Stochastic Response of Prototype Offshore Structure

Abstract

The dynamic responses of a prototype space‐frame offshore structure to both measured and simulated stochastic wave forces are evaluated. A linearized, nondeterministic frequency domain analysis is made on a two‐dimensional model of a prototype offshore production platform located in the Gulf of Mexico. Linear ocean waves are modeled as a zero‐mean, stationary, ergodic Gaussian process represented by a one‐dimensional wave energy density spectrum. Simulated stochastic wave forces are computed via the Morison equation which is modified to account for both the effects of wave‐structure interaction and for the equivalent linearization of the drag force in the timeaverage, mean‐square sense. The dynamic equations of motion for the wavestructure system are solved by the normal mode‐superposition technique. The coupled generalized damping matrix is diagonalized through an optimization procedure. Iterative procedures are used to determine the equivalently linearized drag term and to uncouple the generalized damping matrix. Dynamic responses of the prototype production platform are compared using both simulated and measured wave pressure force spectra.