Nonlinear dynamic response and reliability analysis of drag-dominated offshore platforms

摘要

For slender structures like jack-ups and deep-water jackets, the response to wave loading is frequently of a dynamic character. Due to the drag-type of loading on these structures, pronounced non-Gaussian statistical properties of the response are observed for the highest sea states. The main purpose of this work is to study the stochastic nonlinear dynamic behavior of slender offshore structures, to quantify the sensitivity to various parameters and to assess their importance for nonlinear dynamic response. The parameters considered in this study are related to the environmental loading, the nonlinear soil-structure interaction and the environmental modeling for long term response analysis. The main emphasis in on extreme load conditions. However, a limited study is performed to investigate the influence of nonlinear behavior on the fatigue response also. The second objective is to introduce a procedure for reliability analysis based on a full nonlinear long term response analysis. The findings from the parametric studies will form the basis for the reliability analysis. In this work, present design procedures are reviewed and an efficient procedure for nonlinear dynamic response analysis of fixed offshore platforms is described. The procedure is exemplified by application to two jack-up platforms designed to operate in the Central part of Southern part of the North Sea and to a slender deep water jacket platforms installed in the Central part of the North Sea. Furthermore, the importance of various parameters on the short term nonlinear dynamic response is investigated. The parameters included are: wave kinematic models, wave-current interaction, structural and hydrodynamic damping and nonlinear soil-structure interaction.