Time-domain random dynamic analysis of marine risers and estimation of non-Gaussian bending stress statistics

Abstract

The equations of motion for a finite element model of a marine riser are assembled and transformed to modal form. The modal equations are integrated numerically, and the mode-acceleration method is used to obtain sample time-histories of response. Random processes considered include the maximum bending stress at any point on the riser and stresses at particular locations. Small-displacement theory is used, but the non-linear form of Morison's equation is used for calculating the fluid loading. Response statistics are estimated from sampled values using the maximum likelihood method, assuming a generalized gamma distribution. Probability density functions and upcrossing-rate functions are estimated. Lifetime reliability and fatigue damage rates are calculated from the estimated upcrossing-rate functions.