Discrete Element Modeling

            Recently particle based models gained interests, also among researchers from the agriculture and food processing field. The particle based methods, originally developed for geomechanics and granular matter problems, have found widespread of applications in simulations of bulk materials, thin membranes, agriculture and food handling and biomedical simulations. In our department we have developed and applied a hybrid approach, which couples Mass-Spring System (MSS) methodology with Discrete Element Method (DEM) in a numerical solution. DEM is a family of methods for computing the motion and interactions of a large number of small particles/bodies. The forces which act on each particle are computed from the initial data and the relevant physical laws and contact models. DEM can be used to simulate a wide variety of granular flow and rock mechanics situations. The MSS is characterized by fixed topology of particle connections approximating mechanical properties of continuous material. This approach is frequently used to simulate deformable objects due to conceptual simplicity and computational speed. The hybrid model was developed to simulate the mechanical behavior of isotropic parenchyma tissue under external load conditions in three dimensional space. In MSS-DEM model a three dimensional soft body is described by collection of particles which cover cell walls surfaces and interact via dynamic triangular mesh. The proposed numerical formulations describe multiphase structure of tissue at a microscopic detail. Three important structural features were included: polymer-like cell walls, quasi-incompressible liquid inside cells and gas phase filing intercellular spaces. The solution described here can be considered as a coarse-grain approach in terms representation of cells shape. Less detailed discretization was a tradeoff that saved computational resources for full three dimensional realistic representation of the plant tissues.