bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle Finite Element Analysis of Cutting Processes
Authors: Sabel Matthias , Sator Christian , Müller Ralf
Published: December 2014

Although machining is a well established method in manufacturing, the numerical modeling is complicated since severe changes in the geometry and the topology can occur. Especially the formation of chips and burrs requires a method that tracks the large configurational changes. The particle finite element method (PFEM) combines the benefits of the standard finite element method (FEM) and discrete models, such as molecular dynamics simulations and is therefore well suited to cope with these tasks. In this article, a description of the conceptual realisation and the overall algorithm is given and a numerical analysis of a cutting process is performed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximation of the dual problem for error estimation in inelastic problems
Authors: Widany Kai‐Uwe , Mahnken Rolf
Published: December 2014

In numerical simulations with the finite element method the dependency on the mesh – and for time‐dependent problems on the time discretization – arises. Adaptive refinements in space (and time) based on goal‐oriented error estimation [1] become more and more popular for finite element analyses to balance computational effort and accuracy of the solution. The introduction of a goal quantity of interest defines a dual problem which has to be solved to estimate the error with respect to it. Often such procedures are based on a space‐time Galerkin framework for instationary problems [2]. Discretization results in systems of equations in which the unknowns are nodal values. Contrary, in current finite element implementations for path‐dependent problems some quantities storing information about the path‐dependence are located at the integration points of the finite elements [3], e.g. plastic strains etc. In this contribution we propose an approach – similar to [4] for sensitivity analysis – for the approximation of the dual problem which mainly maintains the structure of current finite element implementations for path‐dependent problems. Here, the dual problem is introduced after discretization. A numerical example illustrates the approach. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of a Bolted Friction Resonator in the Frequency Domain
Authors: Süß Dominik , Willner Kai
Published: December 2014

Joints play an important role in most mechanical applications and the prediction of the dynamical behavior of jointed structures is a challenging task in structural dynamics. Their inclusion leads to, for example, shifts of the resonance frequencies or of the maximal response amplitude within a resonance due to damping effects. In this paper, the focus is on investigating the behavior of a jointed structure within the frequency domain corresponding to the stationary behavior of the system in the time domain. Here the Harmonic Balance Method (HBM) is applied to a friction oscillator containing a bolted lap joint. This structure is modeled on two different ways via Finite Element models with a corresponding three dimensional contact law. The results for the different models are compared to each other. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameterreduktion am Reibschwinger durch Ähnlichkeitskennzahlen
Authors: Kröger Matthias , de Payrebrune Kristin M.
Published: December 2014

Es ist in der mathematischen Auswertung von Bewegungsgleichungen üblich, durch Umformungen und Transformationen die zu untersuchende Parameteranzahl zu reduzieren. Ein Beispiel ist die Transformation in die Eigenzeit. Am Reibschwinger mit Coulomb'scher Reibkennlinie oder linear mit der Relativgeschwindigkeit fallender Reibkennlinie sind zahlreiche Parame‐terreduktionen durch derartige Transformationen möglich. Allerdings muss der Anwender dabei neben der mathematischen Interpretation auch die physikalische Interpretation der Lösung beachten. Dann ist es möglich, den Aufwand für Parameteranalysen relativ gering zu halten. Eine größere Herausforderung ergibt sich, wenn der Reibschwinger fremd‐ und selbsterregt ist oder mehrere Reibelemente gekoppelt werden. Diese Arbeit stellt die Grundlagen und deren Übertragung auf komplexere Reibschwinger vor. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of Strain Gradient Plasticity to Micro‐torsion Experiments
Authors: Bayerschen Eric , Wulfinghoff Stephan , Böhlke Thomas
Published: December 2014

The applicability of a strain gradient crystal plasticity model to size effects observed on microwires in torsion experiments is discussed. Finite Element simulations of simplified cylindrical grain aggregations are presented and the resulting overall mechanical response is compared to experimental data for gold from the literature. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constitutive modelling of thermo‐viscoelastic‐plastic behaviour of adhesively bonded joints
Authors: Kühlmeyer Patrick , Matzenmiller Anton
Published: December 2014

For ductile structural adhesives under thermal and mechanical loading, a thermo‐viscoelastic‐plastic interfacial constitutive model is introduced using a generalised MAXWELL solid in series with a thermal strain element and a ST.‐VENANT body with isotropic hardening for plasticity. The temperature dependency of the viscosity is taken into account on assuming thermorheologically simple material behaviour, while the yield threshold and the hardening parameters depend on empirical functions of temperature. Numerical examples for the model verification and validation are discussed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of Viscoelastic Properties and Damaging Effects of Highly Extensible Polyurea
Authors: Reppel Thomas , Decker Johann , Weinberg Kerstin
Published: December 2014

The present work aims particular at the experimental identification of the viscoelastic properties of polyurea as well as on the onset of the damage.

