The Wave Transformation And Breaking On Gentle Slopes

The limit wave height, that is, breaking wave height, is usually adopted as the design wave height for the offshore structures that are most build on very gentle slopes, hence the breaking height research is very important to engineering application. The most representative methods of wave breaking indices are proposed by Goda and Nelson, but both of them can not reflect the influence of the bottom friction factors and the wave asymmetry on the breaking indices. Yu yang et al present the wave asymmetry with respect to the vertical axis to effect the breaking indices greatly by physical model verification and numerical analysis, but not conducts the thorough research to the relation among the beach slopes ,the bottom friction factors and the breaking indices. Other research results are mainly concerned with the relation among the relative wave height, the beach slopes and the breaking indices, the studies on the breaking height are neither adequate nor perfect by far. In this paper, the wave transformation and breaking on gentle slopes is further studied by the method of combination of numerical analysis and experiment.Firstly, the wave deformation and breaking on a 1/200 slope for regular waves are calculated based on the technology of 2D numerical wave tank by resolving the Laplace equation together with its boundary conditions employing the Boundary Element Method. The analysis and comparisons between numerical results and experiments show that the numerical model used in this paper is reliable.Secondly, without considering the bottom friction effects, 3 sets of numerical calculations based on numerical model presented above are performed for the wave propagations and deformations on different slopes from 1/100 to 1/700, and then a series of analysis focused on finding the influence of the bottom slopes, the relative wave height in deep water, the relative water depth and the wave asymmetry on the breaking indices are conducted. The numerical result shows that the breaking indices are independent of the bottom slopes.Finally, considering the bottom friction effects, the corresponding numerical calculations for the wave shoaling on different slopes as mentioned above is conducted, again. The relations between the wave breaking indices and its dominate factors, such as the seabed slope i, the bottom friction factor/and wave asymmetry factors (T~' / T~", (T~' + T~") , η_c/η_t) is analyzed. As another important achievement of this paper, a relation between the criticalbeach slopes of wave non-breaking on very gentle slopes and bed friction factors is also formulated employing wave energy conservation law and the conditions of wave breaking.