ABSTRACT:

This study aims the investigation of depth effects in the motion response of floating structures. To this end, a Rankine panel method adopting higher-order B-spline basis function is applied in time domain. The topology of sea bottom is assumed to be either constant or varied. Taking the advantage of the Rankine panel method, any bottom topology near floating structures can be considered by distributing the solution panels on the bottom surface. The numerical analysis includes the radiation, diffraction problems and floating motion responses for typical hull forms, e. g. LNG carrier and barge. The result is compared with other numerical solution for validation purpose. The motion RAOs are observed for different water depth and varying bottom topology.

INTRODUCTION

Recently moving inland facilities into coastal area is seriously considered. In coastal area, water waves and floating-body motion have different property by restricted water depth. Therefore considering bottom effect is important to predict the motion responses of such coastal platforms. The motion responses of floating bodies in constant depth have been considered as one of classical problems in marine hydrodynamics, and several methods have been introduced. For instant, strip method has been utilized by Tuck (1970), Tasis et al. (1978), Andersen (1979), Perunovic and Jensen (2003). This method is still used nowadays for practical purpose, however it has limitation as a two-dimensional theory. To complement such limitation, Kim (1999) introduced a new unified theory for the finite-depth effect, showing much improved accuracy. Nowadays, three dimensional panel method programs such as WAMIT (Lee, 1995), which contains solution procedure for constant depth, are available. For an offshore structure, Teigen (2005) has showed motion responses of floating barge over constant and sloped bottom. Ship motion over sloping bottom has been considered by Buchner (2006), Ferreira and Newman (2008) and Hauteclocque et al. (2009).

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