Study On The Evolution Law Of Roll Wave On Slope Surface

Under certain hydraulic conditions,rolling waves will appear in Overland Flow.This special phenomenon will continually evolve and converge with the increase of the flow path,resulting in the increase of the instantaneous water depth,the increase of the flow velocity and the increase of the flow shearing force,resulting in the change of the flow dynamic characteristics of the slope sheet water,thus having a certain impact on the process of soil erosion.Therefore,it is necessary to study the evolution of the rolling waves.At present,the research on the evolution of rolling waves is still shallow,and the changes of hydraulic parameters in each stage of rolling wave evolution have not been discussed.This paper uses an ultrasonic measurement system to measure and calculate the rolling wave hydraulic parameters of 8 kinds of unit-discharges,5 kinds of roughness,and 5 different energy slopes under different cross-sections.The relative parameters are introduced to explore the evolution law of hydraulic parameters at each stage of the evolution process of rolling wave flow.The results show that:(1)The unit-discharge,energy slope,and roughness affect the evolution of the rolling waves.The increase of the unit-discharge promotes the development of the rolling wave,which is mainly reflected in the wave height,which accelerates the growth rate of the wave height,and suppresses the wave velocity and slows down the increasing rate of the wave velocity.The increase in roughness suppresses the development of rolling waves and reduces the wave velocity and wave height.However,in terms of the impact degree,the increase in roughness increases the degree of wave velocity affecting water bodies and reduces the effect of wave height on water bodies.The influence of energy slope on rolling waves is closely related to the roughness.Under the condition of small roughness,the increase of energy slope weakens the impact of wave velocity on the water body and increases the effect of wave height on the water body.Under the condition of large roughness,the increase of the energy slope strengthens the impact of wave speed on water bodies,while in terms of wave height,the energy slope has little effect.(2)The unit-discharge,energy slope,and roughness affect the development process of rolling waves,which are not only reflected in the impact of rolling waves on water bodies,but also promote the shift of the location of rolling waves,that is,the development process of rolling waves is the superposition of the two.(3)The development of the rolling wave is clearly divided into three stages.In the initial development stage,the development of the rolling wave mainly focuses on the development of the wave velocity;in the transitional development stage,the development of the rolling wave mainly concentrated on the development of wave height,and the rolling wave aggregation phenomenon intensified;while in the mature development stage,rolling wave tended to be stable.(4)The unit-discharge interval of rolling waves increases with the increase of the energy slope,and the larger the energy slope,the smaller the degree of change in the interval.The Froude number when the rolling wave disappears is not a certain value,and its value increases with the increase of the energy slope.When the rolling wave disappears,the viscosity-depth ratio is 0.26,and the change of the energy slope has little effect on the viscosity-depth ratio.When rolling waves occur,the range of relative wave speed changes is not large.Under this test condition,1.496 can be taken as the critical value when rolling waves occur.(5)The evolution of the waveform can be studied from the three parameters of the travel area of the wave body,the shape index of the cross section and the wave steepness.It can be seen that the travel area shows a relationship of first increase and then decrease with the increase of unit-discharge.The travel area under different unit-discharge has different relationship with the energy slope;when the unit-discharge is small,the travel area always decreases with the increase of the energy slope,and when the unit-discharge increases to a certain extent,the travel area varies with the energy slope increases.With the increase of the unit-discharge,the section morphology index shows a change law that first decreases and then increases,and when the valley value of the section morphology index appears,the corresponding unit-discharge increases with the increase of the energy slope.When the unitdischarge is small,the cross-section morphology index decreases first and then increases with the increase of the energy slope.When the unit-discharge is large,the cross-section morphology index always decreases;The unit-discharge and energy slope interact with the evolution of the rolling wave,which in turn affects the wave steepness.When the rolling wave moves from the mature development stage to the transitional development stage,the wave steepness gradually increases and the wave body tends to break.It gradually becomes unstable;when the rolling wave changes from the transitional development stage to the initial development stage,the wave steepness suddenly decreases.In the generation area,the wave steepness stabilizes.At this time,the wave height and the wavelength do not change greatly.