bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure inducted stress concentrations in CVI‐CFC materials
Authors: Piat Romana , Schnack Eckart
Published: December 2005

Carbon/carbon materials produced by chemical vapour infiltration consist of carbon fibers embedded in an anisotropic matrix of pyrocarbon. In this study we propose: 1) an approach for hierarchical homogenization of material parameters; 2) an approach for prediction of the stress concentrations in this material. The model estimates material properties on two scales: nano and micro scale. The microstructural morphology of CFC‐material on the nano scale can be represented as distribution of mono crystals of pyrographite. For modeling the response at this scale we utilize the Eshelbi's theory for continuously distributed inclusions. The orientations distribution functions of inclusions (mono crystals) are used for calculation of the homogenized elasticity tensor of pyrographite. The numerical calculations of the stress fields in the samples characterized by different types of pyrocarbon coatings provides us the information about the (failure) regions with maximal (critical) values of stress. The obtained results demonstrate a good coincidence with experimentally identified failure regions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage Detection by Wave Propagation Observation with Laser SpeckleInterferometry
Authors: Schmidt Alexander , Lammering Rolf , Plenge Michael
Published: December 2005

For quality insurance and fault detection, one and three dimensional ESPI (Electronic Speckle Pattern Interferometry) technique is applied to various structures. These experiments are an extension of previous experiments with Holographic Interferometry [4], a related measurement technique. ESPI is a non contact, high resolution Laser measurement technique. It facilitates transient full field vibration measurements that deliver absolute deflections, either one dimensional out‐of‐plane or three dimensional in and out‐of‐plane.

Experiments have been performed with a full scale concrete embedded track segment. Different known artificial defects represent various flaws and voids due to the fabrication process and operation. Wave propagation due to impact is observed and allows for damage detection. ESPI measurements are in good accordance with expectations. An in‐situ measurement setup for quality management of concrete embedded railway tracks has been built. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Re‐entrant corner problems for isotropic materials and layered composites
Authors: Schnack E. , Dimitrov A. , Langhoff T.‐A. , Tsotsova R.
Published: December 2005

Modern materials like composites in different types require new methods in computational fracture mechanics. Besides of classical fracture mechanics we have to solve the asymptotic solution around crack tips. This can be done on the basis of the Kondratievs theorem with the Pietrov‐Galerkin method to solve the unknown eigenvalues for those problems. Additionally, we have to de.ne instead classical modes I, II and III, mode I* up to mode IV* to interpret the computational results for the unknown eigenvalues. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Well Posedness in Continuum Interface Problems
Authors: Utzinger Johannes , Menzel Andreas , Kuhl Ellen , Steinmann Paul
Published: December 2005

By considering continuum interface problems like e.g. the modeling of composites, the possible loss of well posedness of the resulting Boundary Value Problem has to be considered, dependent on the choice of material laws in the bulk and in the interface. In this contribution, the problem is discussed for a bulk material connected to a rigid substrate by an interface layer. The isotropic bulk material is linear elastic while for the interface elasticity and elasticity with damage is investigated. A complex surface acoustic tensor is introduced by applying a decaying surface wave ansatz to the incremental boundary value problem. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of a biphasic and a multicomponent model describing viscoelastic swelling phenomena
Authors: Acartürk A. , Ehlers W. , Karajan N. , Markert B.
Published: December 2005

Biological soft tissues like articular cartilage and their artificial replacement hydrogel have a multicomponent microstructure, consisting of a charged viscoelastic solid matrix saturated by a fluid, which is composed of the liquid solvent and the dissolved anions and cations. Such charged multiphasic materials exhibit a swelling behaviour under varying chemical conditions.

These materials are best described by a macroscopic approach like the Theory of Porous Media (TPM). Starting from this point, a standard two‐phase model is extended by dividing the fluid into the above mentioned components. Therein, the chemical relations describing the behaviour of the ions and their interaction with the other mixture constituents are incorporated. The resulting model covers mechanical as well as osmotic and electrostatic effects. For numerical and simplicity reasons, it is possible to describe the swelling phenomena by a simplified biphasic model, where the ions as a third degree of freedom and their time‐dependent diffusion are neglected. Furthermore, the viscoelastic solid matrix can be replaced by an elastic material.

