Abstract: Maize is one of the most important cereal crops in the world. Maize production is of great significance to alleviate the world food crisis. The maize seeding rate can be adjusted during variable-rate seeding according to the spatial heterogeneity of the farmland environment, which is an important means to break through the bottleneck of maize yield improvement and improve resource utilization efficiency. In this review, the variable-rate seeding of maize was summarized from three aspects:the accurate acquisition of soil fertility indicators, the optimal seeding rate decision-making, and the precise control of seeding rate. The research status was also outlined on the rapid detection of soil fertility indicators using near earth and remote sensing. The spatial interpolation methods of soil attributes and farmland management zoning methods commonly used to accurately express the spatial distribution of soil fertility indicators were summarized. An emphasis was put on the research status and the advantages and disadvantages of variable-rate seeding decision-making methods based on farmland management zones and models. Based on the research ideas of developed countries and combined with the national conditions of China, three seeding decision-making methods based on fuzzy reasoning, field experiments, and machine learning were proposed. The structural composition and working principle of variable-rate seeding control systems were summarized in the developed countries. The research progress was reviewed on the electric drive seed-metering system in the variable-rate seeding process, in terms of the operating speed measurement, seed-metering device driving, seeding delay, and the compensation. The research gap was determined in the variable-rate seeding technology between developed countries and China. The research priorities and development suggestions were proposed for China in the field of variable-rate seeding of maize in the future. Developed countries were carried out the extensive and in-depth research on dynamic detection of soil fertility indicators around spectral analysis, electromagnetic induction, and current voltage four terminal. A variety of dynamic detection equipment was also developed for the soil fertility indicators. However, China is still in the theoretical research stage of in-situ dynamic detection of soil fertility indicators at present. There was few relevant equipment to realize the dynamic detection. Multi indicators high-precision collaborative detection using multi-sensor fusion has been the development trend of dynamic detection of soil fertility indicators. The Kriging and k-means clustering with the geo-statistics were the most studied and applied methods for the soil attribute spatial interpolation and farmland management area division, respectively. In terms of optimal seeding rate decision-making, the seeding rate decision-making on farmland management zone was still occupied the leading position in the field of seeding rate decision-making, due to its simplicity and strong regional adaptability. With the deepening of research on the mechanism of soil fertility affecting maize seeding rate and the continuous accumulation of experimental data for seeding rate decision-making, model-based precision seeding rate decision-making methods will be expected to gradually develop in the future. The variable-rate seeding control system with a controller as the core is the carrier for implementing variable seeding operations and is mainly composed of a human-machine interface, controller, satellite positioning system, communication unit, and seeding unit. Developed countries have realized the various variable-rate seeding control systems with different architectures. The main research was conducted on the electric drive seed-metering control system from the aspects of operation speed detection, seed-metering device driving, and control system architecture optimization. But there was no the core technology of variable-rate seeding in China at present. Much attention can be put on the dynamic detection of soil fertility indicators and the decision-making of the best maize seeding rate. The precision metering and electric drive metering control system of maize can be developed for a maize precision seeding unit with the high seeding quality and response speed for variable seeding operations.
Abstract: A large number of near-obsolete agricultural machinery can be produced with the agricultural intelligentization and the life cycle of machinery equipment in recent years. Among them, the disassembly and recycling of agricultural machinery and equipment can play an important role in the utilization of ecological resources and sustainable agriculture. The recycling of obsolete agricultural machinery products can also greatly contribute to realizing sustainable development and a circular economy under the carbon peak and carbon neutrality. This study aims to perform the integration optimization of obsolete agricultural machinery product disassembly planning and remanufacturing decisions under the requirements of dual carbon target. The economic benefits were also evaluated to consider the carbon emission cost of the disassembly process. Firstly, a disassembly and remanufacturing integrated optimization model (DRIO) was constructed using product depreciation rate, remanufacturing demand and cost. The mathematical model included the profit maximization of remanufacturing product revenue, such as the cost of acquisition, disassembly, remanufacturing, and carbon emission. Secondly, an improved artificial bee colony algorithm (IABC) was proposed to solve the mathematical model. A set of Pareto schemes were obtained with high profit and low environmental carbon emission. The improved ABC algorithm included the population initialization, bee hiring, watch, and bee scout stage. A logistic mapping was introduced to generate high-quality initial solutions. A neighborhood search mechanism was added to the hire and watch bee phases, in order to enhance