The Recoil Process Analysis Based On Multibody Dynamic Method

In deepwater drilling operation,risers are necessary equipment to connect the platform and subsea wellhead.When the platform encounters with harsh environment or loss of dynamic position control,the emergency disconnection sequence(EDS)needs to be performed to disconnect risers from lower marine riser package(LMRP)to secure the well and rig.Because of the existence of over-pull,releasing the LMRP connector transforms stored elastic energy into a rapid movement known as ‘recoil process’.Recoil process may pose a threat to the safety of rig and equipment without proper control,thus it is significant to study the recoil process.The finite difference method and multibody dynamics methods are used to carry out the recoil analysis.The finite difference method and Newmark-beta method is used to obtain the transverse movement of riser during EDS,the platform speed and LMRP’s weight have been considered.Based on the multibody dynamics and computational fluid theory,the longitudinal recoil multibody dynamic model has been established.The research results show that the stress and bending moment of the riser increases during the drift stage;after the disconnection,the LMRP has a large lateral displacement and velocity,the stress and bending moment at the lower flexible joint increase significantly.The LMRP has a minimum distance of 10.12 m and has chances to crash with BOP because of the releasing of stored elastic energy and platform heave.Disconnection leads to the shortening of telescopic joint stroke and tensioner stroke;an obvious 50 seconds time delay has been captured.The ring tension and line tension of the tensioner have a shake period and decrease after recoil.Based on multibody dynamic theory,software mainly for riser recoil analysis has been developed.The software can perform normal riser analysis including static,frequency and recoil.Compared to Deep Riser,the software has faster calculation speed.