Quote: 
What is the reason for the COMSOL TE noise to diverge from the analytic one at low frequencies?
Don't you have to consider the coherent TO noise between the coatings and the substrate?

At low frequency, the adiabatic approximation (used by BGV, Liu & Thorne) breaks down. Basically, it assumes that heat inside the material is not diffusive. The only place that heat flow must be considered is in the volume integral where gradient of expansion is non zero for the dissipation. (see Liu & Torne explanation just above eq 8). This is easier for COMSOL simulation. Since I just press the substrate with static force, and calculate the deformation of the body which, under adiabatic approximation, gives me the temperature change of the body.
If I want to take into account the heat flow, I have to (see Cerdonio)
 solve The stress balance with temperature dependent and
 solve heat equation with expansion dependent (these two equations are coupled).
Then for COMSOL simulation I have to use different setting and I'm not exactly sure how to do this yet.