Note that using the multicomponent model generally results in numerical problems, since the boundary conditions depend on the internal fixed charge density. It is shown that this problem can be solved by including the boundary conditions into the weak formulation. Finally, to compare the different behaviour of the above mentioned models by means of an swelling example, they are implemented into the FE tool PANDAS using stable Taylor‐Hood elements for the spatial discretization. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaption des Morph‐Stoffgesetzes an die Abaqus‐Benutzerschnittstelle
Authors: Besdo D. , Ihlemann J.
Published: December 2005

Das Morph‐Stoffgesetz dient der Nachbildung des mechanischen Verhaltens inelastischer Gummiwerkstoffe unter großen Verformungen und enthält neben Spannungs‐ und Verzerrungstensoren auch deren Zeitableitungen. Für die Implementierung in das Fem‐Programmpaket Abaqus müssen Eulersche Varianten der aktuellen Spannungen und der Materialsteifigkeit bereitgestellt werden.Während sich die Verformungsgröße, nach der die Spannungen abzuleiten sind, als pfadabhängig erweist, entspricht deren Zaremba‐Jaumann‐Zeitableitung dem Tensor der Formänderungsgeschwindigkeiten. Für die Zeitintegration der Eulerschen Zeitableitungen im Stoffgesetz ist ein diesbezüglich geeignetes Beobachtersystem zu identifizieren. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Geometrically exact shells for multibody dynamics
Authors: Betsch Peter
Published: December 2005

In the present work we extend the unified framework for the computational treatment of rigid bodies and nonlinear beams developed by Betsch & Steinmann [1] to the realm of nonlinear shells. In particular, a specific constrained formulation of shells is proposed which leads to the semi‐discrete equations of motion characterized by a set of differential‐algebraic equations (DAEs). The DAEs provide a uniform description for rigid bodies, semi‐discrete beams and shells and, consequently, flexible multibody systems. The DAEs are further discretized by means of an energy‐consistent mechanical integrator. The use of rotational parameters is completely circumvented throughout the whole discretization process. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite element formulation based on the theory of a Cosserat point
Authors: Boerner Eiris F. I. , Wriggers Peter , Rubin Miles B.
Published: December 2005

The theory of Cosserat points is the basis of a 3D finite element formulation allowing for large deformations in structural mechanics, that recently was presented by [1]. First attempts have revealed, that this formulation is free of showing undesired locking or hourglassing‐phenomena. It additionally shows excellent behaviour for any type of incompressible material, for large deformations and sensitive structures such as plates or shells. Within the theory of Cosserat points, the position vectors X and x, are described through director vectorsDi and di by use of trilinear shape functions Ni for an 8‐node brick element.

The special choice of shape functions Ni allows for director vectors with which the deformation can be split into a homogeneous and an inhomogeneous part. This split enables the use of stiffnesses that correspond to different deformation modes. Analytical solutions to the inhomogeneous deformation modes are incorporated in the formulation and avoid the undesired phenomena. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Space‐time DG Method for Porous Media
Authors: Chen Zhiyun , Steeb Holger , Diebels Stefan
Published: December 2005

In this work we present a new coupled space‐time discontinuous Galerkin method for the dynamical analysis of fully‐saturated porous media. The method consists of a finite element discretization in space and time simultaneously. The numerical solution is solved on every time‐slab (Qn = Ω × ℐn), which is in analogy to classical finite difference methods in time. The method is stable and efficient. The computational accuracy can be easily raised by increasing the order of the ansatz functions. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of the Application of NiTi Alloys in Medical Technologies
Authors: Christ Daniel , Reese Stefanie
Published: December 2005

Shape memory alloys are nowadays already established as a material which is able to solve exceptional tasks in practical applications. Particularly, its utilization in the field of medical technologies increases steadily. For example micro tools (staple, catheters) and implants (coronary stents) are made out of Nickel‐Titanium well known as a basic shape memory alloy. Apart from the advantages like the avoidance of auxiliary components and joints in the system and to utilize the high volume specific work of shape memory alloys, NiTi alloys exhibit a good biocompatibility. This property is necessary with regard to either permanent or temporary implants. To optimize the use of NiTi alloys in the scope of medical technologies, the support of the development of applicable tools by numerical simulations is highly recommended. However the complex material behaviour containing a profoundly thermomechanical coupling poses indeed a big challenge to the material modeling and its implementation into a finite element code. Particularly, the material model proposed by Helm [1] proves to be a firm model containing the most common properties of shape memory alloys, as the pseudoelasticity, the shape memory effect and the two‐way effect. In the present contribution the FE modelling of a medical staple used in foot surgery is presented by considering the model of Helm which was investigated by the authors to improve its performance in the finite element method [2]. The foot staple, produced by a group of members of the SFB 459 which is funded by the DFG, avails the shape memory effect to excite the desired clamping effect [3]. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Analysis of a Cyclical Loaded Construction under Corrosion Degradation
Authors: Dudda W. , Badur J.
Published: December 2005

