Research On Scours And Depositions In Front Of Vertical Breakwaters Under Action Of Broken Waves

The scours around coastal structures, such as breakwaters and seawalls, would threaten the safety of structures, and must be considered carefully in the course of designing and building. In view of the vertical breakwater, the scours and depositions in front of breakwaters and other correlative problems under the condition of complex ocean environment (mainly broken waves) were investigated.(1)A numerical wave flume was created. The wave field in front of breakwater was modeled by solving RANS equation and continuity equation. In order to simulate successive long-time wave generation of waves and absorb the reflected waves from a structure, the source generation of waves was adopted. Combined with the Sommerfeld condition, sponge layer for wave damping absorber was used to the open boundary. As for the free surface, the VOF method was applied(2)The previous scholars mostly had researched the scours and depositions in the condition of standing waves, while the research on the scour and deposition in the condition of complex ocean environment is rarely, especially the research on mechanism of scouring and depositing is not enough. In this paper, the velocity fields in front of breakwaters are calculated by the numerical wave flume. Based on the distribution rules of bottom velocity, the mechanism of scouring and depositing in front of breakwater under the action of regular broken waves is analyzed furtherly. It shows that under the condition of regular broken waves, the wave impact on the breakwater after broken, bring the sediment moving to the breakwater. The impacting wave meets with breakwater and climbs up along the breakwater, then it falls back to the beginning position. The falling wave brings the sediment off the breakwater. the scouring and deposition patterns depend on the correlation of the total amount of sediment moving to the breakwater and the total amount of sand moving off the breakwater. If the wave condition is same, with the increasing of sediment size, the scour and deposition patterns can be classified into DSD type, SDSD type and DSDS type. The scouring and depositing patterns in the condition of regular broken wave are compared with that in the condition of regular standing waves also.(3)Through the experiment, the scours and depositions in front of vertical breakwaters under the action of irregular broken waves were studied. According to the relative relationship of wave condition and sand grain size, the scour and deposition patterns can be classified into five types: scour typeâ… , scour typeâ…¡, scour typeâ…¢,deposition typeâ… and deposition typeâ…¡. Through the flow fields analysis, the mechanism of scouring and depositing by irregular broken waves were analyzed. It is shown that the mechanism is similar to that by regular broken waves. But because of the more complex wave motion, the specific scouring and depositing pattern under the action of irregular broken waves, the scour typeâ… is formed. The processes and formation of scour and deposition patterns were in comparison with those induced by standing waves. The criteria of distinguishing scour and deposition patterns are presented according to the scouring results and scouring mechanism. The waves in front of breakwater are divided into three types according to the wave breaking conditions. Under the action of each wave, the different sediment is corresponding to different scouring and depositing pattern. The influences of the foundation size on the scouring were studied also.(4) When the sediment size is relatively fine, through the numerical wave flume, the scouring and depositing patterns in front of breakwater were modeled. And the results were compared with the experimental results. It is shown that this numerical model can simulate the scouring and depositing pattern betterly, the scouring and depositing patterns are about the same as the experimental results, although there are some differences in broken zone.