bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation and Modeling the Mechanical Behavior of Textile Reinforced Composites by Combining the Binary Model and X‐FEM
Authors: Haasemann Georg , Kästner Markus , Prüger Stefan , Ulbricht Volker
Published: February 2009

This paper presents a new efficient modeling strategy based on the combination of Binary Model and X–FEM. It is applied to represent the inner architecture of textile reinforced composites where the fabric is characterized by a complex geometry. Homogenization methods are used to compute the effective elastic material properties. Thereby, the discrete formulation of periodic boundary conditions is adapted. Finally, the results in terms of effective material properties reveal a good agreement with parameters obtained by experimental tests. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization of transmission conditions for analysis of acoustic waves in domains with perforated barriers
Authors: Rohan Eduard , Lukeš Vladimír
Published: February 2009

We consider structures like the muffler of the engine exhaust, where the acoustic waves propagate through periodically perforated barriers. Recently we proposed a homogenized model [6] of the acoustic transmission through the layer with embedded rigid obstacles of arbitrary shapes, which represent the perforation. The homogenized model describes relationship between jump of the acoustic pressures p+ and p− at the discontinuity interface Γ0 and the transverse acoustic velocity g0±, on introducing in–layer acoustic pressure p0 which describes wave propagation along the interface. The coupling between the transversely and the tangential acoustic velocities may become important for certain types of perforations. A sensitivity study was done which reveals remarkable dependence of wave transmission losses on the geometry of the perforation. Examples of 3D perforation geometries were treated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A two‐algebraic turbulence model for compressible flow in turbomachinery cascade
Authors: Dumitrache Alexandru , Dumitrescu Horia
Published: February 2009

The objective of this study is to examine the Baldwin–Lomax turbulence model in a finite volume solver to introduce a computer code for complex two–dimensional flows in turbomachinery. The turbulent model was tested with investigating the turbulent flow over a flat plate and other test cases. Three test cases are presented and the computed results are compared with experimental data. The calculated velocity profile agreed well with the experimental data in plate test case and the solver is validated in test case of flow over a semi NACA–0012 airfoil. The solver is used for flow through a multi–blade cascade of an axial compressor in design condition to show its capability of multi–block solution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of the Reynolds‐stress and dissipation‐rate decay and anisotropy from DNS of grid‐generated turbulence
Authors: Özyilmaz N. , Beronov K. N. , Delgado A.
Published: February 2009

Grid–generated turbulence is a classical but still controversial topic, one open issue being the spatial decay rate of turbulent energy. We study the influence of grid geometry on the Reynolds–stress and dissipation–rate tensors, including the range and exponent of their self–similar spatial decay. DNS using a validated lattice Boltzmann code at mean–flow Reynolds numbers up to 1400 are performed, comparing square grids with blockage ratios from 0.05 to 0.49. A clear picture of spatial distribution and self–similarity emerges for the statistics of interest: Axisymmetry is excellently confirmed. A consistent power law decay is found in the self–similar decay region beyond 10 grid stride lengths downstream. Its exponent of –5/3 can be obtained, for weak turbulence, from a spatial flux balance reminiscent of the constant transport through the inertial range of isotropic turbulence. In the near–grid region, on the other hand, differences in Reynolds stress components are pronounced while those between dissipation tensor components are only recognizable very close to the grid, where a strong dependence on grid porosity is found. A normalization with respect to porosity is proposed that collapses the data from all runs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Similarity Reductions of a Generalized Double Dispersion Equation
Authors: Bruzón M. S. , Gandarias M. L.
Published: February 2009

We apply the Lie–group formalism to deduce symmetries of a generalized double dispersion equation. We derive the ordinary differential equation to which the equation is reduced. We obtain exact solutions which can be expressed by various single and combine nondegenerative Jacobi elliptic function solutions and their degenerative solutions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lie algebra methods in turbulence
Authors: Grebenev V.N. , Oberlack M. , Grishkov A.N.
Published: February 2009

Approximate Lie symmetries of the Navier–Stokes equations are used for the applications to scaling phenomenon arising in turbulence. We show how the scaling groups obtained can be used to introduce the Reynolds number dependence into scaling laws explicitly for stationary parallel turbulent shear flows. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transparent boundary conditions as dissipative closures
Authors: Oliver Marcel , Bühler Oliver
Published: February 2009

