Normal modes analysis with FASTCONT

I don't think that you have something weird .... it seems logical your results ! 

 I'm sorry but I'm not really knowledgeable with the program... Can you please explain me the reason why it's logical? Thanks in advance

By using Fast contact you delete the movement of a rigid body. 

Try to run a simulation by imposing BC : for example U_x = U_y = Uz = 0, keep the Fast contact. Normally, you will eliminate all the rigid body movement.  

Cheers, 

•Fast Contact is applicable when the only non-linearity in the model is contact. (no friction) CONTACT=SLIDE

•Non-linear geometry and material are not supported

Thanks a lot .... Another question: if I have to do a frequency response analysis i'll you the same setting used for the modal analysis? 

What is your end objective from this analysis? 

I have to do a frequency response analysis of this:

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Please refer below online tutorial using OptiStruct.

I'm sorry to bother you again ... I've downloaded the book but I can't find what I'm searching for. I'll try to reformulate the question: I've done a modal analysis with the card FASTCON in order to linearize the contacts, with property type SLIDE as you suggested and the result was good. Now I'm doing an indirect frequency response analysis: for the contacts I'm turned to used, in property type, SLIDE. Is it correct in this case?  
Thanks in Advance

FASTCONT was developed only for nonlinear analysis.You cannot implement FASTCONT for FRF analysis.

You can perform FRF analysis for above shared structure.

Thank you, I understand. The problem is that we have initially a task to do a linear analysis and a FRF of that cart. After a review they told us to use that card (FASTCONT) for penetrations problems so as to make a more accurate analysis. Then for the linear there were no problems, for the modal, as we have said, we use type=SLIDE. The last thing we have left to do is the FRF. So like you said then we have to delete the surface contact and disable the FASTCONT card and make a FRS with a linear model without contact ? Is it correct in this way?

Initially the linear analysis and FRF were without contact**

Please refer below post.