凸齿镇压器与土壤相互作用的三维动态有限元分析

为分析凸齿镇压器与土壤的相互作用、预测不同的作业参数对凸齿镇压器作业效果的影响,该文利用有限元方法,在Abaqus软件中建立了凸齿镇压器与土壤相互作用的三维动态有限元模型。该模型在分析过程中使用任意拉格朗日-欧拉方法对网格进行自适应划分,以解决土体局部变形引起单元畸变而导致分析中断的问题。根据凸齿镇压器的2种工作模式,对模型设置不同的边界条件,探讨不同载荷对凸齿镇压器沉降量和所需牵引力的影响以及不同沉降量对所需载荷及牵引力的影响。搭建了基于室内土槽的凸齿镇压器牵引试验平台,通过土槽试验对有限元分析结果的有效性进行验证。结果表明,有限元求解的牵引力与实测值相对误差为3.4%,并且有限元分析模型运行结果能准确反映土壤的形貌变化特征;任意拉格朗日-欧拉方法有效解决了单元扭曲导致分析不收敛的问题;在恒定速度下,凸齿镇压器的沉降量和所需水平牵引力随着载荷的增大而增大,同样,沉降量的增大导致了所需载荷和牵引力的增加。该三维有限元模型可用于预测凸齿镇压器工作过程中的所需牵引力和土壤表面微形貌加工的作业效果,可为探索凸齿镇压器与土壤相互作用的机理,对凸齿形状进行改良与优化、以及作业条件与参数的选择提供参考依据。

Three-dimensional dynamic finite element analysis of interaction between toothed wheel and soil

Abstract: This study aims to provide a three-dimensional (3D) finite element model to simulate soil and toothed wheel interaction dynamically. A toothed wheel is a novel apparatus that is used for micro-topography preparation. It has a series of peripheral tooth circumscribing rolling wheel. When this device is hauled and rolled across the soil surface, a series of consolidated small depressions are created. Accordingly, the soil is restructured to a desired form, and micro-topography preparation is achieved. To ensure the applicability and effectiveness of micro-topography preparation, depression shapes and capacity should be adapted to ensure the satisfactory volume of collected run-off. Thus, a toothed wheel requires adequate working conditions such as an implemented load and vertical displacement to prepare adequate imprints in the soil surface. Therefore, predicting the interaction behavior between a toothed wheel and soil is of prime importance in helping to enhance operation workability and efficiency. When studying the interaction behavior between a toothed wheel and soil, field experimental studies can give valuable insights, but can also be expensive, and may be limited to certain working conditions. In addition, results are highly dependent on the accuracy of the measuring devices. Yet numerical simulations help to minimize the number of field experimental tests required, and help to interpret test results. FEM is a powerful numerical technique and good at analyzing complex engineering problems, especially for dynamic systems with large deformation and problems related to soil mechanics. Therefore, the FEM approach increasingly shows promise in analyzing the factors affecting the interaction between soil and tillage tools. Yet, by far available models are mainly focused on disk plow, blade, or moldboard. There are few available reports of 3D models that are used to predict toothed wheel working behavior on soil. Consequently, there is a need for a three-dimensional (3D) finite element model to dynamically simulate soil and toothed wheel interaction. However, when a toothed wheel is rolled on soil surface, depressions in the soil model can cause localized large deformation. For a large deformation in FEM, due to unacceptable element distortions, the conventional finite element techniques may suffer from serious numerical difficulties. One possible and robust way to solve dynamic problems involving large deformations is to take advantage of the Arbitrary Lagrangian-Eulerian (ALE) method. In the ALE approach, the mesh motion is taken arbitrarily from material deformation to keep element shapes optimal, where the extent to which material flows through the fixed finite element mesh (Eulerian) or the mesh moves with the material (Lagrangian), may be varied arbitrarily to avoid excessive mesh distortions. This re-meshing technique, allowing for continuous remeshing of deformed elements, can effectively mitigate and eliminate excessive mesh distortion induced by the large deformations during toothed wheel rolling on soil surface. In order to investigate the behavior of the soil and toothed wheel interface and predict the effects of working parameters on toothed wheel working efficiency, in this study, a 3D finite element analysis of soil and toothed wheel interaction was carried out. The Drucker-Prager constitutive material model implemented in a commercial finite code Abaqus was used to model the soil. To efficiently perform a large number of loading increments, and to simplify the treatment of contact, an explicit finite element scheme was used. Through the setting of different boundary conditions, the effects of toothed wheel implement loads on vertical displacements and required draft forces, along with the effects of toothed wheel vertical displacements on required implement loads and draft forces were examined. The results revealed that the ALE technique prevents convergence problems caused by mesh over distortion and preserved the quality of the mesh throughout the numerical simulation, hence it allowed the simulation to run continuously in simulating the soil and toothed wheel interaction. The draft force recorded by the FEA model and the soil bin test were compared to calibrate the FEA model. A test rig and force measurement system was developed based on the indoor soil bin, and then a toothed wheel traction test was performed. The results showed both that the draft force versus time had the same variation pattern, and that the mean relative error of the averaged draft force of FEA compared to the soil bin test was 3.40%. This indicated the results of the FEA solution could meet the requirement of reflecting the dynamic behavior in the toothed wheel working process and achieve the desired accuracy. Comparing the topographic characteristics of the prepared micro-basin, results show that the micro-basin topographic characteristics from the FEA solution were in good agreement with that from the soil bin test. Comparison of numerical and experimental results showed the capability of the presented model of accurately simulating the interaction behavior between toothed wheel and soil. Further investigation was conducted using this model, and the results showed that at constant horizontal velocity, toothed wheel vertical displacement, and draft force increased as the implement load increased. Meanwhile, an increase of vertical displacement also increased implement load and draft force. The present working model can be applied to predict micro-topographical preparation working efficiency and toothed wheel draft force. In addition, it can be utilized for further innovative design of a geometrically optimized toothed wheel and give a technique reference concerning working conditions and parameters.