面向夹持过程仿真的青梗白菜叶柄模型建立与试验

Establishment and Experiment of Discrete Element Model for Brassica campestris L. ssp. chinensis var. communis Petiole during Clamping Process

摘要:

针对青梗白菜收获夹持过程仿真缺乏可靠粘结参数和精确的柔性模型，传统离散元建模对结构形态高度不规则且具有各向异性的多层叶柄仿真误差较大的问题，本文提出了一种精细化离散元建模与参数标定方法。基于叶柄宏观物理特性，提取了表征轴、径向轮廓的几何特征。结合叶柄微观结构形态构建流变本构模型，明确了影响叶柄产生机械损伤的主要因素。运用离散元法构建了由表皮、皮层和维管束3种不同微观力学属性颗粒填充组成的叶柄精细化柔性模型。以破碎临界载荷和破碎临界位移为评价指标，实施挤压筛选设计试验（PBD）、最陡爬升试验以及正交响应面试验（BBD），对不同粘结参数进行标定和优化。试验结果表明，主要影响因素最优组合为皮层-皮层单位面积法向刚度7.13×10^9 N/m^3、皮层-皮层切向强度5.51×10^5 Pa和粘结半径系数2.35。对模型进一步实施剪切精度验证试验，模拟结果和物理结果最大剪切力、最大位移相对误差分别为2.63%、4.11%，表明标定优化参数具有可行性和准确性，可为叶菜低损收获技术研究提供参数选取依据。

Abstract:

Addressing the lack of reliable bonding parameters and accurate flexible models for simulating the clamping process during bok choy harvesting, and the significant errors encountered by traditional discrete element modeling for highly irregular and anisotropic multi-layered petioles, a refined discrete element modeling and parameter calibration method was proposed. Based on the macroscopic physical properties of the petiole, geometric features representing its axial and radial contours were extracted. A rheological constitutive model was constructed by combining the petiole's microstructure, and the main factors influencing mechanical damage to the petiole were identified. Using the discrete element method, a refined flexible model of the petiole was constructed. This model consisted of particles representing three different micro-mechanical properties: epidermis, cortex, and vascular bundles. With critical fracture load and critical fracture displacement as evaluation indicators, screening design experiments (PBD), the steepest ascent experiments, and orthogonal response surface experiments (BBD) were conducted to calibrate and optimize different bonding parameters. The experimental results showed that the optimal combination of main influencing factors consisted of a cortex-cortex normal stiffness per unit area of 7.13×10^9 N/m^3, a cortex-cortex tangential strength of 5.51×10^5 Pa, and a bonding radius coefficient of 2.35. Further shear accuracy validation experiments were performed on the model. The simulation results and physical results showed maximum shear force and maximum displacement relative errors of 2.63% and 4.11%, respectively. This indicated that the calibrated and optimized parameters were feasible and accurate, providing a basis for parameter selection in research on low-damage leafy vegetable harvesting technology.