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See detailA Forcing Fictitious Domain Method to Simulate Fluid-particle Interaction of Particles with Super-quadric Shape
Wu, Mingqiu UL; Peters, Bernhard UL; Rosemann, Tony et al

in Powder Technology (2019), 360(15/January 2020), 264-277

In this work, we develop a new framework to directly simulate super-quadric (SQ) particles in fluid flows based on a forcing fictitious domain method. Specifically, a super-quadric particle function is ... [more ▼]

In this work, we develop a new framework to directly simulate super-quadric (SQ) particles in fluid flows based on a forcing fictitious domain method. Specifically, a super-quadric particle function is used to represent the particle shape of different types in a flexible manner. The immersion of particles in the fluid is handled by imposing rigid solid body motion in the particle domain, as well as adding a local forcing term to the Navier-Stokes equations by calculating the integral of both the pressure gradient and the particle velocity over the whole particle domain. Particle shapes are varied by changing the five super-quadric parameters of the SQ equation. We validate our approach by performing simulations of flow around a fixed particle and sedimentation of a particle in a channel in 2D and 3D. The validation results indicate that the current simulation results show a good agreement with experimental data. Moreover, our method is used to study the flow around fixed non-spherical particles with different orientations and particle Reynolds numbers. The particle Reynolds numbers vary from 0.1 to 3000. The super-quadric particles exemplarily considered in the current study are an ellipsoidal particle and fibre-like particles. We present the results for drag and lift coefficients at different particle orientations and different particle Reynolds numbers. The obtained results lay the foundation to apply the framework to flown through multi-particle systems in the near future. [less ▲]

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See detailMicromechanical model for sintering and damage in viscoelastic porous ice and snow. Part I: Model and calibration
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

in International Journal of Solids and Structures (2019)

Ice and snow are usually classified as a viscoelastic or viscoplastic materials according to temperature, strain rate, pressure and time scale. Throughout experimental studies presented in the literature ... [more ▼]

Ice and snow are usually classified as a viscoelastic or viscoplastic materials according to temperature, strain rate, pressure and time scale. Throughout experimental studies presented in the literature, it has been observed that at very low temperatures or high strain rates, porous ice and snow exhibit brittle behavior, but experience high viscous and plastic flow at temperatures close to the melting point and low rates. At the macroscopic level, nonlinearity is not necessarily attributed to permanent changes in the material or yielding but mainly to micro cracks, intergranular sliding, porosity collapse and crack propagation. In this paper, this complex behavior is described with a full microstructure-based model. Classical rheological models and beam theory are used to describe aspects of creep and fracture of granular ice and snow. [less ▲]

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See detailMicromechanical model for sintering and damage in viscoelastic porous ice and snow. Part II: validation
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

in International Journal of Solids and Structures (2019)

The last decades have witnessed sharp progress in both numerical simulation methods and computing power. Realistic simulation of complex structures such as snow remains challenging. The discrete particle ... [more ▼]

The last decades have witnessed sharp progress in both numerical simulation methods and computing power. Realistic simulation of complex structures such as snow remains challenging. The discrete particle approach now accessible due to advances in parallel processing has shown to be a good alternative for brittle and quasi-brittle materials. A novel numerical model has been described in part I of this study. Ice grains in snow are found near their melting points with an enhanced creep that constantly affects its microstructure. The behavior of snow combines characteristics of polycrystalline ice, which depends on stress rate, temperature, hydrostatic pressure and geometrical proprieties that affects its fracture properties. Snow can pass from porous continuous structure to a granular form or creep intensively when loaded. The herein proposed methodology includes time and pressure dependent bonding properties of ice and predicts large displacements, fracture, and granular flow in snow under the effect of mechanical stress. A micromechanical approach based on particle mechanics and beam theory is used to capture microstructure evolution under external loads. The calibration and validation are based on stress-strain data from some compression tests found in the literature. [less ▲]

