class="MsoNormal">
The user can define maximum and minimum limits of elevation
for any of these flows. If the depth for a particular flow regime violates the
maximum and minimum limits of elevation, the latter will take precedence.<o:p></o:p></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<span style="font-size: large;">Sample simulation results</span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Simulation 1 shows the river reach with a natural inlet
under volume flow rate boundary condition at the left boundary and a rating
curve for the outlet is defined as a pressure boundary condition at the right
boundary. The evolution of water elevation is shown for both
upstream and downstream boundaries simultaneously. The simulation shows smooth variation of
elevations at the boundaries without any fluctuations or nonphysical behavior.
Therefore, this new development in <b><i>FLOW-3D </i></b>v11.1 allows for more natural
variations of the water level for environmental applications.<br />
<br />
<o:p></o:p></div>
<div class="MsoNormal" style="text-align: center;">
<br />
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/QuuhTc_9kiY/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/QuuhTc_9kiY?feature=player_embedded" width="320"></iframe></div>
<br />
<a href="https://youtu.be/QuuhTc_9kiY" target="_blank">Watch it on YouTube </a><br />
<br /></div>
<div class="MsoNormal" style="text-align: center;">
Simulation 1. Evolution of water elevation in a river reach with natural boundary condition at the inlet and a rating curve at the outlet.</div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0Santa Fe, NM, USA35.6869752 -105.9377989999999835.4806132 -106.26052249999998 35.8933372 -105.61507549999999tag:blogger.com,1999:blog-170682242219425983.post-43759432783205614862015-11-03T11:33:00.000-07:002015-11-03T11:52:36.396-07:00Raster Data Interface and Subcomponent Specific Surface Roughness<div class="MsoNormal">
<b><i>FLOW-3D</i></b> allows users to import solids in STL
(StereoLithography) format to represent complex geometries, regardless of the
application – micro fluids, metal casting, water and environmental, aerospace,
etc. While for many industries, the STL format is a very natural and common way
of representing and sharing 3D objects, in the water and environmental
industries there is a preference towards surface-driven representations of the
environment. After all, the earth’s terrain does look like a surface for most
practical purposes.<o:p></o:p></div>
<br />
<span style="font-size: large;">Raster Data Interface</span><br />
<div class="MsoNormal">
<o:p></o:p></div>
<br />
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In the upcoming release of <b><i>FLOW-3D</i></b> v11.1, we have adopted an
industry norm for terrain import: the file format known as the ESRI ASCII raster
format. The details of the format are described <a href="http://resources.esri.com/help/9.3/arcgisdesktop/com/gp_toolref/spatial_analyst_tools/esri_ascii_raster_format.htm">here</a>.
All GIS software packages are able to export in this format. Such *.asc terrain
files will now be able to be imported directly (Figure 1) into the <b><i>FLOW-3D</i></b> user
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Figure 1. Direct import of terrain in <b><i>FLOW-3D</i></b> v11.1 using ESRI ASCII raster terrain format</div>
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<span style="font-size: large;">Subcomponent Specific Surface Roughness</span></div>
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Alongside terrain import, a critical modeling variable in
modeling flood wave propagation, flooding area, etc., is surface roughness. In
particular, the user needs to model local, spatially-varying surface roughness.
In <b><i>FLOW-3D</i></b> v11.1, users will be able to import surface roughness coefficients
in the same ASCII raster format.<o:p></o:p></div>
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More specifically, the user actually imports a raster file
of the land coverage index and provides a simple text file palette conversion
table. This table converts the type of land coverage (sand, vegetation,
built-urban, etc.) defined in the raster file to surface roughness values that are
required by the<b><i> FLOW-3D</i></b> solver. This gives the user a very effective way to
fine tune the surface roughness coefficients without having to regenerate the
entire raster file by simply altering the palette conversion table. The ASCII raster format was chosen because it
remains simple, yet lets the user easily control the surface coefficients that
are mapped over the domain following the land coverage types.<o:p></o:p></div>
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<a href="http://3.bp.blogspot.com/-8zgIXebTFDw/VjfdFq5if1I/AAAAAAAAAIU/7D-d1N2r8WE/s1600/figure%2B2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="http://3.bp.blogspot.com/-8zgIXebTFDw/VjfdFq5if1I/AAAAAAAAAIU/7D-d1N2r8WE/s640/figure%2B2.png" width="640" /></a></div>
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Figure 2. Example of overlay of terrain in <b><i>FLOW-3D</i></b> v11.1 Model Setup Graphical User Interface</div>
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Figure 3. Example of overlay of terrain in <b><i>FLOW-3D</i></b> v11.1 Model Setup Graphic User Interface</div>
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In the same framework of modeling complex flood events, functionality
to overlay actual pictures of the environment, such as river banks, built
structures, and developed housing has been added. <b><i> FLOW-3D</i></b> v11.1 allows users to directly texture
their terrain with corresponding imagery, typically obtained from satellite
imagery.<o:p></o:p></div>
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This operation can be conducted in two stages in <b><i>FLOW-3D</i></b>.
The first stage is during model setup (Figures 2 and 3), so that the user can see
the context of the model he or she is building, making it easier to be sure the
simulation is properly set up. The second stage is during post-processing in
FlowSight. This is where the overlay of the flooding event and the terrain
imagery is used to reveal the extent of the flood zones and the interaction of
the flood wave with the environment.<o:p></o:p></div>
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<span style="font-size: large;">Example Simulations and Conclusion</span></div>
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Figures 4 and 5 show the results from flood routing of the
streams in two different terrains. Upstream elevations have been plotted for
the example cases. Note that the analysis has been done on a terrain overlaid with
surface roughness data. The ability to import raster data and overlay it with
surface roughness provides the user a single platform, i.e., <b><i>FLOW-3D</i></b>, to
conduct the water and environmental studies on the terrain. Typical flood wave propagation
through a stream can be seen in Simulation 1.<o:p></o:p></div>
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<a href="http://2.bp.blogspot.com/-QEpigIAK2r0/VjfeqoPyY8I/AAAAAAAAAIk/3dXSoVdvJUk/s1600/floodv111_2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="387" src="http://2.bp.blogspot.com/-QEpigIAK2r0/VjfeqoPyY8I/AAAAAAAAAIk/3dXSoVdvJUk/s640/floodv111_2.png" width="640" /></a></div>
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Figure 4. Flood event analysis of the example in Figure 2 with overlaid surface roughness data</div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/Lkh7XXxQx_E/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/Lkh7XXxQx_E?feature=player_embedded" width="320"></iframe></div>
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<a href="https://youtu.be/Lkh7XXxQx_E" target="_blank">Watch the YouTube video > </a><br />
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Simulation 1. Flood event analysis of a location on earth. Terrain raster data has been overlaid surface roughness data within <b><i>FLOW-3D</i></b>.</div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0tag:blogger.com,1999:blog-170682242219425983.post-70529508252697597212015-10-27T13:12:00.000-06:002015-10-27T13:12:58.957-06:00P-Q Squared Analysis<div class="MsoNormal">
P-Q<sup>2</sup> analysis is a standard procedure used to optimally match the target gate velocity to the capabilities of the HPDC (High Performance Die Casting) machine’s plunger hydraulic system. Desired fill time and an optimum gate design can be attained by performing P-Q<sup>2</sup> analysis, which in turn, maximizes the efficiency of the HPDC system. <o:p></o:p></div>
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<span style="font-size: large;">Physics</span></div>
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The theoretical basis of the P-Q<sup>2</sup> analysis is the conservation of energy for steady incompressible flow. According to Bernoulli's equation, the metal pressure at the gate is proportional to the flow rate squared:</div>
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<a href="http://3.bp.blogspot.com/-kf2mZ1PwnvM/Vi-gyibE-6I/AAAAAAAAAHo/-hGmbtCGUo0/s1600/equation.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="http://3.bp.blogspot.com/-kf2mZ1PwnvM/Vi-gyibE-6I/AAAAAAAAAHo/-hGmbtCGUo0/s1600/equation.png" /></a></div>
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The assumptions for this analysis are:</div>
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<li>Constant discharge coefficient</li>
<li>Liquid metal has reached the gate</li>
<li>No air in metal stream at the gate</li>
<li>No solidification during the filling</li>
<li>Runner is the main resistance in the flow</li>
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As shown in a typical P-Q<sup>2</sup> diagram below, the machine performance line shows how the die casting machine capabilities vary depending on the flow rate. A larger flow rate demands a larger pressure from the machine to move the plunger at desired velocity. This means that, the higher the pressure, smaller the plunger, and the higher the flow rate, the larger the plunger. The operational window is defined by the fill time, gate velocity, metal pressure, etc. It is important that both the die and machine operate within the operational window (Figure 1).<br />
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Figure 1. Plot showing the operational window</div>
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<span style="font-size: large;">Setting up P-Q<sup>2</sup> analysis</span><o:p></o:p></div>
