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Dr. Weinhart

Thomas Weinhart

Horstring Z117
P.O. Box 217
7500 AE Enschede, NL

Phone: +31 53 489 3301
Email: t.weinhart@utwente.nl
Skype: thomasweinhart

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Discrete Particle Modelling

A code development project. MercuryDPM Homepage

MercuryDPM is a code for discrete particle simulations. That is, it simulates the motion of particles, or atoms, by applying forces and torques that stem either from external body forces, (e.g. gravity, magnetic fields, etc...) or from particle interaction laws. For granular particles, these are typically contact forces (elastic, plastic, viscous, frictional), while for molecular simulations, forces typically stem from interaction potentials (e.g. Lennard-Jones) ....

Figure: Simulation of granular flow through a contraction with 400,000 particles. Two shocks are generated on either side of the contraction and there is interaction where the two shocks meet. The colour of the particles indicates the flow height.

Sintering – Modelling pressure-, temperature-, and time-dependent contacts

A DFG project. Particles in contact (PiKo)

In most realistic situations, where particles come in contact, it can NOT be assumed that the contact properties are independent of pressure, temperature or time. Therefore, this project involves pressure-, temperature-, and time-dependent contact properties and their influence on the macroscopic powder flow behavior. Sintering is chosen as one possible example and starting point, where all these phenomena are relevant.

In realistic processes, a sintering process starts with many separate powder- particles that are, e.g., attracted by electrostatic forces, bound together by capillary forces, or squeezed together by strong pressure. Leaving them alone for long time, diffusion will set in and change the contact properties. At elevated temperatures, the sintering works much faster and from the originally isolated particles, a solid, possibly porous and fragile agglomerate is formed.

The goal of this project is to model the particles in contact, before the particles lose their identity. For this, temperature- and pressure-dependent contact models have to be developed in parallel to contact-measurements (with M Kappl, Mainz). The many-particle simulations will then be adapted to the materials used and experimentally validated (with J Tomas, Magdeburg). As the result of the project, the verified numerical model for the sintering process of many particles will become available. This will then be used for the micro- macro transition in order to obtain better theoretical constitutive relations for a macroscopic description based on the contact-mechanics and -physics.

More material: Poster

Figure: Indenting of a weakly sintered granular bed. The sintering is so weak, that particle contacts easily break.

Computational multi-scale modelling of super-dispersed multiphase flows

A Strategic Innovative Project (SIP1) of the Institute of Mechanics, Processes and Control (IMPACT), Univ. of Twente

Developing good numerical models for dry granular flow is of interest in many industrial processes and geophysics. Granular material shows both solid and fluid behavior. Closed continuous models for granular flow only exist for certain cases, while Discrete Particle Models (DPM) are unfeasible for large-scale simulations. Therefore I am working on a DG finite element model for heterogeneous multiscale modelling of polydisperse, nonuniform dry granular flows, which allows both efficient and reliable numerical simulations.

Figure: A rare view into the iron-ore melting furnace shows the inflow of pellets from an inclined, rotating chute (top left) during an inspection cycle. Improved control of the inflow of such granular matter isdesired by Corus (Photo courtesy: Corus).

A Posteriori Error Estimates of the DG Method for Hyperbolic Systems

A posteriori error estimates are a useful tool to verify the quality of finite element approximations and to control the error in adaptive meshes. We apply the discontinuous Galerkin method to first-order linear hyperbolic systems in two and three space dimensions. We explicitly write down the leading error term and solve local finite element problems to obtain a posteriori error estimates. We present convergence and numerical results for problems from acoustics and electromagnetism.

Collaborators: Slimane Adjerid

Figure: h-adaptive mesh refinement based on local error estimate. Source

Journal Articles

  1. Windows-Yule, K.; Weinhart, T.; Parker, D.J.; Thornton, A.R.,
    The influence of thermal convection on density segregation in a vibrated binary granular system,
    Physics Review E (2014).
  2. Windows-Yule, K.; Weinhart, T.; Parker, D.J.; Thornton, A.R.
    Effects of system packing on the segregation behaviours of granular systems,
    Physics Review Letters (2014).
  3. R. Fuchs, T. Weinhart, J. Meyer, H. Zhuang, T. Staedler, X. Jiang and S. Luding
    Rolling, sliding & torsion of micron-sized silica particles - Experimental, numerical and theoretical analysis,
    Granular Matter (2014) (arXiv)
  4. Weinhart, T., Hartkamp, R., Thornton, A.R., Luding, S.,
    Coarse-grained local and objective continuum description of 3D granular flows down an inclined surface,
    Phys. Fl. 25, 070605 (2013).
  5. Thornton, A.R.; Weinhart, T.; Ogarko, V. and Luding, S.,
    Multi-scale modeling of multi-component granular materials,
    Computer Methods in Materials Science (2013). 13:2 p1-16 (Editor's choice).
  6. Thornton, A.R., Weinhart, T., Luding, S., Bokhove, O.,
    Friction dependence of shallow granular flows from discrete particle simulations ,
    Eur. Phys. J. E 35:127 (2012).
  7. Thornton, A.R., Weinhart, T., Luding, S., Bokhove, O.,
    Modeling of particle size segregation: Calibration using the discrete particle method,
    Int. J. Mod. Phys. C 23, 1240014 (2012).
  8. Weinhart, T., Thornton, A.R., Luding, S., Bokhove, O.,
    From discrete particles to continuum fields near a boundary,
    Granular Matter 14(2), 289-294 (2012).
  9. Weinhart, T., Thornton, A.R., Luding, S., Bokhove, O.,
    Closure Relations for Shallow Granular Flows from Particle Simulations,
    Granular Matter 14(4), 531-552 (2012).
  10. R. Hartkamp, A. Ghosh, T. Weinhart and S. Luding,
    A study of the anisotropy of stress in a fluid confined in a nanochannel,
    J. Chem. Phys. 137, 044711 (2012).
  11. Slimane Adjerid, Thomas Weinhart,
    Asymptotically Correct Discontinuous Galerkin error estimates for linear symmetric hyperbolic systems,
    Applied Numerical Mathematics (2013)
  12. Slimane Adjerid, Thomas Weinhart,
    Discontinuous Galerkin error estimation for linear symmetrizable hyperbolic systems,
    AMS Journal of Mathematics of Computation, 80, 1335-1367 (2011).
  13. Slimane Adjerid, Thomas Weinhart,
    Discontinuous Galerkin error estimation for linear symmetric hyperbolic systems,
    Computer Methods in Applied Mechanics and Engineering, 198(37-40), 3113-3129 (2009).

