Structural Design And Shading Strategy Of Automatic Shading System For Tea Plantation

In recent years,extreme meteorological disasters such as low temperature and high temperature have occurred frequently areas across the south of the Yangtze River,making the physiology and growth of tea trees hindered,resulting in lower yield and quality of famous tea.Shade cultivation technology improves the temperature,light and other small environments for tea tree growth through shade nets,which can effectively ensure the quality of tea leaves during the picking season and improve the economic benefits of the tea industry.However,the traditional shade operation is often manually operated,which has problems of low automation and high labor intensity;the existing internal and external shade systems in facility agriculture production are limited by space and cost factors,and cannot achieve automatic regulation of lifting height,which affects tea garden field management or harvesting operations.In this study,under the impetus of "tea full process unmanned operation test technology products and solutions",in order to address the technical problems of the full process unmanned operation of shade in tea plantations,firstly,the elevated shade net structure and automatic shade movement scheme were designed based on the diagonal structure,and the reliability of the structure and shade operation were verified by finite element analysis.The effect of different shading parameters on the growth and environment of tea trees was studied,and the shading rules during the high temperature period in summer and low temperature period in winter were analyzed;finally,the shading control strategy of tea plantation was established by combining the temperature change characteristics and shading rules of tea plantation throughout the year.This study provides technical support for the realization of automated and scientific shading of tea plantations from the perspective of practical application.The main research contents and results are as follows.(1)Structure design of automatic shading systemBased on the design of the slanting structure as the shade net frame,the mechanical model of the slanting structure is analyzed and simplified based on the design of the loadbearing ratio of the cable,and the design index of the structure parameters is derived,and the inclination angle of the cable is determined to be 20.41°～50.74°.Based on the theory of elastic support continuous beam,the number of cables and cable spacing are used as the optimization parameters,and the uniform arrangement of cable spacing and equivalent pivot point arrangement of cables are designed to obtain the structural parameters under different combinations of cable number and cable spacing.In order to determine the motion structure scheme of the automatic shading system for tea garden,the functional element solution of the system is constructed,and the optional scheme is evaluated and analyzed to determine the optimal motion scheme for opening and closing and lifting the shading net.(2)Finite element modeling and parametric analysis of inclined tension structureThe three-dimensional model is established according to the structural characteristics of the automatic shading system and simplified.The finite element analysis software Workbench was used to pre-process the model,establish the analysis model of the automatic shading system structure,and carry out static analysis on different combinations of cable number and cable spacing design to select the optimal combination;and carry out dynamic load analysis and fatigue life analysis on the structure,and carry out the corresponding stress test.The results show that the inclined structure has the best stress distribution and minimum deformation under the combination of 3 cables and l equivalent pivot point arrangement cable spacing;the maximum stress value under dynamic load condition is 48.01 MPa and the maximum deformation is 10.43 mm,which meets the structural design requirements.(3)Experimental study on the effect of shading structure parameters on the growth and environment of tea treesIn order to determine the optimal shading rate for each season,this study set up different shading net shading rate(35%,55%,70%)tests.Frost damage index and leaf area size were used as measurement indexes in winter,and chlorophyll content and photosynthetic parameters were used as measurement indexes in summer.The results showed that the lowest frost damage index of tea trees was 28.92% in winter when 35%shading was used,and the leaf area,length and width increased by 17.82%,5.38% and12.42%,respectively,compared with the control treatment.The photosynthetic parameters of tea trees were optimal in summer with 55% shade,photosynthetic rate increased by 24%compared with the control treatment,and chlorophyll content increased in all shade.In order to determine the effect of different shade net heights on shade in tea gardens and to investigate the shade pattern of tea gardens in different seasons.In this study,field trials with different shade heights(1.5 m,1.8 m and 2.1 m)were set up with tea canopy temperature as the research object.The results showed that the winter and summer test periods could be divided into three stages in terms of average daily temperature from high to low.The overall effect of winter shade was thermal insulation,with the first stage of winter shade being all-day cooling,the second stage being daytime cooling and nighttime insulation,and the third stage being all-day insulation,with the best thermal insulation effect at 1.5 m height in each stage;the overall effect of summer and autumn shade was daytime cooling and nighttime insulation,with the best cooling effect at 1.5 m height in the first stage and the best cooling effect at 1.8 m in the second and third stages.(4)Shading operation strategy developmentIn order to determine the shade opening and closing time of tea plantations,this study analyzed the temperature change characteristics of tea areas throughout the year based on the theory of effective cumulative temperature,combined with the shade law of each season,and proposed the shade period and temperature segmentation control strategy.The results showed that: the spring tea sprouting and picking period was from March to May,the shade insulation period was from December to February,and the shade cooling period was from June to September.The shade insulation period can be divided into three temperature classes(-5～0℃,0～5℃,5～10℃)based on the daily minimum temperature;the shade cooling period can be divided into three temperature classes(35～40℃,30～35℃,25～30℃)based on the daily maximum temperature,and different shade patterns are given for different shade periods to guide the shade cultivation in tea plantations.