First- and second-order analysis of resonant waves between adjacent barges

Water wave diffraction by two parallel closely spaced rectangular barges is investigated, to characterise the general problem of LNG offloading from a floating plant into a shuttle tanker. It is well known that large free-surface motions, in the gap between the hulls, are predicted by diffraction theory; in model tests amplitudes of at least five times that of the incident wave amplitude have been observed. A second-order diffraction calculation is used, based on a quadratic boundary element method, to examine the behaviour of this characteristic configuration and to examine the influence of spacing between the hulls. The free-surface near-resonant behaviour at first and second order is interpreted in the context of simple linear analytical solutions for three-dimensional flow in an open-ended gap.