bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of persistent slip band‐structures during cyclic loading in finite‐strain crystal plasticity
Authors: Kochmann Dennis M. , Hackl Klaus
Published: November 2010

Cyclic loading of single‐ and polycrystals gives rise to complex structures and patterns on the material's microscale, which highly affect the macroscopic stress‐strain response. The formation of microstructures in finite‐strain crystal plasticity has been reasoned to stem from the non‐quasiconvexity of the underlying energetic potentials. As a consequence of such a lack of convexity, the material reduces its energy by breaking up into fine‐scale fluctuations of minimizing sequences, which correspond to the experimentally observed microstructures. Based on an incremental setting and relaxed potentials, we describe the formation and the time‐continuous evolution of laminate structures during cyclic loading. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vergleich zweier Ansätze zur Beschreibung nichtlinearer Viskoelastizität auf Basis des Maxwell‐Elements
Authors: Landgraf Ralf , Ihlemann Jörn
Published: November 2010

Viele Werkstoffe, wie Kunststoffe oder Elastomere, zeigen viskoelastisches Materialverhalten. Der Ansatz zur Modellierung dieses Materialverhaltens kann mit Hilfe sogenannter rheologischer Ersatzmodelle veranschaulicht werden, wobei ein wichtiger Bestandteil das Maxwell‐Element ist. Da die genannten Werkstoffe zum Teil großen Deformationen unterzogen werden, ist eine Modellierung des gesamten Materialverhaltens und somit auch des Verhaltens eines einzelnen Maxwell‐Elementes im Rahmen der nichtlinearen Kontinuumsmechanik durchzuführen. Es werden nunmehr zwei aus der Literatur bekannte Formulierungsvarianten für die kontinuumsmechanische Beschreibung des Materialverhaltens entsprechend eines Maxwell‐Elementes verglichen. Zunächst werden beide Modelle in einer ideal inkompressiblen Formulierung derart hergeleitet, dass sich bei einem Grenzübergang zur linearen Theorie identische Beziehungen ergeben. Weiterhin erfolgt eine Darstellung der numerischen Umsetzung sowie der Ergebnisse aus numerischen Untersuchungen unter homogenen Belastungen. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary value problems of the theory of viscoelasticity for Kelvin‐Voight materials
Authors: Svanadze Maia M.
Published: November 2010

In this paper, the classical Kelvin‐Voight model of the linear theory of viscoelasticity is considered and the following results are obtained: the fundamental solution of the equation of steady vibrations is constructed, the basic properties of plane waves and elastopotentials are established, the uniqueness theorem of the internal and external boundary value problems (BVPs) are proved, the existence theorems for classical solutions of the BVPs by means of the potential method and the theory of two‐dimensional singular integral equations are proved. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the plane non‐stationary heat transfer in two‐phase hollow cylinder with radially graded material properties
Authors: Ostrowski Piotr
Published: November 2010

This consideration concerns heat transfer in two‐component composite with a deterministic microstructure, which is ‐periodic along the angular axis and has slowly varying effective properties in the radial direction (Fig.1). Therefore, we deal here with a special case of functionally graded materials, FGM, c.f. Suresh, Mortensen (1998). The main aim of this consideration is to capture effect of the discontinuous boundary conditions on the thermal field. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A micro‐sphere approach applied to the modelling of phase‐transformations
Authors: Ostwald Richard , Bartel Thorsten , Menzel Andreas
Published: November 2010

We present an efficient model for the simulation of phase‐transformations in polycrystalline materials. As a basis, we use a thermodynamically consistent, one‐dimensional phase‐transformation model, which is embedded into a micro‐sphere formulation in order to be able to simulate three‐dimensional boundary value problems. The underlying evolution equations are solved efficiently using a newly developed explicit integration scheme that has been proved to be unconditionally A‐stable. A numerical example by means of a deformation in simple shear is additionally provided in this contribution. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermoviscoplasticity of Glassy Polymers in the Logarithmic Strain Space Based on the Free Volume Theory
Authors: Schänzel Lisa‐Marie , Miehe Christian
Published: November 2010

