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Structural Mechanics (structural + mechanic)
Selected AbstractsA new approach to reduce membrane and transverse shear locking for one-point quadrature shell elements: linear formulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2006Rui P. R. Cardoso Abstract In the last decade, one-point quadrature shell elements attracted many academic and industrial researchers because of their computational performance, especially if applied for explicit finite element simulations. Nowadays, one-point quadrature finite element technology is not only applied for explicit codes, but also for implicit finite element simulations, essentially because of their efficiency in speed and memory usage as well as accuracy. In this work, one-point quadrature shell elements are combined with the enhanced assumed strain (EAS) method to develop a finite element formulation for shell analysis that is, simultaneously, computationally efficient and more accurate. The EAS method is formulated to alleviate locking pathologies existing in the stabilization matrices of one-point quadrature shell elements. An enhanced membrane field is first constructed based on the quadrilateral area coordinate method, to improve element's accuracy under in-plane loads. The finite element matrices were projected following the work of Wilson et al. (Numerical and Computer Methods in Structural Mechanics, Fenven ST et al. (eds). Academic Press: New York, 1973; 43,57) for the incompatible modes approach, but the present implementation led to more accurate results for distorted meshes because of the area coordinate method for quadrilateral interpolation. The EAS method is also used to include two more displacement vectors in the subspace basis of the mixed interpolation of tensorial components (MITC) formulation, thus increasing the dimension of the null space for the transverse shear strains. These two enhancing vectors are shown to be fundamental for the Morley skew plate example in particular, and in improving the element's transverse shear locking behaviour in general. Copyright © 2005 John Wiley & Sons, Ltd. [source] Zur Diskussion des Böenreaktionsfaktors G nach DIN 1055-4:2005BAUTECHNIK, Issue 10 2009BayIKBau Robert Hertle Dr.-Ing., Beratender Ingenieur VBI, Prüfingenieur für Standsicherheit vpi Allgemeines; Baumechanik; General Topics; Structural Mechanics Abstract Mit Einführung der DIN 1055-4:2005 fand ein Paradigmenwechsel bei der Beschreibung der Windlasten statt. Das bisherige, deterministische Konzept zur Definition der Windeinwirkung wurde verlassen und durch ein auf stochastischen Überlegungen fußendes ersetzt. Für Konstruktionen und Bauwerke, die nicht schwingungsanfällig unter böigen Windeinwirkungen sind, ergeben sich daraus keine nennenswerten Änderungen bei der rechnerischen Untersuchung. Für die Analyse von schwingungsanfälligen Konstruktionen hat diese Neukonzeption tiefgreifende Konsequenzen. Die bekannte und einfach zu handhabende Ermittlung des Böenreaktionsfaktors auf Grundlage der Normen der achtziger und neunziger Jahre des vergangenen Jahrhunderts wurde durch ein komplexes, unübersichtliches und mit einfachen Ingenieurmethoden nicht mehr zu überprüfendes Berechnungsschema abgelöst. In diesem Beitrag wird dieses Schema diskutiert, und es wird ein einfaches Näherungsverfahren zur Ermittlung der Böenreaktion einer Konstruktion vorgeschlagen, welches, insbesondere vor dem Hintergrund der sonstigen Unschärfen und Unsicherheiten einer Berechnung, ausreichende Genauigkeit zeigt. On the discussion of the gust reaction factor acc. DIN 1055-4:2005. With the introduction of DIN 1055-4:2005 a change of paradigm concerning the description of wind loads took place. The previous concept, based on a deterministic view, was replaced by an approach using stochastic considerations. For constructions and buildings deemed to be not susceptible to gust action, no significant changes within the structural analysis arise. Enormous consequences, on the other hand, have to be faced when analyzing structures susceptible to gust action. The well known and easy to handle method for calculating the gust reaction factor using the standards of the 80th and 90th of the last century, was redeemed by a complex, partly confused calculation scheme which is not checkable with usual engineering tools. In the following paper this calculation scheme is discussed. Following to this discussion, a simplified method for calculating the gust reaction factor is presented. The accuracy of this method lies, having the usual uncertainties and deficits of structural analyses in mind, in an acceptable range. [source] Erdbebenertüchtigung des Feuerwehrgebäudes in Basel durch schwimmende LagerungBAUTECHNIK, Issue 8 2009Hugo Bachmann Prof. Dr. sc. techn. Baumechanik; Bauwerkserhaltung/Sanierung; Structural Mechanics; Maintenance and Renovation Abstract Kürzlich