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To perform P-Q<sup>2</sup> analysis, the <i>Geometry</i> Type of the piston must be defined as <i>Plunger.</i> This can be done when you add the piston to your geometry (<i>Geometry -> Add geometry</i>).<br />
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<a href="http://2.bp.blogspot.com/--aOFMa48Vbw/Vi-f64o2zWI/AAAAAAAAAHI/hP_ncrYZPHY/s1600/figure2.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="348" src="http://2.bp.blogspot.com/--aOFMa48Vbw/Vi-f64o2zWI/AAAAAAAAAHI/hP_ncrYZPHY/s640/figure2.png" width="640" /></a></div>
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Figure 2. <i>Geometry </i>tab</div>
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Enable P-Q<sup>2</sup> analysis by selecting the <i>Perform PQ^2 analysis</i> option in the <i>Details</i> tab of the component, <i>Piston </i>(Figure 2). Enter the machine parameters (Figure 3) to define the machine performance line.<br />
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<a href="http://2.bp.blogspot.com/-teAKH2Pn9aI/Vi-gJDlhsgI/AAAAAAAAAHQ/8C1QD0-5WaI/s1600/figure3.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="223" src="http://2.bp.blogspot.com/-teAKH2Pn9aI/Vi-gJDlhsgI/AAAAAAAAAHQ/8C1QD0-5WaI/s400/figure3.png" width="400" /></a></div>
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Figure 3. Defining machine parameters</div>
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During the design stage, the user specified process parameters may not be optimal, for instance, the resulting pressure is beyond the machine capability. If so, toggle on the <i>Adjust velocity</i> option for the piston velocity to be automatically adjusted to match the machine capability. Now, the flow rate will be adjusted at each time step if the pressure at the piston head is beyond the machine capability. Once the pressure drops below the machine performance line, the piston will then accelerate towards the prescribed velocity. <o:p></o:p></div>
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<span style="font-size: large;">Viewing or Post-Processing The P-Q<sup>2</sup> diagram</span><o:p></o:p></div>
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The P-Q<sup>2</sup> analysis data such as <i>pq2</i> <i>pressure</i>, and <i>pq2 flow rate</i>, are written out in the <i>History Data</i>. They can be accessed in FlowSight by pressing the <i>History data</i> button. In the <i>History Data</i> dialog, select <i>Piston: pq2 diagram</i> in the variable list and press the <i>New plot</i> button to create a plot of the P-Q<sup>2</sup> diagram:<br />
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Figure 4. History data<i> </i>and the P-Q<i><sup>2</sup> </i>diagram</div>
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The P-Q<sup>2</sup> diagram above indicates that adjustment may be needed to bring the pressure down below the machine performance line. You can either toggle on the <i>Adjust velocity</i> option and retry (see Figure 5), or modify your machine parameters.</div>
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<a href="http://3.bp.blogspot.com/-BOa4gVLNnOA/Vi-gbYCMssI/AAAAAAAAAHg/n95mGxb7Qy0/s1600/figure5.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="400" src="http://3.bp.blogspot.com/-BOa4gVLNnOA/Vi-gbYCMssI/AAAAAAAAAHg/n95mGxb7Qy0/s640/figure5.png" width="640" /></a></div>
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Figure 5. Adjusted <i>pq2 diagram</i></div>
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<span style="font-size: large;">Conclusion</span> <o:p></o:p></div>
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<b><i>FLOW-3D</i></b> <b>Cast</b> v4.1 allows you to perform P-Q<sup>2</sup> analysis that helps achieve desired fill time and optimum gate design. The analysis data can be viewed and processed in FlowSight, an integrated post-processor that comes with the <b><i>FLOW-3D</i></b> <b>Cast</b> installation.<o:p></o:p></div>
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Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0tag:blogger.com,1999:blog-170682242219425983.post-76981847276544398582015-10-06T09:57:00.000-06:002015-10-06T13:22:32.979-06:00Batch Post-Processing and Report Generation<br />
In the upcoming releases of <b><i>FLOW-3D</i></b> v11.1, <b><i>FLOW-3D</i></b> <b>Cast</b> v4.1, and <b><i>FLOW-3D</i></b>/MP v6.1, batch post-processing and report generation have been developed hand-in-hand to save users significant time when it comes to visualizing, analyzing and communicating the results of their simulations.<o:p></o:p><br />
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Batch post-processing allows you to define a set of post-processed results that are created in the background while a simulation is running or after it has been completed. So, when you come back to your workstation, your videos, images, and other output will be ready. This is particularly helpful when simulations are huge and post-processing can take a significant amount of time. Report generation can be run after batch post-processing is complete, which combines the results into an HTML file that can be viewed in a browser and easily shared.<o:p></o:p></div>
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<span style="font-size: large;">Flexibility</span><o:p></o:p></div>
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Batch post-processing requests can be defined even if no results are available yet. Context files from other simulations or a previously run simulation can be used. Also, a user-defined template can be applied to a simulation doesn't have results yet. A <i>Context File</i> contains information about layout, views, orientation, variables loaded, etc. Results can be requested ahead of time to be written according to the context file.<br />
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Within batch post-processing, animations, scenario files or images can be ordered – any or all. <i>Scenario Files</i> are essentially “interactive animations” that are played in a special viewer that allows the results to be rotated and zoomed in/out providing much more flexibility for analyzing results.</div>
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The setup of batch post-processing requests is even more flexible when simulation results exist. Certain plots like isosurface, volume render, 2D-clip, line plot, etc. (Figure 1) can be requested ahead of time and generated automatically.<o:p></o:p></div>
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Figure 1. Batch Mode window showing the available types of plots that can be written<o:p></o:p></div>
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Figure 2. Sample results that are requested through Batch Mode. <o:p></o:p></div>
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An example of the batch post-processing is shown in Figure 2. Column 1 allows the user to select the type of plot. In 3D options, an iso-surface, volume render and 2D clip are requested for hydraulic head. In 2D options, another 2D clip is requested and so on. Column 3 allows the user to select the type of output, animation, scenario and image, respectively. In column 4, timelines can be chosen – Selected or Restart. In conclusion, setting up a batch process is very flexible.<o:p></o:p></div>
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<span style="font-size: large;">Avoid Repetition</span><o:p></o:p></div>
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Analysis of many similar simulations (e.g., parametric studies) is much easier with batch post-processing as the repetition of requesting the same post-processing graphical results is eliminated. This can be achieved by simply choosing an already available template. Templates can either be process templates like metal casting and hydraulics or a user-created template. If you choose a process template for metal casting, certain default variables and plots relevant to the metal casting industry will be written. But, if you want to use a customized template that you have created, then choose one from the User Templates tab.<o:p></o:p></div>
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<span style="font-size: large;">More Automation</span><br />
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Avoid the hassle of accessing your workstation at night using Run Batch Process. All you need to do is to choose Run Simulation and Batch Process. This way, the batch processing will start automatically once your simulation has completed. This higher level of automation can be opted for if one or more of the following cases applies:<o:p></o:p></div>
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<li style="text-align: left;">You already know what you want to see from the results and would just like it to be done automatically</li>
<li style="text-align: left;">The results analysis is very complex and would take lots of time to recreate interactively</li>
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Once batch post-processing has completed, the user can assemble the myriad of animations, images and text results into an HTML report by right-clicking on the simulation in the Portfolio and selecting Generate Batch Report. The report will be generated in HTML5 format (sample report in Figure 3) and can be easily sent to your manager, associates, colleagues, and clients. Images and videos will be embedded in the report. You will still have control over the formatting of text, captions, and references.<o:p></o:p></div>
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In conclusion, you can now spend less time on post-processing and reporting and instead run more simulations.<o:p></o:p></div>
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Figure 3. HTML report for an energy dissipative tumbler simulation<o:p></o:p></div>
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<br />Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1tag:blogger.com,1999:blog-170682242219425983.post-4785378448870554102015-09-22T14:02:00.001-06:002015-09-24T13:35:57.469-06:00Solid Propellant Combustion Modeling<div class="MsoNormal">
<span style="font-family: inherit;">Solid fuel combustion is a traditional method of extracting energy from solid objects. However, an important relatively new application of solid fuel combustion is in rocket propulsion. The development of the new Combustible objects model in <b><i>FLOW-3D</i></b> v11.1 was motivated by solid propellant combustion in rockets. The model describes the conversion of solid rocket propellant to gas with a heat source, mimicking the combustion process in solid-fuel rockets. <o:p></o:p></span></div>
