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modal analysis/beam with loads

modal analysis/beam with loads

modal analysis/beam with loads

(OP)
In ANSYS, the only "loads" valid in a modal analysis are displacement constraints. How do you determine the modes of a structure with real loads, such as a beam supporting heavy equipment?
I tried running a static analysis, saved the file, started a new "modal" analysis and requested that Prestress be included, but the results are still for a structure with no loads.

Thanks

RE: modal analysis/beam with loads

>How do you determine the modes of a structure with real loads, such as a beam supporting heavy equipment?

By carrying out a free vibration eigenvalue analysis (antype,modal) like everyone else. This is a modal analysis of a system FREE of external loads, and thus shows potentially how the structure would respond (mode shapes - eigenvectors - and corresponding eigenvalues) to a dynamic load input. If you want to see how your system responds dynamically, run a transient dynamic analysis with a dynamic load input, not a free vibration.


>I tried running a static analysis, saved the file, started a new "modal" analysis and requested that Prestress be included, but the results are still for a structure with no loads.

You can include pre-stress if you want, but make sure the pstres,on option is switched for BOTH the static and the modal analyses (not just one).

Cheers,

-- drej --

RE: modal analysis/beam with loads

and just model the heavy equipment as non structural mass.

Cheers

Greg Locock

RE: modal analysis/beam with loads

I'm going to visit this site more often.. I've written several artiles regarding Dynamic Reponse problems. One such article is in Machine Design magazine "FEA Upate" column. This article includes a sample problem with detailed hand calcuations and a FEA problem for download. Send me a note and I'll forward you a copy.

David R. Dearth, P.E.
Applied Analysis & Technology
E-mail "AppliedAT@aol.com"

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