Numerical Simulation Of Waves, Seabed And Structure Interaction

In port, coastal and offshore engineering, the seabed and structure response under waves is an important research subject with respect to their stability. The efficient approach to solve the above problem is to set up a coupled model describing seabed, wave and structure interaction. So the coupled model is established and used in this dissertation to investigate the seabed response, structure response, seabed and structure response under waves. The main contents and results are as follows:(1)A model for 2D numerical wave tank based on quasi-spline BEM is presented. Numerical results compared with solitary, cnoidal and sine wave theory show that the model has a high accuracy and can be used to simulate various wave conditions.(2)With FEM, a model of seabed dynamic response under waves, which solves Biot equations numerically to simulate pore water pressure's variation in the seabed, is established. The model is validated through comparations of numerical results with experimental data and analytical theory, and can be used to simulate seabed response under wave.(3)The coupled model of wave and seabed interaction is set up by coupling the boundary conditions of numerical wave tank and seabed response model. Results of the model show that the coupling influence is not important for grain sizes under coarse sand. After analysing seabed response in front of vertical breakwater with the model, it is found that the liquefaction area is fixed and methods to prevent seabed from liquefaction are proposed. In addition, an equation for calculation of maximum liquefaction depth is brought up according to analytic solution of saturated seabed under waves.(4)The freak wave is simulated to investigate seabed response with or without presence of vertical breakwater by the coupled model of numerical wave tank and seabed response. Under the freak wave condition, the seabed is much more easier to liquefy especially at the foot of vertical breakwater and the liquefaction range can expand to scores of meters. It will be very danger to the safety of the structure.(5)A fully coupled model to simulate wave and structure interaction is established and the interaction between waves and the sheet pile type structure is investigated. When the elastic modulus or thickness of the sheet pile type structure decreases, the amplitude of structure response increases and higher frequency responses will appear. When considering the wave field behind the structure, the displacement of the structure decreases, but the influence can be ignored when the structure response is very small.(6)The structure response taking the seabed influence into account under the freak wave is investigated. In most situations, the displacement of the caisson is small and overturn will not appear. But the sheet pile's displacement is very large and can lead to instability.