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<span style="font-family: inherit;"><span style="font-size: large;">The <span style="font-family: inherit;">p</span>hysics behind the model</span><o:p></o:p></span></div>
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<span style="font-family: inherit;">The burning of the propellant in the combustion chamber results in increased temperature and pressure of the surrounding gas. In addition, as propellant is burned, the flow domain increases. It is of interest to predict these changes in the flow because the dynamics (e.g., trajectory and velocity) of the rocket depends on them. To account for the changes in the size of the flow domain, a variant of the General Moving Object (GMO) model has been developed. In the augmented model, the geometry component representing the solid propellant is designated as a GMO component of a special type: instead of moving, it changes shape and size. Such deformation of a combustible part can be seen in Simulation 1. If the elastic stresses within the solid propellant need to be modeled, the Fluid-Structure Interaction model will work with this new development.</span><br />
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<span style="font-family: inherit;">The mass source of the combustion gas is assumed to be of stagnation type, i.e., the initial velocity of the exhaust gas is zero. As a result, no additional source term is present in the momentum equations. The combustion rate is defined by the equation below. </span><b style="font-family: inherit;"><i>dm/dt</i></b><span style="font-family: inherit;"> is the combustion rate or, simply, the rate of change of mass of the solid propellant, </span><b style="font-family: inherit;"><i>P</i></b><span style="font-family: inherit;"> is the pressure of the combusting gas, and </span><b style="font-family: inherit;"><i>a</i></b><span style="font-family: inherit;"> and </span><b style="font-family: inherit;"><i>b</i></b><span style="font-family: inherit;"> are empirical parameters.</span></div>
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<span style="font-family: inherit; font-size: large;">How to set up the model</span></div>
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The model requires that the compressible flow model is activated. The solid propellant is defined as a special type of geometry component – combusting and the reaction parameters (a and b) need to be defined. Default values for multiplier and power coefficients are given, but these values can be changed by the user. The default values for multiplier and power coefficients are 1e-05 and 0.5, respectively. These values can be changed by the user.<br />
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<span style="font-family: inherit;"><span style="font-size: large;">An example simulation with results</span><o:p></o:p></span></div>
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<span style="font-family: inherit;">This simulation is of a solid propellant combusting inside a rocket. The design used for the rocket part along with the real part is shown in Figure 1. A cylindrical mesh was used because of the cylindrical geometry of the setup.<o:p></o:p></span></div>
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<span style="font-family: inherit;"><a href="http://4.bp.blogspot.com/-P-cALMlUBWk/Vfs1OJRq5VI/AAAAAAAAAFE/aBB09HO4gZA/s1600/figure%2B3a.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://4.bp.blogspot.com/-P-cALMlUBWk/Vfs1OJRq5VI/AAAAAAAAAFE/aBB09HO4gZA/s320/figure%2B3a.png" width="312" /></a></span></div>
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<span style="font-family: inherit;">Figure 1. The rocket part used for simulation in <b><i>FLOW-3D</i></b> v11.1 along with a real part<o:p></o:p></span></div>
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<span style="font-family: inherit;"><b>Results and Discussion</b><o:p></o:p></span></div>
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<span style="font-family: inherit;">Evolution of gas pressure (evolution with time is shown in Simulation 1), velocity, and combustion gas mass fraction is typically what a user will likely study. Courant number is also shown in the results (Figure 2), which is a ratio of the distance traveled by fluid in one time-step to the mesh cell size. <o:p></o:p></span></div>
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<span style="font-family: inherit;"><b>Courant Number</b><o:p></o:p></span></div>
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Higher values of Courant number indicate that the time-step size may be too big to accurately capture the local flow parameters. In Figure 4, the Courant number stays low inside the ignition chamber but increases as the flow transitions from the chamber to the nozzle. Since the main purpose of studying this case was to simulate the behavior of combustible object, as far as the ignition chamber goes, the Courant number there is low, ensuring an accurate solution. This may not be the case in the nozzle, but the user can reduce the time step to run the simulation at a lower Courant number, if required.</div>
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Figure 2. Planar plots of important variables in <i><b>FLOW-3D</b></i> v11.1</div>
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<b>Explicit vs. Implicit</b><br />
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<span style="font-family: inherit;">By now you might have thought about the numerical complexities involved in this simulation. The overall time-step size is limited by the advection velocity in the nozzle, which may lead to large computation times. An implicit advection scheme could be used to speed up the calculations. However, the time step-size must be carefully controlled to minimize the errors associated with the implicit scheme.</span><br />
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<span style="font-family: inherit;"><b>Pathlines and Circulation</b><o:p></o:p></span></div>
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<span style="font-family: inherit;">Pathlines are excellent mathematical functions and visualization tools to understand the history of a fluid particle in the computational domain. A <a href="http://www.flow3d.com/flowsight" target="_blank">strong visualization tool like FlowSight</a> calculates the pathlines depending on user’s requirements in terms of length, number, etc. Figure 3 shows the combustible part from the bottom (longitudinal direction) in the top-left viewport. The pathlines are calculated and visualized in the main viewport (the figure in the center). At one glance, it can be seen that a significant amount of local circulation is happening, along with a global circulation at the periphery. Such physics may be important to understand while programming the trajectory of a rocket. </span><br />
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<a href="http://2.bp.blogspot.com/-c-hqzNx-QuM/Vfs1OruUHkI/AAAAAAAAAFM/iEZNoGLDM80/s1600/pathlines.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="360" src="http://2.bp.blogspot.com/-c-hqzNx-QuM/Vfs1OruUHkI/AAAAAAAAAFM/iEZNoGLDM80/s640/pathlines.png" width="640" /></a></div>
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<span style="font-family: inherit;">Figure 3. Pathlines of the fluid in the combustible part visualized using FlowSight<o:p></o:p></span></div>
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/sZWBEOTQdtU/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/sZWBEOTQdtU?feature=player_embedded" width="320"></iframe> </div>
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<a href="https://youtu.be/sZWBEOTQdtU" target="_blank">Watch the YouTube video > </a></div>
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<span style="font-family: inherit;">Simulation 1. Deformation of the combustible component and the evolution of pressure over time.</span><o:p></o:p></div>
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Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1tag:blogger.com,1999:blog-170682242219425983.post-32122593365925537312015-09-09T10:01:00.000-06:002015-09-09T11:29:54.736-06:00Thermal Die Cycling ModelThermal die cycling is a standard process die casting facilities use to get their die up to temperature for full production. Think about showing up to work in the morning, mid-winter: your machines are cold! Typically someone will fire the die to get the machines warmed up and then go through a series of “dry shots” where the parts are considered sub-par quality or have a high potential for defects. After a handful of cycles (around 10), the die is hot and has a consistent temperature distribution throughout, ensuring consistent results. The series of dry shots informs you about your cooling channels’ performance and whether you need to re-locate or up the flow rates, before building any tooling. This process can be effectively simulated in <b><i>FLOW-3D</i></b> <b>Cast</b> v4.1, saving valuable time and decreasing costs even more.<br />
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<span style="font-size: large;">The physics behind the model</span><br />
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The Thermal Die Cycling model in<b><i> FLOW-3D</i></b> <b>Cast</b> v4.1 provides accurate calculations for the following physics:</div>
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<li>Assessing thermal distribution of die/tooling</li>
<li>Heat removal rate of the cooling channels and their locations</li>
<li>Thermal analysis of the entire casting process for tooling design to assess large volume (or small volume for prototyping) thermal development and a steady operating state</li>
<li>Parting line cooling during the die spraying and cleaning stages</li>
<li>Cooling of the cover and ejector at different rates during a period of high thermal gradients during the ejection stage</li>
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Apart from the physics there are stages in a thermal die cycling process that can affect the results of the simulation, e. g., leaving the part in the die during the ejection stage changes the nature of the heat transfer for all components involved. Similarly, along with the cooling lines the parting lines should also be modeled. The Thermal Die Cycling model considers all such scenarios to accurately predict the actual process.</div>
