ABSTRACT

This paper deals with the numerical calculations of free surface flow around a ship moving in calm water as well as in waves. The hydrodynamic problem of a surface ship advancing in waves at constant forward speed is analyzed using 3-D sink-source method. The body boundary condition is linearised about the undisturbed position of the body and the free surface condition is linearised about the mean water surface. The potential is represented by a distribution of sources over the surface of the ship and its waterline. The problem is solved by the method of singularities distributed over the hull surface. Hess & Smith (1964) method is used to obtain the density of these singularities. The hull is represented by plane polygonal elements. Numerical solution of the surface ship case is approximately obtained by considering each of these elements as a constant singularity. Potential of any particular point in the free surface around the moving hull is determined by using the 3-D Green function with forward speed which satisfies the boundary conditions for a pulsating source in the fluid. Typical contours of wave patterns around moving surface ships are calculated from the velocity potential. Finally added mass and damping coefficients for heave and pitch with forward speed at =0.2 n F are calculated and compared with the published experimental and numerical results. These will be helpful for the accurate estimation method of relative wave height of a sea going ship and wave breaking load on the deck.

INTRODUCTION

The wave-induced motions of a ship have several implications for ship performance, increased resistance, deck wetness, slamming, vertical acceleration and propeller emergence, etc. while all of these aspects are important subjects in ship hydrodynamics, the fundamental problem remains in estimating the overall motion of the ship in waves.

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