For the viscoelastic part, several relaxation experiments are performed. From the measured data a general viscoelastic model is derived where we use two different approaches. At first we identify a general Maxwell model (combining spring and damping elements for finite deformations) to use a prony series with N elements, which requires the identification of 2N + 1 parameters. At second, a model of generalized fractional elements [3] is employed. Both approaches are studied in detail and are compared to data from literature; furthermore a comparison concerning the effort is presented.

Damaging effects of Polyurea are investigated using tensile tests with and without cyclic loading. In particular we focus on the the onset of damage by cavitation. To this end the recovered specimens were analyzed using a laser microscope; the surfaces of the ruptured areas are compared in terms of quantity and size of voids. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cyclic yield strength in definition of design limits for fatigue and creep
Authors: Gorash Yevgen , MacKenzie Donald
Published: December 2014

This study proposes a cyclic yield strength (CYS, σcy) as a key characteristic for the definition of safe design for engineering structures operating under fatigue and creep conditions. CYS is defined on a cyclic stress‐strain curve, while monotonic yield strength (MYS, σmy) is defined on a monotonic stress‐strain curve. Both values of σcy and σmy are identified using a 2‐steps fitting procedure of the experimental stress‐strain curves using Ramberg‐Osgood and Chaboche material models. Comparison of σcy and fatigue endurance limit σflim on the S‐N fatigue curve reveals that they are approximately equal. Hence, basically safe fatigue design is guaranteed in purely elastic domain defined by the σcy. A typical creep rupture curve in time‐to‐failure approach for creep analysis has 2 inflections corresponding to the σcy and σmy. These stresses separate 3 sections on the creep rupture curve, which are characterised by 3 different creep fracture modes and 3 creep deformation mechanisms. Thus, basically safe creep design is guaranteed in linear creep domain with brittle failure mode defined by the σcy. These assumptions are confirmed for several structural low‐ and high‐alloy steels for normal and high‐temperature applications. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magneto‐Sensitive Elastomers: An Experimental Point of View
Authors: Walter Bastian , Saxena Prashant , Kaschta Joachim , Schubert Dirk W. , Steinmann Paul
Published: December 2014

Magneto‐sensitive elastomers (MSEs) are smart materials changing their shape and mechanical properties in the presence of a magnetic field. Focussing on model systems, silicone based MSEs are prepared by a multi‐step mixing process and characterised using a rotational rheometer (plate‐plate). Data obtained by relaxation tests is used to set‐up a material model coupling the theories of viscoelasticity and magnetoelasticity. The behaviour of MSEs in quasi‐static and dynamic mechanical shear experiments can be successfully predicted by the analytical model using parameters received by fitting the transient experiments. The model is validated for small shear deformations (γ = 0.02) and low magnetic fields (𝔹 = 0.2 T). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A variational approach towards the modeling of equilibrium twin interfaces in a single‐crystalline magnetic shape memory alloy sample
Authors: Wang Jiong , Steinmann Paul
Published: December 2014

In this work, a variational approach is proposed to study the magneto‐mechanical response of a single‐crystalline MSMA sample. By proposing a total energy functional for the whole magneto‐mechanical system, the governing PDE system is derived by calculating the variations of the total energy functional with respect to the independent variables. An iterative numerical algorithm is proposed to solve the governing PDE system. As an example, a MSMA sample with cuboid shape and subject to perpendicularly applied magnetic and mechanical loadings is considered. It can be seen that the magneto‐mechanical response of this sample can be predicted at a quantitative level. The whole procedure of variant reorientation in the sample can also be simulated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of Multi Wall Carbon Nanotubes and Nanotube assemblies by a molecular mechanics approach
Authors: Eberhardt Oliver , Guenther Margarita , Wallmersperger Thomas
Published: December 2014

The present work describes the modeling techniques applied for the investigation of assemblies of Carbon Nanotubes (CNTs) and Multi Wall Carbon Nanotubes (MWNTs). Motivated from possible future applications, for instance in new composite materials, the investigations of the interaction behavior of individual Carbon Nanotubes within an assembly of Carbon Nanotubes is mandatory in order to understand the behavior of larger scale structures made from CNTs, e.g. Carbon Nanotube fibers. The present research applies the Lennard‐Jones potential for modeling the van‐der‐Waals interaction occurring between the nanotubes realizing the interaction behavior. The individual Carbon Nanotubes within the assembly are assumed to be rigid. All van‐der‐Waals bonds are taken into account in order to calculate an overall potential surface describing the behavior of the investigated structure. An example consisting of a Multi Wall Carbon Nanotube made of three armchair Single Wall Carbon Nanotubes (SWNTs) is investigated (with and without additional outer force) with respect to equilibrium positions of the structure. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of material behavior via a Finite Element Model Updating strategy
Authors: Schmaltz Stefan , Willner Kai
Published: December 2014

