bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accuracy and implementation of refined second order semi‐analytical design sensitivities
Authors: Vervenne K. , De Boer H. , van Keulen F. 
Published: March 2011

AbstractAccurate second order design sensitivities of finite element responses play an important role in the optimization process. The semi‐analytical (SA) method is often used to compute these sensitivities. A disadvantage of the SA method is that severe inaccuracies may be observed for shape design variables. To improve the accuracy of the SA method a refined second order method has been proposed and implemented. The improvement has been based on the consistency conditions for rigid body modes and their derivatives. Both analytical and numerical examples indicate a considerable accuracy improvement of the refined method over the standard SA method.
Optimal design in automotive engineering with scattering design variables
Authors: Thomas Vietor 
Published: March 2011

AbstractThe development of a passenger car is a multidisciplinary task. The vehicle has to fulfill demands out of different attributes like vehicle dynamics, driveability, acoustics, thermal and heat management, safety, durability, crash and economics. One main problem is the variability of mechanical quantities responsible for the performance and customer perception of a car. To overcome this, the extension of the conventional deterministic oriented development process to a process which includes stochastic quantities is necessary. In this paper the current deterministic approach is described briefly. It is not possible to perform the extension in a single step. In a first extended version of the process the variability of material parameters is included. In further steps the formulation and solution of stochastic optimization problems for sub‐problems is necessary. Finally the complete approach should fully integrate the variability of stochastic quantities.
Nonnegative Interpolation with Clough‐Tocher Splines of Cubic Precision
Authors: Bastian Marion , Schmidt Jochen W. 
Published: March 2011

AbstractIn ]4[ the Clough‐Tocher splines of quadratic precision are shown to allow always nonnegative interpolation of scattered data. The aim of the present note is to point out that Clough‐Tocher splines of cubic precision are suitable, too. This result extends to range restricted interpolation if the obstacles are piecewise constant. For piecewise linear and continuous obstacles the Clough‐Tocher splines may fail. However, for this type of restrictions it seems to be possible to derive an always working interpolation algorithm by means of the parametric Clough‐Tocher splines recently introduced in ]1[.
Flatness criteria for subdivision of rational Bézier curves and surfaces
Authors: Dyllong E. , Luther W. 
Published: March 2011

AbstractMany of well‐known algorithms in the context of Computer Aided Geometric Design are based on subdivision techniques. Unfortunately, termination criteria for subdivision mostly require a time‐consuming computation of the maximum deviation between any given curve segment and its linear approximation at each subdivision step. We generalize results by Wang for Bézier curves ]3[ and present an approach which in advance specifies the number of necessary subdivision steps to obtain a piecewise linear approximation within an assumed accuracy for a given rational Bézier curve or surface.
Global convergence of Newton's method to the solution of equations of Reissner's Elastica
Authors: Flajs R. , Saje M. , Zakrajsek E. 
Published: March 2011

AbstractThe sufficient conditions under which the generalized solution of a planar elastic, Reissner's type cantilever beam if solely based on the rotation ]5[ loaded by conservative load, exists and is unique, are presented. Sufficient conditions for the global convergence of Newton's method and damped Newton's method with a short step are derived. The point load is also taken into account. The derived inequalities are sharp.
Eigenvalue Reanalysis and Condensation with General Masters
Authors: Hofferek Birgit , Voss Heinrich 
Published: March 2011

AbstractIn design optimization very often several changes of a structure are necessary to reach predetermined demands, and in each step very large eigenvalue problems have to be solved which are small modifications of each other. For large eigenvalue problems condensation methods are used to reduce the number of degrees of freedom to manageable size. In this note we take advantage of preceding computations by implementing eigenvectors of previous models as general masters into condensation.
Multi‐language approach in automatic generation of numerical procedures
Authors: Korelc J. 
Published: March 2011

