ABSTRACT:

This paper deals with the determination of the induced side force and induced heave hydrodynamic coefficients on a vertical, surface piercing cylinder due to a nearby, geometrically identical cylinder subjected to sinusoidal heave motion A numerical method called the Matching Technique is employed to compute theoretical values at various cylinder separation for a full range of frequencies for both deep and shallow water. Comparison with experimental results shows that the analytical method performs well in predicting the behaviour of induced forces between nearby cylinders. These values, although low, may still need to be acknowledged by the naval architect in the design of offshore structures composed of cylindrical members in order to estimate vibrational levels as well as fatigue limits within the structure. The method can also be used to determine the induced forces due to an iceberg nearing an ocean platform

INTRODUCTION

Prediction of cyclic loading conditions on offshore structures will lead to reliable predictions of vibrational levels and fatigue limits within the structure. While many well known procedures and data bases exist for the design of ships, the prediction of cyclic loading on offshore drilling platforms is still developing. The problem examined in this paper is the hydrodynamic effect of the presence of a vertical cylinder near another vertical cylinder In particular, a numerical method is employed to predict the induced horizontal force on a cylinder due to simultaneous sinusoidal vertical heave motion of two adjacent cylinders. A simple case is studied here, where two vertical cylinders in heave motion are considered, although the technique can be extended to cover more general cases. A variety of numerical solution procedures such as the finite element method of Bai [2] or the boundary element method of Yeung [3] can also be considered.

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