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Simulation error

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RSS FeedRSS feed   |   Email notificationsTurn on email notifications   |   3 Replies   Last post: November 26, 2012 6:01am UTC
Sanjay Debnath

Sanjay Debnath

November 8, 2012 4:51pm UTC

Simulation error

Hi ,

I am getting this type of error whey i am trying to start simulation.

"Variables property does not include all variables in Xmesh"

Could anybody can give me any solution/ suggestion.

Thank you
Sanjay

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Ivar Kjelberg

Ivar Kjelberg

November 9, 2012 6:37am UTC in response to Sanjay Debnath

Re: Simulation error

Hi

for me it looks like you are missing some material properties, or that your mesh is not full (some domains are not meshed), difficult to say more just from such a message I agree ;)

--
Good luck
Ivar

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Sanjay Debnath

Sanjay Debnath

November 25, 2012 1:57pm UTC in response to Ivar Kjelberg

Re: Simulation error

Hi Ivar,

Thank you very much for your reply. I guess you have a sound understanding about COMSOl


I have been facing another issue while i was working with COMSOL.(4.3)

The problem is like ....for a particular mesh size I can not simulate below a certain frequency.
If i increase the mesh size then i can do it, i want to simulate my structure below that certain frequency without increasing the mesh size .

The error message I get is "

Failed to find a solution for the initial parameter. The relative error (0.0013) is greater
than the relative tolerance. Returned solution is not converged. :"

Could you please give me any suggestion . IF you need any further info, plz let me know

Thank you
Sanjay



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Ivar Kjelberg

Ivar Kjelberg

November 26, 2012 6:01am UTC in response to Sanjay Debnath

Re: Simulation error

Hi

first of all, COMSOL might find a solution with a coarse mesh, but it can be all wrong, if your mesh is too coarse. You need to have a mesh size that is sufficiently dense to catch the gradients of your dependent variables, and in case of waves that you have at least 5 or more mesh elements per period, in the material. Else you are under sampling and your results will be wrong (even if COMSOL sometimes might converge.

It's like aliasing in sound digital recording, a pure numerical sampling theory effect.

What is tricky is that often the gradient opf the dependent variables are very steep for given initial conditions, so often you need very fine mesh only very locally, and in time dependent , often only for the fist steps (typically for diffusion from a step concentration or thermal boundary limit. Then its worth to cheat a bit and introduce a >0 concentration or temperature locally close to the boundary with the initial conditions, it helps for the convergence. Often this is more critical for concentrations than for T as T is offset by 273°K most of the time, while the concentration is =0 as default initial value, and any c<0 makes people and COMSOL to scream ;)

--
Good luck
Ivar

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