Numerical Investigation On The Interaction Of Internal Solitary Wave And Deepwater Riser

With the development of the world's oil industry, the scope of the exploitation of offshore oil gradually extended to the deep ocean. In the deep sea, the marine structures will suffer more complex and harsher environments. Ocean internal solitary wave id one of these environments. Internal solitary wave has large amplitude and long action time, therefore, in certain conditions it will bring a huge threat to the offshore structures.Since the large amplitude internal solitary wave is strongly nonlinear, and its interaction with the deepwater riser is also strongly nonlinear, especially for elongated flexible risers with large aspect ratio. Therefore, the numerical internal wave tank will be an effective tool for simulating the interaction between the ISW and the deepwater riser.In this thesis, after a brief review of the development on such subjects, the interaction between the ISW and the deepwater riser is considered from four aspects as followed:In chapter 3, based on the fully nonlinear MCC theory, a two-dimensional numerical internal solitary wave tank where the simulating ISW amplitude is able to be controlled is established by use of the velocity-inlet method. Moreover, the ISW in the end of the tank is dissipated by damping layers combined with open channel pressure outlet boundary.In chapter 4, the ISW numerical tank is further developed to three- dimensional case where a ISW with large amplitude can be generated, and the result reaches a certain degree of accuracy.In chapter 5, using the three-dimensional internal solitary wave tank, the interaction between the ISW with large amplitude and the deep-water riser with high aspect radio was numerically simulated and analyzed for predicting the characteristics of the load on the riser due to the ISW. In Chapter 6, based on the time histories of the load on the riser due to the ISW and finite element software ANSYS with transient dynamic analysis, the dynamic response characteristics of the riser under the action of the ISW are obtained.The results show that when internal solitary waves move across the riser, the riser will suffer strong shear flow and large deformation and stress will be produced, while the riser near the interface of the two layers of the fluid will have a maximum deformation and stress. Therefore, it is necessary to consider the impact of the ISW on the deepwater riser in practical ocean engineering.