基于EEPA接触模型的土壤耕作特性模拟及颗粒球型影响分析

Simulation of soil tillage characteristics and influence analysis of particle sphere type based on EEPA contact model

关键词:  土壤耕作  离散元  仿真模拟  EEPA接触模型  颗粒球型

Key words:  soil tillage  discrete element  simulation  EEPA contact model  particle sphere type

摘要:

采用EEPA(Edinburgh elssto-plastic adhesion)接触模型模拟土壤耕作特性，探究颗粒球型对土壤离散元模型仿真精度及计算效率的影响。测定了室内土槽土壤的静态堆积角、轴向压力、耕作阻力、耕作堆积角等土壤特性参数，确定并优化了单球土槽土壤离散元模型仿真参数。建立土槽土壤-挖掘犁铲离散元耦合仿真模型并进行仿真参数验证，耕作阻力模拟值与实测值误差为1.70%。以13 mm为等效粒径确定了单球、双球、三球、四球等4种土壤颗粒的外形尺寸，采用单球、单球变粒径、双球、三球、四球、多球混合等填充方式建立了6种虚拟土槽，以耕作阻力、耕作堆积角、仿真时间为试验指标开展挖掘犁铲耕作过程仿真试验。试验结果表明:6种虚拟土槽的耕作阻力模拟值与实测值相对误差均小于8%，能够满足耕作阻力模拟要求；耕作堆积角模拟值与实测值相对误差为2.32%~20.32%，单球变粒径、四球、多球混合等虚拟土槽耕作堆积角相对误差均小于10%；单球土槽挖掘犁铲耕作仿真时间约为80.44 min，受土壤颗粒填充数量、接触关系及颗粒球型等因素影响，其他填充条件下仿真时间均有显著增加。综合考虑仿真精度及计算效率，土壤耕作阻力模拟时虚拟土槽宜采用单球颗粒填充方式，耕作堆积角模拟时虚拟土槽宜采用四球或多球混合填充方式建立。该研究为土壤-机具互作离散元仿真的建模，EEPA接触模型的参数选择，颗粒球型及填充方法的确定提供了依据和参考。

Abstract:

EEPA(Edinburgh elssto-plastic adhesion)contact model was used to simulate soil tillage characteristics, and the influence of particle spherical shape on the simulation accuracy and computational efficiency of soil discrete element model was explored. The static accumulation angle, axial pressure, tillage resistance, tillage accumulation angle and other soil characteristics parameters of indoor soil were measured. The simulation parameters of single particle soil were determined and optimized, and the plastic deformation ratio was 0. 31, the adhesion energy was 26. 30 J/m², the rolling friction coefficient was 0. 52, the recovery coefficient was 0. 58, the tangential stiffness factor was 0. 39, the static friction coefficient was 0. 67, and the bond branching index was 4. The discrete element coupling simulation model of soil-excavation plough shovel was established and the simulation parameters were verified. The error between the simulated and measured values of tillage resistance was 1. 70%. On the basis of the above research, with 13 mm as the equivalent particle size, the dimensions of four kinds of soil particles, including single-ball, double-ball, three-ball and four-ball, were determined. Six kinds of virtual soil grooves were established by filling methods such as single-ball, single-ball with variable particle size, double-ball, three-ball, four-ball and multi-ball mixing. Taking tillage resistance, tillage accumulation angle and simulation time as the test indexes, the simulation test of digging plough shovel tillage process was carried out. The test results showed that the error between the simulation value of tillage resistance and the measured value iwas less than 8%, and the six virtual soil grooves met the requirements of tillage resistance simulation. The error between the simulated and measured values of tillage accumulation angle was 2. 32%-20. 32%, and the error of tillage accumulation angle using virtual soil troughs such as single-ball variable particle size, four-ball and multi-ball mixing was less than 10%. The simulation time of single ball filling virtual soil trench digging plow shovel tillage was about 80. 44 min. Affected by the number of soil particles, contact relationship and particle ball type, the simulation time under other filling conditions was significantly increased. Considering the simulation accuracy and calculation efficiency, the single-ball particle filling method is suitable for the simulation of soil tillage resistance, and the four-ball or multi-ball mixed filling method is suitable for the simulation of tillage accumulation angle. This study provides a basis and reference for the modeling of soil-machine interaction discrete element simulation, the parameter selection of EEPA contact model, the determination of particle ball type and filling method.