Dynamic characteristics of dwarf Chinese hickory trees under impact excitations for mechanical fruit harvesting

To evaluate the dynamic characteristics of dwarf Chinese hickory trees and the influence of the tree structure on transmission and attenuation of dynamic response, a new method was proposed based on acceleration admittance measurement on dwarf Chinese hickory trees in orchard environment under impact excitation. The primary resonance frequencies of the tree can be determined based on the acceleration admittance measurement. The effect of the tree structure on the vibratory transmission was quantified using the attenuation ratio of the acceleration admittance. A 5-year-old dwarf Chinese hickory tree sample was tested. The responses at three resonance frequencies were analyzed because they were identified as the most effective bands of excitation for the main part of the tree specimen. The results reveal that the variation of the dynamic response along the testing tree is greatly related to the Chinese hickory tree structure. The attenuation ratio of the acceleration admittance at the branch crotches indicates the leader top crotch may amplify the acceleration admittance.