bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bifurcation of a Shaft under Magnetic Load
Authors: Kurnik W. 
Published: March 2011

AbstractThe aim of the paper is to examine interaction between two different instability effects in flexible shafts ‐ rotation in presence of material friction and transverse force of magnetic nature. Such problems arise for instance in multipole induction electric motors and in active vibration control of high‐speed shafts utilising magnetic actuation. A simple magnetomechanical model of the rotor displaying both divergence and flutter instability effects is assumed treating two‐sided magnetic actuators as sources of deflection‐dependent generally nonlinear force of possibly positive or negative sign. The stability region of the trivial equilibrium as well as the near‐critical limit cycles are studied to explain the interaction of both instability effects and the role of the magnetic load.
Stabilitätsuntersuchung von MDOF‐Systemen mit Totzeiten
Authors: Wagner N. , Ruge P. 
Published: March 2011

AbstractUntersucht wird die Stabilität von mechanischen Systemen mit zwei verschiedenen Totzeiten für die Zustandsgrößen; z.B. eine Totzeit τ1 für die Verschiebungen und die zweite Totzeit τ2 für die Geschwindigkeiten. Gegenüber ]3[ erfolgt eine Verallgemeinerung auf MDOF‐Systeme. Die diskrete Beschreibung des kontinuierlichen Prozesses führt auf ein System von Differenzengleichungen, das mit Hilfe eines Ansatzes auf ein nichtlineares Eigenwertproblem abgebildet wird. Die darin enthaltene Matrixexponentialfunktion wird durch eine Padé‐Entwicklung in ein Matrizenpolynom umgewandelt.
Zur Stabilität der Gleichgewichtslagen eines Doppelpendels mit geradlinig geführtem Endpunkt
Authors: Berger A. 
Published: March 2011

AbstractWährend das Auffinden von stationären Punkten eines Potentials auf einer Teilmannigfaltigkeit eines euklidischen Raumes keine Schwierigkeiten bereitet (Lagrange'sche Multiplikatorenregel), ist eine Bestimmung der Stabilität die‐ser Punkte in der Regel nicht ohne weiteres möglich. Da aber derartige Fragestellungen in der Form von Potentialen unter (parametrisierten) Nebenbedingungen bei zahlreichen Anwendungen eine Rolle spielen, wäre die Verfügbarkeit eines (einfachen) Verfahrens wünschenswert, welches über die Stabilität entsprechender Gleichgewichtslagen zu entscheiden gestattet. Wie im folgenden ausgeführt, liefert eine einfache, geometrisch interpretierbare Bedingung ein solches Verfahren. Dessen Nutzen wird am Beispiel eines Doppelpendels mit geführtem Endpunkt demonstriert.
Abstandsberechnung zwischen Flächen höherer Ordnung und konvexen Polyedern
Authors: Buschmann A. , Frik M. 
Published: March 2011

AbstractFür die Bahnplanung uon Robotern ist die schnelle Erkennung von Kollisionen und die Bestimmung der Abstände der Robotersegmente der Umgebung wesentlich. Bei einer detailgetreuen Modellierung sind auch Abstände zwischen gekrümmten Flächen, die hier durch superquadratische Ellipsoide modelliert weden, und konvexen Polyedern zu bestimmen. Der vorgestellte Algorithmus stellt eine Kombination des Verfahrens von BOBROW für konvexe Polyeder und einem eigenen Verfahren für superquadratische Ellipsoide dar.
Moment Interactions of Rigid Bodies
Authors: Grekova E. 
Published: March 2011

AbstractWe consider the problem of gravitationally interacting rigid bodies. We obtain formulae for the potential energy of their interaction and the gravitational moment. The first approximation for the problem of two gravitationally interacting bodies is the problem of a rigid body in a newton field of forces. We consider this problem for a body with rotational symmetry fixed in the centre of mass. There found regimes of regular precession and their stability is investigated. Another considered problem is the motion of an infinite system of rigid bodies fixed by their centres of masses in the points of a cubical lattice. It is assumed that every body interacts gravitationally with its six neighbours. It is shown that the regime of rotation around one of lattice axes is unstable.
Closed‐loop analysis of an articulated railcar train
Authors: Heinzl Ph. , Plöchl M. , Mack W. , Lugner P. 
Published: March 2011

AbstractAn articulated railcar train is modelled by a plane three‐body linkage mechanism guided at two points along a given trajectory with a prescribed velocity of the front point. The closed‐loop system is analyzed using a symbolic‐numerical method leading to ordinary differential equations in minimal coordinates.
Evolution of Wear Patterns on Railway Wheels
Authors: Küsel M. , Brommundt E. 
Published: March 2011

