bluuebunny/crossref_metadata_2025 huggingface dataset:
Nichtlineare Oberflächenmodelle der Bremsscheibendynamik
Authors: Schmalfuss C. , Wedig W. , Ams A.
Published: March 2011

Die KFZ‐Bremse wird als lineares, zeitvariantes Modell mit nur einem Freiheitsgrad und nichtlinearer Bremsscheibenoberflächen‐Formulierung betrachtet. Besondere Aufmerksamkeit wird den Richtungsänderungen der Normal‐und Reibungskräfte bei variablen Oberflächen gewidmet. Ein typischer Effekt ist die Instabilität des Systems Bremsscheibe‐Bremssattel, welche zu Bereichen kritischer Fahrgeschwindigkeiten führt. Untersucht werden stationäre, harmonische und stochastische Anregungen durch Taumelfehler bzw. Oberflächenrauhigkeiten der Bremsscheibe. Der Einfluß dieser Bauungenauigkeiten wird in Stabilitätskarten aufgezeigt.
Distributed Piezoelectric Vibration Absorbers
Authors: Tylikowski A.
Published: March 2011

In the paper the idea of passive vibration absorbers with variable stiffness or damping properties is extended by developing a tunable distributed piezoelectric vibration absorber of transverse vibrations of a circular plate. The problem of steady‐state vibration transmission through an aluminum plate placed in a duct is analysed. The frequency and space characteristics of transverse displacement and velocity in the plate for the open and short external circuits are presented.
Oscillatory Stochastic Systems with Nonlinear Dissipations
Authors: Wedig V. Walter. , Wagner Utz Von.
Published: March 2011

As an example for oscillators with nonlinear dissipation, we consider a piecewise linear and asymmetric damping characteristic which is typical for shock absorbers in wheel suspensions. For white noise excitations, associated Fokker‐Planck solutions are approximated assuming that displacements and velocities of oscillators are independent. To get even better approximations, analytical results of the expected values of the system are taken into consideration. Then, these stationary density approximations are applied to derive adapted orthogonal polynomials by which the stationary probability density is expanded. The analytical results obtained are checked by corresponding Monte‐Carlo simulations.
Nonlinear feedback control for a four‐steering‐wheel mobile robot
Authors: Blaimschein P. , Bremer H.
Published: March 2011

A mobile robot with four steered and driven wheels moving on planar surfaces under nonholonmic constraints is considered. For this system the equation of motion is derived, which can be reduced to a model of a two‐steering‐wheel vehicle under certain assumptions. For reduced state‐space model a nonlinear state‐space transformation and a nonlinear input transformation is derived so that the model becomes exactly linearized. Additionally to the exact state‐space linearization, the systems for the two positions in the plane and the orientation of the mobile robot are decoupled. These three linear and noninteracting systems can then easily be stabilized by linear control theory.
A Stochastic Approach for Helicopter Handling Qualities Assessment in Turbulence
Authors: Perhinschi M. G.
Published: March 2011

A general procedure for analysis of helicopter handling qualities in turbulent atmosphere is formulated based on a linear model of the vehicle, on a simple representation of the turbulence field and on a mathematical model of the human pilot for quantitative evaluations. The approach leads to a linear system with part of the input random. Results from the theory of linear systems with random input, as well as simulation, can be used to predict helicopter handling qualities in turbulence.
Application of the J2 Plastic Flow Theory in Stability Analysis of an Elastic‐Plastic Open Sandwich Cylindrical Shell under Shear Forces and External Pressure
Authors: Jerzy Zielnica
Published: March 2011

The paper deals with linear and nonlinear stability analysis of a free‐supported sandwich cylindrical panel loaded by shear forces and external pressure. The faces of the shell are assumed to be made of an isotropic, compressible material with stress hardening and these are of the same thickness. The core, of the lightweight type, resists transversal forces only. The constitutive relations of the J2 plastic flow theory are assumed in the analysis. Stability equations are derived on the basis of strain energy approach. With the use of Shanley concept the problem is reduced to a set of partial differential equations with the following unknown functions: stress function F, displacement function Ψ and deflection function w. In nonlinear approach the two parametrical deflection function is accepted in the solution and the equilibrium equation is solved by Galerkin method. Finally, a nonlinear stability equation is obtained which makes possible to determine the equilibrium paths and critical loads for the considered shell. Numerical calculations are performed by a special iterative procedure.
Mode Expansion of Viscous and Viscoelastic Taylor‐Couette Flow in Finite Gaps
Authors: Berger Hans‐Reinhard
Published: March 2011

The Taylor‐Couette flow of viscous and viscoelastic second‐order fluids is examined by a low‐dimensional truncated expansion of trigonometric functions. Tie influence of gap width between the cylinders is included up to second order. By comparing the results for the critical Taylor number, obtained from the series expansion, with numerical results from linear stability calculation the truncation is validated with an error of less than two percent.