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See detailComparison of numerical schemes for 3D Lattice Boltzmann simulations of moving rigid particles in thermal fluid flows
Rosemann, T; Kruggel-Emden, H; Wu, Mingqiu UL et al

in Powder Technology (2019), 356(3), 528-546

The Lattice Boltzmann method is an efficient numerical method for direct numerical simulations of particulate flows. For a variety of applications not only the flow but also the heat transfer between ... [more ▼]

The Lattice Boltzmann method is an efficient numerical method for direct numerical simulations of particulate flows. For a variety of applications not only the flow but also the heat transfer between particle and fluid plays an important role. While for non-thermal flows numerous techniques to handle the moving boundaries of particles have been developed, appropriate techniques for the thermal Lattice Boltzmann method are still lacking. The following three issues are of special importance. First, the thermal boundary conditions (Dirichlet or Neumann) have to be fulfilled on the particle surface. Second, reasonable values have to be found for temperature distributions in grid nodes that are uncovered by moving particles. Third, the heat transfer between particulate and fluid phase has to be evaluated in many application, since it is an essential quantity of interest. In this work, we present new numerical schemes for all of these three key aspects. They rely to a great degree on existing schemes for the non-thermal Lattice Botzmann method. In four benchmark cases we assess which of them are the most favourable and we also show to what extend schemes based on the same principles behave similarly or differently in the flow and heat transfer simulation. The results demonstrate that the proposed techniques deliver accurate results and allow us to recommend the most advantageous approach. [less ▲]

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See detailHigh Performance Parallel Coupling of OpenFOAM+XDEM
Besseron, Xavier UL; Pozzetti, Gabriele; Rousset, Alban UL et al

Presentation (2019, June 21)

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See detailPhase field fracture model for viscoplastic materials in large deformations
Kabore, Brice Wendlassida UL; Loew, Pascal Juergen UL; Peters, Bernhard UL

Scientific Conference (2019, June 13)

Phase-field modeling approach to material fracture and damage has received a growing interest among researchers. It has proven to be an effective way to address crack related discontinuities in continuum ... [more ▼]

Phase-field modeling approach to material fracture and damage has received a growing interest among researchers. It has proven to be an effective way to address crack related discontinuities in continuum mechanics. Also, it solves the problem related to tracking the fracture surface by simply representing the fracture phase with a continuous field variable. Recently, phase-field fracture models have been extended to finite deformations, crack nucleation and applied to complex material behaviors such as plasticity and viscoplasticity. In this contribution we describe a viscoplastic model coupled with a phase-field dynamic fracture model in a large strain formulation. The model include damage, history, rate and temperature dependent behavior. A finite element implementation is presented in a staggered time integration. Moreover, we address the crack closure and crack surfaces interpenetration taking into account tension-compression strength asymmetry. Performance of the model on dynamic crack propagation are presented. [less ▲]

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See detailA forcing fictitious domain/immersed boundary method for super-quadric shape of particulate flow simulation of cementitious material
Wu, Mingqiu UL; Peters, Bernhard UL; Dressler, Inka

in International Centre for NumericalMethods in Engineering (2019)

Fictitious domain/immersed boundary method (FD/IBM) has recently been used for particulate flows and complex fluid-solid interaction problems. The advantage of FD/IBM over the body- fitted method is that ... [more ▼]

Fictitious domain/immersed boundary method (FD/IBM) has recently been used for particulate flows and complex fluid-solid interaction problems. The advantage of FD/IBM over the body- fitted method is that it substantially simplifies grid generation for immersed geometries, and it is easier to handle moving boundary situations. FD/IBM even allows the use of a stationary and non- deformation background mesh, as well as it reduces the cost of computation by avoiding generation of a body-fitted mesh for each time step. In this work, we develop a new platform to directly simulate super-quadric (SQ) particles in fluid based on a forcing fictitious domain method. Specifically, a super-quadric particle function is used to represent particle with varying shapes and sizes as encountered for concrete and mortar. The immersion of particles in fluid is handled by imposing a rigidity solid body motion in the particle domain, as well as adding a forcing term to the Navier-stokes equation by integral of pressure gradient and particle related velocity over the whole particle domain. Particle shapes are given by changing the super-quadric parameters of SQ equation. Particle motions, which occur during pumping of cementitious material, can be calculated and tracked by solving Newton’s equations of motions using the extended discrete element method (XDEM)[4] while the data of fluid flow properties are obtained by solving the Navier-Stokes equations which govern the fluid phase. Hence, a particle interface resolving solver is developed by coupling XDEM and IBM. We validate our solver by performing flow around particles and free falling of a particle in the channel at different parameters in 2D and 3D. The final objective of this work is to develop a particle-resolved direct numerical simulation platform to predict highly packed fluids with different shapes of particles and over a wide range of particle sizes. [less ▲]

