Field evaluation of dynamic characteristics of dwarf Chinese hickory trees for mechanical harvest

Abstract

Abstract. To analyze the dynamic characteristics of dwarf Chinese hickory (Carya cathayensis Sarg.) trees for mechanical harvest, a series of dynamic response tests were conducted on three dwarf Chinese hickory tree samples in orchard environment. The mechanical admittance of the main limbs of three tree samples with different structures was tested in this investigation. Their resonance frequencies, as well as the influence of the tree structure on transmission of dynamic response, were analyzed based on the mechanical admittance analysis. The obtained primary resonance frequencies were detected on the main part of the sample trees and the resonance frequencies of the offshoots without secondary crotch were very close to those of the leader limb. The variation of the dynamic response along the tested trees was greatly related to the dwarf Chinese hickory tree structure. The effect of the crotch and chain nodes on the acceleration response of tree branch to impact excitation was quantified using the acceleration admittance attenuation rate. Results obtained from this study revealed that the leader top crotch may amplify the acceleration admittance and the smaller the crotch angle was, the higher the acceleration admittance was amplified. And the leader top crotch with small crotch angle was sensitive to low frequency vibration while the leader top crotch with big crotch angle was sensitive to high frequency vibration. Different from the leader top crotch, significant vibration amplification was only observed on the response at 14 Hz. On the contrary to the dynamic response variation at the crotch, the acceleration admittance along the branch chains with uniform diameter and small angle was affected little.