Dear Mr. Dave,

Actually my client requires that I need to remove all friction effect in the input during modal analysis. What's funny is that nobody knows why and from where this rule came, but everybody needs to follow.

I understand that eingenvalue is a linear calculation and for this reason can't handle with nonlinear boundary conditions like friction. But in my point o view, removing friction effect is not quite realistic. Not considering the friction effect will result in criating several other supports (guides and stops) just to meet the frequency requerement.

So I think that adding in each support a stiffness equal to normal load in operation multiplied by friction coeficient will bring a result near to reality (unitary factor). Why do you suggest a factor of 500 to 1000? With a high factor the pipe horizontal movement in the support location (+Y only, for example) will be restricted, is that correct?

Thank you very much for your help.

Regards,
Roberto