References of "Peters, Bernhard 50002840"
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See detailProcess analysis in thermal process engineering with high-performance computing using the example of grate firing
Peters, Bernhard UL; Rousset, Alban UL; Besseron, Xavier UL et al

in 12th European Conference on Industrial Furnaces and Boilers (in press)

Biomass as a renewable energy source continues to grow in popularity to reduce fossil fuel consumption for environmental and economic benefits. In the present contribution, the combustion chamber of a 16 ... [more ▼]

Biomass as a renewable energy source continues to grow in popularity to reduce fossil fuel consumption for environmental and economic benefits. In the present contribution, the combustion chamber of a 16 MW geothermal steam super-heater, which is part of the Enel Green Power "Cornia 2" power plant, is being investigated with high-performance computing methods. For this purpose, the extended discrete element method (XDEM) developed at the University of Luxembourg is used in a high-performance computing environment, which includes both the moving wooden bed and the combustion chamber above it. The XDEM simulation platform is based on a hybrid four-way coupling between the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). In this approach, particles are treated as discrete elements that are coupled by heat, mass, and momentum transfer to the surrounding gas as a continuous phase. For individual wood particles, besides the equations of motion, the differential conservation equations for mass, heat, and momentum are solved, which describe the thermodynamic state during thermal conversion. The consistency of the numerical results with the actual system performance is discussed in this paper to determine the potentials and limitations of the approach. [less ▲]

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See detailA Discrete Element Framework for Modeling the Mechanical Behaviour of Snow PART I: Mechanical Behaviour and Numerical Model
Kabore, Brice Wendlassida UL; Peters, Bernhard UL; Michael, Mark et al

in Granular Matter (in press)

A framework for investigating the mechanics of snow is proposed based on an advanced micro-scale approach. Varying strain rates, densities and temperatures are taken into account. Natural hazards i.e ... [more ▼]

A framework for investigating the mechanics of snow is proposed based on an advanced micro-scale approach. Varying strain rates, densities and temperatures are taken into account. Natural hazards i.e. snow avalanches are triggered by snow deforming at low rates, while a large group of industrial applications concerning driving safety or winter sport activities require an understanding of snow behaviour under high deformation rates. On the micro-scale, snow is considered to consist of ice grains joined by ice bonds to build a porous structure. Deformation and failure of bonds and the inter-granular collisions of ice grains determine the macroscopic response under mechanical load. Therefore, this study proposes an inter-granular bond and collision model for snow based on the discrete element method (DEM) to describe interaction on a grain-scale. It aims at predicting the mechanical behaviour of ice particles under different strain rates using a unified approach. Thus, the proposed algorithm predicts the displacement of each individual grains due to inter-granular forces and torques that derive from bond deformation and grain collision. For this purpose, the inter-granular characteristics are approximated by an elastic viscous-plastic material law which is based on the temperature-dependent properties of poly-crystalline ice Ih. [less ▲]

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See detailA Discrete Element Framework for Modeling the Mechanical Behaviour of Snow PART II: Model Validation
Peters, Bernhard UL; Kabore, Brice Wendlassida UL; Mark, Michael et al

in Granular Matter (in press)

A micro-scale modelling approach of snow based on the extension of the classical discrete element method (DEM) has been presented in the first part of this study. This modelling approach is employed to ... [more ▼]

A micro-scale modelling approach of snow based on the extension of the classical discrete element method (DEM) has been presented in the first part of this study. This modelling approach is employed to predict the mechanical response of snow under compression dependent on strain rate, initial density and temperature. Results obtained under a variety of conditions are validated with experimental data for both micro- and macro-scale, in particular the broad range between ductile i.e.~low deformation rates and brittle i.e.~high deformation rates regimes are investigated. For this purpose snow is assumed to be composed of ice grains that are inter-connected by a network of bonds between neighbouring grains. This arrangement represents the micro-scale of which the interaction is described by inter-granular collision and bonding. Hence, the response on a macro-scale is largely determined by inter-granular collisions and deformation and failure of bonds during a loading cycle. Consequently, validation was first carried out on micro-scale deformations at different loading rates and temperatures. Hereafter, macro-scale simulations of confined and unconfined, deformation-controlled compression tests have been predicted and were successfully compared to experimental data reported in literature. [less ▲]

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See detailBuffer XDEM
Mainassara Chekaraou, Abdoul Wahid UL; Besseron, Xavier UL; Rousset, Alban UL et al

Scientific Conference (in press)

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See detailHPC Multi-physics Biomass Furnace simulations as a Service
Besseron, Xavier UL; Rusche, Henrik; Peters, Bernhard UL et al

Scientific Conference (2020, November)

