Research On Trees Wind-induced Vibration Characteristics Based On Testing Methods And FEM Simulation

Wind not only threatens the production rate of forests but also has a huge effect on the people who live in the city and their wealth. In order to provide a wind vibration theoretical basis of forest management and regulation after strong wind disaster, this paper study vibration characteristics of Chinese white poplars under strong wind.This article research Chinese white poplars which3years old grows in nursery of Beijing Forestry University. Chinese white poplars are studied by wind vibration tests, numerical simulation and mechanical vibration theoretic analysis. Main research methods are as following:1. The rapid modeling method for trees. This study attempts to provide three-dimensional structure model through fractal theory to study the mechanical properties of trees. Through the "family table" and "UDF library" which are the functionality of Pro/Engineer software, the results is to build a geometric structure of the model with three-dimensional and lays the foundation for analysis wind characteristic in the numerical simulation part.2. Wind vibration test and numerical simulation about the crown of Chinese white poplars. This article sets up finite element model of the crown of single trees which not including leaves and FEM software ANSYS Workbench had been used to analyze. Transverse view mechanical model had been used to build up multiple level branches structure model. Used centrifugal pump fan as the manual wind source, half sine gust of wind had been made to replace natural wind. Acceleration transducers had been used to measure vibration frequency of main trunk and first level branches.3. Established the model of trunk and crown, and simulated the dynamic characteristic by using finite element software ANSYS. The analysis results indicate that there is significant relationship between the distribution of branches and wind resistance mechanism of trees. Under strong wind, for the sake of decreasing the windward area of crown to avoid trees lodging, the stress and trunk and perpendicular to the direction of branches will be under the action of wind perpendicular to the direction of in-plane vibration occurred, when crown in perpendicular to the direction of in-plane asymmetric, trees will lateral movement, and so that the trunk root produce elliptic type rotary.4. In order to research the influence of interaction relation between roots and soil to vibration performance of trees, the natural frequency of four Chinese white poplars had been measured through trunks vibration tests in three different constraint conditions which include natural growth and root-soil friction and fixed end. Then root-soil stiffness connection model, root-soil friction model and fixed end constrained model had been constructed to calculate the natural frequency in those conditions which were mentioned.