基于三维激光扫描的水稻种子离散元建模及试验

在采用离散元法进行精量播种、收获、清选等关键部件的工作过程仿真分析时,需要建立与物料真实形态逼近的三维离散元颗粒模型。目前非规则形状物料常规建模方法是将其近似处理为规则体,导致仿真精度降低。该文以水稻为研究对象,提出一种基于三维激光扫描建立水稻等非规则颗粒材料的三维离散元建模方法,运用三维激光扫描技术获取其点云,利用自动化逆向工程软件Geomagic Studio和SolidWorks对种子进行点云处理和逆向建模,得到种子轮廓模型及其空间坐标信息,并基于颗粒聚合体理论建立水稻种子的三维离散元模型。通过离散元分析软件EDEM分别对三维激光扫描的水稻种子离散元建模和常规椭球体处理离散元建模条件下水稻种子的自然休止角进行仿真测定,并与实际水稻种子自然休止角测定试验结果进行对比分析,得出2种建模方法所得自然休止角与实际试验结果的误差分别为0.24%和8.83%,证明了基于三维激光扫描的水稻种子离散元建模方法的有效性和可行性。该建模方法为提高非规则物料离散元仿真精度提供了一种新手段。

Experiment and discrete element model of rice seed based on 3D laser scanning

In the process of discrete element numerical calculation, the establishment of the particle model is an important factor to affect the accuracy of the simulation.It is necessary to establish the 3-D models of irregular grains for discrete element method whose morphology is approximate to the real grain to analyze and simulate the main working process like precision seeding and precision selecting and classifying seeds.At present, an irregular particle with complex contours is simplified into the regular shape to model, which can lead to reduction of the simulation accuracy. In order to improve the accuracy of the dynamic simulation of the irregular particles, a method of modeling 3-D DEM models was proposed for irregular shape particles like rice grain based on 3-D laser scanning.Five hundreds of Kongyu 131 (rice cultivar) rice seeds were chosen randomly and scanned using CF-30 automatic high precision 3-D scanner.The size distribution of length, width and thickness is in accordance with the normal distribution and the average length, average width and average thickness of the three-dimensional measurement were 7.0 mm, 3.5 mm and 2.4 mm, respectively.The rice seed with the average three-dimensional sizes was scanned and the polygonal contour model and space coordinate information were obtained by the process of treating color, noise removal, point cloud registration, point cloud triangulation, consolidation and model modification using the reverse engineering software Geomagic Studio.The polygonal contour model was imported into SolidWorks and the 3-D DEM model with complex contour of the rice seed based on 3D laser scanning was created by inverse modeling.The 3-D DEM model of the rice seed based on 3D laser scanning was filled by 87 balls particles based on the theory of polymer particles, which was named as Model1.The 3-D DEM model of the rice seed with the same three-dimensional sizes as Model1 was processed usually as regular ellipsoid, which was named as Model 2.In order to test the simulation accuracy for discrete element method of the modeling method of irregular particle based on 3D laser scanning, the simulation prediction of repose angle for Model 1 and Model 2 was done respectively using the discrete element method software EDEM.The repose angle of the Model 1 and the Model 2 were 29.77° and 27.08°, respectively.And the repose angle of the actual rice seeds was measured under the same condition as the simulated experiment condition for comparative analysis.The experimental result of the repose angle was 29.70°. And the measurement errors between the simulation results by two modelling methods and the actual experiment value about repose angle were 0.24% and 8.83%, respectively.The repose angle obtained by Model 1 based on 3-D laser scanning was closer to not only the experimental measured value but also accumulation form, and there was a big error between that by Model 2 based on the usual treatment as regular ellipsoid and the experimental result, which showed that the modeling method of irregular particle for discrete element based on 3-D laser scanning was validated and available.This paper provides a new means to improve simulation precision of irregular particles for discrete element method.