Study On Analytical Solution And Meshless Numerical Simulation Of Slope Runoff-infiltration Coupling

Slope runoff refers to the slope flow of rainfall,snowmelt or irrigation under the action of gravity,which is related to the hydraulic characteristics of the flow,velocity and depth of the water.Soil water infiltration is the process of water flowing from the surface into the soil under irrigation or rainfall conditions.Therefore,the accurate simulation of the process about the slope runoff-infiltration is of great scientific significance for solving the problems of soil erosion and environmental engineering in the watershed.It can not only get a reasonable and effective irrigation method,but also improve the crop yield.What's more,it is to provide a theoretical basis for preventing soil erosion.The slope runoff in this paper is a more complex process including two aspects:one is the infiltration process of soil moisture into the deep underground layer in the process of water flow;the other is the process of surface runoff when the water flow is greater than the infiltration capacity of soil.The hermite radial basis distribution point method is used to simulate the slope runoff infiltration coupling process for the the unsaturated soil water movement equation with the Neumann boundary condition.The main research work and achievements include:(1)Firstly,based on the theory of functional extremum,the functional extremum problem of horizontal imbibition and vertical infiltration under different boundary conditions were put forward for one-dimensional unsaturated soil water movement equation.Secondly,a new analytical solution for unsaturated soil water movement equation is presented based on the variational principle and the least action principle.And it is proved that the analytical solution is a necessary and sufficient condition for the extremal solution of functional problems.Finally,the analytical solution and numerical solution are compared and analyzed by the numerical examples are given.The error results show that the analytical solution obtained by this paper can accurately predict the distribution of soil water content of horizontal imbibition and vertical infiltration problems under the condition of upper boundary saturation and initial water content uniform distribution,which is an effective method.(2)The basic principle of hermite radial basis collocation method is given,and hermite radial basis point collocation algorithm is constructed for one-dimensional and two-dimensional unsaturated soil water movement equations in the process of slope infiltration.Five representative numerical examples of the regular area and the irregular region and the simulation of the actual background problems are given respectively.The results show that the proposed method has good convergence compared with the results of the finite difference method and radial basis collocation method.(3)Numerical simulation is carried out on the actual background problem of slope runoff Infiltration process.Firstly,the infiltration process of soil water on the slope is simulated by the hermite radial basis collocation method,and couples simplified Saint Venant equation-Motion Wave equation by the infiltration rate.Then,the Preissmann implicit method is applied to simulate the runoff process.Finally,the whole slope runoff infiltration process is simulated and coupled by time iteration method.The coupling results show that this paper method can be widely applied to the actual background engineering problem.