Study On The Morphology Of Light Sands And Its Control Measures

In order to meet the similarity of sediment movement and river bed deformation,the light sand as the model sand is mostly used in the moving bed model of water flow and sediment movement at home and abroad.At present,due to the lack of the theory of sediment movement,it is still impossible to effectively avoid the sand wave scale which is generally larger than that of the corresponding scale condition in the model test.This deviation will affect the movement state of water flow and sediment,and reduce the accuracy of the model test result.The sand wave problem of light sand has been paid more and more attention by researchers who engage in water conservancy and water transport engineering.It is of great significance to carry out research on the sand wave shape and resistance of light sand in moving bed model.Based on the combination of theoretical analysis and sink test,the sand wave scale of light sand under the conditions of different particle size,specific gravity and water flow conditions is systematically analyzed.Then the formula for calculating the sand wave scale of light sand is established under multi-factor condition.The movement,shape and resistance characteristics of light sand are revealed,and its main influencing factors and mechanism are disclosed.It puts forward feasible method of controlling light sand wave shape and provides the theoretical basis for the study of water and sediment movement in the moving bed model test and practical engineering applications.Specific conclusions are as follows:(1)This paper analyzes the mechanism of sediment initiation from the aspects of randomness,stress analysis,sand movement,the incipient velocity formula and so on,and states the mutual process between sediment incipient motion and water flow.(2)The results show that the sand movement under different gravity and particle size are basically the same,only the sand wave scales are different.In the range of Fr =0.1?0.32,the wave height is proportional to the particle size and is inversely proportional to the specific gravity.The relative wavelength is inversely proportional to the particle size,which is proportional to the specific gravity.The calculation formula of the wave height is established by comparing the formula of the predecessors and the results of this experiment.(3)The results show that increasing the nonuniformity of light sand is beneficial to control the development of sand wave.(4)The roughness n increases with the increase of particle size and specific gravity.Particle size and relative wave height are important factors affecting the sand drag coefficient f_b~n which is proportional to the relative wave height and particle size.