Effect of leaves in the dynamic response of olive tree branches and their computational model

Abstract

The application of vibration in the mechanical harvesting of fruit trees is a determining factor to achieve fruit detachment. The acceleration required to do so is experimentally determined in expensive tests using different machines and configurations. A simple, appropriate model that could predict the vibration response of plant matter might facilitate these simulations of different conditions and optimise the process. Several mathematical and computational models exist that employ great simplifications and produce uncertain results. We propose a computational model for simulating the dynamic response of branches with and without foliage under forced vibration, applied to the case of the olive tree. We also present a method for characterising the mechanical properties necessary to conduct the simulation using commercial software, Ansys, and the experimental determination of the properties. To do so, we propose some simplifications in the modelling. Next, computational simulations replicate the same conditions as the real vibration tests conducted in the laboratory, and the accelerations produced at the origin and ends of the branches are determined. The results offer a good degree of similarity between the calculated and experimental values in terms of natural frequencies, although some dispersion of transmissibility exits between the origin and ends of the branches, above all for larger branches and when considering their foliage. Branches without leaves had lower natural frequencies. The damping coefficient of branches with leaves was almost twice than ones without although the acceleration transmissibility is much bigger.