Simulations of micro-dynamics of soil, tool, and crop residue using the discrete element method (DEM)

土壤-农具-残茬相互作用不仅是许多农业田间作业的核心，也是农业工程中土壤动力学的基本方面之一。在现代保护性农业系统中，至少30%的农田被前作物的作物残留物覆盖。因此，土壤接合工具（例如犁、圆盘、清扫器等）在田间作业过程中，如耕作和播种，与土壤和作物残留物相互作用。土壤-工具-残留物是一个复杂的系统，因为土壤由离散颗粒组成，这些颗粒具有随机性、非均匀性，并表现出复杂的非线性行为。这样的系统不能使用传统的分析或数值方法建模。在拟议的研究计划中，一个创新的数值方法，离散元法（DEM），将用于开发通用的土壤工具残留物相互作用模型。在模型中，不同大小和形状的多个球体将代表土壤颗粒。颗粒本构律将以这样一种方式定义，即基本颗粒可以形成聚集体，并具有摩擦、内聚、粘性和变形行为，就像真实的农业土壤一样（新奇1）。将使用接触的土壤颗粒之间的键来描述内聚行为。在土壤接合工具的冲击下，粘合剂是可断裂的。模型微观特性（如颗粒弹性模量、粘结强度和颗粒摩擦系数）将被定义为与颗粒尺寸无关，因此它们是通用的（新奇2）。由于DEM颗粒的微观特性是不可测量的，将开发方法来校准微观特性。将使用基础土壤力学试验进行校准，以便校准的微观特性具有通用性，且独立于土壤接合工具（新奇3）。在该模型中，残留物颗粒将由一簇基本球体表示，这些球体以反映真实的作物残留物形状的方式排列。残留物簇将被整合到土壤颗粒中，形成一个非均质模型域，其中包含离散土壤和残留物颗粒的混合物（新奇4）。通用模型将能够预测土壤微观动力学：包括每个单独的土壤和残留物颗粒的力和位移，颗粒组件中的应力分布，以及土壤接合工具表面上的压力分布（新奇5）。模型将使用实验室和现场数据进行验证。农业土壤动力学行为的DEM模拟是一个新兴的领域。对土壤、残留物和工具的微观动力学属性的理解将标志着土壤动力学领域的潜在突破。这将导致新的高性能土壤接合工具的出现，这些工具消耗最小的拖拉机功率，并为可持续农业中的粮食生产创造最佳的土壤和残留物条件。

Soil-tool-residue interaction is not only at the centre of many agricultural field operations, but also one of the fundamental aspects of soil dynamics in agricultural engineering. In modern conservation agriculture systems, at least 30% of an agricultural field is covered by crop residue from the previous crops. Thus, soil engaging tools (e.g. plows, discs, sweeps, etc.) interact with both soil and crop residue during a field operation, such as tillage and seeding. Soil-tool-residue is a complex system, since soil consists of a matrix of discrete particles that are of random, heterogeneous nature, and exhibit sophisticated non-linear behaviours. Such a system cannot be modelled using traditional analytical or numerical methods. In the proposed research program, an innovative numerical method, the discrete element method (DEM), will be used to develop universal soil-tool-residue interaction models. In the model, multiple spheres of various sizes and shapes will represent a soil particle. The particle constitutive laws will be defined in such a way that basic particles can form aggregates and have frictional, cohesive, viscous, and deformable behaviours like real agricultural soil (NOVELTY 1). The cohesive behaviour will be described using bonds between soil particles which are in contact. Bonds are breakable under the impact of soil engaging tools. Model microproperties (such as particle modulus of elasticity, strength of bond, and particle friction coefficient) will be defined to be independent of particle sizes, so that they are universal (NOVELTY 2). As the DEM particle microproperties are not measurable, methods will be developed to calibrate the microproperties. Calibrations will be performed using fundamental soil mechanical tests, so that the calibrated microproperties are universal and independent of the soil engaging tool (NOVELTY 3). In the model, a residue particle will be represented by a cluster of basic spheres arranged in a way to reflect the shapes of real crop residues. Residue clusters will be integrated into soil particles, forming a heterogeneous model domain with a mixture of discrete soil and residue particles (NOVELTY 4). The universal models will be able to predict soil micro dynamics: including forces and displacements of each of individual soil and residue particles, stress distribution in particle assembly, and pressure distribution on the surfaces of soil engaging tools (NOVELTY 5). Models will be validated using laboratory and field data. DEM modeling of dynamic behaviours of agricultural soil is an emerging field. Understanding of micro dynamic attributes of soil, residue, and tools will mark a potential breakthrough in the area of soil dynamics. This will lead to the emergence of new high performance soil engaging tools which consume minimum tractor power and create optimal soil and residue conditions for food production in sustainable agriculture.