In this paper an inverse and iterative method for the identification of material behavior is presented, based on the Finite Element Model Updating (FEMU) strategy. The FE simulations are performed with a commercial FE software code, using a self‐implemented elastic material model at finite strain. The iterative identification procedure is based on an experimental test (numerical) whose measured kinematic values are compared to the corresponding simulated ones. Through an optimization algorithm the material parameters are varied in a way that the least‐squares sum of the kinematic values is minimized and the optimal material parameters yielding the material behavior are identified. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational homogenization and nonlinear effects in heterogeneous fluid saturated porous media
Authors: Rohan Eduard , Lukeš Vladimír
Published: December 2014

For the two‐scale modelling of deforming fluid‐saturated porous structure we apply the asymptotic homogenization approach to the fluid‐structure interaction problem involving linear elastic porous skeleton and the Newtonian compressible fluid. The sensitivity analysis of effective coefficients depending on the geometrical configuration is used to introduce a weakly nonlinear formulation which enables to capture influences of the deformation on the material properties. The paper is devoted to the comparison of the linear and the weakly nonlinear models (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanical Simulation of the Electron Beam Melting Process for TiAl6V4
Authors: Riedlbauer Daniel , Mergheim Julia , Steinmann Paul
Published: December 2014

In the present contribution a nonlinear thermomechanical finite element model with temperature dependent material parameters is used to simulate the electron beam melting process for TiAl6V4. The beam is modeled as a moving heat source and the isentropic split solution scheme is applied. The temperature and stress distribution during the process were simulated and showed sound results from a qualitative point of view. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐Scale and Multi‐Component Approach for Solidification Processes
Authors: Moj Lukas , Ricken Tim , Steinbach Ingo
Published: December 2014

This articel focuses on a thermo‐mechanical model for numerical simulation of solidification processes considering two different scales, both in time and space. The macro‐scale implies two phases (solid and liquid steel), and is described by use of the theory of porous media (TPM). Moreover, a strong thermal coupling is addressed as well as finite J2 elastic‐plastic solid behavior. The physics of solidification during heat dissipation is covered on the micro‐scale in the framework of phase‐field modeling. Therefore, a Ginzburg‐Landau type free energy function is used. After discussing the main model details, a numerical example will demonstrate the principal performance of the presented model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Staggered solution of fluid‐porous‐media interaction using the method of local Lagrange multipliers
Authors: Zinatbakhsh Seyedmohammad , Ehlers Wolfgang
Published: December 2014

Surface interaction among non‐overlapping bulk‐fluid and porous‐medium bodies occurs in different situations, e. g., the interaction of blood with a blood vessel wall, a body of water with an earth dam structure, or acoustic waves with acoustic panels used in soundproofing. These are multi‐field phenomena, comprising various surface‐ and volume‐coupling mechanisms that should be reflected in the corresponding mathematical models. These models, together with appropriate initial and boundary values, assemble a coupled problem, the solution of which reveals the behaviour of the system under external excitations. The solution is commonly done numerically, following a monolithic or a decoupled approach. Here, the focus is on the latter. To design an efficient decoupled scheme, different types of coupling within the problem are addressed. These are the volume coupling between the degrees of freedom (DOF) within each subdomain, and the surface coupling between the DOF on the common boundaries. In particular, the latter constrains the feasible space of the solution of the problem. In this regard, local Lagrange multipliers (LLM) are employed to reformulate the problem in an unconstrained form. Unlike other domain decomposition methods which are based on using global Lagrange multipliers, the LLM method yields a complete separation of the subdomains and, consequently, facilitates parallel solution of the sub‐problems. Moreover, within the subdomains, the penalty method is used to decouple pressure from other DOF. This procedure, on the one hand, reduces the size of the problem that should be solved at the interface and, on the other hand, removes the burden of using mixed finite elements within the subsystems. In the next step, the stability behaviour of the resulting staggered approach is analysed, and the unconditional stability of the method is established. Finally, the method is employed to solve a benchmark example, and using the numerical results, the reliability of the outcomes of the stability analysis is investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational formulation and finite element modelling of electrostatic‐elastodynamic coupling
Authors: Schlögl Tristan , Leyendecker Sigrid
Published: December 2014

Dielectric elastomer actuators (DEA) are composed of a series of single cells, each one equipped with two conductive layers separated by insulating dielectric silicone. As with capacitors, when an external voltage is applied to the conductive layers, an electric field is established. Due to electrostrictive effects of the silicone, the formation of dipoles leads to a contraction of the DEA. These effects are described by the Maxwell equations, the balance of momentum and constitutive material laws. Based on a model for non‐linear electroelasticity that covers the static case only, inertia terms are added in order to obtain a description of the deformation process depending on time. A potential energy function that is composed of Neo‐Hooke material behaviour, electric field energy and coupling terms covers the strong formulation. Combined with the kinetic energy, a Lagrangian forms the basis in a variational setting of the model. By applying a discrete version of Hamilton's principle, a structure preserving integration scheme for DEAs is obtained. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fluid‐structure interaction of an elastic pipe immersed in a coaxial rigid pipe: a model for the Tullio Phenomenon
Authors: Grieser Bernhard , Kleiser Leonhard , Obrist Dominik
Published: December 2014

