[aria.ghiasi]

Hi, I used diffusion method for grid motion. in the fluent user guide it is said that in this method fluent uses a finite element method for calculating nodes positions. So what method? and did I understand right? I mean a finite element method in the middle of FVM?

[KevinZ09]

Yes, you are correct. The Fluent manual indeed says that in the absence of polyhedral cells and hanging nodes, it will use a finite element discretisation to solve the diffusion equation for the mesh displacement velocity. This equation is completely unrelated to the fluid equations. And it makes sense to use a FEM and not a FVM since the solution will give updated positions of the nodes directly, instead of having to interpolate if FVM is used.