Wave drift force and moment on VLFS supported by a great number of floating columns

A calculation method is presented of the wave-induced steady drift force and yaw moment on a very large floating structure (VLFS) comprising a multitude of floating columns. The theory is based on the momentum-conservation principle, and all necessary integrations are analytically implemented. Thus the resultant formulae include only the coefficients of the incident-wave and disturbance potentials at a large distance from the structure. A hierarchical interaction theory developed by Kashiwagi (1998) is applied to determine the disturbance potential due to hydrodynamic interactions among a great number of floating columns and elastic motions of a thin upper deck. Experiments in head waves were also conducted using 64 truncated vertical cylinders arranged periodically in 4 rows and 16 columns. Good agreement is found between computed and measured results. Further, through numerical computations in oblique waves, discussions are made on variation characteristics of the steady force and yaw moment particularly around frequencies corresponding to the near-trapping.