On cfd-online, there was a question about how the fan-controller is connected to the motherboard so that it can receive information about the current temperature. The connection runs via one of the two colored cables that arrive at the upper right corner of the motherboard.
The fan hub is connected directly to the power supply.
The fan hub is connected directly to the power supply.
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"Blast from the past - Part 3" - Solution Mapping
This is about transferring the flow solution from one computational grid to another. Mapping is often used so you don’t have to start the simulation all over again when the geometry changes slightly.
However, solution mapping to another grid could become problematic if the source solution is also based on a very fine mesh. An example of such situation is the DriveAer test case, where the meshes go from 64 million to 128 million to 256 million cells.
The traditional method that is employed by all the CFD solvers is to load the initial guess solution completely and then the interpolation process takes place. In the above example, interpolating the solution for 256 million cell from 128 million cells is extremely difficult due to memory usage. Not everybody has this much RAM to load both solutions simultaneously.
Due to this reasons, Wildkatze only partially loads the solution from the initial guess file. This allows initial guess files of any grid sizes.
The process is very simple. In the old model, the solution is saved with the command:
> save-initial-guess initialGuessFile
In the new model, this file is loaded instead of a restart file after the model has been read in with the command:
> read-initial-guess initialGuessFile
The mapping process is followed by a few initial guess iterations to carefully satisfy the divergence of velocity criteria of the mapped solution. This later results in very rapid convergence.
Otherwise one usually observes high pressure fluctuations at the first (post mapping) iterations, destroying the mapped solution and often resulting in an increased number of iterations to converge.
Mapping in WK also works in parallel with the associated speedup and without additional overhead.
This is about transferring the flow solution from one computational grid to another. Mapping is often used so you don’t have to start the simulation all over again when the geometry changes slightly.
However, solution mapping to another grid could become problematic if the source solution is also based on a very fine mesh. An example of such situation is the DriveAer test case, where the meshes go from 64 million to 128 million to 256 million cells.
The traditional method that is employed by all the CFD solvers is to load the initial guess solution completely and then the interpolation process takes place. In the above example, interpolating the solution for 256 million cell from 128 million cells is extremely difficult due to memory usage. Not everybody has this much RAM to load both solutions simultaneously.
Due to this reasons, Wildkatze only partially loads the solution from the initial guess file. This allows initial guess files of any grid sizes.
The process is very simple. In the old model, the solution is saved with the command:
> save-initial-guess initialGuessFile
In the new model, this file is loaded instead of a restart file after the model has been read in with the command:
> read-initial-guess initialGuessFile
The mapping process is followed by a few initial guess iterations to carefully satisfy the divergence of velocity criteria of the mapped solution. This later results in very rapid convergence.
Otherwise one usually observes high pressure fluctuations at the first (post mapping) iterations, destroying the mapped solution and often resulting in an increased number of iterations to converge.
Mapping in WK also works in parallel with the associated speedup and without additional overhead.
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New Variable Time-Step Scheme in Wildkatze
Wildkatze's ability to perform multiphase simulations at extremely high Courant numbers could cause problems in certain situations.
Although it is desirable for a CFD solver to be stable at higher Courant numbers — that is, at larger time steps — this could negatively impact the accuracy of the results.
Of course, the accuracy of the solution is questionable if the simulation is run at time-step size’s corresponding of Courant numbers above 25 or more. This is specially true when a sharp interface tracking has to be performed. However, Wildkatze's MaxGBCA VOF scheme can still produce a very sharp interface at high Courant numbers.
To address this issue, Wildkatze now allows you to specify a range of time-step sizes (minimum to maximum time step) and a Courant number. Above this Courant number the solver shall use the minimum user specified time-step size. When the Courant numbers are towards lower specified values the maximum time-step values are used.
The key feature of the new method is that the time step size is adjusted using a blending function to ensure a smooth transition. This is particularly important in the simulation of flow problems where surface tension is the driving force, as sudden changes in the time step size disturb the solution too much.
... more text in the comments
Wildkatze's ability to perform multiphase simulations at extremely high Courant numbers could cause problems in certain situations.
Although it is desirable for a CFD solver to be stable at higher Courant numbers — that is, at larger time steps — this could negatively impact the accuracy of the results.
Of course, the accuracy of the solution is questionable if the simulation is run at time-step size’s corresponding of Courant numbers above 25 or more. This is specially true when a sharp interface tracking has to be performed. However, Wildkatze's MaxGBCA VOF scheme can still produce a very sharp interface at high Courant numbers.
To address this issue, Wildkatze now allows you to specify a range of time-step sizes (minimum to maximum time step) and a Courant number. Above this Courant number the solver shall use the minimum user specified time-step size. When the Courant numbers are towards lower specified values the maximum time-step values are used.
The key feature of the new method is that the time step size is adjusted using a blending function to ensure a smooth transition. This is particularly important in the simulation of flow problems where surface tension is the driving force, as sudden changes in the time step size disturb the solution too much.
... more text in the comments
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A delayed St. Nicholas Day gift for our motorsport enthusiasts.
Pressure and Acoustic Monopol Source for a velocity of 50 m/s run with KOmega-DDES.
Pressure and Acoustic Monopol Source for a velocity of 50 m/s run with KOmega-DDES.
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Every time I use ParaView for post-processing large models, I wonder why we don't use a framework like Wildkatze as a visualization server. Then we would already have automatic support for multiple cores using domain decomposition (on the fly), native support for polyhedra, and optimized algorithms for calculating derived quantities such as gradients.
Maybe someone out there is interested in such a project. We even considered making our code available to the PV developers.
Maybe someone out there is interested in such a project. We even considered making our code available to the PV developers.
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We wish all our readers a Merry Christmas, whether you celebrate it now or in January 😊
If you have any wishes, suggestions, or questions, feel free to share them here. Think of it as a wish list for our very special Santa Claus.
If you have any wishes, suggestions, or questions, feel free to share them here. Think of it as a wish list for our very special Santa Claus.
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