AbstractRailway wheels suffer wear, irregular wear patterns develop on their surfaces. Travel comfort and safety are reduced and expensive profiling of the wheels becomes necessary.A common explanation is that initial out‐of‐roundnesses increase because of the oscillations they cause. We develop a model to study these mechanisms. Particularly we take into account the evolution of out‐of‐roundnesses in axial and azimuthal direction on the wheel treads and outline the structure of the governing equations.
Dynamic Control of a Biped Walking Robot
Authors: Loffler K. , Gienger M. , Pfeiffer F. 
Published: March 2011

AbstractThe project of a two‐legged walking robot is presented. For this system a nonlinear control scheme is proposed that is based on the method of feedback linearization. In order to allow for a “dynamically” stable motion, the reference trajectories are computed so that the system remains controllable throughout the entire gait cycle. In simulations the robot is controlled in a running motion, including phases without ground contact. The simulation results show the good performance of the control strategy in a purely dynamic motion.
Random Walkers Cellular Automata for Diffusion Processes
Authors: Vamoş Calin , Suciu Nicolae , Vereecken Harry , Jaekel Uwe , Schwarze Holger 
Published: March 2011

AbstractSmooth concentration fields and balance equations for systems of random walkers are obtained by using the coarsegrained space‐time averaging method from ]5[ and averages over the statistical ensemble. This yields a new cellular automaton numerical model for diffusion processes. The number of particles and the averaging space‐time scale needed to approximate the concentration, with a given precision, are obtained. Applications were made for systems with small concentrations and diffusion in random fields.
Klassifikation serieller, paralleler und hybrider Manipulatoren
Authors: Verhoeven R. , Hiller M. 
Published: March 2011

AbstractEs wird ein abstraktes mathematisches Modell vorgestellt, das auf alle Manipulatoren mit holonomen Zwangsbedingungen anwendbar ist. Es führt auf zwei Typen von Singularitäten, die typischerweise bei parallelen bzw. seriellen Robotern auftreten, diese aber nicht erschöpfend charakterisieren. Eine solche Charakterisierung wid hingegen möglich durch die Unterscheidung zweier Redundanztypen.
Thermally induced interlaminar stress concentrations at laminate corners
Authors: Becker W. , Jin P. P. , Lindemann J. 
Published: March 2011

AbstractSubject of consideration is the stress field in the vicinity of a free rectangular corner of a cross‐ply laminate with symmetrical layup under thermal loading. A closed‐form analytical solution is developed for the near corner stress field and is shown to be in good agreement with comparative 3‐dimensional finite element analyses.
Stress Fields Around an Anisotropic Point Defect in a Quasi‐Continuum
Authors: Dobovcarek I. 
Published: March 2011

AbstractAn anisotropic point defect which is embedded in a homogeneous, isotropic, non‐locally elastic crystal is simulated with the help of the Dirac delta function and a general, constant, at the point of action spatially independent, second order tensor, describing anisotropies of the defect. In such form the defect retains intrinsic local structure. On the other hand, the surrounding medium exhibits a long range order of interaction in the classical form of non‐local elasticity. The resulting equations for displacement fields, stresses, and strains aw discussed using the theory of eigenstrains.
Description of two‐phase materials using Discrete Atom Method
Authors: Kolling S. , Gross D. 
Published: March 2011

AbstractIn metallic alloys, especially Ni‐base superalloys, a certain microstructure, formed by second‐phase coherent precipitates can be observed experimentally. To understand the morphological evolution of the precipitate's shape, a lot of theoretical and numerical work has been done during the past few years. Apart from finite and boundary element investigations founding on continuum mechanics descriptions, one alternative to simulate equilibrium morphologies is to use the Discrete Atom Method (DAM), based on a combination of statistical mechanics and linear elasticity. As an example, the equilibrium and stability of a misfitting isotropic second phase particle is treated by this method, taking into account elastic strain and interfacial energy.
3D Equilibrium Shapes of Misfitting Precipitates in Anisotropic Materials
Authors: Mueller R. , Gross D. 
Published: March 2011

