| This paper takes the method of flume generalized model experiment, theoretical analysis and analogue simulation, basing on the stochastic simulation process of daily average flow in Cuntan hydrometric station, flow structure of spur dike, turbulence characteristics, stress distribution and change laws of dam body and the bed in unsteady flow have been researched. The main research results have the following several aspects:(1)By using two variable Gumbel-logistic model,we analysis the daily flow process of Cuntan hydro logical station in the upper reach of the Yangtze river during19542008, and get the probability of floods and return period when maximum flood peak flow in frequency-diversity years, flood volume in in half a month, maximum flood peak flow in one year come across the effective flood period. Simulating the process of mean daily discharge with the application of the Auto-Regressive Markov model(AR modle), and different return period flood process under condition of the combination of different influence factors obtained.(2) Water drop height in the upper and lower reaches of spur dike during water level rise period and phase period,formula for jetty head velocity and cross section area velocity distribution of mainstream dam axis.(3) When longitudinal current velocity, scouring pit area near downstream dike head、mainstream dam axis of cross section area and flow velocity around dike head is large, and the velocity around downstream slope foot is also large in large flow condition; the transverse current velocity、flow velocity around front slope is large, the transverse current velocity around dike head can achieve25cm/s probably (the prototype is about1.5m/s); velocity on a vertical、velocity around dike head change a lot, velocity on a vertical is big in large flow of downstream slope foot condition, all velocities on a vertical around scouring pit area near dike head is positive value basically (pointing to the surface of water), maximum value of velocity on a vertical comes out of drowning period, and when the frequency of big value of velocity on a vertical is big and there is no spur dike relatively, the longitudinal and the transverse velocity around the dike head at the same position after the spur dike layout, and the velocity along the vertical change is also big. That explains the reason why the silt of scouring pit area near dike head is easy to start up and the dike head and the downstream slope is easy to be damaged by flood.(4) The order of area which vertical turbulence intensity from large to small is: the scouring pit area near downstream dike head、downstream slope and the dike head, mainstream dam axis of cross section area and front slope; the maximum of transverse turbulent motion intensity comes out around the dike head, the transverse turbulent motion intensity of downstream slope is big in large flow condition; the area where the maximum of vertical turbulence intensity is downstream, the vertical turbulence intensity around dike head and downstream dike head is also big. That tells us that spur dike and the bed scouring around is not caused by one reason, in fact, it caused by a combination affect of the longitudinal, transverse and vertical velocity, turbulence intensity and the Vortex scale. So the big flow velocity and the strong turbulence intensity of one area can not state that the area is scoured forcefully, and vice versa.(5) From the point of view of time series, Each part of spur dike dynamic water pressure change process of each part of spur dike and flow change process maintained a good synchrony, but changes in pressure fluctuation is not; No matter how the flow process, the maximum value of dynamic water pressure are near the maximum flood peak flow, maximum fluctuating pressure maximum mostly appears in the fall after the peak flow period; the boundary area of the head of the dam and the upstream slope, the dynamic water pressure on the side of the upper reach of dam head and the middle region of the side of the upstream slope of the dam head, the dynamic water pressure is bigger in the dam’s back water slope foot, water dam in the period of the dynamic water pressure was larger than the rising phase dynamic water pressure constant flow pulsation pressure maximum value appeared in dam head back water slope side, unsteady flow fluctuating pressure maximum value appeared in the downstream slope or the head; flow is small rising phase pulsating pressure is greater than the falling period of fluctuating pressure flow rate is greater than the rising phase falling period pulsating pressure pulsation pressure, shows that the spur dike flood occurred mainly in the peak flow and the larger flow of falling period.(6) Dike head stone from the upstream near the bed surface began to move,with erosion continues, bottom foundation instability leading to rock slope on the continue to fall to cause large area flood dam toe head, maximum peak when passing the dam, dam head within a short time all the basic flood; water flow is not over the dam to the dam, dam crest downstream side of the block stone large sliding to the back water slope, local permeability larger area, the comprehensive effect of dam phreatic flow and turbulent flow conditions, the local depression and collapse, forming the scour pit; scattered stones at the bottom of the migration to the scour pit when a part, large diameter rock scour downstream along the slope climbing to scour downstream of sedimentation and stay here, small particle size of stone in the water to continue down the parade until the fall to near edge of sedimentation,stone and remain in the scour pit, in the vortex and its own gravity gradually sinking and surrounded by or cover.(7) On account of the difference of the type of Jetty head,the damage of Jetty head classifies from the fan hook, Circular hook to Circular straight head in order of size. For the flood process which has the same return period, if the actual annual maximum discharge of the flood peak encounters the maximum discharge of the flood peak in half a month, the peak flow of scour depth plays a leading role upon scouring depth, meanwhile, the total flood volumes of jetty head plays a leading role on the scope of the scour pit.When the actual annual maximum discharge of the flood peak encounter the effective flood cycle, the number of the effective flood cycle plays a leading role on both the scouring depth and the scope of the scour pit. The fastest growing of scope of the pit of happens between the first two larger flood peak. When the dam is long, the width of the scour pit is big at the beginning of the scouring,in the late, on the contrary, it is small. when the select corner is big, the width of the scour is small and scour length and the size of select corner are scarcely relevant. The scouring resistance of the bed is a dynamic process under the influence of unsteady flow.(8) Through the analysis on the single factor analysis of the depth of scour pit,we learn that the depth of scour pit of spur dike closely related to hydro logical factors such as a flood peak discharge and effective flood time and so on. On this basis, through the dimensionless and multiple regression analysis, The condition of unsteady flow is established in mountain area rivers scattered rubble-mound spur dike scour pit depth and length of spur dike and river width, height, maximum peak flow, flood total time effectively, jetty head type coefficient and calculation formula between pick angle, Applied formula of upstream Yangtze admiralty moraine beach along the calculation of scour depth, Indicates that the formula has high calculation precision, can be used in engineering practice. |
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