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Analysis of Pear Dynamic Characteristics Based on Harmonic Response

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 59(6): 1905-1913. (doi: 10.13031/trans.59.11845) @2016
Authors:   Wen Zhang, Di Cui, Zihao Liu, Yibin Ying
Keywords:   Dynamic characteristics, Fruit shape, Harmonic response analysis, Laser Doppler vibrometer, Modes.

Abstract. The dynamic characteristics of fruits are correlated with their mechanical and structural properties. A finite element (FE) harmonic response analysis was used to investigate the dynamic characteristics of pears. First, the pear dynamic characteristics were measured by the acoustic vibration method using a laser Doppler vibrometer (LDV). A sample pear was placed vertically on the vibration stage and excited with a sweeping sine wave signal. The LDV was used to measure the response signal from the top of the pear. A three-dimensional model of the pear was then established by a machine vision-based modeling system. In the FE model, a force excitation was applied to the pear model from the bottom of the pear, and the vertical displacement at the top of the pear model was calculated. The resonance frequencies were extracted from the frequency response curve, and then the corresponding mode shapes were obtained. The results showed that the resonance frequencies of the FE models agreed well with the measured frequencies, indicating that harmonic response analysis is feasible for investigating the pear dynamic characteristics. All of the mode shapes showed a large deformation in the longitudinal direction. Therefore, it would be better to measure these modes from the top of the pear by the LDV method when the pear is placed vertically on the vibration stage. In addition, the effects of material properties and fruit shape on pear dynamic characteristics were investigated. The resonance frequencies increased with increasing Young‘s modulus and decreased with increasing Poisson‘s ratio, density, and mass. It was also found that there were strong linear relationships between the resonance frequencies and height/diameter (h/d) ratio. The obtained results could provide guidance for pear texture evaluation by the LDV method.

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