Applications of the discrete element method in mechanical engineering

Compared to other fields of engineering, in mechanical engineering, the Discrete Element Method (DEM) is not yet a well known method. Nevertheless, there is a variety of simulation problems where the method has obvious advantages due to its meshless nature. For problems where several free bodies can collide and break after having been largely deformed, the DEM is the method of choice. Neighborhood search and collision detection between bodies as well as the separation of large solids into smaller particles are naturally incorporated in the method. The main DEM algorithm consists of a relatively simple loop that basically contains the three substeps contact detection, force computation and integration. However, there exists a large variety of different algorithms to choose the substeps to compose the optimal method for a given problem. In this contribution, we describe the dynamics of particle systems together with appropriate numerical integration schemes and give an overview over different types of particle interactions that can be composed to adapt the method to fit to a given simulation problem. Surface triangulations are used to model complicated, non-convex bodies in contact with particle systems. The capabilities of the method are finally demonstrated by means of application examples. Commemorative Contribution.     

Entschwefelung von gerührtem und ungerührtem Roheisen mit kalkreicher Schlacke unter oxidierender Gasatmosphäre

Aus Betriebsergebnissen bei der Pfannenentschwefelung ist ein negativer Einfluß oxidierender Gasphasen bekannt. Daher war es das Ziel der eigenen Untersuchungen in einer geeigneten Apparatur die Wirkung oxidierender Bedingungen in der Gasphase sowohl auf den Verlauf des Schwefelabbaues in der Schlacke als auch des Schwefeltransportes aus dem Roheisen in die Schlacke zu untersuchen. Oxidierende Gasphasen erwirken bei der Pfannenentschwefelung an der Phasengrenze Schlacke/Gas eine Oxidation des Schwefels aus der Schlacke, ohne jedoch bei ruhender Schlackenschicht ein Oxidationspotential in der Schlacke aufzubauen, das bis zur Phasengrenze Roheisen/Schlacke durchgreift und dort die Entschwefelung des Roheisens durch die Siliciumgehalte stört. Sowohl die Entschwefelung des Roheisens als auch die Oxidation des Schwefels aus der Schlacke werden durch höhere Temperaturen und durch eine Rührwirkung gefördert. Der Schwefeltransport wird bei den ungerührten wie bei den gerührten Schmelzen durch Diffusionsvorgänge gesteuert und auch hier durch steigende Temperaturen und rührende Kräfte begünstigt.     

Das Twinning-Programm der Europäischen Union: Praktische Erfahrungen in der Umsetzung von veterinärmedizinischen Verwaltungspartnerschaften

Zusammenfassung:  Mit Verwirklichung des gemeinsamen Binnenmarktes ab 01.01.1993 wurde ein freier Warenverkehr innerhalb der Europ?ischen Union mit Wegfall zwischenstaatlicher Kontrollen im tiergesundheitlichen und lebensmittelsicher-heitsrelevanten Bereich realisiert. In allen Mitgliedstaaten soll ein vergleichbares Schutzniveau bzgl. des gesundheitlichen Verbraucherschutzes erfüllt werden. In der Praxis hat sich jedoch gezeigt, dass die Anwendung des EU-Rechtes in den neuen Mitgliedstaaten teilweise noch Schwierigkeiten bereitet. Vor diesem Hintergrund sind von der Kommission verschiedene Fortbildungs- und F?rderma?nahmen mit der Zielsetzung entwickelt worden, vorhandene Defizite in diesem Bereich zu minimieren. Dazu z?hlen die seit 1998 von der Kommission initiierten sog. Twinning-Projekte (Verwaltungspartnerschaften) zwischen Beh?rden alter und neuer Mitgliedstaaten. Seit diesem Zeitpunkt wurden mehr als 1100 Twinning-Projekte durchgeführt, davon fast 300 Projekte unter deutscher Leitung (Schwerpunkt: Landwirtschaftlicher Bereich). Im vorliegenden Artikel werden Bedeutung und Inhalte von Twinning-Projekten im Veterin?r- und Lebensmittelbereich dargestellt. Ihr formales Verfahren sowie die in den Verwaltungspartnerschaften gewonnenen Erfahrungen und M?glichkeiten der Verbesserung werden erl?utert.