AbstractIn high temperature application materials, such as Ni‐base alloys, the microstructure is very important for the overall behaviour. A model for predicting the equilibrium microstructure is presented. The model takes interfacial and elastic energy into account. Together with a Boundary Element Method a numerical procedure is presented allowing a realistic simulation in 9D. The simulation displays relevant factors for certain microstructures. For example the influence of particle size and the ratio of the elastic properties of the precipitate and the matrix: is discussed.
Ein viskoelastisches Schädigungsmodell zur Berechnung von Elastomeren mit Berücksichtigung von Temperatureinfluß
Authors: Nasdala L. , Kaliske M. , Rothert H. 
Published: March 2011

AbstractEs wird eine viskoelastische Schädigungsformulierung auf der Basis des generalisierten Maxwell‐Modells für die Berechnung von Elastomerstrukturen bei verschiedenen Temperaturen vorgestellt. Urn zu berücksichtigen, daß eine Deformation im Druckbereich eine größere Steifigkeitsreduktion hervorruft als eine entsprechende Zugbeanspruchung, werden spezielle Druckfunktionen eingeführt. Zur Illustration einer praxisrelevanten Anwendung dient ein Vergleich der Spannungsverteilungen in der Bodenaufstandsfläche eines Neureifens und eines Reifens im Betriebszustand.
Computation of Stresses and Strains in Heterogeneous Bodies by Use of the Discrete Fourier Transform
Authors: Neumann S. , Herrmann K. P. , Muller W. H. 
Published: March 2011

AbstractDiscrete Fourier transforms are used to derive a numerical solution for the stresses and strains in a Representative Volume Element (RVE) which is filled with heterogeneities. The so‐called “equivalent inclusion method” (Mura 1987) is applied to reduce the original problem by determination of an auxiliary strain field. This field is related to the stresses by virtue of a spatially constant auxiliary stiffness tensor. By means of discrete Fourier transforms the resulting Partial Differential Equations (PDE) are mapped onto a linear system of equations which can be solved explicitly. A functional relation for the auxiliary strain field results. It can be solved approximately by means of a Neumann iteration procedure. Two heterogeneity problems of the Kirsch type are considered for which an analytical solution exists against which the accuracy of the numerical method can be checked.
Zu Stabilitätsproblemen bei Mikro‐Makro‐Übergängen
Authors: Schröder J. 
Published: March 2011

AbstractDie Homogenisierung heterogener elastischer Verbundmaterialien erfordert die Modellierung des Materialverhaltens auf verschiedenen Skalen, der Makro‐ und der Mikroskale. Im Rahmen großer elastischer Deformationen betrachten wir mögliche Stabilitätsprobleme auf der Mikroskale und deren Auswirkung auf die Stabilität des makroskopischen Materialverhaltens. Hierbei sind zwei Verzweigungsarten repräsentativer Mikrostrukturen auf der Mikroskale zu unterscheiden, die sogenannten Blochwellen und die Schubdeformationsmodi.
Exact solution of the displacement boundary‐value problem of elasticity for a spindle
Authors: Zabarankin Michail Yu. 
Published: March 2011

AbstractThe exact solution of the displacement boundary‐value problem of elasticity in general case for an elastic medium containing a rigid spindle‐shaped inclusion is constructed. This solution is initially presented by the algebraic comnation of the dilatation function and an arbitrary harmonic vector. Being an analytical function, the Fourier ansform of the dilatation boundary‐value k‐harmonic is determined from the conjugation problem at three parallel mtours in the complex plane. Obtained problem is reduced to Fredholm integral equation with a quasi‐difference kernel.
Über durch Bipotentiale definierte Materialgesetze
Authors: Ban M. , Weichert D. 
Published: March 2011

AbstractEine Verallgemeinerung der Hypothese der normalen Dissipation wurde von de Saxcé durch die Einführung des Bipotentials erreicht. In diesem Beitrag werden einige mathematische Eigenschaften des Bipotentials untersucht.
Ein elasto‐plastisches Rebar‐Modell für die Berechnung von Verbundträgern
Authors: Hohn B. , Kaliske M. , Rothert H. 
Published: March 2011

AbstractFür die Finite‐Elemente‐Berechnung uon Verbundträgern ist eine möglichst effiziente Simulation der Stahlbetonplatte und insbesondere deren Bewehrung erforderlich. Eine diskrete Modellierung der Bewehrung für Untersuchungen der Gesamtstruktur ist meist unrealistisch, da der damit verbundene numerische Modellierungsaufwand zu groß ist. Aus diesem Grund wird an diesem Artikel vorgeschlagen, die Bewehrungsstäbe in den Elementen durch eine Rebar‐Formulierung abzubilden, die keine zusätzlichen Freiheitsgrade erfordert. Für den Betonstahl wird eine elastoplastische Materialformulierung, die sich aus der Superposition beliebig vieler Prandtl‐Elemente zusammensetzt, verwendet. Mit dieser Methode lassen sich verschiedene Spannungs‐Dehnungs‐Beziehungen des Betonstahls abbilden. Abschließend werden verschiedene Möglichkeiten zur Modellierung der Verbundfuge vorgestellt.
Micromechanical Modeling of the Coated Steel Sheets Thermomechanical Behavior
Authors: Ilali I. , Cherkaoui M. 
Published: March 2011

