bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modelling of cracks on different scales in ferroelectric materials
Authors: Gellmann Roman , Ricoeur Andreas 
Published: December 2011

AbstractIn this work we study contributions to the effective fracture toughness of ferroelectric materials arising from effects on macroscopic and mesoscopic scales of the system. On the macroscopic scale, the crack in a ferroelectric material is modeled taking into account an extended theory of stresses at interfaces in dielectric solids [1‐3]. We predict several new effects, such as the “poling effect”, “collinear effect” and the coupling of a Mode‐II shear loading and the Mode‐I SIF. Further, on the mesoscopic scale, we study the influence of polarization switching limited to the fracture process zone (small scale switching) on the fracture toughness. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A ferroelectric and ferroelastic microscopic switching criterion for tetragonal ferroelectrics
Authors: Keip Marc‐André , Schröder Jörg 
Published: December 2011

AbstractThe present contribution addresses the continuum mechanical modeling of ferroelectric/ferroelastic material behavior from a microscopic point of view. An electric enthalpy function for the representation of tetragonal ferroelectrics will be introduced and combined with an energy based ferroelectric/ferroelastic switching criterion. The result is a microscopically motivated material model for the description of ferroelectric and ferroelastic switching effects in electro‐mechanically coupled solids. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Suppression of Electromagnetically Induced Free‐Surface Instabilities in Liquid Metals
Authors: Minchenya Vitaly , Karcher Christian , Chigarev Anatoly 
Published: December 2011

AbstractThe work presented is devoted to studies of foundations of the suppression techniques for electromagnetically induced instabilities of the free liquid metal surfaces. Such instabilities occur, for instance, in a number of technologies for requested refinement of materials like electron beam evaporation or levitation melting, in which the electromagnetic shaping technique is applied. The instability phenomenon in our case has following magnetohydrodynamic background. High‐frequency magnetic field causes Lorentz force density generation within so‐called skin‐layer in the liquid metal, which works as a surface pressure in turn. With increase of the electromagnetic pressure a destabilizing mechanism progresses within the liquid metal domain, which causes a bifurcation. In this paper we discuss application alternating magnetic fields to increase the bifurcation threshold by passive and active redistribution of the Lorentz force density in the near‐surface layers of the liquid metal domain. A novel stabilization system on the basis of a local electromagnetic influence on the liquid metal surface in the high frequency magnetic field is presented. The experimental results are discussed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fluid‐structure interaction in porous media for loaded filter pleats
Authors: Andrä Heiko , Iliev Oleg , Kabel Matthias , Kirsch Ralf , Lakdawala Zahra , Ricker Sarah 
Published: December 2011

AbstractCurrently, the known simulation efforts with respect to fluid‐structure interaction (FSI) are mainly restricted to the study of flow interacting with deformable solid bodies. On the other hand, there is extensive literature on simulation of flow through porous media. In particular, algorithms and software for CFD simulations of filtration processes in the case of rigid filtration medium were presented earlier by Fraunhofer ITWM, see, e.g., [1, 2]. In these papers the deformation of the solid skeleton is neglected. In many cases of water filtration, filtration for hydraulic applications, and even in certain air filtration regimes, the fluid pressure can be quite high, and the deformation of the pleats can be an issue. The deflection of pleats and its effect on the filtration process merits examination because under operating conditions (and especially after a partial loading of the media) the pleats often cannot be anymore considered as rigid porous media. Therefore, in this paper, the deflection is considered for clean media, as well as for partially loaded media. A new model describing the coupled flow and deformation, and corresponding numerical results are presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Stability Analysis of Decoupled Solution Schemes
Authors: Zinatbakhsh Seyedmohammad , Markert Bernd , Ehlers Wolfgang 
Published: December 2011

AbstractMany problems in engineering, physics or other disciplines require an integrated treatment of coupled fields. These problems are characterised by a dynamic interaction among two or more physically or computationally distinct components, where the undergoing mathematical model commonly consists of a system of coupled PDE. Considerable progress has been made in the development of appropriate computational schemes to solve such coupled PDE systems. These attempts have resulted in various monolithic and decoupled numerical solution approaches. Despite the unconditional stability offered by implicit monolithic solution strategies, their use is not always recommended. The reason mainly lies in the complexity of the resulting system of equations and the limited flexibility in choosing appropriate time integrators for individual components. This has motivated the elaboration of tailored decoupled solution schemes, which follow the idea of splitting the problem into several sub‐problems. But selection of the way of splitting can have a direct influence on the stability of the resulting solution algorithm. This necessitates the stability analysis of such an algorithm.Here, we introduce a general framework for the stability analysis of decoupled solution schemes. The approach is then used to study the stability behaviour of established decoupling strategies applied to typical volume‐ and surface‐coupled problems, namely, coupled problems of thermoelasticity, porous media dynamics and structure‐structure interaction. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material properties of anisotropic materials with pores
Authors: Drach Borys , Tsukrov Igor , Piat Romana , Dietrich Stefan 
Published: December 2011

