Study On The Swash Hydrodynamics And Sediment Transport In Swash Zone With Infiltration And Exfiltration

Infiltration and exfiltration have a significant influence on sediment transport in swash zone which has a negative impact on coastal structures.It's helpful to understand the hydrodynamics and bed erosion mechanism in swash zone by analyzing the influence of seepage during the swash process.Furthermore,it can provide a scientific basis for the contruction of coastal protections.In this thesis,the physical flume test combined with numerical simulation is used to study the hydrodynamics and sediment transport under the influence of infiltration,and pressure distribution of sheet-pile groins in Qiantangjiang River are analyzed.The main research contents are as follows:1.The wave run-up from solitary waves over permeable and impermeable slopes experiments were carried out in indoor flume,the swash velocity and swash depths were tested.Comparing the waveform change over permeable slope and impermeable slope,it can be found that swash uprush is faster,maximum swash height is higher and the wavefront is steeper.The wave swash duration can be defined in three stages depending on the waveform change.2.The swash process on gravel beach for solitary wave is studied.The wave height,wave asymmetry,bed tangential velocity development,boundary layer thickness and bed shear stress are discussed respectively.Conclusion as follow:infiltration increase the asymmetry of wave,it shows strong infiltration during uprush,which increases the shear stress.The flow loss caused by infiltration during wave downrush leads to reduction of seabed shear stress.Assessing the effect of sediment effective weight and shear stress variation on shields parameter over permeable slope,it is found that shear stress variation cause by infiltration is in dominant position which would greatly increase the shields parameter and lead to the range of sediment transport increased significantly.3.Through numerical simulation,the influence law of sediment particle size on flow field characteristics and sediment transport is studied.By comparing the sediment shields parameter of the 2mm seabed and the 5.5mm seabed,the three mechanisms of correction:weight correction,shear stress correction by seepage force and shear stress correction by continuity effect were evaluated respectively.It is found that the shear stress correction has the greatest influence on shields parameter and is positively correlated with the infiltration velocity;shear stress induced by "continuity effect" has a greater influence on the gravel slope and can be evaluated by the asymmetry of the bed surface;gravity correction shows larger influence in sandy slope and it mainly occurs in the process of uprush duration.In the other hand,by comparing the swash zone hydrodynamics and sediment transport under solitary wave and periodic waves,the influence of flow regime on it was evaluated.The results show that the change of incident wave would change the hydraulic condition of the swash zone,which also has a great impact on the sediment transport.Due to lower infiltration by periodic waves,the sediment gravity correction caused by seepage force is also weakened.4.Through the three-dimensional numerical model of the groin,simulate the process of tidal wave impact on the Qiantang River sheet-piles groin(SPG),study the pressure distribution law of the coastal protection project under the tidal wave,verify the numerical results by using indoor model test,and thoroughly evaluate the influence of dam permeable rate against the pile pressure.The result shows that the pile pressure difference P0 is the smallest at the dam head and the dam root is the largest.Along the SPG length direction,the P0 peak value increases with the decrease of the water permeability.In the height direction of piles,the value of Po increases with the increase of height,and P0 peak decreases with the SPG permeability increases,the difference of different SPG permeability decreases with the increase of the position height.