An axisymmetric, elastic pipe is filled with an incompressible fluid and is immersed in a second, coaxial rigid pipe which contains the same fluid. A pressure pulse in the outer fluid annulus deforms the elastic pipe which invokes a fluid motion in the fluid core. It is the aim of this study to investigate streaming phenomena in the core which may originate from such a fluid‐structure interaction. This work presents a numerical solver for such a configuration. It was developed in the OpenFOAM software environment and is based on the Arbitrary Lagrangian Eulerian (ALE) approach for moving meshes. The solver features a monolithic integration of the one‐dimensional, coupled system between the elastic structure and the outer fluid annulus into a dynamic boundary condition for the moving surface of the fluid core. Results indicate that our configuration may serve as a mechanical model of the Tullio Phenomenon (sound‐induced vertigo). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Methodenentwicklung zur numerischen Strömungsanalyse von Freispiegelströmungen bei Schaufelwasserrädern
Authors: Schippke Hans‐Henning , Seidel Christian , Dinkler Dieter , Zilian Andreas
Published: December 2014

Es wird ein Berechnungsmodell vorgestellt, mit dem eine numerische Analyse der Strömungsvorgänge innerhalb von Schaufelwasserrädern möglich ist. Das Fluidgebiet, beschrieben durch die inkompressiblen Navier‐Stokes‐Gleichungen, wird mittels der zeit‐diskontinuierlichen Raum‐Zeit‐Finite‐Elemente‐Methode diskretisiert. Die Grenzfläche Wasser‐Luft ist implizit mit Hilfe einer Level‐Set‐Funktion abgebildet, während die Grenzfläche Fluid‐Struktur direkt im Rahmen der Gebietsdiskretisierung abgebildet wird. Unter Verwendung der Shear‐Slip‐Mesh‐Update‐Methode findet die auftretende Netzbewegung Berücksichtigung. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element simulation of the poling process in BaTiO3–CoFe2O4 multiferroic composites
Authors: Avakian Artjom , Gellmann Roman , Ricoeur Andreas
Published: December 2014

The theoretical background of nonlinear constitutive magneto‐ferroelectric behavior as well as the Finite Element implementation are presented. On this basis the polarization in the ferroelectric matrix (BaTiO3) with embedded dielectric‐magnetostrictive particels (CoFe2O4) is simulated and the resulting effects are analyzed. Numerical simulations focus on the prediction of local crystal orientations and residual stress going along with the poling process, in the future supplying information on favorable electric‐magnetic loading sequences. Further, multifield homogenization procedures enable the prediction of the electromagnetomechanical properties of smart multiferroic composites and supply useful means for their optimization. The resulting final state of a poling simulation can be implemented as a starting condition for approximate linear simulations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Magneto‐Visco‐Elastic Model for Magnetorheological Elastomers
Authors: Ethiraj Gautam , Sridhar Ashish , Miehe Christian
Published: December 2014

In this work we present the modular construction and FEM implementation of a material model for magnetorheological elastomers (MRE) that is firmly rooted in micromechanics and performs well against experimental data. Keeping in mind the composite nature at the microscale, we develop a constitutive formulation based on a multiplicative magneto‐mechanical split of the deformation gradient. We consider both Lee‐ and Clifton‐type right and left decompositions. In contrast to other recent formulations [6], this general approach allows the use of highly advanced micromechnically‐based network models for polymers such as [4] and [5] in a modular format and to extend its application for coupled magnetomechanical response. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mathematical Modeling and Numerical Simulation of a Magnetostrictive Euler‐Bernoulli Beam
Authors: Harutyunyan Mané , Simeon Bernd
Published: December 2014

Magnetostrictive (MS) materials change their mechanical behavior in response to the application of an external magnetic field and are widely used as sensors and actuators in different areas. This paper is aimed at the description of the magneto‐mechanical coupling using a model of an isotropic Euler‐Bernoulli‐beam. The simple structure of the model enables the full understanding of the effect of coupling. The main focus lies on the mathematical formulation of a coupled magneto‐elastic problem by means of a PDE with appropriate boundary conditions. The numerical modeling is performed by using the Finite Element Method. Considering linear material laws, stationary and time‐dependent cases have been analyzed. To confirm the theoretical results, corresponding simulations carried out with Matlab are presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of nonlinear continuum dislocation theory to antiplane shear
Authors: Günther Christina , Le Khanh Chau
Published: December 2014