A contribution for analytical and numerical tools that permits of a deterministic evaluation of structure behavior in external conditions, under multiparameter and/or cyclic mechanical, thermal and chemical loads, is the aim of this paper. Particular structure elements undergo the plastic and corrosion degradation and they dissipate energy, which consists of irreversible contributions, like a work on the inelastic strains. The construction and its unit lifetime are estimated according to a dissipated energy criterion. The paper emphasizes the modeling and numerical implementation of degradation effects, such as cyclic plasticity, generated by mechanical and thermal loads, stress corrosion, electrochemical corrosion and low‐cyclic corrosion. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Delaminationsberechnung von Faserverbundstrukturen
Authors: Fiolka M. , Matzenmiller A.
Published: December 2005

Das Ablösen der Einzelschichten unidirektional verstärkter Faserverbundlaminate voneinander ‐ die Delamination ‐ ist eine der gefährlichsten Versagensarten, da sie zum globalen Kollaps der Struktur führen kann. Statische, interlaminare Bruchtests, die zur Ermittlung der Bruchzähigkeit und des Rissfortschrittes dienen, werden mit der Methode der finiten Elemente simuliert. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of multiphasic flow phenomena in deformable porous materials under consideration of thermal effects
Authors: Graf T. , Ehlers W.
Published: December 2005

The consideration of thermal effects in the description of multiphasic flow processes and their interaction with a deformable solid skeleton plays a significant role in a big field of engineering applications, as for example in the modelling of carbon dioxide storage in the subsurface or the remediation of contaminated partially saturated soil by in‐situ‐methods. In this contribution, a continuum mechanical approach based on a multiphasic formulation embedded in the well‐founded framework of the Theory of Porous Media (TPM) is presented to describe the non‐isothermal material behaviour of partially saturated soil. The single constituents are an elasto‐viscoplastic solid skeleton, a materially incompressible pore‐liquid and a materially compressible pore‐gas. The resulting system of strongly coupled differential‐algebraic equations is solved by the FE tool PANDAS that has been designed for the computation of strongly coupled solid‐.uid problems. As a numerical example, the injection process of heated gas in a partially saturated soil is discussed, whereby the capability of the presented model to describe the behaviour of unsaturated soil under non‐isothermal conditions is pointed out. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Galerkin methods in time for semi‐discrete viscoelastodynamics
Authors: Groß Michael , Betsch Peter
Published: December 2005

In semi‐discrete nonlinear elastodynamics, higher order energy and momentum conserving time stepping schemes turned out to be well suited for computing long time motions [1]. In comparison to standard ODE integrators, conserving schemes exhibit superior stability properties which are of utmost importance in a nonlinear .nite element framework. We show that conserving schemes are particularly well suited as starting point for the development of energy consistent schemes for dissipative dynamical systems. In particular, viscoelastic material behaviour is considered. A key advantage of energy consistent schemes lies in the fact that the equilibrium state of viscoelastic systems can be de.nitely reached, independent of the material parameters. In the paper, we compare two Galerkin methods for the temporal discretisation of semi‐discrete nonlinear viscoelastodynamics: the standard continuous Galerkin (cG) method and an enhanced continuous Galerkin (eG) method which ful.ls the total energy balance exactly. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient dynamic investigation of nonlinear 3D soil–structure interaction problems using an iterative coupling approach
Authors: Hagen Christian , von Estorff Otto
Published: December 2005

A domain decomposition approach for the transient analysis of arbitrary three‐dimensional soil–structure interaction problems is presented. The coupling of the subdomains is performed in an iterative manner. For this purpose, a sequential as well as a parallel interface relaxation algorithm have been developed, where the coupling iterations are performed very effectively together with the iterations which are required to solve the nonlinear FEM system of equations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulating the Microstructure of cement‐based Construction Materials
Authors: Hain Michael , Wriggers Peter
Published: December 2005

For a better understanding of material phenomena, it is reasonable to take a deeper look into the microstructure of the material under consideration. In this contribution we focus on hardened cement paste with the goal to determine the effective material properties through simulations of the microstructure and numerical homogenization. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Hydroforming of Metal Sheets with an Efficient FE‐Formulation Based on an Analytical Meshfree Description of a Compressible Fluid
Authors: Haßler Marc , Schweizerhof Karl
Published: December 2005

Hydroforming is very interesting for the automotive industry, as it offers a great variety to efficiently manufacture thin walled structures. In order to simulate such static large deformation processes under hydraulic or pneumatic pressure, an analytical meshfree description of a compressible heavy or weightless fluid is presented. Thus a fully nonlinear formulation of the fluid‐structure‐interaction only based on the surface of the wetted membrane structure and the constitutive equations for the fluid can be derived. Considering physically realistic boundary conditions this formulation finally leads for all combinations of fluids and gas to a symmetric tangential stiffness matrix including several dyadic rank updates, which can be cast into a very efficient solution procedure by sequential applications of the Sherman‐Morrison formula. Furthermore other algorithms such as mesh refinements and structural contact can be restricted to the models for the work piece and the matrix. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Follower loads for high order finite elements
Authors: Heisserer Ulrich , Düster Alexander , Rank Ernst
Published: December 2005

