Tianhu Liu’s research while affiliated with South China Agricultural University and other places

Fruits are susceptible to damage from external loads during harvesting, transport and storage. Fruit damage is determined by its tissue mechanical properties. The aim of this study was to evaluate two theories (Hooke's and Hertz's Laws) on the apparent elastic modulus of pineapple and predict the internal mechanical damage of pineapple under compression. Two multi-scale finite element models (FEMs) were developed to predict the pineapple internal damage. One model, based on Hooke's Law contained three layers, including peel, pulp, and core. Another model, based on Hertz's Law, was a two layers model, including peel and pulp (containing core). The difference of these two FEMs was evaluated in terms of different compression displacements. The results showed that, when the compression displacement ≤10 mm, the Hooke three-layer model was closer to reality. But when the compression displacement >10 mm, the Hertz two-layer model was better in reflecting real pineapple compression. Simulated data confirmed the experimental results and predicted the internal mechanical damage of pineapple. Finite element results indicated that, when a force was applied to the fruit, pulp tissue suffered mechanical damage before peel and core tissue. When the compression level was ≤5% (5.5 mm; 86 N), there was no damage to pulp, core, and peel. But, if compression level >5%, the fruit was damaged. These results indicated that pineapple placed horizontally with an allowable numbers of stackable pineapples must be less than eight. Otherwise, the maximum allowable force of stacked fruit on the lowest one will reach the pulp failure force.

This paper presents a novel nonlinear anti-vibration compliant mechanism with inertia amplification (NAVCM-IA) for low frequency vibration isolation. This compliant mechanism consists of three-dimensional helical rods with stiffness nonlinearities, and an attached horizontally-installed inertia disc which performs as an inertia amplification. With this unique design, beneficial nonlinear stiffness can be achieved, which reduce the dynamic stiffness at equilibrium position and improve the vibration isolation performance at low frequency range. Moreover, the inertia amplification driven by the compliant mechanism achieves an apparent high dynamic mass and, accordingly, a low resonance frequency. The nonlinear compliant mechanism with inertia amplification is validated by experimental prototypes for their special nonlinear features. The proposed NAVCM-IA is a unique passive and adjustable low frequency anti-vibration solution in extensive engineering applications.

Research on the mechanical harvesting of pineapples is currently in its early stages. The purpose of this study is to provide a design and configure a method for multi-flexible-fingered roller pineapple harvester. Depending on the physical and mechanical characteristics of pineapples, the evaluation function for the critical damage condition of the fruit was established. Our experimental results revealed the optimal parameters for pineapple harvesting were as follows: the rollers of the harvesting mechanism should be inclined at 35°, the left flexible fingers should be 120 mm long, the gap between each of the left flexible fingers should be 30 mm, the length of the right flexible fingers should be 150 mm long, and the gap between each of the right flexible fingers should be 10 mm. The harvesting rate was 85% and the damage rate was 5% in the laboratory; in the natural environment, harvesting rate and damage rate were 78% and 8% respectively, and the harvesting speed was about 1 s per fruit, which demonstrated the harvesting machinery could sufficiently meet the usage demand of pineapple harvesting. In the cases of unsuccessful harvesting, failure resulted from mismatched flexible finger length, fruit size, and harvesting posture and position.