ABSTRACT:

A formulation for calculating the steady hydrodynamic loading on a slender ship moving at a constant forward speed and small attack angle in finite water depth is developed. The study is motivated by the need to predict the manoeuvrability of ship with large draft in relatively shallow water. The slender body assumption is used to reduce the problem into a series of two-dimensional boundary value problems that are solved using the boundary element method. The fully non-linear free water surface conditions are imposed on the instantaneous water level. The numerical calculations are performed for the Wigley hull model ship. Effects of the attack angle and finite depth are assessed in the subcritical region.

INTRODUCTION

Predictions of ship manoeuvrability have drawn recent attention after the introduction of the IMO interim standards on ship manoeuvrability in 1993. The ship manoeuvrability prediction requires amongst other things, knowledge of the ship resistance and propulsion characteristics. Part of the resistance arises from the hydrodynamic forces acting on the ship body moving at a constant speed in calm seas. The hydrodynamic force computation is further complicated in that the problem is non-linear due to the non-linear boundary conditions at the unknown free water surface. The computation of ship hydrodynamics had received very significant attention in the past. Maruo and Song (1990) had developed a boundary element solution for a slender ship based on Green's functions in three-dimensions and using the Kelvin sources which satisfied the linearized free surface conditions exactly. Results were presented for the cases of a Wigley hull, a sailing yacht hull and a Series 60 CB= 0.60 hull, with good agreement with existing experimental data. They found that the non-linearity had an insignificant effect on the water surface elevation alongside the ship hull but significantly affected wave resistance.

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