| China is the largest country of fruit production and its fruit planting area and export rank first in the world.However,the north of China has suffered from frost damage and economic losses,which is one of the main bottlenecks restricting the sustainable development of the fruit industry.The traditional orchard frost protection technology includes covering,sprinkling and smoking,which can achieve a certain frost protection effect,but the labor cost is high.At present,frost protection equipment has poor reliability and low automation,which hinder the popularization and application of the equipment.Therefore,it is of great significance for reducing frost damage and improving quality and efficiency to optimize the key parameter of frost protection wind machine and research the intelligent control strategy.The main contents of this study are as follows:(1)A frost simulation experiment and analysis of apple flower frost characteristics has been completed by taking Taishan ZaoXia apple as the research object.The super cooling points of apple flower bud period and full bloom period are determined to be-3.1°C and-2.9°C respectively,and the freezing point was-2.4°C and-2.3°C.By monitoring the spatial-temporal distribution of orchard temperature in the frost period,the height space temperature inversion from 8 m to 12 m above the ground is obvious,the maximum temperature inversion difference is 5.2°C at 06:00 before sunrise,the canopy temperature of fruit trees from 1 m to 3.5 m above the ground is affected by factors such as daytime temperature,humidity and air supply speed.The minimum temperature observation model of fruit canopy is established by multiple regression method through the orchard environmental data monitoring system to provide experimental data and theoretical basis for subsequent research.(2)Based on the heat balance model,an optimization about key parameters of frost protection wind machine which fuses by CFD(Computational Fluid Dynamics)simulation and response surface is proposed.The orchard is simplified into the control box by analyzing the energy transfer mode and temperature distribution during the frost protection process.According to the law of conservation of energy,the convective heat transfer of the orchard in the operation of the frost protection wind machine is analyzed,and the improved heat flux model of the frost protection wind machine is constructed.By analyzing the influence of the key parameters(height of axial fan,tilt angle of axial fan and air supply speed)of the frost protection wind machine on the performance,the range of values of each parameter is preliminarily determined.The response surface method is used to obtain the influence of three factors on the canopy temperature increase of fruit trees as follows:tilt angle>air supply speed>height.The canopy temperature increase prediction model is fitted by regression equation,and the maximum temperature increase is used as the optimization target.The optimization scheme of each parameter is obtained:the depression angle is 20°,the wind speed is 15 m/s,the height is 9.5 m.Using the above optimization parameters,the canopy temperature distribution of fruit trees is obtained by CFD simulation.The results show that the maximum temperature increase is 2.38°C,and the relative error with the predicted value is only 0.059%,which indicates that the key parameters optimization method of frost protection wind machine is feasible..(3)Based on the optimal combination of key parameters of the frost protection wind machine and the climate change during the frost period of the orchard in Taian area,a tower frost protection wind machine is designed.According to the optimal value calculation of the key parameters of the frost protection wind machine,axial fan motor power is determined to be 4 kW,the installation height is 9.5 m,the diameter of the blade is 1 m,and the air volume is 42 300 m~3/h.The stress,deformation and mode of the air supply device and the tower are analyzed by ANSYS.The maximum stress is about 110 MPa and 185 MPa respectively,the maximum deformation is 0.0043 m and 0.0046 m respectively,and the natural frequency of the 6th order of the tower is 38.681 Hz,which shows that the frost protection wind machine can withstand the storm and meet the requirements of strength and stability.In order to increase the frost protection area,360°rotation air supply system is adopted.The air supply speed distribution characteristics at any point of the canopy of the fruit trees at different distances or speeds are obtained to calculate the frost protection area by constructing the air supply speed cubic spline function and the measured point air supply speed.(4)In order to improve the automation degree of the frost protection wind machine,a fuzzy intelligent control strategy is proposed and an automatic control system is designed.Based on the above mentioned minimum temperature observation model of fruit canopy and LSSVM(Least Squares Support Vector Machine),the online temperature prediction model of fruit canopy is constructed.The temperature inversion difference and the temperature difference ratio are input variables to realize real-time change of the rotation speed at different ambient temperatures by fuzzy controller.According to the control strategy,the frost protection wind machine automatic control system is designed with STM32 as the controller.The orchard environment information collected by sensors is transmitted through the wireless network to realize local control of the frost protection wind machine,human-computer interaction and remote monitoring of the frost protection process.The wireless data transmission performance test results in sparse orchards and leafy orchards show that the wireless data transmission success rate at 60 m is 99.44%and 99.16%,respectively.The frost protection wind machine meets the wireless data transmission requirements within 50 m in orchard.(5)In the Orchard Experimental Station of Shandong Agricultural University South Campus,the frost protection performance test and the frost protection effect test under different control modes were carried out.The results show that with the temperature>0°C or the temperature increase range>1°C and the air supply speed>0.6 m/s as the protection boundary conditions,the effective protection radius is from 7 m to 48 m and the protection area is about 7150 m~2.Taking the traditional control mode as the control group,the critical starting temperature is set to-0.5°C.During the first test period,the average temperature increase range of the fuzzy control mode is 0.8°C,which is 60%higher than the average temperature increase range of 0.5°C using the traditional control mode.Within the scope of protection,compared with the traditional control mode,the maximum freezing rate of apple flower buds is?26%,and the maximum freezing rate of fuzzy control mode is?12%,which is reduced by 53.8%.The above data shows that the frost protection wind machine has a good frost protection effect and can meet the requirements. |
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