In order to further clarify and improve the working performance of separating cleaning device of flax threshing material, and study the motion law and characteristics of components of flax threshing material, in this paper, numerical simulation was carried out on the separating cleaning process of flax threshing material based on CFD-DEM method. Simulation results showed that the components of flax threshing material were separated and cleaned under the influence of airflow field, meanwhile, variation curves of quantity and mean velocity of flax seeds in the separating cleaning system were obtained. By referring to streamline distribution of gas-solid coupling, the quantity variation law of components of flax threshing material with time was explored and their motion curves and variation tendency of average velocity were studied. Verification test results showed that the cleaning rate of separating cleaning device for flax threshing material was 92.66% with 1.58% of total separation loss. Compared with simulation results, the test results were 1.34% and 0.93% lower, showing that it is feasible to apply the gas-solid coupling theory and method to simulate the separating and cleaning operation of flax threshing material.
In order to realize seedbed mechanization of whole plastic-film mulching on double ridges and to overcome the difficulty in crosswise belt type soil covering by whole plastic-film, a kind of crosswise belt type whole plastic-film ridging-mulching corn seeder on double ridges was designed in this study. The key components of the sample machine was designed and its working parameters of seedbed soil covering device, crosswise-belt soil covering mechanism and profiling sowing depth adjustment device were determined. After numerical simulation on the film edge and crosswise soil covering by whole plastic-film on double ridges by discrete element method, the velocity and displacement of the oscillating plate, and the variation rule of amount of covered soil with time were explored. Field test results show that, when the advancing velocity of the machine was 0.50 m/s, the qualified rate of soil width covered on film edge of the seedbed reached 96.1%, qualified rate of crosswise soil belt width was 94.5%, qualified rate of soil thickness on seedbed was 95.3%, qualified rate of sowing depth was 89.3%, qualified rate of spacing between crosswise soil belts reached 93.6%, which all met related standards in China and satisfied design requirements, and could realize seedbed mechanization of whole plastic-film mulching on double ridges. Comparison tests on working performances of practical soil covering show a basic consistence with the seedbed soil covering simulation, and verified the effectiveness of the soil covering model built by using discrete element method.
Mechanization of field experiments is the only way to improve crop breeding and seed propagation effects. In order to further clarify and improve the working performance of tapered threshing device for plot breeding, and reduce the remaining seeds in the device, the numerical simulation was carried out on the motion process of materials in the longitudinal-axial tapered cylinder threshing and transmission device of the plot wheat breeding combine harvester based on CFD-DEM method. Simulation results showed that, threshing and transmission of particles and short stalks at axial direction could be realized under the influence of air flow. Meanwhile, the material transference and distribution rule and stream field distribution rule of air flow in the threshing and transmission device were obtained, the variations of velocity and displacement of particles and short stalks with time were obtained; the motion trajectories and forms of particles in different types of retention were also studied. At rotating speed of 1300-1600 r/min for the tapered threshing cylinder in the verification test, the particle retention rate in the enclosure was 0-0.13%, while in the simulation the particle retention rate in the enclosure was 0-0.11%, only a 0.02% difference between them. The results proved a favorable feasibility to simulate the working performance of the tapered threshing and transmission device for plot breeding through gas-solid coupling method.
In order to achieve the construction standard of high mechanized performance of the seedbed with whole plastic-film mulching on double ridges, in this study, the forms of suppression failure were analyzed, and the key factors influencing the suppression performance were determined based on the structure of the seedbed suppression device and its working principles. The discrete element method was adopted for numerical simulation on the suppression process of the seedbed with whole plastic film mulching on double ridges; the parameters during the interaction between the suppression device and seedbed soil were extracted and analyzed, such as contact area, sinkage and horizontal traction resistance trend of press wheels on big ridges and furrows of small ridge. Taking the suppression load on big ridges, suppression load on furrows of small ridge, and advancing velocity of the combined operation machine as the independent variables, qualified rate of suppression as the response value, a mathematical model between the test factors and qualified rate of suppression was established, to explore the influence sequence of the factors on suppression qualified rate. The optimal working parameters of the suppression device were finally obtained: the suppression load on big ridges was 40 N, suppression load on furrows of small ridge was 69.8 N and the machine advancing velocity was 0.98 m/s, and the achieved mean value of suppression qualified rate was 92.6%. Field verification test showed that the mean value of suppression qualified rate was 90.3%, a mere difference of 2.3% compared with the simulation result. The actual operation of the sample machine was basically consistent with the simulation process and could reveal the mechanized suppression operation mechanism of the seedbed with whole plastic film mulching on double ridges, indicating that the established DEM model and its parameter setting were relatively accurate and reasonable.
The agronomic technology of whole plastic-film mulching on double ridges has been widely promoted in the arid region of northwest China, which has caused serious residual film pollution in the field. Mechanized residual plastic-film collecting is the main way, but this way of residual plastic-film collecting is more complicated. To prove the effect of typical film-lifting parts on residual plastic-film collecting performance by a numerical simulation method, further evaluate and select the working parts suitable for residual plastic-film collecting and improve the collecting efficiency, virtual whole plastic-film mulching on double ridges needs to be established. In this study, the film-lifting parts and the double ridge with flexible, deformable, mulching, film interaction model was developed using the discrete element method (DEM). The interaction model was used to simulate the operation process of a typical third-order shovel, hug plate and elastic teeth film-lifting parts. Furthermore, the operation resistance, seed bed disturbance and collecting residual film form under different working conditions were analyzed. The simulation results show that: the disturbance of the ridge from strong to weak is the third-order shovel, elastic teeth and hug plate film-lifting parts; the crushing of the ridge soil from strong to weak is the elastic teeth, the hug plate and the third-order shovel film-lifting parts; the collecting film from strong to weak is the hug plate, elastic teeth and the third-order shovel film-lifting parts; the median value of the horizontal force fluctuation range of the ridge soil on the film-lifting parts is increased, and the increase trend is from large to small in the third-order shovel, elastic teeth and hug plate film-lifting parts (the third-order shovel is 5250 N, 6250 N and 7750 N; the hug plate is 3250 N, 3500 N and 4000 N; and the elastic teeth are 4150 N, 4550 N and 5450 N). The comparative analysis results show that the hug plate film-lifting parts are more suitable for the residual-film collecting of whole plastic-film mulching on double ridges. Field trials were carried out to verify the operational effectiveness of the hug plate film-lifting parts. The results show that the morphological changes of the recovered residual film and the simulated mulching film during the operation of the hug plate-type residual film machine, and the distribution of the surface properties of the ridge after the residual-film collecting are basically consistent with the simulation results, and the film pick-up rate of hug plate film-lifting parts reaches 95.20%, and the established discrete element interaction model is reliable. The research results can provide reference for the research and development of full film duopoly furrow-mechanized residual film-collecting agricultural equipment in the arid region of northwest China.
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