| In recent years,the frequency and severity of wind damage through hurricanes have been increasing,and forests have acted as a natural barrier against disasters and suffered more and more damage.From large-scale leaf shedding and breaking of branches to uprooting of trees,the disaster caused by the hurricane has resulted in the huge losses in the national economy.Therefore,qualitatively and quantitatively exploring the distribution characteristics of the internal flow field of the forest under strong wind load is the current hot issue.The research of wind resistance of trees under wind mainly involves: three-dimensional geometric modeling of trees and loading wind fields in tree models.Analyzing the distribution and change characteristics of wind-related parameters and understanding the movement of trees in the internal flow field under hurricanes,can provide a theoretical basis for the wind resistance of trees and also open up new ideas for forest management.Based on the above background,this paper combines computer modeling and fluid mechanics related knowledge to realize the three-dimensional geometric modeling of trees,and obtains and analyzes the changes of wind-related parameters in the forest under hurricane conditions.Mainly conducted the following research:1.Three-dimensional geometric model construction of tree branches.Based on the point cloud data collected by terrestrial lidar,we studies cherry tree,apple tree and rubber tree respectively.Target registration and splicing of the original point cloud data and removal of noise points from the point cloud;layering the processed point cloud data and clustering according to the shortest path distance to find different clustering center points of each layer;constructing the cluster The connectivity matrix of the adjacent center points is used to realize the reconstruction of the tree branch model by cylinder fitting;according to the composition properties of the tree,the tree branches are automatically classified into the trunk,the first-order branch and the second-order branch,and finally get a complete tree branch model.The experimental results have a good similarity with the original scanned data in shape and distribution,keeping most of the point cloud characteristics of the original data,proving the feasibility of the algorithm.2.Inversion of stand parameters based on foliage clumps.Aiming at the problem that the rubber trees in Hainan,China,suffering wind damage all the year round,two different clones of rubber trees(PR107 and CATAS7-20-59)are used as the research objects,and the spatial watershed algorithm is used to propose The leaves are grouped into one category,namely foliage clump,and the relevant stand parameters of each foliage clump are extracted: leaf area index,foliage clump volume,leaf area density and gap fraction.Construct a tree model based on foliage clumps and establish a rubber tree branch model of two clones.The inversion results of stand parameters show that the angle between the trunk and first-order branch ofrubber tree 1(PR107)is greater than that of rubber tree 2(CATAS 7-20-59),and the gap fraction of rubber tree 1 is lower than that of rubber tree 2.3.Study the distribution and changes of wind-related parameters in the forest under hurricane load.By loading the wind speed,the evolution and distribution characteristics of wind-related parameters(velocity,dynamic pressure and turbulence intensity)are obtained,the differences in wind resistance of different species of trees are analyzed,the causes of the differences are found,and the corresponding forest planting plans and recommendations are given according to the reasons.The simulation results show that because rubber tree 1 has a large branching angle and low gap fraction,forest plot 1 composed of rubber tree 1 has higher velocity,dynamic pressure and turbulence intensity than forest plot 2 composed of rubber tree2,resulting in forest plot 1 is vulnerable to wind damage,and the simulation results are consistent with the actual observations. |
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