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See detailROS networks: designs, aging, Parkinson's disease and precision therapies.
Kolodkin, Alexey UL; Colangelo, AM; Ignatenko, A et al

in NPJ Systems Biology and Applications (2020)

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See detailLowering the obstacles for SMEs to adopt multi-physics biomass furnace simulations by providing a cloud based solution
Rusche, Henrik; Peters, Bernhard UL; Besseron, Xavier UL et al

Scientific Conference (2020, October 14)

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See detailAccelerating fatigue simulations of a phase-field damage model for rubber
Loew, Pascal Juergen UL; Poh, Leong Hien; Peters, Bernhard UL et al

in Computer Methods in Applied Mechanics and Engineering (2020), 370(113247),

Phase-field damage models are able to describe crack nucleation as well as crack propagation and coalescence without additional technicalities, because cracks are treated in a continuous, spatially finite ... [more ▼]

Phase-field damage models are able to describe crack nucleation as well as crack propagation and coalescence without additional technicalities, because cracks are treated in a continuous, spatially finite manner. Previously, we have developed a phase-field model to capture the rate-dependent failure of rubber, and we have further enhanced it to describe failure due to cyclic loading. Although the model accurately describes fatigue failure, the associated cyclic simulations are slow. Therefore, this contribution presents an acceleration scheme for cyclic simulations of our previously introduced phase-field damage model so that the simulation speed is increased to facilitate large-scale simulations of industrially relevant problems. We formulate an explicit and an implicit cycle jump method, which, depending on the selected jump size, reduce the calculation time up to 99.5%. To circumvent the manual tuning of the jump size, we also present an adaptive jump size selection procedure. Thanks to the implicit adaptive scheme, all material parameters are identified from experiments, which include fatigue crack nucleation and crack growth. Finally, the model and its parameters are validated with additional measurements of the fatigue crack growth rate. [less ▲]

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See detailNumerical Analysis of Interaction between a Reacting Fluid and a Moving Bed with Spatially and Temporally Fluctuating Porosity
Rousset, Alban UL; Mainassara Chekaraou, Abdoul Wahid UL; Besseron, Xavier UL et al

Scientific Conference (2020, August 31)

The purpose of this study is to propose a numerical approach that combines low computational costs through the use of high computing efficiency, allowing the realistic use of the design with a sufficient ... [more ▼]

The purpose of this study is to propose a numerical approach that combines low computational costs through the use of high computing efficiency, allowing the realistic use of the design with a sufficient result's accuracy for industrial applications to investigate biomass combustion in a large-scale reciprocating grate. In the present contribution, a Biomass combustion chamber of a 16 MW geothermal steam super-heater, which is part of the Enel Green Power "Cornia 2" power plant,is being investigated with high-performance computing methods. For this purpose, the extended discrete element method (XDEM) developed at the University of Luxembourg is used in an HPC environment, which includes both the moving wooden bed and the combustion chamber above it. The XDEM simulation platform is based on a hybrid four-way coupling between the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). In this approach, particles are treated as discrete elements that are coupled by heat, mass, and momentum transfer to the surrounding gas as a continuous phase. For individual wood particles, besides the equations of motion, the differential conservation equations for mass, heat, and momentum are solved, which describe the thermodynamic state during thermal conversion. The grate system has three different moving sections to ensure good mixing of the biomass parts and appropriate residence time. The primary air enters from below the grate and is split into four different zones. Furthermore, a secondary air is injected at high velocity straight over the fuel bed through nozzles. A Flue Gas Recirculation is present and partly injected through two jets along the vertical channel and partly from below the grate. The numerical 3D model presented is based on a multi-phase approach. The biomass particles are taken into consideration via the XDEM Method, while the gaseous phase is described by CFD with OpenFOAM. Thus, the combustion of the particles on the moving beds in the furnace is processed by XDEM through conduction, radiation and conversion along with the interaction with the surrounding gas phase accounted for by CFD. The coupling of CFD-XDEM as an Euler-Lagrange model is used. The fluid phase is a continuous phase handled with an Eulerian approach and each particle is tracked with a Lagrangian approach. Energy, mass and momentum conservation is applied for every single particle and the interaction of particles with each other in the bed and with the surrounding gas phase are taken into account. An individual particle can have a solid, liquid, gas or inert material phases (immobile species) at the same time. The different phases can undergo a series of conversion through various reactions that can be homogeneous, heterogeneous or intrinsic (drying, pyrolysis, gasification and oxidation). Our first results are consistent with actual data obtained from the sampling of the residual solid in the industrial plant. Our model is also able to predict gas flux behaviour inside the furnace, particularly the flue gas recirculation on the combustion process injection. [less ▲]