Finite element modelling of hydrostatic compaction where the applied pressure acts normal to the deformed surface requires a geometric nonlinear formulation and follower load terms [1, 5, 7]. These concepts are applied to high order [6] (p‐FEM) elements with hierarchic shape functions. Applying the blending function method allows to precisely describe curved boundaries on coarse meshes. High order elements exhibit good performance even for high aspect ratios and strong distortion and therefore allow an efficient discretization of thin‐walled structures. Since high order finite elements are less prone to locking effects a pure displacement‐based formulation can be chosen.

After introducing the basic concept of the p‐version the application of follower loads to geometrically nonlinear high order elements is presented. For the numerical solution the displacement based formulation is linearized yielding the basis for a Newton‐Raphson iteration. The accuracy and performance of the high order finite element scheme is demonstrated by a numerical example. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of Electromechanical Contact on a Microscopic Lengthscale
Authors: Helmich Tobias , Nackenhorst Udo
Published: December 2005

This paper treats the simulation of the contact mode of an atomic force microscope (AFM). The contact forces between the tip and the sample surface is calculated via the van derWaals force in a Finite Element approach, the integration of the contact force a FEM environment is discussed and numerical examples are presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ein Vergleich numerischer Methoden zur Beschreibung von Kontaktvorgängen
Authors: Hesch Christian , Betsch Peter
Published: December 2005

Die am häufigsten zum Einsatz kommende Methode zur Beschreibung eines Kontaktvorgangs ist das sog. NTS‐ (node‐tosegment‐) Element (vgl. [3]). Die NTS‐Methode bewirkt eine punktweise Erfüllung der Kontaktbedingung. Demgegenüber steht die Mortar Methode (vgl. [1]), die eine variationell konsistente Beschreibung des Kontaktvorgangs ermöglicht. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of the EAS‐concept to a p‐version of the finite shell formulation to avoid volumetric locking
Authors: Hommel Jan‐Hendrik , Meschke Günther
Published: December 2005

A modification of the enhanced assumed strain concept is proposed to avoid volumetric locking phenomena in finite elements using higher‐order p‐shell element formulations based on Lagrangean polynomials and a linear finite shell kinematics. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New modelling approach for damped mutilayed composites
Authors: Hu Heng , Belouettar Salim , Daya El Mostafa , Potier‐Ferry Michel
Published: December 2005

The aim of this paper is to get a good approximation of damping properties of viscoelastic damped sandwich structures. Firstly we will compare the classical models based on the kinematics of Kirchhoff‐Love, Mindlin, Reddy or Touratier. In the second stage these models are used to establish the zig‐zag models which describe a piecewise continuous displacement field. These models are compared in the static and the dynamic fields. In all cases the Finite‐Element‐based solution is considered as reference. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of thin polymer films
Authors: Johlitz Michael , Steeb Holger , Diebels Stefan
Published: December 2005

If we bond substrates like metal sheets by a thin polymer film we know about the existence of a boundary layer between the polymer and the substrate. The properties of this boundary layer differ from the bulk properties and influence the overall behavior of the bond. Here we present a mechanical theory based on a scalar‐valued order parameter that allows us to describe these effects. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Density gradient based regularization of topology optimization problems
Authors: Kotucha Gregor , Hackl Klaus
Published: December 2005

In the present paper we focus on the regularization of topology design problems with regard to numerical instabilities such as the occurrence of optimal designs characterized by oscillating material density distributions, for example in the form of the well–known “checkerboard–like” patterns, as well as the dependence of the obtained designs on the used finite–element–mesh. In this context we discuss a regularization approach penalizing spatial oscillations of the material density by means of a penalty functional reflecting the global distribution of the density gradient. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Mixed Finite Element Formulation for Piezoelectric Materials
Authors: Linnemann Konrad , Klinkel Sven
Published: December 2005

A geometrically nonlinear finite element formulation to analyze multi‐field problems as they arise e.g. in piezoelectric or magnetostrictive materials is presented. Here we focus on piezoelectric problems. The formulation is based on a Hu‐Washizu functional considering six independent fields. These are displacements u, electric potential ϕ, strains E, stresses S, electric field $\vec E$, and the electric flux density $\vec D$. The finite element approximation leads to an 8‐node hexahedral element with uand ϕ as nodal degrees of freedom. The fields E, S, $\vec E$, and $\vec D$ are interpolated on element level by employing some internal degrees of freedom. These fields do not require continuity across the element boundaries, thus the internal degree of freedoms are eliminated on element level by a static condensation. The geometrically non‐linear theory allows large deformations and accounts for stability problems. To fulfill the charge conservation law in bending dominated situations exactly a quadratic approximation of the electric potential is necessary. This leads in general to additional nodal degrees of freedom, which is circumvented by the presented formulation by employing appropriate interpolations of $\vec E$ and $\vec D$. Numerical examples show that the locking effect which arise in low order elements are significantly reduced and that the element provides good accuracy with respect to experimental data. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aspects of computational homogenisation of microheterogeneous materials including decohesion at finite strains
Authors: Loehnert Stefan , Wriggers Peter
Published: December 2005