The dynamics of the truncated system of ordinary differential equations describe well the transition from laminar to Taylor‐vortex flow, but no further bifurcations to more complex flows are found. The reason for this behaviour is assumed to be due to the omission of non‐axisymmetric disturbances.
Sensitivity analysis of the human body mechanical model
Authors: Ciglaric I. , Prebil I.
Published: March 2011

The mechanical model of human body is introduced. Model consists of rigid segments connected with joints. Articulated rigid‐multibody model is used as a tool for investigation of the injury mechanism during the car crush event. The sensitivity analysis of proposed mechanical model of human body is discussed. Modified direct approach to the sensitivity analysis is introduced, which enables calculation of the sensitivity coefficients in a straightforward way. The approach is semi‐analytical and is baaed on symbolic derivatives of the differential equations of motion. The results of a case study are presented. They illustrate the intrisinct effect of human body geometry and other influential parameters on head acceleration. It is shown that the sensitivity analysis allows for a deeper insight into human body injury criteria.
Mehrkriterienoptimierung bei der globalen Bahnplanung für elastische Handhabungssysteme
Authors: Frik M. , Markus B.
Published: March 2011

Bei der globalen Bahnplanung für elastische, kinematisch redundante Handhabungssysteme können wahlweise mehrere Randbedingungen, Optimierungskriterien und Suchstrategien (A*, Dijkstra) vorgegeben werden. Alle Lösungen sind bei gleichzeitiger Optimierung von mehreren Kriterien nach dem Konzept der Skalarisierung Edgeworth‐Pareto‐optimal. Ein Planungsbeispiel zeigt, welches Optimierungapotential, gemessen an den Einzelkriterien, vorhanden sein kann. Die Methode der gewichteten Kriterien und die Dietanzmethode werden angewendet.
Some Comparisions of Least‐square and Chebyshev Approximation Techniques Applied for Synthesis of Straight‐Line Generating Mechanisms
Authors: Ibrayev S. M.
Published: March 2011

The experience on the application of least‐square and Chebyshev approximation (LSA and CA) based techniques for synthesis of path generating mechanisms examplified by Chebyshev's “ljambda‐mechanism” is summarized in this article.
Virtuelle Montage von Mechanismen
Authors: Kübler R. , Schiehlen W.
Published: March 2011

Mechanismen sind durch geschlossene kinematische Schleifen gekennzeichnet. Bei ihrer Montage werden häufig vorgefertigte Baugruppen von verschiedenen Herstellern verwendet. In zunehmendem Maße liefern die einzelnen Hersteller nicht nur die Hardware, sondern auch die Software, so daß die Möglichkeit einer virtuellen Montage des Gesamtproduktes während der Entwicklungsphase entsteht. Die Kopplung verschiedener Simulationsprogramme kann jedoch zu numerischen Instabilitäten führen. In diesem Beitrag wird die Stabilisierung gekoppelter Simulatoren auf Mehrkörper‐systeme mit kinematischen Schleifen angewandt. Als Beispiel dient die Radaufhängung eines Automobils mit einer Doppelquerlenkerachse.
Modellbasierte Positions‐ und Kraftregelung eines Schreitfahrwerks
Authors: Schneider M. , Müller J.
Published: March 2011

Für das Schreitfahrwerk ALDURO wird ein nichtlineares Regelungskonzept auf der Basis einer exakten Ein‐/Ausgangslinearisierung vorgestellt. Aufgrund des modellbasierten Ansatzes unter Verwendung der nichtlinearen kinematischen und dynamischen Gleichungen können alle auftretenden Nichtlinearitäten kompensiert werden.
Stochastic Transient Resonance of a Plate Under Rotating Machine
Authors: Sniady P. , Sieniawska R. , Zukowski S.
Published: March 2011

An approach for obtaining the probabilistic characteristics of the plate response due to the excitation caused by rotating machine standing on it is presented. Some method for solving the problem of transient resonance applying the Ito differential formula and a set of Ito type differential equations is proposed.
Konzept zur Bestimmung makroskopischer Moduli von Verbundmaterialien
Authors: Bayreuther C. , Miehe C. , Schröder J.
Published: March 2011

Die Berechnung makroskopischer Moduli ist ein wesentliches Ziel bei der makroskopischen Beschreibung von Verbundmaterialien mit linear elastischem Materialverhalten. Zunächst werden Grundlagen zur Konstruktion analytischer Schätzer für makroskopische Moduli aufgezeigt und ein neues verzerrungsbasiertes nNon‐Dilute Distribution Model” vorgestellt. Anschließend wird basierend auf einer Diskretisierung der Fluktuationen des Verschiebungsfeldes auf der Mikrostruktur eine geschlossene Darstellung der makroskopischen Moduli für beliebige Mikrostrukturen hergeleitet.
Buckling of Shear Loading Plates with Strengthenings
Authors: Kosel Franc , Petrišič Jože
Published: March 2011

The paper treats the influence of either weakening or strengthening of rectangular plates on the critical external buckling load. The plate geometry was chosen so that the buckling process takes place in the elastic range. The simply supported plate is loaded with shear forces per unit length which act on its edges. The results present the buckling coefficient as a junction of the ratio between the thickness of the weakening or strengthening and the initial plate. The buckling coefficient is analyzed as a function of the ratio between the weight of the weakened or strengthened plate and the initial plate weight without weakening or strengthening too.
A General Refined Plate Theory
Authors: Johannes Meenen , Holm Altenbach
Published: March 2011

Starting from the principle of virtual displacements, a plate theory is formulated which includes most classical and refined plate theories as special cases. The force and moment equilibrium and the correct formulation of the boundary conditions is obtained by introducing a certain virtual displacement field, and it w shown that generalized Kirchhoff edge forces are present in some types of higher‐order theories.
A Constitutive Law for Anisotropic Stress Adaptive Bone Remodeling
Authors: Nackenhorst U. , Krstin N. , Lammering R.
Published: March 2011

