Not a problem. nThe floating point exception can occur because of many many reasons. Defining the density as a function of temperature or not, might not be one of these reason. It is a matter of defining the physics of the problem.nDo transient simulation and decrease the time step to a very small value and increase the number of iterations to more than 100. Run few time steps with this conditions. If you get floating point excption, you will need to refine the mesh and try againn