I’m working on a standard case of stratified flow. The model consists of a horizontally oriented circular cylinder moving in vertical direction through stably stratified salt water. This two dimensional case allows for analytic description of the phase of the internal waves generated by the cylinder. The definition of the density distribution in the boundary conditions is my problem. I either define a non stationary case with time dependent density in the flow field or a moving cylinder in a stationary stratified ambient. Which one of these strategies makes sense and how can I define a user function for the density?