A constitutive theory for stress adaptive bone remodeling based on energetic and thermodynamic considerations is presented. The constitutive theory leads to important conclusions about unknown model parameters, such as the relationship between the bone density and the Young modulus of bones tissue. The isotropic theory is extended to anisotropy by use of a fabric tensor description and a strategy for the numerical computation of anisotropic bone remodeling is suggested.
Transmission problem for viscoelastic aging
Authors: Julia Orlik
Published: March 2011

A multi‐phase composite with jumps on the interface is analyzed. The composite components are aging linear viscoelastic (described by the integral Volterra operator of non‐convolution type) and are subjected to isotropic shrinkage (or thermoelastic deformation). First, the theory of Volterra operators is extended to the Bochner‐ Volterra integral operators. Then these results are used to prove existence and uniqueness of the weak solution to the general transmission problem of viscoelasticity with mixed boundary conditions in the class of continuous Sobolev‐valued functions.
Crossover in the dynamics of jerky flow in AlMg polycrystals
Authors: Ananthakrishna G. , Brechet Y. , Fressengeas C. , Kubin L. P. , Lebyodkin M.
Published: March 2011

Jerky flow in A1‐Mg alloys is investigated through the statistics of the stress drops size, and through a dynamic analysis of the stress vs. time records. At low applied strain rate levels, peaked distributions are associated with chaotic dynamics, while at higher strain rates, the unstable behavior is characterized by power law distributions reminiscent of a critical dynamics. In addition, the bands of localized plastic deformation shift from stationary to propagating. This crossover is discussed in terms of a nonlocal model of jerky flow, with a range of negative strain rate sensitivity and spatial interactions of varying strength.
On microstructures occuring in a model of finite‐strain elastoplasticity involving a single slip—system
Authors: Carstensen C. , Hackl K.
Published: March 2011

Starting from a novel variational principle the flow theory of elastoplasticity can be formulated as a minimization problem with respect to the total deformation and the update of the plastic deformation gradient. For a specific model involving a single slip‐system the latter quantity can be eliminated. The resulting minimization problem with respect to the total deformation only turns out to be not quasiconvex, thus giving rise to the occurrence of layered microstructures. Finite element calculations indeed show these layers. The results are, however, mesh‐dependent. To overcome this effect a partial rank one convexification of the potential given is performed.
Determination of Mechanical Parameters of Solder Materials using the Miniature Measuring Method “Small Punch Test” and an Appropriate FE‐Simulation
Authors: Hemann K. P. , Müller W. H. , Nguyen V. S.
Published: March 2011

In order to model the aging of SMT (Surface Mount Technology) solder materials, which is a prerequisite for lifetime predictions of microelectronic joints as well as of the microelectronic package as a whole, it is necessary to know the current mechanical parameters of the solder as accurately as possible.

In fact, the material behavior of solders is strongly affected by a repeated change of the temperature and the associated thermal loads. Consequently, the current, i.e., “remaining” properties of in‐service solders are of special interest. SMT applications use only very small amounts of solder. Therefore, the Small Punch Test (SPT) can preferably be used to secure materials data. The SPT is essentially a miniature version of a deep‐drawing test during which a load‐deflection curve is obtained. In combination with an FE‐simulation the uniaxial stress‐strain behavior and the fracture toughness of the solder material can be determined. It seems worth pointing out that by virtue of this methodology use of standard size specimens, which are not always available, is avoided a priori.
Micro‐mechanical Modelling of a Bi‐crystal Lamellar Composite's Behaviour at Large strain: A Double Scaled Transition Method
Authors: Krummeich R. , Sabar H.
Published: March 2011

Nanoscaled lamellar structures involve complex deformation behaviour at finite strain due to the preserve of a large number of interfaces. The aim of the work is to develop a micromechanical approach based on interfacial operators in the context of statistical continuum mechanics. Using Hill's formalism, constitutive equations at mesoscale (1 μm) are derived from Nemat‐Nasser's finite elastic‐plastic deformation model ]3,5[ and solved numerically by a self‐consistent method ]1[. At micro‐scale (O.1 μm), a thermodynamical process may be defined to describe intrinsic hardening mechanism found to be linearly dependent with the interlamellar spacing's inverse ]4[. Specific crystal plasticity of both phases may then be introduced in the micromechanical approach to obtain a double scale model describing global and local behaviour of a pearlitic ilot under an imposed loading.
Upper‐Bound Solutions for Rock Slope Stability
Authors: Megueddem M. , Siad L. , Zeghloul A.
Published: March 2011

This communication deals with the stability analysis of jointed rock slope under its own weight. The rock mass is crossed by two sets of unfilled joints. The stability analysis is based on the upper‐bound kinematic approach of the yield design theory. It is carried out directly by considering failure surfaces along particular joints and also going through the intact rock. The simple failure mechanism considered yields improvement of known results.
Plastic design of porous elements with statically admissible stress fields
Authors: Mostowski R. , Mieliczuk J. , Dudziak M.
Published: March 2011

Plastic extremum principle (lower bound) of the plasticity theory for porous materials may be wed for effective design of complex shape elements. Basing on properties of earlier determined systems of discontinuity lines the method of statically admissible stress fields was assumed. The method may be usefully employed in engineering practice for plastic design of porous elements.
Simulation des elasto‐plastischen Verhaltens dünner Metallschichten
Authors: Schotte J. , Miehe C. , Schröder J.
Published: March 2011

