Numerical Simulation And Application Of The Coupled Surface-subsurface Hydrodynamic Model Under Furrow Irrigation

Furrow irrigation is one of the main ways of surface irrigation in China.Compared with some pressure irrigation,such as micro irrigation and sprinkler irrigation,it has the advantages of simple facilities,low cost and easy implementation,but there are also low irrigation efficiency and waste of water resources.At the same time,China is a large agricultural country.The proportion of water used in agriculture is high,which is about 62%of the national water use.Therefore,the study of furrow irrigation to improve irrigation efficiency and achieve water conservation will help ease the contradiction between water supply and demand in China.However,most of the mathematical models involved in the irrigation process are nonlinear partial differential equations.It is difficult to find the exact solution of the equation under the complicated conditions.Therefore,the most effective method is to use the numerical calculation method to find out their numerical solution.In this paper,we conduct the algorithm construction and numerical simulation which focuses on the surface water flow and soil moisture movement during the furrow irrigation process and the coupled model between them.The main work and results are as follows:(1)According to the characteristics of surface water movement under furrow irrigation,based on the principle of water balance,a zero inertia model is used to describe its movement process.For the zero inertia model,the grid division is designed firstly,then the basic equation is discreted with the preissmann four point weighted implicit difference scheme,and then the Newton-Raphson method and the preissmann bidirectional scanning method are used to solve the problem.Finally,the advance process of surface flow movement is obtained.It can be seen from the calculation results that the surface water movement process can be simulated well under furrow irrigation.(2)According to the characteristics of soil water movement under furrow irrigation,based on the theory of unsaturated soil water movement,the Richards' equation is used to describe the movement process.For the solution of Richards' equation,firstly,the grid division is designed for the specificity of the solution area and then the alternate direction implicit difference scheme is used to discretize,and then the special boundary conditions are processed by the additional source term method.Finally,the distribution of the negative pressure water head is obtained,and the distribution of the soil water content is obtained.Numerical simulation 1 shows that the algorithm is stable and convergent,and has a good accuracy.Numerical simulation 2 shows that the algorithm can better simulate the movement of soil water under furrow irrigation.(3)The coupling model of the soil hydrodynamics on the surface of the furrow irrigation is constructed.The coupling model includes the zero inertia model describing the movement of the surface flow and the equation of soil water movement caused by water infiltration,namely,the Richards' equation.The surface water depth and cumulative infiltration are used as coupling link to perform the iterative coupling solution.The numerical simulation is completed for the coupling model of the soil hydrodynamics on the surface of the furrow irrigation.The results meet the actual situation,and can meet the requirements of actual work.