Dynamic Characteristics Analysis of Deepwater Riser under Soft Suspension Evacuation Conditions

Aiming at the problem of vibration failure of deepwater riser under the condition of soft suspension emergency evacuation, combined with the Hamiltonian variational and virtual work principle, the finite element method was used to build a 3D nonlinear dynamic model of soft suspension drilling riser; meanwhile, the nonlinear factors such as longitudinal and transverse coupling effect, ocean vortex-excited effect and large deformation of riser were considered. With the help of test parameters and results presented in the literatures, the effectiveness of the nonlinear dynamic model was verified. The field parameters of riser in HYSY981 drilling platform were used to explore the influence of buoyancy modules layout and typhoon return period on the nonlinear vibration response characteristics of soft suspension riser under emergency evacuation conditions. The research results show that the reasonable arrangement of buoyancy modules can reduce the stress and dynamic axial force, and the optimal arrangement method of buoyancy modules can be determined by the built theoretical model; in the high flow rate area, the buoyancy modules layout of the riser should be reduced, the maximum stress and displacement of the riser occur near the top or bottom area, and the safety of the riser at this position should be paid attention to; the currentwise displacement of the riser increases with the increase of the typhoon return period, and the displacement near the upper part changes greatly, so in the evacuation process, the collision between the upper part of the riser and the moon pool should be avoided. The research results provide reference for understanding the vibration response characteristics of soft suspension riser under evacuation conditions.