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<span style="font-size: large;">How do I access the model?</span></div>
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The Thermal Die Cycling model can be accessed in the Casting Models tab of the Models window. On clicking Thermal Die Cycling (Figure 1), a Thermal Die Cycling window will pop up (Figure 2).</div>
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Figure 1. Accessing thermal die cycling in <b><i>FLOW-3D</i></b> <b>Cast</b> v.4.1</div>
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<a href="http://2.bp.blogspot.com/-nKPhcHE7Vv4/Ve9dQZVe14I/AAAAAAAABHU/QClKPUHwur0/s1600/flow3d-cast-thermal-die-cycling-model.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="358" src="http://2.bp.blogspot.com/-nKPhcHE7Vv4/Ve9dQZVe14I/AAAAAAAABHU/QClKPUHwur0/s640/flow3d-cast-thermal-die-cycling-model.png" width="640" /></a></div>
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Figure 2. The Thermal Die Cycling model window in <b><i>FLOW-3D</i></b> <b>Cast</b> v4.1.</div>
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The Thermal Die Cycling model is easy and intuitive to use, however, there are certain requirements for various design stages to ensure that the model gives accurate results that I will talk about in the following paragraphs.<br />
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<b>Requirements for different stages</b></div>
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You can define each step of your own process but the first step must always be “Solidification.” We give you options to define different cooling heat transfer coefficients at all stages during each cycle. The ejection stage allows you to define different values for both the cover and ejector for accurately simulating the differential cooling rates of the cover and the ejector. The difference in cooling rate arises because while the part remains in one side of the die (typically the cover), there will be a different thermal profile between the ejector/cover sides. </div>
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For the rest of the stages, and in between these stages, you can rearrange and re-order as you need. For example, if you were to air dry before and after your lubrication stage, you may in fact remove too much heat so you might test different arrangements of your process. Another problem might be that you are not removing enough heat during the spraying/cleaning stages. This aspect of the analysis is extremely easy to change and can be done in columns 3 thru 5 (Figure 2). Depending on how long you are spraying the die, or what you are spraying with, your heat removal can change. Take room temperature oil for 10 seconds versus cooled water for 1 second, both will react very differently with your die surface temperatures and thus the total heat removed will also differ. We allow you to quickly assess these differences before you have to manufacture any tooling, a huge cost savings and improvement of your bottom line. Now, if these practices do not succeed in maintaining your thermal profile, you know that you will need to re-assess the locations of your cooling channels in order to get your desired outcomes and once again, this is a huge cost savings for your company. Manufacturing a set of die tooling only to find that your cooling lines are inadequately placed is a setback that can be easily avoided using this model and can get your parts to market as fast as possible.</div>
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<b>Accuracy</b><br />
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Finally, this model essentially “turns off” all fluid dynamics calculations and the physics involved are strictly heat transfer based (conduction only). This allows for extremely fast simulation results and can be easily worked into a facility’s workflow. The fully-developed heat distribution throughout your die as your initial condition for your consequent filling and solidification simulations will allow for an accurate assessment of your temperature-related defects. It also helps to identify early solidification issues before you send the designs off to be manufactured, avoiding potentially catastrophic flaws.</div>
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<span style="font-size: large;">Sample simulations</span><br />
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Two sample simulations of a heat exchanger for a consumer product are shown below. Simulation 1 models the die spray stage and evolution of the temperature profile on the 'surfaces' of the two die components, the ejector and the cover. The surfaces where the die components come together during a shot are referred to as the ‘parting lines,’ where a majority of the heat removal will take place. This stage also acts as a cleaning stage in reality, but since we do not model leftover residues, we do not take this into account.<br />
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/LG9tq_Dy6qY/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/LG9tq_Dy6qY?feature=player_embedded" width="320"></iframe> </div>
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<a href="https://youtu.be/LG9tq_Dy6qY" target="_blank">Watch this simulation on YouTube ></a> </div>
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Simulation 1. Cycle 10, Die Spray (Cleaning and Cooling) surface temperature: Notice the heat transfer occurs on all surfaces simultaneously; individual spray jets are not considered at this time.<br />
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/K2OguYt9mOc/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/K2OguYt9mOc?feature=player_embedded" width="320"></iframe></div>
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<a href="http://youtu.be/K2OguYt9mOc" target="_blank">Watch this simulation on YouTube ></a></div>
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Simulation 2 is a cross-sectional view of the die components during the entire tenth, and final, cycle. For this analysis there were 6 stages in each cycle: 1. Solidification, 2. Ejection, 3. Open, 4. Blow Air, 5. Spray lubricant, 6. Closed, and we ran 10 total cycles. On the shop floor this would translate to 10 "shots" in order to develop this temperature profile. Notice the cooling profile at the parting lines, which are the horizontal contours, and how they change with time.</div>
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Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0tag:blogger.com,1999:blog-170682242219425983.post-26100679174475002042015-09-01T11:19:00.000-06:002015-09-01T15:48:40.458-06:00Mooring Lines Model and Wave Absorbing Layer<div class="MsoNormal">
While the Mooring Lines model and the Wave Absorbing layer are two separate developments in <b><i>FLOW-3D</i></b> v11.1, I am going to talk about both in this post because users will often use them together in simulations. The development of the Wave Absorbing layer in <b><i>FLOW-3D</i></b> v11.1 was prompted by the need to minimize wave reflection at open boundaries of the simulation domain; while extensive use of mooring lines in ocean engineering led to the development of the <a href="http://www.flow3d.com/home/resources/modeling-capabilities/mooring-lines" target="_blank">Mooring Lines model</a>. Although these developments can be used hand in hand, completely independent use of each is also possible.<o:p></o:p></div>
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<span style="font-size: large;">Mooring Lines model</span><o:p></o:p></div>
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Mooring systems are common in offshore structures, ship mooring and renewable energy harvesters. A mooring line can extend to thousands of meters, so the effects of mass and fluid drag cannot be neglected. <b><i>FLOW-3D</i></b> v11.1’s new model accounts for these effects to calculate the dynamic behavior of the system. Combined with <b><i>FLOW-3D</i></b>’s General Moving Object model and free-surface flow capability, <b><i>FLOW-3D</i></b> provides a highly-accurate computational solution to cases involving dynamic movement of objects such as a US patrol boat (simulation 1) or a semi-submersible offshore platform (simulation 2), tethered to mooring lines in a body of water.<br />
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/i6fCURf-U9I/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/i6fCURf-U9I?feature=player_embedded" width="320"></iframe></div>
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Simulation 1. Movement of US patrol boat (digital model only) tied to four mooring lines in presence of the waves.<o:p></o:p></div>
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<span style="font-size: large;">What is special about the Mooring Lines model?</span><o:p></o:p></div>
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The Mooring Lines model considers gravitational and buoyant forces, elastic tension, and normal and tangential drag forces. A mooring line is divided into discrete segments for numerical integration of the dynamics equations. Additionally, mooring lines can exist below the computational domain, reducing the requirement of extending the computational mesh all the way to the depth of the water body. For this a <i>Deep Water Velocity </i>(Figure 3)<i> </i>feature is available to capture flow effects on the portion of lines outside the computational domain. A feature called <i>Confined Space </i>(Figure 3) allows the mooring lines to lie on the ground after a certain defined depth inside the computational domain. Figure 1 shows the mooring lines that partially lie on ground.<o:p></o:p><br />
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<a href="http://1.bp.blogspot.com/-uNIEc2W9ZyY/VeS53UZWNQI/AAAAAAAAAC0/c7g08tBURcs/s1600/fig4.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="172" src="http://1.bp.blogspot.com/-uNIEc2W9ZyY/VeS53UZWNQI/AAAAAAAAAC0/c7g08tBURcs/s640/fig4.png" width="640" /></a></div>
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Figure 1. <span style="font-family: Calibri, sans-serif; font-size: 11pt; line-height: 115%;">The
original line length is 100 m but after 70 meter depth it lays flat on ground.</span></div>
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<span style="font-size: large;">Wave Absorbing layer</span><br />