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See detailParallel coupling strategy for multi-physics applications in eXtended Discrete Element Method
Besseron, Xavier UL; Rousset, Alban UL; Mainassara Chekaraou, Abdoul Wahid UL et al

Scientific Conference (2020, June 18)

Multi-physics problems containing discrete particles interacting with fluid phases are widely used industry for example in biomass combustion on a moving grate, particle sedimentation, iron production ... [more ▼]

Multi-physics problems containing discrete particles interacting with fluid phases are widely used industry for example in biomass combustion on a moving grate, particle sedimentation, iron production within a blast furnace, and selective laser melting for additive manufacturing. The eXtended Discrete Element Method (XDEM) uses a coupled Eulerian-Lagrangian approach to simulate these complex phenomena, and relies on the Discrete Element Method (DEM) to model the particle phase and Computational Fluid Dynamics (CFD) for the fluid phases, solved respectively with XDEM and OpenFOAM. However, such simulations are very computationally intensive. Additionally, because the DEM particles move within the CFD phases, a 3D volume coupling is required, hence it represents an important amount of data to be exchanged. This volume of communication can have a considerable impact on the performance of the parallel execution. To address this issue, XDEM has proposed a coupling strategy relying on a co-located partitioning. This approach coordinates the domain decomposition of the two independent solvers, XDEM and OpenFOAM, to impose some co-location constraints and reduce the overhead due to the coupling data exchange. This strategy for the parallel coupling of CFD-DEM has been evaluated to perform large scale simulations of debris within a dam break flow. [less ▲]

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See detailPredicting near-optimal skin distance in Verlet buffer approach for Discrete Element Method
Mainassara Chekaraou, Abdoul Wahid UL; Besseron, Xavier UL; Rousset, Alban UL et al

in 10th IEEE Workshop on Parallel / Distributed Combinatorics and Optimization (2020, June)

The Verlet list method is a well-known bookkeeping technique of the interaction list used both in Molecular Dynamic (MD) and Discrete Element Method (DEM). The Verlet buffer technique is an enhancement of ... [more ▼]

The Verlet list method is a well-known bookkeeping technique of the interaction list used both in Molecular Dynamic (MD) and Discrete Element Method (DEM). The Verlet buffer technique is an enhancement of the Verlet list that consists of extending the interaction radius of each particle by an extra margin to take into account more particles in the interaction list. The extra margin is based on the local flow regime of each particle to account for the different flow regimes that can coexist in the domain. However, the choice of the near-optimal extra margin (which ensures the best performance) for each particle and the related parameters remains unexplored in DEM unlike in MD. In this study, we demonstrate that the near-optimal extra margin can fairly be characterized by four parameters that describe each particle local flow regime: the particle velocity, the ratio of the containing cell size to particle size, the containing cell solid fraction, and the total number of particles in the system. For this purpose, we model the near-optimal extra margin as a function of these parameters using a quadratic polynomial function. We use the DAKOTA SOFTWARE to carry out the Design and Analysis of Computer Experiments (DACE) and the sampling of the parameters for the simulations. For a given instance of the set of parameters, a global optimization method is considered to find the near-optimal extra margin. The latter is required for the construction of the quadratic polynomial model. The numerous simulations generated by the sampling of the parameter were performed on a High-Performance Computing (HPC) environment granting parallel and concurrent executions. This work provides a better understanding of the Verlet buffer method in DEM simulations by analyzing its performances and behavior in various configurations. The near-optimal extra margin can reasonably be predicted by two out of the four chosen parameters using the quadratic polynomial model. This model has been integrated into XDEM in order to automatically choose the extra margin without any input from the user. Evaluations on real industrial-level test cases show up to a 26% reduction of the execution time. [less ▲]

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See detail6-way coupling of DEM+CFD+FEM with preCICE
Besseron, Xavier UL; Rousset, Alban UL; Peyraut, Alice et al

Presentation (2020, February)

In this work, we present our preliminary results on the 6-way coupling of 3 numerical solvers: XDEM for the Discrete Element Method (DEM), OpenFOAM for Computation Fluid Dynamics (CFD), and deal.II for ... [more ▼]

In this work, we present our preliminary results on the 6-way coupling of 3 numerical solvers: XDEM for the Discrete Element Method (DEM), OpenFOAM for Computation Fluid Dynamics (CFD), and deal.II for Finite Element Method (FEM). We relied on the existing preCICE adapters for OpenFOAM and deal.II and we have implemented a new preCICE adapter for the eXtended Discrete Element Method (XDEM), an innovative DEM software developed at the University of Luxembourg. The XDEM adapter permits coupling of the particulate phase of DEM with CFD and FEM: - DEM+FEM is a surface coupling that performs the exchange of surface forces and displacement between the particles and a deformable solid; - DEM+CFD is a volume coupling that performs the exchange of porosity, momentum, drag force and buoyancy between the particles and the fluid. Put together with the pre-existing CFD+FEM coupling, we obtain a 6-way coupled multi-physics solver for particles, fluid and deformable solids. We have tested and evaluated our multi-physics solver on the tutorial case “Cylinder with a flap” derived from the benchmarking case of Turek and Hron, that we extended to include a particulate phase solved by XDEM. [less ▲]