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See detailAn interface resolved immersed boundary method in XDEM for particulate flow simulations
Wu, Mingqiu UL; Peters, Bernhard UL; Rosemann, Tony et al

in International Congress on Particle Technology (2019, April 09)

immersed boundary method (IBM) has recently been used for particulate flows and complex fluid-solid interaction problems. The IBM was first introduced by Peskin to simulate blood flow in a beating heart ... [more ▼]

immersed boundary method (IBM) has recently been used for particulate flows and complex fluid-solid interaction problems. The IBM was first introduced by Peskin to simulate blood flow in a beating heart. Later it has been extended for a different range of applications. The advantages of IBM over the body-fitted method is that it substantially simplified grid generation for immersed geometries, and it is easier to handle moving boundary situations. IBM even allows the use of a stationary and non-deformation background mesh, as well as it reduces the cost of computation by avoiding generation of a body-fitted mesh for each time step. However, the IBM approach is not straightforward to implement and it requires special techniques for cut-off boundary cells as well as special techniques for data point interpolations. Generally, the IBM is classified into two approaches based on the methods of imposing the boundary condition in the immersed body. The first approach is called fictitious domain method with continuous forcing scheme which employs a distributed forcing function to impose a rigidity boundary condition in the solid particle domain. The second one is the discrete forcing approach, which enables a sharp interface to represent the immersed surface. The IBM discussed in this work is a combination of these above two approaches: we first employ the continuous forcing scheme to get a first-step approximation of the immersed body, then use an interpolation polynomial to impose a desired accurate physical boundary for each immersed boundary point based on a least square interpolation reconstruction scheme. Particle motions can be calculated and tracked by solving Newton’s equations of motions using the extended discrete element method (XDEM) while the data of fluid flow properties are obtained by solving the Navier-Stokes equations which govern the fluid phase. Combined this leads to the basic concept of DEM-CFD coupling. Therefore, a particle interface resolved simulation solver is developed by coupling the XDEM and IBM approaches together. Consequently, this solver is then used to handle both static and dynamic particle problems as well as particle packed bed simulations. The validation of the solver can be performed by setting one static sphere in a channel and evaluate the drag coefficients and Strouhal number (when shedding occurs) at various Reynolds [less ▲]

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See detailComparison of boundary treatments in thermal Lattice Boltzmann simulations of moving particles in fluids
Rosemann, T; Kravets, B; Kruggel-Emden, H et al

in Particle Technology Series (2019, April 09)

Various numerical schemes have been developed in recent years to simulate particle-laden flows. The Lattice Boltzmann method (LBM) has emerged as an efficient tool for direct numerical simulations in ... [more ▼]

Various numerical schemes have been developed in recent years to simulate particle-laden flows. The Lattice Boltzmann method (LBM) has emerged as an efficient tool for direct numerical simulations in which the flow field around the particles can be fully resolved. In the thermal Lattice Boltzmann method not only the flow field but also the temperature field is calculated by using one distribution function for the fluid density and one for the fluid temperature. The treatment of curved solid-fluid boundaries is crucial for the simulation of particulate flows with this method. While several aspects of moving boundaries have been discussed in previous studies for the non-thermal LBM, it remains unknown to what extend these findings are transferable to the thermal LBM. In this work, we consider a 3D thermal LBM with a multiple-relaxation-time (MRT) collision operator and compare different techniques that can be applied to handle the moving boundary. There are three key aspects in the LBM that need to be considered at the boundary: the momentum exchange method calculating the drag force acting upon particles, the bounce-back scheme determining the bounce-back of density distribution functions at a boundary, and the refilling algorithm assigning a value to the unknown density distribution functions at lattice nodes uncovered by the particle. First, we demonstrate how the choice of the technique to address these problems in the flow field impacts the results for the temperature field in the thermal LBM. In a second step, we focus on the thermal side where similar techniques need to be applied. We compare different refilling strategies and bounce-back schemes for the temperature distribution functions and assess heat transfer calculation methods for the particle surface. The performance of these implementations is evaluated by comparing the simulation results in terms of accuracy and stability for a moving particle in a channel flow with a Galilean invariant reference system in which the particle’s position is fixed. We conduct this analysis for various Reynolds and Prandtl numbers to test the applicability of the individual techniques to varying flow conditions. Moreover, we demonstrate the potential of the implementation found to be superior by considering a more complex flow field in a particle packing. Our findings serve as a guideline for choosing suitable moving boundary treatments in thermal LBM simulations of particle-laden flows. [less ▲]