In this contribution a new constitutive model of finite thermo‐visco‐plastic behavior of amorphous glassy polymers and details of its numerical implementation are outlined. In contrast to existing kinematical approaches to finite plasticity of glassy polymers, the formulation applies a plastic metric theory based on an additive split of Lagrangian Hencky‐type strains into elastic and plastic parts [1, 3]. The characteristic strain hardening of the model is derived from a polymer network model, the thermo‐visco‐plastic flow rule in the logarithmic strain space uses structures of the free volume flow theory [4]. The integration of this micromechanically motivated approach in a three‐dimensional computational model is the key novel aspect of this work. An important aspect of this work is the model validation based on experimental findings, whereas the excellent performance of the proposed formulation is demonstrated by means of numerical examples. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of thermo‐mechanical loading processes on amorphous thermoplastic polymers
Authors: Müller Susanne , Hempel Philipp , Seelig Thomas
Published: November 2010

A constitutive model for the thermo‐mechanical behavior of amorphous thermoplastic polymers is presented that accounts for the dependence of the macromolecular network and entropic hardening on large temperature changes. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Are plastic yielding and work hardening sensitive to the boundary conditions?
Authors: Le Khanh Chau , Sembiring Pramio
Published: November 2010

The plane strain shear of a single crystal strip with one active slip system placed in a mixed device with one clamped and one free boundary is considered. Since dislocations pile up against only the clamped boundary, the plastic yielding and work hardening differ essentially from those of a hard device, showing clearly their sensitivity to the boundary conditions. An analytical solution to this problem within continuum dislocation theory is found explicitly which exhibits the energetic and dissipative thresholds for dislocation nucleation, the Bauschinger translational work hardening, and the size effects. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Explicit solution of the boundary value problems of the theory of elasticity for solids with double porosity
Authors: Tsagareli Ivane , Svanadze Maia M.
Published: November 2010

In this paper the Aifantis' theory of elasticity for solids with double porosity is considered and the 2D boundary value problem (BVP) of static is investigated. The uniqueness theorem of the internal BVP is proved. The explicit solution the BVP is constructed in the form of absolutely and uniform convergent series for a circle. The numerical solution of the BVP for a circle is obtained. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Anisotropic multiplicative elastoplasticity for the prediction of earings in sheet forming
Authors: Vladimirov Ivaylo N. , Schwarze Marco , Reese Stefanie
Published: November 2010

In this work, the simulation of earings in cup drawing by means of a recently developed anisotropic combined hardening material model is discussed. The model represents a multiplicative formulation of anisotropic elastoplasticity in the finite strain regime with nonlinear kinematic and isotropic hardening. Plastic anisotropy is described by the use of second‐order structure tensors as additional arguments in the representation of the yield function and the plastic flow rule. The evolution equations are integrated by a form of the exponential map that preserves the plastic volume and the symmetry of the internal variables. Finite element simulations of cylindrical cup drawing processes are performed by means of ABAQUS/Standard where the discussed material model has been implemented into a user‐defined reduced integration solid‐shell element. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro‐Mechanical Modelling of Anisotropic Time‐Dependent Healing Effects in Rubber‐like Materials
Authors: Weinhold Georg W. , Itskov Mikhail
Published: November 2010

Filler‐reinforced rubber‐like materials demonstrate deformation induced softening, known as the Mullins effect. This softening can be reversible in a certain range (healing).

The previously introduced concept of network evolution (NE) explains the Mullins effect as the result of a filler‐polymer network rearrangement [1]. It is assumed that debonding of polymer chain segments from rigid aggregates does not effect the number of active segments. Furthermore, debonded chains are still active as a part of a longer chain.

Now, considering the entropic vibration of polymer chains, entanglement of chains to the rough aggregate surfaces is assumed. This process inverse to the NE leads to a micro‐mechanical model of time‐dependent recovery of the deformation induced softening. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FEM Simulation of a Micromechanical Model for Textured Polycrystalline Shape Memory Alloys with n‐Variants
Authors: Wilmanns Stefan , Mahnken Rolf
Published: November 2010

This paper is about the numerical implementation of a known, but advanced model with a projected Newton algorithm and a residual including only two vectors of unknowns. In a complex stress driven example the superelastic behavior is investigated. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Die Nanoindentation als Instrument zur Bestimmung materialspezifischer Kennwerte als Funktion der Temperatur
Authors: Müller Wolfgang H. , Worrack Holger
Published: November 2010

