bluuebunny/crossref_metadata_2025_split huggingface dataset:
The application of multigrid methods to plasticity at finite strains
Authors: Wieners C. 
Published: March 2011

AbstractWe 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

AbstractOptimization 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

AbstractEs 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

AbstractThis 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

AbstractA 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

AbstractA 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

AbstractFür 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

AbstractZur 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractDie 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

AbstractThe 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

AbstractLarge 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

AbstractUsing 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

AbstractThis 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

AbstractDie 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

AbstractDirect 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

AbstractThe 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

AbstractThe 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

AbstractAn 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

AbstractNumerical 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

AbstractThis 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

AbstractIn 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

AbstractBetrachtet 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

AbstractMechanical 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

AbstractWe 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.
On the appropriate treatment of singularly perturbed wave equations
Authors: Schagerl M. , Berger A. 
Published: March 2011

AbstractEngineers 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.
A generalization of Gröbner bases helps to compute singularity theory transformations
Authors: Lunter Gerton 
Published: March 2011

AbstractAccording to singularity theory, many functions admit (local) normal forms under suitable equivalence transformations. Motivated by a dynamical systems problem, where we are interested in symbolically computing bifurcation curves, our goal is to compute the normalizing transformation explicitly.Its computation proceeds stepwise, and resembles Newton's root‐finding algorithm, with the derivative replaced by the tangent space to the orbit under equivalence transformations. At each step we need a solution of a linear equation involving the tangent space, analogous to Newton's algorithm requiring the inverse of the derivative.If the equivalences are right‐transformations, the tangent space is an ideal, and the linear equation is solved by the normal form or 'division' algorithm of Gröbner bases. If left‐right transformations are used, the tangent space consists of sums of ideal and algebra elements. The resulting linear equation can be solved analogously by suitably extending the notions of Groebner basis and canonical subalgebra (SAGBI) basis. See ]9[ for an extended overview, ]8[ for the details.
Moment Functions for Solutions of Random Boundary Value Problems
Authors: Richter M. , Vom Scheidt J. , Starkloff H.‐J. 
Published: March 2011

AbstractBoundary value problems for a class of ordinary differential operators with random coefficients are investigated. The random influences to the differential operators and the inhomogeneous terms are modelled by the class of weakly correlated processes. Using a perturbation method the random solutions can be represented as integral functionals of weakly correlated processes. It is possible to find approximations for the moment functions of the solutions by means of expansions in powers of the correlation length e of the input processes. Especially asymptotic expansions for second‐order moments of the solutions are presented. The results determined analytically are compared with Monte‐Carlo simulations.