The hydrodynamics of ship-like sections in heave,sway,and roll motions predicted using an unsteady Reynolds-averaged Navier—Stokes method

Abstract

The application of strip theory for predicting ship seakeeping response in waves relies on sectional added mass and viscous damping. A Reynolds averaged Navier—Stokes (RANS) approach is adopted to obtain two-dimensional hydrodynamic coefficients that include viscous and rotational flow effects as well as free surface wave generation. Calculations are made for circular and rectangular sections of cylinders swaying, heaving, and rolling in the presence of a free surface, for a range of frequencies. The predicted hydrodynamic coefficients are compared with available experimental and numerical results. The method is successfully validated for sway of a submerged circular cylinder. Good agreement is obtained for sway and heave of a rectangular cylinder at a free surface. For roll, the results are highly sensitive to the mesh applied due to the vortex shedding that occurs at the sharp corners, even at relatively low roll amplitudes. The appropriate density of mesh influences the convection of the vortex, the production of vorticity, and the position of the vortex core. These all have a large impact on fluid damping. A hybrid-based zonal mesh generation approach is proposed to maintain a compromise between necessary mesh refinement and the overall number of cells. Using this technique and a small fixed time step leads to improved predictions of the roll hydrodynamic coefficients, particularly for fluid damping.