Study On Three Dimensional Numerical Simulation Of VIV Characteristics For Marine Riser

Vortex-induced vibration (VIV) is the main cause of fatigue failure of marine risers. As the continuous increase of the depth of offshore oil and gas exploration, the VIV characteristics of flexible marine riser with high aspect ratio of length to diameter are increasingly concerned by the academic and engineering fields. In view of coupling simulation strategy, computational efficiency, computer's hardware configuration and many other difficulties, the three dimensional numerical simulation of marine riser VIV characteristics has been a tricky subject to be studied. In recent years, with the continuous progress of computer's hardware and software and also the rise of high performance parallel computing technology, more and more overseas scholars are carrying out the study of the three dimensional numerical simulation of marine riser VIV characteristics, but the domestic related research work has just begun.Based on the CFD numerical simulation technology, the dissertation has conducted a series of researches on three dimensional coupling simulation of VIV for in-line and cross-flow directions on marine risers. Using CFX as the fluid filed solver, the three dimensional fluid flow is solved with the k ?ωturbulence model, while using ANSYS as the solid filed solver, the riser dynamic response is analyzed with the finite element method based on three dimensional solid element, and the seamless data transfer between fluid-solid interface is realized by using the ANSYS Workbench platform.The feasibility of the coupling numerical simulation scheme is verified by comparing the simulation results with experimental ones, then the simulation of different top preloads has been carried out, and at last, a series of three dimensional coupling simulation work of VIV for actual size of marine riser with different top preloads have been firstly carried out. All of the present work helps us deepen the understanding of the VIV characteristics and study the suppression effect of preload. The obtained results indicate that the riser motion shows unsymmetrical bending deformation phenomenon, the vibration mode of cross-flow showed that the riser vibrates with multi-mode, the in-line dynamical response should not be ignored, and the motion trajectory demonstrates a deformed figure-of-eight in type. It also indicates that when applying a bigger preload, the vibration amplitude is reduced and the excitation mode number is reduced as well, which reflects the inhibitory effects of VIV. The present study would be helpful to provide reference for preload's reasonable determinacy and also riser's design and maintenance.