基于线性滤波法的单株林木抗风有限元模拟

风灾是林木发生破坏的主要原因之一,研究树木结构特征以及受力特点能够深入了解树木在受风荷载作用时各个部位的应力状态,确定其易发生破坏的区域,从而采取对应措施保证林木的安全稳定性。运用线性滤波法可以模拟实际状态下的脉动风模型;利用有限元技术可建立树木的有限元模型。结合两者可以模拟树木受动力风荷载作用的过程,并可计算树木各个部位的应力状态和位移等参数。模型搭建过程分为2个部分:风模拟,即运用线性滤波法编程计算得到随机的时程风场,再通过计算转换为脉动风荷载并施加于单株林木;树的模拟可根据单株树木各部分密度、弹性模量等与树高线性相关的假设,采用ANSYS中的参数化建模法(APDL)编程得到树木模型。最后编制宏文件,得到可以通过更改个别参数达到调节树模型以及脉动风场的命令流文件。在模型加载后,通过对所得到数据进行分析和比较,了解林木的抗风性能。在该模拟中,采用我国华北地区沿海防护林树种黑松为主要研究对象。通过模拟,了解单株黑松在脉动风荷载作用下的力学响应,得知材料的抗剪切性能决定其抗风能力大小,从而可采取相应措施如加固或对林木进行定期修剪,提升林木稳定性。 

Finite element modeling of wind resistance of single trees based on linear filtering method

Wind disaster is one of the main disasters causing damage to forest. Study of structural characteristics and mechanical abilities of trees can help us understand more about the stress state of single trees and the area most likely to break when destroyed by wind, so as to take measures to enhance the safety and stability of the forest. In this study, we used the linear filtering method to simulate the fluctuating wind model which is close to actual conditions. The finite element method was employed to simulate the tree under wind load, and then the stress state and structural displacement of different parts of the tree under the effect of dynamic wind loads were obtained. The process of building the model is divided into two parts: the first is the simulation of wind by applying the linear filtering method, and we calculate the wind field in a specific area; the second part is to construct the finite element model of the tree. Then the tree model is set in this wind field. The variables such as density and elastic module could be controlled by variables related to tree height. Macro file of the model building could be obtained by changing some specific variables of the command stream file. After applying the load, we collect the data and analyze the wind resisting ability of the tree. In this simulation, we choose Pinus thunbergii in the coastal protection forest as our research object. Through simulation, we can know more about the tree’s reaction to the fluctuating wind load and the weakness of the tree in response to the wind load, so as to take appropriate measures such as frequent thinning or reinforcement to enhance the tree’s stability.