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See detailIntegrated micromechanical model for slope stability analysis
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

Scientific Conference (2019, April 09)

Advances in supercomputing hardware have made it possible to handle highly complex geomechanical analysis with large data. Thus, particle-based methods are gaining an ever-increasing interest with ... [more ▼]

Advances in supercomputing hardware have made it possible to handle highly complex geomechanical analysis with large data. Thus, particle-based methods are gaining an ever-increasing interest with massively parallel programs being developed. These methods have been applied to the analysis of failure mechanisms and scenarios such as mass movement in landslides, avalanches under static, dynamic or seismic loading condition. They provide deep insights into the meso and micro-scale mechanisms leading to macroscopic instabilities. This contribution describes a micromechanical model for stability analysis and simulation in natural or man-made slopes under complex loading and boundary conditions. Based on the micromechanics of loose granular and compacted geomaterial, microstructural change, viscoelastic deformations, fracture, and healing are explicitly integrated into a coupled discrete particle and beam lattice model. Stress-based failure criteria and energy based dissipation and frictional contact are employed. Both gravity increase and strength reduction methods have been employed to evaluate the Factor of Safety (FoS) and potential failure surface and compared. With an emphasis on the impact of the microstructure and its spatial variability on stress-induced microcracks and crack propagation, this study outlines material models and properties relevant to stability analysis. Special focus has been put on layered slopes which present varying shear strength along the depth formed over time according to pressure, temperature, and moisture such as snowpack. This microstructural approach unifies geometrical and material information and allows the structural assembling layers of different strength. [less ▲]

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See detailA parallel dual-grid multiscale approach to CFD-DEM couplings
Pozzetti, Gabriele UL; Jasak, Hrvoje; Besseron, Xavier UL et al

in Journal of Computational Physics (2019), 378

In this work, a new parallel dual-grid multiscale approach for CFD-DEM couplings is investigated. Dual- grid multiscale CFD-DEM couplings have been recently developed and successfully adopted in different ... [more ▼]

In this work, a new parallel dual-grid multiscale approach for CFD-DEM couplings is investigated. Dual- grid multiscale CFD-DEM couplings have been recently developed and successfully adopted in different applications still, an efficient parallelization for such a numerical method represents an open issue. Despite its ability to provide grid convergent solutions and more accurate results than standard CFD-DEM couplings, this young numerical method requires good parallel performances in order to be applied to large-scale problems and, therefore, extend its range of application. The parallelization strategy here proposed aims to take advantage of the enhanced complexity of a dual-grid coupling to gain more flexibility in the domain partitioning while keeping a low inter-process communication cost. In particular, it allows avoiding inter- process communication between CFD and DEM software and still allows adopting complex partitioning strategies thanks to an optimized grid-based communication. It is shown how the parallelized multiscale coupling holds all its natural advantages over a mono-scale coupling and can also have better parallel performance. Three benchmark cases are presented to assess the accuracy and performance of the strategy. It is shown how the proposed method allows maintaining good parallel performance when operated over 1000 processes. [less ▲]

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See detailSimulation-based Optimisation Of Selective Laser Sintering/Melting Process
Kabore, Brice Wendlassida UL; Peters, Bernhard UL

in Euro PM2019 Congress Proceedings (2019)

