bluuebunny/crossref_metadata_2025 huggingface dataset:
Unilateral Constrained Bending Vibrations on a Torsional String
Authors: Kreuzer E. , Struck H.
Published: April 2003

Vibrations in long torsional strings result in spatio‐temporal dynamics. In order to actively damp these vibrations the system has to be analysed analytically, numerically and experimentally. Stick‐slip‐effects result in torsional selfexcited vibrations of the string. These vibrations are coupled with bending vibrations which are constrained by the borehole. The straight string was modelled in an experimental setup. The control of the straight string and the unilateral constrained bending vibrations were treated seperately. The dynamics of straight strings were controlled using three different approaches: firstly, a simple PD‐controller with the parameters calculated based on a one‐degree‐of‐freedom oscillator, secondly, the parameters were optimized using a simplex‐method, thirdly, the Karhunen‐Loeve‐transformation was used in order to reduce the dimension of the system. A controller based on the reduced system was implemented and the parameters were optimized with the same simplex algorithm.

The unilateral constrained bending motion were examined at a cantilever beam which was assumed to be constrained in one direction in the middle of the beam. First, the beam was modelled analytically as a continuous system. The two states (contact and no contact) were described separately. The transition between these states were modelled with energy assumptions. Second, the beam was modelled as a Finite‐Element‐System. The numerical results of both methods were compared with experimental data.
A car‐steering problem with random adhesion coefficient
Authors: Damm Tobias
Published: April 2003

Stabilization and disturbance attenuation problems for stochastic linear control systems have been studied recently e.g. in [3, 4, 5]. We recall some results and apply them to a modified version of the car‐steering problem from [1].
On Synchronization of Control Systems
Authors: Ekimov A. V.
Published: April 2003

In the present work the problem of synthesis of synchronizing control is considered. The point is that, instead of stabilization problem we have to construct a special control under which the close‐loop system realized a given programmed motion starting at a fixed moment of time. The theorem on the necessary and sufficient conditions of synchronizability of linear control systems is proved.
Optimal Robust Control of Robotic Systems
Authors: Kiriazov P.
Published: April 2003

There are continuously increasing demands to robotic systems (RS) for faster operation, higher accuracy, and lower energy cost. For the purpose of feedback stabilization, we design decentralized controllers with maximum degree of robustness. The control design criterion is based on a generalized diagonal dominant (GDD) condition proven to be necessary and su.cient for such controllers to be robust against arbitrary, but bounded, disturbances. It is defined by optimal trade‐off relations between the bounds of disturbances, the required accuracy, and the control force limits.
Adoption of the Numerical Method of Chebyshev Polynomials to the Stability Analysis of Delayed DEs
Authors: Szabó Zsolt
Published: April 2003

We propose a new way of the application of the numerical method based on Chebyshev approximation concerning the stability analysis of (periodic) delay‐differential equations. The technique is tested on the delayed Mathieu equation.
Contributions to flatness‐based control of systems with input‐dependent delays
Authors: Rudolph J. , Winkler J.
Published: April 2003

Flatness‐based control of nonlinear systems has been generalized in [1] to systems with time‐delays of constant amplitude. Continuous stirred tank chemical reactors with recycle provide examples of such systems. However, if the volume flow‐rate in the recycle is used as control input the time delay depends on control. This can be avoided by a proper choice of the independent variable, i.e., time transformation: Transported volume is used instead of time. This leads to systems with a time delay of constant amplitude belonging to a class of systems which can be called a generalized type of π‐flat systems [2], barely studied so far. Motion planning and tracking control can be achieved by flatness‐based methods.
Representation and Simulation of Smart Structures in Multibody Dynamics
Authors: Heckmann Andreas
Published: April 2003

This paper presents a methodology for the simulation of smart structures with piezoceramic patches by means of multibody dynamics. Therefore, the theoretical background is outlined adapting a modal multifield approach. Then, an application example is used to illustrate the implemented process chain. This procedure provides the framework for the development of an environment in order to design, optimise and verify all vibration control elements.
Dynamics Modelling and Simulation Environment for Rapid Manipulator Design
Authors: Krenn R. , Schäfer B.
Published: April 2003

For rapid development of space robotics mission scenarios, DLR provides an efficient assembly and simulation environment. It combines a CAD based robotic subsystems data base with kinematic and kinetic software tools for modeling and simulating the behaviour of the entire robotic system. In space environment, redundant manipulators are prefered. This paper addresses two implemented approaches for solving inverse kinematics and kinetics of such kind of systems.
Dynamik von verankerten meerestechnischen Konstruktionen
Authors: Kreuzer E. , Wilke U.
Published: April 2003

The dynamical behaviour of moored structures in ocean engineering in an irregular sea is usually investigated by means of simplified mathematical models. Nonlinear phenomena like the influence of the motion on the mooring geometry or the fluid‐structure interaction are not considered. In this paper a method is described for analyzing the dynamical behaviour of mooring systems including the hydrodynamic forces due to the fluid surrounding the structure. The model for the dynamic analysis is generated using the multibody system method.
Modellierung instationärer Reibkräfte
Authors: Kröger M. , Lindner M. , Popp K.
Published: April 2003

