BACKGROUND: The discrete element method (DEM) shows promise for modeling soil tillage and developing digital twins of tillage and seeding machinery. However, prediction accuracy of energy and agrotechnical indicators depends on the selected particle contact model and matching the model parameters to real soil properties. AIM: Calibration of strength parameters of the contact model for DEM simulation of soil tillage processes. METHODS: To calibrate the parameters of the Hertz-Mindlin contact model enhanced with the Johnson–Kendall–Roberts (JKR) model to consider soil particle cohesion, comparison of shear test results of soil samples with various physico-mechanical properties against corresponding DEM simulations is proposed. The PSG-3M shear testing device was used to determine soil strength and frictional characteristics under various normal stresses. RESULTS: For peat-meadow, dark gray medium loamy, and chernozem heavy loamy soils, the contact model parameters were established as: surface energy 200–250 J/m², Young’s modulus 1.4 MPa, Poisson’s ratio 0.33, static friction coefficient 0.9, and dynamic friction coefficient 0.35. These parameters were experimentally validated and can be applied to simulate various soil conditions. CONCLUSION: The justified contact model enables creation of digital model of soil channels in the Rocky DEM software, facilitating virtual testing of tillage tools. Using this calibrated model makes optimization of tool designs at the digital design stage possible, reducing costs associated with expensive field tests.

Introduction. In modern sowing complexes, the process of transporting and distributing seeds and fertilizers is carried out using an air stream. When simulating the technological processes of these pneumatic systems using computational fluid dynamics and discrete elements, an important step is determining the parameters of the interphase interaction of two-phase air – seed and air – fertilizer flows. Both the possibility of implementing models with computational methods and the complexity of the models used depend on the intensity of interphase interaction.Aim of the Study. The aim is to estimate experimentally the parameters of two-phase flows in the pneumatic system of a sowing complex, where an air stream is used as the carrier phase and a mixture of solid particles of fertilizer granules is used as the dispersed phase.Materials and Methods. The study was conducted using experimental methods. There were used high-speed video shooting, a sail classifier and digital anemometers to analyze air flow and particle motion parameters. The study methodology included the determination of the moisture content of materials, the particle soaring velocity, the volume concentration of phases, and the calculation of hydrodynamic characteristics in various parts of the pneumatic system. Modern approaches to the analysis of two-phase flows were applied taking into account the interaction between the particles and walls of transport channels.Results. The experiments have detected significant differences in flow parameters between horizontal and vertical sections of the pneumatic system. There have been identified the dependence of the aerodynamic characteristics of the particles on their physicalmechanical properties. There was a significant change in the volume concentration of the dispersed phase along the length of the transport pneumatic pipeline of the sowing complex that indicates a transition between different flow modes. The particle drag coefficients showed a clear correlation with the similarity criteria characteristic of the interregion of the Rayleigh curve.Discussion and Conclusion. The conducted studies allowed us to develop a methodology for estimating the parameters of two-phase flows in pneumatic systems and identify key factors affecting the efficiency of transporting and distributing seeds and fertilizers. The results of the study are of practical importance for improving the designs of sowing equipment and developing digital twins of technological processes. Based on the conducted analysis, there have been proposed the topics for further studies including the development of complex CFD-DEM models, which take into account the real operating conditions of pneumatic systems. The work contributes to solving the urgent problem of increasing the seed distribution uniformity in modern tillage complexes.

Introduction. In the context of developing energy-saving technologies and machines based on digital twins, the use of the discrete element method for modeling the technological process of sowing is the most in-demand area. The key advantage of DEM modeling is the ability to minimize the cost of creating new technology through virtual testing and optimization. The quality of the sowing machines is known to directly affect the uniformity of sowing and, ultimately, the yield. Therefore, the creation of adequate digital twins taking into account the physical and mechanical properties of real seeds is an important scientific and practical task. To model the process of sowing peas, it is necessary to solve two main tasks: to select an adequate contact model and calibrate its parameters that is the main aim of this work.Aim of the Study. The study is aimed at determining the parameters of the contact model of a digital twin of pea seeds for modeling using the discrete element method.Materials and Methods. The object of the study is the calibration of the parameters of the Linear Spring Dashpot contact model applied to pea seeds. The stages of the study include: identifying the limitations of calibration methods when modeling seed movement; determining the effect of moisture content and fractional composition of pea seeds on friction coefficients; developing a method for calibrating the contact model taking into account force impact in conditions close to the sowing machine operation; verifying models by comparing DEM modeling with data from field experiments in a coil apparatus. Results. There has been determined the fractional composition of pea seeds showing pronounced polydispersity of the material. The dominant fraction (83.4%) has a diameter of 6.0–7.0 mm, which has been taken into account when parameterizing the DEM model in the Rocky DEM software package to create a representative digital twin. The significant influence of seed moisture content on their friction properties has been experimentally proven. With an increase in moisture content from 9% to 23%, the coefficient of dynamic friction increases that leads to a regular increase in the torque on the sowing machine shaft from 0.3 to 1.0 N·m. There has been has been developed and tested a comprehensive calibration method using the torque on the shaft of the sowing machine as a compliance criterion. There has been defined the range of the main parameters of the Linear spring dashpot contact model, ensuring high modeling accuracy: the coefficient of dynamic friction between seeds kd = 0.14...0.16; the coefficient of dynamic friction of seeds with the walls of the device kd.k = 0.07...0.09. Based on the results of the experiments, there has been developed a nomogram for selecting the dynamic friction coefficient depending on the moisture content of pea seeds. Conclusion. The use of the proposed calibration method based on torque allows the creation of high-precision digital twins suitable for optimizing the design and technological parameters of sowing machines that contributes to improving the quality of sowing and saving resources in agricultural production.

This article examines the pressing issue of verifying contact models in the discrete element method (DEM) for modeling soil tillage processes. Due to the lack of a generally accepted methodology for selecting contact models for various soil types, a comprehensive study was conducted combining field experiments and numerical modeling. A verification method was developed and tested based on comparing experimental data on the draft resistance of a plow body with the results of calculations in the Rocky DEM 4.4 software package. The study yielded reliable experimental values for the draft resistance components and established the ranges of variation for their parameters. A comparative analysis of 10 promising combinations of contact models identified in previous studies was conducted. It was found that the improved Hertz-Mindlin model with the JKR adhesion model provides the best fit to the experimental results. Particular attention is paid to analyzing the influence of surface energy in the JKR model on changes in the rheological properties of the soil medium, which opens up the possibility of predicting soil behavior at different moisture levels. The results of the work are of practical value for the design and optimization of agricultural implements at the stage of their numerical modeling. The accuracy of predicting the draft resistance of the plow body during modeling for the studied soils at a moisture content of 18–25% ranged from 80 to 95%.