A hybrid Boussinesq-panel method for predicting the motion of a moored ship

This paper describes a new computational technique for predicting the wave- induced motion of a restrained floating body in restricted water. A combina tion of established methods is used in an attempt to account for the most i mportant physical processes involved in this complicated problem, while kee ping the computational burden modest. Potential theory is invoked to descri be both the wave transformation over the bathymetry of the harbour, and the hydrodynamic interaction between the waves and the floating structure. Mod ified Boussinesq theory is used to predict the transformation of the waves as they propagate from deep water into to the harbour or bay where the body is moored. This model includes the effects of shoaling, refraction and non -linear wave-wave interaction, and most importantly sub-harmonic generation . This Row is then linearised locally, at the structure, to provide the inc ident wave forcing term in the equation of motion which is solved in the ti me-domain. Linear wave radiation and diffraction forces are computed using a constant-strength panel method, while the instantaneous, non-linear, poin t mooring forces are included exactly. The model is validated for the linea r problem, and non-linear calculations are compared with experimental measu rements for a ship moored in an L-shaped harbour. Qualitatively, the non-li near features of the dynamical system are successfully captured by the mode l. Some tuning, in the form of empirically obtained damping coefficients, i s, however, necessary in order to get a reasonable prediction of the respon se amplitudes near resonance, when the linear hydrodynamic damping is very small. (C) 2000 Elsevier Science B.V. All rights reserved.