Die schnelle Geschwindigkeitsänderung während einer Stick‐Slip‐Schwingung beeinflußt oft die Reibkräfte im Kontakt so stark, dass eine einfache Beschreibung mit einer stationären Reibkraftcharakteristik nicht mehr sinnvoll ist. Die instationären Reibkräfte können mit einer Differentialgleichung anhand der stationären Reibkraftcharakteristik und zweier Zeitkonstanten beschrieben werden. Schwerpunkt dieser Untersuchung ist die experimentelle Verifizierung der Beschreibung sowie Ansätze zur Identifikation der Zeitkonstanten anhand von Geschwindigkeitssprüngen oder ‐rampen.
Motion Planning of Robot Locomotion
Authors: Mladenova C.
Published: April 2003

Since the treatment of robot locomotion is quite closed with this one of human locomotion, the present paper treats the problems of modelling, simulation and motion planning of robot locomotion on the base of knowledge of the skeletal system, as well as on the base of multibody system modelling, simulation and control using some ideas from Lie group theory and differential geometry.
Classification and higher order analysis of manipulator singularities
Authors: Müller A. , Maisser P.
Published: April 2003

A purely algebraic approach to higher order analysis of (singular) configurations of rigid multibody systems with kinematic loops (CMS) is presented. Rigid body con.gurations are described by elements of the Lie group SE(3) and so the rigid body kinematics is determined by an analytical map f : V → SE(3), where V is the configuration space, an analytic variety. Around regular configurations V has manifold structure but this is lost in singular points. In such points the concept of a tangent vector space does not makes sense but the tangent space CqV (a cone) to V can still be defined. This tangent cone can be determined algebraically using the special structure of the Lie algebra se (3), the generating algebra of the special Euclidean group SE (3), and the fact that the push forward map f*, the tangential mapping CqV → se (3), is given in terms of the mechanisms screw system. Moreover the differentials of f of arbitrary order can be expressed algebraically. The tangent space to the configuration space can be shown to be a hypersurface of maximum degree 4, a vector space for regular points. It is the structure of the tangent cone to V that gives the complete geometric picture of the configuration space around a (singular) point. Identification of the screw system and its matrix representation with the kinematic basic functions of the CMS allows an automatic algebraic analysis of mechanisms.
Permeability Studies on Soft Open‐Cell Foams
Authors: Ehlers Wolfgang , Markert Bernd , Diebels Stefan , Nödling Axel
Published: April 2003

The behaviour of fluid‐saturated solid foams can be very well described using multiphasic continuum mechanical models [4]. Concerning permeable soft foams, like e. g. gas‐filled open‐cell polyurethane (PU) foams, the transient compressive response is strongly influenced by the outstreaming pore‐fluid. Following this, it is the objective of the present contribution to point out the macroscopic permeability properties of soft foams including non‐linear phenomena influenced by the pore space deformation at varying flow rates. In particular, based on experimental investigations, an appropriate constitutive setting is presented considering the dependency of the permeability on the deformation state and on the seepage velocity in the sense of a modified Forchheimer ansatz. The constitutive equations are embedded into the macroscopic Theory of Porous Media (TPM), where the numerical treatment of the strongly coupled problem can effciently be performed with the finite element method (FEM). Finally, a numerical example shows the applicability of the presented approach.
The equivalent inclusion technique and its convergence
Authors: Müller W.H.
Published: April 2003

This paper addresses the convergence characteristics of an iterative solution scheme of the Neumann‐type useful for obtaining homogenized mechanical material properties within an RVE. The analysis is based on the idea of “equivalent inclusions” and, within the context of stress/strain analysis, allows modeling of elastically highly heterogeneous bodies with the aid of discrete Fourier transforms. Within the iterative scheme the proof of convergence depends critically upon the choice of an appropriate, auxiliary stiffness matrix, which also determines the speed of convergence. Mathematically speaking it is based on Banach's fixpoint theorem and only results in necessary convergence conditions. However, for all cases of elastic heterogeneity that are of practical importance convergence can be demonstrated.
Reibungsbehafteter Kontakt elastischer Walzen unter nichtsymmetrischer Last
Authors: Walter H. , Braun M.
Published: April 2003

Eine zylindrische Walze, bestehend aus einem starren Kern und einer elastischen Schicht, wird gegen eine starre, ebene Unterlage gedrückt. Der Anpreßvorgang erfolgt quasistatisch, jedoch wird die Haftreibung in der Kontaktzone berücksichtigt. Im Rahmen der linearen Elastizitätstheorie lassen sich die Verschiebungen und Spannungen in der Walze für beliebige Randlasten durch Fourier‐Reihen mit komplexen Koeffizientenfunktionen ausdrücken. Der Anpreßvorgang hängt, auch bei quasistatischer Betrachtung, von der Vorgeschichte der Deformation ab und muß deshalb inkrementell betrachtet werden. Innerhalb der Kontaktzone bilden sich Haft‐ und Verschiebungsbereiche aus.
Classes of Anisotropic Finite Plasticity Models and their Implementation in a Brick‐Type Shell Element
Authors: Apel N. , Miehe C.
Published: April 2003