Bei der numerischen Berechnung von plastischen Deformationen in dünnen Metallfilmen auf Substratträgern, wie sie beispielsweise in der Mikroelektronik in Form von Kupfer‐Leitungsbahnen eine entscheidende Rolle spielen, sind verschiedene Größeneffekte zu berücksichtigen. Hierzu sind aufgrund der speziellen geometrischen Eigenschaften (z. B. Korndurchmesser, Filmdicke) solcher Schichten weitreichende Modifikationen der bekannten Material‐ und Verfestigungsmodelle für Massiv‐Materialien erforderlich. Es werden verschiedene mikromechanisch motivierte Ansätze miteinander kombiniert und die durchgeführten FE‐Simulationen experimentellen Untersuchungen gegenübergestellt.
Strange—Mode Instabilities in Luminous Stars
Authors: Chernigovski S. , Glatzel W. , Fricke K. J.
Published: March 2011

If radiation pressure contributes significantly to the total pressure in models for the envelopes of hot and luminous stars, such as massive objects and Wolf—Rayet stars, strange—mode instabilities with growth rates in the dynamical range do occur. The properties of these mechanical instabilities are reviewed and an intuitive model of the underlying instability mechanism is discussed. Adopting spherical geometry the evolution of the instabilities has been followed into the nonlinear regime by numerical simulation. Multiple shocks are formed and velocity amplitudes above 102 km/sec are reached which can imply direct mass loss of the objects.
Comparison of Several Numerical Methods for Internal Transonic Flow Problems
Authors: Dobeš J. , Fořt J. , Fürst J. , Halama J. , Kozel K.
Published: March 2011

This contribution summarizes results of several numerical methods developed at our department. Presented methods are based on central TVD schemes, upwind TVD schemes with or without Riemann solver, ENO schemes and Lax‐Wendroff type schemes. The results of 2D methods, computed on either structured quadrilateral grids or unstructured grids composed of triangles and quadrilaterals, are compared on 2D axial and radial turbine cascade and 2D axial compressor cascade. A comparison of results, obtained on structured hexahedral grids, is shown for 3D axial turbine cascade of Škoda Pilsen enterprise.
A Field‐Panel Method For Subsonic And Transonic 3D Wing Calculation
Authors: Fokin D. , Wagner S.
Published: March 2011

The development of fast numerical methods for calculating sub‐and transonic flow over 3D configurations is important for numerical optimization purposes. One efficient approach, namely field panel method, is based on the boundary‐element methods solving the full potential equation (see e.g. ]1[). The algorithm incorporates panel methods for calculating the basic incompressible flow and compressible field iterations. The purpose of the present work is to develop a mathematically well based and efficient numerical field‐panel method for the analysis of transonic flow over 3D wings, that could be further used for design and optimisation of transonic wings in a given range of free stream Mach numbers.
Low‐Dimensional Approximations of Random Vibration Systems
Authors: Wunderlich R. , Vom Scheidt J. , Starkloff H.‐J.
Published: March 2011

The paper considers the computation of moment functions of the response of large‐scale randomly excited vibration systems. Since standard methods fail because of enormous computational problems dimension reduction techniques are applied. We find approximations of the desired response characteristics of the large‐scale system by solving a suitable reduced‐order system.
Spatial Friction as Standard NLCP
Authors: Glocker Christoph
Published: March 2011

Coulomb friction problems can be stated as quasi‐variational inequalities. These are variational expressions of certain non‐smooth pseudo‐potentials which have to be minimized in the sense of a two‐person non‐cooperative constrained game, consisting of the normal and the tangential player. In this paper we show that spatial Coulomb friction applied to the rolling contact problem in rigid body dynamics may be formulated as a nonlinear complementarity problem in standard form, i.e. as 0 ≤ x f(x) ≥ 0 with continuous and differentiable x → f(x).
Weight‐Minimal Laminate Structures Under Stress Constraints
Authors: Hansel W. , Becker W.
Published: March 2011

The determination of weight‐minimal laminate structures requires the well‐aimed employment of structural optimization. In contrast to the common parameter optimization in which the design variables fiber orientation and layer thickness are varied continuously, a layerwise topology optimization offers more flexibility. Starting from an initial laminate lay‐up with sufficient strength, the topology of each individual ply is varied by removing unnecessary material. The final design is well adapted to the local load fluxes.
Optimal Rendezvous with Constraints on Circular and Elliptical Orbits
Authors: Istratie V.
Published: March 2011

This work studies the optimum rendezvous with minimum fuel consumption two space vehicles on circular and elliptical orbits, the surveyor vehicle being equipped with a low thrust installation, their motion equations being written in the three‐dimensional space, in relative motion; the space origin being the target vehicle. Optimal controls to be determined being the acceleration due to thrust, related to the minimum fuel consumption. By means of the Legendre‐Clebsch condition it is demonstrated that the formulated optimization problem is, indeed, a minimum problem.
An efficient shape parameterization concept for structural optimization
Authors: Kegl M.
Published: March 2011

This paper describes a shape parameterization concept that may be used efficiently in structural shape optimization. It relies on the assumption that the finite element mesh is defined as a convective mesh, following automatically the shape changes of a conveniently parameterized body. Suitable parameterization of the body is achieved by combining the design element technique and a convenient design element. The design element in turn is defined as a rational (tensor‐product) Bézier body. It represents a general‐purpose design element, serving as the geometrical data provider for the response and sensitivity analysis for virtually any finite element type.
Structural optimization in nonlinear mechanics
Authors: Schwarz St. , Kemmler R. , Ramm E.
Published: March 2011

