Dynamic Time History analysis of MDOFs with rigid parts

[sarian]

Dear Support Team

I'm trying to model a simple 3DOF system that is constructed by several rigid bars connected with rotational springs. A rigid column (along Z axes) that is connected to the ground by link element and all translations as well as torsional degrees of freedom are modeled as rigid by applying high stiffness values. So, two degrees of freedom (Rx and Ry) exist at the bottom of the column. A horizontal rigid bar (located in X-Y plane) is connected to the end of column by means of another link element that is representing the third degree of freedom (Rz) in the same manner (high stiffness values for other 5 degrees of freedom). After sensitivity analysis I could finally find the optimum stiffness values that are high enough to simulate rigidity in bars without affecting modal characteristics of system. Unfortunately, when I'm running dynamic time-history analysis the convergence does not occur even under excitation by simple harmonic loads. The analysis will be completed if I reduce the assumed values of stiffness but consequently I will loose the appropriate modal parameters. I have tried all proposed solutions for obtaining convergence but It seems not to work for me. Is there any other way to model the rigid parts?
It would be a nice favor if you can kindly guide me
Many thanks

[huffte]

A model would help define the situation much more clearly, sarian. Do you have any damping in the system? The default is none. Maybe a small amount of damping would be in order?

[sarian]

Dear Tim
Many many thanks. I could resolve the problem by adding damping based on your suggestion.