Disturbance observer-based composite recoil controller design for deepwater drilling riser systems after emergency disconnection

This paper investigates the recoil dynamic modeling of the riser system after emergency disconnection and proposes a recoil control scheme based on a disturbance observer. First, considering the differences in structure and mass of the riser and buoyancy block at various depths in practical drilling engineering, a spring-mass-damper with four degree of freedoms recoil dynamic model of the riser system is established. Then, denote friction force of fluid discharge and heave motion of platform as external disturbances during the recoil process, a disturbance observer is designed and its convergency conditions are addressed. Third, based on above disturbance observer, a composite recoil controller is proposed to suppress the recoil response of the riser system. Simulation results indicate that: (i) the recoil model algorithm proposed can correctly depict the recoil response characteristics of the deepwater drilling riser systems after disconnection under friction force and heave motion disturbances; (ii) the designed disturbance observer is effective under both different disturbance models and those with stochastic signals; (iii) the composite recoil controller presented based on the disturbance observer can significantly suppress the recoil response and ensure the axial structural safety of the riser system; (iv) compared several existing recoil controllers in which the dynamic model of disturbance is required, while in the recoil controller proposed in this paper, it is not needed thereby providing a more applicable option.