I am trying impose free-free boundary conditions in analyzing free vibrations of a beam. I have coded up in Matlab. I used to restrict the corresponding degrees of freedom with the related boundary condition before. But, for free-free case that method is not responding and I get complex frequencies.
Arash Imani Aria, I am not sure which software you use. Seems some of the software are not able to deal with modal analysis without boundary conditions. There is some interesting discussion in the below link .
https://www.researchgate.net/post/Is_it_possible_to_perform_modal_analysis_without_using_boundary_conditions_fixed_support_in_Abaqus
Arash Imani Aria, below link has some explanation about how to compute the eigenvalues. If your matrix is real and symmetric, you should be able to get the real eigenvalues.
https://www.researchgate.net/post/Is_it_possible_to_analyze_frequency_response_of_free_no_constraint_structure2
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