Experimental Research On Layer Thickness Of Wave Overtopping Flow And Secondary Wave Conditions Over Sloping Breakwater

Breakwater is an important sea defense to prevent the coastal area from hitting by tides and waves. Sloping breakwater is one of the most common structure type in breakwater. If the design embankment top elevation is low, waves will cross over the crest top in a great deal and to be the phenomenon of wave overtopping. Waters on the crest will form overtopping flow, wash or even destroy the crest, and then come into being a series of new waves behind the breakwater in the harbour. The new waves which are called "secondary waves" have lots of influence on the berthing stability of the ships. Lots of researches pointed out that the strength of wave overtopping can be measured by the wave overtopping discharge, and then have the direct influence on the overtopping flow on the crest and secondary waves.This paper reviewed the formulas on the mean overtopping discharge of the sloping breakwater, layer thickness and velocity of wave overtopping flow, and transmission coefficient about the secondary waves. Based on the typical section of sloping breakwater, physical experiments for the mean overtopping discharge, layer thickness of wave overtopping flow on the crest and the secondary wave behind the breakwater for regular waves and irregular waves are carried out. The differences of mean overtopping discharge between the experimental results for regular waves and the advanced SPM method, and the results for irregular waves and the three chief experienced forlumas:standard method, VDM method and Owen method are analyzed.The variations of mean overtopping discharge with relative embankment top elevation and wave steepness are studied.We emphatically studied the relationship between the mean wave overtopping discharge and the layer thickness of wave overtopping flow, secondary wave height, wave period and wave spetrum.This paper preliminarily established the relationship between non-dimensional mean overtopping discharge and relative layer thickness of wave overtopping flow, secondary wave height transmission coefficient, period variation and energy variation. The experimental results could provide reference to practical engineering design and to parameter adjustment for associated numerical model about the wave overtopping on the crest.