DAMPING PROPERTIES OF PLUM TREES SHAKEN AT THEIR TRUNKS

摘要

Investigations of the energy requirements of tree shakers have shown that the measured energy far exceeded the energy predicted by theoretical calculations. Two main reasons have been established for this: first, a given root and soil mass is also part of the vibration system, and second, the existing methods for determining damping coefficients for soils and the tree canopy (drop test, hammer striking) are not suitable, especially if displacements are of great amplitudes. In the current study, a direct energy method was used to measure effective damping coefficients of the root-soil body and of primary limbs. Measurements have shown that the vibrating soil mass has a large damping capacity, and its logarithmic decrement approaches p (i.e., the energy requirement equals the theoretical working capacity of the vibrating system). Measurements were carried out in a 12-year-old plum orchard. Trunk diameters varied between 130 and 250 mm, the respective canopy radius varied between 2.2 and 3.0 m, and each tree had five to seven primary limbs. The total damping loss originated mainly from the vibrating soil mass and tree canopy. A calculation method was developed to determine these loss contributions. By varying the attachment height on the trunk, different contribution ratios were achieved and the calculated and measured values were compared