bluuebunny/crossref_metadata_2025 huggingface dataset:
Computation of the Temperature between Brake Disk and Pad
Authors: Rudolph M. , Popp K. , Hogenkamp W.
Published: June 2004

The authors present a computation method which is based on an analytical approach describing the temperature distribution due to a moving heat source. This approach has been adapted to the technical problem of the diskpad contact and programmed in MATLAB. In particular, the inhomogeneous pressure distribution in the contact plane has been taken into account. Further, FE‐calculations have been conducted to ascertain the correctness of the analytical approximation. By this combination of analytical and numerical methods an efficient calculation of the contact temperature became possible which is by far faster than corresponding FE‐calculations. The results have been confirmed by measurements using a brake test rig and an IR‐camera system.
On Some Property of the Natural Frequencies of Elastic Chains
Authors: Strobach Daniel , Braun Manfred
Published: June 2004

In this paper we consider plane oscillations of a chain consisting of an elastic spring with concentrated mass points attached to it. It is shown that the sum of squared reciprocal natural frequencies does not depend on the number and distribution of the attached masses. For an arbitrary chain, an equivalent simple oscillator with one or two degrees of freedom can be constructed having the same sum of squared reciprocal natural frequencies as the original chain. Results are also specialized to regular chains with equal masses at equidistant spacing.
Dynamic Shape Control of a Flying Cantilever by Piezoelectric Actuation
Authors: Zehetner Ch. , Irschik H.
Published: June 2004

The present contribution is concerned with active suppression of plane flexural vibrations of a cantilevered panel. The vibrations of the panel are produced by imposed forces and by a prescribed large rigid‐body motion of the cantilevered end, such that the panel appears to fly with respect to an inertial frame. The rigid body motion defines a floating reference configuration of the panel. With respect to the latter, the vibrations are assumed to remain in the elastic regime and to be moderately large. The cantilever is considered to be equipped with integrated piezoelectric actuators. It is the scope of the present paper to derive a spatial shape of these actuators such that the vibrations can be completely suppressed by the piezoelectric actuation. This inverse problem is exactly solved in the context of an equivalent single‐layer Kirchhoff‐theory for thin panels rigid in shear. Coupling to the electric field is taken into account. The presented solution of the shape‐control problem is intended to serve as a benchmark test for the field of intelligent wings. For comparison sake, 3‐dimensional Finite Element computations are performed.
Analysis and Active Rejection of Chatter in Rolling Mills
Authors: Holl Johann , Schlacher Kurt , Keintzel Georg , Eisenköck Norman
Published: June 2004

This contribution is concerned with a vibration phenomenon in multistand rolling mills called (third octave) chatter. In order to analyse the dynamical system, which is nonlinear in nature, a mathematical lumped parameter model of the plant is presented. This model comprises the mill stands, the strip as a coupling element of neighbouring mill stands and the hydraulic actuators. By means of the mathematical model of the coupled system the third octave chatter can be explained by an instability of the dynamic system. For the purpose of an active vibration rejection a nonlinear controller based on the PCH structure of the hydraulic system is designed.
Elasto‐plastic deformation in a spherical pendulum
Authors: Dibold M. , Gerstmayr J. , Irschik H.
Published: June 2004

Heavily loaded deformable structures performing rigid body motions may exhibit elastic as well as plastic strains, particularly when the elastic stiffness and the yield stress are considerably lowered by catastrophic environmental influences. The dynamic equations are derived from the Newton‐Euler equations. Plastic strains are included by an additive split of the total strains. Exemplarily we study the movement of a spherical pendulum.
Rekursive Lösung der Bewegungsgleichung von elastischen Mehrkörperketten
Authors: Ferrara Paolo , Bremer Hartmut
Published: June 2004

Roboterarme, Manipulatoren, Konstruktionswerkzeuge sind derzeit auf hohe Genauigkeit und Schnelligkeit optimiert. Diesen Anforderungen entsprechend sind deren Arme und Getriebe steif und unnachgiebig gebaut. Dies ist mit hohem Eigengewicht verbunden. Dort wo Gewichteinsparung, Leichtbau oder auch Kosteneinsparungen an Bedeutung gewinnen, werden starre Elemente durch nachgiebige ersetzt werden müssen. Die Nachgiebigkeit ist dabei nicht nur von Nachteil. Nachgiebige Elemente sind z.B. geradezu prädestiniert für hybride Antriebe, wo Position und Kraft gleichzeitig geregelt werden. Auch Laufmaschinen, die meist der Natur nachempfunden sind, könnten mit nachgiebigen Beinen natürlicher, leichter und flexibler gebaut werden. Die Schwierigkeiten der Handhabung elastischer Mehrkörper liegen darin, dass sich, durch die auftretenden Verformungen, das Verhalten des elastischen Systems gegenüber dem starren drastisch ändert. Bauteilverformungen pflanzen sich von Element zu Element fort. Der Versuch, einzelne Kettenglieder als elastische Balken zu beschreiben und diese modular zu einem System zusammenzufügen, soll die Komplexität der Beschreibung verringern und die Interpretation sowie die messtechnische Kontrolle einzelner Terme erleichtern.
A 3D Finite Element Solver for Multibody Systems Based on Implicit Runge‐Kutta Schemes
Authors: Gerstmayr J. , Schöberl J.
Published: June 2004

