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

This research was sponsored by the Branch of Marine Oiland Gas Operations of the United States Geological Survey,Department of the Interior, and the Joint Program in OceanographicEngineering between the Massachusetts Institute ofTechnology and Woods Hole Oceanographic Institution.

A comparison between predicted and measured dampingcontrolled dynamic response of an operational single pileplatform (AMOCO's South Marsh Island Block 33B platform) ispresented. In the predictive analysis, a finite element modelof the structure and a theoretical assessment of dampingphenomena are combined with a response prediction methodwhich utilizes the principle of reciprocity of ocean waves.The result is a versatile expression for the estimation ofthe dynamic response fatigue life of a platform in a directionallyspread sea. In addition, the data analysis performedon wind, wave and response time histories, recorded inMarch, 1980, is carefully described. A method is presentedwhich uses biaxial accelerometer data to infer platform modalorientations and to estimate wave spreading. Finally,modal natural frequencies and damping ratios are estimatedusing the Maximum Entropy Method (MEM) of spectral analysis.Good agreement between predicted and estimated responsecharacteristics is attained.

Submitted in partial fulfillment of the requirements for the degree of Ocean Engineer at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution January 1982