We discuss two constitutive models formulated in terms of logarithmic strains suitable for the description of elastoplastic material response. We consider two different approaches to the definition of the plastic deformation. The first is based on the introduction of a plastic map yielding a multiplicative decomposition of the deformation gradient into an elastic and plastic part. The second one uses an additive decomposition of the current metric. A quantitative analysis of both approaches by means of numerical examples of sheet metal forming processes are presented.
Eine geschlossene Darstellung für die Ableitung von Potenzreihen nichtsymmetrischer Tensoren
Authors: Itskov M. , Aksel N.
Published: April 2003

Isotrope Tensorfunktionen, die in Form einer Potenzreihe in bezug auf nichtsymmetrische Argumenttensoren definiert sind, spielen eine große Rolle in der numerischen Mechanik. In der finiten anisotropen Plastizität und insbesondere Einzelkristall‐Plastizität hat sich beispielsweise die Exponentialfunktion des räumlichen Geschwindigkeitsgradienten als sehr hilfreich erwiesen. Bei symmetrischen Argumenttensoren stellt man die Ableitung einer Potenzreihe mit Hilfe einer geschlossenen Formel dar, die auf der Spektralzerlegung basiert. Da jedoch nichtsymmetrische Tensoren im allgemeinen keine Spektralzerlegung (in der Diagonalform) zulassen, ist man gezwungen, sehr aufwendige numerische Prozeduren heranzuziehen. In diesem Beitrag stellen wir eine geschlossene Darstellung für Tensorpotenzreihen und ihre Ableitung vor. Diese Darstellung ist durch die Eigenwerte des Argumenttensors formuliert und gilt für alle Tensoren zweiter Stufe, symmetrische und nichtsymmetrische, mit oder ohne Spektralzerlegung. Im Sonderfall eines Argumenttensors mit einer Spektralzerlegung reduziert sich diese Darstellung auf die wohlbekannte Lösung für isotrope Funktionen symmetrischer Tensoren (siehe z.B. [1]).
A Study on Finite Orthotropic Plasticity using Generalized Measures
Authors: Löblein J. , Schröder J. , Gruttmann F. , Mehling V.
Published: April 2003

A numerical study of anisotropic plasticity using generalized strain and stress measures [1] according to [2] is presented. The constitutive frame is described and an algorithmic implementation is proposed. The coaxiality of generalized and standard deformation measures is exploited for the numerical treatment of the projection tensors.
Aspects of the theoretical and numerical formulation of single crystal plasticity at finite strains
Authors: Schotte J. , Miehe C. , Lambrecht M.
Published: April 2003

We give an overview about an incremental variational formulation of single crystal plasticity at finite strains and discuss an approach to the computation of the exponential map and its derivatives based on a spectral representation.
Controlled Deployment of a Tethered Satellite System
Authors: Barkow Bernhard
Published: April 2003

The deployment of a tethered satellite system undoubtedly represents one of the most critical phases in a tether mission: due to its complicated dynamics, high amplitude oscillations are likely to rise in the system, and it will take a long time to reach the desired stable radial equilibrium state. Based on a viscoelastic space billiard model, a targeting strategy is developed in this paper, which makes use of the system's chaotic nature and allows to steer the system into its equilibrium faster and more efficiently compared to conventional strategies.
A Time‐Stepping Algorithm for Stiff Mechanical Systems with Unilateral Constraints
Authors: Funk K. , Pfeiffer F.
Published: April 2003

This paper presents a stable implicit first order time‐stepping method for the simulation of stiff mechanical systems with unilateral constraints and Coulomb friction. It ensures that the unilateral constraints are fulfilled directly on the displacement level. The resulting linear complementarity problem is formulated in a very compact nonstandard way. A modified form of Lemke's algorithm is presented to solve it.
On the Description of Partially Saturated Soils by the Theory of Porous Media
Authors: Ehlers Wolfgang , Graf Tobias , Diebels Stefan
Published: April 2003

In this contribution, a multi‐phase soil model based on the Theory of Porous Media (TPM) is presented. The model is fully coupled in the following constitutive phases: An elasto‐plastic or elasto‐viscoplastic solid skeleton, a materially incompressible pore‐liquid (water) and a materially compressible pore‐gas (air). The interaction of the solid skeleton and the pore‐fluids is specified by a capillary pressure‐saturation relation, whereas the mobilities of the fluid phases in the pore‐space of the solid skeleton are described by the so‐called relative permeabilities. Finally, a gravity governed initial‐boundary‐value problem solved by the FE method is presented.
Lösung komplexer dynamischer Aufgabenstellungen mit expliziten Verfahren auf Parallelrechnern
Authors: Grochla Joachim , Köppe Heinz , Gabbert Ulrich
Published: April 2003

Die Finite‐Elemente‐Simulation des nichtlinearen und zeitabhängigen Verhaltens komplexer mechanischer Strukturen unter Berücksichtigung von nichtlinearem Materialverhalten, großen Verformungen und Kontakteinflüssen soll genaue Aussagen zur Deformation und Stabilität mechanischer Strukturen liefern. Die Grenzen der Computersimulation werden von der Rechenzeit und der verfügbaren Speicherkapazität der vorhandenen Hardware bestimmt. Die Verwendung von expliziten Zeitintegrationsverfahren zur Lösung der semidiskreten Bewegungsdifferentialgleichungen ermöglicht eine Reduzierung der erforderlichen Speicherressourcen durch den Verzicht auf den Aufbau von Element‐ und Systemmatrizen sowie der Rechenzeit durch die Parallelisierung der Berechnungssoftware, für die sich die expliziten Verfahren sehr gut eignen. Ausgehend von einer vorhandenen speziellen Finite‐Elemente‐Software wurde ein Parallelisierungskonzept auf der Basis von MPI entwickelt und getestet, das eine schnelle Lösung großdimensionierter FE‐Probeleme der Strukturmechanik erlaubt und hier kurz vorgestellt wird.
3D Surface Smoothing for Arbitrary FE‐Meshes by Means of an Enhanced Surface Description
Authors: Helnwein P.
Published: April 2003