AbstractPractice shows that at the research stage of derivation of a new numerical software different languages and different platforms are the best means for assessment of performances and failures of the numerical model. By the classical approach, re‐coding in different languages would be extremely time consuming and is never done. The paper presents the use of symbolic and algebraic systems for improved quality control of automatically generated numerical procedures. With the symbolic concepts the code is automatically generated for several languages and for several platforms from the same basic symbolic description.
Dependency of the Bypass‐Transition on the Initiating Disturbance
Authors: Heiken S. , Demuth R. , Laurien E. 
Published: March 2011

AbstractNumerical Simulations are made by integration of the three‐dimensional Navier‐Stokes equations for the early stages of the turbulent spot development in accelerated flat plate boundary layers. Serveral initial finite amplitude disturbances are stretched and develop a steep velocity gradient in the spanwise direction. The structure, visualized by tracer particles, becomes more complex and looks similar to a turbulent spot, shown in experiments by Elder.
Constraint partitioning in dynamic iteration methods
Authors: Arnold M. 
Published: March 2011

AbstractDynamic iteration (waveform relaxation) is a well approved approach to the numerical solution of coupled instationary differential equations that is based on a splitting into several subsystems. If the subsystems are coupled by constraints then there is no generic way to assign these constraints to the subsystems. In the present paper we consider three partitioning strategies for constraints that couple two differential‐algebraic systems. An error analysis shows that the stability of the dynamic iteration method depends strongly on the partitioning of the constraints.
Developments in Multirating for Coupled Systems
Authors: Andreas Bartel , Michael Günther 
Published: March 2011

AbstractIn technologically computer‐aided design, the demand for a refined modelling yields the numerical simulation of coupled systems. Often the dynamics of these systems can be described as initial value problems of ordinary differential equations, which are characterised by largely varying time constants. A natural approach is to use multirate integration schemes which integrate the subsystems by their inherent step size. The realisation of the couplings of these subsystems, however done, is the crucial point.To begin, we give a short survey on multirate behaviour and its possible numerical exploitation in one‐step‐schemes. Based on the conception of generalised multirate, we classify multirate methods by the means, which compute the coupling terms for the internal stages: On one hand, extra/interpolation, on the other hand, the incremental formulation, which yields a genuine one‐step‐method. For the latter approach, we discuss the multirate W‐method as an example and give finally test results for a multirate version of Prothero‐Robinson's equation and the Inverter‐Chain.
Uniform pointwise convergence of finite difference schemes for quasilinear convection‐diffusion problems
Authors: Torsten Linss 
Published: March 2011

AbstractWe study convergence properties of an upwind difference scheme on layer‐adapted grids for the discretization of a class of singularly perturbed quasilinear two‐point boundary value problems. We derive conditions that are sufficient for uniform convergence in the maximum norm, with respect to the perturbation parameter, of the method. These conditions are easy to check and enable one to immediately deduce the rate of uniform convergence.
Advanced Methods to Compute Multiphase Turbulent Reacting Flows
Authors: Heinz S. 
Published: March 2011

AbstractPDF and FDF methods do not require approximations for chemical reactions, which makes them extremely valuable for reacting flow calculations. The performance of these methods depends significantly on the accuracy of simulating small‐scale mixing processes. It is illustrated, in which way models may be developed that simulate mixing for various phases as a multi‐scale process in dependence on different factors. Further developments towards a system of very accurate and (less expensive) simplified methodologies for reacting flow calculations are pointed out.
A Conforming Exponentially Fitted Finite Element Scheme for the Semiconductor Continuity Equations in 3D
Authors: Angermann L. , Wang S. 
Published: March 2011

AbstractThe paper presents an exponentially fitted tetrahedral finite element method for the decoupled continuity equations in the drift‐diffusion model of semiconductor devices. This finite element method is based on a set of piecewise exponential basis functions constructed on a tetrahedral mesh. Error estimates for the approximate solution and its associated flux are given, where the error bounds depend on some first‐order seminorms of the exact solution, the exact flux and the coefficient function of the convection terms.
Spectral Schemes on Triangular Elements
Authors: Heinrichs W. , Loch B. 
Published: March 2011