We apply the nonlinear dislocation theory to the problem of antiplane constrained shear in a single crystal with one slip system. By taking dissipation into account, the relaxed energy functional has to be minimized. We show that, up to a threshold strain, no dislocations are nucleated and therefore the plastic slip is zero. Since this threshold value depends on the width of the specimen, a size effect takes place. The stress strain curve turns out to be a hysteresis loop exhibiting the work hardening due to the dislocation pile‐up. It is shown that the Bauschinger effect holds true. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of the effective viscoelastic material behavior of textile reinforced composites using a multi‐scale approach
Authors: Branke Dominik , Kästner Markus , Pohl Martin , Ulbricht Volker
Published: December 2014

The increasing importance of constructive lightweight in modern engineering science involves the use of advanced materials like textile reinforced composites. In order to reduce development costs, efficient numerical simulations are needed to model the macroscopic behavior of the final product. Focussing on long term phenomena, which are important when parts made of composites with rate‐dependent material behavior are assembled by bolted or screwed joints, a two‐step homogenization procedure is used to obtain an effective homogeneous equivalent material at the macroscopic scale. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microscale modeling and homogenization of rope‐like textiles
Authors: Fillep Sebastian , Mergheim Julia , Steinmann Paul
Published: December 2014

This contribution deals with rope‐like textiles. On the macroscopic level rope‐like textiles are characterized by a large length‐to‐thickness ratio, such that a discretization with beam elements is numerically efficient. To capture the contact behavior the representative volume element is explicitly modeled by means of a volumetric micro sample. A suitable, beam‐specific FE2 method is developed, which connects the homogeneous macro level to a fiber structured micro sample. This contribution investigates the determination of the nonlinear constitutive behavior of rope‐like textiles. Selected examples for the macroscopic behavior of microscopic heterogeneous fiber structured materials are presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isolating low‐frequency deformations for efficient multigrid methods: a geometrically exact 2D beam model
Authors: Schröppel Christian , Wackerfuß Jens
Published: December 2014

We propose a novel technique for low‐frequency approximations of boundary‐value problems. In contrast to the standard Ritz‐Galerkin approach, the shape functions are given on the logarithmic space of the deformation function. The method is able to capture the complex interplay of the rotational and the translational components of the deformation. It is likely to be particularly efficient in the context of multigrid algorithms. c 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim 15
A phase‐field approach for the modeling of nematic liquid crystal elastomers
Authors: Keip Marc‐André , Bhattacharya Kaushik
Published: December 2014

Liquid crystal elastomers combine the elastic properties of rubber with the orientational properties of liquid crystals. Amongst the various types of liquid crystal elastomers, nematic elastomers are one special class. Nematic elastomers undergo a phase transition from a high‐temperature isotropic state to a low‐temperature nematic state, which is generally accompanied by large deformations. In the present contribution, a phase‐field model for the continuum‐mechanical description of nematic elastomers will be introduced. The model is implemented into the finite element method and employed for the simulation of domain evolution under specified initial boundary conditions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Voxel‐based fast solution of the Lippmann‐Schwinger equation with smooth material interfaces
Authors: Merkert Dennis , Andrä Heiko , Kabel Matthias , Schneider Matti , Simeon Bernd
Published: December 2014

The FFT‐based homogenization method proposed by Moulinec and Suquet [1] in 1994 to solve the Lippmann‐Schwinger equation has recently become more popular due to its computational speed and accuracy. It is based on regular voxel grids and can work on segmented CT images directly. Given an interface description on the sub‐voxel scale we show that using interface voxels with an appropriately chosen stiffness significantly enhances the accuracy of the computed effective properties and decreases voxelation effects in the solution. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two Way Coupled Micro/Meso Scale Method for Wind Farms
Authors: Class Andreas , Viellieber Mathias , Moussiopoulos Nicolas , Barmpas Fotios
Published: December 2014

Wind turbines extract energy from the approaching flow field resulting in reduced wind speeds, increased turbulence and a wake downstream of the wind turbine. The wake has a multitude of negative effects on downstream wind turbines. This includes reduced efficiency and increased unsteadiness resulting in vibrations and potentially in material fatigue. Moreover, the maintenance can increase compared to non‐interfering wind turbines. The simulation of these effects is challenging. Computational fluid dynamics (CFD) simulations of these large and complex geometries requires exceedingly large computational resources. With present Reynolds Averaged Navier‐Stokes (RANS) or Large Eddy Simulation (LES) based CFD methods it is virtually impossible to perform such simulations of the interaction between individual wind turbines in a complete wind turbine farm. Coupling to the mesoscale accounting for local weather situations becomes yet more challenging. This is due to the wide range of length and time scales that have to be considered for these simulations and therefore the tremendous computational power needed to perform such simulations. To investigate these effects we propose to combine ideas from existing methods, the Coarse‐Grid‐CFD (CGCFD) ( [1]) developed at the KIT and the meso‐/ micro scale method developed at the University of Thessaloniki ( [2]). Goal of the proposed methodology is to provide a numerical method that allows to implement a wind farm in a meso‐scale weather simulation which includes two‐way coupling. Thus both the micro and the meso scale wind and energy production of wind farms can be addressed. This proposed multi scale coupling strategy can also be applied in two hierarchies reducing the numerical effort of the global approach yet more. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and Simulation of solidification processes in polymer melt flows
Authors: Descher Stefan , Wünsch Olaf
Published: December 2014

