boundary condition for seats in a vehicle cabin model

[mohamm21]

Hi,
i am performing a modal analysis of a vehicle cabin with fluid structure interface in ANSYS. i have included seats as well in the model.
For the boundary condition of seats, i have constrained all the degrees of freedom for seat elements.
when i perform the modal analysis there is no difference in the mode sahpe and frequencies for the vehicle model with seats and without seats.

can anyone tell me whats the problem and where i am wrong.
i would be grateful for ur help
thank you

quadris
automotive engineering

 

[Drej]

Without more details it's difficult to give any help. You would expect there to be a definite change in frequency and mode shape with the inclusion of the seats, assuming that their relative mass/stiffness is significant wrt the rest of the structure. Have you remembered to specify material properties for these items? Why do you need to constrain the seats? Are you constraining them such they they play no part in the solution? Do the seats have their own mode shapes/freqs - you would expect so? Shouldn't the seats only be joined by mesh (or constraint equations, say) to the cabin in some way, rather than using "d" commands? Etc. etc...