An analytical solution of different configurations of the linear viscoelastic normal and frictional-elastic tangential contact model

In the current study an analytical solution describing the impact of a spherical particle on a rigid wall is derived. The contact is linear viscoelastic in normal and frictional-elastic in tangential direction. Due to its simplicity, the model combination considered is one of the most common in the framework of the Discrete Element Method especially for large-scale simulations. The linear viscoelastic normal model is realized according to Zhang and Whiten [1996. The calculation of contact forces between particles using spring and damping models. Powder Technology 88, 59-64.] assuming a contact to be ceased when the normal force attains a value of zero. In literature the frictional elastic tangential model is employed in three different configurations following Cundall and Strack [1979. A discrete numerical model for granular assemblies. Geotechnique 29, 47-65], Di Maio and Di Renzo [2004. Analytical solution for the problem of frictional-elastic collisions of spherical particles using the linear model. Chemical Engineering Science 59 (16), 3461-3475] and Brendel and Dippel [1998. Lasting contacts in molecular dynamics simulations. In: Herrmann, H.J., Hovi, J.-P., Luding, S. (Eds.), Physics of Dry Granular Media. Kluwer Academic Publishers, Dordrecht, 1998, p. 313]. The differences among these configurations are briefly explained, whereas the focus is set on the two most accurate model formulations given in the first two papers. All important final collision properties as positions and velocities are derived in an analytical form. Based on these results a comparison with experimental data of particle/wall and particle/particle collisions by Foerster et al. [1994. Measurements of the collision properties of small spheres. Physics of Fluids 6(3), 1108-1115], Lorenz et al. [1997. Measurements of impact properties of small, nearly spherical particles. Experimental Mechanics 37(3), 292-298] and Gorham and Kharaz [2000. The measurement of particle rebound characteristics. Powder Technology 112(3), 193-202] is performed, showing very good agreement especially for the model configuration of Di Maio and Di Renzo. The analytical solution as derived here helps understanding the complex collision process and can be applied for the evaluation of integration methods or in the context of an event-driven discrete element method.     

Reactive navigation through multiscroll systems: from theory to real-time implementation

In this paper a new reactive layer for multi-sensory integration applied to robot navigation is proposed. The new robot navigation technique exploits the use of a chaotic system able to be controlled in real-time towards less complex orbits, like periodic orbits or equilibrium points, considered as perceptive orbits. These are subject to real-time modifications on the basis of environment changes acquired through a distributed sensory system. The strategy is inspired to the olfactory bulb neural activity observed in rabbits subject to external stimuli. The mathematical details of the approach are given including simulation results in a virtual environment. Furthermore the proposed strategy has been tested on an experimental environment consisting of an FPGA-based hardware driving an autonomous roving robot. The obtained results demonstrate the capability to perform a real-time navigation control.     

加强交流合作共赴美好未来

北京国际防水展览会已经成为我们行业的一次重要盛会，对经济和社会产生了积极的影响。前年我对展会的访问．使我有机会亲眼看到北京一片欣欣向荣的景象。北京现代而宏伟的建筑以及高质量的防水产品标准都给我留下了深刻的印象。我相信2006年的展会必将再一次成为建筑和防水行业前进的推动力。     

Numerical Calculations of Spray Roasting Reactors of the Steel Industry with Special Emphasis on Fe2O3‐Particle Formation

This work presents numerical calculations for the lay‐out of spray roasting reactors for the steel industry. In these reactors, a pickling liquor based on water and HCl containing FeCl₂ is regenerated in a combustor leading to the formation of Fe₂O₃ particles. For the lay‐out of these reactors, detailed knowledge of the flow and temperature field, the associated gas phase reactions, and especially, of the formation of the Fe₂O₃ particles is required. An extended particle formation model is presented which is based on earlier work. Finally, results for an industrial spray roasting reactor are given showing the potential of the numerical tools developed for the improvement of the technical lay‐out of such thermal reactors.     