AbstractMicromechanical model is developed to determine be macroscopic thermomechanical behavior of metallic coated sheets. To study the thermoelastoplastic behavior of such heterogeneous materials (in general, substrate + inter‐phase + coating), classical localization and homogenization techniques are used in the framework of continuum mechanics with small perturbations hypothesis. Coatings are considered as a multi‐laminated medium in which every layer or phase exhibits an anisotropic thermoelastoplastic behavior with plane and perfect interfaces. The real heterogeneous material is replaced by a fictitious homogeneous one called Equivalent Homogeneous Material (E.H.M.). To consider the effect of anisotropy, the Hill's yield criterion for anisotropic strain‐hardening materials is used The interface problem is solved by introducing the interfacial operators of solid mechanics. One general “three‐phase” model is proposed and considered in the case of damaged coating by taking into account the coupling between plasticity and damage phenomena. First results show the effects of damaged or undamaged metallic coating on elastoplastic behavior of coated steel sheets.
Designing of components made from porous materials. Lines of stress discontinuity
Authors: Mielniczuk J. , Mostowski R. 
Published: March 2011

AbstractUsing the earlier formulated pasticity theory and the extremum principles for porous materials some properties of stress dicontinuity lines in plane stress and plane strain are described. For a given porosity the geometry of lines (angles) and the critical value of external loading (pressure) can be determined.
Collapsing cylindrical shock waves in gases with low absorptivities
Authors: Hirschler T. 
Published: March 2011

AbstractIn the self‐similar formulation of the collapse of a cylindrical shock wave in radiating gas the temperature gradient at the shock front is an undetermined quantity. Together with the absorptivity an arbitrary choice of these two variables is the basis of a parametric study. The paramretric study focuses upon gases with low absorptivities and is extended up to the isothermal limit where the absorptivity is equal to zero. In this context it is shown that the heat flux at the shock front is almost negligible. For gases with low absorptivities the assumption of an adiabatic shock front is therefore a sufficient accurate approximation.
Numerical Simulation of Inviscid Shock Interactions on Double‐Wedges
Authors: van Keuk J. , Ballmann J. 
Published: March 2011

AbstractIn supersonic and hypersonic flight double wedge geometries can cause very complex interaction phenomena between different wave types. These interactions can sometimes lead to anomalously high pressure and heat loads on the contour of aerospace planes like the ELAC1 configuration developed in the Collaborative Research Center (SFB 253) in Aachen. For the numerical simulation of such flows one has to use a method that should be both robust and accurate. The algorithm used here is based on the DLR FLOWer‐Code extended by several Upwind‐Splitting Methods for the physically correct description of the inviscid flux vector. Numerical solutions of 2 D inviscid shock interactions on double‐wedge geometries are presented and compared with corresponding results of other authors.
Towards Technical Application of Large Eddy Simulation
Authors: Breuer M. 
Published: March 2011

AbstractThe paper is concerned with the computation of high Reynolds number circular cylinder flow (Re = 3900/140,000) based on the large eddy simulation (LES) technique. Because this flow involves a variety of complex flow features encountered in technical applications, successful simulations for this test case, especially at high Reynolds numbers, can be considered as the first step to real world applications of LES. Based on an efficient finite‐volume LES code, a detailed study on different aspects influencing the quality of LES results was carried out. In the present paper, some of the results are presented and compared with experimental measurements available.
Random Vibration Systems with Weakly Correlated Random Excitation
Authors: Starkloff H.‐J. , Von Scheidt J. , Wunderlich R. 
Published: March 2011

AbstractIn the paper asymptotic expansions for second‐order moments of solutions to ordinary differential equations with weakly correlated random inhomogeneous terms are presented. Such equations arise e.g. in the mathematical modeling of vibration systems with an external random excitation. The given expansions allow an efficient approximative computation of moment functions of the solution process, particularly when the number of degrees of freedom is large.
Adaptive Optimal Stochastic Trajectory Planning in real‐time using neural network approximations
Authors: Aurnhammer A. , Marti K. 
Published: March 2011

