2.4.4. Calibration of the Discrete Element Parameters for the Stacking Angle Test

In the simulation of the stacking angle test for the phloem, the inner diameter and height of the cylinder were consistent with those used in the physical test. The interior of the cylinder was set as a particle factory, where the particles were generated freely by the "static" method. This ensured that the phloem was distributed in a relatively dispersed state inside the cylinder, avoiding a situation where an uneven distribution would result in a significant error in the stacking angle after being static. The total mass of the generated particles was 20 g. Subsequently, the particles were allowed to fall freely under gravity, and the simulation model was conducted for 1 s to reach a static equilibrium state. After, the cylinder was lifted vertically at a speed of 4 mm/s. The phloem particles would flow out slowly from the bottom of the cylinder, eventually forming a stable phloem particle heap on the bottom plate, as shown in Figure 8.

**Figure 8.** Ramie phloem stacking angle discrete element simulation test: (**a**) before stacking; (**b**) after stacking.

In the simulation of the stacking angle test for the xylem, the dimensions of the device and partition were consistent with those used in the physical test. Thirty-six neat piles of ramie xylem particles were generated at the right wall of the device. After the xylem particle heap and partition became stable, the partition was given a speed of 0.1 m/s to lift upward, and the xylem particle heap began to roll to the left to form the stacking angle. The discrete element simulation of the stacking angle test for the xylem is shown in Figure 9.

**Figure 9.** Ramie xylem stacking angle discrete element simulation test: (**a**) before stacking; (**b**) after stacking.
