Multi-stage and multi-objective optimization of anti-typhoon evacuation strategy for riser with new hang-off system

Abstract

A new hang-off system has been proposed to improve the security of risers in hang-off modes during typhoons. However, efficient anti-typhoon evacuation strategies have not been investigated. Optimization model and method for the anti-typhoon evacuation strategies should be researched. Therefore, multi-objective functions are proposed based on operation time, evacuation speed stability, and steering stability. An evacuation path model and a dynamic model of risers with the new hang-off system are developed for design variables and constraints. A multi-objective optimization model with high-dimensional variables and complex constraints is established. Finally, a three-stage optimization method based on genetic algorithm, least square method, and the penalty function method is proposed to solve the multi-objective optimization model. Optimization results show that the operation time can be reduced through operation parameter optimization, especially evacuation heading optimization. The optimal anti-typhoon strategy is evacuation with all risers suspended along a variable path when the direction angle is large, while evacuation with all risers suspended along a straight path at another direction angle. Besides, the influencing factors on anti-typhoon evacuation strategies indicate that the proposed optimization model and method have strong applicability to working conditions and remarkable optimization effects.