This work deals with the modelling and simulation of solidification processes in polymer melt flows. Two models describing the latent heat and the rheological behaviour were implemented in a finite volume code. The models are empirical and their parameters are identified using experimental results obtained from investigations with a rotational rheometer and a differential scanning calorimetry. First results of the simulation of a solidifying channel flow are shown. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the effect of surface roughness in transonic high Reynolds number flow through slender channels
Authors: Kluwick Alfred , Kornfeld Matthias
Published: December 2014

In the present study transonic weakly three‐dimensional flows at high Reynolds numbers in slender channels, as they are found e.g. in micro nozzles and turbo‐machines of micro‐electromechanical‐ systems (MEMS), are considered. The channel height is taken to be so small that the viscous layers forming at the channel walls start to interact strongly rather than weakly with the predominantly inviscid core flow and, therefore, the classical boundary layer approach fails. The resulting viscous‐inviscid interaction problem is formulated using matched asymptotic expansions and found to be governed by a triple deck structure. As a consequence, the properties of the inviscid core region and the viscous wall layers have to be calculated simultaneously in the interaction region. Weakly three‐dimensional effects caused by surface roughness, upstream propagating flow perturbations and boundary layer separation are discussed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flow and heat transfer of non‐Newtonian fluids in enameling dies
Authors: Bari´ c Emil , Steiner Helfried , Brenn Günter
Published: December 2014

The present work analyses computationally the flow inside wire enameling dies within the framework of the lubrication theory approximation. Non‐Newtonian flow behavior and heat transfer are accounted for as well. It is shown that the developed approach most accurately predicts the momentum and heat fluxes along the wire. As such it is proven as a reliable and computationally efficient tool for the design of flow optimized die shapes. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Least‐squares finite element methods for the Navier‐Stokes equations for generalized Newtonian fluids
Authors: Serdas Serdar , Schwarz Alexander , Schröder Jörg , Turek Stefan , Ouazzi Abderrahim , Nickaeen Masoud
Published: December 2014

In this contribution we present the least‐squares finite element method (LSFEM) for the incompressible Navier‐Stokes equations. In detail, we consider a non‐Newtonian fluid flow, which is described by a power‐law model, see [1]. The second‐order problem is reformulated by introducing a first‐order div‐grad system consisting of the equilibrium condition, the incompressibility condition and the constitutive equation, which are written in residual forms, see [2]. Here, higher‐order finite elements which are an important aspect regarding accuracy for the present formulation are investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
2D und 3D numerische Strömungsanalyse von Kraftwerkstrennpfeilern
Authors: Ostermann Lars , Seidel Christian
Published: December 2014

Die numerische Untersuchung von Wasserkraftwerken ist ein wichtiges Instrument des wasserbaulichen Entwurfs und wird bei der Entwicklung und Optimierung von Wasserkraftwerken neben den experimentellen Untersuchungen am physikalischen Teilmodell oder Vollmodell im Wasserbaulabor eingesetzt. Bei den numerischen Strömungsuntersuchungen werden sowohl 2D‐ als auch 3D‐Verfahren erfolgreich verwendet. Bei den 2D‐Verfahren kommen schwerpunktmäßig vor allem flachwassergleichungsbasie Verfahren zum Einsatz, da besonders für diese Verfahren auf Grund ihrer weitverbreiteten Anwendung bei der Untersuchung strömungsmechanischer Fragestellungen im Wasserbau eine Vielzahl von Erfahrungswerten vorliegt, die häufig durch Insitu‐Messungen verifiziert sind. Die Güte der mit 2D‐Verfahren zu gewinnenden Ergebnisse bei der Optimierung von Wasserkraftwerken wird anhand der Optimierung des Kraftwerktrennpfeilers untersucht und im Vergleich mit den Ergebnissen der 3D‐Strömungsanalyse und den Experimenten am physikalischen Teilmodell gezeigt. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the possibility of using Coanda Effect for Unmanned Aerial Vehicles – a numerical investigation
Authors: Rašuo Boško , Mirkov Nikola
Published: December 2014

In this paper we present numerical results of conceptual design study of an UAV which uses Coanda Effect for lift production. Results indicate the ability of manuveuring by creating asymmetric flow patterns which lead to uneven lift production and resulting force with horizontal component necessary for establishing forward flight conditions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical prediction for multiple roll systems with negative gaps
Authors: Willinger Bettina , Delgado Antonio
Published: December 2014

