Crystallization And Resolution Modeling Based On Two-phase Solute Transport In Variably Saturated Soil

Study on movement and cumulative process of soil moisture and containing soluble salts in saturated-unsaturated soil zone plays a major role in preventing saline soil and treating soil secondary salinization, computing and predicting transport of nutrient and pollutant in soil, achieving sustainable land use and agricultural development, etc. There are currently a large number conceptual model and mathematical description models have been greatly developed to describe the soil water movement and solute transport process in saturated-unsaturated soil zone, but most models are limited to the restrictions of convective-diffusion characteristics, set the dissolved salt migrating with the water flow in soil aqueous as the inspection object. There is a certain gap between academic study and practice requirements of production forecasting. Based on the theory of water flow and soil salinity transport, enlightened by existing salt and water movement models, this dissertation introduce soil inner evaporation model, respectively build the dissolved phase salt movement model and crystalline phase salt numerical model, eventually established the crystallization and resolution modeling based on two-phase solute transport in variably saturated soil. Those models which were testified by several typical cases were reasonable and feasible, and providing a new idea to simulate and predict the water and salt movement and accumulation status.Firstly, the dissertation discusses the background of soil salinization development and prevention; reach a conclusion that understanding the rules of soil water movement and salt accumulation process meets the essential requirements of salinity control treatment. the paper review development history of theoretical and applied research on water movement and salt migration, and summarize the main features of numerical methods and water-salt dynamics models, analyze the current major problems of movement models, to present the main contents of this article.Secondly, based on Darcy’s law and mass conservation principle, the mechanism of soil evaporation was analyzed, the concept and model of soil moisture inner evaporation was introduced, to establish the basic equation of water movement. The relationship equations of important variables in the basic equation were derived, and the finite element numerical method was adopted to solve soil water movement model. Thirdly, the soil salt was divided into the crystalline phase and dissolved phase to build the cystallization and resolution models based on two-phase solute transport in variably saturated soil, and the two-phase models were reduced to a series of algebraic equations with the finite element method. Following, the dissertation present a detailed analysis on the discrete process of exchange term between crystalline phase and dissolved phase. Solution of matrix equation was either Gaussian elimination or the preconditioned conjugate gradient method and the ORTHMIN procedure. At the latter part of the article, several typical cases were used to testify those new dynamics models. It is shown from mass balance analysis and comparison analysis that the calculated results are correct and reasonable. Finally research results and works of the paper were summarized, and the some improvement suggestion and future development were outlined.