| As continuous increasing of China's crop production,damage of disease also shows a scaled outbreak,plant protection technologies have a closely relation to the damage of disease.Reduction of cultivated land area and requirement of modern agronomy decided a rational close planting,but there would be a high plants canopy density when the close planting crops grew to the middle and late period.As the main plant protection methods,general spray technology of chemical prevention cannot achieve uniform deposition of the liquid among the plants.As an effective mean to solve the problem,airflow-assisted spray can not only second atomization fog drops,but also can change local porosity of the canopy and form a ventilation channel to enhance the deposition in the canopy.However,most studies focused on qualitative analysis of spray deposition by auxiliary airflow,and few researches focused on the effect of auxiliary airflow on crop canopy.In this paper,canopy porosity of plants under the action of auxiliary airflow was qualitatively and quantitatively analyzed from the perspective of canopy porous media characteristics.Conclusions are as follows:(1)Design of auxiliary airflow source and dispenser meet the requirements of the tests.Deformation of the same lateral branch under different wind speed was obtained through the test.It was found that deformation of lateral branch was positively correlated with the change of wind speed.With the increase of wind speed,lateral deformation gradually increased not in a linear increased relationship,but increased in power function form at a certain wind speed,and there was a difference in the increase of different parts.At the same wind speed,deformation of the lateral branches at different parts was different: deformation of the upper and middle lateral was larger than that of the lower lateral.The result may be related to length,diameter and position of the lateral branch.The finite element analysis showed that length of stem had the greatest effect on its deformation.(2)Due to different growth stages at different parts of cotton stems,the corresponding density showed certain difference.Young's modulus measured at upper part of the stem was 94.2%,81.1% at middle branch and 73.7% at lower part.Young's modulus of stem from large to small in the order as following: trunk,lower part of the branch,the middle branch and the upper branches.Length of the samples had a certain effect on test results,but does not affect the accuracy of results.(3)Three-dimensional modeling of cotton stems have been established,giving stems of material properties,then the biomechanical model of cotton stems was expressed.Deformation of different lateral branches was obtained by fluid-solid coupling simulation method and the simulation results had a good agreement with the physical test conclusions,which proved that fluid-solid coupling method was feasible using in this study and also proved the accuracy of the establishment for mechanical model.Simply modeling of cotton stems was established and deformation of cotton stems and leaves was analyzed by fluid-solid coupling method,which can be obtained of the deformation of cotton leaves under simulated conditions.(4)A method for calculating crop porosity was proposed.To abstract simplify cotton plants,using the results of finite element analysis to deduce the change of projection area of stem and leaf,then expressed the parameters of cotton crop porosity change under different wind speed.(5)A method of measuring crop porosity was proposed.Test platform was designed for experiments,which results showed that auxiliary air flow had a great improvement on crop porosity.When the wind speed was small,it had less effect on middle and lower layer porosity.When the wind speed was increased,it had little influence on the upper porosity,while it had good effect on perturbation of middle and lowelayers.The ever-increasing wind speed cannot always increase crop porosity. |
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