Experimental Study On Unsteady Open-channel Flow Incipient Motion Of Uniform Gravel

Along with development of speed up the pace of construction of water conservanc-y,channel unsteady flow problem increasingly prominent,the unsteady flow in the sediment is imminent.Besides flood formation under the influence of rainstorm flash floods was unsteady flow,water flow rate have larger amplitude,the water not constan-cy also stronger.And the use of the original constant flow sediment formula is intodu-ced into the unsteady has not apply,so it is very necessary that research the unsteady flow influence to incipient motion and transport.First of all,this paper compares of the domestic and foreign researchers arrangeme-nt using the tail-gate sand experiment,reach and the water level,flow velocity and flow rate can be synchronized observation at the same time.In this paper,the innovation in technology,using real-time surveillance video and water level has reached the require-ment of synchronization and at the same time,using image processing technology to deal with video analysis,get bed sediment transport rate.At constant uniform streaming video to image processing,get the cross section of sand transport rate,use shields incipient motion curve,incipient velocity,Parker dimen-ensionless sediment rate method to analyze the incipient motion,using get Parker dimensionless sediment rate for sediment incipient motion way,contrast of incipient drag force,incipient velocity.Technological innovation are used to get the unsteady flow transport rate,mainly studied the following contents:Use of different period under the same amplitude different period,the different amplitude to under same period of 60 experiments on unsteady flow.Make use of the experiments results superposition average processing was carried out on the water level,the average sediment discharge and smooth handle.When the same transport rate,find the unsteady flow and sediment start(stop)the depth of the water comparised with a constant flow of incipient motion depth were analyzed;Finally got the incipient motion the laws between the different period and amplitude.For researchers at home and abroad to rise period compared with the transport rate of decline,the location of the maximum sediment discharge and sediment transport rate formula has always been controversial about the problem,by using the experimental data,found the rise period and decline period of the relationship between the transport rate,and the position of the maximum sediment discharge;Using the experimental data of the friction velocity,water depth and sediment discharge before and after the relationship between the maximum,found the influence incipient motion and bedload sediment transport of the main two factors for the bed shear stress and sediment lag,when unsteady properties is small,the bedload sediment transport rate and synchroni-zation,the bed shear stress with the increase of the constancy,sediment gradually lag behind friction velocity,but is located in the largest water depth before,when the constancy increases to a certain depth of the maximum sediment rate of lagging behind;According to the bed shear stress is influence incipient motion and bedload sediment transport mode,reasonable defines a unsteady factor,order of magnitude as the O(1);Defines an unsteady coefficient,average sediment transport rate and the relationship between the unsteady coefficient;finally deduces an unsteady flow sediment formula.