An efficient finite element (FE) formulation and a time‐integration scheme for the simulation of multibody systems are derived. The absolute nodal coordinate formulation is chosen. In the discretized form, a constant mass matrix and a nonlinear stiffness matrix follow from a variational formulation. According to the classical assumptions of multibody systems, only small deformations but large rotations are taken into account. A special decomposition of the Green strain tensor leads to a stiffness matrix which is multiplicatively composed of the rotation matrix of the rigid body rotation and the small strain stiffness matrix, which has to be computed only once. Thus, Runge Kutta schemes of higher order accuracy can be solved efficiently.
Generic Inverse Kinematics Approach for Robotics Applications
Authors: Krenn R. , Schäfer B.
Published: June 2004

The concept of DLR's new light‐weight robot generation is a modular one. It offers an almost infinite number of kinematics configurations. For pre‐simulations a virtual assembly and modeling tool was developed that supports online simulations using commercial multi‐body simulation software. Here, a key feature is the generic implementation of the inverse kinematics in order to deal with arbitrary kinematics. The paper addresses a method that combines the advantages of two basic algorithms and that can be easily implemented in MBS software.
Modellierung und Regelung baumstrukturierter, hybrider Mehrkörpersysteme
Authors: Mitterhuber R. , Bremer H.
Published: June 2004

Es wird eine Modellbildungs‐ und Regelungsstrategie von kettenförmigen, teils elastischen Mehrkörpersystemen am Beispiel von zwei Knickarmrobotern mit je sechs Gelenken vorgestellt. Während der eine Roboter eine Standard‐ Industriemaschine ist, besitzt der zweite so schlanke Arme, dass deren Elastizität nicht vernachlässigt werden kann. Die Roboter fahren eine vorgegebene Trajektorie, wobei ihre Ende.ektoren miteinander im Kontakt stehen.
Spatial Tracks in Multibody Simulation. Theory and Simple Roller Coaster Example
Authors: Schott K. , Tobolář J.
Published: June 2004

A calculation method for spatial tracks has been developed which is based on the numerical solution of the Frenet equations for spatial curves. The spatial track can be used in multibody simulations of vehicle dynamics. As an application example of this method a simple roller coaster model has been generated. The results are reasonable and show that multibody simulations are suitable to evaluate the vehicle dynamics of a roller coaster ride.
Numerik viskoelastischer Stoffgesetze mit fraktionalen Zeitableitungen
Authors: Aschenbrenner Lars , Dinkler Dieter
Published: June 2004

Zur Beschreibung des viskoelastischen Werkstoffverhaltens eignen sich Werkstoffgesetze mit gebrochenen Zeitableitungen, da sie das Materialverhalten auch über große Frequenzbereiche mit wenigen Materialparametern zutreffend wiedergegeben. Mit dem hier verwendeten Exponentialalgorithmus mit inneren Variablen gelingt es, den numerischen Aufwand auch gegenüber einer laufzeitoptimierten Entwicklung der Grünwaldreihe zu reduzieren und gleichwertige Ergebnisse zu erhalten.
On sensitivity investigations of thin‐walled shell structures using transient finite element analysis and finite perturbations
Authors: Ewert E. , Schweizerhof K.
Published: June 2004

In standard stability investigations of structures applying the finite element method usually the bifurcation and snapthrough points are detected. For practical design purposes not only the equilibrium state itself is significant but also the safety of the stable equilibrium state. The sensitivity, which quantifies the safety, can be investigated by introducing finite perturbations at a certain load level and considering the perturbed motion. In this contribution the application of Liapunov Characteristic Exponents (LCE) for the judgement of the perturbed motion is investigated.
An Anisotropic Porous Media Model of the Intervertebral Disc
Authors: Karajan Nils , Ehlers Wolfgang , Markert Bernd
Published: June 2004

On the microscale, the human intervertebral disc is a complex arrangement of mostly water, collagen (arranged in fibre bundles), proteoglycans and proteins. Attempting to separately describe each component would yield a too elaborated model, even by todays computing power. Therefore, an appropriate macro model needs to be developed. This can be done by splitting the disc into two distinct regions, which are a gelatinous core (nucleus pulposus) surrounded by a pliant, fibrous composite tissue (annulus .brosus). The nucleus may be considered as an isotropic material, whereas anisotropic effects have to be included for the annulus. This is due to the present fibres, which are not arranged in ideal chaos, but are assumed to be helically arranged yielding a locally orthotropic material.
Viskoelastizität von Elastomeren bei großen Deformationen
Authors: Zecha Holger , Lee Seokho , Miehe Christian
Published: June 2004