the colony search with less local optimality. A roulette wheel was also used in the scout bee phase. The motor was one of the main recycling and remanufacturing components of agricultural machinery, indicating the strong universality and high recycling-remanufacturing profit. Finally, the effectiveness and feasibility of the system were verified by an example of combined harvester disassembly. A collection was generated for the reuse, recycling, and remanufacturing of parts of the motor EOL decision. The results show that the economic benefits of the improved DRIO model were improved by 62.1% and 54.8%, respectively, compared with the DRIO-D and DRIO-R models. The carbon cost of the DRIO and DRIO-R models was about 50% less than that of the DRIO-D model. The characteristic index was chosen to measure the convergence of the super volume reaction non-inferior solution, and the dispersion degree of the reaction solution was measured by the spacing. The solution time of IABC was shortened by 19.3%, and the number of feasible solutions increased by 28.6%, compared with the classical. The improved DRIO model presented better economic benefits than DRIO-D and DRIO-R models. The IABC shared better performance, in terms of robustness and convergence. The solution time of IABC was shortened by 47.8%, and the number of feasible solutions was doubled than before. In the super volume value, the artificial bee colony algorithm (2.695) was similar to the ant colony algorithm (2.377), but both were smaller than the IABC algorithm (2.813). In the spacing measure, the ant colony algorithm (0.052 3) was lower than the artificial colony algorithm (0.068 2), but the IABC (0.041 6) was the lowest. Therefore, the integrated optimization model of disassembly planning constructed can be effectively improved the economic benefits of the disassembly and recycling of waste agricultural machinery recycling products, for less carbon emissions. The finding can provide an important basis for the formulation of relevant standards, together with the decision support for the green design of agricultural machinery.
Abstract: The performance of plant protection drones can depend mainly on the atmospheric environment in plateau areas. In this study, a plant protection unmanned aerial vehicle (UAV) rotor test bench was designed with adjustable rotor speed and real-time monitoring of engine speed, rotor lift, and output torque. The rotor speed was adjusted via the engine throttle, where the throttle line was pulled by the servo crank. The output speed of the engine was achieved to adjust the rudder angle, according to the PWM signal duty cycle. A set of data acquisition software was developed for the rotor test bench, in order to monitor engine speed, rotor lift, and torque parameters, and then display them in real time. The overall structure of the test bench consisted of the rotor, transmission, power, data acquisition, and servo control system, together with the platform. A sensor, control, and data acquisition were built with a data acquisition card as the core, and then the infrared remote control was added to increase the safety of the test. The rotor test bench was equipped with a DLE430 dual-cylinder inline two-stroke engine, with a rotor radius of 1.51 m, an airfoil of NACA 8-H-12, and a blade number of 2. This design fully met the technical indicators of the rotor system in the test state, such as the strength, stiffness, vibration, and accuracy. The blade element momentum was adopted to explain the aerodynamic characteristics of blades. The computational fluid dynamics (CFD) simulation was used to complete the solution. The rotor aerodynamic performance was numerically simulated at the speeds of 800, 1 000, and 1 200 r/min, respectively, within the altitude of 0, 1, 2, 3, and 4 km, respectively. The second-order upwind scheme was used in the numerical simulation, indicating a more accurate performance than the first-order upwind scheme. A systematic investigation was made to explore the effects of blade angle and rotor speed on rotor lift, test bench torque, and power using quadratic rotation orthogonal experiments and response surface method (RSM). The rotor performance tests were conducted, where the lift was taken as an indicator. The viewing performance tests of spread rotor test benches were also carried out, where the torque and power were as indicators. The quadratic regression equations were established for the lift, torque, and power. The relationship was determined between the rotor lift, test bench output torque, as well as the power and blade angle. The rotor speed shared a significant correlation and a good fitting level. The experimental results show that the rotor power decreased significantly with the increase of altitude, whereas, the descent rate increased. The power increased with the increase of speed at the same altitude. Furthermore, the power at an altitude of 2 km decreased by about 26% at a rotor speed of 1 000 r/min, compared with an altitude of 0 km. The optimized rotor speed was 1 116 r/min, the blade angle was 10.44°, the maximum lift was 356.28 N, the torque was 227.35 N·m, the power was 26.54 kW, and the efficiency of the rotor test bench was 85.92% at an altitude of 4 km. Compared with the experiment at an altitude of 134 meters, the lift of the rotor at an altitude of 1.941 km decreased by 22.38%, which was consistent with the decrease of 20.22% in numerical simulation. The driving torque of the rotor decreased by about 24.21%, and the engine power difference was about 3.99%. There was a reasonable range in the error ratio between the experimental and simulation. In addition, the variation trend of the experimental results was consistent with the numerical simulation, indicating a relatively small error. The main reason for the error was the frictional resistance of the power device composed of the rotor and engine in the experimental device during sliding. The findings can provide a strong reference for the high-load plant protection UAV at high altitudes.