During the last years, the development and application of new composite materials gained more and more importance. For engineering applications it is necessary to get effective material properties of such materials. In this contribution we present some aspects of computational homogenisation procedures of microheterogeneous materials which can show decohesion in a cohesive zone around the particles. Due to the decohesion we get finite deformations and .nite strains within the RVE. The geometrical and material nonlinearities cause the main dif.culties. The homogenization procedure leads to an effective stress strain curve for the RVE, and for the nonlinear elastic case one can also obtain effective material parameters. It is necessary to do statistical tests in order to get a representative result. Here we set a special focus on the adaptive numerical model, the statistical testing procedure and the different boundary conditions (pure tractions and pure displacements) applied on the RVE. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phenomenological and Numerical Simulation of Shape Memory Alloys at Finite Strains
Authors: Luig Patrick , Müller Christoph , Oberste‐Brandenburg Claus , Bruhns Otto
Published: December 2005

A phenomenological material law for pseudo elastic NiTi shape memory alloys (SMA) is presented. The model was derived from a thermodynamical framework and is well‐suited to describe the thermomechanical coupled behaviour of the material. The material law, which was originally derived for small deformations, was extended to finite deformations using the Eulerian frame, in particular Hencky's logarithmic strain and the logarithmic rate.

A first emphasis is on the physical interpretation of the material parameters and their identification. A second focus lies in the presentation of a structural example for the implementation of the material law into a commercial Finite Element code. Additionally a comparison of the numerical and experimental data of the presented example is performed. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Procedure for the implicit post buckling analysis with finite elements by stabilising the global stiffness matrix
Authors: Mueller Michael
Published: December 2005

A simple procedure for the post buckling analysis is shown. In comparison to the arc length method no additional variable is required. The algorithm finds the solution for a prescribed time step. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Biological Activities in Organic Materials
Authors: Ricken Tim
Published: December 2005

In this contribution a triphasic model (solid, interstitial water containing nutrients) is proposed for the phenomenological description of transversely isotropic saturated tissues including the phenomena of growth. This is done within the framework of a macro‐mechanical description based on the Theory of Porous Media (TPM). Thereby, the constitutive equation of growth is determined by the state of stress and the local content of nutrients which are responsible for the mass exchange. The transversely isotropic behavior of the solid influences both the stress response and the internal fluid flow, which is considered using an invariant formulation of the Helmholtz free energy, transversely isotropic stress response and transversely isotropic permeability functions. After presenting the developed framework of the calculation method some representative numerical examples are examined. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Poroelastodynamic Boundary Element Method in Time Domain: Numerical Aspects
Authors: Schanz Martin , Kielhorn Lars
Published: December 2005

Based on Biot's theory the governing equations for a poroelastic continuum are given as a coupled set of partial differential equations (PDEs) for the unknowns solid displacements and pore pressure. Using the Convolution Quadrature Method (CQM) proposed by Lubich a boundary time stepping procedure is established based only on the fundamental solutions in Laplace domain.

To improve the numerical behavior of the CQM‐based Boundary Element Method (BEM) dimensionless variables are introduced and different choices studied. This will be performed as a numerical study at the example of a poroelastic column.

Summarizing the results, the normalization to time and spatial variable as well as on Young's modulus yields the best numerical behavior. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On an implicit particle method for simulation of forming processes
Authors: Schilling O. , Reese S.
Published: December 2005

Task is the simulation of forming processes using particle methods. We implemented some mesh‐free methods (the element free Galerkin method [1] and others) and the finite element method in one programme system which permits a direct comparison. For the mesh‐free methods a moving least squares approximation is applied. The shape functions are not zero or one at the nodes, thus essential boundary conditions cannot be imposed directly [2]. We use a penalty method to enforce essential boundary conditions and contact conditions. The contact algorithm (normal contact of nodes to C1‐continuous surfaces) is checked by means of the element free Galerkin method and the FEM on the basis of numerical examples which deal with forming processes. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Primal and Dual Penalty Methods for Contact Problems with Geometrical Non‐linearities
Authors: Vondrák Vít , Dostál Zdeněk , Dobiáš Jiří , Pták Svatopluk
Published: December 2005

The nonlinearity caused by two or more bodies in contact is often source of computational difficulties. Probably the most popular solution method is based on direct iterations with the non‐penetration conditions imposed by the penalty method [1]. The method enables treatment of other non‐linearities such as in the case of large displacements.