This paper describes a novel approach to the problem of 3D surface smoothing by introducing an enhanced surface description of the structural model. The idea of the enhanced surface model is the introduction of an independent vector field for the description of the surface normal field. It is connected to the discretized surface by means of a weak form of the orthogonality conditions. Surface smoothing then is applied element‐by‐element using the interpolation of the surface patch and the nodal normal vectors.
Dynamics of Layered Structures with Bonded Piezoelectric Material
Authors: Mesecke‐Rischmann S. , Lammering R.
Published: April 2003

For the proper design of plate and shell composite structures with piezoelectric patches bonded to the surfaces of a host structure, appropriate finite elements are presented. The linear piezoelectric effect is taken into account so that the displacements and the electric potential serve as independent variables. The electric potential can be condensed on the element level and does not enter the system of equations. This condensation has the advantage of a more efficient calculation especially for dynamic problems. With dynamic examples the two formulations are compared with each other and with solutions from the literature, which prove the accuracy and the efficiency of the formulations.
Numerische Modellierung von Hochdruckhydraulikschläuchen mit Geflechtsverstärkungen
Authors: Rattensperger H. , Eberhardsteiner J. , Mang H.A.
Published: April 2003

In dieser Arbeit wird ein Modell für die numerische Simulation von Hochdruckhydraulikschläuchen vorgestellt. Dabei werden das Matrixmaterial (Gummi) und die Verstärkungseinlagen (Draht‐ oder Textilgeflecht) dieser Verbundstruktur im Rahmen einer Finite Elemente (FE) Berechnung getrennt betrachtet. Die Verstärkungseinlagen werden durch Rebar‐Elemente repräsentiert, deren nichtlineares mechanisches Verhalten mittels eines Stabgittermodells beschrieben wird.
Nonlinear Surface‐Related Shell Theories – Theoretical and Numerical Aspects
Authors: Schlebusch Rainer
Published: April 2003

The numerical simulation of contact problems demands the mapping of data from the middle surface of the shell to the outer surface. This step can naturally be circumvented, if one of the outer surfaces is used as the reference surface in the shell formulation.
Galerkin‐type space‐time finite elements for volumetrically coupled problems
Authors: Steeb Holger , Diebels Stefan , Ehlers Wolfgang
Published: April 2003

The study focuses on error estimation techniques for a coupled problem with two constituents based on the Theory of Porous Media. After developing space‐time finite elements for this mixed problem, we extend the numerical scheme to a coupled space‐time adaptive strategy. Therefore, an adjoint or dual problem is formulated and discussed, which is solved lateron numerically. One advantage of the presented technique is the high flexibility of the error indicator with respect to the error measure.
Supervision System of Machining Process States
Authors: Lipiński D. , Kacalak W. , Krzyżyński T.
Published: April 2003

Due to non‐linear, multidimensional and random character of most processes of machining, an use of analytical methods to process monitoring is difficult, time‐consuming and expensive. An application of algorithms which base on models in real processes is very limited, especially in the case of grinding processes. On the one hand, such methods require realistic and exact models of monitored process, on the other hand, they can characterize restrictive hypothesis concerning the process modeled. Most of model‐basing learning algorithms have an application to linear and steady‐state processes. However, majority of monitored processes are non‐linear, and, additionally, of nonstationary character. The system of monitoring proposed in the paper bases on artificial intelligence methods, which makes it possible to exclude from it a model of the grinding process.
On Modelling of Stochastic Processes of Abrasive Wear and Durability of Grinding Wheel
Authors: Kacalak W. , Kasprzyk M. , Krzyżyński T.
Published: April 2003

The aim of the paper is to present modelling of abrasive wear and grinding wheel durability by means of probabilistic description of abrasion and crush dressing of grinding wheels. Relations describing distributions of active grain age and its change during of grinding are determined. A practical application of the models proposed in the paper, using empirical data, makes it possible to determine other quantities which are very difficult to estimate in an experimental way.
On the Identification of the Parameters of a Viscoelastic Material Law for Polymeric Foams
Authors: Ehlers Wolfgang , Klar Oliver
Published: April 2003

In this paper, the gradient‐based sequential quadratic programming (SQP) technique is used to determine the parameters of a finite viscoelastic material law for the description of polymeric foams. Due to the cellular structure of foams, the resulting non‐linear behaviour is reproduced by an Ogden‐type law in the framework of the Theory of Porous Media (TPM) [1]. The conformity between experimental data and numerical simulation is improved by the minimization of a least squares functional under consideration of equality and inequality constraints. The result is shown by a finite element based back‐analysis of unconfined compression tests.
On Modelling and Experimental Verification of Micro‐Smoothing Process in Extra Low Temperatures
Authors: Kacalak W. , Kasprzyk M. , Krzyżyński T. , Lewkowicz R. , Ściegienka R.
Published: April 2003

