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Normal modes analysis with FASTCONT

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Hello everybody, I do a 'normal mode' analysis in a model without contact and I get 8 rigid displacements. Then I create the contact surface (with type Freeze) and I active the FASTCON card. So I do again the normal mode analysis but I obtain only 7 rigid displacements. Someone can help me? 

Thank so much for the help 

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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, 

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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

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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?

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