Universität Stuttgart
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Item Open Access Simulation of cracking and failure of concrete structures(1990) Cervenka, Vladimir; Eligehausen, RolfThe computer simulation of the cracking process in concrete structures is performed by means of the program system SBETA. The program is based on nonlinear hypo-elastic constitutive model, which covers all important, experimentally derived material properties, namely, cracking, nonlinear stress-strain law in compression, softenning in compression and tension, biaxial failure function, etc. The nonlinear fracture mechanics is included by means of the fictitious crack model and smeared crack approach. Two examples of computer simulation of concrete fracture are shown. In the first example, the failure mode of a pull-out test is presented. In the second example, the process of the crack development and shear failure of a reinforced concrete beam is simulated.Item Open Access Issues in designing object management systems(1990) Clow, Geoff; Plödereder, ErhardThis paper summarizes the discussions of the Object Management System (OMS) session at the Chinon Workshop. The session identified numerous capabilities which might be required in an OMS. The facilities which were agreed upon as essential to an OMS are presented in Section 1, OMS Core Facilities. A number of issues in the realization of these and other capabilities, influenced in part by specific application scenarios, are discussed in Section 2, OMS Requirements Issues. Promising applications requiring further investigation can be found in Section 3, Perceptions for the Future. Some global observations on the past and future conduct of the OMS field are summarized in Section 4, Concluding Observations.Item Open Access Biophysical investigations of the in vitro effects of shock waves and ultrasound(1993) Brümmer, Franz; Suhr, Dierk; Irmer, Ulrich; Bachleitner, Christoph; Hülser, Dieter F.To investigate the interactions of ultrasonic waves with biological tissues, we developed and standardized several in vitro models. Using these systems - artificial stones, human erythrocytes, L1210 mouse leukemia cells, multicellular spheroids, cavitation assay - we are able to elucidate the mechanisms of interaction as well as the cause of clinically observed side effects.Item Open Access Dynamics of poling PVDF between 25°C and 120°C(1991) Eberle, Gernot; Eisenmenger, WolfgangPVDF films with high β-content are poled in an electric field of 60 MV/m at temperatures between 25°C and 120°C. At 25°C the alignment of dipoles takes place in a central poling zone during several hours of poling. When the temperature is increased to 120°C the poling time necessary to align the dipoles in this narrow zone is reduced to several seconds. In addition, at temperatures higher than 90°C and increased poling times the central poling zone first increases but later decreases in its dielectric displacement. Simultaneously in a 10 μm regime adjoining the positive electrode a secondary displacement zone starts to grow. The strong reduction of this peak under short circuit conditions indicates hetero-charge accumulation in front of an anode.Item Open Access Computer simulation of anchoring technique in reinforced concrete beams(1990) Cervenka, Vladimir; Pukl, Radomir; Eligehausen, RolfThe load transfer in reinforced concrete structures by means of anchoring elements is very common in modern concrete technology. Anchoring elements are often inserted in the bottom surface of a structure and the load is transfered by tensile action of the concrete. In case of shear failure, the anchores are located in the most exposed tensile zone of beams. The shear failure can be thus influenced by anchoring elements. This effect was analysed by means of the finite element program SBETA, which is based on the nonlinear-elastic constitutive model. The comparison with experiments for several loading configurations was made. In the second part a computer simulation of similar experiments was conducted.Item Open Access Computer simulation: splitting tests of concrete thick-walled rings(1992) Pukl, Radomir; Schlottke, Bernd; Ozbolt, Josko; Eligehausen, RolfTwo non-linear program systems are used for a computer simulation of splitting failure of thick-walled concrete rings under internal radial pressure. Results of the numerical analyses for plane stress models, axisymmetrical model and 3D model are compared with available experimental data and empirical formulas. It is shown, that the behavior observed in experiments can be simulated, using advanced material models, namely the non local microplane model and SBETA material model based on the crack hand theory. With increasing outer radius of the ring, a size effect can be observed.Item Open Access Strategien zur Reduktion der energiebedingten CO2-Emissionen(1992) Voß, AlfredEine robuste und flexible Politik zur Minderung der energiebedingten Treibhausgase sollte entsprechend dem Effizienzgebot zunächst die CO2-Minderungsmöglichkeiten, deren ökonomischer Nutzen allein schon größer ist als ihre Kosten, ausschöpfen. Die Ausnutzung der hier vorhandenen Treibhausgasminderungspotentiale erlaubt es der Bundesrepublik Deutschland und den anderen Industrieländern auch, eine Schrittmacherrolle zu übernehmen, ohne die Volkswirtschaft einseitigen Belastungen auszusetzen. Schritte und Maßnahmen in dieser Richtung tragen dabei gleichzeitig zur Realisierung mehrer Ziele, wie der Reduzierung der sonstigen Schadstoffbelastungen der Luft, der Preiswürdigkeit der Energie und der Ressourcenschonung bei. Eine effizienzorientierte Treibhausgasminderungspolitik wird dabei auf keine der vorhandenen Optionen, die einen spürbaren Beitrag zur CO2-Reduktion leisten können, verzichten können.Item Open Access Integrierte Ressourcenplanung und Least Cost Planning - neue Anwendungsbereiche für die Optimierung(1994) Voß, Alfred; Hoecker, HildegardIRP ist ein Planungsprozeß, in dem alle Möglichkeiten der Strombereitstellung sowie der Beeinflussung der Nachfrage (Nachfragemanagement) nach gleichen Kriterien gegeneinander abgewogen werden. Das heißt: Wenn es kostengünstiger ist, Energie einzusparen, sollen vorrangig Investitionen in die Verringerung des Energieverbrauchs getätigt werden, statt Strom zu produzieren bzw. neue Kraftwerke zu bauen. Ziel des Planungsprozesses ist die kostenminimale Bereitstellung der Energiedienstleistung durch eine optimale Kombination von strombereitstellenden und nachfragebeeinflussenden Maßnahmen. Der zu deckende Energie- bzw. Strombedarf wird demnach nicht als gegeben hingenommen, sondern als direkt beeinflussbar angesehen.Item Open Access SQL/XNF - processing composite objects as abstractions over relational data(1993) Mitschang, Bernhard; Pirahesh, Hamid; Pistor, Peter; Lindsay, Bruce; Südkamp, NorbertAn extension to SQL, called the SQL extended normal form (XNF), is discussed. It enhances relational technology by a composite object facility, which comprises not only extraction of composite objects from existing databases but also efficient navigation and manipulation facilities provided by an appropriate application programming interface. The language itself allows sharing of the database among normal form SQL applications and composite object applications. It provides proper subsetting of the database and subsequent structuring, exploiting subobject sharing and recursion, all based on its powerful composite object constructor concept, which is closed under the language operations. XNF is integrated into the relational framework, thus benefiting from the available technology such as relational engine and query optimization.Item Open Access Prospects of the German multibody system research project on vehicle dynamics simulation(1992) Schiehlen, WernerThe German Research Council (DFG) decided 1987 to establish a nationwide research project devoted to dynamics of multibody systems. In this project 14 universities and research centers are cooperating with the goal to develop a general purpose multibody system software package. This concept provides the opportunity to use a modular structure of the software, i.e. different multibody formalisms may be combined with different simulation programmes via standardized interfaces. For the DFG project the database RSYST was chosen using standard FORTRAN 77 and an object oriented multibody system datamodel was defined. According to the modular concept the requirements of vehicle system dynamics as tire models or railway wheel-rail models, respectively, are easily met. The Iltis benchmark problem is used to demonstrate some features of the object oriented datamodel.