Der Beitrag befasst sich mit der Darstellung eines Materialmodells zur Beschreibung der viskoelastischen Eigenschaften von Elastomeren bei großen dreidimensionalen Deformationen. Auf der Basis neuer Versuchsergebnisse erfolgt (i) eine geeignete Spezifizierung der in dem Modell auftretenden konstitutiven Funktionen und (ii) die Anwendung eines diskreten Relaxationsspektrums zur Erfassung des viskoelastischen Verhaltens. Numerische Simulationen werden mit ein– und mehrachsigen experimentellen Daten verglichen.
Stability Problems of Micro‐to‐Macro Transitions in Finite Plasticity
Authors: Becker Martin , Miehe Christian
Published: June 2004

Stability problems on the micro‐scale have a substantial influence on the macroscopic material behavior. For example micro‐instabilities such as the buckling of stiff fibers of a micro‐heterogeneous material result in a considerable softening of the macroscopic behavior. Instability phenomena of this kind lead to the problem of non‐convex homogenization where the size of the representative volume element has to be determined. These problems as well as the interaction between micro‐ and macro‐instabilities are examined within an incremental variational formulation of inelasticity.
Numerical Investigations on the Plastic Memory Effect of PTFE Compounds
Authors: Kletschkowski Thomas , Schomburg Uwe , Bertram Albrecht
Published: June 2004

To describe the nonlinear material behaviour of thermoplastic materials via the example of Polytetrafluorethylene (PTFE), a viscoplastic material model of overstress type is proposed. The approach is motivated by a rheological model, consisting of a rate‐independent elastoplastic element with an endochronic flow rule and a nonlinear elastic element in parallel connection with a nonlinear Maxwell model. For the generalization to three dimensions, the theory of finite viscoplasticity based on material isomorphisms is applied. To describe the non‐isothermal plastic memory effect, thermally induced plastic strains and a scalar back stress (inside the equilibrium branch) are taken into account.
Validation of constitutive laws for simulations of the dynamic response of plates
Authors: Stoffel Marcus , Schmidt Rüdiger , Weichert Dieter
Published: June 2004

If strain rate dependent deformations of metal plates are studied, it is necessary to use viscoplastic laws for the simulations of the structural response. For this purpose an e.cient viscoplastic model is searched in this study.
Application of the Dunford‐Taylor Integral to Isotropic Tensor Functions
Authors: Itskov M.
Published: June 2004

In the present contribution closed‐form representations for isotropic tensor functions and their derivative are formulated using the Dunford‐Taylor integral. These representations are given in terms of eigenvalues of the tensor argument and are valid for all second‐order tensors defined as a linear mapping over the n‐dimensional real vector space. The solution obtained is especially useful for non‐symmetric tensor functions where representations based on the spectral decomposition in diagonal form cannot generally be applied.
On the variational formulation of models for materials with microstructure
Authors: Svendsen Bob
Published: June 2004

The purpose of this short note to show how one can utilized the direct thermodynamic formulation of models for materials with microstructure to obtain a thermodynamically‐consistent variational principle for such models.
Application of Relaxation Techniques to Nonconvex Isotropic Damage Model
Authors: Gürses Ercan , Lambrecht Matthias , NaMiehechname Christian
Published: June 2004

A new energy relaxation technique for nonconvex inelasticity is applied to an isotropic damage model. The increasing damage yields nonconvex incremental potentials indicating the instability of the material and the development of finescale microstructures. The microstructures are resolved as first‐order laminates by convexifiaction techniques.
Static and extending interface cracks with contact zones in anisotropic as well as in piezoelectric bimaterials
Authors: Herrmann Klaus , Loboda Volodymyr
Published: June 2004

An interface crack with an electrically permeable and mechanically frictionless contact zone in a piezoelectric bimaterial under the action of a remote mixed mode mechanical loading as well as thermal and electrical fields is considered in the first part of this paper. By use of the matrix‐vector representations of thermal, mechanical and electrical fields via sectionally‐holomorphic functions the problems of linear relationships are formulated and solved exactly both for an electrically permeable and an electrically impermeable interface crack. For these cases the transcendental equations and clear analytical formulas are derived for the determination of the contact zone lengths and the associated fracture mechanical parameters.

A plane strain problem for a crack with a frictionless contact zone at the leading crack tip extending stationary along an interface of two semi‐infinite anisotropic spaces with a subsonic speed under the action of various loading is considered in the second part of this paper. By introducing of a moving coordinate system connected with the crack tip and by using the formal similarity of static and propagating crack problems the combined Dirichlet‐Riemann boundary value problem is formulated and solved exactly for this case as well and a transcendental equation is obtained for the determination of the real contact zone length. It is found that the increase of the crack speed leads to an increase of the real contact zone length and the correspondent stress intensity factors which increase significantly for a quasi‐Rayleigh wave speed.
On the application of a slip‐based interface model for textile reinforced concrete
Authors: Richter Mike , Lepenies Ingolf , Zastrau Bernd W.
Published: June 2004

The macroscopic material properties of textile reinforced concrete (TRC) are essentially a.ected by the bond behavior between the fiber reinforcement and the surrounding matrix. If the brittle matrix is cracked the successive debonding of the fibers can be assumed to be the main reason for the high ductility of TRC. Based on pullout tests a slip based analytically treatable interface model with a piecewise linear shear stress – slip relation and numerically solvable models are developed.
Local and non‐local ductile damage and failure modelling at large deformation with applications to engineering
Authors: Svendsen Bob , Reusch Frederik , Klingbeil Dietmar
Published: June 2004

