Study On The Wind Characteristics Of Trees And The Method Of Determining The Degree Of Permeability

Trees play many functions in human society,such as regulating the climate,purifying the air,fixing the soil,preventing wind and reducing noise.Wind-induced disasters from trees not only affect the regulation function of trees on climate and ecology,but also cause significant economic losses.Tree permeability is one of the important characteristics of tree structure,which has an important impact on the wind-induced stress of trees and the characteristics of the wind field near the trees.Therefore,studying the determination method of tree permeability and the wind characteristics of trees is important for the study of tree wind resistance.significance.The test in this paper is mainly carried out in the wind tunnel laboratory.The test wind field is Type B.The wind speed is controlled by the fan.The wind speed conditions are 0m/s,6m/s,8m/s,10m/s,12m/s,14 m./s,the test subject selects saplings that are similar in appearance to r eal trees.Porosity is defined as the ratio of the area of light-transmitting pores to the area of the canopy,which is an important characteristic parameter of tree structure.Therefore,this article focuses on the method of determining the degree of tree permeability,the variation of the degree of permeability and windward area with wind speed,the force characteristics of trees at different wind speeds,and the influence of the variation of the degree of permeability on the force of trees,mainly as follows: Expanded in several aspects:1.Use a digital camera to take color images of trees under different wind speeds,and then apply the threshold method and watershed algorithm in image processing technology to process the photos to obtain the transpa rency of individual trees from the pixel level.Then compare the transparency of the trees obtained by the method in this paper with the transparency obtained by the predecessors using the image processing tool Photoshop,and the results show that the diff erence of the transparency of the three trees under each wind speed state is between 2%-8%.In time,it shows that the method is feasible.And this method has the advantages of not requiring manual intervention and simple operation.2.Use a multi-spectral camera to take multi-spectral images of trees,and use the image processing software ENVI to process the multi-spectral images of trees.First,distinguish the tree and the background part according to the temperature difference between the tree and the background.Then,according to the spectral characteristics of the trees,a method of using the normalized vegetation index of greenness to distinguish the canopy and pores in the multi-spectral image is proposed.Finally,the transparency of the trees is determined from the pixel level.The relative error of this method is between 2% and 6% compared with the transparency obtained by using the image processing tool Photoshop of the predecessors,indicating that the method is also feasible.3.To explore the relationship between the degree of tree transparency and wind speed,windward area and wind speed.Take pictures of trees under different wind speed conditions and calculate the transparency and windward area.The results show that the degree of transparency of trees increases with the increase of wind speed;the windward area of trees decreases with the increase of wind speed.4.In order to explore the wind-induced force characteristics of trees and the influence of changes in the degree of permeability on the force of trees.Use a dynamometer to measure the force of trees under different wind speeds and different degrees of permeability.The results show that the downwind resistance and the overturning moment play a dominant role on the trees,and as th e wind speed increases,the downwind force on the trees and the overturning moment and the wind speed show a power function increasing relationship.Changes in the degree of permeability can affect the force characteristics of trees.Under the same wind environment,as the degree of permeability increases,the downwind force and overturning moment of the trees will gradually decrease.