We study the systematic development of subgrid closures via transparent boundary conditions in spectral space in one of the simplest possible settings: passive tracer transport in a doubly–periodic shear flow that has small support in the spectral domain. The resulting closure schemes have small dissipation rate errors and are only minimally over–dissipative for unsteady flows. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interaction of the Filter and Spatial Discretisation Operators for Large‐Eddy Simulation Using the Approximate Deconvolution Model
Authors: Tomm S. , von Terzi D. A. , Fröhlich J.
Published: February 2009

The Approximate Deconvolution Model (ADM) for Large–Eddy Simulation is an approach for the computation of turbulent flows. The main idea of ADM is to approximate the unfiltered data in the filtered Navier–Stokes equations by deconvolution of filtered values. This is achieved via repeated filtering. Thereby problems may arise for cases where the order of the spatial discretisation scheme is too low or lower than the order of the filter operation. The interaction of the discretisation and the filtering was investigated for one–dimensional forced Burgers turbulence. For this study, both the order of the filter operator and the order of the spatial discretisation of the derivatives were varied independently. It was found that the use of ADM with low–order discretisation schemes can not be recommended. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic study of turbulent Poiseuille flow with wall transpiration
Authors: Vigdorovich Igor , Oberlack Martin
Published: February 2009

An incompressible, pressure–driven, fully developed turbulent flow between two parallel walls, with an extra constant transverse velocity component, is considered. A closure condition is formulated, which relates the shear stress to the first and second derivatives of the longitudinal mean velocity. The closure condition is derived without invoking any special hypotheses on the nature of turbulent motion, only taking advantage of the fact that the flow depends on a finite number of governing parameters. By virtue of the closure condition, the momentum equation is reduced to the boundary–value problem for a second–order differential equation, which is solved by the method of matched asymptotic expansions at high values of the logarithm of the Reynolds number based on the friction velocity. A limiting transpiration velocity is obtained, such that the shear stress at the injection wall vanishes, while the maximum point on the velocity profile approaches the suction wall. In this case, a sublayer near the suction wall appears where the mean velocity is proportional to the square root of the distance from the wall. A friction law for Poiseuille flow with transpiration is found, which makes it possible to describe the relation between the wall shear stress, the Reynolds number, and the transpiration velocity by a function of one variable. A velocity defect law, which generalizes the classical law for the core region in a channel with impermeable walls to the case of transpiration, is also established. In similarity variables, the mean velocity profiles across the whole channel width outside viscous sublayers can be described by a one–parameter family of curves. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spreading of thin liquid droplets on rotating disks
Authors: Boettcher Konrad , Brandt Heiko , Ehrhard Peter
Published: February 2009

In many industrial processes solids are coated to obtain specific surface properties, as e.g. corrosion resistance, mechanical, optical, or electrical properties. Even today many of such coating processes are not fully understood and the choice of parameters is mainly based on experience. Hence, a prediction of the complete hydrodynamic process in its dependency on the parameters appears highly desirable. This would e.g. allow for a precise prediction of the (liquid) layer thickness and shape and help to optimize the quality of the coating. A common coating technique is the so–called spin coating. The coating agent is dissolved or suspended in a liquid, brought onto the solid, spread by rotation, and the carrier liquid is finally removed by evaporation or by chemical reactions. In this article an evolution equation is derived from lubrication theory, valid for thin liquid layers. The model involves a dynamic contact angle, centrifugal, capillary, gravitational, and molecular (London–van–der–Waals) forces. The evolution equation without molecular forces can even be solved analytically, provided the capillary number is small. Otherwise a numerical integration of the governing equations is engaged. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Steady and oscillatory analysis of porous catalysts in fluidized beds
Authors: Raja Sekhar G.P. , Prakash Jai , Kohr Mirela
Published: February 2009

In this paper, we consider the steady /oscillatory flow field within a porous particle contained in a fixed or fluidized bed, in which the spherical porous particle is placed in a spherical envelope of fluid. Stokes equations are employed inside the fluid envelope and Brinkman/Darcy equations are used inside the porous region. We compute drag force acting on the particle and hence the overall bed permeability of the bed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulations Of Three Dimensional Glottis Flows
Authors: Klostermann Jens , Schwarze Rüdiger , Triep Michael , Brücker Christoph
Published: February 2009

A detailed numerical investigation of the transient three dimensional flow downstream of the human glottis is performed. For the present work a threefoldly scaled up realistic static model of the vocal folds and a transient inflow function, which is obtained from experimental data is applied to the CFD model. In the numerical simulations transient flow features like forming ring vortexes and axis switching are resolved which are also known for elliptical and rectangular jets. Similar structures can also be identified in the results of the time–resolved PIV measurements. The influence of the ventricular folds and the geometrical variation of the glottis contacts are also considered in the numerical study. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of turbulent jet flows
Authors: Louda Petr , Příhoda Jaromír , Kozel Karel
Published: February 2009