In this paper we are concerned with application of a variant of the FETI domain decomposition method that enforces feasibility of Lagrange multipliers by the penalty [5]. The dual penalty method, which has been shown to be optimal for small displacements, is used in inner loop of the algorithm that treats large displacements. We give results of numerical experiments that demonstrate high efficiency of the FETI method with the dual penalty. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determining Material Parameter of Solder Alloys by Nanoindentation
Authors: Weinberg K. , Sterthaus J. , Müller W. H.
Published: December 2005

Environmental awareness motivates the replacement of traditional plumbiferous solder joints in microelectronic devices by new material alloys. In our group mechanical properties of some lead‐free alloys are determined by nanoindentation experiments. We use a Microsystems‐Nanoindenter Machine with Berkovich tip and apply standard techniques to extract the material properties from the measured load‐displacement curves. To assess the quality of our experimental results we model and analyze the setup by finite element computations. By comparing the real (input) material data with the results determined from the load‐displacement curves we analyze the obtained data in dependence of strength and stiffness of the materials under consideration. For low‐strength material we point out deviations. By inverse analysis we adapt numerically elastic modulus and yield stress to experimentally measured load‐displacement curves. To obtain information on the material's work hardening we suggest the use of a blunt indenter tip, e.g., a spherical indenter. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Nonlinear Galerkin Scheme Involving Vectorial and Tensorial Spherical Wavelets for Solving the Incompressible Navier‐Stokes Equation on the Sphere
Authors: Fengler Martin J.
Published: December 2005

The spherical Navier‐Stokes equation plays a fundamental role in meteorology by modelling meso‐scale (stratified) atmospherical flows. This article introduces a wavelet based nonlinear Galerkin method applied to the Navier‐Stokes equation on the rotating sphere. In detail, this scheme is implemented by using divergence free vectorial spherical wavelets, and its convergence is proven. To improve numerical efficiency an extension of the spherical panel clustering algorithm to vectorial and tensorial kernels is constructed. This method enables the rapid computation of the wavelet coefficients of the nonlinear advection term. Thereby, we also indicate error estimates. Finally, extensive numerical simulations for the nonlinear interaction of three vortices are presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Solution of Transonic Flow in SE1050 Cascade
Authors: Foř J. , Fürst Jiří , Dobeš Jiří , Halama Jan , Kozel Karel
Published: December 2005

The SE1050 cascade is an open test case (QNET network) of plane turbine cascade measured at the IT ASCR wind tunnel. The two regimes with subsonic and supersonic outletMach number were selected for numerical simulation. Several numerical methods have been developed and also several turbulence models have been implemented. Comparison of computed results and experimental data gives us opportunity to discuss main features of transonic flow field in well designed turbine cascade, possibilities of its numerical capturing (grid quality, numerical viscosity, turbulence model, boundary layer transition) and its influence on prediction of energy losses. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large Eddy Simulation of turbulent confined coaxial swirling jets
Authors: García‐Villalba Manuel , Fröhlich Jochen , Rodi Wolfgang
Published: December 2005

Large eddy simulations of swirling flow in a coaxial‐jet combustor are reported. Two experimental test cases have been chosen from the literature. In both cases the configuration consists of two coaxial jets which enter into an expansion duct with the annular jet being swirled, the inner jet unswirled. The main features of the flow are well predicted in the simulations. The mean velocities and the turbulent fluctuations are compared with the experimental data and show good agreement. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of 2D and 3D backward facing step flows
Authors: Kozel Karel , Louda Petr , Příhoda Jaromír
Published: December 2005

The work deals with numerical modelling of flow through 2‐dimensional (2D) and 3‐dimensional (3D) backward facing step. In laminar case, we apply several higher order upwind and central discretizations and compare numerical results with measurements. The turbulent regime is considered in 2D as well as in 3D and influence of secondary flow is observed. Different modifications of low‐Re two equation turbulence models and an explicit algebraic Reynolds stress model (EARSM) are considered. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of analytical and numerical solution for optimal vortex diffuser design
Authors: Mehrle Andreas H. , Gittler Philipp
Published: December 2005

