| Sediment incipient motion has always been one of the basic problems in water conservancy research,which is of great significance to the study of river sediment transport rate and riverbed evolution.In nature,mountain torrents,storm surges,tsunamis and other natural disasters generally cause severe sediment movement.Usually,these flows have a strong non-steady,so the study of sediment incipient motion under the action of unsteady flow is more practical significance.First of all,for the experimental study of sediment incipient motion,the real sediment is used as the experimental sample.However,due to the real sediment particles are too small and limited by the experimental equipment,it is impossible to start the experiment of single particle sediment and analyze the interaction between sediment particles.Compared with the real sediment experiment,using the spherical sediment to simulate the real sediment has many advantages,such as amplifying the experimental phenomenon and making the experimental conditions closer to the theoretical analysis,which can provide more accurate and wider data for the sediment incipient experiment.Secondly,the research on the influence of sediment interaction on the incipient velocity of sediment is focused on numerical simulation,and this study is extended from numerical simulation to physical model,which can lay a theoretical foundation for the study of sediment group incipient motion.Based on the wave flume flow system,the starting experiment is carried out by using the solid sphere of polymer material,namely the spherical sediment,to simulate the sediment particles.The glass hemisphere is used to form the bed surface of sediment incipient motion,and the high-speed camera is used to capture the incipient moment of sediment incipient motion.Under the action of constant flow and unsteady flow,the incipient velocity of single particle and multi-particle sediment incipient motion are measured respectively.The experimental incipient velocity data are used to verify the theoretical formula of sediment incipient motion.The main research results are as follows:In terms of theoretical research,the calculation formula of inertial force in Morison equation is introduced into the sediment rolling balance equation to obtain the sediment starting formula under the action of unsteady flow.Based on the two-dimensional theoretical analysis model and combined with the experimental characteristics,the two-dimensional theoretical formula is extended to the three-dimensional theoretical formula.Under the action of constant flow and unsteady flow,the physical experiment was carried out to obtain the starting velocity of single-particle spherical sediment,and the experimental data are used to verify the theoretical derivation formula.The results show that the three-dimensional theoretical derivation formula is basically consistent with the experimental data.In terms of the start-up of multi-particle sediment,under the action of constant flow and unsteady flow,the start-up experiment of multi-particle spherical sediment was carried out to mark a spherical sediment in the sediment group,and the influence of other interfering sediment on the start-up velocity of marked sediment was analyzed.The location characteristics of disturbed sediment were classified,and eight different arrangements were set.The experiments were carried out under the conditions of constant flow and unsteady flow,and the starting velocity of marked spherical sediment was obtained.Compared with the starting of single particle sediment,the influence of interaction between sediment on the starting velocity of sediment is analyzed. |
