Discussion Forum

September 3, 2010 2:20pm UTC

FSI and Damped Eigenfrequency Analysis (Comsol v4.0a)

Hi to all,
I'm trying to solve some FSI models which correctly ran with version 3.5a.
The models calculated the eigenfrequencies of a solid structure vibrating in a fluid environment. Thanks to the "Damped Eigenfrequency analysis", that was possible, and results were correct.
Now, unfortunately with version 4.0a, without changing any BC, the eigensolver always fails with the error "singular matrix".
Clearly such a study is not a "default" one (as usual, the Fluid Flow module does not have any defaul analysis for the frequency domain) and thus I don't know if it is already possible with v4.0a.
I'm wondering if it is a problem regarding the Fluid Flow equations (they cannot be converted in their frequency counterpart) or regarding the eigensolver.
Is this last already able to solve Damped Eigenfrequency analyses too?
Is there someone which has already tried (also with other physical couplings) this kind of analysis?
Thanks in advance for the answer.

Alessandro

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

September 6, 2010 10:24am UTC in response to Ivar Kjelberg

Re: FSI and Damped Eigenfrequency Analysis (Comsol v4.0a)

Hi Ivar,
I've tried to do with v4.0a a tutorial of v3.5a about thermoelastic damping of a beam. Even if physics is different, I think the procedure is similar to mine in the case of the FSI analysis.
The analysis fails with a similar error to the one found in the FSI case.
Thus I think such kind of analysis is still not possible...(or maybe it requires some tuning that I don't know...) :-(...
What a pity...!
An other clue about such an impossibility is the fact that there are some missing tutorials in v4.0a, which instead were present in v3.5a.
Maybe the Damped Eingenfrequency analysis is still a work in progress for what concerns v4.0a.
Hi, let's see in Paris!


Alessandro

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse

April 12, 2011 11:57am UTC in response to Alessandro Ricci

Re: FSI and Damped Eigenfrequency Analysis (Comsol v4.0a)

Hi Alessandro,

I am new to FSI and i am trying to model a stirrer in a pot of liquid.
Now this is a cantilevered vibrating stirrer and my first task is to find its 1st resonance frequency when it is submerged in the liquid.
It seems you have been doing this for a while, could you please help me out with this?

Also, i could not figure out how to input a vibration input condition to the stirrer, you have any idea how to do this?

I am working in v3.5a only, could not get used to the new GUI !!

Thanks,

Pranav

Reply  |  Reply with Quote  |  Send private message  |  Report Abuse