耙压式除草轮与水田土壤作用的流固耦合仿真分析及验证

为探明水稻机械除草过程中,除草轮的工作阻力大小变化及水田土壤的动态行为,该文利用ANSYS软件的显式动力分析模块LS-DYNA对耙压式除草轮在水田环境下的作业过程进行仿真分析。采用ALE(Arbitrary Lagrange-Euler)多物质耦合算法建立了土壤-水两物质耦合有限元模型;运用流固耦合算法分析除草轮与土壤-水模型的相互作用过程。采用有交互作用的正交试验方法选取土壤种类、水层厚度和除草轮旋转速度3个因素进行仿真试验分析,得到各因素及其一级交互作用对除草轮和土壤-水模型的耦合应力和土壤扰动率的影响规律。利用多目标优化设计方法综合评判仿真试验结果,综合评分结果表明,在不同的土壤工作环境下,除草轮在水层厚度为60mm、转速为160r/min的作业条件下均可获得较优的工作性能。影响除草轮和土壤-水模型耦合应力的因素主次顺序为:土壤种类水层厚度土壤种类×水层厚度土壤种类×除草轮转速除草轮转速水层厚度×除草轮转速。影响土壤扰动率的因素主次顺序为:土壤种类除草轮转速土壤种类×水层厚度土壤种类×除草轮转速水层厚度水层厚度×除草轮转速。为验证仿真结果,进行了田间试验和土槽试验,根据仿真所得耦合应力值推导出除草轮所受土壤反作用力扭矩值,与田间实测值相对误差为8.84%;仿真所得土壤扰动率与土槽试验实测值相对误差为9.86%;仿真所得综合评分结果与试验综合评分结果相对误差为7.02%。仿真分析结果可为轻简式水稻除草机应用在不同稻区的田间作业参数提供参考。

Validation and analysis of fluid-structure interaction between rotary harrow weeding roll and paddy soil

Abstract: In order to investigate the variance of the resistance on the weeding roll and the dynamic behavior of the paddy soil in the condition of paddy field, LS-DYNA, the explicit analysis module of ANSYS, was adopted to simulate and analyze the operating process of the rotary harrow weeding roll in this paper. The soil model was built by MAT147 in LS-DYNA, an elastic-plastic model using the Mohr-Coulomb yield criterion. In order to simulate the paddy field in reality when weeding, a soil-water combined model was established using the Multi-Material ALE(Arbitrary Lagrange-Euler) algorithm, which was considered to be an ALE finite element model. By using the Multi-Material ALE algorithm, the different materials were allowed to exchange and transport in the ALE mesh. The interaction process between the weeding roll and the soil-water model was analyzed by the Fluid-Structure Interaction algorithm. Type of soil (factor A), thickness of water layer (factor B) and rotary velocity of weeding roll (factor C) were selected as three factors of the orthogonal simulation experiment with reciprocal action to explore the effect regularity on coupling stress and destruction of soil caused by the factors and the primary reciprocal actions between each factor. The comprehensive evaluation of simulations results were carried out by the multi-objective optimization design method. The results show that in three types of soils the optimal performance of the weeding roll could be obtained when the water layer thickness was 60 mm and the weeding roll rotary velocity was 160 r/min. The sequence of factors in affecting the coupling stress was type of soil > thickness of water layer > type of soil × thickness of water layer > type of soil × rotary velocity of weeding roll > rotary velocity of weeding roll > thickness of water layer × rotary velocity of weeding roll. The coupling stress was reported to be the minimal in the condition of clay soil, and the maximal in the condition of sandy clay soil. The coupling stress was reported to decrease slightly with the increasing thickness of water layer, and increase first and then decrease within a narrow range with the increasing rotary velocity of weeding roll. The sequence of factors in affecting the destruction of soil was type of soil > rotary velocity of weeding roll > type of soil × thickness of water layer > type of soil ×rotary velocity of weeding roll > thickness of water layer > thickness of water layer × rotary velocity of weeding roll. The destruction of soil was reported to be the minimal in the condition of clay soil, and the maximal in the condition of sandy clay soil. The destruction of soil was reported to drop slightly first and then rise with the increasing thickness of water layer, and increase with the increasing rotary velocity of weeding roll. The field trail and the soil box test were carried out to validate the simulation results. The deviation between the torsion derived from the coupling stress and the one obtained from the field trail was 8.84%, and the deviation between the destruction of soil obtained from the simulation and the one from soil box test was 9.86%, and the deviation between the score of the comprehensive evaluation obtained from the simulation and the one from experiments was 7.02%. The results of field trail and soil box test are basically coordinated with the simulation, which prove the methods of modeling and simulation adopted in this research. The results provide references to the performance and the efficacy of the portable paddy field weeder operating in different rice growing districts and working conditions with different working parameters.