Modeling Method For Wheat Grains And Plants In The Mature Period And Simulation Analysis And Experimental Study Of Cutting And Threshing Process

Wheat is one of the most important grain crops in China.,and its stable production and harvesting is of great significance to guarantee food security and economic stability.Mechanized wheat harvesting was currently the most important way and means in the wheat production process.Traditional approaches to design and analysis rely on time-consuming and costly experimental methods,leading to extended design cycles.Utilizing digital design and numerical simulation methods for studying the wheat harvesting process enables a more in-depth investigation of the operation mechanism,reducing design costs and shortening optimization cycles.Therefore,this paper combined domestic and foreign wheat grain and plant modeling methods and harvesting process simulation and analysis of the current situation,based on the determination of the physical and mechanical characteristics of the wheat grain and plant parameters,put forward a feasible and common grain and plant modeling method,accurately established the wheat grain and plant model,and used a combination of experimental and simulation methods to verify the feasibility and accuracy of the grain model and plant model,systematically investigated the wheat plant harvesting operation mechanism,effectively reduced the design cost,and shortened the design and optimization cycle of the harvesting equipment.The feasibility and accuracy of the grain model and plant model were verified using a combination of experimental and simulation methods,and the harvesting process and threshing process of wheat plants were systematically analyzed by experiments and simulations.These researches and analyses provided scientific references for the design and optimization of key components of harvesting machines.The main contents and conclusions of this paper are as follows:(1)Measurement and analysis of shape and size and physical-mechanical properties of wheat grains and plantsOn the basis of analyzing the geometry of wheat grain,the basic modeling concept of approximating the shape of wheat grain as ellipsoid and double ellipsoid was proposed.Through analyzing shape error,mass error,and moment of inertia error,the double ellipsoid was found to be closer to the actual wheat grain.Regarding wheat plant geometry and size analysis,we simplified the wheat plant into wheat ears and straws.The spike comprises the rachis and 15 to 22 spikelets,staggered on both sides of the rachis.Each spikelet contains 1 to 4 grains and glumes.The stalk consists of 4-6 hollow internodes,varying in length,outer diameter,and wall thickness.Water content,stiffness coefficient,modulus of elasticity,friction coefficient,and collision recovery coefficient of the wheat grain and plant were measured and calibrated using appropriate test equipment and methods.(2)General modeling method and experimental validation for wheat grainFor the first time,a double ellipsoid modeling method was proposed,and four wheat varieties were selected as the research objects based on the length-to-thickness ratio.The double ellipsoid combined sphere model,single ellipsoid combined sphere particle model,and single ellipsoid equation model were established for the four wheat varieties,respectively.Static stacking angle,’self-flow screening,’ and dynamic stacking angle tests,along with simulation tests,were conducted.Comprehensive analysis of the errors between the simulation results and the real test results of the double ellipsoid combined sphere model,the single ellipsoid combined sphere model,and the single ellipsoid equation model was performed under various motion states.The results indicated that the overall simulation results of the double ellipsoid particle model were closer to the real test values,demonstrating higher model accuracy and better applicability than the single ellipsoid particle model.The surface roughness of the combined sphere model closely resembled that of real wheat grain compared to the single ellipsoid model.(3)General modeling method and experimental validation for wheat plantsThe geometrical model of the plant was constructed by selecting key characteristic parameters,and the coordinates of the constituent sphere arrangement were determined.The Hertz-Mindlin model served as the contact model between particles,and the parallel bonding model(PBM)was employed as the bonding model between plant organs and their constituent spheres.Using geometric and mechanical models,a flexible wheat plant model based on discrete elements method was established.The modeling method was universal,enabling the establishment of plant models for different wheat varieties by inputting the corresponding parameters.Comparison of plant stacking,grain vibration separation,and impact threshing tests on wheat plants with simulation results showed that the geometric and mass accuracy of the wheat plant population model was relatively precise.Ignoring minor parts such as wheat awns,leaves,and leaf sheaths had a negligible effect on geometric and mass parameters.Additionally,the mechanical parameter measurements used in this paper to obtain contact and adhesion mechanical parameters were accurate and could be directly applied in the discrete element simulation of the wheat plant model.(4)Experimental study and simulation analysis of the cuttinging process of wheat plantsBased on discrete element simulation of the wheat cuttinging process,two wheat straw models were constructed.The geometric modeling method of the annular stalk model and the calculation method of the constituent spherical particle coordinates and bonding mechanical parameters were elaborated in detail.Cutting tests and simulations were carried out under quasistatic conditions,and the results showed that the peak cutting force of the linear particle model was closer to the actual value,while the cutting force and displacement curves of the annular particle model closely matched the actual test results.The effects of various moisture content,stalk outer diameter,and cutting speed on the peak cutting force were determined by establishing a single stalk pendulum cutting test setup.The quasistatic parameter simulations revealed larger errors in annular stalk particles at different speeds compared to the linear stalk particle model.Furthermore,two parameter calibration methods for dynamic cutting were proposed.The reciprocating cutter table,kinematic ally analyzed for its mechanism,was independently developed to ascertain the changes in displacement,velocity,and acceleration over time.A singlefactor test explored the influence of operational parameters—cutting speed,feeding speed,and cutting height—on the peak cutting force.Cutting operation quality under different cutting speed ratios was assessed using a high-speed camera.Through the joint simulation of the wheat plant harvesting process based on DEM-MBD verified the feasibility of the two calibration methods.It was found to be more accurate and feasible to use the intermediate value of the effective cutting speed corresponding to the calibration value of the bonding radius multiplier for simulating the harvesting process.Subsequently,the orthogonal test optimized structural and operating parameters,yielding a maximum cutting speed of 1.91 m/s,a cutting speed ratio of 1.05,and a slip angle of 33.82°.The predicted value of the peak cutting force was 9.88 N,the leakage rate was2.39%,and the operating efficiency was 727 plants/min.(5)Experiment and simulation analysis of threshing process of wheat plantsThe tangential flow ripple drum threshing device was constructed,and its threshing mechanism was analyzed.The threshing effect and plant status in the threshing area at different time periods,under various structures and operating parameters,were analyzed using a high-speed camera.The quality distribution of grains and impurities was also statistically examined.Test results indicated that feeding quantity had no significant impact on the overall grain loss rate,while a moderate increase reduced impurity content.Drum speed increase reduced loss rate,but excessive speed raised trash rate.Expanding the threshing gap increased both loss rate and trash rate.Simulation analysis of the threshing process revealed that simplifying the glume area in the wheat plant model increased the direct impact load on the grain,resulting in the center of mass distribution of the grain being closer to the inlet than in actual tests.Neglecting glume and blade parts in the wheat plant model led to a lower impurity rate of the rejects in the simulation compared to actual test results.Additionally,high relative motion speed between the threshing drum ribs and the plant,coupled with the use of mechanical parameters measured under quasi-static conditions for threshing simulation,made the bonding bond between the grain and the spike shaft more prone to fracture under dynamic impact loading.This affected the mass distribution of grains in the threshed material.To enhance the accuracy of the threshing simulation results in describing the real operation process,bond strength between grains and spike shafts at different rotational speeds was calibrated through a single-factor test,yielding optimal correction coefficients for bond strength at different rotational speeds.