The contribution deals with optimization of wing tip devices, so called vortex diffusers. A comparison is given between an analytical approach for obtaining the optimal circulation loading and the results of a numerical investigation using a lifting line method. The purpose of most wing tip devices is to reduce the induced drag of the main wing by converting vortex energy into thrust. In order to achieve an optimal design, a variational formulation originally proposed by Betz and Prandtl for air screws is applied to the circulation distribution of the diffuser blades. In extension to the inviscid formulation, a viscous correction is applied in order to account for frictional forces. In an effort to validate the analytical results, a comparison is given with numerical solutions from a lifting line method. The loading of the diffuser blades is parametrized and optimized with respect to resulting thrust by use of a quasi‐Newton gradient method. Comparison shows that, knowing the velocity distribution in the near wake of the wing, considerable decrease of induced drag may be achieved making use of vortex diffusers. Although actual circulation loading may differ between the analytical and numerical estimation, resulting thrust agrees within a few percent. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multigrid Algorithm for Hybrid Joint PDF Simulations in Complex Geometries
Authors: Rembold Benjamin , Jenny Patrick
Published: December 2005

In hybrid joint probability density function (joint PDF) algorithms for turbulent reactive flows the equations for the mean flow discretized with a classical grid based method (e.g. finite volume methods (FVM)) are solved together with a Monte Carlo (particle) method for the joint velocity composition PDF. When applied for complex geometries, the solution strategy for such methods which aims at obtaining a converged solution of the coupled problem on a sufficiently fine grid becomes very important. This paper describes one important aspect of this solution strategy, i.e. multigrid computing, which is well known to be very efficient for computing numerical solutions on fine grids. Two sets of grid based variables are involved: cell‐centered variables from the FVM and node‐centered variables, which denote the moments of the PDF extracted from the particle fields. Starting from a given multiblock grid environment first a new (refined or coarsened) grid is defined retaining the grid quality. The projection and prolongation operators are defined for the two sets of variables. In this new grid environment the particles are redistributed. The effectiveness of the multigrid algorithm is demonstrated. Compared to solely solving on the finest grid, convergence can be reached about one order of magnitude faster when using the multigrid algorithm in three stages. Computation time used for projection or prolongation is negligible. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On effectiveness of parallelization of upwind difference LU‐scheme fornumerical modelling of spatial flows in airbag combustion chamber
Authors: Rychkov Alexander , Shokina Nina
Published: December 2005

The technology of parallelization of the upwind LU difference scheme is presented for numerical modelling of three‐dimensional non‐stationary flow in the airbag combustion chamber. The parallel computations are done in the High Performance Computing Center Stuttgart (Germany). (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large Scale Oscillations in the Continuous Casting Process
Authors: Schwarze Rüdiger , Rückert Antje , Leonhardt Ronny , Obermeier Frank
Published: December 2005

Long‐term oscillations of the flow in a continuous casting tundish are investigated numerically and experimentally. The numerical model is based on the Reynolds averaged Navier‐Stokes equations (URANS). A comparison between numerical results and experimental data from a water model is presented. Frequencies due to long‐term oscillations are resolved in the simulation. These frequencies are in satisfactory agreement with the experimental results of LDA measurements. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical modelling of interaction process of low‐temperature plasma
Authors: Shokin Yu. I. , Rychkov A. D.
Published: December 2005

The problem of the interaction of high‐temperature reactive gas mixture with semi‐infinite solid propellant plate is investigated. The ignition conditions of the plate are determined in the framework of the well known model of burning powder with constant surface temperature when the heat flux into plate is limited by some critical value. The gas medium is generated due to the fluid (water or methane) evaporation under the action of the impulse electric high‐powered discharge in the semi‐closed volume. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Forms of Unsteady Flow in a 2‐D Channel
Authors: Sobieski W. , Badur J.
Published: December 2005

The paper describes results of a numerical simulations of air flow in a turned off, 2D channel with the plain nozzle. Simulations are based on an earlier experiment, carried out by Dyban, Mazur and Epik (1971). In the featured channel it has been observed several bifurcation forms, depending on the flow velocity and geometry relations. Basing on the numerical simulations results, the integral characteristics of the flow areas has also been presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Premixed Turbulent Combustion Modelling Using Level Set Approach
Authors: Vítek Oldřich , Polášek Miloš , Kozel Karel , Macek Jan
Published: December 2005

The paper deals with a level set approach application to SI engine combustion modelling, which is based on solving an additional transport equation to determine the flame front propagation. The presented work is an extension of the paper [6]. The influence of engine speed, air excess, swirl number, engine load as well as application of different turbulence model, in.uence of mesh coarseness and model fine‐tuning constants are investigated and the results are presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of Finite‐Motion Parameters of Serial Chains via Measurement of 6 × 6 Stiffness Matrices
Authors: Abel Annette , Colonna Frank , Kecskeméthy Andrés
Published: December 2005