The numerical analysis of ductile damage and failure in engineering materials is often based on the micromechanical model of Gurson [1]. Numerical studies in the context of the finite‐element method demonstrate that, as with other such types of local damage models, the numerical simulation of the initiation and propagation of damage zones is strongly mesh‐dependent and thus unreliable. The numerical problems concern the global load‐displacement response as well as the onset, size and orientation of damage zones. From a mathematical point of view, this problem is caused by the loss of ellipticity of the set of partial di.erential equations determining the (rate of) deformation field. One possible way to overcome these problems with and shortcomings of the local modelling is the application of so‐called non‐local damage models. In particular, these are based on the introduction of a gradient type evolution equation of the damage variable regarding the spatial distribution of damage. In this work, we investigate the (material) stability behaviour of local Gurson‐based damage modelling and a gradient‐extension of this modelling at large deformation in order to be able to model the width and other physical aspects of the localization of the damage and failure process in metallic materials.
A Finite Interface Crack Interacting With A Subinterface Crack In Metal/Piezoelectric Ceramic Bimaterial
Authors: Tian Wen‐Ye , Gabbert Ulrich
Published: June 2004

The “pseudo‐traction‐electric‐displacement’ method was adopted to solve the interaction problem between a finite interface crack and a subinterface crack in metal/piezoelectric bimaterial. After deriving the fundamental solutions for a finite interface crack and a special subinterface crack respectively loaded by the normal and tangential concentrated tractions and the concentrated electric displacement, the present interaction problem was reduced to a system of integral equations, which may be solved numerically. The crack tip mode I stress intensity factor was calculated and detailed comparisons of the results derived under the compound mechanical‐electric loading conditions and those derived under the purely mechanical loading condition are performed.
Dynamical Calculation of Plane Frameworks using Boundary Integral Equations
Authors: Alvermann Steffen , Schanz Martin , Antes Heinz
Published: June 2004

The beam bending problem according to Timoshenkos theory can be solved using the Finite Element method. Here, the Boundary Integral Method is applied to the bending problem in frequency domain, providing an analytical solution for beams and systems of beams like trusses. An example is presented to demonstrate the method.
A Structural Optimization Viewpoint on Configurational Mechanics
Authors: Barthold F.‐J.
Published: June 2004

The paper focuses on the kinematical foundation of structural optimization as well as configurational mechanics. Within both disciplines, modifications of the reference configuration are described. The derivation of the Eshelby tensor using a variational approach known from sensitivity analysis as part of structural optimization is outlined.
Homogenisierungsbasierte Mehrgitter‐Transferoperatoren für nichtlineare heterogene Materialien
Authors: Bayreuther C.G. , Miehe C.
Published: June 2004

Mehrgitterverfahren ermöglichen eine effiziente Lösung großer Gleichungssysteme, die bei Finite Element‐Diskretisierungen nichtlinearer Randwertprobleme auftreten können. Bei heterogenen Materialien bedingt der Einsatz solcher Löser die Konstruktion spezieller Transferoperatoren. Diese Aufgabe wird mit Hilfe von Homogenisierungstechniken gelöst. Die neuen Strategien werden anhand repräsentativer Modellprobleme mit bekannten Verfahren verglichen.
Optimization of Microstructures by Evolution Strategies
Authors: Bohn Niels , Gabbert Ulrich
Published: June 2004

Evolution strategies can be classified as a type of direct methods, requiring only information about the objective function. Contrary to analytical methods, the calculation of gradients is not necessary. Thus the method is applicable to a wide range of problem classes.The paper introduces the basic algorithm of an evolution strategy and shows its application on the basis of two simple examples from the field of discrete optimization.
A microscopical model for electric‐mechanical contact
Authors: Boso Daniela P. , Zavarise Giorgio , Schrefler Bernhard A.
Published: June 2004

In this paper a model to deal with electric‐mechanical contact problems in the framework of the FEM is presented. On the basis of some micro‐mechanical studies, a new approach is developed to define the non‐linear constitutive law that governs the normal force‐displacement behaviour and the electric resistance of the contacting surfaces.
Volume and Surface Based Homogenization Procedures for Cosserat Continua
Authors: Diebels S. , Steeb H. , Ebinger T.
Published: June 2004

The deformation of a beam lattice is investigated as a two‐dimensional model of a foam. Forces, moments, displacements and rotations are averaged leading to stress, couple stress, strain and curvature on the macroscale. Therefore, the effective medium is assumed to be micropolar.
Investigation of the stress and strain profiles during intrusion and torque of a premolar
Authors: Dorow Christina , Sander Franz‐Guenter
Published: June 2004

