Hydrodynamics of ship-like sections in heave, sway and roll motions using RANS

A two-dimensional approach using a commercial RANS solver (ANSYS CFX10) is presented here to obtain the hydrodynamic coefficients of cylinders swaying, heaving and rolling in presence of a free surface. The results derived in the time and frequency domains are compared with available experimental and numerical results. The method is successfully validated for a submerged circular cylinder swaying. Particularly good agreement is obtained in the medium frequencies range for a rectangular cylinder swaying and heaving at a free surface. For roll, the problem happens to be highly mesh-sensitive due to the complex mechanism of vortex shedding occurring at the sharp corners, even at low roll amplitudes. Mesh density at the corners influences the smearing of the vortex, the prediction of vorticity and the position of the cores, which have a large impact on fluid damping. A hybrid mesh technique is proposed to overcome the compromise between mesh refinement and low total number of cells.