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A wave damping algorithm has been added to help minimize surface wave reflection from open mesh boundaries and their interference with the solution. Simulation 1 and Simulation 2 have Wave Absorbing layers at the outflow boundaries (where waves are leaving the computational domain).</div>
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<span style="font-size: large;">Where can I find the new developments?</span><br />
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Mooring lines can be added through the <i>Springs and Ropes</i> window in the <i>Meshing and Geometry </i>tab as shown below. The original Springs and Ropes Model is still available for users.<br />
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Figure 2. Accessing Springs and Ropes model in Meshing and Geometry tab.</div>
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Figure 3. Mooring Lines model (appears after clicking on Springs and Ropes model in Figure 2)</div>
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In the same way that users define a component type as a solid, lost foam, etc., they can now define the component as a <i>Wave Absorbing type</i> (Figure 4).<br />
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Figure 4. Wave Absorbing component</div>
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<span style="font-size: large;">Wait, how do the Springs and Ropes and the Mooring Lines model differ?</span><br />
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The Springs and Ropes model assumes that the ropes are weightless and always straight when stretched; rope tension is uniform; and rope dynamics is ignored. The Mooring Lines model calculations do not use these assumptions. Having said that, a user may still find the Springs and Ropes model useful if the conditions fall within the assumptions of the model.</div>
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<span style="font-size: large;">Physics and simulation setup</span><o:p></o:p><br />
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To demonstrate the power of the model, a simulation of a semi-submersible offshore platform tethered to the sea bottom was set up. This platform is tethered by twelve high modulus polyethylene (HPME), SK78 EA mooring lines rated at 630 tons minimum breaking load rope. A severe sea state with 10 meter high non-linear propagating waves is defined. Remember that we have used a Wave Absorbing layer at the outflow to nullify the reflecting effect of these non-linear waves at the boundary.</div>
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In this simulation, the mooring lines are tethered to the sea bottom. Other than the mooring lines dynamics, relevant physics activated in this simulation are:<o:p></o:p></div>
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<li>Offshore platform and fluid are fully coupled in dynamics</li>
<li><span style="font-family: Symbol; mso-bidi-font-family: Symbol; mso-fareast-font-family: Symbol;"><span style="font-family: 'Times New Roman'; font-size: 7pt; font-stretch: normal;"> </span></span>Mooring lines to constrain the offshore platform</li>
<li>Non-linear wave generation using the Fourier series method</li>
<li>Wave absorbing boundary to minimize wave reflection at the outflow boundary</li>
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<b>Mooring lines details and setup</b><o:p></o:p><br />
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The mooring lines created for this simulation are high modulus polyethylene ropes rated at 630 tons minimum breaking load with a linear density of 5.1 kg/m and diameter of 105 mm. A total of 12 mooring lines are used in the simulation and are coupled in groups of 3 (red, green and blue). There are 4 such groups in the simulation. These groups are referred as quadrants in the simulation. If groups are in order from left to right in the simulation view, then quadrant 1 refers to the leftmost group (group 1) in simulation view, quadrant 3 corresponds to group 2, quadrant 2 corresponds to group 3 and quadrant 4 corresponds to the rightmost group (group 4).<o:p></o:p><br />
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<b>Simulation and observations</b><o:p></o:p><br />
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Shown in the animation are the moored platform and the maximum tensile force on one mooring line from each quadrant. The tensile force on all 12 mooring lines could have been plotted but in order to keep the plot visually readable, only one line from each quadrant is plotted. An interesting observation is that the maximum tensile force is reached in the line listed in quadrant 1. As one would expect, the mooring lines start drifting in the direction of the waves, causing an increase in tension (tautness) of the lines.<br />
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Simulation 2. Dynamics of a semi-submersible moored offshore platform and the maximum tensile force on one line in each quadrant.<o:p></o:p></div>
Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1tag:blogger.com,1999:blog-170682242219425983.post-46357812782595798732015-08-25T11:59:00.001-06:002015-09-06T14:03:08.318-06:00Improved RuntimeDevelopers at Flow Science are constantly working to improve the performance of our solver. We want to provide our users the same experience, i.e., accuracy and ease of use of <i><b>FLOW-3D </b></i>and <i><b>FLOW-3D</b></i> <b>Cast</b>, but with shorter runtimes. In the upcoming releases - <i><b>FLOW-3D</b></i> v11.1 and <i><b>FLOW-3D</b></i> <b>Cast</b> v4.1 - the results are the same, but the computational time is significantly reduced.<br />
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<span style="font-size: large;">Performance and Optimization</span><br />
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Before I jump into the results, I would like to provide some insights into the typical process of performance optimization of a code. Performance analysis involves <i>finding the bottlenecks</i> - the parts of the code that slow down the calculations the most. Code profiling techniques help us identify if a specific function has performance issues.<br />
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For example, we have three functions in our code – <i>funcA</i>, <i>funcB</i> and <i>funcC</i>. When we profile the code we will know how much runtime is spent in each of these functions. Let’s say that <i>funcA</i> eats up 90% of the runtime, while the other two functions take the remaining 10%. In such a case, it only makes sense to target <i>funcA</i>. We can target other functions, but the returns on optimizing <i>funcA</i> will give the best results.<br />
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<span style="font-size: large;">Finding the Bottleneck</span><br />
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Profiling showed that for most applications the pressure solver in <i><b>FLOW-3D</b></i> was the most computationally intensive component (typically about 30-40% of total simulation time). Also, for Fluid Structure Interaction (FSI) problems, the FSI solver was found to consume a large chunk (70-80%) of the total computational time, dwarfing even the time spent in the pressure solver. Because the pressure solver is used more widely, we decided it would benefit more of our users to optimize it first.<br />
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<span style="font-size: large;">Optimizing the Solver</span><br />
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Optimization is the second step towards improving the overall runtime of the code. While there are many techniques involved in optimizing a certain segment of the code, the most important ones for this development were:<br />
<ul>
<li>Optimizing vector-vector calculations</li>
<li>Optimizing matrix-vector calculations</li>
<li>Storing the sparse matrix in an efficient and compact way</li>
</ul>
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<span style="font-size: large;">Improvements in Runtime</span><br />
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Different tests were conducted after the optimizations were made. They are represented by the bar graphs below.<br />
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<a href="http://4.bp.blogspot.com/-fVl7Mp4rRQ8/Vdyw5r_6NUI/AAAAAAAABFE/Gsxi8DF30cA/s1600/Computational-time-for-a-1.3-million-cell-weir-simulation.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="Computational time for a 1.3 million cell weir simulation" border="0" height="339" src="http://4.bp.blogspot.com/-fVl7Mp4rRQ8/Vdyw5r_6NUI/AAAAAAAABFE/Gsxi8DF30cA/s640/Computational-time-for-a-1.3-million-cell-weir-simulation.jpg" title="Computational time for a 1.3 million cell weir simulation" width="640" /></a></div>
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Figure 1. Computational time for a 1.3 million cell weir simulation with <i><b>FLOW-3D</b></i> v11.1<br />
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In Figure 1, ITMIN is the minimum number of iterations of the pressure solver. Irrespective of the number of iterations there is a decrease in elapsed time compared to the original solver. But as the number of iterations increase, the performance gains are more significant. For ITMIN=10, the elapsed time has dropped down by more than 50%. Figure 2 shows some real-world applications where significant improvements in runtimes are observed.<br />
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<a href="http://1.bp.blogspot.com/-nkX3NmEFfuc/VdyxCqTubOI/AAAAAAAABFM/scqThnfKkO8/s1600/Computational-time-comparisons.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img alt="Computational time comparisons" border="0" height="324" src="http://1.bp.blogspot.com/-nkX3NmEFfuc/VdyxCqTubOI/AAAAAAAABFM/scqThnfKkO8/s640/Computational-time-comparisons.jpg" title="Computational time comparisons" width="640" /></a></div>
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Figure 2. Computational time comparisons for some typical real-world applications of <i><b>FLOW-3D</b></i><o:p></o:p><br />
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<span style="font-size: large;">How Will Users Benefit?</span><br />
