Ship sinkage and trim predictions based on a CAD interfaced fully nonlinear potential model

We present the results of a model for ship fluid-structure interaction simulations based upon the potential flow theory. The govering Laplace equation is complemented by non penetration boundary conditions on the boat surface and by fully nonlinear kinematic and dynamic water free surface conditions, written in semi-Lagrangian form. The hull is represented as a three dimensional rigid body subjected to the action of gravity and hydrodynamic forces. The spatial discretization of the fluid dynamic problem is carried out by means of an iso-parametric collocation Boundary Element Method (BEM), which only requires the discretization of the domain boundary surfaces. In such framework, the markers at which the free surface kinematic and dynamic boundary conditions are collocated correspond to the nodes of the computational grid. The application of such spatial discretization results in a system of Differential Algebraic Equations (DAE), which is time-integrated by means of an implicit Backward Differentiation Formula (BDF) scheme. As for the hull rigid body equations, they are added to the DAE system, so as to obtain a strong coupling between the fluid dynamic and structural solvers. Exploiting the simplicity of the surface grids required by BEM, the solver is fully integrated with CAD data structures. At the start of each simulation, the CAD file describing the hull is imported and used to automatically generate the computational grid. At each time step, the CAD surface is displaced in the current position, to obtain the proper horizontal positioning of the water nodes in contact with the hull. The model has been implemented in a stand alone C++ software (WaveBEM). The results of the simulations are compared with sinkage, trim experimental data available for the DTMB-5415 hull.