The work deals with numerical modelling of several turbulent 3D jet flows: steady impinging jet, steady free jet in cross–flow, synthetic free jet (unsteady) and synthetic impinging jet (unsteady). The numerical method is based on artificial compressibility method with dual time extension for unsteady cases. Space discretization uses cell–centered finite volume method with third order accurate upwind approximation for convection, the time discretisations are implicit. Turbulence is modelled using two–equation eddy viscosity models and by explicit algebraic Reynolds stress model (EARSM by Wallin and Hellsten). The results of first three cases are compared with measurements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stokes‐Einstein Behaviour for Liquids with Bounded Potentials at High Densities
Authors: Mausbach P. , May H.‐O.
Published: February 2009

By means of molecular dynamics simulations we investigate the Stokes–Einstein behaviour of the Gaussian Core Model liquid at high densities. From a recent analysis at moderately high densities, we found that the Stokes–Einstein factor grows linearly with the viscosity. We show that at high densities the behaviour is similar, but there are slight departures at lower temperatures and higher densities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of flows in sinusoidally‐walled channels
Authors: Weingartner B. , Kuhlmann H.
Published: February 2009

Incompressible viscous flow in a channel with sinusoidally–walled boundaries is investigated numerically. The ultimate aim of the investigation is the computation of the linear stability with respect to two– and three–dimensional perturbations of the basic two–dimensional flow. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of fluid flow and heat transfer in coolant ducts of friction clutches
Authors: Wünsch Olaf , Mölter Stefan
Published: February 2009

This paper deals with the numerical simulation of the fluid flow in coolant ducts as wall as the calculation of temperature field in fluid and solid of a friction clutch. The simulations are carried out by means of commercial software based on a finite volume method in a relative framework, where the fluid flow is not time dependent. The results in dependence of rotation speed and slip velocity show interesting secondary flow in the ducts. Different flow pattern have distinct influence on the temperature field and the heat transfer. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Design of axisymmetric ducts for incompressible flow with vorticity.
Authors: Pavlika V.
Published: February 2009

In this paper a numerical algorithm is described for solving the boundary value problem associated with axisymmetric, inviscid, incompressible, rotational (and irrotational) flow in order to obtain duct wall shapes from prescribed wall velocity distributions. The governing equations are formulated in terms of the stream function and the function as independent variables where for irrotational flow can be recognized as the velocity potential function, for rotational flow ceases being the velocity potential function but does remain orthogonal to the stream lines. A numerical method based on finite differences on a uniform mesh is employed. The technique described is capable of tackling the so–called inverse problem where the velocity wall distributions are prescribed from which the duct wall shape is calculated, as well as the direct problem where the velocity distribution on the duct walls are calculated from prescribed duct wall shapes. The two different cases as outlined in this paper are in fact boundary value problems with Neumann and Dirichlet boundary conditions respectively. Even though both approaches are discussed, only numerical results for the case of the Dirichlet boundary conditions are given. A downstream condition is prescribed such that cylindrical flow, that is flow which is independent of the axial coordinate, exists. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermofluiddynamics in liquid media during biotechnological processes under high pressure
Authors: Rauh C. , Delgado A.
Published: February 2009

In bio/ chemical engineering high pressure (HP) processing up to several GPa represents a novel technique to selectively influence (bio–)chemical reactions resulting from temperature and pressure sensitivities differing between the occuring reactions. Therefore, thermofluiddynamical effects leading to inhomogeneous process conditions (pressure, temperature) show an important influence on the process results. To predict and improve mass, momentum and energy transport within the HP vessel and the impact on desired chemical reactions spatiotemporal numerical simulations are a useful tool in process analysis and design. The present contribution deals with mathematical modelling of the enzyme inactivation in HP processing of liquid biotechnological media. For the first time a transport equation for the scalar quantity “enzyme activity” is deduced. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flare gas extraction by a Laval nozzle
Authors: Steinrück Herbert , Kornfeld Matthias , Braun Stefan
Published: February 2009

It is proposed to use a double Laval nozzle as ejector pump to extract flare gas from compressor packings. The efficiency and stability of possible operating points will be discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transmission of sound in a wedge‐shaped layer of fluid with a rigid bottom
Authors: Borejko Piotr
Published: February 2009