In the present study geometrically and materially nonlinear response is considered in topology and shape optimization in order to introduce more realism into the structural design. Typical objectives are to minimize the weight or to maximize the structural ductility or the critical load factor of a construction. The crucial point of the optimization procedure is the sensitivity analysis. In case of path‐dependent problems, such as elastoplasticity the sensitivities are also path‐dependent and have to be determined after each incremental step. With respect to the specific features of either topology or shape optimization different methods of sensitivity analysis are applied. The entire optimization procedure is verified by several design problems.
On a numerical method for the regularization of descriptor systems
Authors: Benner P.
Published: March 2011

We discuss a numerically stable algorithm, originally proposed in ]3[, that computes a regularizing output feedback for descriptor systems. In ]3[, the system is transformed to a condensed form via a sequence of singular value decompositions (SVDs). We show that the expensive SVDs can be replaced by reliable, more efficient orthogonal decompositions. Moreover, we demonstrate how the feedback is obtained from our slightly different condensed form.
Enge Schranken für den Effektivzinssatz nach der PAngV bei einem Annuitätenproblem
Authors: Detmers F. , Herzberger J.
Published: March 2011

Ein spezielles Problem stellt die Ermittlung des Effektivzinssatzes einer geänderten Annuität gegenüber der ursprünglichen Annuität dar. Daraus ergibt sich die Aufgabe, eine formelmäßige Abschätzung des Zusammenhangs zwischen den eindeutigen positiven Wurzeln zweier zugeordneter Polynome zu finden. In unserem Modell wird diese Aufgabe bei Anwendung der deutschen Preisangabeverordnung (PAngV) mathematisch gelöst.
Multigrid Simulation of Electromagnetic Actuators
Authors: Schinnerl M. , Langer U. , Lerch R.
Published: March 2011

A recently developed multigrid simulation scheme for coupled magneto‐mechanical systems is presented. This scheme allows the efficient calculation of 3D dynamic motions of elastic ferromagnetic materials in a magnetic field. The 3D mechanical problem is discretized with nodal elements and the 3D magnetic problem with edge elements. Both meshes may be chosen independently and therefore, they can be adapted to the physical requirements of the mechanical and magnetic field. By applying fast multigrid solution techniques, very short solution times can be achieved even for large scale 3D problems. Using the developed scheme the transient behavior of a solenoid valve is calculated.
The application of multigrid methods to plasticity at finite strains
Authors: Wieners C.
Published: March 2011

We present a general method for the formulation of incremental plasticity at finite strains and the combination with multigrid methods. Therefore, the algorithms analyzed in ]5[, ]6[ for Prandtl‐Reuß‐plasticity are transfered to nonconvex energy functionals. The efficiency of the multigrid solver is demonstrated on a large scale numerical example in three space dimensions.
Multidimensional Stepsize Control
Authors: Callies R.
Published: March 2011

Optimization problems in technical simulation often lead to boundary value problems for systems of highly nonlinear ordinary differential equations with piecewise defined right hand sides and a large number of exceptional points with reduced differentiability. Classical integration schemes show a poor performance due to the large number of restarts of the integrator; integration intervals end before the stepsize control has stabilized. The new approach does not only use the information of the preceeding integration step for stepsize control, but also information from the preceeding iteration step, if the boundray value problem is solved by an iterative algorithm. Multistage search techniques improve the efficiency of the determination of the exceptional points. These new techniques are tightly coupled with the progress of the Newton process. The numerical solution of the boundary value problem is by the new multiple shooting code JANUS which fully exploits the new integration techniques.
Berechenbare Schranken von Taylorkoeffizienten analytischer Funktionen
Authors: Neher M.
Published: March 2011

Es werden Verfahren vorgestellt, um Schranken für Taylorkoeffizienten von auf dem Computer verfügbaren analytischen Standardfunktionen oder ihrer Verkettungen zu berechnen. Die Verfahren beruhen auf verschiedenen Modifikationen der Cauchy'schen Koeffizientenabschätzung. Bei praktischen Berechnungen auf dem Computer wird durch Intervallarithmetik sicher gestellt, dass alle auftretenden Diskretisierungs‐und Rundungsfehler erfasst werden.
Parallel two‐step W‐methods
Authors: Schmitt B. A. , Weiner R. , Podhaisky H.
Published: March 2011

This paper deals with two‐step W‐methods for stiff initial value problems which allow the parallel solution of the stage equations. Special methods of order 3 and 4 are tested for both sequential and parallel implementations and compared with efficient sequential codes. The results show that the methods are already competitive in a sequential implementation and have a high level of parallelization especially in combination with Krylov solvers for linear equations of large dimensions.
A finite volume method to compute the steady state temperature distribution in premature or newborn infants
Authors: Fischer B. , Ludwig M. , Meister A.
Published: March 2011

A mathematical model is developed and used for a computer simulation of the thermoregulation of premature infants. We propose a finite volume technique for the solution of the associated partial differential equation on an unstructured grid. Emphasis is laid on the model and the validation of the numerical scheme. Beside various test runs using real life data, we present a discrete maximum principle for the steady state solution with respect to the non‐convex computational domain. Keywords: Finite volume method, Thermoregulation, Maximum principle.
The ε‐Uniform Convergence of a Defect‐Correction Method on a Shishkin Mesh
Authors: Fróhner A. , Linss T. , Roos H.‐G.
Published: March 2011

A defect correction method based on finite difference schemes is considered for a singularly perturbed boundary value problem on a Shishkin mesh. The method combines the stability of the upwind difference scheme and the higher‐order accuracy of the central difference scheme. The almost second‐order convergence of the scheme with respect to the discrete maximum norm, uniformly in the perturbation parameter ε, is proved. Numerical experiments support the theoretical results.
Stabilisierte Hyperschallflugbahnen
Authors: Callies R. , Wimmer G.
Published: March 2011

