Large-scale DES computations of the forward speed diffraction and pitch and heave problems for a surface combatant

This paper aims at presenting the most resolved solutions to date for the ship forward speed diffraction and pitch and heave problems, and discuss the method that enables these computations. Large-scale DES computations (60-115 million grid points, 276-500 processors) of ship hydrodynamics problems are presented for the DTMB model 5512 surface combatant. The forward speed diffraction problem is studied at Fr = 0.28 with waves of amplitude a = 0.006 and wavelength λ=1.5, with the ship static allowing the overset assembly to be a pre-processing step. In the pitch and heave problem the ship faces head waves at Fr = 0.41 with waves of amplitude a = 0.006 and wavelength λ=1.5, with the ship is allowed to pitch and heave, thus requiring dynamic overset grid processing. The code CFDShip-Iowa version 4 and the overset assembly code Suggar were modified to carry out some large scale simulations of free surface ship hydrodynamics. These modifications were focused on reducing the memory requirement and optimizing the per-processor and parallel performance at the implementation and algorithmic levels, plus the addition of a lagged mode for the overset domain connectivity computation. The simulation results show very significant improvements in the local flow and free surface results, but minor in forces and moments when compared with previous URANS computations performed with grids with about three million points.