Particularly good results in micro‐smoothing of steel work‐pieces surfaces by means of imperial micro‐finishing films, and difficulties in obtaining proper machining effects for aluminium and its alloys and also for other high plasticity materials in surrounding temperature, have caused examining of this process in extra low temperatures. Carrying out the process in extra low temperature, and at the same time in vacuum, makes it possible to obtain extra smooth surfaces of elements made from aluminium. The paper presents the experimental stand which is adapted for operations in extra low temperatures and results of micro‐smoothing processes.
Inverses Rechnen zur Identifikation der Materialparameter des Cosserat‐Kontinuums
Authors: Scholz Bernd , Ehlers Wolfgang
Published: April 2003

Bei der Anwendung der Cosserat‐Theorie treten neben den Verschiebungsfreiheitsgraden zusätzliche Rotationsfreiheitsgrade auf. Zur Beschreibung der Deformation wurden demzufolge ein nicht‐symmetrischer Verzerrungstensor sowie ein Krümmungstensor eingeführt. Diesen erweiterten Deformationsmaßen werden über konstitutive Beziehungen ein nicht‐symmetrischer Spannungstensor sowie ein Momentenspannungstensor zugeordnet. Dabei treten neue Materialparameter (z. B. die interne Länge) auf, deren Identifikation das Ziel der vorgestellten Arbeit ist. Da die zusätzlichen Rotationsfreiheitsgrade nur bei inhomogener Deformation aktiviert werden, sind zur Bestimmung der Materialparameter des Cosserat‐Kontinuums inhomogene Versuche sowie deren Nachrechnung als Randwertproblem erforderlich. Dazu stehen an Hostun‐Sand durchgeführte Biaxialversuche zur Verfügung.
Contribution to the propeller aerodynamic interference
Authors: Vrdoljak Milan
Published: April 2003

Propeller wake can significantly change the flowfield at the downstream lifting surfaces and therefore influence its aerodynamic coefficients. The numerical model of the propeller presented here is using discrete vortices to form vortex sheet that is leaving each blade. Model is also applicable for combination of lifting surface and propeller using undeveloped propeller vortex sheet in determination of aerodynamic interference of the propeller on the downstream lifting surface, wing or tail for small angle of attack. This low computational cost numerical model is suitable for implementation in component build–up method used in preliminary estimation of aerodynamic coefficients for different propeller aircraft configurations.
Parallele numerische Strömungssimulation bei Fluiden mit Gedächtnis
Authors: Andoleit B.
Published: April 2003

Es wird ein Verfahren zur numerischen Simulation einer stationären, isothermen und schleichenden Strömung eines inkompressiblen, viskoelastischen Fluides beschrieben. Die Gedächtnisintegrationen wird, nicht wie herkömmlich auf einem Prozessor, sondern parallel auf mehreren Prozessoren durchgeführt.
An Applicable Boundary Condition at the Moving Contact Line in Case of a Free Surface Reorientation after Step Reduction in Gravity
Authors: Gerstmann J. , Michaelis M. , Dreyer M. , Rath H.J.
Published: April 2003

In this study the sudden change in the acceleration level on a free surface in a right circular cylinder is investigated numerically. The intention to describe the .uid motion encounters the difficulty modelling the moving contact‐line problem. In the numerical simulations the Navier slip boundary condition and a model for the dynamic contact angle are used. The model for the dynamic contact angle γd includes the dependence on the Capillary number as well as the contact angle hysteresis. We achieved very good agreement with experimental data.
New Zonal, Spectral Solutions for the Navier‐Stokes Layer and Their Applications
Authors: Nastase A.
Published: April 2003

New zonal, spectral forms for the axial, lateral and vertical velocity's components, density function and absolute temperature inside of compressible three‐dimensional Navier‐Stokes layer (NSL) over flattened, flying configurations (FC), are here proposed. The inviscid flow over the FC, obtained after the solidification of the NSL, is here used as outer flow. If the spectral forms of the velocity's components are introduced in the partial differential equations of the NSL and the collocation method is used, the spectral coefficients are obtained by the iterative solving of an equivalent quadratical algebraic system with slightly variable coefficients.
Film flow over strongly undulated bottom profiles at low Reynolds numbers – Analytical results
Authors: Scholle Markus , Wierschem Andreas , Aksel Nuri
Published: April 2003

Film flows occur in many technical processes (e.g. coating techniques) as well as in nature. In this paper we establish a new analytical method in order to calculate both the velocity field and the surface shape of a two–dimensional gravity driven film flow of a Newtonian fluid down a periodically varying bottom topology. We discuss the special case of a sinusoidal bottom shape.
Analytische Lösungen zur Oszillirenden Rohrströmung für einige nichtkreisförmige Rohrquerschnitte
Authors: Zlatanovski T.
Published: April 2003

Das Ziel dieser Arbeit ist, mögliche analytische Lösungen zur oszillierenden Strömung einer newtonschen oder viskoelastischen Flüssigkeit durch gerade Rohre von nichtkreisförmigem Querschnitt zu erhalten. Im Falle oszillierender Strömung einer viskoelastischen Flüssigkeit beschäftigt uns im besonderen die analytische oder numerische Berechnung der in der Querschnittsebene existierenden Sekundärströmung, die bei der laminaren Rohrströmung einer newtonschen Flüssigkeit oder im Falle des kreisförmigen Rohrquerschnittes nicht in Erscheinung tritt.
LES of a Confined Configuration using Oscillating Inflow Conditions
Authors: Düsing Michael , Sadiki Amsini , Janicka Johannes
Published: April 2003