Für ein Hyperschallflugzeug berechnet man optimale, dreidimensionale Flugbahnen unter neuartigen Stabilisierungsbeschränkungen. Dabei muß eine “gutmütige” optimale Nominaltrajektorie in jedem Bahnpunkt genügend Spielraum bieten, um weitere Kriterien zu erfüllen. Ein Beispiel ist der Aufstieg eines Hyperschallflugsystems, wobei bei einem Triebwerksausfall ein Notlandeplatz erreichbar sein muß: Die Zusatzforderung verursacht starke Deformationen der ursprünglichen Flugbahn. Zu jedem Punkt der Nominalbahn ist ein sekundäres Optimalsteuerungsproblem zu lösen. Das Problem läßt sich als Randwertaufgabe für ein System hoch nichtlinearer Differentialgleichungen formulieren; die Stabilisierungsforderung wird adaptiv punktweise erfüllt. Die numerische Lösung erfolgt mit dem neuen Mehrzielverfahren Janus.
Flugbahn‐Optimalsteuerung für ein Hyperschall‐Flugsystem zur Verringerung des instationären Wärmetransfers
Authors: Dinkelmann M. , Wächter M. , Sachs G.
Published: March 2011

Zur Reduzierung der hohen thermischen Belastung im Hyperschallflug wird ein Lösungsansatz vorgelegt, der den Zusammenhang von instationärem Wärmetransfer und Bewegung des Flugzeugs erfaßt und in einem Gesamt‐Optimierungsprozeß behandelt. Bei der Beschreibung des instationären Wärmetransfers und der Dynamik des Flugsystems wird Wert auf eine realistische Betrachtungsweise gelegt. Dadurch gestaltet sich das mathematische Modell des Gesamtsystems sehr komplex. Die vorgelegten Ergebnisse zeigen, daß eine substantielle Reduzierung der thermischen Belastung durch eine geeignete, optimale Steuerung der Flugbahn erzielt werden kann.
Transonic laminar interacting boundary layers in narrow channels
Authors: Kluwick A. , Gittler Ph.
Published: March 2011

The investigation of transonic viscous‐inviscid interactions is hampered by the fact that the nonlinear small disturbance equation which governs the external flow has to be solved simultaneously with the nonlinear boundary layer equations. This poses an extremely difficult numerical problem which has been treated so far with limited success only. However, if the medium is confined in a sufficiently narrow channel, the flow outside the viscous wall layers is one‐dimensional in the leading order approximation which in turn allows the derivation of a solution in closed form. This significantly simplifies the construction of numerical solutions which nevertheless display essential features of transonic flows associated with the transition from subsonic to supersonic conditions or/and vice versa.
Visualization of Supersonic Flow past EOS
Authors: Ting C.‐C.
Published: March 2011

The visualization of supersonic flow around EOS ]1[ involves analyzing shock wave positions and vortices at large angles of attack. The applied experimental methods include color Schlieren, oil film and vapor screen techniques. Depending on the Mach number and the angle of attack various vortex structures are observed on the leeward side.
Airfoil Design and Optimization
Authors: Lutz Th.
Published: March 2011

The aerodynamic efficiency of mildly swept wings is mainly influenced by the characteristics of the airfoil sections. The specific design of airfoils is therefore one of the classical tasks of aerodynamics. Since the airfoil characteristics are directly dependent on the inviscid pressure distribution the application of inverse calculation methods is obvious. The direct numerical airfoil optimization offers an alternative to the manual design and attracts increasing interest.
Laminar‐turbulente Transitionsvorgabe im DLR Navier‐Stokes‐Löser FLOWer
Authors: Krumbein A.
Published: March 2011

Die Modellierung der laminar‐turbulenten Transition in Navier‐Stokes‐Lösern ist eine notwendige Anforderung für die Berechnung von Strömungskonfigurationen in der Luftfahrtindustrie. Häufig werden quantitativ oder sogar qualitativ richtige Ergebnisse nur unter Berücksichtigung der Transition erzielt. Eine Technik zur Transitionsvorgabe zerteilt das Berechnungsgebiet in laminare und turbulente Bereiche, die durch Transitionslinien auf der Konfigurationsoberfläche festgelegt sind. Die Transitionslinien werden ins Oberflächennetz abgebildet, womit eine Einteilung in laminare und turbulente Stücke vorliegt. In direkter Nachbarschaft zu laminaren Wandsegmenten werden laminare Raumgebiete erzeugt, deren Ausdehnung in Wandnormalenrichtung variabel ist. Turbulenzgrössen (z.B. μt) werden in geeigneter Weise numerisch behandelt. Vorgestellt werden Ergebnisse an mehrkomponentigen, 2‐und 3‐dimensionalen Konfigurationen (3‐Element‐Profil, Hubschrauber, Flügel‐Rumpf‐TW‐Pylon).
Performance of Turbulence Models of Second Order in Predicting Turbulent Mixing in Jet Exhaust behind Aircraft Engines
Authors: Sadiki A. , Maltsev A. , Janicka J.
Published: March 2011

