I have come across the paper attached in which a 1D fluid piston is modelled. I have question on the boundary conditions (BCs) of the system. Essentially, the problem consists of a fluid chamber in contact with a spring (a mass -spring system). ALE is used to move the mesh. I am not certain about the BCs of the fluid. I think the fluid velocity, and the mesh velocity are both set equal to the piston velocity at the right hand side boundary and that pressure and density are interpolated. In the left, I have set velocity of fluid and mesh to zero. Am I correct so far? Thank you in advance!