In actual turbulent flow problems, in particular in gas turbine combustion chambers, flows are three dimensional, recirculating and turbulent in confined and complex geometries. Instationarities due to turbulence, combustion instabilities and oscillating inflow conditions require a highly time and spatial resolving procedure. 3D Large Eddy Simulations (LES) are therefore used in this work to study two confined coaxial air jets with oscillating velocity inflow conditions. The influences of the inflow, in particular frequency (f = 0 ÷ 1600 [Hz]) and amplitude, on the velocity are analysed.
Direct Numerical Simulation of Hypersonic Flow over a Cavity
Authors: Klutchnikov I. , Ballmann J.
Published: April 2003

An open rectangular cavity has served as a generic geometry in shock tunnel experiments with laminar flow being two‐dimensional upstream of the cavity. A high order central difference scheme with flux‐corrected transport has been employed to simulate the flow under the assumption that the inflow profile upstream of the cavity is laminar. The high order in space enables to reproduce well vortical structures and possible transition to turbulent flow.
Application of harmonic polynomials as complete solutions of Laplace equation in an inverse heat conduction problem
Authors: Hożejowski L. , Hożejowska S. , Piasecka M.
Published: April 2003

The area of interest is the issue of heat transfer into Freon 123 flowing through a narrow vertical channel. The paper presents a computational procedure whose aim is to determine a local heat transfer coefficient. In the described experiment thermosensitive liquid crystals were used for measuring temperature on the heating surface. Since the temperature distribution can be approximated with a linear combination of harmonic polynomials, the heat transfer coefficient is expressed with the use of these polynomials. solving differential equations, PWN, Warszawa 1960 (in Polish)
Numerical Investigation of Particulate Flow over a Backward‐Facing Step
Authors: Kubik A. , Kleiser L.
Published: April 2003

Flow separation and recirculation caused by a sudden expansion in the channel geometry in the form of a backwardfacing step (BFS) appear in numerous practical applications. Additionally, BFS flow has been used as a generic test case to study fundamental flow properties, such as separation or re‐attachment. In the present work, BFS flow laden with dispersed particles is investigated by numerical simulations using a spectral element method [1]. The motion of the dispersed particles is computed by Lagrangian particle tracking. In a first step, only the influence of the flow on the particles is accounted for, while possible effects of the particle motion on the flow are neglected. Spatial distribution of the particles is investigated, and effects of different wall‐particle interaction models on the computational results are examined.
Transport of fluids in capillary porous solids
Authors: Ricken Tim
Published: April 2003

Capillarity is a well known phenomenon in physics and engineering. The term denotes the transport of liquids and gas, against the force of gravity in narrow tubes, cracks and pores, caused by the intermolecular forces of cohesion and adhesion of the constituents involved. We will exclusively investigate the rise of liquids in porous bodies due to the capillarity phenomenon. Well‐known examples are the capillary rise in drying processes in soils with small pores and the moisture motion in walls consisting of bricks or concrete. The treatment of the capillary problem, based on thermomechanical investigations, yields the result that the capillarity force is a volume interaction force and depends on the free Helmholz energy functions of the solid phases and the density gradient of the liquid. The aim of this investigation is the numerical simulation of the behavior of liquid and gas phases in a rigid porous body at rest. An example will demonstrate the usefulness of the proposed theory.
Modified k – ω Model for Simulation of Cavitating Flows
Authors: Sorgüven Esra , Schnerr Günter H.
Published: April 2003

Although cavitating flows are generally turbulent, the interaction of turbulence and cavitation dynamics is still not well understood. In general, two‐equation models are employed, which were originally developed for single‐phase flows. Therefore they fail by handling cavitation based flow phenomena with very high density variations (dependent on operating condition up to 40000:1). This sudden change of the density causes strong pressure gradients, secondary flows and local compressibility. The aim of this study is to enhance the Wilcox's k‐? model with empirical correlations in order to simulate turbulent cavitating flows more precisely and effciently.
The Structure of Dispersion Relation in Hyperbolic Thermoelasticity
Authors: Dobovšek Igor
Published: April 2003

For a system of field equations of hyperbolic thermoelasticity we derive a propagation condition for a thermoelastic disturbance in a form of homogeneous plane wave in deformation and temperature. The corresponding dispersion relation is given in an explicit form, together with the discussion of di.erent types of homogeneous thermoelastic plane waves that may emerge from the resulting system of coupled PDEs.
Zur Berechnung der Schallabstrahlung umströmter Körper
Authors: Rung T. , Eschricht D. , Yan J. , Thiele F.
Published: April 2003