AbstractFirst we consider the Poisson Problem with homogeneous Dirichlet boundary conditions on a triangle. The mapping between square and triangle is realized by mapping an edge of the square onto a corner of the triangle. Then standard Chebyshev collocation techniques can be applied. Numerical experiments demonstrate the expected high spectral accuracy. Further, it is shown that finite difference preconditioning can be successfully applied in order to construct an efficient iterative solver. Finally, a domain decomposition technique is applied to the patching of rectangular and triangular elements.
Stabilized FEM with shock‐capturing for advection‐diffusion problems
Authors: Knopp T. , Lube G. , Rapin G. 
Published: March 2011

AbstractStabilized FEM of streamline‐diffusion type to advection‐diffusion problems may exhibit local oscillations in cross‐wind direction(s). As a remedy, a shock‐capturing variant is considered as an additional consistent (but nonlinear) stabilization. We present some preliminary results of the numerical analysis. The shock‐capturing method has been applied within the numerical solution of the k/e turbulence model of incompressible flow problems for the arising nonlinear advection‐diffusion problems.
The lid‐driven cavity revisited: Stability of two‐dimensional flow
Authors: Albensoeder S. , Kuhlmann H. C. , Rath H. J. 
Published: March 2011

AbstractThe lid‐driven cavity has been studied quite extensively both experimentally and numerically. Today it is the most wide‐spread benchmark problem in CFD. Despite this fact, the linear stability of the steady two‐dimensional flow has hardly been considered, not even for the square cavity. In the present study we revisit this classical problem and calculate the linear stability of the two‐dimensional flow with respect to three‐dimensional perturbations for various aspect ratios. The structure of the critical modes as well as the instability mechanism are addressed.
Stability of hydrothermal‐wave states
Authors: Leypoldt J. , Kuhlmann H. C. , Rath H. J. 
Published: March 2011

AbstractThe half‐zone model is investigated for unit aspect ratio, zero gravity, and Prandtl numbers Pr = 1.5 … 7 by numerical simulations. For thermocapillary Reynolds numbers Re > Rec, the 2D stationary flow is unstable to 3D travelling waves. In the simulations, standing waves can be generated slightly above Rec. It is found, that these states are unstable and decay into either a clock‐or a counter‐clockwise propagating wave. Amplitude equations are used to quantitatively describe the instability of the standing wave states and to estimate the range of Pr within which only travelling waves are stable.
Domain Optimization for the Navier‐Stokes Equations by an Embedding Domain Technique
Authors: Slawig Thomas 
Published: March 2011

AbstractA class of domain optimization problems for the two‐dimensional stationary Navier‐Stokes equations is studied. An embedding domain technique provides an equivalent formulation of the problem on a fixed domain, a reduction of the computational effort for the solution of the state equations, and moreover a simply computable formula for the derivative of the cost functional with respect to the domain. Existence of a solution to the class of domain optimization problems is proved. Numerical examples show the reliability of the derivative formula.
Coherent Vortex Simulation (CVS) of two‐dimensional turbulence
Authors: Schneider Kai , Farge Marie 
Published: March 2011

AbstractWe present a new turbulence model to compute fully developed turbulent flows. The method is based on the solution of the wavelet filtered Navier‐Stokes equations in vorticity‐velocity formulation using an adaptive wavelet discretization. As application we present a Coherent Vortex Simulation (CVS) of a two‐dimensional mixing layer and compare the results with those obtained with Direct Numerical Simulation (DNS).
Settling velocity of porous particles using the particle‐in‐cell model
Authors: Zlatanovski T. 
Published: March 2011

AbstractWe extend the particle‐in‐cell model to the case of settling porous particles. The particle swarm is assumed to consist of identical unit cells each containing a porous particle surrounded by a fluid shell. The steady axisymmetric creeping flow in this multifield unit cell model is assumed to be governed by the Stokes equation in the fluid shell and the Brinkman equation in the porous particle. Analytical solutions for the case of porous‐sphere‐in‐cell and porous‐spheroid‐in‐cell model are obtained.
Konvektiver Wärmeübergang bei instationärer Anströmung
Authors: Mocikat H. , Pražák J. , Göppert St. , Herwig H. 
Published: March 2011

