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Accelerated granular matter simulation
Umeå University, Faculty of Science and Technology, Department of Physics. (Interactive multiphysics and complex mechanical systems)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Accelererad simulering av granulära material (Swedish)
Abstract [en]

Modeling and simulation of granular matter has important applications in both natural science and industry. One widely used method is the discrete element method (DEM). It can be used for simulating granular matter in the gaseous, liquid as well as solid regime whereas alternative methods are in general applicable to only one. Discrete element analysis of large systems is, however, limited by long computational time. A number of solutions to radically improve the computational efficiency of DEM simulations are developed and analysed. These include treating the material as a nonsmooth dynamical system and methods for reducing the computational effort for solving the complementarity problem that arise from implicit treatment of the contact laws. This allow for large time-step integration and ultimately more and faster simulation studies or analysis of more complex systems. Acceleration methods that can reduce the computational complexity and degrees of freedom have been invented. These solutions are investigated in numerical experiments, validated using experimental data and applied for design exploration of iron ore pelletising systems.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2015. , 14 p.
Keyword [en]
discrete element method, nonsmooth contact dynamics, multibody dynamics, granular media, simulation, projected Gauss-Seidel, validation, iron ore pellets, pelletising balling circuit, model reduction, design optimization
National Category
Other Physics Topics Computational Mathematics
Identifiers
URN: urn:nbn:se:umu:diva-110164ISBN: 978-91-7601-366-3 (print)OAI: oai:DiVA.org:umu-110164DiVA: diva2:861212
Public defence
2015-11-12, Naturvetarhuset, N460, Umeå universitet, Umeå, 13:00 (English)
Opponent
Supervisors
Funder
VINNOVA, 2014-01901
Note

This work has been generously supported by Algoryx Simulation, LKAB (dnr 223-

2442-09), Umeå University and VINNOVA (2014-01901).

Available from: 2015-10-22 Created: 2015-10-15 Last updated: 2015-10-22Bibliographically approved
List of papers
1. Examining the smooth and nonsmooth discrete element approaches to granular matter
Open this publication in new window or tab >>Examining the smooth and nonsmooth discrete element approaches to granular matter
2014 (English)In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 97, no 12, 878-902 p.Article in journal (Refereed) Published
Abstract [en]

The smooth and nonsmooth approaches to the discrete element method (DEM) are examined from a computational perspective. The main difference can be understood as using explicit versus implicit time integration. A formula is obtained for estimating the computational effort depending on error tolerance, system geometric shape and size, and on the dynamic state. For the nonsmooth DEM (NDEM), a regularized version mapping to the Hertz contact law is presented. This method has the conventional nonsmooth and smooth DEM as special cases depending on size of time step and value of regularization. The use of the projected Gauss-Seidel solver for NDEM simulation is studied on a range of test systems. The following characteristics are found. First, the smooth DEM is computationally more efficient for soft materials, wide and tall systems, and with increasing flow rate. Secondly, the NDEM is more beneficial for stiff materials, shallow systems, static or slow flow, and with increasing error tolerance. Furthermore, it is found that just as pressure saturates with depth in a granular column, due to force arching, also the required number of iterations saturates and become independent of system size. This effect make the projected Gauss-Seidel solver scale much better than previously thought.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keyword
discrete element method;multibody dynamics, granular media, contact, explicit time integration, linear solvers
National Category
Mathematics
Identifiers
urn:nbn:se:umu:diva-87019 (URN)000331358000002 ()
Available from: 2014-04-08 Created: 2014-03-18 Last updated: 2017-12-05Bibliographically approved
2. Outlet design optimization based on large-scale nonsmooth DEM simulation
Open this publication in new window or tab >>Outlet design optimization based on large-scale nonsmooth DEM simulation
2014 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 253, 438-443 p.Article in journal (Refereed) Published
Abstract [en]

