| The quality of arable land is an important guarantee to promote food production capacity and achieve sustainable development.As the drawbacks of traditional farming techniques gradually emerge,conservation tillage is receiving more and more attention.Mechanical subsoiling is an important part of conservation tillage technology.Subsoiling can break the bottom layer of the plow and eliminate the compaction effect.It can improve soil permeability so that water and fertilizer can penetrate more downward and increase crop nutrient absorption,and ultimately improve crop yield.However,there are still some problems in subsoiling technology,such as large tillage resistance,large energy consumption and unsatisfactory subsoiling effect.Moreover,the same structure of subsoiling shovel will have a large change in working effect under different working environments.Purple soil is the main type of cultivated soil in southwest China.It is rich in mineral nutrients and have high fertility,which makes it valuable for agricultural use.Purple soil is clayey soil that tend to reunite,bond,and harden under the addition of the humid climate in southwest China.In the computer-aided design of subsoiling shovel,it is necessary to have a purple soil model that conforms to the actual purple soil in order to accurately design and optimize the subsoiling shovel.Based on the above,this paper took the winged subsoiling shovel and the typical purple soil in southwest China as the research object,designed a part of soil parameter determination test independently and established the discrete element model of purple soil in southwest China by combining the experimental design method.Then the method of obtaining subsoiling effect parameters was explored and optimized in EDEM software.The winged subsoiling shovel was designed,optimized and verified by using purple soil discrete element model in the simulation environment.Then the Janssen approximate stress analysis method was used to improve the existing soil tank of the indoor test platform and the winged subsoiling shovel with the best parameter group was manufactured and verified in the indoor test platform.The main research contents and conclusions are as follows:(1)The parameter calibration of discrete element model for purple soil.The intrinsic parameters and contact parameters of purple soil were determined by self-designed experiments,and the repose angle was used as an index to evaluate the similarity between simulated soil and actual soil.The purple soil used in the experiment was loamy sandy soil,in which coarse gravel accounts for 25.85%,sand accounts for 73.24%,and silt and clay account for 0.91%.The soil density was 1650kg/m~3 and the water content was10.54%.The average repose angle of soil was 34.11°.Particle-particle static friction coefficient ranged from 0.5 to 1 and particle-45 steel from 0.7 to 1.2.Using EDEM simulation software,a mathematical model was established with nine parameters as factors and repose angle as evaluation index.The parameter group of the simulated soil model with the highest similarity to the actual soil was obtained as follows:the particle surface energy was 0.134J/m~2,the particle-particle rolling friction coefficient was 0.231,the static friction coefficient of particle-45 steel was 1.045,the rolling friction coefficient of particle-45 steel was 0.228,the particle Poisson’s ratio was 0.33,the particle shear modulus was 5×10~7Pa,the particle-particle static friction coefficient was 0.75,the particle-particle recovery coefficient was 0.3,and the particle-45 steel recovery coefficient was also 0.3.The soil model under this parameter group was simulated and verified.The average repose angle was 34.8159°and the relative error between the simulated repose angle and the actual was 2.07%.(2)The design and simulation optimization of the winged subsoiling shovel.The method of obtaining subsoiling effect parameters was explored and optimized in EDEM software.The horizontal resistance of subsoiling shovel was defined as the average resistance when traveling to 1.0-1.7s.The soil disturbance section area was defined as the graphic area surrounded by disturbed particles on the section 200mm away from the center of the subsoiling shovel when the subsoiling shovel traveled to 1.2s.Taking the installation height,installation angle and upward angle of subsoiling shovel wings as optimized parameters and tillage efficiency as evaluation index,a mathematical model was obtained by experimental design.The best parameter group of shovel wing with maximum tillage efficiency was obtained as follows:the installation height was 160mm,the installation angle was 18.433°,and the upward angle was 51.455°.The maximum tillage efficiency predicted by the model was 122.881mm~2/N.Verified in the simulation environment,the tillage efficiency was 120.090 mm~2/N,with a relative error of 2.3%from the tillage efficiency predicted by the model.After optimization,the tillage efficiency of the subsoiling shovel with the best parameter group increased by 20.866%.(3)The design of soil bin and test of subsoiling performance.Improvements were made to the previous generation of soil bin.The wall of the new soil bin was made of transparent acrylic material,and the equation of the compressive stress of the soil in the bin on the wall was obtained by using Rankine stress coefficient and Janssen approximate stress analysis method.Using purple soil samples and self-made purple soil-acrylic samples for direct shear test,the internal friction coefficient and the friction coefficient of soil-acrylic required in the equation were obtained.The coefficient of internal friction of the purple soil for the test was measured to be 0.364,and the coefficient of friction with the acrylic plate was 0.177,thus the equation for the variation of compressive stress with the soil depth was obtained.Using the finite element method to calibrated and optimized the wall of the soil bin.The long side walls required 9 sets of bolts and nuts to fix,the maximum stress appeared at the bolt hole in the middle of the plate at 48.249 MPa and the maximum displacement appeared in the middle of the plate at 1.819 mm.Only two sets of bolts and nuts were needed on the short side wall.The maximum stress appeared at the bolt hole at the upper end of the plate,which was 41.161MPa,and the maximum displacement appeared in the middle of the plate,which was 2.225 mm.After the installation of the improved soil bin,the tillage efficiency of the winged subsoiling shovel was verified in the indoor soil bin test platform.The tillage efficiency of the three actual verification tests were 108.506 mm~2/N,110.179 mm~2/N and 115.071mm~2/N,respectively.The relative errors between the actual and simulated values were 9.65%,8.25%and 4.18%,respectively,with an average relative error of 7.36%.The average relative error between the actual and the theoretical value was 9.46%. |