AbstractAn approach based on cavity compliance contribution tensor is utilized for evaluation of effective stiffness of anisotropic materials with irregularly shaped pores. The shapes considered in the present work were extracted from the X‐ray computed microtomography of a carbon/carbon composite sample. The cavity contribution tensors of individual pores were calculated numerically and then employed in the micromechanical modeling procedure. It was shown that presence of pores with total porosity of p = 9.13% results in approximately 20% reduction in the material's Young's moduli. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and homogenization of textile reinforced composites based on the isogeometric analysis
Authors: Haasemann Georg , Kerber Thomas , Ulbricht Volker 
Published: December 2011

AbstractIn this contribution, the isogeometric analysis is used to compute the effective material properties of textile reinforced composites. The isogeometric analysis based on non‐uniform rational B‐splines (NURBS) provides an efficient approach for numerical modeling because there is no need for a mesh generation. There are further advantages such as the availability of a geometry representation based on NURBS in computer‐aided design software and the possibility to apply different refinement methods which do not change the geometry of the numerical model. These properties motivate the combination of the isogeometric analysis with the homogenization method. Therefor, the unit cell model representing the inner architecture of a textile reinforced composite is defined using NURBS. In order to compute the effective mechanical properties of the heterogeneous material, the homogenization method with periodic boundary conditions is applied. Finally, two examples demonstrate the advantages of this approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Probabilistic homogenization of solid foams
Authors: Hohe Jörg , Beckmann Carla 
Published: December 2011

AbstractThe present study is concerned with a numerical procedure for prediction of uncertainties in the effective properties of solid foams. The approach is based on the multiple homogenization analysis of small‐scale testing volume elements. Their microstructure is defined in terms of random variables with known probability distribution. Using a discretization of the space of the random variables, the probability distribution for the effective properties can easily be determined from the homogenization results and the probability for occurrence of the underlying microstructures of the testing volume elements. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear homogenization of metal‐ceramic composites with lamellar microstructure
Authors: Piat Romana , Sinchuk Yuriy 
Published: December 2011

AbstractUsing nonlinear homogenization methods for the computation of the material response of metal‐ceramic composites with lamellar microstructure is a power approach to do computation less costly in comparison to finite elements modeling. A modified secant homogenization method is utilized in this study for simulation of inelastic behaviors of the composite micro‐constituents. A nonlinear homogenization method is based on a linear homogenization scheme for multilayer composites. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Meso‐Macro Modelling of Coated Forming Tools under Thermal Shock Conditions
Authors: Sauerland Kim‐Henning , Mahnken Rolf 
Published: December 2011

AbstractIn hybrid‐forming processes workpieces are heated up before forming in order to reduce the forming forces. They are innovative methods for the production of components with graded properties, particularly with regard to tailored material properties and geometrical shape. During service life the forming tools are subjected to cyclic thermal shock loading conditions which can result into damage and failure. For improvement of the tool durability in the hybrid‐forming process coated forming tools with multilayered coating systems are considered to be applied in future.This contribution shows the actual state of work for the development of a twoscale FE model for the simulation of the multilayered coated forming tool. Within this model the three‐dimensional model of the forming tool builds the macromodel. On the macrolevel the multilayered coating is discretized with one element over the coating thickness. The mesomodel of the coating considers the actual layer design with metallic and ceramic layers. The macro‐meso transition is realized with a Taylor‐assumption. As the microscale is not considered in our model, the constitutive equations are formulated on the mesoscale. The meso‐macro transition is done using volume averaging procedures. Furthermore, a damage model is included for particular layers. The scalar damage variable is used in a thermo‐mechanical coupled model for simulation of a reduced heat transfer through a partially damaged layer. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stall‐delay modelling of wind turbine blades
Authors: Dumitrescu Horia , Cardos Vladimir 
Published: December 2011

AbstractMost aerodynamic design tools for horizontal‐axial wind turbines are based on the blade‐element momentum theory (BEM). Due to the nature of this theory, the design tools need 2‐D steady sectional lift and drag curves as an input. In practice, flow over a wind turbine rotor blade is neither two‐dimensional nor steady, and is affected by rotation. Pioneering experiments have identified a consequence: at inboard rotor blade sections stall is delayed. This so‐called Himmelskamp effect [1] gives a larger lift than predicted and, as a result, a higher power and loading than expected. Consequently, an aerodynamic model is needed to explain and predict sectional lift and drag under rotating conditions. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimentelle Untersuchung elektroosmotischer Strömungen in Mikrokanälen mit internen Elektroden
Authors: Gizewski Carsten , Moeller Jan , Ehrhard Peter 
Published: December 2011