Since it is known from literature [1, 2, 3] that root resorption can occur even with small intrusive forces and torque moments, it is very interesting to find out the stresses and strains which are induced in the tooth support unit when a tooth is subjected to external loads and which lead to the resorption process. In this study a three‐dimensional Finite Element model of a lower premolar was generated using Computer Tomography (CT) data. Intrusive forces of 0.5N and torque moments of 3Nmm respectively were applied to the tooth crown. The three principal stresses and strains as well as the hydrostatic pressure and the volumetric strain were calculated within the premolar, the surrounding periodontal ligament (PDL) and alveolus.
A parallel computational approach for free surface flows with structural interactions
Authors: Genkinger Steffen , Wall Wolfgang A. , Ramm Ekkehard
Published: June 2004

An appropriate treatment of instationary free surface flows is of great relevance to many problems in engineering and applied sciences. In this context the presence of structural interactions constitute an additional challenge on the one hand but on the other hand even further broadens the application area. In this study we present a partitioned implicit approach for the efficient and robust treatment of free surface flows within fluid structure interaction simulations.
An Explicit Multi‐Body Contact Algorithm
Authors: Hahn Carsten , Wriggers Peter
Published: June 2004

For the reliable and efficient solution of multi‐body contact problems involving large nonlinear deformations, an explicit time integration scheme is considered. For this kind of algorithms, a semi‐implicit approach for fulfillment of the contact constraints is presented. To apply this method to three‐dimensional problems, the solution of local equilibrium problems is required at the contact surface. An iterative form of the proposed scheme is used to decrease computational effort. Also some remarks are given with respect to contact detection.
Numerical simulation of microstructures based on incremental variational formulations and relaxation methods
Authors: Hoppe Ulrich , Hackl Klaus
Published: June 2004

The use of an incremental variational principle allows the calculation of inelastic material behaviour by means of an elastic potential. Missing quasiconvexity of this potential is a serious deficiency, because the existence of regular solutions cannot be guaranteed and finite–element approximations may become mesh–dependent. These problems can be overcome by the use of relaxed potentials. Results of a rank–one relaxation algorithm for a single–slip plasticity model are presented.
Analysis of inelastic effects in wrinkled membranes
Authors: Hornig J.
Published: June 2004

Membranes are very suitable for carrying tensile loads, but they fail partially or completely if compressive in‐plane loads occur. Since membranes do not possess any flexural stiffness they can not carry compressive in‐plane loads. In this case membranes wrinkle. It is essentially to take effects of membrane wrinkling into account. Modern materials applied in membrane structures show not only pure elastic but also viscoplastic or plastic behavior. The question rises, how to treat inelastic effects if wrinkling occurs. The presented method is applicable to elastic‐plastic deformation processes in connection with membrane wrinkling. An approach based on a modified Roddeman theory is used (see [1] and [2]). Due to the existence of unrecoverable deformations, one has to reformulate the wrinkling criterion. As an example, a strain space formulation of plasticity (see Besdo and Tietze [3]) is incorporated into the wrinkling algorithm.
A numerical method for computing the response of composites with periodic microstructure
Authors: Kassbohm Sven , Müller Wolfgang H.
Published: June 2004

The stress‐strain response of a periodic structure due to an applied eigenstrain field is investigated. The periodic structure allows reduction of the problem to a representative volume element (RVE) problem. A review of Fourier series as a particular method of solving the set of differential equations is given, and an example problem is studied. Results of the latter method are compared to results obtained using discrete Fourier transforms in a different way.
Density gradient enhanced topology optimization of continuum structures
Authors: Kotucha Gregor , Hackl Klaus
Published: June 2004

The formulation of topology optimization problems for continuum structures usually requires the introduction of the material density as design variable. In this context the design domain is discretized by finite elements and a constant density distribution within the elements is assumed. To prevent the occurrence of optimal designs characterized by extended regions with intermediate density values, special penalty methods are used. The introduction of those methods results in discontinuities in the global density distribution and often leads to designs containing unfavourable microstructures such as the well‐known checkerboard patterns. To obtain designs free of microstructures, we propose a global density gradient based regularization and discuss the results of numerical studies of several maximum‐stiffnessdesign problems based on the presented approach.
The effect of functional overloading on crestal bone loss around a dental implant
Authors: Lenz Jürgen , Schindler Hans J. , Rong Qiguo , Schweizerhof Karl , Riediger Dieter
Published: June 2004

At the end of the bone remodeling process, frequently funnel‐like collapses of the cortical bone (crestal bone losses) are clinically registered around the neck of dental implants. It is generally suspected that either inflammations or mechanical “overloading” of the bone during the clinical loading phase are responsible for this phenomenon. From the results of this numerical simulation we conclude that overloading might indeed be a major cause for these bone losses.
The Optimal Design of Extrusion Dies by the Finite Element Method
Authors: Lotfi A.
Published: June 2004

In this work, a method for calculation of the optimal shapes of axisymmetrical converging dies by the finite element method is presented. The shape optimization problem considered in this paper is to find the best shape of the die such that the flow rate will be uniform at the die exit.The optimization problem is to minimize an objective function by varying a part of boundary (ie: the shape of die) subject to constraints imposed by the metal forming problem. In this method, the B‐spline functions allow us to determine the shape of the die, using its control points as design variables.
Computational modelling of failure with the discontinuous Galerkin method
Authors: Mergheim Julia , Kuhl Ellen , Steinmann Paul
Published: June 2004

