Development of a stochastic wave force function on ocean-structures

Abstract

The wave forces exerted on structures are of vital importance in the design of marine structures. Circular piles are frequently used to provide most or all of the support for such structures. The forces exerted by waves of similar properties vary greatly. These variations are the result of fluctuations in fluid particle velocities and accelerations as well as by eddies and turbulence around piles caused by rapidly reversing flow. Consequently, a deterministic approach to wave force prediction appears to be impossible. As an alternative, a probabilistic approach was developed in this paper. The method applied here utilizes a multiple linear regression analysis to develop a relationship between wave parameters which are relatively easy to observe and the parameters used in the Morison force equation. They include the velocity and acceleration of water particles and the drag and mass coefficients and are considered to be random variables. The assumption of their lognormal distribution was reasonably well verified. Using Monte Carlo simulation these regression relations were then utilized to generate the frequency function of the wave forces. The wave force function can best be described as stationary periodic process. It can then be used as an input function for a probabilistic dynamic analysis of offshore structures.