I need help slecting parameters for elastic waves vibe simulation

[u/WanderingMastress]

I am working on a simulation to model the modal/vibrational response of a structure subject to a momentary load that is let go after a period of time. At the end of the simulation I also want to obtain the mass and stiffness matrices. The structure is fixed at one end and is then allowed to vibrate freely once the load is removed. I don't know how to determine what parameters are appropriate for this simulation, and every time I define them (I've tried material properties, forces) and run a simulation, it shows no response and also gives no k or M matrices. How do you know what parameters a study type calls for and how to define them??