*2.4. Hazelnut Harvester Simulation Parameters' Setting*

The establishment of a discrete element model is mainly divided into two kinds, which are geometric model establishment and particle model establishment. According to the design parameters, the 3D modeling software SolidWorks was used to build the 3D model of the hazelnut harvester and to simplify its model parts. The simplified 3D model was imported into Rocky, and a fluid domain model was created. The fluid domain model was meshed with a structured meshing method, with a total of 2.57 million mesh cells and 460,000 nodes. The fluid domain model is shown in Figure 5.

**Figure 5.** Harvester fluid domain model: (**a**) pickup device fluid domain model; (**b**) fluid domain model of wind separator.

Based on Rocky software, a three-factor, three-level Box–Behnken simulation experiment was conducted with the sieve plate angle, distance of the sieve plate, and air flow rate as factors and hazelnut net fruit rate as the index. The simulation experimental results provide guidance and comparative verification for subsequent field tests. The establishment of the material particle model in Rocky is the basis of the simulation analysis, and the realistic degree of its model directly affects the simulation results. In this paper, we take Liaoning hazelnut No. 3 as the research sample, through the dimensional analysis of hazelnut and leaf drop, where the average diameter of hazelnuts is 22 mm as a round ball, and the average diameter of leaf drop is 36 mm as a disc shape with a thickness of 0.5 mm. In Rocky, the stem model of particles can be created directly, and the shape of leaf drop is sphero-polygon, with a vertical aspect ratio of 1.8, a horizontal aspect ratio of 0.1, and an angle number of 80; the shape of the hazelnuts is spherical. The particle models are shown in Figure 6. In order to distinguish the size of hazelnuts, their diameter was set at 80% of hazelnuts above 18 mm and the rest at 20%.

**Figure 6.** Particle mixture model: (**a**) hazelnut model; (**b**) leaf model.

The material inlet was used to set the simulation particle entry position, direction, and time. A particle inlet in the Geometries module was created, and the entry port was set as a rectangular inlet according to the actual geometry of the feeding device. The length was set as 0.15 m, width as 0.25 m, alignment angle as 90◦, and incline angle as 270◦. The inlet at the feeding port of the picking device and the feeding port of the sorting device was set. According to the simulation needs, the feeding time was set to 0~2.5 s. The number of particles was estimated according to the actual machine output, the hazelnuts and leaves in the mixture picked up by the machine were sieved, and the feeding volume was set to 1.6 kg/s for hazelnuts and 0.15 kg/s for leaves. Particle entry simulation parameters are shown in Table 1.

**Table 1.** Particle inlet settings.


In order to ensure the authenticity of the simulation test and reduce the simulation time, hazelnuts and leaves were selected as the study objects in this simulation. The simulation test only considers the interaction between hazelnut, leaf, and hazelnut harvester, ignoring the influence of other impurities on the simulation. Each part of the hazelnut harvester is endowed with material characteristics, and the entire device is made of structural steel. The values of material density, Poisson's ratio, Young's modulus, and dynamic and static friction factors of the particles directly affect the simulation results. We imported the data from the hazelnut stacking angle experiment and the static friction experiment into the EDEM database for analysis and obtained these simulation parameters. The parameters of material mechanical properties and interparticle contact parameters of hazelnuts and leaves are shown in Table 2.


**Table 2.** Simulation parameters.
