## WaveSolver and Eigen Analysis

Numerical methods and mathematical models of Elmer
CrocoDuck
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### Re: WaveSolver and Eigen Analysis

I see, that clarifies. Thanks.

As for your question:
raback wrote: 21 Aug 2020, 16:59 The same applies to "Pressure Velocity". That being said, I don't really recall what it would do in harmonic case. Does it play a role whether you have it or not? This is also taken care by the library.
I commented out and used a sort of "blank" boundary condition:

Code: Select all

``````Boundary Condition 1
! Pressure Velocity = Real 0
End
``````
It delivered the same results.
CrocoDuck
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### Re: WaveSolver and Eigen Analysis

Hey guys. If you are interested, I did a little accuracy study of the solution. I am quite satisfied. Results are here: https://computational-acoustics.gitlab. ... ed-part-2/.

Cheers!
raback
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### Re: WaveSolver and Eigen Analysis

Hi Croco

Nice work! This kind of diligent work is needed to push the code into new areas. And actually before your tests this was not possible since the wave equation hadn't been tested for eigen analysis.

A note on the output of eigenmodes. You will get the modes as timesteps in vtu file if you add in Simulation section "vtu: Eigen Analysis = Logical True". This will tell the vtu output to number the files according to eigenmodes. There could be iterative or time dependent problems where for each iteration we solve a slightly modified eigenvalue problem. So therefore this is not the default in output.

I don't remember whether the solver can deal with p-elements. However, you might want to test whether "Element = p:2" improves results.Certainly there is always a significant cost in increasing the element order but for wave problems going quadratic may pay off.

-Peter
CrocoDuck
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### Re: WaveSolver and Eigen Analysis

Hi!
raback wrote: 13 Sep 2020, 01:19 Hi Croco

Nice work! This kind of diligent work is needed to push the code into new areas. And actually before your tests this was not possible since the wave equation hadn't been tested for eigen analysis.
Cool! I am glad this was interesting for you.
raback wrote: 13 Sep 2020, 01:19 A note on the output of eigenmodes. You will get the modes as timesteps in vtu file if you add in Simulation section "vtu: Eigen Analysis = Logical True". This will tell the vtu output to number the files according to eigenmodes. There could be iterative or time dependent problems where for each iteration we solve a slightly modified eigenvalue problem. So therefore this is not the default in output.
Ha! Nice, I did not know that. I will try. I definitely need to give another good read at the manuals, so many things I keep on missing.
raback wrote: 13 Sep 2020, 01:19 I don't remember whether the solver can deal with p-elements. However, you might want to test whether "Element = p:2" improves results.Certainly there is always a significant cost in increasing the element order but for wave problems going quadratic may pay off.
Cool stuff. I will try that too.
CrocoDuck
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### Re: WaveSolver and Eigen Analysis

Tested both of "vtu: Eigen Analysis = Logical True" and "Element = p:2". They work like a charm, and p:2 boost the accuracy a lot. Good stuff.
raback
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### Re: WaveSolver and Eigen Analysis

Nice!

In your case can you determine that it is more efficient to get the added accuracy using the p strategy (vs. h strategy)? The theory says that for smooth problems p should be better. You can go p=3, 4, 5,... but I would suspect that the sweep spot is p=2 or p=3.

The integration rules for the p-elements may be rather costly. There might be some room for improvement here. The number of points grow now as p^3.

-Peter