Abstract: Corn whole plastic film mulching on double ridges has been the main production mode of maize planting in arid regions of Northwest China in recent years. An effective technical way can be widely used to stabilize the corn yield. Among them, the vertical roller-type corn harvest header can greatly contribute to the simultaneous harvesting of corn ears and stalks. Specifically, the grip and convey device can effectively shorten the length of the harvesting header. The vertical roller group can reduce the impact force between ears and picking rollers, even the picking loss. The stalks can also be cut in a centralized way. However, the current integrated device of grip and convey is often scratched on the surface of the plant stem by the sharp chain teeth, resulting in more broken stems on the harvesting head. In this study, the grip-convey device was designed for the vertical roll-type header of the corn combine harvester, in order to achieve the smooth gripping and conveying of maize plants without damaging the stalks. The grip and convey gap were adaptively adjusted with the plant stem thickness, in order to improve the clamping stability with the low rate of broken stems in the grip and convey device of the vertical roll-type corn header. The device was composed of the reel chain and grip-convey mechanism. The reel chain mechanism was for the orderly feeding of individual maize plants, and the reciprocating cutter to complete the cutting of plant roots. The grip-convey mechanism was used to realize the effective clamping and conveying of cut plants on the vertical roll-type corn header. In addition, a fold line path of the grip-convey channel was formed under the joint action of large and small chain clamping pulleys, as well as the bilateral grip chains. The clamping channel clearance was adjusted, when the stalk passed through the channel, according to the stalk diameter under the tensioning mechanism of the bilateral griping and conveying chains. There was a more reasonable clamping force on the grip and convey mechanism, and a more reliable clamping conveying, compared with the integral chain structure. An optimal combination was also achieved in the process of the toggle-feed in, grip-cutting, and grip-conveying, where the effective reel section chain length of the reel chain mechanism was 500 mm, the length of the grip and convey channel was 1 100 mm, the maximum grip and convey capacity of the harvesting head was 3, and the vertical distance between the grip rails was 40 mm. Furthermore, the grip channel between the two-reel chain was adjusted to 15-25 mm under the grip rail chain clamping pulley and the tension device. The response surface method (RSM) was used to analyze the effects of the forward speed of the harvest, the rotating speed of the drive sprocket, the angle of the harvesting head, and the feeding angle of the plant on the operation performance of the grip and convey device. The test results showed that the total ear loss rate was 0.83%, and the broken stem rate was 0.12% when the forward speed of the harvest was 2.8 m/s, the rotating speed of the drive sprocket was 1 210 r/min, the angle of the harvesting head was 18°, and the feeding angle of the plant was 60°. The total ear loss rate and the broken stem rate were reduced from 2.8% to 0.83% (30%), and from 1.3% to 0.12% (12%), respectively. This finding can provide the theoretical basis and technical reference for the high quality and low damage of vertical roll-type corn harvesting.
