On the probabilistic distribution of loads on a marine riser

Marine risers are subjected to various types of loads, such as axial tension and bending moments arising from the motions of an offshore platform in association with waves, winds, and currents. They are also exposed to internal and external pressure loads caused by internal flows and external water pressure respectively. The aim of this study is to quantify the probabilistic distribution of loads on a marine riser to aid in the determination of the nominal design values. Two methods are investigated here. The first one is to select a set of credible scenarios in association with site-specific metocean data, and then perform dynamic riser analysis to describe the probabilistic distribution of the loads. The second one is to develop a metamodel to predict the loads as a function of multiple input variables; a method that can also characterize the probabilistic load distribution by running a Monte Carlo simulation. A numerical example shows that the metamodel-based method is more appropriate to describe the loads at low exceedance probability. The characteristics of the loads on a marine riser are observed to be highly random and hence, the design loads must be determined based on the distribution of the influencing parameters.