MODELING THE SOIL-TOOL-ROOT OR -STEM INTERACTION WITH COUPLED DISCRETE ELEMENT AND MASS-SPRING METHODS László Pásthy and Kornél Tamás Department of Machine and Product Design, Faculty of Mechanical Engineering, Budapest University of Technology and Economics, Műegyetem rkp. 3., H-1111 Budapest, Hungary E-mail: pasthy.laszlo@gt3.bme.hu, tamas.kornel@gt3.bme.hu ABSTRACT In the course of this research, a so-called mass-spring method was implemented in an in-house developed two- dimensional discrete element software, which enables the simulation of deformable, tear-able bodies, such as plant residues (stems or roots), or other agricultural fibrous materials. The operation of the numerical methods was illustrated with simulations where a rigid plate was moved horizontally against a plant residue modeled by the mass-spring method, pulled in an assembly of particles modeled by the discrete element method, and pulled in a combination of these. When evaluating the results, it was found that the improved numerical methods are able to work stable both separately and in interaction with each other, thus in the future it is possible to take plant residues as stems and roots into account during the simulations of the tillage process with their coupled application. INTRODUCTION The behaviour of granular materials can be effectively simulated with the discrete element method (DEM) (Cundall and Strack 1979), which has been used not only by researchers but also by engineers in the last decade. In the main steps of the method the reaction forces are calculated in the contacts between the rigid particles, and then the acceleration vector, velocity vector and the position of the partciles are calculated. Thus, processes based on the behaviour of particles such as tillage, mixing of granules and powders can be modeled with computer simulations. However, since during these simulations the solid bodies in contact with the particles are taken into account as rigid, the applicability of the method is limited by the magnitude of the force acting on the solid bodies. When these contact forces cause a significant deformation in the solid body, which already affects the movement of the particles, the discrete element method simulation alone is not sufficient, another calculation procedure is required to model the deformation of the solid body, which can run parallel with the discrete element method. Such simulations, which use several numerical methods, are called coupled simulations, the development of which is currently an intensively researched area. A possible method for calculating the deformation of solid bodies is the so called mass-spring method, which models the solid body with mass points, springs and dampings. The method is primarily used to simulate the movement of two-dimensional surfaces. The LapSim software (Woodrum et al. 2006), for example, is a medical simulation program that models the movement of different tissues using the mass-spring method. The procedure is also used in software modelling clothing and textile (Gräff et al. 2004, Rony et al. 2007) and graphic- animation software (Derakhshani 2013). In addition to modeling two-dimensional surfaces, József Sebestyén extended the method to three-dimensional bodies in his master’s thesis (Sebestyén 2018), thus the deformation of 3 dimensional objects can also be modeled with the developed procedure. The advantage of the method is that even real-time simulations are possible due to the low computational requirements. Another advantage of the mass-spring method is the easy understanding and application compared to other numerical methods. One possible area of application of the mass-spring method can be the modeling of plant residues (stems or roots) left inside and on the surface of the soil as deformable bodies that can even tear. Although there was no reported example of the use of the mass-spring method for the modeling of stems or roots in the literature, the consideration of stems and roots in tillage simulations is increasingly of concern to researchers these days. In previous research, plant residues were mostly modelled with rigid spheres (Mao et al. 2020, Wang et al. 2020), multiple cylinders that are rigidly connected (Zeng et al. 2020), hinged spheres and cylinder elements (Guo et al. 2018) or deformable elements made up of rigid cylindrical elements (Bourrier et al. 2013, Tamás and Bernon 2021). These elements however were not capable of tearing or were able to tear only at the connection of the rigid cylinder elements. The mass- spring method, on the other hand, allows the deformation of all parts of the modeled body and the tear can occur in more places than in the case of the stem or root models used so far. The aim of this research was to develop a coupled numerical method that enables the modeling of the interaction between granular materials and deformable bodies, as well as the modeling of the tear of deformable bodies using coupled discrete element method and mass- spring method. Furthermore an other aim was to to implement the procedure in a self-developed two- dimensional software, as well as to illustrate its functionality with soil tillage modeling simulations where a deformable plant residue, a rigid tool and a soil as a granular material are taken into account. Communications of the ECMS, Volume 37, Issue 1, Proceedings, ©ECMS Enrico Vicario, Romeo Bandinelli, Virginia Fani, Michele Mastroianni (Editors) 2023 ISBN: 978-3-937436-80-7/978-3-937436-79-1 (CD) ISSN 2522-2414