Dieser Artikel behandelt die Berechnung des abgestrahlten Lärms umströmter, stumpfer Körper. Das Verfahren beruht dabei auf der Trennung von Quellberechnung und Ausbreitung des Schalls ins Fernfeld. Die Fernfeldberechnung erfolgt auf Grundlage der Gleichung von Ffowcs‐Williams und Hawkings. Der hierzu verwendete Löser wird anhand analytischer Lösungen der linearen Wellengleichung validiert. Das Verfahren wird auf die Umströmung eines generischen Fahrzeugaußenspiegels mit Re=5.2×105 angewendet, für den experimentelle Daten als Vergleich vorliegen. Die Simulation der Quellen erfolgte dabei mit einer Detached‐Eddy Simulation.
Structure of weak laminar hydraulic jumps in single layer and two layer fluids
Authors: Kluwick A. , Exner A. , Cox E.A.
Published: April 2003

We consider the occurrence of hydraulic jumps in near critical single layer and two layer flows under the assumption that viscous effects are confined to a thin laminar boundary layer adjacent to the solid boundary. In the limit of large Reynolds number this leads to a structure problem formed by the classical triple deck equations supplemented with a novel nonlinear coupling condition which allows for the passage through the critical state. In the case of positive hydraulic jumps this passage is achieved by the local thickening of the boundary layer which acts as a viscous hump. Conversely, the pressure drop at the wall associated with negative hydraulic jumps causes the boundary layer to decrease locally thereby forming a local indentation required for the Froude number to pass through one in this case.
Modelling Fire Events in Long Tunnels
Authors: Gasser I.
Published: April 2003

We consider a fluiddynamic model derived to describe tunnel fires. The derivation of the model and results obtained by the model are discussed.
Existence and Approximation of Solutions of a System of Quasilinear Differential Equations
Authors: Omerspahić Alma
Published: April 2003

This paper deals with the behavior, approximation and stability of some solutions of the system of quasilinear differential equations. The behavior of solutions in the neighbourhood of an arbitrary curve is considered, with extraordinary attention on some special cases. The obtained results contain an answer to the question on approximation as well as stability of solutions whose existence is established. The errors of the approximation are defined by the function that can be sufficiently small. The theory of qualitative analysis of differential equations and topological retraction method are used.
A fast method to implement non‐local discrete transparent boundary conditions for the Schrödinger equation
Authors: Arnold A. , Ehrhardt M. , Sofronov I.
Published: April 2003

Discrete transparent boundary conditions (DTBCs) for the time‐dependent Schrödinger equation were introduced in the numerical simulations of whole space problems in order to reduce the computational domain to a finite region. They include a convolution w.r.t. time with a weakly decaying kernel that leads to very costly numerical evaluation for large‐time simulations. As a remedy we construct approximate DTBCs with a kernel having the form of a finite sum‐of‐exponentials, which can be evaluated in an efficient recursion.
Dimension Reduction methods for Infinite Dimensional Systems
Authors: Steindl Alois
Published: April 2003

From experiments and also from computer simulation of dynamical systems it is well known that for many dynamical phenomena in physics or engineering, which are modelled by infinite dimensional dynamical systems, the asymptotic behavior can be accurately described by replacing the original infinite dimensional system by a low dimensional system represented by so‐called essential variables. Such a dimension reduction of a dynamical system turns out to be central, both for a qualitative and quantitative understanding of its behaviour.

In [1] Approximate Inertial Manifolds are presented, which perform extremely well for nonlinear evolution equations, but don't work as expected for the dynamics of a fluid conveying tube. By comparing the results for different internal damping values it can be seen that the larger gaps and the location of the cluster point in the spectrum for the weaker damping improve the approximation quality considerably.
Knowledge‐based Diagnosis Aiding in Regulation Thermography
Authors: Knaf Hagen , Lang Patrick
Published: April 2003

Regulation Thermography is a diagnostic tool in the medical science based on the measurement of the body's thermoregulation ability – the so‐called thermogram. The expert's rules for the interpretation of a thermogram can be modelled using Fuzzy Logic. In the present article this modelling process is briefly explained; it leads to a Fuzzy Inference System capable of evaluating thermograms with respect to e.g. signals for the presence of Breast Cancer. Some of the main points of a comparison between the expert rules and the result of a stepwise linear discriminant analysis performed on classified thermograms are presented.
Phase Coexistence and Critical Point of the Stell‐Hemmer Fluid
Authors: May H.‐O. , Mausbach P.
Published: April 2003

By means of a Gibbs ensemble Monte Carlo method we calculate the gas‐liquid coexistence line for a Stell‐Hemmer fluid in three dimensions. We estimate the critical point using a scaling law where the critical exponent is β = 0.32.
Interval Arithmetic in Maple with intpakX
Authors: Grimmer Markus
Published: April 2003

intpakX, a Maple package for interval arithmetic created in 1999 by I. Geulig and W. Krämer [1,3], is based on intpak, an experimental Maple package that was created by A.E. Connell and R.M. Corless in 1993 [2].

intpakX contains basic data types and operators for interval arithmetic as well as a variety of numerical methods using intervals. It offers the possibility to compute verified numerical results with a Computer Algebra System and at the same time display the results graphically.

