| Field management is one of the important links of agricultural mechanization production in our country.At present,the field management equipment of high stem crops in our country is lack and single in function.The traditional operation equipment has low ground gap,so it is difficult to work in the middle and late period of crop growth,which restricts the improvement of field management level and becomes one of the short boards of the whole mechanization development.The high gap operation device is an effective solution to the above problems.In this paper,aiming at the problem of top dressing in the middle and later stages of high stem crops,a precision mixed fertilization device is designed to match the high gap chassis.The device adopts the side deep fertilization scheme.After the three kinds of nitrogen,phosphorus and potassium fertilizers are proportioned according to the actual demand,they are discharged into the soil near the root system of the crops to improve the fertilizer utilization rate;in order to adapt to the width In order to meet the needs of wide and efficient operation and avoid the instability of the gravity center of the high gap chassis caused by the too long fertilizer box,the pneumatic centralized row fertilization scheme is adopted.In this paper,the key components of the centralized and row fertilization device are designed.Through theoretical analysis,computer simulation analysis and experimental research methods and means,the influence law of the key components on the operation quality of the key components is studied.Finally,the key components are integrated for trial production of the whole machine.The research content of this paper mainly includes the following aspects:(1)Calibration method of friction coefficient in discrete element simulation of granular fertilizerIn this paper,Plackett-Burman multi-factor significance screening test is carried out for four kinds of particle characteristics test methods: split cylinder method,tilt method,drawing plate method and inclined plane method.The analysis of variance of test results shows that the significant factors and factors influencing the measurement results are different from each other.According to the results of variance analysis of split cylinder method,inclined method and inclined plane method,a new method of friction coefficient calibration based on the overall characteristics of particulate materials is proposed.The simulation test was combined with the real test,and the static friction coefficient between the urea particles and the PVC material was 0.41,the static friction coefficient between the particles was 0.36,and the rolling friction coefficient between the particles was 0.15.The Calibrated coefficients are validated by the bottomless cylinder method.The angle of repose simulation test results are 30.57 degrees,the real test results are 31.74 degrees and the relative error is 3.69%.Under different water content conditions,the relative error between the actual test angle of repose and the simulated angle of repose under the calibrated coefficients is not greater than 4.59%.There is no significant difference between the simulation results and the real test results.The validity of the calibration coefficients is verified by the test results.(2)Test of Suspension Velocity of Granular Fertilizer Based on EDEM-Fluent CouplingThis paper provides a reference for the design of pneumatic fertilization device,and takes three kinds of granular fertilizers,large granular urea,diammonium phosphate and potassium sulfate,as test objects.The suspension velocity of materials was simulated by the coupling method of computational fluid dynamics and discrete element method.The Lagrangian model was used to simulate the gas-solid two-phase flow.The experimental results show that the suspension velocity of large granular urea is 7.21-12.97m/s,the suspension velocity of diammonium phosphate is 7.68-12.48m/s,and the suspension velocity of potassium sulfate is 11.09-18.15m/s.Through the bench test,the suspension velocity of large granular urea is 6.68-12.48m/s,diammonium phosphate is 7.22-11.96m/s,potassium sulfate is 9.46-17.81m/s,the relative errors are 5.3%,5.1% and 7.2% respectively.When the volume fraction of granular fertilizer is 1%,3.5%,6% and 8.5%,the suspension speed of granular fertilizer group is measured.The suspension speed of granular fertilizer group decreases with the increase of volume fraction.Under different volume fraction of granular fertilizer,the ratio of simulation test results to real test results is approximately constant,which is supposed to be due to the influence of particle sphericity on suspension speed.The results show that the correction coefficient of the suspension velocity of large granular urea is 0.90,that of diammonium phosphate is 0.96,and that of potassium sulfate is 0.84.Therefore,the simulation test of particle suspension velocity through fluid solid coupling simulation has a high accuracy,which verifies the feasibility of the method of measuring the suspension velocity of materials based on EDEM-Fluent gas-solid two-phase flow coupling simulation.