Study On Mechanical Response Of Robinia Pseudoacacia Under Wind Load

With the improvement of ecological environment,China's forestry economic development is very rapid.As one of the main natural disasters,wind disaster will bring huge economic losses to forestry production every year,while seriously destroying the stability of forest ecosystem.Therefore,it is of guiding significance to study the mechanical response of trees under wind load and predict the ultimate wind speed that trees can bear.In this paper,the Robinia pseudoacacia in Junma No.5 stand forest farm of Dongying City,Shandong Province is taken as the research object.The wind speed and other measured tests are carried out in the forest farm,and the root samples of Robinia pseudoacacia are excavated and taken back to the laboratory to be buried in the remolded soil for pull-out test to obtain the root soil interface friction coefficient needed for simulation.Based on the fractal theory of plants,according to the tree height,DBH and other information of Robinia pseudoacacia standard wood,use MATLAB to establish the spatial coordinates of each branch point,and import the coordinates into the classic ANSYS module to complete the rapid modeling of Robinia pseudoacacia model using command flow.Finally,import the established Robinia pseudoacacia model into the workbench to establish the wind field and soil model.The flow field simulation is based on the fluent module in the workbench.The time history data of fluctuating wind speed with spatial correlation is obtained by MATLAB programming using linear filtering method.Then the UDF(User Define Function)function in fluent is used to read the wind speed data to the entrance of the wind field to realize the simulation of fluctuating wind field.Finally,the two-way fluid structure coupling of the fluctuating wind field and Robiniapseudoacacia model is completed by the transient analysis module and fluent fluid module in the workbench.The results show that:It is found that the maximum friction between root and soil is affected by the diameter,depth of burial and moisture content.The maximum friction increases with the increase of diameter and depth of burial,but increases first and then decreases with the increase of moisture content.The friction coefficient of root soil interface required for numerical simulation is calculated through the test results.Combined with the measured wind speed data and the wind speed data provided by Hekou meteorological station,four kinds of wind speeds(3.5m/s,15m/s,19m/s,23m/s)are selected for simulation,and the fitting results are verified by the measured displacement data of Robinia pseudoacacia.According to the fluid structure coupling simulation data,when the wind passes through the trees,it will cause the trees to swing irregularly.When the wind force level is within the range of trees,the displacement trend of the top of Robinia pseudoacacia is from static to maximum swing,and then gradually decreases.When the wind speed reaches 23m/s,the top displacement of Robinia pseudoacacia continues to increase,and the Robinia pseudoacacia model has obviously shifted,at this time,the model has been unstable.According to the stress analysis of the Robinia pseudoacacia model,under the wind speed of 23m/s,the transverse shear stress of the branch is close to the shear strength value,and the transverse tensile stress has exceeded its tensile strength value,which leads to the transverse tensile failure.The maximum stress appears at the nodes of the trunk and branch.At the same time,the tensile stress of the root system of Robinia pseudoacacia is greater than its tensile strength,which is the instability of the Robinia pseudoacacia model main cause.The results of numerical simulation in this paper can well restore the mechanical response of Robinia pseudoacacia under the fluctuating wind load and predict the wind speed of damage.The two-way fluid structure coupling of Robinia pseudoacacia under the fluctuating wind load based on CFD(Computational Fluid Dynamics)technology can well restore the stress characteristics of trees under the fluctuating wind load.By changing the tree modeland material parameters,the mechanical response of different kinds of plants under the wind load can be simulated,which is helpful to understand the mechanical mechanism of tree damage under the wind disaster,and has reference to the selection of windbreak plants in different areas Guiding significance.