ABSTRACT:

The present paper describes a selection of recent research relating to random wave forces acting on slender structural members. A brief review of prediction methods for random wave forces is initially given, and recent research into three specific aspects of random wave forces is then described. These relate to (i) the effects of multi-directional waves; (ii) the intermittent forces acting on sections near the water surface; and (hi) wave slamming forces on horizontal cylinders. For the first two cases, corresponding to multi-directional wave loading and to intermittent loading, comparisons are presented between available experimental data, numerically simulated data and theoretical predictions.

INTRODUCTION

The prediction of wave loads on offshore structures is an important component of offshore design. For structures comprised of slender members, wave force predictions are traditionally based on the Monson equation, in which the wave force at any section of a member is expressed directly in terms of the fluid kinematics which would occur at that section" s location (e.g. Sarpkaya and Isaacson, 1981). The application of the Monson equation to regular waves is straightforward in principle and requires that the kinematics be obtained by an appropriate wave theory. For the case of random waves, the Monson equation may be applied to develop the statistical properties of the forces. These relate to the effects of multi-directional waves; the Intermittent forces acting on sections near the water surface; and wave slamming forces on horizontal cylinders near the free surface. In the case of multi-directional waves, the estimation of forces on a structure is complicated because of the continuously changing direction of the incident flow kinematics associated with the multidirectional waves. The spectral and probabilistic properties of the force taking this into account have been described by Isaacson and Nwogu (1989).

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