The modeling of near‐field jet from aircraft engines is considered as an important task for a subsequent study on chemistry and micro‐physics in far‐away spatial regions of the aircraft wake. The main goal of this study is to investigate the performance of transport equation turbulence and mixing models for the prediction of near‐field jet exhaust plumes. Turbulence is modelled with three different models (two different linear second order moment closures (Reynolds stress transport models) and k‐model). Scalar fluxes are modeled by corresponding transport equation models. Finite‐rate chemistry is considered. Results, obtained with and without chemical reactions, show that turbulence and mixing modeling effects on the chemistry and flow field are significant and should be taken into account in modeling of near‐field exhaust plumes.
Numerical simulation of large scale hydrogen explosions in complex geometries
Authors: Bielert U. , Kotchourko A. , Burgeth B. , Breitung W.
Published: March 2011

Large hydrogen air clouds represent a serious hazard during severe accidents in nuclear power plants as well as in facilities of the developing hydrogen technology. The accident scenarios are dominated by large time and length scales with complicated boundary conditions. The combustion can proceed as an accelerating turbulent flame with possibly transition to detonation. Such problems require a careful selection of the physical and chemical models as a fully detailed calculation is not yet feasible. An extension of the well known eddy break‐up model together with the k‐‐model was calibrated at a large set of experiments on different scales. It was demonstrated that this model gives good results for a large range of parameters.
Partial premixing in diffusion flame quenching
Authors: Favier V. , Vervisch L.
Published: March 2011

Using Direct Numerical Simulation, we focus on the development of partial premixing in laminar diffusion flame quenching. Calculations are performed in the configuration of a 2‐D diffusion flame squeezed by a pair of vortices. First, the flame undergoes strong finite rate chemistry effects, linked to high levels of strain rate induced by vorticity. Then quenching develops, leading to edge‐flames. During the creation of the hole within the reaction zone, the response of the laminar diffusion flame burning rate to strain rate variation is investigated. Depending on the flame structure, strong differences between DNS results and the behavior of a steady 1‐D flamelet are observed, on account of partial premixing.
Investigations of Turbulence Modulation in Turbulent Particle Laden Flows
Authors: Geiß S. , Sadiki A. , Maltsev A. , Dreizler A. , Janicka J.
Published: March 2011

This paper presents the results of experimental and numerical analyses of high particle laden turbulent flows. The dispersed phase consists of non‐reacting solid mono‐dispersed particles with variable diameter between 60μm and 1500μm. Experiments using Laser Doppler Anemometer (LDA) and Phase Doppler Anemometer (PDA) show in agreement with earlier investigations that small particles attenuate turbulence while large particles enhance turbulence. More detailed investigations are, however, needed to clearly identify and quantify such influences. In order to obtain preliminary information about the performance of the k‐model, mostly used for the majority of the numerical models, in predicting the physical features of modulation, some numerical calculation results obtained by use of Euler/Lagrange method and a modified version of the k‐model are compared to the experimental data.
Zur Modellierung komplexer partikelbeladener Strömungen mit der kinetischen Theorie granularer Medien
Authors: Indenbirken M. , Strauss K.
Published: March 2011

Die Partikelbewegung in verdünnten feststoffbeladenen Gasströmungen wird häufig mit der kinetischen Theorie granularer Medien (engl.: kinetic theory of granular flows, KTGF) beschrieben. Dieses aus der kinetischen Gastheorie abgeleitete Modell basiert auf der Kontinuumsannahme für beide Phasen (dem sog. Euler/Euler‐Ansatz) und ist in seiner ursprünglichen Formulierung vor allem für einfache Strömungsformen geeignet. Hier werden neue Ansätze vorgestellt, die die Verwendung der KTGF auch bei komplexen Strömungen mit ausgeprägten Partikel‐ Wand‐Kollisionen ermöglichen. Dazu ist es erforderlich, die beschreibenden Kollisionsintegrale auszuwerten und die nicht elementar integrierbaren Ausdrücke zu approximieren. Als Resultat werden neuartige Randbedingungen sowie ein erweitertes Konzept zur Beschreibung der Partikel‐Partikel‐ Wechselwirkungen vorgestellt.
Parallel DNS of Turbulent Non‐Premixed Flames with Adaptive Chemistry
Authors: Marc Lange , Jürgen Warnatz
Published: March 2011

Direct numerical simulations (DNS) have become one of the most important tools to study turbulent combustion. Computation time is still a main limiting factor for the DNS of reacting flows, especially in the case of using detailed chemical mechanisms. The computation of the chemical source terms is one of the most time‐consuming parts in such DNS. An adaptive evaluation of the chemical source terms is used in the presented DNS of turbulent diffusion flames. This leads to a decrease of the time needed for this part of the computation by more than a factor of five without any significant loss of accuracy of the results.
The motion of a swarm of particles travelling through a quiescent, viscous fluid
Authors: Machu G. , Meile W. , Nitsche L. , Schaflinger U.
Published: March 2011

The motion and shape evolution of viscous drops made from a dilute suspension of microscopic, spherical glass beads sedimenting in an otherwise quiescent liquid is investigated for conditions of low Reynolds number and infinite Bond number. The key stages of deformation of single drops and pairs of interacting drops are identified. Of particular interest are (1) the coalescence of two trailing drops, (2) the subsequent formation of a torus, and (3) the break‐up of the torus into two or more drops in a repeated cascade. All the. phenomena described above can be explained within the realm of Stokes flow, without resort to interfacial tension or inertial effects.
Experimental investigation of viscous drop formation from a needle
Authors: Meile W. , Machu G. , Schaflinger U.
Published: March 2011