AbstractDer Einfluss instationärer Strömungen, z.B. rotierender oder pulsierender Prallstrahlen, auf den Wärmeübergang an einer angeströmten Platte wird mit Hilfe gemessener Temperatur‐und Wärmestromfelder untersucht. Die Bewertung der Strömungsvarianten mit Wärmeübergangs‐Koeffizienten a bzw. Nußelt‐Zahlen Nu ist problematisch, weil α unstetig werden kann und die charakteristische Länge der Nu‐Zahl für verschiedenste Düsenkonstruktionen schlecht vergleichbar ist. Deshalb wird eine neue Auswertung mit Hilfe der Parameter “Leistung des Prallstrahls” sowie einer Effektivitäts‐Kennzahl E vorgestellt.
Upstream travelling waves in the boundary layer of a horizontal mixed convection flow
Authors: Steinruck H. 
Published: March 2011

AbstractThe propagation of small disturbances in a mixed convection boundary layer flow over a horizontal plate is considered. Employing an asymptotic analysis with respect to a small buoyancy parameter K = Gr/Re2 a triple deck structure of the perturbed flow field is found. Two effects contribute to the pressure perturbation in the lower deck: The displacement of the outer field and the buoyancy in the main deck. Linearizing the perturbation equations and taking the Fourier transform with respect to time and the coordinate parallel to the wall the dispertion relation is derived. Considering the case that the buoyancy induced pressure dominates the displacement induced pressure upstream travelling waves are found. These waves are confined to the boundary‐layer and exist only in the case of the flow over a cooled plate. Furthermore a stationary downstream growing mode exists which indicates that the solution of the boundary layer equations is not unique.
The Calculation of Velocity of Sound near the Liquid‐Gas Transition
Authors: Avsec J. , Marcic M. 
Published: March 2011

AbstractThe paper features the mathematical model of thermodynamic functions of state in gas‐liquid region for pure refrigerants with the help of classical thermodynamics and statistical thermodynamics. To calculate the thermodynamic properties of real fluid we used models on the base of Lennard‐Jones intermolecular potential.
Coating by Capillary Transport through Porous Media
Authors: Baumbach V. , Dreyer M. , Rath H. J. 
Published: March 2011

AbstractA coating device which works with the help of a porous medium is considered. The fluid of interest is a surfactant solution which passes a porous medium before it is deposited on a solid substrate. A hydrostatic model for the process is proposed which assumes the validity of DARCY's law as well as an approach for slot coaters developed by Higgins and Scriven (1980). Emphasis will also be placed on the experimental determination of the porous media permeability and porosity. Moreover the model is compared with experimental results.
Neglect of the Fluid Extra Stresses in Volumetrically Coupled Solid‐Fluid Problems
Authors: Diebels S. , Ehlers W. , Markert B. 
Published: March 2011

AbstractUsually the fluid flow through porous media is described by Darcy 's law or generalizations of it. In this contribution, Darcy 's law is derived from the theory of porous media. To archive this, the fluid extra stress (frictional stress) is neglected in comparision with the momentum exchange (drag force) between the fluid phase and the solid skeleton of a two‐phase model. This common assumption is motivated by the results obtained from a microscopic capillary model in combination with a dimensional analysis of the continuum mechanical model. This analysis shows that the influence of the fluid extra stress decreases with increasing number of capillary tubes per area element.
Mixing in two‐dimensional turbulent reactive flows
Authors: Gerlinger W. , Schneider K. , Bockhorn H. 
Published: March 2011

AbstractEnhanced transport and mixing of scalars in turbulent flows are of major importance, in particular, when chemical time scales are smaller or of the same order as the the mixing time. We present direct numerical simulation of the mixing of passive and reactive scalars in two‐dimensional flows dominated by coherent vortices These organized structures have a significant impact on the mixing dynamics in turbulence. By means of a Fourier‐pseudospectral method the instationary equations are numerically integrated. To quantify the mixing, we consider statistical properties, i.e. the variance decay and histograms to approximate the probability density functions of the scalars. Also, the influence of a chemical reaction on mixing are investigated.
Structure and Extinction of Laminar Ethanol/Air Spray Flames
Authors: Gutheil E. 
Published: March 2011