We consider the application of a nonsmooth discrete element method to geometric design optimization of a balling drum outlet used in production of iron ore balls. The geometric design optimization problem is based on the need for homogeneous flow of balls from the balling drum onto a wide belt conveyor feeding a roller screen (sieve). An outlet with two design variables is investigated and the optimal shape for the given system and production flow is found by exploring the design space with 2000 simulations.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Nonsmooth discrete element method, Design optimization, Mineral processing, Balling drum
National Category
Other Physics Topics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-85493 (URN)10.1016/j.powtec.2013.11.046 (DOI)000332430600056 ()
Note

This project was supported by LKAB, ProcessIT Innovations, UMIT Research Lab and Algoryx Simulations

Available from: 2014-02-05 Created: 2014-02-05 Last updated: 2017-12-06Bibliographically approved
3. Parametrization and validation of a nonsmooth discrete element method for simulating flows of iron ore green pellets
Open this publication in new window or tab >>Parametrization and validation of a nonsmooth discrete element method for simulating flows of iron ore green pellets
Show others...
2015 (English)In: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 283, 475-487 p.Article in journal (Refereed) Published
Abstract [en]

The nonsmooth discrete element method (NDEM) has the potential of high computational efficiency for rapid exploration of large design space of systems for processing and transportation of mineral ore. We present parametrization, verification and validation of a simulation model based on NDEM for iron ore green pellet flow in balling circuits. Simulations are compared with camera based measurements of individual pellet motion as well as bulk behavior of pellets on conveyors and in rotating balling drum. It is shown that the NDEM simulation model is applicable for the purpose of analysis, design and control of iron ore pelletizing systems. The sensitivity to model and simulation parameters is investigated. It is found that: the errors associated with large time-step integration do not cause statistically significant errors to the bulk behavior; rolling resistance is a necessary model component; and the outlet flow from the drum is sensitive to fine material adhering to the outlet creating a thick coating that narrows the outlet gaps.

Place, publisher, year, edition, pages
Elsevier, 2015
Keyword
Granular materials, Discrete element method, Validation, Iron ore pellets, Pelletizing, Balling circuit
National Category
Computational Mathematics Chemical Engineering
Identifiers
urn:nbn:se:umu:diva-109902 (URN)10.1016/j.powtec.2015.05.040 (DOI)000361263300051 ()
Available from: 2015-10-16 Created: 2015-10-09 Last updated: 2017-12-01Bibliographically approved
4. Warm starting the projected Gauss-Seidel algorithm for granular matter simulation
Open this publication in new window or tab >>Warm starting the projected Gauss-Seidel algorithm for granular matter simulation
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

The effect on the convergence of warm start-ing the projected Gauss-Seidel solver for nonsmoothdiscrete element simulation of granular matter are in-vestigated. It is found that the computational perfor-mance can be increased by a factor 2 to 5.

Keyword
Discrete elements, Nonsmooth contact dynamics, Convergence, Warm starting, Projected Gauss-Seidel
National Category
Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-110062 (URN)
Note

Submitted 2015

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-20
5. Adaptive model reduction for nonsmooth discrete element simulation
Open this publication in new window or tab >>Adaptive model reduction for nonsmooth discrete element simulation
2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

A method for adaptive model order reduction for nonsmooth discreteelement simulation is developed and analysed in numerical experiments.Regions of the granular media that collectively move as rigid bodies aresubstituted with rigid bodies of the corresponding shape and mass dis-tribution. The method also support particles merging with articulatedmultibody systems. A model approximation error is defined used for de-riving and conditions for when and where to apply model reduction andrefinement back into particles and smaller rigid bodies. Three methodsfor refinement are proposed and tested: prediction from contact events,trial solutions computed in the background and using split sensors. Thecomputational performance can be i

National Category
Computational Mathematics
Identifiers
urn:nbn:se:umu:diva-110063 (URN)
Note

Submitted 2015

Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2015-10-20

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