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I am a senior lecturer at the Department of Mechanical Engineering, Stellenbosch University, South Africa . 

My research is mainly on the numerical modelling of granular flow problems.  As part of my Matsers study, I made used of the Discrete Element Method (DEM) to model excavator bucket filling.  As part of my PhD I developed a Material Point Method computer code (MPM, also called Particle-in-Cell Method) for the modelling of large deformation problems.  MPM is a so-called "meshless" finite element method and I focused on the modelling of granular flow such as silo discharge and excavator bucket filling as well as geotechnical applicartions such as bearing capacity and slope stability.

Currently I am working on a European Union funded project together with seven other universities and companies all of Europe and Scandinavia.  The project's aim is to improve the Material Point Method and to apply it to unique industrial problems where large deformation is dominant.  These problems are difficult to solve using other continuum based methods, such as the finite element method, due to severe distortion of the element mesh.

Postgraduate students focus on the calibration of material properties for use in DEM simulations.  Agricultural and mining industrial problems are also analysed and optimised.  Examples include bulk materials handling such as conveyor belts and transfer chutes and agricultural centrifugal fertiliser spreaders.

Download our research brochure for more informatrion and pictures: Granular Materials Research Group 

Master Summary - Title: Forced Granular Flow (December 2000)

The main goal of the thesis is to validate the ability of discrete element methods (DEM) to predict forced granular flow.  Granular flow occurs in a broad spectrum of industrial applications.  The thesis focuses on earthmoving processes typical of the mining and agricultural industries.  Existing soil mechanics soil-tool models are also investigated and general flow behaviour in and around blades and buckets are established. Soil mechanics theories are used to predict the draft forces on a flat blade moving through granular material.  Corn and wheat grains are used as material.  The rupture (slip) lines in front of the blade are predicted by soil mechanics and compared to experimental results.  A two-dimensional test bench is used to visualise the flow of the granular material.  Forces and moments that act on the tools are measured.

DEM can be used to model industrial granular flow with large displacements.  Two types of earthmoving equipment are simulated.  The first is a flat blade and the second is a bucket.  The forces on these tools are determined using DEM and compared to experimental results.  The ability of DEM to predict material compressibility, the flow of material in and around the tools, the rupture lines and the bucket fill rate are investigated.  A particle relative displacement method is used to determine the rupture lines.

PhD Summary - Title: The Modelling of Granular Flow using the Particle-in-Cell Method (April 2004)

Granular flow occurs in a broad spectrum of industrial applications that range from separation and mixing in the pharmaceutical industry, to grinding and crushing, blasting, stockpile construction, flow in and from hoppers, silos, bins, and conveyer belts, agriculture, mining and earthmoving. Two totally different approaches of modelling granular flow are the Discrete Element Method (DEM) and continuum methods such as Finite Element Methods (FEM).

Continuum methods can be divided into nonpolar or classic continuum methods and polar continuum methods. Large displacements are usually present during granular flow which, without remeshing, cannot be solved with standard finite element methods due to severe mesh distortion. The Particle-in-Cell (PIC) method, which is a so-called meshless method, eliminates this problem since all the state variables are traced by material points moving through a fixed mesh. The main goal of this research was to model the flow of noncohesive granular material in front of flat bulldozer blades and into excavator buckets using a continuum method. A PIC code was developed to model these processes under plane strain conditions. A contact model was used to model Coulomb friction between the material and the bucket/blade.

Analytical solutions, published numerical and experimental results were used to validate the contact model and to demonstrate the code’s ability to model large displacements and deformations. The ability of both DEM and PIC to predict the forces acting on the blade and bucket and the material flow patterns were demonstrated. Shear bands that develop during the flow of material were investigated. As part of the PIC analyses, a comparison between classic continuum and polar continuum (Cosserat) results were made. This includes mesh size and orientation dependency, flow patterns and the forces acting on the blade and the bucket. It is concluded that the interaction of buckets and blades with granular materials can successfully be modelled with PIC. In the cases conducted here, the nonpolar continuum was more accurate than the polar continuum, but the polar continuum results were less dependent on the mesh size. The next step would be to apply this technology to solve industrial problems.

