| Sediment settlement,sediment incipient and lifting are important problems in hydraulic engineering,Marine engineering,environmental engineering and other fields.Therefore,scholars at home and abroad have been deeply studying it.In this paper,based on the review of previous studies,the shape coefficient of natural sediment particles,non-uniform motion of natural sediment particles in hydrostatic sedimentation,the critical condition of natural sediment particles lifting,the influence of shape on the lifting probability,the starting velocity formula of natural sediment particles with shape factors and the influence of shape on the starting probability are studied.The main research contents and results are as follows:(1)1100 natural sediment particles with diameter between 2mm and 12mm were selected and their shape coefficients were statistically analyzed by Corey shape coefficients.The hydrostatic sedimentation test of single sediment and the total drag coefficient of natural sediment particles under non-uniform motion were carried out by a self-designed settling device.The results show that the shape coefficients of each particle size of natural sediment particles basically conform to the normal distribution,with the mean value of 0.66 and the standard deviation of 0.12.The non-uniform motion state of natural sediment is divided into steady motion state and accelerated motion state.The acceleration coefficient An is introduced,and the relationship between the total drag coefficient C_Dand the shape coefficient S_f,the particle Reynolds number Re and the acceleration coefficient An is explored.The semi-empirical formula of the total drag coefficient under the non-uniform motion state of natural sediment particles is obtained.(2)Based on the sedimentation data of natural sediment particles collected,the formula of constant uniform motion drag coefficient of natural sediment particles is fitted out on the basis of the content in the first part,and the formula of uniform sedimentation velocity of natural sediment particles is obtained,which includes the shape coefficient of natural sediment particles.On this basis,the uniform settling velocity formula is introduced into the uplift probability formula of Cheng,and the uplift probability formula with shape coefficient is obtained.When the uplift probability P=5%,the critical condition of uplift of natural sediment particles in the near-bottom turbulent rough area is obtained:ω/u_*=1.6,and the suspension index z=4 is obtained.The influence of shape coefficient of natural sediment particles on the uplift probability was analyzed qualitatively.The same analysis was carried out for calcareous sand particles.Because the shape of calcareous sand particles was more irregular than that of sediment particles,it was found that the influence of the shape of calcareous sand particles on its lifting probability was much more obvious than that of sediment particles.(3)On the basis of the formula of uniform motion resistance coefficient of natural sediment particles obtained in the above part,this paper applies the formula of constant resistance coefficient with shape coefficient to the force analysis of natural sediment particles starting,adopts the rolling starting mode,quantifies sediment starting criteria with sediment starting probability,and establishes the starting velocity formula of sediment particles.Based on the measured data collected,the parameters in the formula are determined,and the average starting velocity of vertical sediment particles is obtained.The influence of different shapes of sediment particles on starting is explored through starting tests.The influence of sediment particle shape on starting probability was analyzed by theoretical formula. |
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