The theory of generalized rays is applied to the problem of determining the exact shape of the pressure pulse received at very large ranges, in the case of a sound source in a 3° perfect wedge of fluid. The time variation of the pressure at the point source is assumed to be given by a Heaviside unit function H(t). It is found that horizontal refraction and backscattering have a pronounced effect on the overall appearance of the received pulse: at very large down–slope (normal to the apex line) ranges, the shape of the received pulse does not change much, while, at very large cross–slope (parallel to the apex line) ranges, it changes drastically. Thus, in a 3° perfect wedge of fluid, long–range down–slope propagation (exclusively affected by backscattering) seems to be nondispersive, but long–range cross–slope propagation (affected by horizontal refraction and backscattering) seems to be highly dispersive. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation and dissipation of ocean surface waves
Authors: Ellermann Katrin
Published: February 2009

Ocean surface waves constitute one of the most important sources of external forces that act on ships and offshore structures. Most ocean waves are generated by wind, but various other effects such as currents, ground and coastal topology, breaking and wave–wave interaction have an influence on the growth and dissipation of wave energy at specific frequency ranges. These water waves are inherently random in nature and their exact shape is difficult to describe, even when confining the described area to a small range. While many different approaches exist to describe the spectral characteristics of ocean waves, some of the processes which affect the generation of waves are still poorly understood. This paper addresses some techniques which serve to describe seaway spectra with respect to the subsequent analysis of dynamic mechanical systems in the ocean such as ships, platforms and pipelines. Advantages and limits of the different approaches are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dissipation‐induced subcritical flutter in the acoustics of friction
Authors: Kirillov1 Oleg N.
Published: February 2009

We consider a gyroscopic system under the action of small dissipative and non–conservative positional forces, which has its origin in the models of rotating elastic bodies of revolution in frictional contact such as the singing wine glass or the squealing disc/drum brakes. The spectrum of the unperturbed gyroscopic system forms a spectral mesh in the plane ‘frequency versus gyroscopic parameter’ with double semi–simple purely imaginary eigenvalues at the nodes. In the subcritical range of the gyroscopic parameter the eigenvalues involved into the crossings have the same Krein signature and thus their splitting due to changes in the stiffness matrix, which break the rotational symmetry of the body, cannot produce complex eigenvalues and, therefore, flutter. We establish that perturbation of the gyroscopic system by the dissipative forces with the indefinite matrix can lead to the subcritical flutter instability even if the rotational symmetry is destroyed. With the use of the perturbation theory of multiple eigenvalues we explicitly find the linear approximation to the domain of the subcritical flutter, which turns out to have a conical shape. The orientation of the cone in the three dimensional space of the parameters, corresponding to gyroscopic, damping, and potential forces, is determined by the sign of an explicit expression involving the entries of both the damping and potential matrices. With the use of a time–dependent coordinate transformation we demonstrate that the conical zones of flutter for the original autonomous system coincide with the zones of the subcritical parametric resonance of the rotationally symmetric flexible body with the load moving in the circumferential direction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient Simulation of Elastic Waves Propagation in Anisotropic Media
Authors: Lisitsa Vadim , Lys Egor
Published: February 2009

The paper deals with finite–difference (f‐d) approach to simulation of elastic waves' propagation in anisotropic elastic media with general symmetry. Any implementation of this approach claims resolution of two key problems:

construction of an effective f‐d scheme itself; we propose to use the Lebedev's scheme (LS) being a natural generalization of Virieux staggered grid scheme (VS) widely used for isotropy; we prove that LS possesses better dispersion properties in comparison with well known Rotated Staggered Grids Scheme (RSGS).

stable domain distension. The Perfectly Matched Layers(PML) useful for isotropic problems can be unstable in the case of anisotropy. Lebedev scheme allows one to use Optimal Grids (OG) which gives a possibility to implement efficient and low cost domain distension.

(© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Localization of acoustic sources in subsonic jets
Authors: Obrist Dominik , Kleiser Leonhard
Published: February 2009

The sound in the acoustic far–field of a round jet is generated by a multitude of unsteady flow structures with different length and time scales. Most likely, different components of the noise spectrum are created by different structures in the jet which emit sound in different directions. Based on Lighthill's acoustic analogy, we present a method for relating flow structures of the jet with far–field noise spectra and their associated directivity patterns. The method allows to determine what kind of noise (with respect to frequency and emission direction) is generated at a given streamwise location. We illustrate the method with numerical results for a round isothermal jet. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Coupled FE‐BE Analysis of Smart Lightweight Structures for Active Noise and Vibration Control
Authors: Ringwelski Stefan , Gabbert Ulrich
Published: February 2009

Over the past years much research and development has been done in the area of active control in order to improve the acoustical and vibrational properties of thin–walled lightweight structures. An efficient technique for actively reducing the structural vibration and sound radiation is the application of smart structures. In smart structures piezoelectric materials are often used as actuators and sensors. The design of smart structures requires fast and reliable simulation tools. Therefore, the purpose of this paper is to present a coupled finite element–boundary element formulation, which enables the modeling of piezoelectric smart lightweight structures.

