Influence of Lateral Leaf Number on Vibration Characteristics and Energy Dissipation of the Walnut (Juglans regia) Branch–Leaf–Fruit Subsystem

During the harvest period, the role of lateral leaves in the dynamic behavior of the walnut (Juglans regia) branch–leaf–fruit subsystem remains unclear, and vibration harvesting parameter selection still lacks targeted guidance. To address this issue, a local walnut branch–leaf–fruit subsystem was studied by combining a discrete dynamic model, free-vibration tests, forced-vibration tests, and MATLAB simulations to investigate the effects of lateral leaf number on system dynamics. A representative single-fruit subsystem with six lateral leaves was selected, and four leaf number conditions (zero, two, four, and six) were examined. High-speed imaging was used to identify leaf motion patterns, while natural frequencies and fruit tracking point displacement responses were measured. The results showed that lateral leaves mainly exhibited three motion modes during vibration: spin, swing, and spin–swing compound motion. Under the six-leaf condition, spin motion was dominant. As the number of lateral leaves increased from 0 to 6, the first-order natural frequency decreased from 13.92 ± 6.37 Hz to 8.79 ± 4.03 Hz, a reduction of 36.8%. Forced-vibration results showed that increasing lateral leaf number significantly reduced the displacement response of the fruit tracking point in the non-excitation directions. Under the six-leaf condition, the maximum displacements in the Y- and Z-directions were reduced by 56.0% and 55.8%, respectively, compared with the leafless condition, indicating that the forced response became more concentrated in the main excitation direction. In the original MATLAB model, lateral leaves were simplified as fixed lumped mass damping elements, and the predicted results differed from the experimental trends. After introducing dynamic damping parameters matched to leaf motion patterns, the simulated trends became closer to the experimental results. These findings indicate that lateral leaf number is an important structural factor affecting the natural characteristics and directional forced responses of the walnut branch–leaf–fruit subsystem. The results provide theoretical and experimental references for optimizing vibration parameters and supporting low-damage, high-efficiency walnut vibration harvesting.