Progress has been performed for decades, in terms of physical knowledge, numerical techniques and computer power, that allows to address more and more complex simulations. For many applications, engineers have to implement complex "modeling systems", coupling several models and softwares, representing various parts of the physical system. We address in this article model coupling techniques using Schwarz's methodology, which is based on domain decomposition methods. The basic principle is to reduce the resolution of a complex problem into several simpler sub-problems, thanks to an iterative algorithm. These methods are particularly well suited for industrial codes, since they are very few intrusive. We firstly discuss a coupling test case between two monophasic/diphasic tridimensional models, using Telemac-Mascaret and OpenFOAM software systems. Secondly, we analyze such a coupling for an operational engineering study of a water intake for a hydroelectric plant and a short comparison with physical model results.