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Frequency-Stationary simulations in Acoustics
Posted 15 nov 2022, 15:01 GMT-5 Acoustics & Vibrations, Studies & Solvers Version 6.0 4 Replies
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Hi,
I have a model constituted by :
a pressure acoustics wave equation, which transforms into an Helmholtz equation in frequency domain (complex solution p)
for some reason, the wave velocity of the latter depends on another spatial field N, which is in turn a solution of a stationary PDE (say a Poisson equation to take a simple example), whose coefficients depends on the acoustic field p.
The two equations are therefore bi-directionally coupled and must be solved together. The problem is that the pressure acoustics problem requires a frequency-domain solver, whereas the stationnary PDE requires a staionnary solver, and I cannot get how to program a single study containing both.
One turnaround is to use "Helmholtz equation" instead of "Pressure acoustics", because Helmholtz is solved by a stationnary solver also. This is what I do for now, and this works perfectly, but for further complexification (coupling with structure vibration), I would prefer to use "Pressure Acoustics".
As far as I understand, there exists such hybrid solvers named "Frequency-Stationary" in other contexts (here with RF module for example), but not in a general context. Maybe I could build that by myself ? How ?
Any hint would be welcome.
Thank's a lot.
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Hi Oliver,
A frequency domain study as you mention for the Pressure Acoustics, Frequency Domain interface does use a Stationary Solver (this can be seen in the solver configurations). Therefore, I think it is possible that a PDE interface, such as the Poisson Equation interface you mention, could be solved using a frequency domain study step. A simple test could be to solve the Poisson Equation in 1D with zero source term and Dirichlet boundary conditions on the left and right boundaries using a frequency domain study step. The analytical solution (linear trend) should be able to be verified.
When you try to set this up in your model, do you encounter any specific error message or issue? I wonder if it is more related to how you specify the manual coupling rather than the solver configurations.
Best,
Mark
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Dear Mark, thank you very much for your quick answer.
In fact, it is not a Poisson equation but a "Transport of a dilute species", that I want to solve with a stationary equation, coupled with the "Pressure acoustics" frequency domain (sorry I should have said that directly...)
When you try to set this up in your model, do you encounter any specific error message or issue? I wonder if it is more related to how you specify the manual coupling rather than the solver configurations.
The problem arises when I add the frequency domain solver (which you suggest might also solve the transport equation or whichever stationary problem). This is what I get :
As you can see, Transport of diluted species is unchecked (and uncheckable) because COMSOL considers that it cannot be solved with a frequency domain solver despite, as you mentioned :
Frequency Domain interface does use a Stationary Solver (this can be seen in the solver configurations)
I had the same remark and wondered whether I could build by myself some "weird study" including a stationary solver, but I don't have even any clue on how to compile both equations.
I wonder if it is more related to how you specify the manual coupling rather than the solver configurations.
The sound velocity in pressure acoustics depends on N, the solution of the transport equation and the convection velocity in the latter depends on abs(p), the local peak pressure amplitude. All the coupling is made through a list of variables.
Thank's very much again.
Best regards, Olivier.
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Hi Oliver,
At least in version 6.0 and 6.1, I think there can be a way to use the Stationary Solver of the Frequency Domain Study step to solve the transport of diluted species physics. Have a look at the attached model and screenshot, where the model configuration for the study step has been modified in the study settings.
If not, then probably your work around is the best idea. You could use pressure acoustics with acoustic structure interaction for the built in coupling, and then manually add the transport PDE from the mathematics branch if that would be easier to setup.
Best,
Mark
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Mark,
Your screenshot makes perfect sense and exactly solved my problem. I knew "Modify model configuration for study step" for other purposes but I did not know that it also allowed to specify explicitely the solver used for each physics. Great feature !
Thank's a lot !
Best, Olivier.