In order to adapt Selective Laser Sintering (SLS) and Melting (SLM) to final products and volume production, many scientists have turned to statistical analysis for quality and process stability. Most of ... [more ▼]

In order to adapt Selective Laser Sintering (SLS) and Melting (SLM) to final products and volume production, many scientists have turned to statistical analysis for quality and process stability. Most of which are based on extensive experiments aiming at finding statistical correlations between input parameters such as layer thickness, orientation, scan speed, powder bed temperature, laser power... and resulting strength and residual stress of the manufactured part. However, the rise of computer simulation based on mathematical models allows predictions at a much lower cost. Mathematical modelling of SLS/SLM involves molecular level thermodynamics and thermo-mechanical behaviour of the powder material. In this study, we employ the newly developed Extended Discrete Element Model to reproduce the SLS process including the mechanisms of sintering and the evolution of fracture properties and self-supporting ability. Results show that such microscale model offers high precision and flexibility for finding optimal process parameters. [less ▲]

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See detailRate-dependent phase-field damage modeling of rubber and its experimental parameter identification
Loew, Pascal Juergen UL; Peters, Bernhard UL; Beex, Lars UL

in Journal of the Mechanics and Physics of Solids (2019)

Phase-field models have the advantage in that no geometric descriptions of cracks are required, which means that crack coalescence and branching can be treated without additional effort. Miehe and ... [more ▼]

Phase-field models have the advantage in that no geometric descriptions of cracks are required, which means that crack coalescence and branching can be treated without additional effort. Miehe and Schänzel (2014) introduced a rate-independent phase-field damage model for finite strains in which a viscous damage regularization was proposed. We extend the model to depend on the loading rate and time by incorporating rubber’s strain-rate dependency in the constitutive description of the bulk, as well as in the damage driving force. The parameters of the model are identified using experiments at different strain rates. Local strain fields near the crack tip, obtained with digital image correlation (DIC), are used to help identify the length scale parameter. Three different degradation functions are assessed for their accuracy to model the rubber’s rate-dependent fracture. An adaptive time-stepping approach with a corrector scheme is furthermore employed to increase the computational efficiency with a factor of six, whereas an active set method guarantees the irreversibility of damage. Results detailing the energy storage and dissipation of the different model constituents are included, as well as validation results that show promising capabilities of rate-dependent phase-field modeling. [less ▲]

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See detailIdentification of optimal process parameters in selective laser sintering
Kabore, Brice Wendlassida UL; Estupinan Donoso, Alvaro Antonio UL; Peters, Bernhard UL et al

Scientific Conference (2019)

Selective Laser Sintering (SLS) is an efficient method for manufacturing complex geometries with high strength and durability. The SLS process subjects a powder bed to thermal cycles allowing theparticles ... [more ▼]

Selective Laser Sintering (SLS) is an efficient method for manufacturing complex geometries with high strength and durability. The SLS process subjects a powder bed to thermal cycles allowing theparticles to coalesce into a solid part without being completely melted. The thermal cycles along withthe thermo-mechanical properties of the powder dictate the properties of the manufactured part.Choosing optimal parameters that lead to functional parts with the desired stiffness, density andstrength requires extensive testing. Microscales models such that Molecular dynamics and DiscreteParticles offer great flexibilities and capacity to reproduce the SLS process from the physical point ofview [1].This study presents a multi-physical model based on the Extended Discrete Element Method forsimulating the thermodynamics and thermo-mechanics that take place in the SLS process as well asthe microstructure evolution of the part. A thermo-viscoelastic constitutive model for discreteparticles is coupled with heat transfer, sintering and fracture to predict.A genetic algorithm is employed to identify optimal process parameters, namely laser power,scanning speed, preheating temperature and layer thickness in an automated iterative process. Theseparameters are identified so that the density and strength of the cooled part meet the target values. [less ▲]