The present contribution is concerned with the computational modelling of failure with the discontinuous Galerkin method, which is attributed to Nitsche's work. In the present work a hybrid method is introduced which consists of the discontinuous Galerkin method and an interface approach. Thereby the DG method is used to model the precritical continuous state, whereby the continuity condition along an internal surface is enforced weakly. The interface approach is applied in the post‐critical state to allow for a jump in the displacements, controlled by a constitutive law. Finally the applicability of the proposed method is illustrated by means of a computational model problem.
Finite element analysis of liquid filled structures under gravity loading
Authors: Rumpel T. , Schweizerhof K.
Published: June 2004

The large deformation analysis of membrane or shell structures loaded and/or supported by liquid can be based on a finite element description for the structure only. Then in statics the effects in the liquid have to be considered by using the equations of state for the liquid, the information about the current volume and the current shape of the structure. The interaction with the structure is then modeled by a pressure resulting from the liquid always acting normal to the current wetted structural part. This description can be easily used to model the filling process without all the difficulties involved with standard discretization procedures. In addition the consistent derivation of the nonlinear formulation and the linearization for a Newton type scheme results in a particular formulation which can be cast into a very efficient solution procedure based on a sequential application of the Sherman‐Morrison formula.
Dynamic dam–reservoir–interaction – treatment of radiation damping by the “Mixed–Variables–Technique”
Authors: Trinks C. , Ruge Peter
Published: June 2004

In this paper, a method for the consistent description of a fluid channel of infinite extent in a fully coupled time–domain dam–reservoir interaction analysis is proposed. The method is based on an analytical solution with respect to the unbounded dimensions of the reservoir. Thus, an accurate representation of radiation damping is achieved.
Effiziente Parameteridentifikation bei Stoffgesetzen für inelastische technische Gummimaterialien
Authors: Besdo D. , Ihlemann J.
Published: June 2004

Das Materialverhalten technischer Gummiwerkstoffe bei großen Verformungen ist ausgeprägt nichtlinear und zeigt komplizierte inelastische Effekte. Die Anpassung der Materialparameter entsprechender Stoffgesetze an ein konkretes Material erfolgt in der Regel durch den Vergleich mit Messungen einfacher Belastungszustände. Ein Beispielstoffgesetz zeigt, daß für diese Anpassung durchaus auf Standardalgorithmen mit gut kontrollierbarem Konvergenzverhalten zurückgegriffen werden kann, sofern einerseits das Stoffgesetz hinreichend robust ist, und andererseits geeignete numerische Umsetzungen der Algorithmen bereitgestellt werden.
Identification of Material Parameters for Inelastic Constitutive Models: Design of Experiments
Authors: Harth Tobias
Published: June 2004

In order to determine the material parameters of a constitutive model, identification experiments of different kinds have to be performed. Usually, the data of those experiments result from tension‐relaxation and tension‐compression tests at different strain rates as well as from creep tests with different hold stresses. However, these experiments are very expensive. Thus, the most important experiments to obtain good parameter estimates should be analyzed. The aim of this research is to find an experimental design which optimizes the balance between the accuracy of the parameter estimates and the experimental costs.
Characterization of the mechanical behavior of nonlinear viscoelastic materials in the range of high strain rates
Authors: Ottenberg Matthias , Weber Herbert
Published: June 2004

A method is presented by which the short term behavior of the uniaxial relaxation moduli of nonlinear viscoelastic materials can be determined. For this purpose the wave propagation in prestrained rods which are impacted at one end is studied in the Fourier domain. Measurement of the strain or particle velocity at three positions yields the complex moduli from which the relaxation moduli follow.
Parameter Identification for Granular Materials in Consideration of Micro Rotations
Authors: Scholz Bernd , Ehlers Wolfgang
Published: June 2004

Granular materials, as for example sand, show a complex stress‐strain behaviour depending on the stress state and the load history. Furthermore, in experiments the occurrence of a shear band is observed, which results in the localization of the plastic strains. For the consideration of the micro rotations in the shear band, the model is extended by the Cosserat theory, which leads to the regularization of the mathematically ill‐posed localization phenomenon. The aim of the present contribution is the identification of the material parameters of the proposed model. Therfore, a gradient based method is applied. Other methods, e. g. evolution strategies, are inapplicable because of their enormous computational costs.
Displacements and rotations in shear‐deformation of T‐S material
Authors: Sikora Zbigniew , Michalak Rafal , Wyroslak Mariusz
Published: June 2004