Multiple roll coaters with deformable rolls are widely spread for the coating of thin liquid films with a wet film thickness of only a few microns and below on continuous substrates. The presented analytical solution for multiple roll systems offers for the first time the possibility to predict the performance of multiple roll coaters with a nip feed system and negative gaps. The solution is based on a previously presented solution of the authors for roll pairs and extended to multiple roll systems. The results are validated with experimental data from literature and the main influencing factors of multiple roll systems are investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of a Turbulent FSI Benchmark Case
Authors: Reimann Thorsten , Ali Awais , Sternel Dörte Carla , Schäfer Michael
Published: December 2014

In an effort to expand the capabilities of a validated simulation environment for fluid‐structure interaction to turbulent flows, we present the simulation of a turbulent FSI benchmark case with large displacements in a simplified two‐dimensional unsteady RANS setup. We find a fair agreement to experimental data that encourages further refinement of our approach and future three‐dimensional simulations with eddy‐resolving schemes. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary Layer Heat Transport in turbulent Rayleigh‐Bénard Convection in Air
Authors: du Puits Ronald , Resagk Christian , Willert Christian
Published: December 2014

We study the convective heat transfer in a large‐scale Rayleigh‐Bénard (RB) experiment which is called the “Barrel of Ilmenau”. We present the results of flow visualization and Particle Image Velocimetry (PIV) measurements of the near wall flow field in a plane perpendicular to the surface of the heated bottom plate. The experiment was run in a smaller rectangular inset that was placed inside the larger barrel. The Rayleigh number amounts to Ra = 1.4 × 1010. The aspect ratios were Γx = 1 in flow direction and Γy = 0.26 perpendicular to the vertical flow plane. The measurements have been undertaken using a 2 W continuous wave Laser in combination with a light sheet optics and various cameras. Due to the slender geometry of the cell, the mean wind is confined in one direction where the Laser light sheet is aligned parallel. The flow was seeded with droplets of 1...2 µm size generated using an ordinary fog machine. Flow visualization as well as the PIV data clearly show the intermittent character of the boundary layer flow field that permanently switches between “laminar” and “turbulent” phases. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct Numerical Simulation of turbulent heat transfer behind a backward‐facing step at low Prandtl number
Authors: Niemann Martin , Fröhlich Jochen
Published: December 2014

The paper presents Direct Numerical Simulations of the turbulent flow of a low Prandtl number fluid over a backward‐facing step with heat transfer. The backward‐facing step flow is investigated as a generic configuration for sudden changes in cross section. Several simulations are reported: for isothermal conditions, for heat transfer with the Prandtl number of air, and for heat transfer with the Prandtl number of liquid sodium. The simulation for air is compared to results from literature. The differences induced by reduction of the Prandtl number are then assessed by comparison of the two cases. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Consistent implementation of real fluid EOS in pseudopotential lattice Boltzmann models
Authors: Khajepor Sorush , Dewar Marius , Wen John , Chen Baixin
Published: December 2014

Pseudopotential lattice Boltzmann models have emerged as successful methods to simulate liquid‐vapor coexistence systems. However, the equation of state (EOS) of such systems, which is found to be thermodynamically consistent, is unique and lacks the potential to cover a broad range of physical fluids. In this study, we employ multiple pseudopotentials and extend the consistent EOS to enhance the capability of pseudopotential models in reproducing a wider range of thermodynamic states. The new system has the format which preserves the consistency between the lattice pressure tensor and the free energy density. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the behaviour of thin liquid layers at curved solid edges
Authors: Sommer Oliver , Wozniak Günter
Published: December 2014

The knowledge of the behaviour of thin liquid layers on solid surfaces is of fundamental interest as far as basic research and applications like technical covering or lubrication processes are concerned. The subject is currently of increasing importance, particularly due to stronger requirements of thin liquid layer functionalities. We therefore studied the development of the liquid layer thickness distribution field as well as the liquid layer disturbance propagation on a plane solid surface in the vicinity of a curved solid edge experimentally using LIF technique. The investigation focusses on the influence of the initial layer thickness as well as on liquid properties like viscosity and surface tension on the liquid film behaviour, especially close to solid edges. Selected experimental results are shown highlighting relevant quantities with respect to disturbance propagation and validation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model Predictive Control of two‐phase flow using a diffuse interface approach
Authors: Hinze Michael , Kahle Christian
Published: December 2014

We propose a feedback control strategy for the stabilization of two‐phase flow with variable densities, where we use an inexact variant of Model Predictive Control, called Instantaneous Control. The physical system is governed by the Cahn–Hilliard Navier–Stokes system with different densities proposed in [1]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stress‐driven local solution approach to quasistatic brittle delamination
Authors: Thomas Marita
Published: December 2014

This contribution reports on a model describing the rate‐independent evolution of brittle delamination between two elastic bodies
$\Omega_{+} \subset {\rm I\!R}^{d}$
and
$\Omega_{-} \subset {\rm I\!R}^{d}, d \geq 2$
, bonded along a prescribed contact surface
$\Gamma_{C} \subset {\rm I\!R}^{d-1}$
, over a fixed time interval (0, T). In contrast to [1], which is set in the framework of energetic solutions, here the existence and properties of so‐called local solutions are studied; a detailed discussion and a rigorous mathematical analysis of this model can be found in [2]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The sensitivity of optimal states to time delay
Authors: Gugat Martin , Herty Michael
Published: December 2014

