In its most simplest form dynamic stiffness is considered to be Maximum force (peak to peak) / maximum displacement (peak to peak). It can also be described as the following. So, one can also consider it to be response of a system due to unit input Eq. 4-9).
Perhaps we have different purpose to analyze. Let me tell you first, i have a case, please see the picture below..
displacement constraint is imparted at left side of the plate, and exciter at node 9 is given by applying force with non spatial field (usually we use impact hummer in actual condition).
At the result i need inertance frequency value such as this picture:
after that we take inertance frequency (from the picture the frequency should be in torsional mode) at node 9 and node 45 into rigidity equation and get the value of rigidity. But if sol 111 can calculate the value of rigidity (in kN.m/rad) automatically is better for me.
So please give me the solution, i also attach bdf for the sample of case.
It is trivial to setup a frequency response run to obtain the Graph (Inertance Vs. Frequency) and identify the Torsional mode excitation once you have loading as function of frequency available. (in this instance it can be unity). Beyond that, the calculation of the result interpretation and the rigidity is left to the engineer. Nastran does not directly produce the rigidity results. I will leave it to others on this forum who has experience in extracting "rigidity" from frequency response results to comment further.
You may find the following link useful in setting up the frequency response problem in nastran/patran.
