Simulation Analysis And Experimental Study On The Interaction Of The Plug Seedling-Planter-Soil Based On Discrete Element Method

With the deepening of research on seedling raising and transplanting technology,the requirements of agricultural producers for planting quality have significantly increased.The field working environment is complex,and many parameters affect the interaction between the plug seedling and the transplanting mechanism.The functional relationship between the various targets and parameters is tricky,and there is a strong interaction between the parameters.In this thesis,the oil sunflower plug seedlings were taken as the research object,obtaining the change rules of pot damage and contact stress distribution through the free drop impact test of plug seedlings.The discrete element simulation parameters of the plug seedling-planter-soil interaction model were calibrated.Based on the deep integration of agricultural machinery and agronomy,high-speed photography,discrete element simulation,and experimental research were used to study the interaction between the plug seedling-planter-soil and the collision damage of plug seedlings during transplanting.The conclusions are as follows:（1）Through the free drop collision test of the plug seedlings,the effects of drop height,contact material,and different specifications of plug seedlings on the pot damage were obtained.A pressure distribution measurement system acquired the collision impact force of the oil sunflower seedling,and orthogonal experiments were conducted to establish a regression model for the plug specification,contact material,and drop height.It was obtained that the order of influence on the collision impact force is plug specification>drop height>contact material by significance analysis.（2）The change rule of the contact stress distribution of significant influencing factors under free-drop collision on pot damage.The collision contact area between the plug seedlings and contact materials from large to small was soil,steel,and ABS plastic.The collision contact area of the plug seedlings of different plug specifications was 50plug,72 plug,and 105 plug from the largest to the smallest.The average contact stress of the collision between the 105 specifications oil sunflower seedling collision and the steel plate was significantly higher than that of the 50 and 72 plug,and the average contact stress ranged from 18.1 to 22.9 k Pa.A linear regression model between the collision impact force and the matrix loss rate was established based on the pressure distribution measurement system’s pressure data.（3）A pressure distribution measurement system was used to conduct a free drop collision test on the entire plug seedling and pot.The relative error between the collision impact force of the plug seedling against the steel plate（soil）and the collision impact force of the pot against the steel plate（soil）was less than 15%.Therefore,the pot can be used to replace the entire plug seedling for drop collision test,which provides the basis for the next discrete element simulation.（4）The Hertz-Mindlin with bonding model was used to build a simulation model of the pot based on essential physical parameters.The significance parameters and optimal intervals affecting the collision impact force were determined using the Plcakett-Burman and steepest climbing tests.A Box-Benhken test was conducted on the significant parameters to establish a regression model between the collision impact force and simulation parameters.The optimal parameter combination was obtained through optimization analysis:the rolling friction coefficient between the pot and pot was 0.35,the bond stiffness was 0.53 MN·m^-3,and the bond radius was 1.97 mm.The relative error was 3.65%,which verified the model’s reliability.（5）A discrete element simulation model for the probe of a soil compactness meter was established to verify soil particles’adhesion parameters and determine the soil’s simulated adhesion parameters.A discrete element model was selected for the relationship between the pot and the soil based on the Hertz-Mindlin with JKR model.An orthogonal experiment with four factors and three levels was designed to establish a regression model between each element and the collision impact force.The optimal parameter combination was obtained through optimization analysis:the recovery coefficient between the pot and soil was 0.37,the static friction coefficient between the pot and soil was 0.84,the rolling friction coefficient between the pot and soil was 0.35,and the surface energy is 1.04 J/m².The relative error between the simulated collision impact force and the actual collision impact force was 0.38%,which verified the model’s reliability.（6）A discrete element model of the planter-soil interaction was established to simulate the hole drilling process and compared it with high-speed photography experiments.It was concluded that the disturbance range of soil particles in the horizontal and longitudinal sections gradually increases with the movement of the planter,and the velocity variation of soil particles at the contact interface between the horizontal and longitudinal sections in different regions presents a trend of first increasing,then decreasing,and finally tending to stabilize.Through analyzing the movement and variation rules of soil particles in different depths of soil layers in different directions during hole drilling,it was obtained that the velocity of soil particles in the shallow layer varies significantly in the X and Y directions,while the velocity of soil particles in the deep layer varies significantly in the Z direction（7）Taking the hole longitudinal length and hole depth as evaluation indicators,soil bin tests and discrete element simulations were conducted under different factors to obtain the variation rules of dynamic soil behaviour on the hole size under various factors.Through orthogonal experiments with three factors and three levels,a regression model was established between each element and the hole longitudinal length and hole depth,and the optimal parameter combination was obtained:the forward speed was 1.25 km/h,the planting depth was 80 mm,and the soil compaction was 140～150 N/cm².（8）A discrete element model of the interaction of the planter-soil-plug seedling was established to simulate the movement of plug seedlings during the transplanting.The movement rules of the plug seedlings during the transplanting and the movement rules of the soil of the contact interface during plug seedlings falling into the hole were obtained.Taking the pot damage rate as an index,the pot damage rate of transplanting process was studied from a microscopic perspective.It was revealed that during seedling grafting and loading,the collision between the plug seedling and the planter was particularly severe,and the pot damage rate reached 22.48%.During hole drilling and planting,the pot damage rate was 22.53%,which increased by 0.05%compared to the pot damage rate during seedling grafting and loading.When the duckbill leaves the soil in an open state,the pot damage rate was 22.75%,which increased by 0.27%compared to the pot damage rate during seedling grafting and loading.（9）The validity of the discrete element model of the interaction of the plug seedling-planter-soil was verified through a comparative analysis of physical tests and simulation simulations of the pot damage of the oil sunflower plug seedling with and without the planter in soil.Using soil compaction,seedling age,and plug specification as experimental factors and matrix loss rate as valuable indicators,a 3-factor and 3-level orthogonal test of plug seedling touchdown collision was designed.A regression model between each element and matrix loss rate was established.Based on the analysis of significance and interaction,it was found that the plug specification and seedling age significantly impacted the pot damage.（10）The distribution of contact stress and the variation rules of pot damage were proposed during the transplanting process.It was found that when the seedling age was fixed,the contact areas of different specifications of oil sunflower plug seedling ground contact from small to large was:105 plug,72 plug,and 50 plug.With the increase of seedling age,the contact area of the exact specification of the seedling gradually decreased.Based on the pressure data collected by the pressure distribution measurement system,a fitting equation between the collision impact force of the oil sunflower plug seedling and the matrix loss rate during the transplanting process was obtained,and the coefficient of determination（R²）was close to 1,indicating an excellent fitting effect.