Study On Hydrodynamic Characteristics Of Pontoon-plates Type Floating Breakwaters

The construction of harbors steps into deep sea water area with execrable circumstances. The conventional breakwaters can not be fit for the construction in deep water. Therefore, it is very significant to explore the breakwaters with good performance of dissipating waves, which can be fit for poor foundation, high demanding of water circulation and cheap cost.For these reasons, the two new types of floating breakwater, the pile-restrained pontoon-plates floating breakwater and mooring chain restrained pontoon-plates floating breakwater, are proposed in this dissertation. Based on the model test, and by numerical investigation, the hydrodynamic prosperities of the two new types of floating breakwater are investigated. Additionally, the hydrodynamic prosperities of mooring chain restrained floating breakwater is studied by the physical model test and numerical investigation.Firstly, the transmission coefficients, motion responses and mooring chain forces of the floating breakwater under regular wave action are researched by experiments. The influences of relative pontoon width, wave height, relative drag coefficient of mooring chain, mooring chain stiffness, angle at anchor point and relative pontoon draught on the hydrodynamics characteristics are investigated. The correlativity between transmission coefficients and mooring chain forces are studied. The experimental results demonstrate that relative width, mooring chain stiffness and angle at anchor point have large effect on transmission coefficients, motion responses and mooring chain forces.Secondly, the experimental study and numerical model investigation are conducted on the pile-restrained pontoon-plates floating breakwater under regular wave actions in the finite water depth. The emphasis of the experimental investigation is on the characteristics of disspating coefficients and motion responses of the pile-restrained pontoon-plates floating breakwater. The influences of relative width, wave height, width of plates, distance between pontoon and plate, relative draught of pontoon on the dissipating coefficients and heave motions are discussed. The correlation between dissipating wave coefficients and heave motions are analyzed. The experimental results indicate that the transmission coefficient is less than 0.5 when the relative width is 0.2. Even under the long period wave (the wave period is from 1.28s to 1.55s) action, the transmission coefficient of the pile-restrained pontoon-plates floating breakwater decrease to 0.8. According to the experimental results, it is proposed that the pile-restrained pontoon and one plate floating breakwater has good ability of dissipating wave. Based on linear time-domain theory, the integral function is established, and solved by the boundary element method. By Newton second's law, the time-domain motion equations of the mooring chain restrained pontoon-plates floating breakwater are built and solved by the fourth order Runger-Kutta method. On the basis of the theories above, the time-domain numerical model is developed. Using this numerical model, the dissipating coefficients and heave motion responses are calculated. And the numerical results of dissipating coefficients and heave motion are compared with experimental results. Additionally, the horizontal forces on pile of the pile-restrained pontoon-plates floating breakwater are calculated at the same time.Thirdly, the experimental investigation and numerical model study are developed on mooring chain restrained pontoon-plates floating breakwater. The influences of the number of plate and pontoon draught on the transmission coefficients are discussed. The method of building numerical models of the floating of mooring chain restrained pontoon-plates floating breakwater is the same with that of the pile-restrained pontoon-plates floating breakwater. The The catenary theory is utilized to calculate the mooring chain forces. The model can reflect the characteristics of transmission coefficients, motion responses and mooring chain forces. Both the experimental results and numerical results show that By using the numerical model, the motion responses and mooring chain forces of mooring chain restrained pontoon-plates floating breakwater and pontoon floating breakwater are all calculated under different wave action. The results indicate that the motion responses and mooring chain forces of mooring chain restrained pontoon-plates floating breakwater are less than that of the pontoon floating breakwater, and the mooring chain restrained pontoon-plates floating breakwater has better dissipating wave ability than mooring chain restrained pontoon floating breakwater.