Simplified body nonlinear time domain calculation of vertical ship motions and wave loads in large amplitude waves

Abstract

A strip theory based partially nonlinear time domain code is extended to include body nonlinearity in the calculation of radiation and diffraction forces, which expresses the dependence of hydrodynamic forces on the time changing underwater hull shape. The body nonlinear Froude–Krylov and hydrostatic forces are combined with the body nonlinear radiation and diffraction forces. The radiation forces are represented in terms of impulse response functions, infinite frequency added mass and radiation restoring coefficients. Additionally, a semi-empirical technique is employed to include the surge mode to overcome one of the strip theory two-dimensional simplifications. The method is used to calculate the wave induced vertical motions and bending moments on a modern Cruise Ship. Results from the time domain code in regular waves with different steepnesses, with and without nonlinear radiation and diffraction forces, are calculated and compared. Similarly, the analysis is carried out for design regular waves and is compared with model test experimental data obtained in a seakeeping tank.