Experimental validation of viscous free surface flow computation around fast NPL catamarans at large drift angles

Simulation of ship manoeuvres is one of the most important problems of ship hydrodynamics. The reliability of manoevring prediction depends substantially on the accuracy of the hydrodynamic models. At present the existing hydrodynamic models are based mostly on approximations of emperical data obtained for a special series of ships with variation of main geometric parameters. However, the development of more general tools like CFD (Computational Fluid Dynamics) is becoming very important, because lately the design of non-standard ships became common business of the European shipbuilding industry. The focus of the present paper is the validation of viscous flow computations using RANS-equations (Reynolds Averaged Navier Stokes) performed for catamarans with NPL hull forms. Steady single-phase computations utilizing a double body concept and unsteady flow simulations considering a free surface have been conducted at moderate Froude numbers and large drift angles. To validate these predictions, numerous captive model tests using a twin hull configuration of NPL hull folms have been undertaken. The computational results have been experimentally proven being capable of reliably predicting the hydrodynamic forces and moments on the hull for a wide range of drift angles.