Neben mechanischen Beanspruchungen sind mikroelektronische Bauteile stets einer wechselnden thermischen Belastung ausgesetzt. Für die Gewährleistung zuverlässiger Fügeverbindungen ist daher die Kenntnis der materialspezifischen Kennwerte der Fügewerkstoffe in Abhängigkeit der Temperatur zwingend erforderlich. Die Nanoindentation erlaubt es aus einem Härteversuch Härte, Elastizitätsmodul und Fließgrenze der Probenmaterialien zu ermitteln. Eine zusätzliche HOTSTAGE‐Erweiterung ermöglicht zudem Messungen zwischen Raumtemperatur und +500°C. Neben dem Kalibrierwerkstoff Fused Silica und einem Kupferwerkstoff wurden verschiedene bleifreie Lote indentiert. Während bei Quarz und Kupfer die Entlastungskurve nahezu ideal verläuft und die implementierte Auswertesoftware korrekte Werte berechnet, neigen die Lotmaterialien bei steigenden Temperaturen zum Kriechen und die automatisierte Bestimmung der Materialkonstanten gestaltet sich somit schwierig. Diesem Problem versucht man sich nun mit einem viskoelastischen Materialmodel anzunähern. Ziel ist es dabei aus dem Kriechverhalten viskoelastische Parameter zu berechnen, die dann wiederum benutzt werden sollen, um die materialspezifischen Kennwerte bestimmen zu können. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gradient Plasticity for Single Crystals
Authors: Wulfinghoff Stephan , Böhlke Thomas
Published: November 2010

The kinematic relationship between classical single crystal kinematics and geometrically necessary dislocations will be clarified by a demonstrative example. The starting point for the dynamics is the contribution of geometrically necessary dislocations to the free energy, which leads to a kinematic hardening law. A simple two‐dimensional shear example will be discussed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of a steady flow guided by flexible walls
Authors: Bach Karolina , Hetzler Hartmut , Seemann Wolfgang
Published: November 2010

Flexible channels conveying fluid may loose stability by divergence or flutter, thus leading to undesirable dynamic behaviour. A lot of investigations have already been done on this subject, each involving structural models expressing a specific type of stiffness. The aim of this contribution is to investigate and compare systematically the influence of various types of structural stiffness on the stability behaviour of the coupled problem. Therefore, a simple, yet general model is built. The fluid is bounded by a rigid and an elastical supported, flexible wall, which exhibits bending and extensional stiffness and considers effects of pre‐load. The influence of the various characteristics on the stability of the steady state is discussed and a perturbation approach is used to investigate the influence of small nonlinearities. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Execution of active reduction of vibrations by means of kinematic excitations
Authors: Białas Katarzyna
Published: November 2010

The major objective of this study is to show how to carry out the process of structural and parametrical synthesis that is understood as a method intended to seek for the structure and parameters of a discrete model of the system with active suppression of vibrations. Active components are implemented as mechanical components with kinematic excitations. The other objective is to analyze how the active subsystem interacts with the overall investigated structure. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of freeze‐thaw‐cycles in liquid‐ and gas saturated porous media
Authors: Bluhm Joachim , Ricken Tim , Bloßfeld Wolfgang Moritz
Published: November 2010

In this contribution, a quadruple macroscopic model for the simulation of freeze‐thaw cycles in liquid‐ and gas filled porous media is presented. In effect, this model describes the following aspects: expansion of ice during freezing, liquid and gas pressure on the surrounding surfaces, capillary effecs, temperature distribution, and the influence of filter velocities. The main focus lies in the description of capillary effects before and during the phase transition. The illustrated results of the numerical example show that the simplified model is capable of predicting physical and experimental observations. Besides the influence of the heat of fusion, especially, the capillary suction in liquid‐ and gas filled porous media will be presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transformated Hypergraphs in Synthesis of Vibrating Beam‐Systems
Authors: Buchacz Andrzej
Published: November 2010

In this paper the characteristics of subsystems obtained by the approximate and exact method were compared, because purpose is to answer to the question ­ if the method can be used to nominate the characteristics of mechatronic systems. In this paper frequency‐modal analysis have been presented for the mechanical system, that means flexibly vibrating free beam. The model of the beam was presented in the five‐vertex hypergraph, which in case of approximate frequency‐modal analysis we can imitate in three‐vertex hypergraph. Such formulation maybe the introduction to synthesis of flexibly vibration complex beam systems with constant cross‐section. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mathematical and physical aspect of the solution to the Lamb's problem for nonlocal visco‐thermo‐elastic medium
Authors: Gawinecki Jerzy August , Rafa Józef , Łazuka Jarosław
Published: November 2010