AbstractThe paper presents the structure and extinction of both mono‐ and bidisperse ethanol/air spray flames in the counterflow configuration. A similarity transformation for monodisperse spray flames is extended to polydisperse spray flames, and the resulting one‐dimensional formulation accesses the use of detailed chemical reaction mechanisms as well as detailed transport. For the ethanol/air system, 38 species and 331 elementary reactions are used. At high strain, the droplets cross the gas stagnation plane, reverse and return towards their injector. For this situation, the width of the chemical reaction zone of bidisperse and monodisperse sprays with the Sauter mean radius is almost the same. However, the droplet oscillation causes the spray flame of the bidisperse spray to strongly increase the total spray flame thickness. For the injection velocity of the spray studied here, the droplets returning to their injector hit the boundary of the computational domain as strain is increased whereas the monodisperse spray flame extinguishs at a considerably higher value of gas strain rate. Thus, the extinction behavior of the bidisperse spray flame is not represented by the monodisperse spray flame with the Sauter mean radius. The model is also suitable to predict pollutant formation.
Some Recent Findings on Turbulent Diffusion Flames from DNS
Authors: Kai Luo 
Published: March 2011

AbstractDirect numerical simulation (DNS) is a valuable tool for the study of complex interactions between turbulence and combustion, thanks to its ability to resolve the wide range of time and length scales involved. Its application in the fundamental study of turbulent diffusion flames has been particularly fruitful in recent years, which led to some new findings, improved understanding of known phenomena and the development of new theories and models. This paper is concerned with the effects of heat release from finite‐rate chemistry on compressible turbulence. The present DNS results reveal intricate interactions among combustion, turbulent transport and mixing.
Computing Virtual Mass by Direct Numerical Simulation
Authors: Niemann J. , Laurien E. 
Published: March 2011

AbstractBubbles resist acceleration with an apparent added mass. An improved knowledge of this virtual mass is desirable for accurate models of bubbly flows, for instance, in a two‐fluid‐model. A high‐resolution, two‐phase numerical code based on a volume‐of‐fluid method is used to compute the virtual mass of air and vapour bubbles in water. The dependency of virtual mass from void fraction is investigated. A well known analytically obtained equation of this dependency is confirmed and the hitherto undetermined quadratic term, which is of importance for medium and high void fractions, is established. A dependency on bubble size and shape is investigated.
A Three Variable Formalism for Turbulent Reactive Sprays
Authors: Rumberg O. , Rogg B. 
Published: March 2011

AbstractA suitably defined PDF is set up for the statistical treatment of a liquid spray dispersed in a gaseous carrier phase. The formulation is full in the sense that the PDF allows for the mathematical description of the totality of all liquid‐ phase an gas‐phase variables. The evolution of this PDF in time is governed by a PDF transport equation, which is modelled and solved via a Monte‐Carlo method. The numerical results clearly indicate the usefulness of the method for laminar and turbulent reacting flows.
Development of a New Cavitation Model based on Bubble Dynamics
Authors: Sauer J. , Schnerr G. H. 
Published: March 2011

AbstractThis paper presents a numerical approach for a cavitation model that bases on a combination of the Volume‐of‐Fluid technique with a model predicting the growth and collapse process of bubbles. The cavitation model is applied for the simulation of cavitating nozzle flows and cavitating flow over a NACA 0015 hydrofoil and showed it's capability to resolve characteristic effects of cavitation such as the cyclic formation of the cavitation cloud, the formation of the re‐entrant jet and the local occurrence of hydrodynamic pressure peaks due to bubble cloud collapse.
Large Eddy Simulation of a Turbulent Reacting Jet‐Flame
Authors: Steiner H. , Bushe W. K. 
Published: March 2011

AbstractThe high nonlinearity of the chemical reaction terms requires a closure model for the chemical source terms occurring in the spatially filtered scalar transport equations. Based on the Conditional Moment Closure hypothesis a new model was recently proposed for LES of non‐premixed combustion. The new model was applied to an LES of a piloted jet flame to assess the model's robustness and predictive capabilities.