Experimental calibration of parameters of the contact model of the digital twin of the soil environment by the method of discrete elements

Currently, the discrete element method (DEM) is considered one of the promising methods for simulating the processes of tillage and sowing by working bodies of agricultural implements. Calibration of the parameters of the contact model used is an important step in discrete element simulation to obtain adequate results. To calibrate the parameters of the Hertz-Mindlin JKR contact model used we used the Hertz contact model to describe normal forces, the Mindlin-Deresevich model for tangential forces, and the Johnson-Kendall-Roberts (JKR) model for forces accounting for soil particle adhesion. Calibration is used by comparing the results of physical tests to determine penetration forces. The PSG-MG4 static penetrometer and similar model tests implemented by an identical device in the Rocky DEM software package. The results of calibration of the parameters of the MDE contact model of the soil environment showed that of the selected parameters (Poisson's ratio 0,3, static friction coefficient 0,9, dynamic friction coefficient 0,7, particle diameter 5 mm, Young's modulus 100 MPa), the nature of the change in the penetration force of the simulated soil environment is significantly influenced by surface energy. Based on a comparison of the results of field and model experiments, a nomogram has been developed for selecting the value of the surface energy of the simulated soil environment depending on the humidity of the real soil for the Hertz-Mindlin JKR contact model for lightloamy mechanical chernozem. The calibration results for surface energy from 120 to 160 J/m2 correspond to optimal soil moisture in the range from 14% to 25%.The results obtained should be used in modeling the technological process of tillage and the development of digital counterparts of tillage and sowing machines based on them to predict energy and agrotechnical indicators. Based on the results of the conducted research, it is planned in the future to create a digital twin of the soil channel with calibration of the physicomechanical properties of various types of soil.