wurde das Hauptgebäude der Berufsfeuerwehr Basel-Stadt aus dem Jahre 1943 auf spezielle Erdbebenlager aus Gummi und auf Gleitlager gestellt. Es handelt sich um die erste derartige Erdbebenertüchtigung eines bestehenden Gebäudes nördlich der Alpen. Im Vergleich zu einer konventionellen Verstärkung waren die Baukosten bedeutend geringer, und es war keine temporäre Ausquartierung des Betriebes in ein teures Provisorium erforderlich. Zudem ist die resultierende Erdbebensicherheit erheblich größer und die Schadensanfälligkeit bei schweren Erdbeben wesentlich geringer als es bei einer konventionellen Verstärkung der Fall wäre. Seismic upgrading of the fire brigade building in Basel by base isolation. Recently, the main building of the professional fire brigade of the city and canton Basel-Stadt built in the year 1943 was placed on special seismic elastomeric bearings and on sliding bearings. This is the first such seismic upgrading of an existing building in the north of the Alps. Compared to a conventional strengthening the buildingcosts were significantly smaller, and no temporary transfer of the operation into an expensive provisional building was necessary. Moreover, the resulting seismic safety is considerably higher and the vulnerability to a severe earthquake essentially smaller than in case of a conventional strengthening. [source] Mit Schrauben Bewehren , Neue ErgebnisseBAUTECHNIK, Issue 4 2009Martin Trautz Univ.-Prof. Holzbau; Baumechanik; Timber Construction; Structural Mechanics Abstract Selbstbohrende Vollgewindeschrauben ermöglichen wirkungsvolle Verstärkungen und Versteifungen sowie leistungsfähige Fügungen von Holzbauteilen. Dabei werden gezielt die hohe axiale Zugfestigkeit und Dehnsteifigkeit sowie der kontinuierliche Verbund der Schrauben genutzt, um ähnlich einer Bewehrung im Stahlbetonbau die schwachen Tragrichtungen des Holzes senkrecht und schräg zur Faserrichtung zu ertüchtigen. Die Bemessung der verschiedenen Schraubenkonfigurationen kann mit Hilfe der aus dem Stahlbetonbau bekannten Stabwerkmodelle erfolgen, die den inneren Kraftfluss im Bauteil bzw. im Anschluss nachbilden und eine einfache Dimensionierung der Schrauben ermöglichen. In mehreren Versuchsreihen mit Bauteilverstärkungen und -fügungen im Jahr 2007 an der RWTH Aachen konnte die erfolgreiche Anwendung dieses Konstruktionsprinzips gezeigt werden. Darauf aufbauend wurden in einem Fortsetzungsprojekt im Jahr 2008 veränderte und verfeinerte Schraubenkonfigurationen konstruiert und auf ihr Festigkeitsverhalten hin untersucht. Versuche an stahllamellenverstärkten Brettschichtholz-Trägern und biegesteifen Rahmenecken unter positiver und negativer Momentenbelastung zeigten eine hohe Leistungsfähigkeit, die das Potential der Methode nachdrücklich untermauert. Self-tapping screws as reinforcement , new results. Self-tapping continuously threaded screws can be used as elements for reinforcement or joints in timber construction because of their high axial strength and excellent bonding properties. The layout of the reinforcing or joining screws can be derived from strut-and-tiemodels which are common in concrete design and follow the internal flow of forces. Several series of tests in 2007 already showed the high potential of this construction method on various joint details and reinforced timber elements. Based on this success in 2008 further tests were taken out on joints and timber beams with altered and more sophisticated screw configurations. Hereby the load-bearing capacity of timber beams reinforced with steel lamellas and rigid frame corners connected with self-tapping screws was extraordinary and demonstrated once more the high potential of this design method. [source] Non-linear dynamic contact of thin-walled structuresPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Thomas Cichosz In many areas of mechanical engineering contact problems of thin,walled structures play a crucial role. Car crash tests and incremental sheet metal forming can be named as examples. But also in civil engineering, for instance when determining the moment,rotation characteristics of a bolted beam,column joint, contact occurs. Effective simulation of these and other contact problems, especially in three,dimensional non,linear implicit structural mechanic is still a challenging task. Modelling of those problems needs a robust method, which takes the thin,walled character and dynamic effects into account. We use a segment,to,segment approach for discretization of the contact and introduce Lagrange Multipliers, which physically represent the contact pressure. The geometric impenetrability condition is formulated in a weak, integral sense. Choosing dual shape functions for the interpolation of the Lagrange Multipliers, we obtain decoupled nodal constraint conditions. Combining this with an active set strategy, an elimination of the Lagrange multipliers is easily possible, so that the size of the resulting system of equations remains constant. Discretization in time is done with the implicit Generalized-, Method and the Generalized Energy,Momentum Method. Using the "Velocity,Update" Method, the total energy is conserved for frictionless contact. Various examples show the performance of the presented strategies. