Slender ship procedures that include the effects of yaw, vortex shedding and density stratification

The accurate determination of hydrodynamic loads on moving ships is important for hull form design and optimization and structural design purposes. This is especially true at the preliminary design stage during which time quick predictions of the forces and moments acting on a ship advancing steadily with, and without, yaw would be extremely useful. hi view of this, simple numerical cross-flow algorithms has been developed. The numerical procedures are based on slender body theory, which is used to convert the three dimensional problem into a series of two dimensional wavemaker problems in the plane of transverse sections, marching in small steps from the bow section towards the stem. Fluid density stratification, vortex shedding, finite water depth and nonlinear free surface effects can be allowed for in the algorithms. A procedure for handling density stratified flow has been developed and successfully used for the calculation of surface and interfacial waves created by a prolate spheroid. Vortex shedding is modelled using the discrete vortex method. A hybridization of the discrete vortex and boundary element methods is achieved and illustrated in a test case of predicting the forces acting on an oscillating flat plate. The wavemaker, with the fully nonlinear free surface conditions, is used for calculating the generated wave pattern and wavemaking resistance of a Wigley hull. The effects of finite water depth on wavemaking resistance are calculated. The hybrid boundary element-discrete vortex method is used for determining the hydrodynamic forces and moments acting on a yawed Wigley hull.