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See detailThe XDEM Multi-physics and Multi-scale Simulation Technology: Review on DEM-CFD Coupling, Methodology and Engineering Applications
Peters, Bernhard UL; Baniasadi, Maryam UL; Baniasadi, Mehdi UL et al

in Particuology (2019), 44

The XDEM multi-physics and multi-scale simulation platform roots in the Ex- tended Discrete Element Method (XDEM) and is being developed at the In- stitute of Computational Engineering at the University ... [more ▼]

The XDEM multi-physics and multi-scale simulation platform roots in the Ex- tended Discrete Element Method (XDEM) and is being developed at the In- stitute of Computational Engineering at the University of Luxembourg. The platform is an advanced multi- physics simulation technology that combines flexibility and versatility to establish the next generation of multi-physics and multi-scale simulation tools. For this purpose the simulation framework relies on coupling various predictive tools based on both an Eulerian and Lagrangian approach. Eulerian approaches represent the wide field of continuum models while the Lagrange approach is perfectly suited to characterise discrete phases. Thus, continuum models include classical simulation tools such as Computa- tional Fluid Dynamics (CFD) or Finite Element Analysis (FEA) while an ex- tended configuration of the classical Discrete Element Method (DEM) addresses the discrete e.g. particulate phase. Apart from predicting the trajectories of individual particles, XDEM extends the application to estimating the thermo- dynamic state of each particle by advanced and optimised algorithms. The thermodynamic state may include temperature and species distributions due to chemical reaction and external heat sources. Hence, coupling these extended features with either CFD or FEA opens up a wide range of applications as diverse as pharmaceutical industry e.g. drug production, agriculture food and processing industry, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology. [less ▲]

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See detailA Discrete-Continuous Method for Predicting Thermochemical Phenomena in a Cement Kiln and Supporting Indirect Monitoring
Copertaro, Edoardo UL; Estupinan Donoso, Alvaro Antonio UL; Peters, Bernhard UL

in Engineering Journal (2018), 22(6), 165-183

Thermochemical phenomena involved in cement kilns are still not well understood because of their complexity, besides technical difficulties in achieving direct measurements of critical process variables ... [more ▼]

Thermochemical phenomena involved in cement kilns are still not well understood because of their complexity, besides technical difficulties in achieving direct measurements of critical process variables. This article addresses the problem of their comprehensive numerical prediction. The presented numerical model exploits Computational Fluid Dynamics and Finite Difference Method approaches for solving the gas domain and the rotating wall, respectively. The description of the thermochemical conversion and movement of the powder particles is addressed with a Lagrangian approach. Coupling between gas, particles and the rotating wall includes momentum, heat and mass transfer. Three-dimensional numerical predictions for a full-size cement kiln are presented and they show agreement with experimental data and benchmark literature. The quality and detail of the results are believed to provide a new insight into the functioning of a cement kiln. Attention is paid to the computational burden of the model and a methodology is presented for reducing the time-to-solution and paving the way for its exploitation in quasireal-time, indirect monitoring. [less ▲]

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See detailSOFTENING AND MELTING MODELING OF IRON ORE PARTICLES USING A CFD-DEM COUPLING METHOD
Baniasadi, Mehdi UL; Peters, Bernhard UL

Scientific Conference (2018, September 25)

The iron-bearing particles start softening and melting because of the weight of burden above and the high temperature in the middle of the blast furnace so-called cohesive zone. In this region, as ... [more ▼]

The iron-bearing particles start softening and melting because of the weight of burden above and the high temperature in the middle of the blast furnace so-called cohesive zone. In this region, as particles are softened, the void space between particles decreases. As the temperature increases further, the softened particles start melting and generate two different liquids: molten iron and slag. Then the generated liquids trickle down to the lower part of the blast furnace. The softening and melting process forms the impermeable ferrous layers forcing gas to flow horizontally through the permeable coke windows. These phenomena have a big effect on the operation of the blast furnace, and since it is not possible to interrupt the blast furnace to investigate details of the phenomena occurring inside, the numerical simulation becomes more practical. In this contribution, the eXtended Discrete Element Method (XDEM) as an advanced numerical tool based on the discrete-continuous framework, is used. Within this model, the gas and liquid phases are described by computational fluid dynamics (CFD) and the soft-sphere discrete element approach (DEM) is used for the coke and iron ore particles. Continuous phases are coupled to the discrete entities through mass, momentum, and energy exchange. Moreover, the internal temperature distribution of the particles is described. The particle’s deformation, temperature, melting, and shrinking along with the saturation of molten iron and slag are examined using the XDEM method. [less ▲]