Other

  1. Weinhart, T., Luding, S., Thornton, A.R.,
    From discrete particles to continuum fields in mixtures,
    AIP Conf. Proc. 1542, 1202-1205 (2013)
  2. Thornton, A.R.; Krijgsman, D.; de Voortwis, A.; Orgarko, O.; Luding, S.; Fransen, R.; Gonzalez, S.l Bokhove, O.; Imole, O.; Weinhart, T, A review of recent work on the Discrete Particle Method at the University of Twente: An introduction to the open- source package MercuryDPM,
    Discrete Element Methods 6 (2013), Conference Proceedings.
  3. A.R. Thornton, D. Krijgsman, R. Fransen, S. Gonzalez, D. Tunuguntla, A. ten Voortwis, S. Luding, O. Bokhove, T. Weinhart Mercury-DPM: Fast particle simulations in complex geometries,
    EnginSoft Year 10, No. 1 (2013)
  4. Thornton, A.R., Weinhart, T., Bokhove, O., Zhang, B., van der Sar, D. M., Kumar, K., Pisarenco, M., Rudnaya, M., Savceno, V., Rademacher, J., Zijlstra, J., Szabelska, A., Zyprych, J., van der Schans, M., Timperio, V., Veerman, F. (2010) Modeling, optimization of algae growth.
    Proceedings of the 72nd European Study Group Mathematics with Industry, 25-29 Jan 2010, Amsterdam, Netherlands. pp. 54-85. CWI.
  5. Weinhart, T.,
    A Posteriori Error Analysis of the Discontinuous Galerkin Method for Linear Hyperbolic Systems of Conservation Laws,
    PhD Thesis, Virginia Tech (USA), 2009.
Conferences (Talks unless stated otherwise)

University of Twente, Enschede

2014 (planned)

Advanced Programming in Engineering: lecturing 25% and grade.

Programming in Engineering: organize, lecture 50%.

Programming in Engineering summer course: organize, lecture 50%.

2013

Advanced Programming in Engineering: lecture 25% and grade.

Programming in Engineering: organized, lectured 50%.

Programming in Engineering summer course: organized.

2012

Advanced Programming in Engineering: lectured 25%, updated script and graded.

Programming in Engineering summer course: organized.

2011

Programming in Eng. summer course: organized, added material, lectured 50%, gave oral exams.

Programming in Engineering: lectured 50% and gave oral exams.

Advanced Programming in Engineering: lectured 25%, updated script and graded.

Particles to Continuum - Micro-Macro Methods: lectured 25%

Complex Analyis: taught individual lecture.

Scientific Computation: tutored computer class and graded.

2010

Programming in Engineering summer course: lectured 50%, gave oral exams.

Advanced Programming in Engineering: lectured 25%, and graded.

Particles to Continuum - Micro-Macro Methods: lectured 25%

Finite Elements: taught individual lectures.

Scientific Computation: tutored computer class and graded.

Virginia Polytechnic University, Blacksburg, VA, USA

2009

Integral Calculus Spring: lectured and assigned course grades, developed lesson plans and exams

2008

Integral Calculus Fall: lectured and assigned course grades, developed lesson plans and exams

Integral Calculus Spring: lectured and assigned course grades, developed lesson plans and exams

2007

Math Emporium: assisted math students in computer lab, administered online tests and quizzes.

Integral Calculus Fall: lectured and assigned course grades, developed lesson plans and exams

Integral Calculus Spring: lectured and assigned course grades, developed lesson plans and exams

2006

Differential Calculus: lectured and assigned course grades, developed lesson plans and exams, holding office hours, introducing programming in Mathematica.

Integral Calculus Fall: lectured and assigned course grades, developed lesson plans and exams

Integral Calculus Spring: lectured and assigned course grades, developed lesson plans and exams

2005

Math Lab: tutored for undergraduate math courses. Vector Geometry Recitation Fall: taught weekly recitation class supplementing lecture, graded

Vector Geometry Recitation Spring: taught weekly recitation class supplementing lecture, graded

2004

Vector Geometry Recitation Fall: taught weekly recitation class supplementing lecture, graded

Vector Geometry Recitation Spring: taught weekly recitation class supplementing lecture, graded

Math Emporium: assisted math students in computer lab, administered online tests and quizzes.

2003

Math Emporium: assisted math students in computer lab, administered online tests and quizzes.