Consumer attitude and behaviour towards tomatoes after 10 years of Flandria quality labelling

In recent years, trust in food safety and food quality has decreased as a result of consecutive food crises. Consequently, numerous quality labels signalling process-related credence characteristics have been established. One of these labels is the Belgian Flandria quality label for fresh fruit and vegetables. Based on cross-sectional data collected through a self-administered consumer survey ( n  = 373), this paper addresses consumer attitudes, behaviour and perception towards tomatoes in general, and the Flandria tomato label in particular. Buyers, who constitute 26.8% of the sample, perceive Flandria tomatoes as superior to other tomatoes because of their guarantee of origin, better taste and stricter production control. However, they also report the strongest perception of Flandria as an ordinary tomato as compared to non-buyer segments. Overall, findings indicate that the Flandria label – after being intensively used for 10 years for a wide range of other fruits and vegetables besides tomatoes – has become fairly standard for tomatoes with little perceived differentiation apart from its certified production and origin.     

Numerical simulation of grate firing systems using a coupled CFD/discrete element method (DEM)

The objective of this study is to simulate the motion and chemical conversion of solid fuels in a packed bed moving on a forward acting grate. The approach considers a packed bed to be composed of a large number of individual (currently spherical) particles, which have different properties and sizes. Each of these particles undergoes a sequence of processes such as heating, drying, pyrolysis and char combustion. Chemical species and energy are released from the solid phase mix and react in the cross flowing gas phase.This approach for the simulation of a reacting moving bed on a forward acting grate is coupled to the numerical simulation of the reacting flow in the combustion chamber above the grate. For the reacting granular flow the 2D-version of the discrete element code of the Department of Energy Plant Technology (LEAT) is used. For the reacting flow in the combustion chamber the 3D-CFD code ANSYS-CFX has been applied. The concept of discrete element modelling with special emphasis on the multi-physics coupling and the coupling of DEM with ANSYS-CFX is introduced, and the necessary framework is presented. Results are shown for the fluid flow in the combustion chamber and the solid flow on the grate.     

Nano- and micro-scale free volume in ultrafine grained Cu–1 wt.%Pb alloy deformed by equal channel angular pressing

Nano- and micro-scale free volumes in ultrafine grained Cu–1 wt.%Pb alloy deformed by equal channel angular pressing (ECAP) were examined by a combination of radiotracer diffusion measurements, transmission electron microscopy, depth milling by focused ion beam, and positron annihilation spectroscopy. The positron lifetime spectroscopy revealed the existence of vacancy-type defects, presumably related to grain boundary states, and vacancy clusters. The positron annihilation sites probed by coincident Doppler broadening spectroscopy are surrounded by both Cu and Pb atoms, implying preferred nucleation of nanovoids near small Pb inclusions. Larger free volume defects, such as nano- and submicron-sized pores and submicrometer cracks, were directly observed by the focused ion beam technique. Ultra-fast penetration of liquid tracer solution in the sample bulk was established in the radiotracer diffusion experiments. The results provide an unambiguous proof of the existence of open porosity in ultrafine grained Cu–Pb alloy deformed by ECAP. Under specific deformation conditions, a connected network of open channels, which promotes long-range penetration of a liquid radiotracer solution, was shown to form during the severe deformation. The relative volume fraction of the percolating porosity was estimated at about 2 × 10⁻⁶.     

Versioning Support in the HyperProp System

This paper discusses version control for hypermedia models with composite nodes that allow distinct representations of the same information segment to be treated as versions. Several problems arise from the possibility of a node being contained in different nested compositions, as well as being presented (edited) with different representations. The paper discusses these issues, relating partial solutions proposed in several hypermedia models and presenting the proposal defined in the Nested Context Model of the HyperProp system.     

Wasserstoffspeicherung im Fahrzeug

Efficient and clean hydrogen storage technologies for future vehicles will be crucial to secure our future individual mobility. State-of-the-art hydrogen storage systems do net yet fulfil the stringent requirements of the automotive industry and the final customer. Future development targets and prospects for different automotive hydrogen storage systems shall be discussed in this article.