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Re : modal analysis

Shyamsananth Madhavan

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Hi,
I was doing a modal analysis of structure.I gave a prescribed displacement at a node, got the first frequency.
When u give force instead of displacement , the frequency value differs.
I know that force doesnot play a role in eigen frequency analysis..

But how come prescribed displacements effect the eigen frequency evaluation???? Can anyone explain the theory or suggest a book ...


1 Reply Last Post 2010年8月1日 GMT-4 03:57
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)

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Posted: 1 decade ago 2010年8月1日 GMT-4 03:57
Hi

I believe it is because if you give a prescripted displacement you "fix" your other end, so you go from a "fixed-fixed" situation (with prescribed displacement) to a "fixed -free" case (with a force instead of a fixed displacement that is ignored anyhow by default for an eigensearch). Such changes in BC's are for me sufficient to give (very) different modes and frequencies

--
Good luck
Ivar
Hi I believe it is because if you give a prescripted displacement you "fix" your other end, so you go from a "fixed-fixed" situation (with prescribed displacement) to a "fixed -free" case (with a force instead of a fixed displacement that is ignored anyhow by default for an eigensearch). Such changes in BC's are for me sufficient to give (very) different modes and frequencies -- Good luck Ivar

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