The present paper focuses on the shape evolution and deformation of single drops and pairs of trailing drops made from dilute suspensions during gravitational sedimentation in an otherwise quiescent homogeneous liquid. The presented experimental results are only one part of a comprehensive investigation also including theoretical considerations and numerical simulations. This paper presents the characteristic phenomena through both flow visualization and detailed PIV‐measurements including subsequent derivation of the streamline pattern.
Simplified Two‐Fluid Model for the Simulation of Two Phase Bubbly Flows
Authors: Saptoadi D. , Laurien E.
Published: March 2011

An engineering application model to calculate two‐phase bubbly flows is developed on the basis of the equations of the two‐fluid model. With the used assumptions, the momentum and energy equation of the gas phase are always satisfied, and one has to solve only the continuity equation of the gas phase. The modeling of gas‐liquid interaction will also be discussed. The simplified model is verified by comparison to an experimental investigation of a bubble column.
Numerical Investigation of Performance Losses in a Centrifugal Pump due to Cavitation
Authors: Wursthorn S. , Schnerr G. H.
Published: March 2011

Numerical simulations of cavitating pump flow in consideration of centrifugal and Coriolis force are performed. For the simulations a homogeneous model for the liquid‐vapor two‐phase flow is used. The pump investigated is a radial type of low specific speed (nq = 18) with parallel shroud and hub. Numerical results such as detailed visualizations of the unsteady vapor distribution and time averaged pressure distribution in comparison with experiments are provided.
Nonlinear Effects in the Sound Field of the Circular Piston
Authors: Koníček Petr , Bednařík Michal , Servenka Milan
Published: March 2011

This paper deals with the numerical modelling of the directional sound beams in the tube. The solution of KZK equation with and without the boundary layer is presented. The importance of boundary layer in directional sound beams modelling is shown here.
Wave propagation in a one‐dimensional poroelastic column
Authors: Schanz M. , Cheng A. H.‐D.
Published: March 2011

In Biot's theory of porous media a second compressional wave, known as the slow wave, has been identified. An analytical solution in the Laplace transform domain is obtained showing clearly two compressional waves. For the special case of an inviscid fluid, a closed form exact solution in time domain is obtained using an analytical inverse Laplace transform. For the general case of a viscous fluid, solution in time domain is evaluated using the Convolution Quadrature Method of Lubich. Using properties of two different real materials, the wave propagating behavior, in terms of stress, pore pressure, displacement, and flux, are examined. Of most interest is the identification of second compressional wave and its sensitivity of material parameters.
Zur Behandlung des Elastizitätsproblems in Gebieten mit Ecken
Authors: Knobloch S.
Published: March 2011

Betrachtet wird tin Randwertproblem aus der linearen ebenen Elastizitätstheorie in einem Gebiet mit einer Ecke, deren Innenwinkel > π ist. Die Lösung gehört nicht zu H2, was für die numerische Behandlung problematisch ist. Als Ausweg dient die Zerlegung in einen singulären Teil mit singulären Funktionen und Spannungsintensitätsfaktoren und einen reguläreren Teil, der zu H2 gehört. Kennt man die singulären Funktionen und die Spannungsintensitätsfaktoren, kann man Randwertprobleme für den Teil, der zu H2 gehört, numerisch lösen und die eigentlich gesuchte Lösung durch Hinzufügen der singulären Teile erhalten. Es werden Formeln zur Berechnung der Spannungsintensitätsfaktoren bereitgestellt, in die aber die unbekannte Lösung eingeht, so daß ein iterativer Algorithmus vorgeschlagen wird.
Regular and chaotic motion of a kicked pendulum: A Markovian approach
Authors: Berger A.
Published: March 2011

Mechanical devices subject to impulsive excitation may exhibit very complicated dynamics. Though desirable, a complete analysis of the statistical morphogenesis of (the maps induced by) such systems usually is highly demanding. We therefore focus on a special class of maps nevertheless wide enough to comprise a number of interesting examples. Furthermore, an approximation technique tailored to this specific class is shown to improve Markovian approximation techniques discussed in the literature.
Numerical continuation of homo/heteroclinic orbits with an oscillatory approach to stationary point
Authors: Kohout M. , Schreiber I. , Kubíček M.
Published: March 2011

We formulate a boundary value problem to locate homoclinic or heteroclinic orbits approaching a stationary point in an oscillatory manner so that velocity vectors on the orbit close to the stationary point are used rather than eigenvectors. A Newton method combined with multiple shooting can be used to numerically find the orbit truncated to a finite time interval. This is an extension of an earlier method proposed for 'nonoscillatory' homo/heteroclinics ]1,2[. We have incorporated this procedure into a continuation algorithm, so that a parameter dependence can be obtained. The method has been applied to Rössler system and can be applied to travelling waves.
Squeeze film of micropolar fluid‐theory and application
Authors: Kucaba‐Pietal Anna
Published: March 2011

The squeeze flow of micropolar fluid between two plates is considered. The upper plate is rigid and the lower is porous. The analytical solution to the problem is derived for the general form of boundary conditions imposed on microrotation vector on the wall.
On the appropriate treatment of singularly perturbed wave equations
Authors: Schagerl M. , Berger A.
Published: March 2011

Engineers frequently find themselves concerned with the following situation: One is not interested in certain effects of a model, expecting them to have no significant influence, and one therefore simply neglects them‐even if the type of the governing equations is changed. Having obtained a sound knowledge about the thus simplified problem one would nevertheless like to take into account the effects neglected at first, preferably as some sort of small perturbation. By means of an example from dynamics we point out that such an approach may necessitate some careful analysis: More often than not the perturbations turn out to be of rather singular type.