Coupling of general Lagrangian systems

This work is devoted to the coupling of two fluid models, such a s two Euler systems in Lagrangian coordinates, at a fixed interface. We define coupling conditi ons which can be expressed in terms of continuity of some well chosen variables and then solve the coupled Riemann problem. In the present setting where the interface is characteristic, a particula r choice of dependent variables which are transmitted ensures the overall conservativity.