外激振力作用下果树树干能量流
Study on Energy Flow of Fruit Trees Under External Excitation Force

研究在外载荷作用下，果树由激振位置传递到果树枝干各部分的能量大小情况，分析果树形态结构对能量传递的影响。选择两棵“Y”型果树和一棵三叉枝果树进行试验，将测试得到的加速度信号进行拟合，得到加速度函数， 再对加速度函数对时间积分得到速度函数，进而求出果枝各测点的动能，将这部分动能视为外激振载荷由激振位置传递到各测点的能量。在正弦振动载荷激励下，果枝上的加速度值符合正弦函数变化规律，且果枝加速度信号频率与外界激振频率几乎一致。能量在流经分叉点处产生分流，并更多的流向果枝直径大的一侧；能量在主干上的传递效率高于侧枝上的传递效率；激振频率为20Hz时，能量传递效率较高，果实最大瞬时速度和摆动幅度较大，果实更容易脱落。
Under external loads, the vibration energy transfer from excitation position to the branches of fruit trees, and we analyze the effects of fruit tree morphology on energy transfer. Two "Y" type of fruit trees and three branches of fruit trees are chosen as the test samples, and the acceleration signal is fitted to get the acceleration function. Then the speed function can be obtained by the integral of the acceleration function and the kinetic energy of the measuring point on the branches of fruit tree can be also calculated.The kinetic energy we calculated can be regarded as external loads transfer to energy of each point. The value of the acceleration in the branches is accord with the variation of sine function under the sinusoidal excitation, and the branch acceleration signal frequency and the excitation frequency are almost the same. When the energy flowing goes through the bifurcation point, it would be shunted, and more energy move to the side branches with large diameter. The efficiency of transmitting energy in the trunk is higher than the lateral branch; When the excitation frequency is 20Hz, the efficiency of transmitting energy is better, and the maximum of the instantaneous velocity of fruits and amplitude of swing are much larger. So, fruits become easier to fall off.