I have a fairly large structure I am trying to model as sitting on sandy soil. I realize that to be really accurate I would need non-linear (sim pro only, dont have it) so I have been using a spring fixture to simulate sinking into it. This works generally well, but if a part is bending and lifting, the spring fixture resists motion away from it as well. What I would really like it a surface the model can push into (1 inch per 115PSI is the random number I am using), but can pull away without restraint. Short of modelling a large block of rubber (and trying to get the stiffness correct) is there any other approach I can take?
What you're after is a non-linear spring, which I'm not sure whether Soildworks Simulation has (and if they do, whether sim pro has it).
My next questions ares what are you specifically doing, what are you after answer wise, and how accurate are you trying to be? All of these determine how best to approach this.