The paper describes the theoretical background of the coupled approach in which the finite element method (FEM) is applied for the modeling of the passive vibrating shell structure as well as the surface attached piezoelectric actuators and sensors. The boundary element method (BEM) is used to characterize the corresponding sound field. In order to derive a coupled FE–BE formulation additional coupling conditions are introduced at the fluid–structure interface. Since the resulting overall model contains a large number of degrees of freedom, the mode superposition method is employed to reduce the size of the FE submodel. To validate the accuracy of the proposed approach, numerical simulations are carried out in the frequency domain and the results are compared with analytical reference solutions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shape optimization for the Helmholtz equation
Authors: Seifrt František , Leugering Günter , Rohan Eduard
Published: February 2009

The aim of our work is to develop optimal dielectric composite structures with specific qualities. The task is to design interfaces of given material components such that the originated structure attains certain optical properties. Propagation of the electromagnetic waves in the composite is described by the Helmholtz equation. Success of the structure is enumerated by the objective function which is to be minimized. Interfaces of the given materials are parametrized by the cubic B–spline curves. The design variables are afterwards the positions of B–spline control points. For objective function evaluation one forward computation of the Helmholtz equation is needed. To get the sensitivity of the objective function we solve the backward (adjoint) equation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of micromachining of C45 steel by single abrasive grain
Authors: Chodor Jaroslaw , Kukielka Leon
Published: February 2009

Grinding is a very complicated processing. To increase quality of product and minimize the cost of abrasive machining, we should know physical phenomena which exist during the process. The first step to solution of this problem is analysis of machining process with a single abrasive grain. In the paper [1] the thermo–mechanical models of this process are presented, but in this work attention is concentrated on chip formation and his separation from object for different velocity of abrasive grain. The phenomena on a typical step time were described using step–by–step incremental procedure, with updated Lagrangian formulation. Then, the finite elements methods (FEM) and dynamic explicit method (DEM) were used to obtain the solution. Application was developed in the ANSYS system, which makes possible a complex time analysis of the physical phenomena – states of: displacements, strains and stress. Numerical computations of the strain have been conducted with the use of two methodologies. The first one requires an introduction of boundary conditions for displacements in the contact area determined in modeling investigation, while the second – a proper definition of the contact zone, without the necessity to introduce boundary conditions in the contact area. Examples of calculations for the intensity of stress in the surface layer zones were presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homotopic Arnold tongues deformation of the MHD α2‐dynamo
Authors: Günther Uwe , Kirillov Oleg N.
Published: February 2009

We consider a mean–field α2–dynamo with helical turbulence parameter α(r)=α0+γΔα(r) and a boundary homotopy with parameter β∈[0,1] interpolating between Dirichlet (idealized, β=0) and Robin (physically realistic, β=1) boundary conditions. It is shown that the zones of oscillatory solutions at β=1 end up at the diabolical points for β=0 under the homotopic deformation. The underlying network of the diabolical points for β=0 substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for β=1. Using perturbation theory we derive the first–order approximations to the resonance (Arnold's) tongues in the α0βγ‐space, which turn out to be cones in the vicinity of the diabolical points, selected by the Fourier coefficients of Δα(r). The space orientation of the 3D tongues is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α‐profiles leading to oscillatory dynamos, and it explicitly predicts the locations of the spectral exceptional points, which are important ingredients in the recent theories of polarity reversals of the geomagnetic field. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hyperelliptic functions and geodesic equations
Authors: Hackmann Eva , Lämmerzahl Claus
Published: February 2009

A method for solving geodesic equations in Schwarzschild–de Sitter space–times and higher dimensional Schwarzschild space–times is presented. The solutions are derived from Jacobi's inversion problem on a Riemann surface of genus 2 restricted to the set of zeros of the theta function, which is called a theta–divisor. In its final form, the solutions are given in terms of derivatives of Kleinian sigma functions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spectrum asymptotics for the linearized thin film equation
Authors: Kitavtsev G. , Recke L. , Wagner B.
Published: February 2009

