Hello dear Dr.Krack!
I have the mass and stiffness matrices of the finite element model of a free structure. Of course the linear system made by these matrices have 3 rigid modes and the first three natural frequencies are zero! When trying to compute the linear FRF of this system using your codes, I notice that the results are not close to the test structure's FRF results. I think some additional modifications need to be made to the system or your codes to account for the free-free boundary condition of the system. What do you think those modifications would be?
I thank you in advance for your attention!
Hello Mahdi Aahi,
the code also balances the zeroth harmonic (static) on default. This equation is ill-posed, of course, if rigid body motion is possible, the Jacobian will be singular. A simple workaround is to remove the static balance and zeroth harmonic from your unknowns. If rigid body motion is possible only in some bodies/substructures you can proceed analogously.
Hope this helps.
Best regards
Malte Krack
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