Study On Sediment Incipient Motion And Transport Law Of Slopes

The law of sediment incipient motion and sediment transport is an important part in the study of mechanics of sediment transport and river dynamics.In the study of sediment problems,the randomness of flow conditions and the randomness of the location of sediment particles on the bed must be considered.Therefore,in order to further analyze the sediment incipient motion and sediment transport rules of uniform bulk sediment,this paper studies the sediment incipient motion mechanism.Firstly,the positional relationship of sediment particles on bed surface was studied experimentally.Secondly,the entrainment probability,incipient motion velocity and bed-load transport rate of sediment are studied theoretically.Finally,the nonlinear dynamic characteristics of sediment transport are analyzed by nonlinear method.The main results are as follows:?1?Derived from the characteristics of sediment incipient motion,the quantitative parameters of the positional relationship of sediment particles on the bed surface were redefined based on the research of Han Qiwei and Paintal.Then,the experimental measurement was carried out by a self-designed experimental device,and the value ranges and distribution rules of the uniform sand prominence e₁?e₂?e₃,relative prominence₁e??₂e???₃e,the shading angle and the exposure angle were obtained through sample statistical analysis.?2?Based on the position relation of sediment particles on bed surface and the incipient motion mechanism of sediment,the entrainment probability formula of uniform granular sediment is derived theoretically.Firstly,the instantaneous bottom velocity u_b,the exposure angle?and the relative prominence?₂e of water flow were taken as random variables.Secondly,the influence of the three factors on sediment incipient motion is considered synthetically.Finally,the entrainment probability formula is obtained by the combination of probability theory and mechanical analysis.At the same time,the formula of this paper is compared with the classical formula of sediment entrainment probability.It is found that the formula in this paper has a more perfect theoretical basis than the predecessors,and the change trend and calculated value of the formula are also more reasonable.?3?Firstly,the influences of the instantaneous bottom velocity u_b,the exposure angle?and the relative prominence₂e?on sediment incipient motion were considered.Secondly,the influence of sediment incipient motion standard is introduced.Finally,the incipient motion velocity formula of uniform granular sediment is derived theoretically by using the method of probability theory and mechanical analysis.At the same time,it is compared and analyzed with the measured data and other formulae,and the results show that the formulae in this paper are of high accuracy under different sediment incipient motion standards,and can be used to calculate the sediment incipient motion velocity of natural rivers.?4?The mechanism of bed-load motion on the slope is analyzed.Based on Engelund's basic model of bed load transport rate,the formula of bed load transport rate of uniform bulk sediment on slope is derived.In the process of derivation,the assumptions of the basic model of bed-load transport rate were improved,such as the total probability of sediment incipient motion,the number of movable sediment particles N_b,the critical incipient shear stress?48?_cand the average bed-load velocityu_s.Finally,the measured data are used to verify the results and the comparison analysis with other classical sand transport rate formulas shows that the formulas in this paper have clearer physical concepts and higher computational accuracy.?5?Based on the cusp-catastrophe model of nonlinear theory,the influence of water flow conditions and the relative position of sediment particles on the bed surface on the nonlinear dynamic characteristics of sediment transport process was analyzed.The state variables and control variables of the cusp-catastrophe model were obtained,and a cusp-catastrophe model that can qualitatively describe sediment transport was established.A nonlinear bed-load sediment transport formula was constructed by coordinate transformation and topological transformation.In this paper,the formula is compared with the measured data of bed-load sediment transport rate,based on the same theory formula of bed-load sediment transport rate and the classical formula of bed-load sediment transport rate.The results show that the calculated value and measured value of the bed-load sediment transport rate formula in this paper are in good agreement,which verifies the good applicability of the formula and proves that the nonlinear bed-load sediment transport rate formula in this paper is reasonable.In addition,on the basis of the above research,the nonlinear bed-load sediment transport rate formula for channel with large specific drop is derived and verified by the measured data.