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Special decompositions for eigenproblems in structural mechanicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2006A. Kaveh Abstract The main objective of this paper is to study those matrices which can be written as the sum of two Kronecker products. Special decompositions are proposed. Applications are extended to the eigensolution of problems from structural mechanics. It is also shown how the analysis of structures can be performed without finding the inverse of the structural matrices. Copyright © 2006 John Wiley & Sons, Ltd. [source] Fixed-grid fluid,structure interaction in two dimensions based on a partitioned Lattice Boltzmann and p -FEM approachINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2009S. Kollmannsberger Abstract Over the last decade the Lattice Boltzmann method, which was derived from the kinetic gas theory, has matured as an efficient approach for solving Navier,Stokes equations. The p -FEM approach has proved to be highly efficient for a variety of problems in the field of structural mechanics. Our goal is to investigate the validity and efficiency of coupling the two approaches to simulate transient bidirectional Fluid,Structure interaction problems with geometrically non-linear structural deflections. A benchmark configuration of self-induced large oscillations for a flag attached to a cylinder can be accurately and efficiently reproduced within this setting. We describe in detail the force evaluation techniques, displacement transfers and the algorithm used to couple these completely different solvers as well as the results, and compare them with a benchmark reference solution computed by a monolithic finite element approach. Copyright © 2009 John Wiley & Sons, Ltd. [source] A study on the lumped preconditioner and memory requirements of FETI and related primal domain decomposition methodsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2008Yannis Fragakis Abstract In recent years, domain decomposition methods (DDMs) have emerged as advanced solvers in several areas of computational mechanics. In particular, during the last decade, in the area of solid and structural mechanics, they reached a considerable level of advancement and were shown to be more efficient than popular solvers, like advanced sparse direct solvers. The present contribution follows the lines of a series of recent publications on the relationship between primal and dual formulations of DDMs. In some of these papers, the effort to unify primal and dual methods led to a family of DDMs that was shown to be more efficient than the previous methods. The present paper extends this work, presenting a new family of related DDMs, thus enriching the theory of the relations between primal and dual methods, with the primal methods, which correspond to the dual DDM that uses the lumped preconditioner. The paper also compares the numerical performance of the new methods with that of the previous ones and focuses particularly on memory requirement issues related to the use of the lumped preconditioner, suggesting a particularly memory-efficient formulation. Copyright © 2007 John Wiley & Sons, Ltd. [source] A methodology for the formulation of error estimators for time integration in linear solid and structural dynamicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2006I. Romero Abstract In this article, we present a novel methodology for the formulation of a posteriori error estimators applicable to time-stepping algorithms of the type commonly employed in solid and structural mechanics. The estimators constructed with the presented methodology are accurate and can be implemented very efficiently. More importantly, they provide reliable error estimations even in non-smooth problems where many standard estimators fail to capture the order of magnitude of the error. The proposed methodology is applied, as an illustrative example, to construct an error estimator for the Newmark method. Numerical examples of its performance and comparison with existing error estimators are presented. These examples verify the good accuracy and robustness predicted by the analysis. Copyright © 2005 John Wiley & Sons, Ltd. [source] Theory and numerics of geometrically non-linear open system mechanicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2003E. Kuhl Abstract The present contribution aims at deriving a general theoretical and numerical framework for open system thermodynamics. The balance equations for open systems differ from the classical balance equations by