In our paper we constructed the solution of the initial‐boundary value problem so‐called Lamb's problem for the half space occupied with visco‐thermo‐elastic medium. The visco‐elastic medium was described by Biot model, where the thermal influencely by Gurtin and Pipkin model. Using the Cagniard de Hoop method we obtained the solution of the Lamb's problem to the considered system of integro‐differential equations. Based on the constructed solution of the above mentioned problem, we described the type of waves which propagate in the visco‐thermo‐elastic medium and the domain of their influence. The propagation of the Rayleigh's wave were investigated. We discovered the new Rayleigh's wave in visco‐thermo‐elastic medium (second Rayleigh's wave) and named it GRL‐wave (Gawinecki‐Rafa‐Łazuka ‐ wave). Finally, we determined the exact geometric description of new kind of waves in visco‐thermo‐elastic medium:

• cone waves (Schmidt's type)

• surface waves of the Rayleigh's type (among theim new one) and the character of their origin. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pseudoelasticity of Shape Memory Alloys ‐ a 1D Material Model and Finite Element Implementation
Authors: Kohlhaas Benedikt , Klinkel Sven
Published: November 2010

This contribution is concerned with the formulation of a 1D‐constitutive model accounting for the pseudoelastic behavior of shape memory alloys. The stress‐strain‐relationship is idealized by a hysteresis both in the compression as in the tension loading range. It is characterized by an upper loading path, which is to be ascribed to the transformation of the lattice to a martensitic structure. Unloading the material, a lower path is described, because of the reverse transformation into austenitic lattice. The constitutive model is based on a switching criterion which serves as a potential function for the evolution of the internal state variables. The model distinguishes between local and global variables to describe the hysteresis effects for the compression and tension range. A strain driven algorithm which captures the complete nonlinear material behavior is presented. The boundary value problem is solved for a truss element applying the finite element method. A consistent linearization of the nonlinear equations is derived. Simple examples will demonstrate the applicability of the proposed model. For future developments the usage of shape memory alloys within civil engineering structures is aimed. The advantage of the material is the very good damping behavior and the potential to overcome great strains. Both properties are distinguished to be of engineering interest. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zero Leakage Sealings for Reciprocating Compressors
Authors: Kotesovec Bernhard , Steinrück Herbert
Published: November 2010

The piston rod of a reciprocating compressor is sealed with elastic cylindrical sealing elements. Across the sealings the pressure drops from the operating pressure to the ambient pressure. The lubrication gap between the elastic sealing and reciprocating piston rod is studied with the aim to find conditions of a leakage free sealing. The flow in the lubrication gap and the elastic deformation of the sealing are determined simultaneously. The netflow during one cycle of the reciprocating piston rod is calculated. It turns out that maintaining zero leakage is very sensible. Indeed the outbound flow during out‐stroke has to be equal the inbound flow during the instroke. By prescribing a special shape of the undeformed sealing zero leakage can be attained — at least theoretically for certain operating conditions. It turns out that temperature dependent material data and a model for cavitation is necessary. The model, its numerical implementation and results will be discussed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The exact and approximate method in mechanical system's analysis
Authors: Buchacz Andrzej , Płaczek Marek
Published: November 2010

The main aim of this work is to present results of the mechanical system's analysis based on the exact and approximate Galerkin's methods. The considered system is the flexural vibrating one‐dimension bending beam. The exact and approximate method were used to assign the dynamic flexibility of the considered system and results of this work were juxtaposed to verify the approximate method's accuracy. The correction coefficients were introduced into the approximate method to unify results of both methods. The aim of this work was to check accuracy of the approximate method and to verify if this method may be used to mechatronic system's analysis, where it is impossible to use the exact method. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effective computational methods for the solution of ferroelectroelastic problems under complex loading
Authors: Semenov Artem S. , Liskowsky Albrecht C. , Neumeister Peter , Balke Herbert
Published: November 2010