AbstractIn dieser Arbeit werden elektroosmotische Strömung in einem Mikrokanal mit internen Elektroden untersucht. Es wird das Konzept den Mikrokanals vorgestellt. Die experimentellen Untersuchungen basieren auf dem μPIV‐Vefahren, mit welchem zwei Komponenten des Geschwindigkeitsfeldes im kompletten Kanal gemessen werden können. Unter Verwendung der Kontinuitätsgleichung wird dann die dritte Geschwindigkeitskomponente, und damit das vollständige Geschwindigkeitsfeld, durch numerische Integration rekonstruiert. Die Messungen können damit, ohne Einschränkung, zur Validierung von theoretischen Ergebnissen dienen. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transitional intermittency in a rough wall boundary layer
Authors: Jonáš Pavel , Hladík Ondřej , Mazur Oton , Uruba Václav 
Published: December 2011

AbstractThe transitional intermittency factor distributions were evaluated from the wall friction records acquired in the rough wall boundary layer under free stream turbulence. Important characteristics of by‐pass transition were derived from the factor distributions. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of particles movement in cellular flows under the influence of magnetic forces
Authors: Hriberšek Matjaž , Steinmann Paul , Ravnik Jure , Vogel Franziska 
Published: December 2011

AbstractA numerical model of particle motion in fluid flow under the influence of hydrodynamic and magnetic forces is presented. As computational tool, a flow solver based on the Boundary Element Method is used. The Euler‐Lagrange formulation of multiphase flow is considered. In the case of a particle with a magnetic moment in a nonuniform external magnetic field, the Kelvin body force acts on a single particle. The derived Lagrangian particle tracking algorithm is used for simulation of dilute suspensions of particles in viscous flows taking into account gravity, buoyancy, drag, pressure gradient, added mass and magnetophoretic force. As a benchmark test case the magnetite particle motion in cellular flow field of water is computed with and without the action of the magnetic force. The effect of the Kelvin force on particle motion and separation from the main flow is studied for a predefined magnetic field and different values of magnetic flux density. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Morphing of Flying Configuration Using Spanwise Movable Leading Edge Flaps, in Supersonic Flow
Authors: Nastase Adriana 
Published: December 2011

AbstractThe computation of the flow over flattened wing‐fuselage flying configuration (FC) with movable leading edge flaps in spanwise direction is here considered. Hyperbolical potential solutions are given in closed form and are used for the determination of hybrid solutions for the Navier‐Stokes layer, over this FC with the flaps in retracted and in open position. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Investigation of Dense Turbulent Sprays with an Eulerian Approach and DQMOM
Authors: Gumprich Werner , Sadiki Amsini , Sommerfeld Martin 
Published: December 2011

AbstractThe spray characteristics of the injected liquid fuel predominantly influence the combustion and emissions in IC‐engines and gas turbines. This is predetermined by a dense spray region in which droplet‐droplet interaction processes play a significant role. In order to accurately describe and control the dense spray behavior in modern engines, an appropriate numerical modeling tool is needed. This contribution aims at including droplet‐droplet interactions into an Eulerian approach coupled to the Direct Quadrature Method of Moments (DQMOM) in order to describe evaporating droplet polydispersity and analyze dense turbulent sprays phenomena. Among the advantages of the Eulerian approach are a lower computational cost through optimal parallel computing and a straightforward liquid‐gas phase coupling. To assess the designed tool, numerical results are compared to Phase Doppler Anemometry (PDA) measurements of a hollow‐cone water spray. The experiment provides comprehensive validation data that include gas velocities, droplet size distribution, droplet mass fluxes and droplet velocities. Turbulence is captured by two different k‐ε based models. Preliminary results show that the designed tool is able to capture the process under study in a satisfactory way. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Small‐scale mixing at the turbulent/non‐turbulent interface in turbulent jets
Authors: Steiner Helfried , Walchshofer Christian 
Published: December 2011

AbstractThe numerical simulation of the turbulent mixing between the turbulent core flow region and the non‐turbulent irrotational ambient region requires a reliable modelling of the mass and momentum transfer in the intermittent zone. The dominant role of the small‐scale whirling motion in the turbulent entrainment process particularly challenges the subgrid‐scale (SGS) modelling in Large‐Eddy Simulation (LES). The present work carried out a Direct Numerical Simulation (DNS) of a round jet to analyze the scalar mixing conditions near the turbulent/non‐turbulent interface. The obtained statistical results widely confirm existing experimental and analytical findings made in previous studies on the momentum transfer. An a priori test of the DNS data reveals the limits of the standard Smagorinsky‐type SGS‐model for the eddy diffusivity in the description of the subgrid‐scale mixing near the interface. The extension to a dynamic SGS‐model using non‐constant, flow dependent model coefficients does not lead to a substantial improvement. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Study on the Influence of Particle Inertia in Particle‐Driven Gravity Currents
Authors: Häuselmann Oliver , Henniger Rolf , Kleiser Leonhard 
Published: December 2011