Abstract: A ramie stripping machine has been commonly used in modern agriculture in recent years. However, the current manual feeding and back-pulling cannot fully meet the large-scale production, due to the high operational intensity, low safety, and unstable stripping quality. In this study, a double-drum stripping device was designed to replace the manual feeding and reverse-pulling in an automatic ramie fiber stripping machine. There were also the different mechanical properties between the ramie fiber layer and the woody part. Firstly, some measurements were performed on the physical dimensions and mechanical property parameters of "Chuanzhu No. 11" ramie stalks. Then, the technical solution of a double clamping mechanism was proposed with the synchronous belt clamping and conveying, motor-driven clamping mechanism flipping and changing position, and double-drum reverse stripping. The ramie stalks were fed directly, and then stripped at the base and tip of the ramie stalks in turn by the changing position of the clamps. The toothed rubber clamping plate was used to hold the stalks. The grooves and projections of the toothed rubber plate were firmly held to prevent the stalks crushed by the clamps and slipping out. The operation of the ramie stripping machine was divided into four steps:the straw feeding, base stripping, tip stripping, and collecting ramie skin. The key components mainly included the transposition clamping, lateral feeding, and ramie stripping device. The mechanical analysis of double-drum ramie stalk stripping showed that the stripping force was closely related to the drum speed. A mechanical test was carried out to investigate the relationship between the stalk feeding angle and stripping force. The results showed that the stalk feeding angle and stripping force shared a highly significant negative linear correlation. The structural design and theoretical analysis were performed on the main components in the ramie stripping device and clamping mechanism. After that, the structure and motion parameters of the ramie stripping machine were determined, including drum speed, reverse-pulling speed, and feeding angle. Furthermore, a single-factor simulation model was established using ANSYS/LS-DYNA to simulate the process of stripping and the amount of xylem removal, the loss of the bast fiber layer, and the force of the feeding direction. Previously, the ramie stalk actual stripping process was analyzed and a simulation model was developed. The structure of the ramie stalk was also analyzed during this time. The optimal ranges of parameters were achieved for a better stripping effectiveness:the roller speed of 350-650 r/min, the reverse-pulling speed of 0.2-0.4 m/s, and the feeding angle of 5°-15°. A three-factor and three-level orthogonal test was conducted, according to the Box-Behnken method. The results showed that the drum speed, reverse-pulling speed, and feeding angle posed the significant effects on the fiber percentage of fresh stalk, and the impurity rate of raw fiber using ANOVA and response surface analysis. In addition, a significant coupling effect was found in the interaction of drum speed and reverse-pulling speed, as well as each experimental factor, but there was no a simple linear relationship. The optimal operating parameters were obtained for the ramie stripping machine with the reverse-pulling clamping:the stripping drum speed of 450 r/min, the reverse-pulling speed of 0.32 m/s, and the feeding angle of 11°. Finally, the validation test of the ramie stripping machine prototype was carried out using the optimized parameters. A better performance was achieved in an average fresh stem fiber yield of 5.03% and an average impurity rate of 1.14% of raw ramie, fully meeting the national technical standards of the ramie stripping machine. The transposition clamping device can be expected to realize the ramie clamping and feeding, as well as the automatic reverse pulling. The simple and optimal structure of the ramie stripping machine was had improved the performance and quality of ramie stripping. The finding can provide a technical reference for the development of an automatic lightweight ramie stripping machine.
Abstract: A helicopter is widely used in forestry disease and pest control. An application tank of helicopter is taken as a loading container of the liquid medicine. It is very necessary for the reasonable anti-shaking structure inside the helicopter medicine tank for the aviation operation stability and energy consumption. In this study, the structural design was optimized to place an anti-shaking grid structure in the inner chamber of the tank, in order to reduce the stability of the helicopter that caused by the shaking of the liquid during operation. Numerical simulations were carried out on the Fluent's Volume of Fluid (VOF) with the Realizable turbulence models. Evaluation indicators were selected as the variation of the free liquid surface waveform and the pressure magnitude at the internal reference point for the variable speed excitation of the pillbox. The maximum flow velocity of liquid was then determined to simulate the liquid sloshing in the empty tank along the excitation direction. The position of the damping grid structure was also determined, according to the formula of energy dissipation of liquid sloshing around the flow resistance. The simulation results show that the maximum pressure at the reference point increased with the increase of the height of the grid. But the time to reach the maximum pressure was similar. Specifically, the liquid slosh frequency was lower at the grid height of 100mm. The pressure value was smaller at the reference point with the grids number of 9, and then tended to be relatively stable, as the number of grids increased gradually. A medicine tank shaking test bench was constructed to simulate the flight conditions of helicopter operation, in order to verify the anti-shaking effect. The test results showed that the greater the acceleration was, the greater the maximum impact force on the inner wall of the powder cabinet was, and the earlier the maximum impact force time was. The greater the liquid filling rate was, the greater the maximum impact force on the inner wall of the cabinet was. The maximum pressure increased by 27.7% at the liquid filling rate of 0.8, compared with the liquid filling rate of 0.6. There was the consistent shape trend of the free liquid surface under different liquid filling rates. But the time of violent shaking was advanced with the increase of liquid filling rate. At the same time, the tank with the higher liquid filling rate was not susceptible to the secondary impact of the liquid after excitation. Furthermore, the time decreased for the liquid level to stabilize with the gradual increase of the forward tilt angle of the medicine tank under different working conditions. Once the forward tilt angle of the medicine tank changed from 0° to 10°, the time decreased by 44.6% for the liquid level to stabilize. It was the much longer to stabilize, when the medicine tank was tilted, the side of which the lower liquid level was wobbled more violently. A vertical damping grid structure was obtained with a height of 100mm and a number of 9 grids after optimization of numerical simulation. A comparison of the simulation and test showed that the anti-shaking damping grid structure was effectively reduce the slosh amplitude of the liquid inside the cabinet after excitation. The time was reduced by 54.8% than before from the beginning of sloshing to the liquid level of the empty tank, indicating the better inhibition effect. The experimental design and the reasonable grid structure can provide a strong reference for the subsequent research on the anti-sloshing structure inside the tank of a helicopter.
