Numerical Simulation Of Overtopping Flow Against Sea Dikes Under Solitary Waves

Disastrous waves are always great threats to human activities of production in theoffshore and coastal area. Tsunami waves are the most destructive waves which alsohave the widest range of impact. Although the probability of the appearance oftsunamis is small, once one is formed, coastal areas without adequate protection willundoubtedly devastated. The damaging effects of the tsunami-like solitary waves on theseawall should be taken into consideration in the engineering design which allowswaves overtopping on the seadikes. It is an important subject for design andmaintenance of seadikes to understand the complicated flow structures of theovertopping again seadikes under the effect of the shallow water waves of largeamplitude. The purpose of the study is to examine the dynamic characteristics of theovertopping flow on the crest and landward slopes of seadikes of different forms indetail through numerical simulation.The numerical wave flume is implemented through the second development ofFlow3D. The governing equations are the RANS equations and the continuity equation.RNG k-ε model is used for turbulence closure equations and the VOF method isadopted to simulate the movement of the free surface. The Goring approach isimplemented to generate solitary wave in the numerical wave flume. Four examples arecarried out for validation of the numerical wave flume. It is found that the computedregular waves are in good agreement with the theoretical solution, the computed waveheights of the solitary waves are closer to the target heights, the computed maximumrunup of solitary waves on a vertical wall is very close to the high-order analyticalsolution of solitary wave, and the experiments of solitary waves overtopping made byHsiao&Lin(2010) is well reproduced..In the next part, the validated numerical wave flume is used to simulateovertopping on simple dikes in regular waves. Four tests with different widths of dikecrest and wave heights are carried out. Then the distribution of thickness and velocity of overtopping flow on the crest and landward slope of the dikes are examined andcompared with the semi-theoretical semi-empirical formula proposed by Schüttrumpf&Oumeraci (2005). The computed results of overtopping flow thickness and velocityon the dike crest are basically consistent with Schüttrumpf&Oumeraci formula, butthe flow velocity reaches a peak at the connection point of crest and landward slope ofa dike, where apparently reinforcement is most required.Finally, for two different profiles of seadike, the overtopping flows of a solitarywave are simulated. For a simple seadike with different crest widths, combined withdifferent wave heights,12cases are finished in computation. The overtopping flowthickness and velocity at several cross-sections on the crest and landward slope areobtained. Then, an empirical formula is established through fitting these simulatedresults. For the composited profile of seadike of the Chemical Industrial Park inShanghai, the overtopping of a solitary wave is simulated at the condition of theextreme tide level of500year return period. The distribution of water flowcharacteristics are examined in detail during the process of overtopping flow underattack of these extreme shallow water waves.