Download complete PhD thesis:  ccoetzee2004b.pdf  (size 6.3 Mb)

Publications in Refereed Scientific Journals 
 
  1. Coetzee, C.J., Vermeer, P.A., Basson, A.H., 2005, The Modelling of Anchors using the Material Point  Method, International Journal for Numerical and Analytical Methods in Geomechanics, 29:879-895          (pdf 313K)
  2. Coetzee, C.J., Basson, A.H., Vermeer, P.A., 2006, Discrete and Continuum Modelling of Silo Discharge, R&D Journal, A Publication of the South African Institution of Mechanical Engineering, 22(2):26-38        (pdf 512K)
  3. Coetzee, C.J., Basson, A.H., Vermeer, P.A., 2007, Discrete and Continuum Modelling of Excavator Bucket Filling, Journal of Terramechanics, 44:177-186 (pdf 1.5Mb)
  4. Coetzee, C.J., Els, D.N.J., 2009, Calibration of Discrete Element Parameters and the Modelling of Silo Discharge and Bucket Filling, Computers and Electronics in Agriculture, 65, 198-212 (pdf 3.8Mb)
  5. Coetzee, C.J., Els, D.N.J., 2009, Calibration of Granular Material Parameters for DEM Modelling and Numerical Verification by Blade-Granular Material Interaction, Journal of Terramechanics, 46, 15-26 (pdf 3.7Mb)
  6. Coetzee, C.J., Els, D.N.J., Dymond, G.F., 2009, Discrete Element Parameter Calibration and the Modelling of Dragline Bucket Filling, Journal of Terramechanics, Available online: doi:10.1016/j.jterra.2009.03.003 (pdf 1.3Mb)
  7. Coetzee, C.J., Els, D.N.J., 2009, The Numerical Modelling of Excavator Bucket Filling using DEM, Journal of Terramechanics, 46, 217-227 (pdf 6.7Mb)

 

Publications in International Symposia

  1. Els, D.N.J., Coetzee, C.J., Friction Forces in a Vertically Pushed Granular Column, International Symposium on Reliable Flow of Particulate Solids III, Porsgrunn, Norway, August 1999
  2. Coetzee, C.J.; Els, D.N.J.: Modelling Excavator Bucket Filling with DEM, Proceedings of the Fifth World Congress on Computational Mechanics (WCCMV), July 7-12, 2002, Vienna, Austria, Editors: Mang,H.A.; Rammerstorfer,F.G.; Eberhardsteiner,J., Publisher: Vienna University of Technology, Austria, ISBN3-9501554-0-6, http://wccm.tuwien.ac.at/  (pdf 290 K)
  3. Beuth, L., Vermeer, P, Coetzee, C.J., Bonnier, P., van den Berg, P., 2007, Formulations and Validation of a Quasi-Static Material-Point, International Symposium on Numerical Models in Geomechanics, Rhodes, Greece, 25-27 April 2007 (pdf 215 K)
  4. Beuth, L., Benz, T., Vermeer, P., Wieckowski, Z., Coetzee, C.J., 2007, Large deformation analyses using the Material-Point Method, 17th International Conference on Computer Methods in Mechanics, CMM 2007, June 19 - 22, Lodz-Spala, Poland (pdf 330 K)
  5. Coetzee, C.J., 2009, The Modelling of Bulk Materials Handling using the Discrete Element Method, 1st African Conference on Computational Mechanics - An International Conference, AfriComp, January 7 - 11, Sun City, South Africa (pdf 2.6 Mb)
  6. Beuth, L., Więckowski, Z., Vermeer, P.A., Coetzee, C.J., 2009, The Modelling of Large Deformation Geotechnics using the Material Point Method, 1st African Conference on Computational Mechanics - An International Conference, AfriComp, January 7 - 11, Sun City, South Africa
  7. Jassim, I., Coetzee, C.J., 2009, A Contact Algorithm for Non-Structured MPM Meshes, 18th International Conference on Computer Methods in Mechanics, CMM 2009, 18-21 May, Zielona Gora, Poland

Publications in National Symposia

  1. Vogler, U., Coetzee, Corné J., Vermeer, P.A.: Simulation of Field Model Tests by two different Numerical Approaches. DGGK, AK 1.6 "Numerik in der Geotechnik": Workshop: Nachweise für Böschungen und Baugruben mit numerischen Methoden, S. 37-46, Weimar 2003 (pdf 600 K)
  2. Coetzee, C., 2008, Calibration of Discrete Element Parameters and the Modelling of Bulk Materials Handling, Conveyors and Bulk Materials Conference, 6 & 7 August 2008, Midrand, South Africa (pdf 2.2 Mb)

©2009