一种计算机模拟的针阔林木抗风性能分析

Computer simulations for wind resistance analysis of broadleaf and coniferous forests

自然界中的强风常常对树木造成不可逆破坏,分析强风穿过时树林内部的气流情况有利于评估树木的抗风性,更好地理解如何减轻风的影响。以阔叶树和针叶树为原型,提取了二者叶团簇和枝干构造的特点,建立两种结构不同的树木模型,组合成树林模型,在3个不同叶面积密度下进行风力作用下的仿真模拟实验。分别使用改进的k-ε双方程模型和k-ω双方程模型以设置风环境,并且用龙格-库塔法分析求解湍流模型。k-ε双方程模型下,当叶面积密度分别为1,5和10 m~2/m~3时,阔叶林背风侧20 m处的最低风速与入口风速相比下降了49.60%,67.23%和80.40%,针叶林分别为55.13%,68.90%和78.29%。k-ω双方程模型展示了阔叶树林内部风场的复杂性。结果表明,叶面积密度与树林挡风能力之间是非线性关系,树林的挡风能力随叶面积密度的上升而增强,增强到一定程度后上升幅度减缓。不同的树木结构会导致风场的变化,影响同等强度风荷载下的受损概率和挡风能力。叶面积密度高、树冠体积大的树木更容易在强风中受到损害。

Strong winds in nature often cause irreversible damage to trees.Analyzing the airflow inside the forest when strong winds pass through can help assess the wind resistance of trees and comprehensively understand how to mitigate the effects of wind action.Under the premise of taking broadleaf and coniferous trees as prototypes,the characteristics of leaf clusters and branch structures which play a major role in the reconstruction of broadleaf trees and coniferous trees were extracted.The two tree models with different structures were established and formed precisely in order to compose the forest models used in the computer simulations.The computer simulations under wind loading were carried out with three different leaf area densities applied to the leaf cluster portion of the tree models.The improved k-ε two-equation turbulence model and k-ω two-equation turbulence model were used to set up the wind environment,and the Runge-Kuta method was used to analyze and solve the turbulence model.When the leaf area densities were 1,5 and 10 m~2/m~3 individually,the minimum wind speed at 20 m on the leeward side of broad-leaf forest decreased by 49.60%,67.23% and 80.40%,and the coniferous forest decreased by 55.13%,68.90% and 78.29%,respectively.When discussing the differences between different models,the k-ω two-equation turbulence model demonstrated more detailed results on the airflow within broadleaf forests than the k-ε two-equation turbulence model.In general,the results showed that the relationship between leaf area density and forest wind resistance was nonlinear.The wind-blocking effect of the forest increased with the leaf area density,reducing the rise after reaching a certain extent.Different structures of the tree models lead to changes in the wind field,impacting the probability of damage to trees under same wind loading and the wind-blocking effect of the forest.Concretely speaking,the trees with high leaf area density and large canopy volume were more susceptible to damage in strong winds.The analysis of the various parameters of the forest under wind loading is conducive to quantifying the wind damages of different types of forests,which in turn can help to construct more reasonable windbreak forests.