ABSTRACT:

The flow field around a horizontal circular cylinder in two-dimensional regular water waves is simulated by a finite-difference method based on the Navier - Stokes equations. The numerical simulations are carried out at the intermediate Keulegan- Carpenter number 1 to 3. The complicated interaction of vortices and the drop of inertia force coefficients at this region show good agreement w1th the results of model test in towing tank. It is also shown that the pressure distributions on the cylinder surface are simulated with the sufficient degree of accuracy.

INTRODUCTION

It is well known that wave forces on a submerged horizontal cylinder in regular water waves is scarcely influenced by the viscosity when the Keulegan-Carpenter number is less than unity. In this case potential theories, such as one by Ogilvie (1963), can be effectively employed for the estimation of wave forces. However, for Keulegan-Carpenter number (Kc) exceeding 1an important part of the wave forces is generated by the viscous effects, i e., flow separation, vortex shedding and interactions. In the higher Keulegan-Carpenter number region (Kc > 10) the empirical formula by Sarpkaya and Isaacson (1981) is often used for the estimation of wave forces, assuming that the fluid field is equivalent to a plane oscillatory flow. However, it is recently noted that the flow field caused by the water waves about a horizontal cylinder is quite different from a plane oscillatory flow. In the experimental results by Koterayama and Tashiro (1978), it is shown that the wave forces in regular waves differ from those predicted by the experimental results derived from the case of a plane oscillatory flow Chaplin (1984a) (1984b) clarified that the nonlinear component of inertia force occupies almost one half of the total inertia force for Keulegan-Carpenter numbers approaching.

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