This paper describes a procedure for identifying geometric and stiffness parameters of a mechanical serial chain of know structure by measuring spatial 6×6 stiffness matrices at different positions. The method uses standard optimization routines to determine model parameters such that the model stiffness matrix features in the Frobenius norm the closest distance possible to the measured matrix. From this local identification, a rough model of parameters of finite‐motion is created, from which new measuring positions are guessed. By applying this step repeatedly, a model for finite‐displacement parameters can be obtained by a sequence of small force‐displacement tests. The method is tested with a dummy device consisting of a revolute joint connecting two rigid links dressed with soft material to mimic for example muscle masses of a surrogate mechanism for the elbow joint of a human arm. Two robots grasping the upper and lower arm generate the motion while the force measurement is carried out by a six‐axis force sensor. This makes the method potentially suitable for detecting anatomical parameters by in‐vivo measurements. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and Numerical Investigations for Cyclic Thermal Shocks
Authors: Gockel Franz‐Barthold , Mahnken Rolf
Published: December 2005

Thermal shock is an extreme form of thermo‐mechanical loading. Detailed investigations of thermal shock and live time analysis close to reality are necessary in industrial engineering in order to get a good prediction of life expectancy of high quality and safety relevant machine components. The first part of this paper concentrates on experimental investigations of macroscopic quantities like temperature, deformation, damage and crack propagation. Additionally first results on parameter studies for finite element thermal shock simulations on the thermal‐mechanical problem are summarized. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Alternative high resolution sensor to hot‐wire and hot‐film anemometer
Authors: Hölling Michael , Barth Stephan , Peinke Joachim
Published: December 2005

We present a new type of high resolution sensor for turbulent flow measurements based on the optical detection of a deflected cantilever. The Laser‐Cantilever‐Anemometer (LCA) can be used in air as well as in water without any changes in setup. Experiments for testing the functionality of this sensor in turbulent air flows show that the measured data with the LCA match the data obtained with a hot‐wire anemometer up to several kHz. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element model updating for damage detection
Authors: Kompalka A. S. , Reese S.
Published: December 2005

In this contribution we derive the iterative finite element model updating algorithm. The ability of the method to detect the damage is verified by means of a simulation with a reference finite element model. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transfer Function and the State Space Model Identification of a Funnel Shaped Piezoelectric Structure for the Controller Design Purposes
Authors: Nestorović‐Trajkov Tamara , NachKöppename Heinz , Gabbert Ulrich
Published: December 2005

For the controller design purposes in order to suppress vibration magnitudes of a funnel shaped piezoelectric shell structure the mathematical model of the structure was identified in the form of the transfer function and the state space representation. The excitation of the structure with different signal types as well as the measurement of the responses were achieved using the piezoelectric actuator and sensor patches attached to the funnel. From the frequency responses obtained as a ratio of the Fast Fourier Transforms between the appropriate sensor and the actuator signals, discrete‐time transfer functions were determined by best curve fitting of the model‐based frequency response. For the state space model identification the subspace based identification approach was used. Obtained models were used for the optimal LQ controller design. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of the Running‐State of Railway Wheelsets
Authors: Reicke L. , Popp K.
Published: December 2005

High‐speed trains require a reliable monitoring of the current running‐state to detect exceptional running‐conditions which can occur due to track irregularities, wear in the wheel‐rail contact or chassis damages. A sophisticated monitoring not only classifies the running‐state in terms of safe operation but also derives the causes to enable condition‐based maintenance.

The running‐state can be characterized by the dynamic interaction in the contact patch inducing forces and torques and leading to forced and self‐excited structural vibrations of the wheelset. It is very difficult to measure structural vibrations directly and therefore it is convenient to observe them by accelerations in longitudinal, transversal and vertical direction at the left and right axle‐boxes of each wheelset. The transient behavior of structural vibrations can be well analyzed by timefrequency transforms. A decomposition into the principal eigenmodes is achieved by model‐based preprocessing. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimentelle Untersuchung zum anisotropen Verhalten eines Polypropylen‐Schaums
Authors: Schmitt Joachim , Diebels Stefan
Published: December 2005

An Beispiel eines Polypropylenschaums wird ein anisotropes elastisch‐viskoplastisches Stoffmodell vorgestellt. Über einachsige Druckversuche werden die nötigen Parameter ermittelt und die Besonderheiten des anisotropen Modells anhand von Fließ.ächenschnitten verdeutlicht. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Buckling and damage of dynamically loaded plates in shock tubes
Authors: Stoffel Marcus , Schmidt Rüdiger , Weichert Dieter
Published: December 2005

In this study circular metal plates are subjected alternately to impulsive loadings in shock tubes. The aim is to develop an experimental method to measure the buckling shapes of shock wave‐loaded plates during the impulse duration. Furthermore, the measurements are used to validate failure modes predicted in finite element simulations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)