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Modal analysis on hollow beam

Good morning, I am studying a cantilever hollow beam both with FEM (Ansys) and MULTYBODY (MSC Adams).

Do anybody knows why I get different mode shapes performing modal analysis with the two codes? (e.g. 3rd mode in Adams is torsional while ansys has not any torsion modes!!)

Thank you very much

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Do you have the same degrees of freedom in both cases? i.e. in Ansys, do you use a 2D or a 3D beam?

Gopinath Venkatesan's picture


I agree with rayoly's comments. Please use beam4 or other 3D beams. (So I presume that your Adams solution is correct).

I have a small doubt in using Adams view package, Is that not a rigid body dynamics tool? Did you use flexible body for the analysis?

Can you please explain on how you used Adams/View package to do modal analysis? Thank you.


University of Oklahoma 

I used beam4 elements with ansys (5 elements) while I used 5 elements in ADAMS linking their center of masses with a beam --> elastic property.

In this way I thought I get a flexible beam even with ADAMS, and ADAMS simulations give me this idea too.

I am gonna check how to explain better what I did with the two codes, thank you for your willingness. 


Stefano Galiasso
Automotive Engineer (Bachelor)
Mechanical Engineer (Master degree, currently attending)

Gopinath Venkatesan's picture


Did you try to compare with the analytical solution, ωn2=(E I/ρ A)βn4 where Cos[βn L] Cosh[βn L]+1=0, and n=1,2,3...

(read as Omega_squared=(E I/ρ A) (beta raised to power 4), subscript n for nth mode)

βn=1.8751, 4.6941, 7.8548, ...  



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