P.A. Bailey

Dynamic behaviour of rigid mono- and multi-hulled vessels in waves, incorporating non-linear excitation

This paper presents a time domain model for the prediction of ship motions in waves. Fluid forces and moments acting on the ship are represented by convolution integral expressions, which therefore account for fluid memory effects. The required impulse response functions are obtained from transforms of frequency domain data evaluated using a three-dimensional potential flow analysis based on a source distribution over the mean wetted surface of the vessel. Convolution integrals are used to describe both the radiation and diffraction contributions to the ship motion problem. Non-linear restoring and Froude-Krylov excitation forces are determined at each time step using the instantaneous underwater portion of the hull. The results are presented in head and oblique regular waves for a fast hull form, namely an NPL round bilge series, in both mono-hull and catamaran configurations. Initially, the wave amplitude conforms to the concept of linearity, allowing for the validation of the numerical procedures. Subsequently, the effects of non-linear excitation are investigated by increasing the amplitude of the regular waves.