Random Starting Behavior And Transport Mechanism Of Bedload Sediment

The law of bed load incipient motion and transport is of great significance to promote the theoretical development of sediment research,river channel development and management,the safety of water conservancy projects,and the prediction of river bed evolution trend.Based on high-speed camera technology,this paper has carried out sediment initiation and bed load movement characteristic experiments.Based on the above experiments,the sediment initiation,bed load movement,and sediment transport rate are studied by combined with theoretical analysis.The main work and innovation results are as follows:(1)The incipient velocity formula of non-uniform sediment is established by constructing the corresponding relations of different incipient parameters under the same incipient standard.Based on the previous research,the quantitative parameters of the sediment particles were redefined and analyzed by tank test.The results show that the exposure angle and the direction angle of the drag force obey the normal distribution,and the relative Through the test of the force of the water flow on the particles,the drag force coefficient and the uplift force coefficient formula are established force arm obeys the exponential distribution.A formula of the incipient probability of sediment is established,which takes into account both the fluctuation of flow and the randomness of particle position on the bed surface.Based on the flume experiment,the formula of uniform bed load transport rate is established under low-intensity sediment transport,and the corresponding relationship of different starting parameters is constructed under the same dynamic standard.The formula of the incipient velocity of non-uniform sediment is established.Verification by the actual measurement data of flume test in other literature,the formula for incipient flow velocity of non-uniform sediment in this paper has higher calculation accuracy.(2)The mechanical mechanism and statistical law of sediment saltation are further revealed,and the velocity formula of non-uniform bed load is established.Through the experiment of the force of the water flow on the particles,the drag force coefficient and the lift force coefficient formula are established respectively.Verified by the measured data of settlement test,the formula of drag force coefficient and the formula of lift force coefficient in this paper have good applicability.Based on high-speed imaging technology,the saltating particle impact bed surface process was observed,accurately determined the impact point location,constructed the saltating particle impact model,defined the impact point position parameters,and analyzed the position parameters.The experimental results show that the impact offset angle and impact surface angle obey normal distribution.Based on the previous research,the mechanical mechanism and statistical law of sediment saltation are further revealed.The uniform bed load velocity,non-uniform sediment velocity coefficient,and non-uniform bed load velocity formula are constructed through the bed load velocity experiment.Verified by the actual measurement data of the flume experiment in this article and other documents,the calculated value of the non-uniform bed load movement velocity formula in this article is in good agreement with the actual measured value.(3)The formulas of uniform bed load transport rate,bed load transport gradation,and non-uniform bed load transport rate are constructed.Based on the measured data of flume experiments in other literature,the formulas of incipient probability,the thickness of moving layer with high-intensity sediment transport rate are established.On this basis,the formulas of uniform bed load sediment transport rate based on the incipient probability theory is constructed respectively.Based on the starting probability and the relationship of the particles,the probability of heterogeneous sediment starting is calculated.Then,bed load transport gradation formula and non-uniform bed load transport rate are constructed.Verification by flume experiments in other literature and measured data from natural rivers,the formulas from this paper have good applicability.