Submarine Motions in Confined Waters. INSEAN Technical Report No. 5

This technical report concerns the work element WE-4.2 within the WEAO EUCLID RTP 10.17 project "Submarine Motions in Confined Waters". The theoretical model adopted at INSEAN to study the manoeuvring of submarines near the air-water interface is described and related assumptions and limits are discussed. The features of the solution algorithm are also outlined. These are based on the use of a Navier-Stokes solver combined with a Level-Set technique to handle the free surface evolution. The problem is solved on an overlapped multi-grid with a Chimera algorithm to improve the efficiency and accuracy of the solution. The solver is applied to analyse the interaction of a submarine with regular incoming waves when the body advances with constant speed and with/without a drift angle. In this context, a pressure decomposition strategy is considered to separate the incoming wave effects from the flow perturbations connected with the wave-submarine interaction. The cases prescribed by the related INSEAN unsteady numerical test matrix have been simulated and the results are reported in terms of submarine loads and free-surface deformations. The numerical parameters (grid generation, convergence and uncertainty) connected with the numerical solution are also discussed. Mean values and amplitudes of the loads estimated in steady-state conditions are compared with the MARINTEK experiments in waves. The INSEAN solver proved to be able to handle the submarine manoeuvring in waves. The challenge to overcome for a practical use of CFD tools (i.e. for accurate and relatively fast simulations) is represented by the CPU-time and memory requirements.