Drift forces on compact offshore structures in regular and irregular waves

Abstract

A theory is introduced to determine second order wave (drift) forces on hydrodynamically compact structures, whereby the influence of the water depth is fully considered. The method is based on perturbation theory and on integration of the hydrodynamic pressures over the instantaneous wetted surface of the body (near field solution). The theory is applied to calculate drift forces on the barge type structure EPOS in three different water depths. Model tests are also conducted to compare results with theory. The practical significance of determining drift forces is illustrated by calculating mean and extreme drift displacements of the EPOS structure moored on location in the natural seaway. The influence of heave and pitch motions on the steady surge drift motion are considered.