葡萄藤防寒土与清土部件相互作用的离散元仿真参数标定

为系统地研究中国北方地区沙壤土质地的葡萄藤防寒土及其与清土机清土部件常用材料(Q235钢、橡胶)相互作用的离散元仿真参数,以构建准确的土壤离散元仿真模型,该文选用整合延迟弹性模型(hysteretic spring contact model,HSCM)和线性粘附模型(liner cohesion model,LCM)作为土壤颗粒间的接触模型;基于土壤堆积试验,以土壤颗粒间恢复系数、静摩擦系数、滚动摩擦系数和土壤粘附能量密度为因素,以土壤堆积角为指标,利用EDEM进行通用旋转中心组合模拟试验,采用Design-Expert软件对试验数据进行回归分析,以实测的土壤堆积角作为优化目标值,获得土壤颗粒间的最佳接触参数组合;利用土壤屈服试验获得HSCM模型参数;基于斜面滑动法原理,利用倾斜板试验台测得土壤与Q235钢和橡胶之间的静摩擦系数,并以此为基础,采用土壤滑落试验,以滑动摩擦角为响应值,对土壤颗粒与Q235钢和橡胶之间的恢复系数和滚动摩擦系数进行寻优,得到最优解参数组合。为验证标定优化的离散元模型参数的准确性,采用刮土板土槽试验和仿真试验进行对比分析,获得刮土板在土槽试验和仿真试验中的水平前进阻力分别为228.36 N和213.79 N,两者之间的相对误差为6.38%,表明仿真模型中土壤的物理力学特性与实际土壤基本一致,验证了葡萄藤防寒土离散元仿真参数标定结果和研究方法准确可靠。研究结果可为基于离散元法研制适用于北方地区沙壤土质地的葡萄藤防寒土清土机提供理论基础和技术支撑。

Calibration of discrete element simulation parameters of grapevine antifreezing soil and its interaction with soil-cleaning components

Grapevine in seasonally frozen regions needs to be warm-insulated by soil in winter with the antifreezing soil removed in spring most mechanically by a soil removal machine. The purpose of this paper is to simulate the interaction between the insulating soil (with sandy loam texture) and the soil-cleaning materials (Q235 steel, rubber) commonly used in the soil removal machine, based on the discrete element method. The simulation model was constructed based on properties of the soil by integrating the hysteretic spring contact model (HSCM) and the linear cohesion model (LCM) as the contact model between soil particles. We took soil-soil restitution coefficient, soil-soil frictional coefficient, soil-soil rolling coefficient and soil cohesion energy density as the determinants and the soil accumulation angle as an evaluation index. The 4-factor universal rotation center combination simulation test, based on the EDEM, was used to regress the relationship between the determinants and the index using the Design-Expert software. The results showed that the soil-soil frictional coefficient was the only parameter that did not have significant effects on the soil accumulation angle. The best contact-parameter combination between soil particles was obtained by taking the physically measured soil accumulation angle as the optimization objective, which gave 0.51 for the soil-soil restitution coefficient, 0.65 for the soil-soil frictional coefficient, 0.06 for the soil-soil rolling frictional coefficient, and 10 495 J/m3 for the soil cohesion energy density. The associated soil accumulation angle was 31.74o, with a relative error of 0.83% compared with the physically measured results. The universal testing machine for soil yield test was used to obtain the HSCM model parameters based on the change in penetration stress with the displacement, and the resultant soil yield strength was 0.38 MPa. The static frictional coefficient between soil and Q235 steel as well as the rubber measured by the inclination test bench was 0.38 and 0.48 respectively. These data and the EDEM were used to conduct the simulation test of the soil slip, with the restitution coefficient and the rolling frictional coefficient between soil and the materials taken as the determinants and the sliding frictional angle as evaluating index. Regressing the test date with the two-factor universal rotation center combination test showed that the rolling frictional coefficient between soil and the materials had a significant effect on the sliding frictional angle between soil and the steel plate and rubber. In contrast, the restitution coefficient between the soil and the materials impacted significantly on the sliding frictional angle between the soil and the rubber but not on the soil and the steel plate. The restitution coefficient and the rolling frictional coefficient between the soil and the Q235 steel as well as the rubber were optimized by using the measured sliding frictional angle as the optimization objective. The resultant restitution coefficient and the rolling frictional coefficient were 0.60 and 0.37 respectively for the soil and the Q235 steel, and 0.61 and 0.23 respectively for the soil and the rubber. Soil bin test and simulation test of the scraper were conducted to verify the calibrated discrete element model parameters. The horizontal forward resistance of the scraper in the soil bin test and simulation test was 228.36 and 213.79 N respectively, with a relative error of 6.38%. The results presented in this paper have important implications for using discrete element method to analyze the removal of grapevine-insulating soil.