苹果颗粒离散元接触参数标定与仿真试验

为精准确定红富士、花牛和黄元帅苹果的接触参数，该研究基于离散元法对3种苹果颗粒的仿真模型进行接触参数标定试验。首先，创建3种苹果的离散元填充模型，并通过电子秤、万能试验机等试验设备，确定其本征参数。其次，通过碰撞弹跳试验、斜面滑移试验和斜面滚动试验，得到红富士、花牛和黄元帅苹果与亚克力板的碰撞恢复系数分别为0.473、0.432和0.466；与亚克力板的静摩擦系数分别为0.435、0.536和0.519；与亚克力板的滚动摩擦系数分别为0.0077、0.0138和0.0088。最后，通过堆积角试验、最陡爬坡试验确定二次回归正交旋转组合试验，得到红富士、花牛和黄元帅同种苹果间的碰撞恢复系数分别为0.487、0.3348和0.469；静摩擦系数分别为0.584、0.869和0.644；滚动摩擦系数分别为0.084、0.096和0.093。试验结果表明，红富士、花牛和黄元帅苹果仿真试验与物理试验的休止角相对误差分别为5.95%、6.55%、8.67%。研究结果可为苹果物理特性和低损采收技术研究提供理论依据和模型支撑。

Calibrating and simulating contact parameters of the discrete element for apple particles

Apples are one of the most important fruits in China, due to their high nutritional value and storage resistance. The apple industry has been an important pillar of agricultural industry. Mechanical harvesting is also constantly improving in agricultural machinery. However, there are some complex forces among apples and harvesting equipment in the process of mechanical harvesting, even damage to apples. Some of the forces cannot be directly measured using physical experiments. While traditional experiments are required the preliminary verification, leading to the time-consuming and labor-intensive. Discrete element simulation can be expected to evaluate the apple damage. In this article, a series of calibration experiments were conducted on the contact parameter using via the simulation models using the discrete element method. Red Fuji, Hua Niu, and Delicious apple particles were taken as the research objects. A contour map of apple was drawn using SolidWorks, and then imported into EDEM platform. A discrete element model of the apple was established with a smoothness of 3 and a minimum spherical radius of 3 mm. The physical parameters of the apple were then calibrated using drainage and compression tests. The density of the Red Fuji apple was 923 kg/m³, the Poisson''s ratio was 0.33, the elastic modulus was 2.1 MPa, and the shear modulus was 1.4 MPa; The density of Hua Niu apples was 924 kg/m³, Poisson''s ratio was 0.34, elastic modulus was 2.23 MPa, and shear modulus was 1.49 MPa; Delicious apple density was 871 kg/m³, Poisson''s ratio was 0.37, elastic modulus was 3.16 MPa, and shear modulus was 2.09 MPa. Furthermore, the contact parameters between apples and acrylic plates were calibrated using collision bounce, inclined sliding, and a combination of bench and simulation tests. The collision recovery coefficient between Red Fuji apples and acrylic plates was 0.432, the static friction coefficient was 0.536, and the dynamic friction coefficient was 0.0138; The collision recovery coefficient between Hua Niu Apple and acrylic board was 0.473, the static friction coefficient was 0.435, and the dynamic friction coefficient was 0.0077; The recovery coefficient of collision between Delicious apple and acrylic board was 0.46, the static friction coefficient was 0.519, and the dynamic friction coefficient was 0.0088. The steepest climbing test and the three-factor quadratic regression orthogonal rotation combination test were carried out to establish a quadratic regression equation between the stacking angle and the significance factor. The equation was solved with the actual physical experiment stacking angle as the target value. The optimal parameters of simulation were then obtained: the collision recovery coefficient of Red Fuji apple was 0.487, the static friction coefficient was 0.584, and the dynamic friction coefficient was 0.084; The collision recovery coefficient between Hua Niu Apple and Apple was 0.348, the static friction coefficient was 0.869, and the dynamic friction coefficient was 0.096. Delicious apple collision recovery coefficient was 0.469, static friction coefficient was 0.644, and dynamic friction coefficient was 0.093. The calibrated parameters can serve as a strong reference for the discrete element method. The finding can also provide theoretical basis and model support to the apple physical properties and mechanical harvesting.