AbstractIn Optimal Stochastic Trajectory Planning (OSTP) of industrial robots, the problem can be represented by a variational problem under stochastic disturbances. Using deterministic substitute problems obtained from stochastic optimisation theory, the corresponding deterministic substitute variational problem can be solved approximatively via mathematical programming techniques. However, due to the computationally expensive algorithms involved, these techniques can be used for off‐line calculations only. Hence, neural networks are trained to solve the trajectory‐planning problem in real‐time and to provide suitable solutions for on‐line applications.
Prozeßspezifische Roboteroptimierung
Authors: Burgmair R. , Pfeiffer F. 
Published: March 2011

AbstractEs werden Zielfunktionen und Nebenbedingungen zur numerischen Optimierung der Lage, Reglerkoeffizienten und der Fügerichtung von Robotern, die Objekte mit großen Auslenkungen montieren, vorgeschlagen. Das nichtlineare Vektoroptimierungsproblem wird mit einem SQP‐Algorithmus gelöst, Optimierungsergebnisse werden gezeigt.
The interaction problem for the locally cooled free convection boundary layer
Authors: Exner A. , Kluwick A. 
Published: March 2011

AbstractThe free convection boundary layer which forms on a heated vertical flat plate of constant temperature is investigated in the vicinity of a localized disturbance of the wall temperature. In a small region the wall is cooled in a prescribed manner. The short strong disturbance results in an interaction problem which is solved numerically. If the disturbances are sufficiently weak, the interaction equations can be linearised allowing for analytical solutions. For strong disturbances, a numerical calculation of the non‐linear interaction problem is performed.
On Optimal Control of Mobile Robots
Authors: Kiriazov Petko 
Published: March 2011

AbstractThere are continuously increasing demands to mobile robots (MR) for faster operation, higher accuracy, and lower energy cost. A unified direct‐search optimization approach is proposed which employs parameterized control laws consistent with the Pontryagin Maximum principle. We define mostly appropriate input‐output pairs and transform the given two‐point boundary‐value problem into a system of shooting equations. The control parameters which are not in the input‐output pairs are used for time/energy optimization. Existence of solutions is guaranteed under a weak and reasonable condition. The approach is applied on a dynamic model of a MR having two independently driven wheels.
A Priori Constraint Elimination
Authors: Ales Krajnc , Darko Beg 
Published: March 2011

AbstractThe problem of steel frames optimal design, when it is written in mathematical programming form, gives a moderate number of unknowns and a huge number of constraints. A typical frame has about 50 unknowns and 20000 constraints. The large number of constraints, which are complex functions of many parameters, represents a problem for most non‐linear programming solvers. In order to reduce the number of constraints, we developed a method, which eliminates a large portion of constraints without their costly evaluation. The method is based on the problem specific constraints organization, where the constraints are organized into sets. It turns out that we can remove individual constraints from a set by simply comparing constraint parameters.
Wavelet filtering of three‐dimensional turbulence
Authors: Farge Marie , Pellegrino Giulio , Schneider Kai 
Published: March 2011

AbstractWe present a new vortex tube extraction method for three‐dimensional turbulent flows. The method is based on an orthogonal wavelet decomposition of the vorticity vector field. The coherent part of the flow is reconstructed from the strongest wavelet coefficients using an universal threshold criterion. As example we present the vortex tube extraction of three‐dimensional homogeneous isotropic turbulence.
Querschnittsoptimierung unter mehrfacher Belastung
Authors: Mikulski L. 
Published: March 2011

AbstractMit Hilfe des Maximumprinzips kann gezeigt weden, daß die Optimierung der durchlaufenden Träger, die simultan verschiedene Belastungsfälle aushalten, und dabei die maximale Spannung (Verschiebung) minimal halten, ein Mehrpunktrandwertprobem (MPRWP) ist. Die maximale Spannung (Verschiebung) soll unter verschiedenen Neben‐bedingungen minimal sein J(U) = minU {maxx σx}. Als Steuervariablen wird die Höhe des rechteckigen Querschnitts und auch die Lage der Unterstützungspunkte gewählt. Durch die Einführung des Steuerungsparameter p kann das Zielfunktional auf das Mayerischesproblem zurückgeführt werden. Das erhaltene Mehrpunktrandwertproblem mit Dimension 161 kann mit Hilfe des Dircolprogramm gelöst werden.