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Hi, I'd like to model a box floating in open water, that means that wave generation and especially wave absorption should be modelised. I've modeled this on Hypermesh with the solver Radioss In this model, there are 2 sorts of interaction : - fluid/fluid : air with water - fluid/structure : both fluids with the box. First, I've used an ALE model for the fluids. I've tried to use both MAT/LAW51 (multimaterial) and MAT/LAW37 (biphasic material) in order to model this, but everytime there is a leakage and the computation can't run until the end (negative rho error). I've also tried to use MAT/LAW11 (bound) because it doesn't work properly with a biphasic material (negative rho error). Then, I've tried with an SPH model with IN and OUT condition, so that the computaiton doesn't take into account the air/water interaction, the computation also stops because of a leakage. For the fluid/structure interaction, I've used INTER/TYPE18 and INTER/TYPE7 respectively for ALE and SPH model. I have to set a STfval value for the stiffness. I use the formula of the Help page : stfval=rho*v²*A_el/GAP = 66.667avec - rho=rho_water = 0.001g/mm3; - v=10 mm/ms , initial velocity of the box when it is dropped in the water; - A_el = lagragien element surface =500 * 500 mm² ; - GAP= 1.5 * E_el = 1.5 * 250 = 375mm With this value, the box is floating in the air, the only way i've found a value that models reality was by dichotomy.. That's not convenient for further simulation with different initial data.... Should you have any suggestion to model an infinite water volume (so wave absorption) and for the stiffness value, please contact me. Sincerly yours, Emmanuelle