Non-linear wave diffraction around a moored ship

The objective of this research, part of the FP5 REBASDO Programme, is to examine the effects of directional wave spreading on the nonlinear hydrodynamic loads and the wave run-up around the bow of a floating vessel (FPSO) in random seas. In this work, the non-linear wave scattering problem is solved by employing a quadratic boundary element method. An existing scheme (DIFFRACT developed in Oxford) has been extended to deal with uni-directional and directional bi-chromatic input wave systems, calculating second-order wave diffraction under regular waves and focused wave groups. The second order wave interaction with a floating vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and the experimental measurements conducted at Imperial College shows excellent agreement. The second-order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wavestructure interaction; otherwise a major underestimation of the wave impact on the structure could occur.