Improved recoil dynamic analysis of the deepwater riser system after emergency disconnection

摘要

The riser recoil after emergency disconnection is a complicated multi-coupling process. However, most existing analytical models simplify the tensioner as a constant stiffness spring, divide the riser system into different finite element segments, and do not consider the coupling effect between the riser movement and the fluid discharge. An improved recoil dynamic model that couples the tensioner model, the riser finite element model (FEM), and the fluid discharge model is proposed to address the shortcomings of existing models. The model is solved by the Newmark-β integral method. The improvement of the model is verified from the aspects of the tensioner model, riser model, and coupling effect. Results show that the three aspects have great influences on the recoil analysis, and the improved model can efficiently identify the recoil characteristics. The recoil displacement of the improved model is lower than that of the simplified model with a constant stiffness spring. The riser simulated by a FEM with several segments can refine the axial stress along with different positions of the riser and capture the possible dynamic compression. The coupling effect exacerbates the oscillation of the discharged friction and suppresses the recoil response. The key factors influencing the recoil and fluid discharge, including the platform heave frequency and amplitude and the volume of the air pressure vessels (APVs) of the tensioner, are analyzed on the basis of the proposed model.