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

土壤-工具-残留物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%的农田被前茬作物的残留物覆盖。因此，土壤啮合工具(如犁、圆盘、扫地等)在田间作业中，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，因为土壤是由离散的颗粒组成的矩阵，这些颗粒具有随机性、异质性，并表现出复杂的非线性行为。这样的系统不能用传统的分析或数值方法来建模。在拟议的研究计划中，将使用一种创新的数值方法-离散单元法(DEM)来建立通用的土壤-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表示一个土壤颗粒。颗粒本构定律将以这样的方式定义，即基本颗粒可以形成集合体，并具有与真实农业土壤一样的摩擦、粘性、粘性和可变形行为(新颖性1)。粘聚力行为将用接触的土壤颗粒之间的结合来描述。在土壤啮合工具的影响下，粘合是容易断裂的。模型的微观特性(如颗粒弹性模数、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(新颖性2)。由于DEM颗粒的微观性质是不可测量的，因此将开发一些方法来校准这些微观性质。将使用基本的土壤力学测试进行校准，因此校准的微观性质是通用的，不受土壤接合工具的影响(新颖性3)。在该模型中，残留物粒子将由一簇基本球体表示，这些基本球的排列方式反映了真实作物残留物的形状。残留物集群将被整合到土壤颗粒中，形成一个由离散的土壤和残留物颗粒混合而成的异质模型域(新颖性4)。通用模型将能够预测土壤微观动力学：包括每个土壤和残留物颗粒的力和位移，颗粒组合中的应力分布，以及土壤啮合工具表面的压力分布(新颖性5)。模型将使用实验室和现场数据进行验证。农业土壤动态行为的DEM模拟是一个新兴的领域。了解土壤、残留物和工具的微观动力学属性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啮合工具的出现，这些工具消耗最少的拖拉机功率，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.