AbstractWe present two‐dimensional numerical simulations of particle‐driven gravity currents in a lock‐exchange configuration. The fluid is described in an Eulerian framework, whereas the particles are tracked in a Lagrangian manner. The study is restricted to dilute suspensions, allowing to neglect particle‐particle interactions. The particle forces considered are buoyancy and the Stokes drag. We study the influence of particle inertia on the flow evolution by performing simulations with different Stokes numbers. We also consider the case where particle inertia is neglected. Generally, we observe significant changes in the form and structure of the gravity current with increasing particle Stokes numbers. Particularly, the formation of Kelvin‐Helmholtz vortices is more and more suppressed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of Lamb waves with Spectral Finite Elements
Authors: Bumb Andreas , Lammering Rolf , Hennings Bianca 
Published: December 2011

AbstractFor the analysis of the elastic wave propagation at high frequencies, the spectral finite element method (SFEM) is under investigation. The SFEM uses high‐order shape functions which are composed of Lagrange polynomials with nodes at the Gauss‐Lobatto quadrature points. In this way we obtain a diagonal mass matrix which makes an explicit time scheme more efficient. In a numerical example a computation by Montjoie of an elastic wave propagation within a Reissner‐Mindlin (RM) model is presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Increasing the scanning range of Lamb wave based SHM systems by optimizing the sensor design and excitation frequency
Authors: Duczek Sascha , Willberg Christian , Gabbert Ulrich 
Published: December 2011

AbstractThe objective of the paper is to investigate and to optimize parameters which effect the excitation of Lamb waves generated by adhesively bonded piezoceramic actuators. Particularly, the influence of the adhesive layer and the resonances of the actuator are examined both numerically and experimentally. Understanding these properties helps to develop energy efficient structural health monitoring (SHM) systems, meaning that less energy is needed to excite waves with the same scanning range.Knowing the main influence parameters a numerical optimization is proposed, which is aimed at increasing the range of the excited waves by optimizing the sensor geometry and the excitation frequency. Various tests with different test specimens have been performed. An evolutionary based algorithm is used to find the optimal configuration. It has been found that small changes in the geometry and an optimized excitation frequency elevate the amplitudes of the signal measured with a piezoelectric transducer significantly. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inhomogeneous Plane Waves in Monoclinic Crystals subject to a Bias
Authors: Simionescu‐Panait Robin Olivian 
Published: December 2011

AbstractHere we investigate the conditions of inhomogeneous plane waves propagation in monoclinic crystals subject to initial electromechanical fields. We obtain the components of the electroacoustic tensor for the class 2, resp. m, of the monoclinic system. For particular isotropic directional bivectors we derive the decomposition of the propagation condition, and we show that the specific coefficients are similar to the case of guided wave propagation in monoclinic crystals subject to a bias. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electromagnetic flow rate measurement in turbulent liquid metal channel flow
Authors: Jian Dandan , Karcher Christian 
Published: December 2011

AbstractFlow control in hot aggressive melts is a big challenge for metallurgical and glass technology applications. For instance, during the production of float glass, the glass melt solidifies on the top of a liquid tin bath. To achieve a spatially homogeneous glass thickness, both global and local control of the thermofluiddynamic transport phenomena in the tin bath are crucial. The concept a global flow control involves the coupling of the non‐contact electromagnetic flow rate measurement technique of Lorentz force velocimetry and the non‐contact flow driving technique of electromagnetic pumps based on rotating permanent magnets. The paper presents a model experiment using the low‐melting test melt GaInSn as well as numerical simulations using the commercial code FLUENT/MHD. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electromagnetic interaction of moving conductors with magnets: kinematic solutions for infinitely long square and cylindrical geometries
Authors: Kirpo Maksims , Boeck Thomas , Thess André 
Published: December 2011

AbstractThe electromagnetic drag force on a point dipole near a moving conductor caused by the induced electric currents is investigated by numerical and analytical computations. Our focus is on prototypical configurations for Lorentz force velocimetry, i.e. velocity measurement from the electromagnetic drag force on the dipole. We examine the particular cases of conducting infinite bars of square or round cross‐section, which are moving with constant velocity in the field of arbitrary oriented magnetic dipole. In addition, we study the laminar liquid‐metal flow in a square duct. The motion of the conductor is prescribed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)