Enhanced numerical methods for the solution of three‐dimensional nonlinear electromechanically coupled boundary value problems are considered. A vector potential finite element formulation with return mapping algorithm and consistent tangent operator is developed. The accuracy and robustness of the algorithms are assessed with the help of numerical examples concerning a ferroelectroelastic analysis of structures under complex multiaxial non‐proportional loading. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the General Solution of Coupled Problems: Comparison of Monolithic and Partitioning Approaches
Authors: Zinatbakhsh Seyedmohammad , Markert Bernd , Ehlers Wolfgang
Published: November 2010

Coupled systems arise whenever there is a dynamic interaction between two or more functionally distinct components. The mathematical model for such a phenomenon consists of a system of coupled partial differential equations (PDE) in space and time, that has to be solved, either analytically or numerically, in order to describe or predict the response of the system under specific conditions. In spite of the natural accuracy of the analytical methods, they are less favourable due to their disability to treat more complex problems. Instead, different numerical schemes have been developed during the last decades, which are specialised to solve various coupled problems. These methods can be divided into two main categories, namely,monolithicandpartitionedapproaches. The main goal of this work is to study the general ideas behind monolithic and partitioned solution schemes for the pure differentially coupled systems. In the next step, the coupled problem of linear thermoelasticity is considered as benchmark example and theisothermalandisentropicoperator‐splitting schemes as two typical decoupling methods for this problem are presented. A canonical initial boundary‐value problem has also been solved monolithically as well as by using the a.m. operator‐splitting schemes and using the acquired results, the efficiency and stability of the methods are compared. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zur Homogenisierung mechanischer Materialparameter in heterogenen Lotwerkstoffen
Authors: Müller Wolfgang H. , Brandmair Andreas
Published: November 2010

In der Mikroelektronik spielen die Gruppe der Lotwerkstoffe eine wichtige Rolle. Sie stellen zwischen einzelnen Komponenten, wie beispielsweise Chip und Platine, nicht nur die elektronische, sondern auch die mechanische Verbindung her. Ihre Stabilität ist deshalb zur Lebensdauervorhersage mikroelektronischer Bauteile von besonderer Bedeutung. Die unterschiedlichen verwendeten Legierungen weisen dabei eine gemeinsame Charakteristik in ihrem Alterungsprozess auf. Die Mikrostruktur ändert sich aufgrund von Entmischung und nachfolgender Vergröberung. Da die eingesetzten Materialmengen meist sehr gering sind, ist eine Änderung der Mikrostruktur bei der Zuverlässigkeitsvorhersage nicht zu vernachlässigen. Von besonderem Interesse ist deshalb, die unterschiedlichen Größenskalen zu berücksichtigen, insbesondere wie sich die mikrostrukturelle Änderung auf die makroskopischen Materialparameter auswirkt. Da eine exakte Simulation der sich zeitlich ändernden Strukturen zu großen Problemen bei Netzerstellung und Modellierung führt, wird eine Homogenisierung der benötigten Materialeigenschaften durchgeführt. Die so erhaltenen effektiven Materialparameter sollen das reale Werkstoffverhalten möglichst genau wiedergeben und so einfache Simulationen zur Festigkeitsanalyse ermöglichen. Zunächst wird eine Methode vorgestellt, aufgrund äquivalenter Formänderungsenergie die elastischen Konstanten eines komplett anisotropen Lotwerkstoffes zu bestimmen. Dabei kommen finite Elemente, gekoppelt mit einem Generator unterschiedlich entmischter Strukturen zum Einsatz. Von besonderem Interesse ist dabei die zeitliche Entwicklung der homogenen Materialparameter. Weiterhin wird ein Ausblick gegeben, wie die Homogenisierung plastischer und viskoser Materialparameter durchgeführt werden kann. Insbesondere wird darauf eingegangen, welche Parameter zur Zuverlässigkeitsanalyse heterogener Lotwerkstoffe besonders relevant sind. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of Cosserat material parameters obtained by homogenization of a Cauchy continuum
Authors: Branke Dominik , Brummund J. , Haasemann G. , Ulbricht V.
Published: November 2010

