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Steinau an der Straße, Germany

Mahmoudi A.H.,University of Luxembourg | Hoffmann F.,InuTech GmbH | Peters B.,University of Luxembourg
Applied Thermal Engineering | Year: 2016

The main aim of this study was to present a new approach for modeling multi-phase systems of granular media in which solid phases are fully resolved while the surrounding gas phase is semi-resolved. The presented method is based on a volume averaging model implemented in the XDEM framework in which the fluid phase is a continuous phase and individual particles are tracked with a Lagrangian approach. In the semi-resolved model, the gas phase is described on a length scale smaller than the particles size. This method facilitates mesh generation for complex geometries. Moreover, it is computationally less expensive than a fully resolved model since it allows for coarser grids to solve gas flow through the void space between particles. In this work, the proposed model is used to predict heat-up of steel particles and pyrolysis of wet wood particles in a packed bed. Numerical results have been compared with experimental data and good agreements were achieved. Detailed results in both gas and solid phases are presented, which highlight the process heterogeneities of non-uniformly packed beds. © 2015 Elsevier Ltd. All rights reserved.

Sondergaard N.,InuTech GmbH | Renno J.,University of Southampton
Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering and USD 2014 - International Conference on Uncertainty in Structural Dynamics | Year: 2014

Curved and straight beams are present in many built-up structures. These beams are often connected to each other and analysing the wave behaviour of these structures has numerous benefits, especially in them mid-and high-frequency range. Developing analytical models for such structures can be achieved for isotropic, homogeneous beams. However, analytical models for beams with complicated constructions, e.g. laminated, sandwiched or periodic, are more difficult to find and in some cases, impractical to set up. In this paper, the wave behaviour of curved beams is considered. In particular, the power flow between straight and out-of-plane, curved, i.e., helical beams is considered. The study takes advantage of a numerical method, the wave and finite element (WFE) method, which is a technique that can be used to resolve wave behaviour in arbitrarily complicated straight and curved waveguides. The latter allows investigating the power flow in beam structures that can have arbitrarily complicated cross-sections and even waveguides that comprise periodic cells. Numerical examples are presented to demonstrate the effect of out-of-plane curvature on the power flow in beam structures.

Michael M.,University of Luxembourg | Vogel F.,InuTech GmbH | Peters B.,University of Luxembourg
Computer Methods in Applied Mechanics and Engineering | Year: 2015

This study proposes an efficient combination of the Discrete Element Method (DEM) and the Finite Element Method (FEM) to study the tractive performance of a rubber tire in interaction with granular terrain. The presented approach is relevant to all engineering devices interacting with granular matter which causes response forces. Herein, the discrete element method (DEM) is used to describe the dynamics of the granular assembly. On the one hand, the discrete approach accounts for the motion and forces of each grain individually. On the other hand, the finite element method accurately predicts the deformations and stresses acting within the tire tread. Hence, the simulation domain occupied by the tire tread is efficiently described as a continuous entity. The coupling of both methods is based on the interface shared by the two spatially separated domains. Contact forces develop at the interface and propagate into each domain. The coupling method enables to capture both responses simultaneously and allows to sufficiently resolve the different length scales. Each grain in contact with the surface of the tire tread generates a contact force which it reacts on repulsively. The contact forces sum up over the tread surface and cause the tire tread to deform. The coupling method compensates quite naturally the shortages of both numerical methods. It further employs a fast contact detection algorithm to save valuable computation time. The proposed DEM-FEM coupling technique was employed to study the tractive performance of a rubber tire with lug tread patterns in a soil bed. The contact forces at the tread surface are captured by 3D simulations for a tire slip of sT=5%. The simulations showed to accurately recapture the gross tractive effort TH, running resistance TR and drawbar pull TP of the tire tread in comparison to related measurements. Further, the traction mechanisms between the tire tread and the granular ground are studied by analyzing the motion of the soil grains and the deformation of the tread. © 2015 Elsevier B.V.

Sondergaard N.,InuTech GmbH | Chappell D.J.,Nottingham Trent University
Journal of Sound and Vibration | Year: 2016

We propose wave and ray approaches for modelling mid- and high-frequency structural vibrations through smoothed joints on thin shell cylindrical ridges. The models both emerge from a simplified classical shell theory setting. The ray model is analysed via an appropriate phase-plane analysis, from which the fixed points can be interpreted in terms of the reflection and transmission properties. The corresponding full wave scattering model is studied using the finite difference method to investigate the scattering properties of an incident plane wave. Through both models we uncover the scattering properties of smoothed joints in the interesting mid-frequency region close to the ring frequency, where there is a qualitative change in the dynamics from anisotropic to simple geodesic propagation. © 2016 Elsevier Ltd.

Mahmoudi A.H.,University of Luxembourg | Hoffmann F.,InuTech GmbH | Peters B.,University of Luxembourg | Besseron X.,University of Luxembourg
International Communications in Heat and Mass Transfer | Year: 2016

Conversion of biomass as a renewable source of energy is one of the most challenging topics in industry and academy. Numerical models may help designers to understand better the details of the involved processes within the reactor, to improve process control and to increase the efficiency of the boilers. In this work, XDEM as an Euler-Lagrange model is used to predict the heat-up, drying and pyrolysis of biomass in a packed bed of spherical biomass particles. The fluid flow through the void space of a packed bed (which is formed by solid particles) is modeled as three-dimensional flow through a porous media using a continuous approach. The solid phase forming the packed bed is represented by individual, discrete particles which are described by a Lagrangian approach. On the particle level, distributions of temperature and species within a single particle are accounted for by a system of one-dimensional and transient conservation equations. The model is compared to four sets of experimental data from independent research groups. Good agreements with all experimental data are achieved, proving reliability of the used numerical methodology. The proposed model is used to investigate the impact of particle size in combination with particle packing on the char production. For this purpose, three setups of packed beds differing in particle size and packing mode are studied under the same process conditions. The predicted results show that arranging the packed bed in layers of small and large particles may increase the final average char yield for the entire bed by 46 %. © 2015 Elsevier B.V.

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