How to set boundary condition for free floating model in thermal simulation?

Hi,

I am doing thermal simulation. Below is the simplified model. I am checking how stress and deformation when temperature change from 180C to 0C for below assembly.

My question is how I can set the boundary condition which enough to hold parts, and doesn't affect the simulation? I would like to solve considering the assembly in free floating like situation...

Is there any option to do this, like free floating? Or ...kind of method or situation to put the assembly on top of some surface without restricting deformation?

Someoen says, I can choose...boundary condition smartly....so it can hold the assembly and solve it without restricting the parts deformation. would you comment if you know or hint?

Thanks,

Cheol

SolidworksSimulation