水稻钵苗柔性苗叶离散元模型构建与参数标定

Discrete Element Model Construction and Parameter Calibration of Flexible Leaves in Rice Pot Seedlings

摘要:

针对水稻钵苗薄壁苗叶离散元模型建模难,导致气力抛秧仿真分析时柔性苗叶与气流场互作关系分析受限,缺乏苗叶适用模型表征钵苗姿态变化对其运动轨迹影响的问题,本研究以三叶一心期水稻钵苗为研究对象,提出一种基于多视场角图像拟合的苗叶离散元模型逆向重构方法。该方法利用单元网格对苗叶连续轮廓进行离散化表征,将苗叶空间形态关系映射为颗粒坐标信息,并基于Hertz-Mindlin with Bonding V2接触模型,构建水稻钵苗柔性苗叶离散元模型。以柔性苗叶相对挠度为评价指标,通过Plackett-Burman试验对影响苗叶相对挠度的参数进行显著性筛选,并基于Box-Behnken试验建立苗叶相对挠度二阶回归模型。明确了单位面积法向刚度、单位面积切向刚度和粘结比例系数对苗叶柔性具有显著影响。采用标定后的参数进行仿真试验,结果显示,仿真与物理试验相对误差为2.51%,验证了所建模型的有效性。可为后续建立适用于气力抛秧仿真分析的水稻钵苗离散元模型提供参考。

Abstract:

Regarding the challenge of constructing a discrete element model for the thin-walled leaves of rice pot seedlings, which limits the simulation analysis of pneumatic seedling throwing due to the lack of a suitable leaf model to characterize the effect of seedling posture changes on its trajectory under the interaction between flexible leaves and airflow fields, taking rice pot seedlings at the three-leaf and one- heart stage as the research object, a reverse reconstruction method for the discrete element model of seedling leaves was proposed based on multi-view image fitting. This method discretized the continuous contour of the leaves using unit grids, mapped the spatial morphological relationships of the leaves into particle coordinate information, and constructed a discrete element model of the flexible leaves of rice pot seedlings based on the Hertz-Mindlin with Bonding V2 contact model. Using the relative deflection of the flexible leaves as the evaluation index, the parameters affecting leaf relative deflection were screened for significance through a Plackett-Burman design. A second-order regression model for leaf relative deflection was established based on a Box-Behnken design. It was clarified that normal stiffness per unit area, tangential stiffness per unit area, and bonding ratio significantly affected leaf relative deflection. Simulation tests performed with the calibrated parameters showed a relative error of 2. 51% between the simulation and physical experiment, verifying the validity of the constructed model. The research result can provide a reference for the subsequent development of discrete element models suitable for simulating pneumatic seedling throwing.