Optimization Design Of Flexible Riser And The Reliability Analysis Of Riser Interference

Riser system is a necessary equipment for offshore oil and gas exploitation.Among them,flexible risers have become one of the most commonly used riser forms for offshore oil and gas exploitation due to its low bending stiffness and strong corrosion resistance.However,flexible risers have a significant motion response under environmental loads and is prone to various forms of failure.Therefore,it is of great significance to design a reasonable riser global configuration.Steep wave configuration of the flexible riser is formed by adding buoyancy modules in the middle of the riser and anchoring the end of the riser to the seabed,which has good compliance and stability.Reasonable buoyancy modules deployment method can improve the motion performance of the steep-wave flexible riser system.Therefore,a multi-objective genetic algorithm was developed in this work to optimize the deployment of buoyancy modules of the steep wave flexible riser system.The Pareto solution set of the maximum effective tension of the suspension point and the anchor point are obtained.Flexible riser system have large displacements in extreme sea conditions and are prone to interference damage.Based on the Huse wake model and the Blevins wake model,steep wave flexible riser interference models were established separately,comparative analysis was carried out to study the wake effect on riser interference.The sensitivity analyses of flexible riser interference were carried out to study the influence of floater offset,marine growth,drag coefficients,current velocity and buoyancy loss of floater on riser interference.The support vector regression model was established to predict riser interference distances.The results show that the support vector regression model has good generalization ability.Considering the uncertainty of the riser system parameters,the riser interference reliability analysis was carried out.According to the riser interference analysis criterion,the performance function was established,and support vector regression model was used to replace the implicit performance function to calculate the riser interference probability.To study the influence of wave randomness on riser interference,it is assumed that the limit interference distance of the riser obeys the extreme value distribution.The response surface between the distribution parameters and the basic random variables was fitted,and the implicit performance function was transformed into an explicit one by transformation so that the failure probability was calculated.Considering the randomness of waves,the probability of riser interference failure increased from 2.33% to 3.38%,which indicates that the randomness of waves has a certain influence on the probability of riser interference failure.