Basic Research On Mechanism Of Wind-Induced Vibration Reduction Of Populus Bolleana

Wind damage has a significant impact on single tree and the whole forest ecological system. In the forests, trees in the wind might be induced stem bending even destroyed, thus affecting the quality and yield of wood. At present various types of wind damage will have a trend of increase, whether occurrence frequency or strength. Therefore, the research on the mechanism of wind-induced vibration of trees has great significance to protect forest resources and the guidance of forest management.This paper based on the field observation, establish the morphological equation of trunk of Populus bolleana. Through analysis the relationship between the frequency and geometric shape parameters of Populus bolleana, establish the calculation model of frequency of Populus bolleana. Calculate the damping ratio of Populus bolleana by free vibration. Calculation results show that damping ratio will decreased with main branches removed, thus crow play an important role in dissipating energy of trees vibration. Test out the elastic modulus of trunk of Populus bolleana by two different methods, and the testing results of two methods have better agreement.Based on the random vibration theory, established the finite element model of Populus bolleana by ANSYS, and analysed the random vibration response of the trees structure under wind load by building the relationship between the spectrum of wind load and the response of structure in frequency domain. Combined with the analysis of experimental found that the average relative error between results of random vibration analysis and field test results is 8.6%. The frequency of wind that influenced the vibration of Populus bolleana is very low and within the first three nature frequencies of Populus bolleana. The influence of high-order vibration modes on displacement response of Populus bolleana is not distinct. In the wind-induced vibration of Populus bolleana, branches and trunk have the same frequency and opposite direction of vibration. The vibration amplitude of the branches are greater than the vibration amplitude of the trunk. When removing all of the branches, the vibration energy of trunk place in a wider frequency bands and the vibration response of trunk would be more sensitive for the frequency of the wind.Using random perturbation method to calculate the mean, variance and coefficient of variation of the displacement response variance of the trees under the wind load. The dispersion of trunk stiffness have the greatest influence to the dispersion of displacement response variance of the tree. The dispersion of crown mass have the least influence to the dispersion of displacement response variance of the tree. Screens structure parameters, establishes contrast model by ANSYS, analyzes the impact of structural parameters on the wind-induced vibration reduction of tree structure.