If a higher order continuum theory is used in a numerical simulation, the material parameters have to be derived. The experimental determination is laborious and sometimes impossible. Alternatively homogenization methods can be used for the numerical identification of overall material parameters. A short introduction to the micropolar continuum and the homogenization approach is followed by the discussion of the identified properties. Therefore some parameter studies are presented. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A non‐conforming finite element for limit analysis of periodic composites
Authors: Chen M. , Hachemi A. , Weichert D.
Published: November 2010

In this work, a non‐conforming three‐dimensional finite element coupled with direct methods and homogenization technique is presented for the limit analysis of periodic metal‐matrix composites. Using this element, which is constructed from bilinear shape functions and enriched by internal second‐order polynomials, limit analysis of composite material can be efficiently carried out. Accuracy and overall performance are illustrated through comparison with different structural solid elements in the context of direct as well as incremental methods. It is shown that the limit domain of periodic composites for different fiber distributions and volume fractions provides a foundation for the structural design. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical modelling and two‐scale simulation of epoxy/glass composites with interphases and interfaces
Authors: Fleischhauer Robert , Dal Hüsnü , Kaliske Michael
Published: November 2010

Composite systems consisting of glass fibres and epoxy matrix with interphases and interfaces will be considered in the modelling approach. The interphase forms the transition zone between the epoxy matrix and the glass fibre. The interface is the layer between the glass fibre and the surrounding interphase. The macroscopic strength of the composite material is intrinsically related to the bond strength of the polymeric/solid interface and the micromechanical characteristics of the three phases (epoxy, glass and interphase). Homogenization is an appropriate methodology to link these two scales to predict the overall physical behaviour of the composite. The nonlinear behaviour of amorphous polymers, cohesive interface elements and the elastic behaviour of glass fibres as part of the considered composite material are presented, as well as a representative example to show the necessity of taking interface influences into account. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Homogenization of Piezoelectric Materials using FE2
Authors: Khalaquzzaman Md. , Ricker Sarah , Müller Ralf
Published: November 2010

Due to the growing interest in determining the macroscopic material response of inhomogeneous materials, computational methods are becoming increasingly concerned with the application of homogenization techniques. In this work, two‐scale classical (first‐order) homogenization of electro‐mechanically coupled problems using a FE2‐approach is discussed. We explicitly formulated the homogenized coefficients of the elastic, piezoelectric and dielectric tensors for small strain as well as the homogenized remanent strain and remanent polarization. The homogenization of the coupled problem is done using different representative volume elements (RVEs), which capture the microstructure of the inhomogeneous material, to represent the macro material response. Later this technique is used to determine the macroscopic and microscopic configurational forces on certain defects. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acoustic Band Structures and Homogenization of Periodic Elastic Media
Authors: Stadler Michael , Schanz Martin
Published: November 2010

Dispersion curves and frequency dependent velocity surfaces of periodic heterogeneous elastic media are determined from unit‐cell problems using quasi periodic boundary conditions. Effective material parameters are obtained using a least square optimization of the phase velocities in the heterogeneous and the effective, generally anisotropic, homogeneous medium. For efficiency, a preconditioned iterative eigenvalue solver and a model order reduction scheme are used. This “dynamic” homogenization procedure is validated for frequencies below the first stop band employing FEM calculations on a finite structure consisting of an array of unit‐cells and the effective homogeneous material. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of homogenized diffusion properties in micro‐cracked porous materials
Authors: Timothy Jithender Jaswant , Kruschwitz Jens , Meschke Günther
Published: November 2010

Methods of micromechanics [2, 3] are used to obtain homogenized diffusion properties for intact and micro‐cracked porous materials. A two scale homogenization technique is proposed. A REVuc that represents the porous microstructure is modelled as a spherical pore‐space inclusion in a matrix, whose diffusion coefficient does not depend on the microstructure geometry but only on the porosity. For cracked porous materials, a REVc is modelled with the diffusion coefficient for intact porous materials as the matrix phase with ellipsoidal inclusions representing micro‐cracks. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spreading of Gas from a Line Source in the Flow over Two‐dimensional Hill
Authors: Antos Pavel , Mazur Oton , Uruba Vaclav
Published: November 2010

Flow around the two‐dimensional hill is of great interest in engineering application, namely in transport and dispersion of pollutants in atmosphere. A case of polynomial shaped 2D hill with the line source of tracer gas has been studied in detail. Experimental study of both, the time‐averaged velocity field and the binary‐mixture concentration field has been done. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parallel Simulation of a Compressible Jet Including Nozzle Modelling
Authors: Bühler S. , Luginsland T. , Obrist D. , Kleiser L.
Published: November 2010

