Damping estimation, response prediction and fatigue calculation of an operational single pile platform

Abstract

A comparison between predicted and measured damping controlled dynamic response of an operational single pile platform (AMOCO's South Marsh Island Block 33B platform) is presented. In the predictive analysis, a finite element model of the structure and a theoretical assessment of damping phenomena are combined with a response prediction method which utilizes the principle of reciprocity of ocean waves. The result is a versatile expression for the estimation of the dynamic response fatigue life of a platform in a directionally spread sea. In addition, the data analysis performed on wind, wave and response time histories, recorded in March, 1980, is carefully described. A method is presented which uses biaxial accelerometer data to infer platform modal orientations and to estimate wave spreading. Finally, modal natural frequencies and damping ratios are estimated using the Maximum Entropy Method (MEM) of spectral analysis. Good agreement between predicted and estimated response characteristics is attained.