苜蓿草植株离散元模型建立与参数标定

Establishment and Parameter Calibration of Discrete Element Model of Alfalfa Plant

摘要:

苜蓿草收获装备作业性能影响草捆品质，需对苜蓿草物料的物理特性参数、接触特性参数和力学特性参数等特性进行实验测定。采用离散元方法，基于柔性纤维颗粒模型构建苜蓿茎秆离散元模型，基于柔性薄壳颗粒模型构建苜蓿叶片离散元模型，基于线弹性力学模型构建茎秆与叶片关节模型。以物料茎秆休止角、茎秆三点弯曲、叶片滑移角和叶片圆筒压缩实验结果为目标，通过Plackett-Burman实验、最陡爬坡实验、中心复合实验和单因素实验，对影响仿真实验结果的茎秆与叶片的力学和接触参数进行标定。结果表明,仿真茎秆挠度与物理实验平均值相等;仿真茎秆休止角与物理实验平均值相对误差为 0.46%;仿真叶片圆筒压缩密度与物理实验平均值相对误差为0.82%;仿真叶片滑移角与物理实验平均值相对误差为0.15%。标定的参数能够真实反映苜蓿草的物料特性，研究结果可为苜蓿草收获机械优化设计提供理论依据和模型基础。

Abstract:

The performance of harvesting equipment affects the quality of bales. The physical properties （geometry and density）, contact properties （static friction coefficient, dynamic friction coefficient and collision recovery coefficient） and mechanical properties （blade elastic modulus and stalk deflection） of alfalfa materials were tested. Using the discrete element method, the clover stalk discrete element model was constructed based on the flexible fiber particle model, the clover blade discrete element model was constructed based on the flexible thin shell particle model, and the stalk and blade joint model was constructed based on the linear elasticity model. Aiming at the results of stalk resting angle, stalk three-point bending, blade slip angle and blade cylinder compression test，Plackett-Burman experiment, Steepest ascent experiment, center composite experiment and single factor experiment were used to calibrate the mechanics and contact parameters of stalk and blade that affected the simulation results. The results showed that the simulation stalk deflection was equal to the mean value of physical experiment. The relative error between the resting angle of simulated stalk and the mean value of physical experiment was 0.46%. The relative error between the compression density of simulated blade cylinder and the mean value of physical experiment was 0.82%. The relative error between the simulation blade slip angle and the physical experiment average was 0.15%. The calibration parameters can truly reflect the material characteristics of alfalfa, and the research results can provide theoretical basis and model basis for the optimal design of alfalfa harvesting machinery.