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Pressure solver is a critical component of the overall fluid dynamics equations solver because of its use in most CFD applications. Therefore, this new development in <i><b>FLOW-3D</b></i> v11.1 and <b><i>FLOW-3D </i>Cast </b>v4.1 will save valuable time for our current and potential users. This is not the end of it, though. As I am writing this post, our developers are working on further optimizing the pressure solver and have plans to apply the same techniques to increase the speed of <i><b>FLOW-3D</b></i>’s finite element (fluid-structure interaction/thermal stress) and core gas solvers.Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com1Santa Fe, NM, USA35.6869752 -105.9377989999999835.4806132 -106.26052249999998 35.8933372 -105.61507549999999tag:blogger.com,1999:blog-170682242219425983.post-42963857455788458092015-08-18T11:34:00.001-06:002015-09-09T10:05:59.529-06:00Active Simulation Control Editor's Note: In the next few months, we will be rolling out a series of blog posts announcing the new developments that will be released in <i><b>FLOW-3D</b></i> v11.1 and <b><i>FLOW-3D</i> Cast</b> v4.1. Subscribe to the Flow Science blog to receive updates on developments such as Active Simulation Control, new Squeeze Pin and Mooring Lines models, an interface to add raster data to your simulations, decreases in runtime, and more straight to your inbox.<br />
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<span style="font-size: large;">When design stage is critical</span><br />
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Many real-world processes involve actions that are triggered when a certain design stage or any prescribed objective or limitation is reached, independent of real timing. Active Simulation Control is a powerful new feature in the upcoming release of <i><b>FLOW-3D</b></i> v11.1 that allows users to decide the course of a simulation depending on the design stage of the process. The motivation behind this new development was to extend the idea of probe-controlled events to general objects in order to make simulation control more flexible and robust, hence the name "Active Simulation Control." <o:p></o:p><br />
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<span style="font-size: large;">What makes Active Simulation Control so powerful?</span><br />
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<a href="http://www.flow3d.com/active-simulation-control" target="_blank">Active Simulation Control</a> was developed to give users greater flexibility to control their simulations. The focus of the simulation is shifted from determining the exact real time of triggering an event to controlling the design stage of the process. Users can now set an action to take place whenever a certain objective is attained, be it a certain percentage of fluid, fluid velocity, fluid depth or any variable that can be conceived. Active Simulation Control works using the following simple rules that, combined, provide a flexible and powerful feature to users:<br />
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<ul><li>A component/object can have multiple probe-controlled events</li>
<li>An event can be triggered by multiple probe conditions</li>
<li>An event can contain multiple actions</li>
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There are more options such as the choice of logic condition between multiple probe conditions. These logic extensions allow the user to accurately and efficiently simulate real-world design stages.<br />
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<span style="font-size: large;">Is this feature difficult to implement?</span><b><span style="font-weight: normal;"><span style="color: #3d85c6; font-family: Courier New, Courier, monospace;"><b><br />
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</b></span></span><i>FLOW-3D</i></b> v11.1 allows user to intuitively use the new feature through its graphical users interface. Setting up Active Simulation Control involves a simple two-step process.<br />
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<ol><li>Create a probe that records the value of a variable</li>
<li>Set up the event that will be triggered when the value of recorded variable at the probe reaches a certain (or range) of value(s) </li>
</ol><ol></ol><i>Yes, it is that simple!</i><br />
<span style="font-size: large;">What does the new feature look like?</span><br />
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<tr><td class="tr-caption" style="text-align: center;">The Active Simulation Control window pops up from the Events tab</td></tr>
</tbody></table>The Active Simulation Control window pops up from the Events tab (in red ellipse).<br />
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<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-qGlz2cCQ1xA/Vcy7jwSGTdI/AAAAAAAABDI/IkD8D73LOak/s1600/active-simulation-control-window-flow3d.png" style="margin-left: auto; margin-right: auto;"><img alt="Active Simulation Control Window" border="0" height="372" src="http://4.bp.blogspot.com/-qGlz2cCQ1xA/Vcy7jwSGTdI/AAAAAAAABDI/IkD8D73LOak/s640/active-simulation-control-window-flow3d.png" title="Active Simulation Control Window" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Active Simulation Control Window</td></tr>
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This window shows one event that is triggered when History Probe 1 detects that the free-surface elevation is greater than or equal to 221. If that happens then the solver will impart a velocity to the chute gate without any time delay (instantaneous action). Event condition logic allows the user to choose if the action should be triggered when only one of the events happen or any or all. Yet again, very flexible.<br />
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<span style="font-size: large;">Is there a detailed example with results?</span><br />
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Yes, we have put together an example from the high pressure die casting industry as just one of many examples of how you can use Active Simulation Control. High pressure die casting is the typical process for casting complex, thin-walled parts such as transmission covers, alternator housings and other intricate shapes. In the HPDC process, molten metal is poured into a shot sleeve and a plunger forces the metal into runners that feed the metal into the cavity of the die. A significant challenge in the HPDC process is moving the plunger in such a way that the metal initially begins moving without entraining a significant amount of air. However, once the metal reaches the gates, the plunger is moved very rapidly to atomize the melt and fill the part quickly. This phase is called "transition to fast shot."<br />
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<b><span style="font-size: small;">Relevance</span></b><br />
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The determination of when the plunger motion should be transitioned to a fast shot varies between different manufacturers but is generally based on a point in time when metal has arrived at all the gates. Active Simulation Control is a great tool for this purpose. In this example, this condition can be detected by placing history probes in the gates and detecting when the fluid fraction at all probes is greater than 0.5. Active Simulation Control automatically detects when transition to fast shot should occur and changes the plunger velocity without requiring the user to analyze the results, determine the appropriate time, and then restarting the simulation.<br />
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<o:p></o:p><br />
<b><span style="font-size: small;">Events and Actions</span></b><br />
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In our example, an HPDC simulation of a pump cover is shown. The initial plunger motion is completed using the Barkhudarov method available in Utilities menu under Calculators, Shot Plunger Speed, to minimize air entrainment. Probes are defined in each of the four gates to monitor the arrival of metal. Once metal has reached all four gates, fast shot phase is automatically initiated.<o:p></o:p><br />
Another useful feature of Active Simulation Control is the ability to change the output frequency when the fast shot begins to capture the rapid filling sequence once the fast shot begins.<br />
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/eGgM6idLWX8/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/eGgM6idLWX8?feature=player_embedded" width="320"></iframe><br />
<span style="font-size: large;">The Results</span><br />
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In the animation above, three views of the filling are shown. In the lower left corner, the full geometry including the part, the runners and gates, and the shot sleeve are visible. A view of just the gates with the probes (red balls) is shown at the bottom. Plots at the top of the screen show the fraction of metal at the probes in the gates and the plunger velocity. Notice that the transition to fast shot automatically occurs when the metal reaches the gates as specified by Active Simulation Control. A time dial - a unique feature of <a href="http://www.flow3d.com/flowsight" target="_blank">FlowSight</a> - is shown on the lower right. The dial is useful for indicating the progression of time during fast shot. Once the fast shot begins, the output rate becomes very fast.<span id="goog_1330865556"></span><span id="goog_1330865557"></span>Adwaith Guptahttp://www.blogger.com/profile/03301960384392590469noreply@blogger.com0Santa Fe, NM, USA35.6869752 -105.9377989999999835.4806132 -106.26052249999998 35.8933372 -105.61507549999999tag:blogger.com,1999:blog-170682242219425983.post-67982695235901416672014-03-17T15:48:00.004-06:002015-08-18T09:01:46.816-06:00Combined Sewer Overflow (CSO) hydraulicsToday's post is about a simulation for a municipal application. I usually draw on work-related inquiries for these blog posts, and this week a municipal design consultancy called asking about how we handle the combined sewer overflow problem (heads up the answer is very well!). Typically there are two important aspects, one is understanding the straight hydraulics in both a transient and a steady state sense, the other is the characterization of particulate dynamics in the flow stream. In this case, the interest was purely on understanding the hydraulics under various upstream water elevations and pressures, in both free stream and fully pressurized conditions.<br />
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<tr><td class="tr-caption" style="text-align: center;">Geometry of interceptor sewer with regulator vault access in<br />
