Study Of The Influence Of Bed Roughness On The Hydrodynamic Properties Of Dam-break And Non-breaking Solitary Wave

Investigating the hydrodynamic characteristics of dam-break flow and wave runup processcontributes to formulating reasonable disaster prevention and mitigation strategies,which is important to the protection of the environment and human life.For the theoretical research on dam-break wave tip region,researchers have not yet formed a unified and clear understanding of the horizontal velocity distribution there.Different theoretical models have been derived.As for the research on non-breaking solitary wave runup,some studies analyzed the influence of the bottom friction,but quantitative relationships between the bottom friction effect and bed roughness,as well as the beach slope,are still unclear.In this study,theoretical and experimental methods are utilized to reveal the mechanisms of bottom friction on the hydrodynamic characteristics of dam-break flow and non-breaking solitary wave during their propagation and runup processes.Firstly,dam-break flow properties on a horizontal rough dry bed are obtained through theoretical derivation.Based on the assumption that the horizontal velocity profile in the wave tip region follows a vertically parabolic distribution with shear extending to the water surface,new analytical solutions were derived with respect to the simplified force balance or the horizontal momentum equation,respectively.The force balance based model shows the relation between water depth h and distance from the tip s in the wave tip region as h?s1/3,whereas a complex and implicit h?s relation between h?S1/3 and h?S1/2 is confirmed after applying the momentum equation.Comparing with other models,the present momentum equation based model gives the best agreements with experiments,which can illustrate the general spatial distribution of the wave profile in the wave tip region.The model predicts that surface particles converge towards the tip front at a constant flow convergence rate.The vertical velocity increases monotonically from the bed to the water surface and its magnitude increases when approaching the wave tip.Taking into account the relative streamline distribution and total flow field feature in the wave tip region,the present model can reproduce the uniform flow convergence pattern at the wave tip front.Secondly,the effect of bed roughness on the non-breaking solitary wave runup is explored through a series of laboratory experiments.The experimental results show that during the runup process,the shoreline moving velocity increases initially and then decreases.The water surface slope of the forward swash region gradually changes from dipping landward to dipping seaward,while the water surface slope of the backward swash region is observed to be always dipping seaward.The bottom friction plays different roles in the wave runup process for different beach slopes.Under the same incident wave condition,the maximum runup height on a steel bed was found to be larger than that on a sandpaper bed over a 10° beach slope,whereas the same runup heights were observed for different beds over a 45° beach slope.Through the analysis of the runup duration,shoreline motion,runup profile and maximum runup height,it is found that the large water depth,small resistance force and short effecting distance lead to the small energy dissipation at a steep slope,therefore the retarding effect of bed roughness is weakened.In addition,by introducing the runup similarity parameter,quantitative relationships between the maximum runup height and the bed roughness,the beach slope and the incident wave height,were analyzed.On the basis of Synolakis(1987),a new empirical model was proposed,after incorporating an enhancement coefficient and a reduction coefficient,which can predict the maximum runup of the non-breaking solitary wave along various slopes with different sloping angles and bottom roughnesses more accurately.