With the new version intpakX v1.0, intpakX has been updated and redesigned to work with Maple7. This paper shows the range of features of intpakX and gives some examples of their use.
Transient RankingMethods for the Simplification of Nonlinear DAE Systems in Analog Circuit Design
Authors: Wichmann Tim
Published: April 2003

Symbolic analysis of analog circuits using computer algebra is limited by the complexity problem: even for small circuits the symbolic equation systems get too large to be handled efficiently. In the past years simplification techniques have been developed which reduce the complexity of such equation systems. In this paper we are focusing on simpli fication techniques for equations modeling nonlinear transient analog circuits. Here it is necessary to control the dynamic behavior of the simplified system. For this, we developed two different methods which predict the influence of a simplification on the equations' transient solution. We will describe both methods and compare their efficiency and accuracy.
On Fuzzy Logic Compenstion System of Irregular Disturbances in a Process of Fine Machining
Authors: Kacalak W. , Lipiński D. , Krzyżyński T. , Lenartowicz M.
Published: April 2003

In the paper the analysis of sources and results of irregular disturbances in a process of fine machining is presented. A description of events causing the disturbances and an advisability of use of thermal and elastic systems for compensating relative position deviations of cutting tool and a piece are given. A compensation system with the application of fuzzy logic and detailed algorithms and programs for various compensation strategies are proposed. It is shown that compensating actions should depend on a present relative tool‐piece position and its first derivative.
On Optimisation of Detail Recognition in a Process of Super‐Fast Grinding of Ceramics
Authors: Lenartowicz M. , Krzyżyński T. , Lipiński D. , Kacalak W.
Published: April 2003

Most of digital picture processing systems are used in mass production. While making use of intelligent systems of standard recognition, digital picture processing can be applied in lot production or small lot production, and their ability to learn enables them to recognize parts of di.erent shapes. In the present paper, a system based on fuzzy logic principles was introduced. It has an application in the automation of the feed of machined elements into the machine working space during machining of ceramics.
Gestaltoptimierung von Bögen für verschiedene Belastungsfälle
Authors: Mikulski Leszek
Published: April 2003

In dieser Arbeit widmen wir uns der Gestaltoptimierung von Bögen, die simultan verschiedenen Belastungsfälle aushalten und dabei die maximale Verschiebung (Spannung) minimal halten. Die optimierten Bögen besitzen längs ihrer Länge einen veränderlichen Querschnitt, sind durch Eigengewicht und Nutzlast belastet. Betrachtet werden verschiedene Fälle gleichzeitiger Belastung der Bögen, z.B. für einen Bogen mit zwei inneren Unterstützungen werden sechs verschiedene Belastungsfälle angenommen. Als Optimierungskriterium wird die maximale Verschiebung oder die maximale Spannung ausgewählt. Die Querschnittshöhe und die Lage der inneren Unterstützungspunkte sind die veränderbaren Steuergrößen in dieser Aufgabe. Die Nebenbedingungen (Beschränkungen) sind geometrischer Art, die Steuergrößen und das Gesamtgewicht des Bogens betreffend. Die Probleme der Gestaltoptimierung lassen sich mathematisch als optimale Steuerungsprobleme formulieren. Zur Lösung der hier formulierten Problemstellung wird das Maximumprinzip verwendet. Das Maximumprinzip erlaubt es, das Problem der optimalen Gestaltung als ein Mehrpunktrandwertproblem (MPRWP)für ein Differentialgleichungssystem aufzuschreiben. Die Dimension des MPRWP stellt üblicherweise eine große Beschränkung dar und entscheidet über numerische Schwierigkeiten. Für die numerische Lösung wird das Hybridverfahren verwendet, welches eine Verbindung der Mehrziel und Kollokationsmethode ist. Die Aufgabe wurde mit einem leistungsfähigen Programm Dircol gelöst.
Constraint preconditioning for linear systems in elasticity
Authors: Geilenkothen A.
Published: April 2003

The mixed variational formulation of elastic deformation of a material body leads to a constraint minimisation (or saddle‐point) problem. Using the PEERS finite element space to discretise the problem one gets an indefinite system of linear equations. To solve this system, preconditioners with similar saddle‐point patterns will be applied. The results of numerical tests with this preconditioning strategy show its efficiency for linear systems with up to more than half a million unknowns.
The streamline–diffusion method for a convection–diffusion problem with a point source
Authors: Roos Hans–Görg , Zarin Helena
Published: April 2003

A linear singularly perturbed convection–diffusion problem with a point source is considered. The problem is solved using the streamline–diffusion finite element method on a class of Shishkin–type meshes. We prove that the method is almost optimal with uniform second order of convergence in the maximum norm. We also prove the existence of superconvergent points for the first derivative. Numerical experiments support these theoretical results.
Dynamic iteration may fail for partitioned network simulation
Authors: Günther Michael
Published: April 2003

In many technical applications, complex systems are composed of subsystems that are modelled independently using a network approach. This co‐modelling ansatz is completed very naturally by a co‐simulation approach based on dynamic iteration, where the respective DAE submodels are solved iteratively. For partitioned electric network simulation we show that this approach may fail. As alternative we discuss overlapping techniques based on topological network information.
On A‐stability for some two‐step W‐methods
Authors: Podhaisky H. , Weiner R. , Schmitt B.A.
Published: April 2003

In this paper we prove the A‐stability for some sequential and parallel two‐step W‐methods (TSW‐methods and PTSW‐methods) which have been constructed recently for the numerical solution of large stiff ODE systems. To show that the spectral radius of the amplification matrix of a fixed method is less than one we apply Schur's criterion recursively to the characteristic polynomial of the amplification matrix. The computations can be done automatically using computer algebra tools, e.g. Maple 7.