Study On Some Key Aspects Of Numerical Simulation Of Flow And Sediment

In this dissertation, theoretical and numerical analysis have been carried out in the research on the depth-integrated 2-dimensional hyperconcentration river and 3-dimensional flow and sediment mathematical models. The main contents are summarized as following:(1) Advancements of the basic theory on river dynamics and sediment mathematical model are summarized. Technical difficulties of the mathematical model are pointed out as well as the solutions are proposed.(2) Data of Bingham shear stress of hyperconcentration flow have been used for training for several times by artificial neural net. The result shows that if in most runs the Bingham shear stress of the hyperconcentration flow is greater or less than a critical value, the training results accord well with the measured data, while others do not. Several training tests give nearly the same results. It can be deduced that there indeed exists a critical value of Bingham shear stress, and when the shear stress exceeds this critical value, flow performs as Bingham fluid. For flow with a hyperconcentration of powdered phenolic, this critical value is about 3.2 x 10-1 Pa.(3) 37 runs flume data of suspend sediment capacity containing hyperconcentration flow and middle concentration flow and lower concentration flow are trained by artificial neural net. All of the results showed much consistency with the measuring data. It is suggested that hyperconcentration flow and lower concentration flow may be expressed in a general suspend sediment capacity formula. Several formulas are compared and Dou Guoren's formula is verified most correctness and recommended in mathematical model.(4) Based on the fact that there exists an essential relationship between river morphology and the just upper stream discharge and sediment quantities when a dynamic equilibrium state is reached , that is, river regime, a postulate is put forward for hyperconcentration flow to generalize the river morphology. This postulate agrees well with both the flume data and the field data on a branch of the Yellow River. An example is also given to demonstrate its application in numerical simulation.(5) A depth-integrated 2-dimensional mathematical model for hyperconcentration sediment river is established in which coupling flow-sediment field is adopted. The relationship of the time step versus the space step is also presented. On the constringency condition, the author suggested that it should include both flow field constringency and sediment field constringency, while the latter requires the stability of sediment capacity. The calculation of this paper shows that primary recovery coefficient may reduce while the water depth of the river decreasing during the reservoir filling up, which keeps consistency with the existed experiential formulas. The theoretical results are also applied in the model. The measured data on the physical model of the Xiaolangdi reservoir verified the model well. After some simplifications the model can be popularized to apply on clear or lower sediment concentration river simulation.(6) The finite volume method (FVM) is adopted to solve the 3-D governingequations as well as their boundary conditions in the mathematical model. A 3-d suspended sediment module is accomplished on the former work. The boundary conditions such as inlet and outlet conditions, the sediment concentration near the bottom, the interaction between the suspended load and the bedload are also discussed.(7) Several reasons for iteration dissipation in SIMPLE algorithm are analyzed, and a method called unconventionality step correction is presented to solve this problem. Also its advantages and application steps have been presented. It's mathematical basis and physical nature are also discussed.(8) Some disadvantages of the present free water surface computation method are discussed. The paper demonstrated that the gradient of depth-averaged dynamic pressure should be brought into consideration in dealing with the free water surface, because t...