In this paper we describe linear stability properties for the special type of thin film equation corresponding to a presence both destabilizing van der Waals and stabilizing Born forces in the intermolecular interactions. The final stage of the evolution described by such type equation is characterized by the slow–time coarsening dynamics after formation of an array of droplets. Finally the dynamics converges to one stationary droplet. We derive analytically the asymptotics for the spectrum of the thin film equation linearized at one droplet steady state with respect to small parameter ϵ (describing the form of droplet) tending to zero. This asymptotics is confirmed by numerical investigations as well. The analytical approach can be applied also for the investigation for the spectrum of the thin film equation linearized at an array of droplets. Our results considerably extend the ones derived in [4]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Numerical Analysis of the External Round Thread Rolling
Authors: Kukielka Krzysztof , Kukielka Leon
Published: February 2009

The papers [1] describe modeling of the contact problem in the external thread rolling process. This paper shown an application of obtained model for the thread with round outline. The mathematical model of process, were presented. The variational and finite element method, were used. The algorithm of numerical analysis in ANSYS system, were elaborated. Numerical computions of displacements, strains and stresses have been conducted without the necessity to introduce boundary condition in the contact zone – a proper definition of the contact zone by single surface auto 2D. Exemplary results of numerical analysis for various condition of the process realization in the discretized model has been presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution multiplicity of circular plate
Authors: Marko Lubomir
Published: February 2009

We deal with the number of solutions for the system of von Kármán equations for a thin elastic circular plate of constant thickness. The plate is subjected to a uniform compressive thrust along its edge in the midplane of the plate. The thrust is proportional to a real parameter λ. We assume rotationally symmetric case. Let λ1<λ3<…λn… be the critical values of the real parameter. For λ∈[λn,λn+1] the multiplicity of solutions in dependence of parameter λ is analyzed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Existence and uniqueness results for a class of nonlinear differential systems with second‐order differences
Authors: Luca‐Tudorache Rodica
Published: February 2009

In a real Hilbert space we investigate the existence, uniqueness and asymptotic properties of the strong and weak solutions to an infinite nonlinear differential system with second–order differences, subject to an extreme condition and initial data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crystallization problem with symmetries of composite lattices in statistical crystal theory as bifurcational symmetry breaking problem
Authors: Makeev Oleg , Loginov Boris
Published: February 2009

Bifurcation theory methods under group symmetry conditions are applied to crystallization problem with composite lattices in statistical crystal theory. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of shot peening on surfaces in Ansys application
Authors: Szyc Marcin , Kukielka Leon
Published: February 2009

ABSTRACT: Paper presents the posibility to application of Finite Element Method (FEM) to analysis of strain and stress states in surface layer of object. The application in Ansys/Ls – Dyna programme using incremental procedure in updated Lagrangian formulation was developed. Examples of calculations of influence of different distance of leaving traces for the strain and stress field in the surface layer zone were presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dependence of accuracy of ESPRIT estimates on signal eigenvalues: the case of a noisy sum of two real exponentials
Authors: Alexandrov Theodore , Golyandina Nina , Timofeyev Alexey
Published: February 2009

This paper is devoted to estimation of parameters for a noisy sum of two real exponential functions. Singular Spectrum Analysis is used to extract the signal subspace and then the ESPRIT method exploiting signal subspace features is applied to obtain estimates of the desired exponential rates. Dependence of estimation quality on signal eigenvalues is investigated. The special design to test this relation is elaborated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Component‐Based Software Realisations of Monte Carlo and Stochastic Galerkin Methods
Authors: Krosche Martin , Matthies Hermann G.
Published: February 2009

In this paper we present a component–based software realisation of the Monte Carlo and Stochastic Galerkin methods for simulating stochastic models with uncertain parameters described by random fields. The system supports parallel and distributed computations and focuses on the reusability and extensibility of the provided components and frameworks. Third–party software is interfaced to avoid cost–intensive reimplementations. The mentioned schemes are compared with respect to their convergence by considering a stationary groundwater flow model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Evaluation of Functionals based on Variance Minimisation
Authors: Pajonk Oliver , Niekamp Rainer , Matthies Hermann G.
Published: February 2009

Numerically evaluating the effect of a functional on a function is a very common task in scientific computing. The definite integral of a function over a domain is an example, differentiating a function in a certain point into a certain direction is another one.

We developed a generic method to compute the effect of a functional using a linear approximation formula. The method is designed to generate the nodes and weights needed to approximate different functionals using a single set of tools: it regards the target function as a stochastic field and uses a user–defined covariance function for this field to minimise the error made by the approximation formula.

