Optimization of an anti-recoil control scheme based on improved NSGA-II for a deep-water drilling riser after emergency disconnection

Abstract

Once ED (emergency disconnection) occurs, the recoil response of a deep-water drilling riser is commonly controlled by tuning anti-recoil valves via a PLC, and researchers are devoting efforts to readjusting the valve opening employing various control technologies. Distinctively, this study tries to convert the anti-recoil issue into a multi-objective optimization problem by introducing penalty functions for the required constraints in a successful anti-recoil control. At first, a parametric analysis for the recoil dynamics of a deep-water drilling riser is conducted. It has found that the anti-recoil valve opening coefficient Cv has a slight effect on the pressure drop when Cv≥0.2, while the effect becomes remarkable when Cv<0.2 accompanied by a jump phenomenon; The variation of high-pressure air volume has a negligible effect on the recoil response. However, if some air vessels are pumped out and discharged when the riser travels upward at the moment of ED, the volume reduction can significantly increase the LMRP-BOP clearance while it increases the risk that piston stroke exceeds limitation. Then, a novel anti-recoil scheme is proposed that the recoil process is roughly regulated by altering high-pressure air volume and accurately controlled by adjusting anti-recoil valve at Cv≥0.2. Finally, an optimization approach based on improved NSGA-II is developed. The effectiveness has been verified by recoil analysis of a deep-water drilling riser after ED adopting a set of optimized parameters, which can be a workbench for further study with more objectives, variable parameters and constraints.