additional terms arising from possible local changes in mass. In contrast to existing formulations, these changes not only originate from additional mass sources or sinks but also from a possible in- or outflux of matter. Constitutive equations for the mass source and the mass flux are discussed for the particular model problem of bone remodelling in hard tissue mechanics. Particular emphasis is dedicated to the spatial discretization of the coupled system of the balance of mass and momentum. To this end we suggest a geometrically non-linear monolithic finite element based solution technique introducing the density and the deformation map as primary unknowns. It is supplemented by the consistent linearization of the governing equations. The resulting algorithm is validated qualitatively for classical examples from structural mechanics as well as for biomechanical applications with particular focus on the functional adaption of bones. It turns out that, owing to the additional incorporation of the mass flux, the proposed model is able to simulate size effects typically encountered in microstructural materials such as open-pored cellular solids, e.g. bones. Copyright © 2003 John Wiley & Sons, Ltd. [source] The generation of hexahedral meshes for assembly geometry: survey and progress,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2001Timothy J. Tautges Abstract The finite element method is being used today to model component assemblies in a wide variety of application areas, including structural mechanics, fluid simulations, and others. Generating hexahedral meshes for these assemblies usually requires the use of geometry decomposition, with different meshing algorithms applied to different regions. While the primary motivation for this approach remains the lack of an automatic, reliable all-hexahedral meshing algorithm, requirements in mesh quality and mesh configuration for typical analyses are also factors. For these reasons, this approach is also sometimes required when producing other types of unstructured meshes. This paper will review progress to date in automating many parts of the hex meshing process, which has halved the time to produce all-hex meshes for large assemblies. Particular issues which have been exposed due to this progress will also be discussed, along with their applicability to the general unstructured meshing problem. Published in 2001 by John Wiley & Sons, Ltd. [source] On singular behaviors of impedance-based repeatable control for redundant robotsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 4 2001Chau-Chang Wang This article addresses the association between the unstiffening phenomena in structural mechanics and the algorithmic singularities encountered in the impedance-based repeatable control algorithms used to command redundant manipulators. It is well known that velocity control schemes such as the pseudoinverse control schemes do not guarantee repeatability for redundant manipulators. In other words, for a closed end-effector trajectory, the joints do not, in general, exhibit a closed trajectory. One way to overcome this problem is to model each joint with compliance and incorporate a second-order correction term for the pseudoinverse. With this model, the joint configuration adopted by the manipulator at a given point in task space is one which minimizes the artificial potential energy of the system and is locally unique. In terms of statics, this is equivalent to saying that the elastic structure reaches its static equilibrium under external load. Keep this analogy in mind. We know that the impedance control commands the manipulator to mimic the behavior of an elastic articulated chain. For any phenomena observable on a real elastic structure, we should be able to find its counterpart embedded in the impedance control. In this article, we analyze the performance of such repeatable control algorithms from the point of view of structure mechanics. Singularities in the algorithm are examined and their significance in mechanics are also discussed. © 2001 John Wiley & Sons, Inc. [source] A finite element formulation based on the Cosserat point theoryPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Eiris F. I. Boerner The theory of Cosserat points is the basis of a 3D finite element formulation for large deformations in structural mechanics, that recently was presented by [1]. First investigations [2] have revealed, that this formulation is free of showing undesired locking or hourglassing-phenomena. It additionally shows excellent behaviour for any type of incompressible material, for large deformations and sensitive structures such as plates or shells. The formulation initially was restricted to a Neo-Hookean material. This work will present the extension to a general elastic Ogden material and the verification of the chosen model. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||