Studying On Hydrodynamic Characteristics Of Semi-circular Breakwaters With Numerical Model

Semi-circular breakwater is a new type of breakwater with good prospect forapplication. Since it is applied in Tianjin Port and the Deep Channel ImprovementProject of the Yangtze River Estuary, a number of experiences about the design andbuilding of this kind of breakwater has been accumulated. However, thehydrodynamic characteristics, the mechanism of the interaction between waterwaves and semi-circular breakwaters have not been studied in details, as well as thenumerical model. In this paper, the mechanism of the interaction between water waves andsemi-circular breakwaters is studied by theoretic analysis and analyzing theexperimental record. The numerical model is built according to the character of thistype of breakwaters. The numerical model and numerical techniques are developedto simulate wave breaking and moving boundaries. In order to fit complicatedboundaries, the hybrid method of Boundary Element Method and Finite DifferenceMethod is adopted to discrete the governing equations and boundary conditions. Thenumerical model, numerical techniques and numerical methods are integrated in awhole numerical simulation system, and the hydrodynamic characteristics ofsemi-circular breakwaters are studied with this system. Usually, the interaction between water waves and breakwater is considered as ahydrodynamic problem in local area, and is treated with potential flow theory. Byanalyzing experimental results, it is found that waves can break near the breakwatereven when the top of the breakwater is submerged. When wave breaking occurs,strong eddies appears, and the flow around the breakwater cannot be described withpure potential flow theory. Thus, a wave breaking model is developed based on theconcept of dissipation of wave energy, and the potential flow theory is modified. The combined method of "Tracing Point of Intersection" and "Thin Layer ofWater" is applied to treat the moving boundary problem. The "Sponge layer" methodis used at the open boundary, and the "Source term" is added in the governingequation to generate waves. The total numerical system is verified with a number ofexact solutions and experimental data, especially with the experimental results aboutsemi-circular breakwaters, and the results show that the model and numericalmethods developed in this dissertation are reliable and accurate. A number of numerical experiments are carried out to study the hydrodynamic摘 要characters of the semi-circular breakwaters, and the wave parameters and theparameters of the shape of the breakwaters are taken into consideration in theseexperiments. The simplified formula for calculating the total wave forces onsubmerged, alternately submerged and emerged semi-circular breakwaters has beenderived from the numerical results. The existed formula for calculating thecoefficients of reflection and transmission are modified and expanded by analyzingthe new experimental data and numerical results.