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Discrete element method (DEM)
The DEM is essentially a numerical technique to model the motion of an assembly of particles interacting with each other through collision. It is quit efficient for investigating phenomena occurring at the length scale of a particle diameter. The performance of numerics relies on several factors, including the geometric representation and contact detection algorithm used.
Element Tests
Micro-Macro Transition and Anisotropy
Discrete particle modeling (DPM) is based on Lagrangian tracking of particles combined with computational fluid dynamics (CFD) for the continuous phase. It has been widely used over the last decade to study the complicated flow behaviors in gas-solid fluidized beds. This type of models falls in between the two-fluid model (TFM) used for simulations of large industrial processes, and the direct numerical simulations (DNS) applicable only for small scale systems. In this method, the flow field of the liquid phase is computed from the volume-averaged Navier-Stokes equations. Two-way coupling is achieved via the momentum sink/source term which includes the fluid-particle drag force. Accurate drag relations, therefore, are a critical requirement in simulations based on DPM to be successfully used in the design and optimization of industrial processes.
Friction and Cohesion
Title of the project
Micro-macro relations for flow through fibrous media
Project aim
The goal of this project is to develop a multi-scale computational method that uses a single hierarchical data-structure as basis - involving also multiple fields. Starting from meso-scopic structures (particles or domains) a grid is constructed on a hierarchical data structure. Algorithms and methods from various disciplines like computational fluid dynamics (CFD), discrete element method (DEM), finite element method (FEM), etc., have to be combined. The scientific challenge is to understand systems with strongly different particle sizes with gas-, fluid-, and solid-like behavior at the same time. This involves multi-physics, micro-systems, (moving) interfaces and multi-field problems in general. More specific, such systems occur in grinding or comminution and transport of particulate systems - before and during processing of modern, high-performance materials.
Progress
The basic properties of Delaunay Triangulation (DT) data structures are reviewed. Besides several other tasks that can be performed by DT, it can also be used as an collision detection mechanism in discrete element method (DEM) and some potentials and challenging aspects of this data structures are studied. When the computational costs are compared with alternative, e.g., Linked Cell (LC) methods for different number of particles, the performance is similar and linear in particle number. The major advantage of Delaunay edges/triangles/tetrahedra is that, they can be used not only for contact detection but also for our FEM/CFD coupling as a mesh and for the micro-macro transition.In the next stage, a finite element (FE) based model for the viscous and incompressible fluid flow through a regular porous media composed of rigid (immobile) particles/fibers is considered, and an analytical-numerical approach is employed to calculate the associated transverse permeability. The effects of anisotropy, i.e., in particle shape or orientation, as well as porosity, i.e., volume fraction, on the overall permeability are studied in detail. The representation proposed is compared with the well known Carman-Kozeny (CK) equation. The results from this study can be used for verification and validation, i.e., as a closure relation, of more advanced coarse-grained models for particle-fluid interaction and for the coupling of DEM with FEM or CFD. For more details see the list of publications.
Dosing of Powders
A DT is the set of lines joining a set of points together such that each point is joined to its nearest neighbors. It is the dual graph of the Voronoi diagram (VD) and has a node for every Voronoi cell and an edge between two nodes if the corresponding cells share an edge.