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The Twinning-Programme of the European Union: Experiences in the implementation of Twinning- projects in veterinary and food affairs. Since 01.01.1993 a common market was built up within the EU with cancelling of border controls of foods, animal products and living animals. An equal level of consumer protection should be established in all member states. In practice however, implementation of EU food and feed legislation in the new member states often causes problems. To reduce deficiencies in this field, the EU commission developed several measures of training and strenghtening for new member states. These measures include the so called Twinning-projects between competent authorities of old and new member states, which have been initiated since 1998. More than 1100 Twinning projects have been performed so far, including about 300 projects in Germany (with emphasis on agriculture). This article shows meaning and contents of Twinning-projects in the field of veterinary and food affairs. Formal procedures, experiences and possibilities of improvement of twinning-projects are described.

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Eingegangen: 16. Januar 2008     

Zoonotic Brugian lymphadenitis. An unusual case with florid monocytoid B-cell proliferation

Human infection with a zoonotic Brugia species in the United States is uncommon. Positive identification of the filarial nematode is required for histopathologic diagnosis. Many cases may go unrecognized because of the nonspecific clinical manifestations and the nondiagnostic histologic changes occurring in involved lymph nodes. A case of zoonotic Brugia lymphadenitis is described in a patient from Rhode Island, in which a small nongravid female worm was identified in a lymph node biopsy specimen. The lymph node also showed a spectrum of reaction changes including the presence of florid monocytoid B-cell proliferation, which has not been described in association with zoonotic Brugian filariasis.     

Darstellung komplexer Betriebsschlacken des LD-Verfahrens im Quasidreistoffsystem

Aus der Darstellung der Schlackenzusammensetzungen im Quasidreistoffsystem ist die Lage der Schlacken zur Kalksättigungslinie deutlich zu erkennen. Die Sublanzenschlacken lassen den Schlackenweg während der letzten Blasminuten erkennen, durch Bodenspülung und Nachspülen wird eine geringe Annäherung an die Kalksättigungslinie erreicht. Aus der Lage der Schlacken im Quasidreistoffsystem läßt sich der Einfluß der Temperatur auf den Verlauf der Kalksättigung entlang unterschiedlicher T-X-Schnitte bestimmen.     

DIN-Norm-orientierte Standard-Spezifikationen für Rührwerke

DIN Standard-Oriented Specifications for Stirring Systems. Stirring as a unit operation is characterised by universal application possibilities for material and energy transmission in process industries. DIN standards provide an overview of the wide variety of equipment in technical use and define the conditions for low-cost, exchangeable standard stirring systems. In many cases important process parameters are fixed only for a limited time. Possible operation time should be long, therefore performance reserves are justified; they will be useful for later tasks as well as for improving safety of existing processes. Engineering of such stirring systems requires definition of standard stirring tasks. This article deals with economic aspects, defines standard stirring tasks as well as design conditions and shows the principal engineering data of standard stirring systems for stainless steel vessels up to 20 m³ by means of pictures, tables and nomograms. In conclusion, adequate processing of construction materials as well as surface finishing and practical work with standard specifications for stirring systems are discussed.     

Growth of electrodeposited γ-manganese dioxide from a suspension bath

The addition of solid particles of manganese oxides to the electrolyte of a manganese dioxide production bath (suspension bath process=SBP) allows the anodic current density to be increased to values more than twice that used in the conventional EMD process. This is possible even with the use of titanium anodes which are sensitive to passivation if the current density exceeds critical values. Analysis of deposition conditions and properties of the SBP-EMD shows that the SBP-EMD resembles and EMD which has been deposited at very low current densities. These low current densities are realized by the adsorption of the suspended particles on the anode surface, thereby promoting dendritic crystal growth on the adsorbed particles and increasing the real anode surface by up to a factor of ten. This assumption is able to explain most of the properties found for the SBP-EMD, e.g. X-ray pattern, potential drop, hardness of the deposit, low specific surface area, low content of combined water and high electronic conductivity.     

Effect of center block structure on the physical and rheological properties of ABA block copolymers. Part II. Rheological properties

The effect of the chemical structure of the center block on the rheological properties of ABA block copolymers with polystyrene end blocks has been investigated. The chemical structure of the center blocks investigated in the present paper are polybutadiene, polyisoprene, ethylene/butene copolymer, ethylene/propylene copolymer and polydimethyl-siloxane. The chemical structure of the center block was found to have a pronounced effect on the rheological properties of the ABA block copolymer melts. The long range relaxation times of these block copolymer melts increases with increasing incompatibility between the styrene block and the center block. However, the rheological properties of the block copolymers are not influenced significantly by the glass transition or the entanglement molecular weight of the center block.