Experimental Study On Generalized Model Of Single Sediment Under Unidirectional Flow

Sediment incipient motion and sediment particle motion are the basis of studying sediment motion mechanics,and are particularly important link in the riverbed evolution.They not only promote the development of the basic theory of sediment motion mechanics,but also have important guiding value to the application of hydraulic engineering.Due to the fast flow speed and small particle size of sediment,the sediment particles moving in the flow cannot meet the requirements only by general measurement methods.so it is difficult to study the whole process of sediment movement,which is also the reason why the movement characteristics of sediment particles have not been further studied in the past.In this paper,the single particle motion model experiment under the action of steady flow and unsteady flow is carried out.The generalized sediment model was used to simulate the roughness of moving sediment particles and bed.The flow velocity of single particle centroid was measured by a flow meter.The motion mode of single particle was obtained by side shooting with a high-speed camera.The motion characteristics of single particle under the action of steady flow and unsteady flow were explored and analyzed.Motion characteristics of single particle under steady flow.The motion law of single particle with different particle sizes under different roughness of bottom plate was explored.and the influence of single particle exposure and single particle size on single particle starting was analyzed.The results show that the main motion forms of single particle are rolling,rolling and sliding,sliding and jumping,and the ratio of the jump length to the jump step length is about 0.371.The horizontal velocity of single particle is positive,the vertical velocity of single particle is positive and negative,and it approximately satisfies the normal distribution.The rolling velocity of the single particle is lower than the slip and jump velocity.and the ratio of the average velocity of single particle to the flow velocity is in the range of 0.18-0.45.The starting velocity of single particle increases with the increase of relative exposure of single particle.Single particle with larger particle size is easier to start,and single particle with smaller particle size is more difficult to start.Motion characteristics of single particle under unsteady flow.The motion law of single particle with different particle size under different roughness of bottom plate and different flow acceleration was explored.The influence of flow acceleration,single particle exposure and single particle size on single particle starting was analyzed.The results show that the single particle presents the main motion forms of rolling and sliding,sliding and jumping,and the greater the flow acceleration,the greater the fluctuation of the trajectory.The single particle jump length and jump height increase with the increase of the flow acceleration.The horizontal velocity of single particle is positive,the vertical velocity of single particle is positive and negative,and it approximately satisfies the normal distribution.The horizontal velocity and vertical velocity of single particle increase with the increase of flow acceleration,and the average velocity of single particle decreases with the increase of particle size.When the flow acceleration is constant,the starting velocity of single particle increases with the increase of relative exposure of single particle,and the starting velocity of single particle decreases with the increase of particle size.The existence of flow acceleration reduces the starting velocity of single particle.