[SOLVED] Comparing with Comsol: many questions for you :D

Numerical methods and mathematical models of Elmer
raback
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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by raback » 08 Mar 2017, 19:10

Hi

Some more information would be needed. I think that indeed Comsol uses a 2nd order elements even though when saving the .mphtxt file it looks like a linear mesh. Are we sure that it stops there. Basically when using p-elements the element order could be further increased.

If the polynomial order is the same there can be some additional numerical tricks. In Elmer we have stabilization with various methods and experimental flux corrected transport. Comsol has also something, perhaps better tricks. Maybe you can share your findings in more detail and dig into the Comsol settings what could the settings be.

-Peter

mzenker
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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by mzenker » 09 Mar 2017, 12:33

Hi,

we had a COMSOL demo version to test some time ago. AFAIR Comsol can generate a report with all the settings listed. So that could be of some help here.
Just a suggestion.

Matthias

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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by JamesMarine » 10 Sep 2019, 11:21

I tried to re-run this case and learn to use Elmer for acoustic cases, but when runing the solver, the below errors occurs:

SingleSolver: Attempting to call solver
SingleSolver: Solver Equation string is: helmholtz equation

Program received signal SIGSEGV: Segmentation fault - invalid memory reference.

Backtrace for this error:
#0 ffffffffffffffff

Does anyone know what is the reason for this?

kevinarden
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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by kevinarden » 10 Sep 2019, 11:48

It is the error that occurs when you point to the wrong body. I downloaded your mesh and sif and the mesh was body 1 not body 2

Body 1
Target Bodies(1) = 2
Name = "Body 1"
Equation = 1
Material = 1
End

Changed to
Target Bodies(1) = 1

and it ran.

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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by JamesMarine » 10 Sep 2019, 13:11

Thanks, kevinarden! It works.

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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by JamesMarine » 16 Oct 2019, 17:11

I continue to recieve the message that "WARNING:: IterSolve: Numerical Error: Too many iterations were needed. ", is there anything to worry about this?

kevinarden
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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by kevinarden » 16 Oct 2019, 20:25

It means it has not converged to the criteria specified. It may be a good solution, but the math is not converged to the tolerances requested. It could also be a solution but not a correct one.

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Re: [SOLVED] Comparing with Comsol: many questions for you :D

Post by kevinarden » 16 Oct 2019, 20:29

you specified

Linear System Max Iterations = 500
Linear System Convergence Tolerance = 1.0e-10

which is the default. You con increase the iterations and/or decrease the convergence tolerance.

Convergence can also be improved by a finer mesh and/or higher order elements.

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