LONG-TERM WAVE FATIGUE ANALYSIS OF DEEPWATER DRILLING RISER

As a dynamic,fatigue sensitive structure,long-term fatigue performance of the deepwater drilling riser is an important design consideration.A method of long term wave fatigue analysis for deepwater drilling riser is presented,which can be used to calculate the long term fatigue of drilling risers subjected to 1st order wave force,wave frequency vessel motion and 2nd order low frequency vessel motion.Using the proposed method,according to the short term fatigue case defined by the wave scatter diagram,random wave and random vessel motion require to be simulated based on the dual parameters wave spectrum and the RAO(response amplitude operator) of the drilling vessel.Then,nonlinear dynamic analysis of the drilling riser under random wave loads and vessel motion boundary condition should be performed.Based on the response time history obtained by dynamic analysis,considering the probabilities of short term cases in the wave scatter diagram,using self-developed special program to calculate the long term wave fatigue.In an example,long term wave fatigue of the deepwater drilling risers with length of 1 500 m in south China sea is implemented.The effect of drilling vessel motion,top tension and wallthickness of the riser joint on fatigue damage of drilling riser is mainly investigated.The calculation method of the long term wave fatigue of the deepwater drilling risers is simple and practical,which is applicable to engineering practice.