Spectral Analysis of Ocean Wave Forces on Piling

Abstract

A computational formula is developed for determining, from the sea-surface spectral density, the spectral density function of the force per unit length at a point on a vertical pile. An accurate and simple approximation for the formula is presented and used to explain the near proportionality between the spectral densities of force and sea surface measured in the ocean near Davenport, Calif. The computational formula and its approximation are extended to provide procedures for the determination of the spectral density of either total force or total overturning movement on a structure consisting of an array of vertical cylinders. The approximation leads to a particularly simple relationship in which the spectral density for the total structure is the spectral density for a single pile times a function which characterizes the geometry of the array. To illustrate the procedure, the total force spectral density is computed for a four-pile instrument platform in 49 ft of water.