the far back. Flow enters from left, all walls not shown.</td></tr>
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The 'lay of the land' here is that we have an interceptor sewer carrying the flow under potentially free surface or pressurized conditions. A T-junction allows some of the fluid to make its way to a regulator vault which can then discharge some of the fluid into a separate culvert through a vertical drop-shaft.<br />
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To clarify the geometry I created a rotating animation so that you can see the inflow, the regulator vault and the drop shaft where some of the fluid exits into an underlying culvert from different viewpoints:<br />
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I ran two scenarios. In the first scenario we begin with a stagnant low level of fluid in the main sewer, then adjust the inflow boundary condition with time to simulate a rising water level. Initially this only increases the flow rate and fluid elevation in the interceptor sewer. At a given height the water begins to 'overflow' into the regulating vault section of the structure. The fluid then exits into the culvert.<br />
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This animation shows some additional filling detail:<br />
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<iframe allowfullscreen="" class="YOUTUBE-iframe-video" data-thumbnail-src="https://i.ytimg.com/vi/GiG5U49wQYM/0.jpg" frameborder="0" height="266" src="https://www.youtube.com/embed/GiG5U49wQYM?feature=player_embedded" width="320"></iframe><br />
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In the second scenario, we restart the simulation once the fluid occupies the full volume of the interceptor sewer, and then continue to increase to upstream pressure: the sewer interceptor now operates under pressurized conditions. What is interesting to observe here is that while the sewer interceptor chamber now runs under fully pressurized, confined flow conditions, the regulator vault continues to operate under free surface conditions due to the limiting effect of the regulating slide gate.<br />
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Finally, although this wasn't asked for, it is noteworthy that particle tracking can be included in the analysis. <b><i>FLOW-3D</i></b> can assign particle sources of different sizes and densities and fully couple their behaviors with the hydraulics of the flow. We can use particles as tracers of course, but more dynamically sophisticated behaviors are equally straightforward to implement.<br />
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As always I encourage you to sign-up (top right of the page) so that you will be notified of future posts!<br />
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I leave you with a <a href="http://www.flow3d.com/resources/news_12/fall/hydraulic-design-of-a-sewer-transition.html" target="_blank"><b>link</b></a> to an interesting read on a related topic, "<i><a href="http://www.flow3d.com/resources/news_12/fall/hydraulic-design-of-a-sewer-transition.html" target="_blank">Testing a Complex Hydraulic Design of a Sewer Transition with <b>FLOW-3D</b>. Comparison with a Physical Model</a></i>," by Daniel Valero, Rafael García-Bartual, Ignacio Andrés and Francisco Valles of the <a href="http://www.upv.es/" target="_blank">Polytechnic University of Valencia</a>.<br />
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<tr><td style="text-align: center;"><img border="0" height="217" src="http://4.bp.blogspot.com/-ecirRM8UujA/Uydo4F0TtYI/AAAAAAAAAXY/doITLb1O-xI/s1600/velocity-magnitude-distribution-large-view.png" style="margin-left: auto; margin-right: auto;" width="320" /></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><a href="http://www.flow3d.com/resources/news_12/fall/hydraulic-design-of-a-sewer-transition.html" target="_blank">Hydraulic Design of a Sewer Transition</a></td></tr>
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cheers all<br />
<br />
john wendelboUnknownnoreply@blogger.com4tag:blogger.com,1999:blog-170682242219425983.post-2942998257642811982014-02-24T14:27:00.001-07:002015-08-17T16:58:22.220-06:00Thermal Plume Analysis using FLOW-3D<div class="separator" style="clear: both; text-align: center;">
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<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; margin-left: 1em; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-JfavOjYvmKw/UwfHZjqptJI/AAAAAAAAAT0/WQ240MlC85s/s1600/SA+thermal+FLOW-3D+setup.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="209" src="http://1.bp.blogspot.com/-JfavOjYvmKw/UwfHZjqptJI/AAAAAAAAAT0/WQ240MlC85s/s1600/SA+thermal+FLOW-3D+setup.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><b><i>FLOW-3D</i></b> Model Setup - Two power-plant outflow ducts <br />
are located near the power-plant on the left bank.</td></tr>
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Hello again. I received an inquiry this week about our ability to model the <b style="font-style: italic;">near field structure of thermal plumes, </b>generated by the discharge of warm waters from power plant cooling systems.<br />
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The framework of this request was the EPA 316(a) and (b) set of regulations, and in fact these modeling methods for thermal plumes are very closely tied to those used to evaluate the <b><i>hydraulic zone of influence</i></b> (<b>HZI</b>) of Cooling Water Intake Structures (CWIS). You can learn more about modeling <b><i>HZIs</i></b> by downloading <b><a href="https://flow3d.sharefile.com/requireduserinfo.aspx?id=sa6cbcf192cf4fe4b&type=send" target="_blank">this webinar</a> </b>which presented last December (YouTube link <a href="http://www.youtube.com/watch?v=-qwOStWlRdg" target="_blank"><b>here</b></a> if you want the audio!)<br />
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Getting back on topic,<b style="font-style: italic;"> FLOW-3D</b> resolves the Navier Stokes equations including detailed free-surface dynamics, in 3D and with a number of advanced turbulence models available, and also fully couples density changes (via temperature changes, varying initial conditions, or changes in salinity, turbidity, etc). In addition, spatial scales of tens of kilometers upstream or downstream nowadays are very efficiently handled in high detail, no need to simplify anything down to 1D or 2D models, certainly not on the basis of computational time, that rational simply no longer exists.<br />
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<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-s-xDUcKvQV8/UwfPpxycwrI/AAAAAAAAAUE/Uqc9r56_Lb0/s1600/SA+thermal+plume+topo.jpg" imageanchor="1" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="202" src="http://3.bp.blogspot.com/-s-xDUcKvQV8/UwfPpxycwrI/AAAAAAAAAUE/Uqc9r56_Lb0/s1600/SA+thermal+plume+topo.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">"Lay of Land" - Bathymetry and geospatial layout of the power-plant, ducts, bridges and weir.</td></tr>
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I might add that what I have witnessed (over and over from running similar simulations) is that these flows, in particular the thermal structures (or indeed upstream entrainment probability maps) <b><i>are in fact <u>highly</u> three dimensional</i></b>: the vertical structures and distributions of flow parameters are anything but uniform through the water column, and the detail of the bathymetry is very significant. My take home message here is to use a 3D solution in order to model these phenomena accurately.<br />
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This said, even if the flow characteristics turn out to be complex, these types of simulations are actually quite straightforward to set up in <b><i>FLOW-3D</i></b>. In particular our free gridding approach to meshing fluid and solid quantities makes not only the setup, but also subsequent modifications in the parameter space (such as flow conditions or new geometric configurations) extremely efficient: whether it's the initial meshing of the problem, or subsequent iterations, the meshing operations are in all cases minimal.<br />
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<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://1.bp.blogspot.com/-Vkd18A7OkyM/UwfXv0_L0RI/AAAAAAAAAUU/84ZOPx6rXHY/s1600/SA+thermal+plume.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="369" src="http://1.bp.blogspot.com/-Vkd18A7OkyM/UwfXv0_L0RI/AAAAAAAAAUU/84ZOPx6rXHY/s1600/SA+thermal+plume.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Thermal Plume Map, in the fluid (left) and on the river bed (right indents)</td></tr>
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In this example the bathymetry represents a junction in the San Antonio River, and I added some detail (the power plant, the exhaust ducts, exhaust volume flow rates and densities), and turned on the additional physics that relate to thermal plumes (density evaluation, turbulence model, and mass sources), not much to it!<br />
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Typically then we would look at the three dimensional temporal and spatial distributions of the fluid density or temperature (in this case I used density as a proxy), and then maybe would take some 2D plane cuts to get a sense of what regions are affected and when.<br />
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What I found really interesting is that FlowSight (<b><i>FLOW-3D</i></b>'s next generation post-processor) allows you to color components (rather than fluids, i.e., the river bed itself) by fluid property on the contact surface.<br />
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What this means is that we can very easily <i><b>map the regions of the <u>river bed</u> which will be affected by the thermal plume</b></i>. If you are looking at benthic communities, this is the way to do it!<br />
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Here is an animation of the result of this simulation. If you click on the little full screen icon (bottom right of the video) you will get a better view of what is going on. The right hand side window is a view of the fluid with the exhaust's thermal signature, as is the top left window, the middle left is a 2D vertical plane cut just downstream of the bridge, and the lower left window is that view I mentioned, where we see the thermal signature on the river bed itself, as opposed to in the fluid.<br />