Circular jet flows play an important role for many technical applications. Realistic simulations of such flows require modelling of the nozzle geometry to represent the turbulent state of the boundary layer at the nozzle exit. An available high‐order finite‐difference code for solving the compressible Navier‐Stokes equations on a cylindrical grid was adapted to account for the nozzle geometry within the simulation domain. The code was parallelized using the message‐passing interface MPI to be able to complete the simulations within acceptable turn‐around times. Validation of the implementation was performed by checking the convergence behaviour of the spatial discretization schemes. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of shear and normal forces in standard and shear flow sequencing batch reactor (SF‐SBR)
Authors: Mansour Hussam , Kowalczyk Wojciech
Published: November 2010

The purpose of this contribution is to compare the shear and the normal stresses in two different types of bioreactors. In the first one (SBR), the granules are generated by liquid and bubbles flow, whereas in the second one (SF‐SBR), the shear rate is achieved by installing a rotating cylinder inside the reactor. Such shear flow can be applied for anaerobic process in the wastewater treatment. The results demonstrate the effective role of the process parameters and the reactor geometry on the shear and normal stresses and consequently on the granulation process. Hereby, the different tendencies of the velocity fields, the particle sedimentation as well as Taylor vortices in (SF‐SBR), are observed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Significance of Truckenbrodt's Energy and Momentum Coefficients for Loss Calculation in Ramified Pipe Systems
Authors: Niessner Herbert , Codan Ennio
Published: November 2010

For one‐dimensional simulation of flow in ramified pipe systems loss prediction in junctions is essential. In the standard literature (e.g. [1]) total pressure loss coefficients serve this purpose. Elementary formulas follow from the principle of momentum and some simple assumptions [2]. They yield rather crude estimates, often twice as large as experimental values. Modifications described by Idelchik [3] look nice, but after all turn out to be not more accurate. We explain deviations and propose improved loss formula based on Truckenbrodt's energy and momentum coefficients [4], thus paying regard to velocity distributions over pipe cross‐sections. We further discuss extraction of the coefficient's values from experiments. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental investigation of the particle‐wall‐impact under particular consideration of the wall surface influence on the particle trajectory and the transition between sliding and adhering impact
Authors: Schade Klaus‐Peter , Wozniak Günter
Published: November 2010

We present results of the experimental investigation of the impact of particles on a rough wall. The particle‐wall impact influences considerably the behavior of particle laden gas flows. The aim of the present work is to study the influence of the wall roughness on the particle trajectory and the particle rotation after impact. The measurements were carried out in a special test facility, which allows the investigation of single particle‐wall impacts. Particle velocities and trajectories were recorded by a video system and evaluated by using a particle tracking technique. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lateral Vortex Dynamics behind Ahmed body
Authors: Uruba Vaclav
Published: November 2010

The flow‐field in the wake of Ahmed body was studied experimentally. The study is oriented on unsteady behavior of the lateral vortex pair arising in the wake as well as on the wake itself. The time‐mean characteristics of the wake flow are presented. The dynamical behavior of the longitudinal vortex pair is studied in details. The Stereo Time‐Resolved PIV method was applied in the wake plane perpendicular to the mean flow. Two variants of Ahmed Body with slat angle 25 and 35 degrees are investigated respectively. Comparison shows considerable differences in the vortex pair topology and dynamics of the cases in question. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Meshless Boundary Method for Computation of Stokes Flow with Particles in the Semicircular Canals of the Inner Ear
Authors: Boselli Francesco , Obrist Dominik , Kleiser Leonhard
Published: November 2010

Benign paroxismal positional vertigo (BPPV) is modeled by introducing free‐floating particles (canaliths) which settle inside the semicircular canals (SCC). The Stokes flow induced by a canalith is evaluated by coupling the force coupling method (FCM) to the method of fundamental solutions (MFS). The proposed methodology results in a straightforward meshless boundary method for the simulation of bounded Stokes flow with finite‐size particles. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Active Control of Separating Boundary Layer
Authors: Florin Frunzulica , Alexandru Dumitrache , Horia Dumitrescu , Octavian Preotu
Published: November 2010