The resulting formulas are optimal in an average case sense: all possible realisations of this stochastic field are taken into account while computing the solution. This results in nodes and weights that evaluate the target functional applied to any realisation with a minimised average error. The space of all realisations of such a stochastic field can be of infinite dimension whereas classical approaches often only consider a finite dimensional space of functions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topology Optimization of 3D Elastic Structures Using Boundary Elements
Authors: Bertsch Christine , Cisilino Adrián P. , Langer Sabine , Reese Stefanie
Published: February 2009

A numerical approach for the topological optimization of 3D linear elastic problems using boundary elements and the topological derivative is presented in this work. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From Inviscid to Viscous Aerodynamical Global Optimal Shape's Design
Authors: Nastase1 A.
Published: February 2009

The refinement of the global aerodynamical optimal design (OD) of the shape of a flying configuration (FC) can be performed by improving of the start solutions for the optimization and/or of the optimization strategy itself. The proposed strategy is the own developed iterative optimum–optimorum theory. The study is here focused on the further improvement of her new, original, reinforced, zonal, spectral solutions for the partial–differential equations (PDEs) of the three–dimensional compressible Navier–Stokes layer (NSL), which govern the flow over the FCs, in subsonic and supersonic flow. These NSL's solutions, which are good suited for the computation and, especially, for the global optimal design, use the analytical potential solutions of the flow over the same FC twice: firstly as outer flow, at the NSL's edge (instead of the parallel flow used by Prandtl in his boundary layer theory) and, secondly, the velocity's components are products between the corresponding potential velocities and polynomial expansions with arbitrary coefficients, which are used to satisfy the NSL's PDEs. The use of analytical elliptical potential solutions leads to subsonic and the use of hyperbolical potential solutions leads to supersonic stabilized and rapid convergent NSL's solutions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization under consideration of uncertain input quantities
Authors: Pannier Stephan , Sickert Jan‐Uwe , Graf Wolfgang
Published: February 2009

This contribution presents an approach to account for imprecise data within an optimization task in view of engineering applications. In order to specify imprecise data the concept of imprecise probabilities is utilized, applying the generalized uncertainty model fuzzy randomness. Considering the fact, that the uncertainty affects both the objective function and the constraints, the optimum and the respective design is obtained imprecise. In view of decision making for engineering applications the optimization is converted to account for information reducing methods, e.g. determination of failure probabilities, defuzzification and robustness assessment. The introduced methods and algorithms are focused on a numerical treatment to solve nonlinear industry–sized problems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of various design parameters on the quality of optimal shape design in topology optimization analysis
Authors: Kutylowski Ryszard , Rasiak Bartosz
Published: February 2009

The paper presents the discrete structural topology optimization problem. The analysis was made for the formulation of optimal design with a compliance minimization (as the objective functional) of statically loaded continuum structures with constraints forced on mass of the structure. Two different algorithms were compared (one taken from the literature and the second originally prepared) in order to study influence of design parameters formulation on the calculations results. Optimal topologies were presented and discussed for several 2D examples, with various optimization process parameters in order to get the best results in the shortest possible time. Other goal of presented research is to find out the possibilities of applying proposed algorithm in the designing process of bridge girders. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Time Schedule Optimization of Satellites
Authors: Tietjen Jan , Büskens Christof , Knauer Matthias
Published: February 2009

For an effective monitoring of environmental activities by a satellite, the main goal is to achieve maximum coverage throughout a short period of time. Due to technical restrictions of the satellite hardware, it is only possible to use the camera for a limited time period per orbit, while rotating around the Earth. The main goal is to determine the time intervals for which the coverage with respect to given target areas is maximized and the restrictions such as contact to ground stations are satisfied. To obtain a continuous objective function for the sequential quadratic programming method, the coverage is modelled by polygons integrated on a sphere. For acceptable computing times, special investigations had to be made in order to achieve fast gradient computations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Padé Approximations of and preservation of quadratic Lyapunov functions
Authors: Solmaz Selim , Corless Martin , Shorten Robert
Published: February 2009

We investigate whether or not quadratic Lyapunov functions are preserved under Padé approximations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploiting Mixed Precision for Computing Eigenvalues of Symmetric Matrices and Singular Values
Authors: Drygalla Volker
Published: February 2009

The use of higher precision preconditioning for the symmetric eigenvalue problem and the singular value problem of general non–structured non–graded matrices are discussed. The matrix Q from the QR–decomposition as a preconditioner, applied to A with higher precision, in combination with Jacobi's method seems to allow the computation of all eigenvalues of symmetric positive definite matrices rsp. all singular values of general matrices to nearly full accuracy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Algebraic multigrid preconditioning for iterative eigensolvers
Authors: Krüger Marcel
Published: February 2009

