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Re-use a displacement in an eigenfrequency analysis
Posted Jun 24, 2010, 11:43 a.m. EDT 5 Replies
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I am trying to analyse the eigenfrequency of a device after an initial stress-deformation in Comsol 4.
I have tried to use the stationary solution as a initial condition for the eigenfrequency step but the osscilation still hapens around the non deformed state.
It is possible that this is a plotting problem, the plot showing only the displacement from the first geometry and not the deformed state.
My questions are:
Is this the right way, or how would I go about doing this the right way?
How do I get a deformation into a new geometry? (in order to get a fresh start)
Is there any guide / model for Comsol 4 explaining this type of models? (e.g. the "Resonator Folded" and "Capacitive Pressure Sensor" for Comsol 3.5a)
//Martin
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try a buckling analysis, and look how the solver is set-up, this usually prestresses the model with a static analysis, stores the solution and follows by an eigenfrequency buckling analysis.
If you look carefully at all the study steps you should understand what is going on, then basically its just to switch to "egenmode analysis" and select the first n (and not 1) solutions
have fun Comsoling
Ivar
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thank you for the fast reply.
I assumed you meant for me to add the buckling analysis to my project and look at the generated solver sequence.
Is there any model in the model library that I can check?
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unfortunately I cannot propose a model, but juts make a metal cantelever beam x=0.01 y=0.1 z=1m and fix it at the lower surface (-Z) and apply some -Z load, (eventually also a torque) on the top surface, and run a standard bucling analysis as COMSOl proposes it by default in V4
Then look carefully at all the "Study tree settings
You can then change the "bucling analysis" setting to turn it into a standard eigenvalue anaysis, withthe appropriate field, and ask for solving the first 6-9 modes and not just the 1st one, this will give you a stressed eigenvalue analysis. You can then lso comapre wih or without the non-linear terms (eigenvalue analysis is always linear, butcan be linearised around a point defined by a non-linear static load case)
Hope this helps
Ivar
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Thank you that solved my fist question!
There really should be a tutorial or something how to work the solver sequences in V4.
Now over to my second question; Is it possible to get the deformed geometry into a new geometry?
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in V3.5 you could save the mesh and reimport it, have not tried it out on V4, if its not there yet, it will certainly come
Ivar