In the design and computation of optimal controls for systems that evolve in time, usually the effect of delay is ignored. However in the implementation of the computed optimal controls in the control systems often delays occur, for example through transmission via digital communication channels. The question to be addressed is whether such small delays can have large effects on a system that is steered by an optimal control. We show that for a system that is governed by the wave equation with L2‐norm minimal exact Dirichlet boundary control, for arbitrarily small time‐delays there are initial states such that the terminal energy is almost twice as big as the initial energy. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Studying Dynamical Principles of Human Locomotion using Inverse Optimal Control
Authors: Clever Debora , Hatz Kathrin , Mombaur Katja
Published: December 2014

Human movement, as for example human gait, can be considered as an optimal realization of some given task. However, the criterion for which the naturally performed human motion is optimal, is generally not known. In this article we formulate an inverse optimal control problem to study the relevance of four different optimization criteria in human locomotion. As a walking model we use an actuated three dimensional spring loaded inverted pendulum (3D‐SLIP), which is able to mirror the typical shape of the center of mass trajectory in human gait. Using a direct all‐at‐once approach, the weighting of the optimization criteria and the position of the footsteps are optimized in such a way, that the center of mass trajectory of the resulting optimal state fits real motion capture data as good as possible. Numerical experiments show, that whereas the so called capture point seems to have a great impact on human walking, minimization of the vertical center of mass movement does not show any relevance at all. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Canonical Wiener–Hopf and spectral factorization of large‐degree matrix polynomials
Authors: Böttcher Albrecht , Halwass Martin
Published: December 2014

We present a novel Newton method for canonical Wiener–Hopf and spectral factorization of matrix polynomials. The initial vector results from solving a block Toeplitz‐like system, and the Jacobi matrix governing the Newton iteration has nice structural and numerical properties. The local quadratic convergence of the method is proved and was tested numerically. For scalar polynomials of degree 20000, a superfast version of the method implemented on a laptop typically reqired about half a minute to produce an initial vector and then performed the Newton iteration within one second. In the matrix case, the method worked reproachless on a laptop with 8 Gigabyte RAM if the degree of the polynomial times the squared matrix dimension did not exceed 20000. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FETI‐DP with different scalings for adaptive coarse spaces
Authors: Klawonn Axel , Radtke Patrick , Rheinbach Oliver
Published: December 2014

An adaptive coarse space for the FETI‐DP domain decomposition method based on generalized eigenvalue problems is presented. For details on the FETI‐DP algorithm, see, e.g., [1]. The method is a variation of a method proposed in [2, 3], where deluxe scaling was used. Here, an extension is presented, which allows several other scalings. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Space–time DG methods for the coupled electro–mechanical activation of the human heart
Authors: Karabelas Elias , Steinbach Olaf
Published: December 2014

We consider the coupled system of time–dependent nonlinear partial differential equations modeling the electromechanical response of human heart tissue. Instead of time–stepping schemes we use a discontinuous Galerkin finite element method in the space–time domain to be able to resolve the solution in space and time simultaneously. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some common properties of certain continual and discrete convolutions
Authors: Vasilyev Alexander , Vasilyev Vladimir
Published: December 2014

We consider discrete analogues of general Calderon–Zygmund operators and study their Fredholm properties in corresponding discrete spaces. We give also a comparison between discrete and continual cases. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards an AD based diagnosis of singularities of DAEs
Authors: Lamour René , Estévez Schwarz Diana
Published: December 2014

The detection of singular points of DAEs is a challenging task, which has not been sufficiently considered so far. Combining automatic differentiation (AD) with the projector based analysis of DAEs, it becomes possible to monitor singularities while integrating the DAE. In this brief outline we restrict our considerations to linear DAEs. The corresponding treatment of nonlinear DAEs is based on linearization and can be found in the cited literature. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of Two Suboptimal Sensor Placement Strategies in Thermo‐Elastic Models
Authors: Herzog Roland , Riedel Ilka
Published: December 2014

We are interested in thermo‐elastic deformations of solid bodies, in particular of machine tools. The goal is to estimate the displacement at a certain point of interest from a few temperature measurements. We present a method to find nearly optimal sensor positions, which allow an accurate and robust estimation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution of large scale parametric eigenvalue problems arising from brake squeal modeling
Authors: Quraishi Sarosh , Schröder Christian , Mehrmann Volker
Published: December 2014

We present a proper orthogonal decomposition (POD) based approach for the accurate solution of parametric eigenvalue problems arising from brake squeal modeling. We compare this approach to a traditional method based on modal decomposition which is very popular in industry. The proposed approach is more accurate than the traditional method especially for parametric studies and for studying non‐proportionally damped systems. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)