The structure of persistent and transient shear bands in granular materials by experimental modeling a quite idealized assembly of two‐dimensional particles, Taylor‐Schneebeli (T‐S) material, is investigated. Flexible stress‐controlled boundaries make possible biaxial compression test (samples 100 cm high and 30‐100 cm wide), i.e. they avoid constraining the motion of particles within the shear bands. The displacement, volumetric strain, void ratio, rotation of the particles, rotation of their neighborhoods can be examined within the shear bands. The importance of particle's rotations inside shear bands can justify the micropolar description of granular materials. For measurement at the microstructure level a conventional digital video technique is used. New digital image processing (DIP) techniques are used for analysis at the microscopic level, giving localization, displacements and rotations of each T‐S rods. Short description of a new plane strain experimental stand and an example of DIP analysis for a selected experimental test are presented. Some comments due to the mathematical model description of granular bodies is also given.
About the propeller influence on aircraft stability derivatives
Authors: Vrdoljak Milan
Published: June 2004

Propellers can significantly effect aircraft flying characteristics and stability. Depending on the aircraft configuration this influence of propeller on aircraft stability derivatives can be more emphasized, as for example with single pusher propeller. Methods still used in prediction of propeller stability derivatives are based on blade element theory with the axial component of induced velocity determined from the classical propeller momentum theory. This could lead to uncorrect prediction of induced flow near the propeller and its wake. In presented paper propeller model and prediction of its influence on the aircraft stability derivatives is based on the propeller vortex theory. The numerical model is using discrete vortices to form vortex sheet that is leaving each propeller blade. This model is suitable for implementation in component build–up method used in prediction of propeller driven aircraft stability derivatives and it can be applicable for different aircraft configurations.
Finite element mesh adjusted to singularities applied to 2D flow
Authors: Burda Pavel , Novotný Jaroslav
Published: June 2004

We apply the finite element method to solve the Navier Stokes equations for the incompressible fluid flow either in axisymmetric tube with abrupt changes of diameter or in a channel with backward and forward steps. We first discuss the asymptotic behaviour of the solution in the vicinity of nonconvex internal angles where the velocity components as well as pressure posses singularities. Compared with usual adaptive strategy based on a posteriori error estimates, in this paper we suggest and apply an alternative approach for the mesh refinement near the corners. It makes use of the asymptotic behaviour near the corners. We present numerical results and comment on the pros and cons with respect tu usual adaptive refinement strategy.
Improvements in mixing operations of water treatment plants by the use of a SUPG stabilized Finite Element Method
Authors: Vellando P. , Lucas T.
Published: June 2004

This work shows the achievements obtained in the improvement of the mixing operations in water treatment plants, thanks to the hydrodynamic analysis of the mixing processes carried out by the use of a SUPG stabilized FE model.
Accurate three‐dimensional simulation of lid‐driven cavity flow
Authors: Albensoeder Stefan , Kuhlmann Hendrik C.
Published: June 2004

The numerical simulation of the one‐sided lid‐driven cavity is a classical benchmark problem. However, no reliable results are available for three‐dimensional flows slightly above their onset. In this study, we develop an accurate numerical code based on collocation methods for solid and periodic boundary conditions in span direction. The corner singularities of the problem are reduced by incorporation of analytical solutions. A convergence study is performed and, as an example, the bifurcation from the primary instability is calculated in a cavity with a square cross‐section.
Instabilities and bifurcations in lid‐driven cavity flows
Authors: Kuhlmann Hendrik C. , Albensoeder Stefan
Published: June 2004

The three‐dimensional flow of an incompressible Newtonian fluid in a rectangular slab is calculated numerically using a pseudo‐spectral method. The fluid motion is driven by two facing sidewalls which can move in parallel or anti‐parallel directions. Examples for bifurcations from two‐dimensional to three‐dimensional flows are given for spanwise periodic systems. For a comparison with previous experimental results rigid end walls are also considered. Differences between periodic and rigid end conditions are highlighted.
SUPG stabilization of meshfree methods for convection‐dominated problems
Authors: Fries Thomas‐Peter , Matthies Hermann G.
Published: June 2004

Streamline‐Upwind/Petrov‐Galerkin (SUPG) stabilization of meshfree methods with stabilization parameters calculated from standard formulas, which have their roots in mesh‐based methods, often leads to unsatisfactory results. A new procedure for obtaining adequate SUPG stabilization parameters for meshfree methods is presented. It is shown that the Kronecker‐δ property is very advantageous for a successful stabilization because this leads to local stabilization criteria. If the meshfree shape functions lack this property, a stabilization based on local properties – i.e. on nodes in the neighbourhood – cannot be sufficient for highly convection‐dominated problems.
Natural Convection in Wide Spherical Shells
Authors: Futterer B. , Brucks A. , Hollerbach R. , Egbers C.
Published: June 2004

We have studied the problem of natural convection in wide spherical shells both experimentally and numerically, and find that there are critical Rayleigh numbers at which the convection changes in fundamental ways. For sufficiently low Ra the convection is steady, but above a certain value it becomes time‐dependent, with plumes dripping off the south pole in distinct pulses. For higher values still these convective pulses become irregular in time. The experimental results show though that even at these very high Rayleigh numbers the convection remains purely axisymmetric. A two‐dimensional numerical code is therefore used to study these flows in more detail, and reveals the same transition from steady to periodic to chaotic behavior. Finally, the dependence of the critical Rayleigh number and the period on the Prandtl number are explored.
Wärmeübergang am angeströmten und gleichzeitig bewegten Kreiszylinder mit und ohne Krümmungseffekt
Authors: Gampert B. , Beyene T.
Published: June 2004

