适收期芒果果实离散元模型构建与接触参数标定

Construction of DEM Model and Calibration of Contact Parameters for Mango Fruit at Optimal Harvest Maturity

摘要:

针对芒果机械化低损伤收技术与装备研究中离散元仿真模型与关键接触参数缺失，无法有效揭示芒果果实与机械部件接触时的作用机理问题，以适收期台农芒和蛋芒两种典型芒果为研究对象，测定其物理参数，并利用三维扫描技术与 EDEM 仿真分析结合的方式构建芒果果实离散元模型。对两种芒果分别进行自由落体碰撞试验、斜面滑动和滚动试验，获得两种芒果在 EVA 材料上的碰撞恢复系数、静摩擦因数、滚动摩擦因数分别为 0.499、0.478、0.0378 和 0.590、0.481、0.0220;在橡胶材料上的碰撞恢复系数、静摩擦因数、滚动摩擦因数分别为 0.388、0.723、0.0376 和 0.420、0.779、0.0179。采用双摆线试验，测得台农芒和蛋芒同种芒果间的碰撞恢复系数分别为 0.312 和 0.294。通过芒果堆积角试验、最陡爬和旋转正交组合试验，构建仿真试验堆积角的二次回归模并化得到台农芒和蛋芒同种芒果间的静摩擦因数分别为 0.280 和 0.302;滚动摩擦因数为 0.0252 和 0.0195。采用圆筒提升试验验证堆积角仿试验的相对误差分别为 3.84% 和 4.35%, 验证了芒接触参数标定的准确性。

Abstract:

Aiming to address the shortage of discrete element simulation models and key contact parameters in research on low-damage mechanized mango harvesting, which has limited the accurate interpretation of interaction mechanisms betwveen fruit and mechanical components, two typical cultivars at optimal harvest maturity, Tainong and Egg were selected. The physical parameters of the fruits were measured in detail, and a discrete element model of mango fruit was developed by integrating threedimensional scanning with EDEM simulation analysis, ensuring that the geometric features and material attributes of the model were consistent with the actual samples used in the experiments. To obtain accurate contact parameters for typical engineering materials used in harvesting equipment, free-fall impact, inclined-plane sliding, and rolling tests were conducted separately for the two cultivars under identical test conditions. On EVA material, the measured coeficients for Tainong and Egg were as follows: coefficient of restitution was 0. 499 and 0. 590, static friction coefficient was 0. 478 and 0. 481, and rolling friction coefficient was 0. 037 8 and 0. 022 0, respectively. On rubber, the corresponding values were coefficient of restitution of 0. 388 and 0. 420, static friction coefficient of 0. 723 and 0. 779, and rolling friction coefficient of 0. 037 6 and 0. 017 9, respectively. In addition, fruit-to-fruit collision behavior was analyzed using a double pendulum test, which yielded same-cultivar coefficients of restitution of 0. 312 for Tainong and 0. 294 for Egg, providing essential data for modeling fruit-to-fruit contact in discrete element simulations. To further calibrate the inter-fruit friction parameters, angle-ofrepose experiments were combined with the steepest-ascent method and a central composite rotatable design to establish a quadratic regression model describing the simulated repose angle. Through optimization of this model, the static friction coefficients between fruits of the same cultivar were determined to be 0. 280 for Tainong and 0. 302 for Egg, while the rolling friction coefficients were 0. 025 2 and 0. 019 5. Model accuracy was verified using a lifting-cylinder validation test. The simulated repose angles exhibited relative errors of 3. 84% for Tainong and 4. 35% for Egg, indicating that the calibrated contact parameters were both accurate and reliable. These results demonstrated that the discrete element model can effectively reproduce the mechanical behavior of mangoes during contact and motion. In conclusion, a discrete element simulation model of mango fruit at optimal harvest maturity was established and a complete, experimentally calibrated set of contact parameters was obtained. The model accuracy was verified through multiple independent experiments. The research can provide a dependable simulation foundation and theoretical basis for analyzing contact processes between mango fruits and mechanical components, and it offered valuable reference data for the design and optimization of actuating components, conveying systems, and end-effectors used in low-damage mechanized mango harvesting equipment, thereby supporting the development of efficient and high-quality mango harvesting technologies.