An Experimental Study On Overtopping Against Sea Dikes Under Solitary Waves

Disastrous waves like such as tsunami and storm surgeoccurr occasionally, which are always great threats to human activities ofproduction and life in the offshore and coastal area. The sea dike is animportant sea defense to prevent the coast area from disastrous waves.The most popular sea dike structure type is the sloping breakwater. Froma large number of sea dike damage cases caused by marine disasters, theovertopping of breakwater is one of the most main reasons. Thetsunami-like solitary wave impacts the breakwater, flow over the crest,wash the crest and inner slope, then destroy the structure and stability.According to different forms of sea dike model, the physical modelexperiments are implemented in a wave flume to research the dynamiccharacteristics of wave overtopping, such as the wave overtoppingdischarge, the wave pressure distribution and the variation of flow fieldon the crest of sea dike.For simple dikes, a series of physical model experiments are carriedout to study the related parameters affecting the solitary waveovertopping discharge in different water depth and relative wave height.The solitary wave overtopping discharge increases with the increase ofthe relative wave height and with the decrease of the levee free-board.Based on the study, a new empiric formula on the solitary waveovertopping is proposed. Compared with previous research results, thevalidity of the formula is verified. The PIV experiments are carried out tostudy on the dynamics characteristics of wave overtopping flow, such asthe profile of overtopping water, the pressure distribution on the crest, thevariation of flow field. Detailed flow field structure is given. In order toverify the feasibility of PIV measurement, we compare the overtoppingdischarge calculated by PIV measurement data with the direct measurement of the overtopping discharge. Both are confirmed with agood agreement. By means of analyzing the flow field, the velocity of theovertopping flow increases along the crest, and decreases with theincrease of relative wave height. The maximum flow rate zone is alwaysin the front of the overtopping flow. The maximum wave pressureappears in the front of sea dike and decrease along the crest.For composited sea dike, by using the high-speed camera and theflow visualization approach, the profiles of the overtopping and thechange of the wave pressure on the crest are studied for the cases withdifferent values of the relative wave heights. With the increase of relativewave height, the overtopping on crest become fiercer and the maximumwave pressure increases, the position of maximum wave pressure moveson the landward slope direction.