Numerical And Experimental Studies On Vortex-induced Vibrations With Fluid-structure Interaction For Submarine Free-span Pipelines

As an important component of the offshore oil and gas storage and transportation system, submarine pipelines are playing the significant roles in the offshore exploitation. They are called as the lifeline of the offshore oil and gas fields. The security production of the offshore oil and gas fields depends largely on the safe operation of the submarine pipelines. Due to the special structural style, the vortex-induced vibrations (VIV), the'lock-in'phenomenon and the fluid-structure interaction (FSI) of the submarine free-span pipelines can occur when they exposed to the ocean current. The complicated hydrodynamic behavior is apt to result in the loss of the structural stability and the fatigue damage.The two-dimensional numerical simulation is limited in this research because the structural responses of the submarine free-span pipelines are distributed axially. Based on the two-dimensional standard k ?εturbulence model in conjunction with the structural governing equations, a quasi three-dimensional numerical model incorporating the hydrodynamics module and the structural dynamics module is developed in this dissertation to depict the VIV and the FSI of the submarine free-span pipelines accurately. The essence of the presented numerical model is to solve a three- dimensional problem by using a set of two-dimensional numerical simulations. To deal with the grid movement induced by the structural vibration in the numerical simulation of the FSI problem, a new generation method of the dynamic block- structured grid based on the previous researchers'work is proposed in this dissertation. In this method, the movement of the grid block around the moving structural boundary is combined with the regeneration of the inner-block grid to avoid the aberrance of the grid.The proposed quasi three-dimensional numerical model in conjunction with the dynamic block-structured grid generation method is applied successfully in the studies on the VIV and FSI problem of the submarine free-span pipelines. The structural responses and dynamical characteristics are analyzed in detail by numerical approach. Based on the flow visualization, the hydrodynamics of the flow field including the flow separation, the vortex shedding and the wake pattern are discussed. The nonlinear...