(3)Simulation optimization and experiment of pneumatic variable mixing fertilizer device based on discrete element methodIn order to improve the utilization rate of fertilizer,a variable ratio fertilization device was designed to realize the real-time application of three kinds of fertilizers on demand.Based on the discrete element method,the influence of the angle of fertilization pipe on the transportation capacity of large granule urea,diammonium phosphate and potassium sulfate was analyzed.The simulation results show that when the inclination angle of fertilizer pipe is greater than 50 degrees,the transportation efficiency of fertilizer in the fertilization pipe can meet the maximum fertilization rate According to the classical design method of Venturi tube,the paper designs the air conveying fertilizer pipe,studies the influence of gas velocity on the error of fertilizer amount through the coupling method of computational fluid dynamics and discrete element method.It is found that with the increase of conveying gas velocity,the quality of fertilizer applied in the target area gradually increases,and the error between the actual total fertilizer amount and the target total fertilizer amount is found However,when the transport gas velocity is greater than 30m/s,the error of potassium sulfate fertilization gradually increases,and the reduction effect of total fertilizer amount error is not significant.Therefore,the transportation gas speed of 30m/s is the most economic wind speed.The experimental results show that the error of single fertilizer amount is controlled within 5.33%,the error of total fertilizer amount is not more than 4.66%,and the mixing uniformity of three fertilizers is more than 94.4%.(4)Design and experiment of mass flow sensor for granular fertilizerBased on the principle of electrostatic induction,a mass flow sensor of solid particle fertilizer is designed in this paper.Because of the friction and collision between the fertilizer particles and the air,the wall of the fertilizer discharge pipe and itself,the fertilizer particles carry electric charge.In the process of the falling of the fertilizer particles,the ring electrode is induced with a weak equal amount of different electric charge.At last,it is output by the current amplification circuit induced current.Taking the large granule urea,superphosphate and potassium chloride as the research objects,the calibration of the inductive current and the mass flow of granular fertilizer was carried out,and the test results of the detection accuracy of three kinds of fertilizers were carried out.The results showed that the average measurement errors of the three kinds of fertilizers were 3.9%,5.1%,5.9%,and the standard deviations of the errors were 5.21,7.98,11.29,respectively.Statistical analysis shows that the measurement errors of the three fertilizers accord with the normal distribution,and their mathematical expectations are 3.74%,4.93% and 5.22%,respectively.The solid particle fertilizer mass flow sensor studied in this paper can meet the needs of real-time detection of solid particle fertilizer mass flow,and provide reference for the research of variable fertilizer closed-loop control.(5)The design and experiment of the pneumatic collecting and discharging fertilizer mixing deviceIn order to meet the needs of top dressing in the middle and later stage of corn growth,a precision mixing and fertilizing machine matched with highland gap chassis was designed.In this paper,the pneumatic centralized and row fertilization scheme is adopted,and the throwing type fertilizer mixer is designed to mix the three kinds of fertilizers discharged from the variable ratio fertilizer device through the motor driven blade rotation,and then transported to the fertilizer distributor designed as a cone-shaped structure.The computer fluid dynamics(CFD)and discrete element method(DEM)were used to simulate the angle of fertilizer outlet of distributor,the structure and layout of bellows at the upper end of distributor.The experimental results show that the comprehensive performance is optimal when the angle of fertilizer outlet is 45o and a vertical corrugated pipe with length of at least 570 mm should be arranged at the upper end of fertilizer distributor,so as to avoid the operation of fertilizer particle flow due to pressure difference And adhere to the pipe wall.In June 2019,the National Agricultural Machinery Quality Supervision and Inspection Center conducted a field test on the machine.The test results showed that the error of fertilization amount was 2%,the stability coefficient of variation of total fertilizer amount was 2%,and the consistency coefficient of variation of fertilizer amount of each row was 3%.The fertilizer application device could meet the top dressing requirements of high stem crops in the cultivation period. |
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