Abstract: This study aims to explore the heat transfer characteristics of flow boiling in the minichannels under the action of phase separation structure. A test section of parallel counterflow minichannel was also fabricated with the different structures of phase separation. Furthermore, the pressure difference between the downstream and counterflow channel confined the bubbles to discharge the gas phase from the high- to the low-pressure channel through the phase separation film. The gas phase separation was realized under the high- and low-pressure switching between adjacent channels. Two kinds of structure channels were fabricated:Type 1 phase separation structure channel (SPS1 channel) (Structure of Phase Separation, SPS) with few vents, and type 2 phase separation structure channel (SPS2 channel) with multiple vents, compared with the SPS3 channel without phase separation structure. The aqueous glycerol solution with a mass fraction of 30% was used as the test working medium. The flow boiling test was performed on the rectangular minichannel with a cross-section of 2 mm×2 mm under the effective heat flux density is 151.43 kW/m2, the mass flow rate of 121.25 kg/(m2·s), and inlet temperature of 70℃. A systematic investigation was made to clarify the effects of high- and low-pressure switching cycles on the comprehensive performance and phase separation structures on the flow boiling heat transfer and temperature uniformity in minichannels. A high-speed camera was used to determine the length-to-diameter ratio of confined bubbles and the gas phase separation. An analysis was made to explore the heat transfer enhancement of the minichannel flow boiling under the action of the phase separation structure. The results show that the local saturated boiling heat transfer coefficient was the highest, and the total pressure drop was the lowest when the high- and low-pressure switching cycle was 120 s under the experimental conditions. An optimal value was achieved in the high- and low-pressure switching cycle. There was little difference in the boiling curve before the ONB point, while after the ONB point, the wall superheat of SPS2 and SPS3 channels was lower at the same heat flux. The maximum coefficients of local saturation boiling heat transfer in the SPS2 and SPS3 channels increased by 18.87% and 26.65%, respectively, compared with the SPS3. More importantly, the temperature uniformity of the SPS2 channel was the best in the two-phase region, SPS1 was the second, and SPS3 was the worst. The wall temperature standard deviations were reduced by 10.81% and 18.91%, respectively, along the SPS1 and SPS2 channels. The visual analysis results show that the phase separation structure reduced the length-to-diameter ratio of the confined bubbles, leading to the flow pattern transformation in the channel. Enhanced heat transfer was achieved in the first half cycle of the high- and low-pressure switching cycle. The length-to-diameter ratios of confined bubbles in the SPS1, SPS2, and SPS3 downstream channels were-119%, -157%, and 122% in the unit time, respectively. The phase separation structure can be expected to effectively enhance the heat transfer performance of flow boiling, and then improve the temperature uniformity of minichannels. The finding can provide new ideas for the application of the phase separation structure in minichannel heat exchangers.annel heat exchangers.
Abstract: Hydro-mechanical transmission (HMT) is one type of mechanical-hydraulic stepless transmission. There is a better tradeoff between the stepless speed regulation of hydraulic and efficient speed change of mechanical transmission. Clutch control is closely related to the appropriate timing of engagement and separation, due to the great influence of disturbance on the quality of the shifting process. It is necessary to clarify the shifting clutch for the higher quality of HMT during shifting. However, a strong nonlinear system is coupled with the HMT under modeling error and external load disturbance. In this study, the shifting clutch pressure control was proposed using disturbance feedforward compensation. The dynamical model of shifting and the mathematical model of the clutch in the sliding were also established using the composition and working principle of HMT. The optimal linear-quadratic model was achieved, where the jerk, sliding power, and shifting time were taken as the evaluation indexes during shifting, while the performance index of the quadratic function was the state control variable. The total disturbance during shifting was also estimated to rapidly respond to the disturbance using the first-order disturbance observer. The compensation gain of disturbance was introduced into the feedforward term of the controller, in order to realize the disturbance feedforward compensation. After that, the feedforward compensation gain was obtained, according to the disturbance estimate $\hat d $ and compensation coefficient