The objective is a comparative study of iterative solvers for eigenproblems arising from elliptic and self–adjoint partial differential operators. Typically only a few of the smallest eigenvalues of these problems are to be computed. We discuss various gradient based preconditioned eigensolvers which make use of algebraic multigrid preconditioning. We present some algorithms together with numerical results. Performance characteristics are derived by comparison with the solutions of standard problems. We show that known advantages of algebraic multigrid preconditioning (e.g. for boundary–value problems with large jumps in the coefficients) transfer to AMG–preconditioned eigensolvers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetric Permutations for I‐Matrices to Avoid Small Pivots During Incomplete Factorization
Authors: Mayer Jan
Published: February 2009

Incomplete LU–factorizations have been very successful as preconditioners for solving sparse linear systems iteratively. However, for unsymmetric, indefinite systems small pivots (or even zero pivots) are often very detrimental to the quality of the preconditioner. A fairly recent strategy to deal with this problem has been to permute the rows of the matrix and to scale rows and columns to produce an I–matrix, a matrix having elements of modulus one on the diagonal and elements of at most modulus one elsewhere. These matrices are generally more suited for incomplete LU–factorization. I–matrices are preserved by symmetric permutation, i.e. by applying the same permutation to rows and columns of a matrix. We discuss different approaches for constructing such permutations which aim at improving the sparsity and diagonal dominance of an initial block. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On a stopping rule for iterative orthogonalization of symmetric matrices
Authors: Popa Constantin
Published: February 2009

In this paper we consider three versions of Kovarik's iterative orthogonalization algorithms, for approximating the minimal norm solution of symmetric least squares problems. Although the convergence of these algorithms is linear, in practical applications we observed that a too big number of iterations can dramatically deteriorate the already obtained approximation. In this respect we analyse the above mentioned Kovarik–like methods according to the modifications they make on the “machine zero” eigenvalues of the problem (symmetric) matrix. We establish a theoretical almost optimal formula for the number of iterations necessary to obtain an enough accurate approximation, as well as to avoid the above mentioned troubles. Experiments on collocation discretization of a Fredholm first kind integral equation ilustrate the efficiency of our considerations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Support size restrictions on time‐frequency representations of functions on finite abelian groups
Authors: Krahmer Felix , Pfander Götz , Rashkov Peter
Published: February 2009

We obtain uncertainty principles for finite abelian groups that relate the cardinality of the support of a function to the cardinality of the support of its short–time Fourier transform. These uncertainty principles are based on well–established uncertainty principles for the Fourier transform. In terms of applications, the uncertainty principle for the short–time Fourier transform implies the existence of a class of equal norm tight Gabor frames that are maximally robust to erasures. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on numerical simulation methods of the railway vehicle‐track dynamic interaction
Authors: Yoshimura Akiyoshi , Miwa Masahiro , Kawasaki Yoshiyuki
Published: February 2009

A very efficient numerical simulation method of the railway vehicle–track dynamic interaction is described. When a vehicle runs at high speed on the railway track, contact forces between a wheel and a rail vary dynamically due to the profile irregularities existing on the surface of the rail. A large variation of contact forces causes undesired deteriorations of a track and its substructures. Therefore these dynamic contact forces are of main concern of the railway engineers. However it is very difficult to measure such dynamic contact forces directly. So it is important to develop an appropriate numerical simulation model and identify structural factors having a large influence on the variation of contact forces.

When a contact force is expressed by the linearized Hertzian contact spring model, the equation of motions of the system is expressed as a second–order linear time–variant differential equation which has a time–dependent stiffness coefficient. Applying a well–known Newmark direct integration method, a numerical simulation is reduced to solving iteratively a time–variant, large–scale sparse, symmetric positive–definite linear system.

In this study, by defining a special vector named a contact point one, it is shown that this time–variant stiffness coefficient can be expressed simply as a product of the contact point vector and its transpose and so the Sherman–Morrison–Woodbury formula applied for updating the inverse of the coefficient matrix. As a result, the execution of numerical simulation can be carried out very efficiently. A comparison of the computational time is given. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quasi‐Minimal Residual Eigenpairs
Authors: Zemke Jens‐Peter M.
Published: February 2009

We consider the extraction of approximate eigenpairs from a given Krylov subspace that are optimal, or at least quasi–optimal with respect to the normwise backward error. An algorithm based on Newton–Grassmannian optimization and a simple example are given; a useful graphical method of comparison with other extraction methods is briefly sketched. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)