STUDY ON COMBINED SEA ENVIRONMENTAL DESIGN CRITERIA FOR MARINE RISERS

摘要

The motion equation of lateral vibration of marine risers conveying flowing fluid subjected to ocean environmental loads is derived. Sampling analysis is made on the 15 storm processes of Bohai Sea and sequences of simultaneous wave height and current velocity dominated by wave and current respectively are obtained. Then the optimal distribution type of each sequence and the corresponding characteristic values are determined. Importance Sampling Procedure is applied to stochastic simulation to compute the wave height and current velocity under joint probability 0.01 (that is 100 yr. combined return period). Finally, taking the marine riser containing flowing fluid as a model, the maximum stress on the marine riser is regarded as the control condition to determine the combined design criteria. Comparisons with results of other methods show that the combined environmental design criteria and the stress response of the marine risers are very sensitive to small variation of the current velocities in high current sea areas.