This study sought to construct and empirically validate a discrete element method (DEM) particle model representing post-tillage soil blocks. This model was developed to facilitate a detailed examination of granular movement and contact mechanics during the shaping process of planting chambers for rape plants. The research specifically targeted the sticky, cohesive soil prevalent in rice paddy fields of the middle and lower Yangtze River region. Simulations were conducted using EDEM software to improve the accuracy with which soil-tool interactions are predicted for the design and optimization of mechanical transplanters. The physical and bonding parameters of the sticky soil were calibrated using the Hertz-Mindlin with Johnson-Kendall-Roberts (JKR) contact model and Hertz-Mindlin with Bonding contact model. A particle replacement method was adopted to create a discrete element model of cohesive soil aggregates with different shapes and sizes after rotary tillage. The accumulation angle of soil aggregates was used as the evaluation index in both the simulation and physical experiments. Design-Expert software was used to design a four-factor, three-level simulation experiment to identify the optimal parameter combinations for the physical and mechanical properties of the sticky soil and the JKR contact model, which comprised a soil-soil static friction coefficient of 0.32, soil-soil rolling friction coefficient of 0.10, soil-steel static friction coefficient of 0.51, and surface energy of soil for the JKR model of 5.50 J/m². Next, the steepest climbing test and Box-Behnken orthogonal combination test were then used to narrow down the range of values for the significant factors and identify the optimal parameter combinations for the bonding contact model parameters, which included a bonding bond normal contact stiffness of 2.1×10⁶ N/m, a bonding bond tangential contact stiffness of 2.2×10⁶ N/m, a normal ultimate stress of 0.55 MPa, a tangential ultimate stress of 0.55 MPa, and a bonding radius of 12 mm. Field experiments were conducted using a flat box device to measure the soil evenness and firmness after ridge formation and compaction by a rotary tiller. The results of these experiments were compared with the discrete element simulation optimization results. The relative errors between the field test results and the simulation test results for soil flatness and compaction were 10.7% and 9.8%, respectively, which indicated good accuracy of the parameters calibrated and optimized by EDEM discrete element simulation software. Overall, this research can provide a reference for understanding the working mechanism and optimizing the parameters of soil touching components in rape transplanting equipment.

Blade groups have been limited to the violent vibration of the machine in the sticky and heavy consolidated soil of the oil tea plantation forest. In this study, the blade groups were designed with layered cutting and throwing ditching in the oil tea forest, in order to obtain better ditching with low power consumption. The control group was then set as the single outer cutter and a positively mounted throw blade. The interaction between soil and cutting blade was analyzed under the ditching environment and fertilization agronomic requirements of oil tea forests with the sticky and heavy consolidated soil. The kinetic differential equations were established for the relative slip of soil particles along the surface of the throwing blade. The motion behavior of soil particles was then determined using the kinetic analysis. The eccentricity coefficient was obtained as the key influencing factor on the performance of cutting and throwing in the blade group. The sliding angle was optimized at the maximum working radius r1, setting angle, and the blade axis rotational speed. The single factor and quadratic orthogonal rotational tests were carried out with the power consumption and stability coefficient of ditch depth as the evaluation indexes. EDEM-RecurDyn simulation was coupled to clarify the influence of the eccentricity coefficient, the sliding angle at the maximum working radius r1, the setting angle, and the blade axis rotational speed on each index. A second-order polynomial response surface model (RSM) was then constructed for the power consumption and stability coefficient of ditch depth. The cyclic approximation was also optimized using the NSGA-III. The optimal combination of parameters was determined: eccentricity coefficient of 1.3, the sliding angle at r1 of 64.7°, setting angle of 55.1°, and blade axis rotational speed of 301 r/min. The torque fluctuation tests were conducted with/without layered cutting and throwing. The torque fluctuation was reduced by 21.53 % for the blade groups with the layered cut and throw ditching, compared with the control group. A systematic investigation was made on the soil disturbance by the optimal parameter blade group during a single-layered cutting and throwing of the soil. The continuously alternate layered operation of layered cutting and throwing ditching blade group was used to break up and disturb the consolidated soil. The relative errors of power consumption and stability coefficient of ditch depth between simulation and field test were 10.25 % and 4.55 %, respectively, under the optimal parameter blade group. The mechanical properties of the simulated soil model were basically consistent with the actual suitable for the movement of soil particles. The accuracy of the coupled model was verified in the power consumption, where the simulated values were less than the measured in the field test. The residual roots and gravel were attributed to the variation in the actual furrowing environment. The power consumption and stability coefficient of ditch depth were 25.96 kW and 88.31 %, respectively, for the field tests. The specific power consumption of the layered cutting and throwing ditching blade group was reduced by 8.31% (0.298 kW·h/m³) for the optimal combination of parameters. The stability coefficient of ditch depth fully met the technical requirements of national standards. The finding can provide theoretical support and reference for the design and optimization of ditching blade groups in oil tea forests.