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See detailDEM simulation of dense granular flows in a vane shear cell: Kinematics and rheological laws
Qi, Fenglei UL; Kiesgen de Richter, Sebastien; Jenny, Mathieu et al

in Powder Technology (2020)

The rheology of dense granular flows is investigated through discrete element method (DEM) simulation of a vane shear cell. From the simulation, profiles of shear stress, shear rate, and velocity are ... [more ▼]

The rheology of dense granular flows is investigated through discrete element method (DEM) simulation of a vane shear cell. From the simulation, profiles of shear stress, shear rate, and velocity are obtained, which demonstrates that the flow features in the vane shear cell are equivalent to those in the classic annular Couette cell. A novel correlation for the shear viscosity is formulated and leads to a new expression for μKT in the kinetic theory analysis. The μKT formulation is able to qualitatively capture the μ-I relation in the shear cell. A correlation length is added in the energy dissipation term to account for the effects of the particle motion correlation. A simplified correlation length model is derived based on DEM results and is compared with the literature. The modified granular kinetic energy equation is able to correctly predict the granular temperature profiles in the shear cell. [less ▲]

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See detailFatigue phase-field damage modeling of rubber using viscous dissipation: Crack nucleation and propagation
Loew, Pascal Juergen UL; Peters, Bernhard UL; Beex, Lars UL

in Mechanics of Materials (2020), 142

By regularizing sharp cracks within a pure continuum setting, phase-damage models offer the ability to capture crack nucleation as well as crack propagation. Crack branching and coalescence can ... [more ▼]

By regularizing sharp cracks within a pure continuum setting, phase-damage models offer the ability to capture crack nucleation as well as crack propagation. Crack branching and coalescence can furthermore be described without any additional efforts, as geometrical descriptions of the cracks are not required. In this contribution, we extend our previous phase-field model for rate-dependent fracture of rubbers in a finite strain setting (Loew et al., 2019) to describe damage under cyclic loading. The model is derived from the balance of mechanical energy and introduces a fatigue damage source as a function of the accumulated viscous dissipation under cyclic loading. We use uniaxial cyclic tension to present the influence of the fatigue material parameters and to confirm the model’s energy balance. The parameters are subsequently identified using monotonic and cyclic experiments of a plane stress nature. Finally, the model is validated by separate experiments, which demonstrate that the model accurately predicts (fatigue) crack nucleation as well as propagation. [less ▲]

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See detailData Centric Engineering and Data-Driven Modelling - Computational Engineering Lab Report 2019
Bordas, Stéphane UL; Peters, Bernhard UL; Viti, Francesco UL et al

Report (2019)

https://www.cambridge.org/core/journals/data-centric-engineering

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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 detailVerlet buffer for (X)DEM
Mainassara Chekaraou, Abdoul Wahid UL; Rousset, Alban UL; Besseron, Xavier UL et al

Scientific Conference (2019, July 26)

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 complex and heavy in computation time. Those simulations perform at each time step a collision detection to generate a list of interacting particles that is one of the most expensive computation parts of a DEM simulation. The Verlet buffer method, which was first introduced in Molecular Dynamic (MD) (and is also used in DEM) allows to keep the interaction list for many time step by extending each particle neighborhood by a certain extension range, and thus broadening the interaction list. The method relies mainly on the stability of the DEM, which ensures that no particles move erratically or unpredictably from one time step to the next: this is called temporal coherency. In the classical and current approach, all the particles have their neighborhood extended by the same value which leads to suboptimal performances in simulations where different flow regimes coexist. Additionally, and unlike in MD (which remains very different from DEM on several aspects), there is no comprehensive study analyzing the different parameters that affect the performance of the Verlet buffer method in DEM. In this work, we apply a dynamic neighbor list update method that depends on the particle's individual displacement, and an extension range specific to each particle and based on their local flow regime for the generation of the neighbor list. The update of the interaction list is analyzed throughout the simulation based on the displacement of the particle allowing a flexible update according to the flow regime conditions. We evaluate the influence of the Verlet extension range on the performance of the execution time through different test cases and we empirically analyze and define the extension range value giving the minimum of the global simulation time. [less ▲]

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