Finite element explicit dynamics simulation of motion and shedding of jujube fruits under forced vibration

Current fruit motion response simulations during vibration harvesting mainly adopt linear theoretical calculation methods for the fruit motion patterns analysis, which cannot reflect some nonlinear vibration features of fruits under real conditions and cannot simulate the fruit-branch vibration separation process. In this paper, the finite element (FEM) explicit dynamic simulations technique was combined with experimental and modal analysis to investigate and simulate the dynamic responses of the Jun jujube fruit-stem system under various forced vibration conditions. According to the obtained results, the greater the fruit vibration amplitude, the greater the maximum stress on the stem during vibration, while the maximum stress position depends on the vibration direction. The fruit-stem system resonance can be triggered at a specific mode depending on the vibration method and mode shape. Due to its nonlinearity, the fruit-stem system has primary resonance with an excitation frequency close to the natural frequency and a sub-harmonic resonance with an excitation frequency close to an integer multiple of the natural frequency. The stress failures can be employed as criteria for material failures at the connection between the branch and the fruit. Accordingly, the fruit shedding process from the branch can be accurately simulated during vibratory harvesting, and the fruit shedding movement can be effectively predicted under complex excitation conditions.