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In conclusion, if mapping thermal plumes is your business, I would say <b><i>FLOW-3D</i></b> is a pretty phenomenal tool to conduct such studies, for its accuracy, robustness and speed, but also for the ease of use and simplicity in model setup, and of course the ease with which one can visualize and analyze results!<br />
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Cheers all, until next time, any questions feel free to write directly.<br />
<br />
John WendelboUnknownnoreply@blogger.com2tag:blogger.com,1999:blog-170682242219425983.post-85002038532721604892014-02-09T15:13:00.003-07:002015-08-17T17:11:15.250-06:00FLASH FLOOD Simulation using FLOW-3D<br />
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<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-EPrOAs4v5kQ/UvcE0LPt2GI/AAAAAAAAARc/pgUw3_HZVWM/s1600/runoff+topo.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="172" src="http://3.bp.blogspot.com/-EPrOAs4v5kQ/UvcE0LPt2GI/AAAAAAAAARc/pgUw3_HZVWM/s1600/runoff+topo.jpg" width="320" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><i>Topography used in this study, the top layer is porous, <br />the lower layer is bedrock</i></td></tr>
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Today I found myself curious about <b>flash floods</b>. As <i style="font-weight: bold;">FLOW-3D </i>users already know we usually do very well for extreme event modeling, complex free surfaces, etc. Oddly enough the first question was, could we model precipitation? Historically our code hasn't particularly been used for flood plain/watershed type problems. I presume mostly because 2D solutions work just fine for the most part, and so I took a morning out of my week to sort this out, the result I thought was exhilarating! In the case of flash floods my conclusion is we do it very well (and are very effective computationally).<br />
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The two main models used here are the <b>mass source</b> and the <b>porous media models</b>.<br />
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<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-rPFUQGXUSl0/UvcCvZhZIdI/AAAAAAAAARQ/W20LEUgKTtY/s1600/runoff+0.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="141" src="http://3.bp.blogspot.com/-rPFUQGXUSl0/UvcCvZhZIdI/AAAAAAAAARQ/W20LEUgKTtY/s1600/runoff+0.jpg" width="200" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><i>Initial condition before rainfall*</i></td></tr>
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The way this simulation is set up is that we have a topography with an upper layer which is a porous media, this layer overlaps a bedrock which is impermeable. In addition the upper layer is defined as a source of fluid on its upper surface. In this simulation I am modeling a flash flood with intense precipitations lasting 180 minutes. The lower layer is bedrock, and as expected initially, the flow is governed by both seepage into the upper, permeable layer and the usual advection/Navier Stokes behaviors. Once the permeable layer is saturated, we start seeing more of the surface water dynamics, which in turn turn lead to torrential flows down in the lower elevations of the canyons.<br />
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<table cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: right; text-align: right;"><tbody>
<tr><td style="text-align: center;"><a href="http://3.bp.blogspot.com/-QAiCZpd3lLs/UvcCvSaFHQI/AAAAAAAAARU/JmOWHJawYqk/s1600/runoff+0a.jpg" imageanchor="1" style="clear: right; margin-bottom: 1em; margin-left: auto; margin-right: auto;"><img border="0" height="142" src="http://3.bp.blogspot.com/-QAiCZpd3lLs/UvcCvSaFHQI/AAAAAAAAARU/JmOWHJawYqk/s1600/runoff+0a.jpg" width="200" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><i>Intermediary stage, the ground is still<br />mostly soaking water</i></td></tr>
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Valuable, actionable information is easily visualized as a result of the effort. In this case we simulated two situations concurrently: the run-off and subsequent torrent formed in a canyon (to the right of the domain), and the run-off from mini-canyons into an adjacent pre-existing body of water (to the left of the domain).<br />
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The precipitation map can be fully defined both spatially and temporally across the entire domain, and porous behaviors can be modeled both for saturated and un-saturated media.<br />
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<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="http://4.bp.blogspot.com/-xAyQ9yIzzEM/UvcBWeiYLII/AAAAAAAAAQ8/rRlck8zVJy8/s1600/runoff+1.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="286" src="http://4.bp.blogspot.com/-xAyQ9yIzzEM/UvcBWeiYLII/AAAAAAAAAQ8/rRlck8zVJy8/s1600/runoff+1.jpg" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><i>Torrent formations following heavy precipitation. Note the water pooling and main torrent formation in the canyon on the right, and the strands of heavy discharge into the pre-existing body of water on the left.</i></td></tr>
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Here is the animation of the event: <br />
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<iframe allowfullscreen='allowfullscreen' webkitallowfullscreen='webkitallowfullscreen' mozallowfullscreen='mozallowfullscreen' width='320' height='266' src='https://www.youtube.com/embed/OMjk-jFXh9k?feature=player_embedded' frameborder='0'></iframe></div>
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You can also view the video on youtube <a href="http://youtu.be/WBsXJRrskFk" target="_blank">here</a>.<br />
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Finally it's very interesting to look at the time series of water depth located at a probe placed near the lower end (elevation wise) where I was expecting to see the great volume flow and water pooling. Initially, while the porous layer is actively absorbing water, we see no surface water pooling. Then once the layer becomes saturated, we observe a rapid increase in water depth, until we finally observe the steady state balance between the influx of precipitation and the outflow via the torrent.<br />
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<a href="http://4.bp.blogspot.com/-N3a2-wgtorc/Uvf6rrgdt7I/AAAAAAAAARs/qmrbP0koLPs/s1600/precipitation+water+depth.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="344" src="http://4.bp.blogspot.com/-N3a2-wgtorc/Uvf6rrgdt7I/AAAAAAAAARs/qmrbP0koLPs/s1600/precipitation+water+depth.jpg" width="640" /></a></div>
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Finally I note that you can be a lot more sophisticated with the mapping of the precipitation rates by simply tiling your domain into various sub-components (they can be of arbitrary shape by the way):<br />
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<a href="http://4.bp.blogspot.com/-Uo5JSfTflJw/Uvf9e5gXx1I/AAAAAAAAAR4/lavVrJqeFIU/s1600/runoff+topo+map.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="320" src="http://4.bp.blogspot.com/-Uo5JSfTflJw/Uvf9e5gXx1I/AAAAAAAAAR4/lavVrJqeFIU/s1600/runoff+topo+map.jpg" width="640" /></a></div>
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Cheers all, don't forget to sign-up for email updates (top right of this page) if you want to be notified of future posts!<br />
<br />
jw<br />
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<i>*All simulations post-processed with FlowSight, coming soon in <b>FLOW-3D</b> v11</i></div>
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Unknownnoreply@blogger.com2tag:blogger.com,1999:blog-170682242219425983.post-43571381262588446362014-02-09T12:40:00.000-07:002015-08-17T17:08:31.115-06:00Type II spillway modelizationAs customary for a first blog post, <b>hello world!</b><br />
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This spillway was designed following USBR guidelines (type II), where the engineers were interested in validating their designs without having to resort to physical lab models (expensive, and which also have their own sets of scaling problems).<br />
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The steps to analyze these types of problems in <b><i>FLOW-3D </i></b>are straightforward:<br />
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<i>Post-processed with FlowSight, coming soon in <b>FLOW-3D</b> v11</i><br />
<ul>
<li>Generation of a 3D CAD model based on the design blue prints (I happen to use Rhino3D, works pretty well for me)</li>
<li>Geometry import in <b><i>FLOW-3D</i></b> in the STL format</li>
<li>The usual <b><i>FLOW-3D</i></b> simulation steps:</li>
<ul>
<li>set the boundary conditions</li>
<li>set the initial conditions</li>
<li>choose your physical models (in this case turbulence and air entrainment)</li>
<li>choose your outputs (hydraulic quantities, Froude #, etc.)</li>
</ul>
</ul>
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In the case of spillways, which have fairly large spatial scales compared to the water depth, it is EXTREMELY advantageous to use the code's domain removing capabilities. The best way to do this is to follow a 4 step approach:</div>
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<ol>
<li>Run the simulation with a coarse grid. This run will take 10 minutes at most, and even if this won't catch the full manifestation of the hydraulic jump, it will be enough to give you a good idea of where the fluid regions will be active.</li>
<li>Equipped with that information go back into your CAD package and create a domain removing solid which conforms reasonably well with the complement of your fluid form (my method is to super-impose a picture of the simulation result within my CAD model).</li>
<li>Add this new solid component to your simulation as a domain removing component.</li>
<li>You can now massively crank up the resolution of your simulation to fully capture the detail of the energy dissipation mechanism in good detail. </li>
</ol>
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You can watch the video on <a href="http://www.youtube.com/watch?v=GnophUikIL4&feature=youtu.be" target="_blank">youtube here</a>!</div>
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cheers all</div>
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<div>
jw</div>
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Unknownnoreply@blogger.com0