In dieser Arbeit werden Wärmeübergänge am angeströmten und gleichzeitig bewegten Kreiszylinder mit und ohne Krümmungseffekt aus den Grenzschichtgleichungen mit Hilfe von analytischen und numerischen Lösungen bestimmt. Es werden Fälle bei denen die Wandgeschwindigkeit größer oder kleiner als die Anströmgeschwindigkeit ist untersucht. Es wird eine laminare inkompressible Strömung konstanter Stoffwerte angenommen.
The Mechanics of Drug Dissolution
Authors: McMahon N. M. , Crane M. , Ruskin H. J. , Crane L.
Published: June 2004

A numerical method for approximating the mass flux from a dissolving cylindrical drug compact, a tablet, is presented. The tablet consists of alternating layers of drug and inert material. The dissolution takes place in a non‐reactive medium using a standard stirring device and is considered to be two dimensional and steady. A finite difference scheme is used to generate an approximation to the concentration boundary layer. By integrating across the velocity* concentration profile at the trailing edge, the mass flux is estimated. This value differs by 0.9% from the recent estimate of Crane et al. who used a Pohlhausen approximation to the concentration boundary layer. The finite difference concentration profile at the trailing edge also agrees very well with the equivalent Lévêque exact solution. We conclude that the finite difference model is behaving as expected.
Homogenisierungsmethoden zur Berechnung der Sauerstoffdiffusion und ‐reaktion in Faserverbundstrukturen
Authors: Nasdala Lutz
Published: June 2004

Die diskrete Modellierung von Faserverbundstrukturen führt zu einem sehr großen numerischen Aufwand, so dass die Materialeigenschaften von Fasern und Matrix in der Regel gemittelt werden müssen. Bei der Berechnung von Sauerstoffdiffusions‐ und ‐reaktionsvorgängen ergibt sich die Schwierigkeit, dass aufgrund der Oxidation die Massenbilanz nicht erfüllt werden kann. Die Güte des gemittelten Materialparametersatzes hängt neben den Ausgangsmaterialien auch wesentlich davon ab, ob die Diffusion in oder quer zur Faserrichtung betrachtet wird.
Modeling and Simulation of Fires in Vehicle Tunnels
Authors: Teleaga I. , Gasser I. , Struckmeier J.
Published: June 2004

Starting with compressible Navier‐Stokes equations we derive a new fluid model by applying a low‐Mach number asymptotic. The model is used to simulate fire events in vehicular tunnels.
Numerical Solution of Transonic Turbulent and Two‐phase flow in Turbine cascades
Authors: Dobeš Jiří , Fořt Jaroslav , Halama Jan
Published: June 2004

Presented model of transonic flow with condensation is based on Navier‐Stokes equations for mixture, algebraic turbulence model and Hill's approximation for the description of liquid phase [2]. Two finite volume methods are introduced. Numerical results for single‐phase 2D flow of air in turbine cascade SE1050, two‐phase 2D flow in Laval nozzle and two‐phase 2D flow in turbine cascade SE1050 are presented.
Numerical Simulation of Particles in Steel Strand Casting Flow
Authors: Javurek Mirko , Kaufmann Bernhard
Published: June 2004

The liquid steel flow and the particle transport of non‐metallic inclusions in the liquid domain inside the strand of a continuous steel casting system are numerically investigated. The whole liquid domain inside the solidified shell is simulated, and the loss of liquid steel due to solidification is considered. Assuming a constant drift velocity, a kind of Euler‐Euler multiphase model is implemented to calculate the particle behavior inside the liquid steel respectively the particle removal at the boundaries. Both steady and unsteady simulations of the particle behavior are performed. The influence of particle size (0 to 1 mm), casting speed and slab format is considered for the particle concentration distribution along and across the strand.
Numerical Modeling of Fluid‐Structure Interaction with Free Surface Flows
Authors: Kölke Andreas , Walhorn Elmar , Hübner Björn , Dinkler Dieter
Published: June 2004

For the numerical analysis of interactions of immiscible two‐fluid flows and lightweight elastic structures a discretization method based on stabilized space‐time finite elements is applied. The level set method provides a description of the material distribution and interface location of the two‐phase fluid. The choice of an enriched basis allows the capturing of discontinuous gradients of fluid variables, introduced by changing material properties at the interface.
Propagation of Acoustical Waves in an Axisymmetrical Duct With Swirling Mean Flow
Authors: Boltalova N. , Schemel C. , Thiele F. , Michel U.
Published: June 2004

A 3D axisymmetric Computational Aero Acoustic (CAA) procedure is extended to predict the propagation and radiation of the unsteady disturbances from a duct with swirling mean flow into the far field. Based on axisymmetric mean flow and acoustical boundary conditions, the 3D task is decomposed into a series of 2D problems using Fourier series expansions in the azimuthal direction. The numerical procedure is validated by the analytical solution within a solid body rotational, subsonic mean flow in a straight circular duct and the numerical results show a very good agreement.