Menu

Discussion Forum

New Discussion
Filter

Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

the result of building half model to modal ansys(or eigenfrequency ansys ) is different with the whole model?

Posted Oct 19, 2012, 9:32 a.m. EDT Geometry, Parameters, Variables, & Functions, Results & Visualization, Structural Mechanics Version 4.3, Version 4.3a 2 Replies

Hao Yongcun
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

I build two models to modal ansys, one is half model and the other is whole model(the model is symmetrical),but the results i got is different. frist , the number of whole model`s modal Shape under 20KHz is more than the half model`s. second, in the same modal Shape, the two model`s eigenfrequency is different, at a difference of a few Hz
i want to know why ? who can help me ,thanks a lot!

Attachments:

2 Replies Last Post Oct 19, 2012, 2:25 p.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Oct 19, 2012, 1:59 p.m. EDT
Hi

if you apply one symmetry to an object (via a plane) you need to run 2 eigenfrequency runs, one with symmetry, one with antisymmetry conditions, else your re estraining yourself to roughly half the modes, as the symmetry mode is fixed in the normal direction. If you have 2 symmetry plane (1/4 model) then you need to do 4 cases with all combinations of symmetry / antisymmetry loads tocover all modes

Also the mode frequency might vary depending on the mesh density/quality (and the mesh symetry) so some & difference is not astonishing, uit the differenece should reduce with a higher mesh density

--
Good luck
Ivar
Hi if you apply one symmetry to an object (via a plane) you need to run 2 eigenfrequency runs, one with symmetry, one with antisymmetry conditions, else your re estraining yourself to roughly half the modes, as the symmetry mode is fixed in the normal direction. If you have 2 symmetry plane (1/4 model) then you need to do 4 cases with all combinations of symmetry / antisymmetry loads tocover all modes Also the mode frequency might vary depending on the mesh density/quality (and the mesh symetry) so some & difference is not astonishing, uit the differenece should reduce with a higher mesh density -- Good luck Ivar
Nagi Elabbasi Facebook Reality Labs
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 1 decade ago Oct 19, 2012, 2:25 p.m. EDT
I just want to repeat Ivar’s point about geometric symmetries and mode shapes. Even if a part is symmetric it will have roughly as many non-symmetric modes as symmetric ones. Only if you are sure that your loading is also symmetric can you ignore the non-symmetry modes.
I just want to repeat Ivar’s point about geometric symmetries and mode shapes. Even if a part is symmetric it will have roughly as many non-symmetric modes as symmetric ones. Only if you are sure that your loading is also symmetric can you ignore the non-symmetry modes.

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content