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See detailVerlet buffer for broad phase interaction detection in Discrete Element Method
Mainassara Chekaraou, Abdoul Wahid UL; Rousset, Alban UL; Besseron, Xavier UL et al

Poster (2018, September 24)

The Extended Discrete Element Method (XDEM) is a novel and innovative numerical simulation technique that extends the dynamics of granular materials or particles as described through the classical ... [more ▼]

The Extended Discrete Element Method (XDEM) is a novel and innovative numerical simulation technique that extends the dynamics of granular materials or particles as described through the classical discrete element method (DEM) by additional properties such as the thermodynamic state, stress/strain for each particle. Such DEM simulations used by industries to set up their experimental processes are complexes and heavy in computation time. Therefore, simulations have to be precise, efficient and fast in order to be able to process hundreds of millions of particles. To tackle this issue, such DEM simulations are usually parallelized with MPI. One of the most expensive computation parts of a DEM simulation is the collision detection of particles. It is classically divided into two steps: the broad phase and the narrow phase. The broad phase uses simplified bounding volumes to perform an approximated but fast collision detection. It returns a list of particle pairs that could interact. The narrow phase is applied to the result of the broad phase and returns the exact list of colliding particles. The goal of this research is to apply a Verlet buffer method to (X)DEM simulations regardless of which broad phase algorithm is used. We rely on the fact that such DEM simulations are temporal coherent: the neighborhood only changes slightly from the last time-step to the current time-step. We use the Verlet buffer method to extend the list of pairs returned by the broad phase by stretching the particles bounding volume with an extension range. This allows re-using the result of the broad phase for several time-steps before an update is required once again and thereby its reduce the number of times the broad phase is executed. We have implemented a condition based on particles displacements to ensure the validity of the broad phase: a new one is executed to update the list of colliding particles only when necessary. This guarantees identical results because approximations introduced in the broad phase by our approach are corrected in the narrow phase which is executed at every time-steps anyway. We perform an extensive study to evaluate the influence of the Verlet extension range on the performance of the execution in terms of computation time and memory consumption. We consider different test-cases, partitioners (ORB, Zoltan, METIS, SCOTCH, ...), broad phase algorithms (Link cell, Sweep and prune, ...) and grid configurations (fine, coarse), sequential and parallel (up to 280 cores). While a larger Verlet buffer increases the cost of the broad phase and narrow phase, it also allows skipping a significant number of broad phase execution (> 99 \%). As a consequence, our first results show that this approach can speeds up the total .execution time up to a factor of 5 for sequential executions, and up to a factor of 3 parallel executions on 280 cores while maintaining a reasonable memory consumption. [less ▲]

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See detailA co-located partitions strategy for parallel CFD-DEM couplings
Pozzetti, Gabriele UL; Besseron, Xavier UL; Rousset, Alban UL et al

in Advanced Powder Technology (2018)

In this work, a new partition-collocation strategy for the parallel execution of CFD–DEM couplings is investigated. Having a good parallel performance is a key issue for an Eulerian-Lagrangian software ... [more ▼]

In this work, a new partition-collocation strategy for the parallel execution of CFD–DEM couplings is investigated. Having a good parallel performance is a key issue for an Eulerian-Lagrangian software that aims to be applied to solve industrially significant problems, as the computational cost of these couplings is one of their main drawback. The approach presented here consists in co-locating the overlapping parts of the simulation domain of each software on the same MPI process, in order to reduce the cost of the data exchanges. It is shown how this strategy allows reducing memory consumption and inter-process communication between CFD and DEM to a minimum and therefore to overcome an important parallelization bottleneck identified in the literature. Three benchmarks are proposed to assess the consistency and scalability of this approach. A coupled execution on 280 cores shows that less than 0.1% of the time is used to perform inter-physics data exchange. [less ▲]

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