Flow control refers to the ability to alter flows with the aim of achieving a desired effect: examples include drag reduction, noise attenuation, improved mixing or increased combustion efficiency among many other industrial applications. The reduction and control of the viscous drag force exerted on bodies moving in a fluid is of great technical interest. Several active and passive methods to achieve a delay of separation in the boundary layer have been developed and are being developed. In this paper we present a new concept for boundary layer separation control that is based on the synthetic jet concept which converts acoustic oscillations into mean fluid motions. We use synthetic jets as methods for Coanda effect's amplification. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation and analysis of molten flow in the shot sleeve of die casting process
Authors: Laouar Roudouane , Wünsch Olaf
Published: November 2010

This work presents a numerical study of the flow of molten metal in the shot sleeve of horizontal high‐pressure die casting machine during the injection process. The analysis of the wave of the molten metal created by plunger motion can be of help in reducing porosity in manufactured parts caused by air entrapment. The used numerical model, which considers the problem as two‐dimensional, is based on the conservation equations of mass and momentum. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the intrinsic permeability of aluminium foam — Measurements and analytical calculation
Authors: Liebl Christoph , Lion Alexander
Published: November 2010

A measuring system for the determination of the intrinsic permeability of highly porous materials is presented. The evaluation of the measurements is conducted on the basis of the Theory of Porous Media (TPM). By adjusting the calculation to the measurement results achieved with polyethylenglycol (PEG) 300 and open‐cell aluminium foam, the intrinsic permeability of the metal foam is determined. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Uniform Slip Flow on a Cylinder
Authors: Crane L. J. , McVeigh A. G.
Published: November 2010

In this paper, we determine the shear stress along the entire length of a stationary cylinder having radius a, under uniform axisymmetric flow, with velocity U0, in the slip regime. Investigating motion at small and large axial distances, we employ asymptotic series techniques to obtain the shear stress coefficient in non‐dimensional form. For intermediate regions, we obtain a solution using the Rayleigh approximation method. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transonic viscous inviscid interactions in a slender Laval nozzle
Authors: Meyer Georg , Kluwick Alfred
Published: November 2010

Transonic, high Reynolds number flows through a Laval nozzle, which is so narrow that the classical boundary layer correction can no longer be considered to be an effect of higher order, are considered. As a consequence the properties of the inviscid core and the viscosity dominated boundary layer region can no longer be determined in subsequent steps but have to be calculated simultaneously. The resulting interaction problem for laminar flows in a small nozzle is presented for perfect gases. Representative solutions including the internal structure of pseudo‐shocks forming in the diffuser part of the nozzle and being strongly associated with the chocking phenomenon will be presented. The linear stability of the various flow regimes observed in the nozzle will be discussed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐fluid spatial instability with velocity defect in the basic flow
Authors: Otto Thomas , Boeck Thomas , Rossi Maurice
Published: November 2010

The initial state of liquid atomization by a fast gas stream is considered by viscous linear spatial stability analysis for parallel two‐fluid flow. The unbounded basic velocity profile is characterized by boundary layers near the interface and different asymptotic velocities. By computing generalized spatial branches we identify conditions for absolute instability when a velocity deficit is introduced to account for the conditions near the nozzle. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A first Integral of Navier­Stokes equations for two‐dimensional flows
Authors: Scholle M. , Haas A.
Published: November 2010

As wellknown, Bernoulli's equation is obtained as the first integral of Euler's equations in the absence of vorticity. Even in case of non‐vanishing vorticity, a first integral from Euler's equations is obtained by using the so called Clebsch transformation [1] for inviscid flows. In contrast to this, a generalisation of this procedure towards viscous flows has not been established so far. In the present paper a first integral of Navier‐Stokes equations is constructed in the case of two‐dimensional flow by making use of an alternative representation of the fields in terms of complex coordinates and introducing a potential representation for the pressure. The associated boundary conditions are also considered. The first integral is a suitable tool for the development of new analytical methods and numerical codes in fluid dynamics. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Double Channel Membrane Pump
Authors: Steinrück Herbert , Zackl Wilhelm , Müllner Markus , Neth Harald
Published: November 2010

The flow through a double channel membrane pump is modeled by a time dependent potential flow. The total forces on the fluid are determined as a function of the position of the lateral pistons. It turns out that the total force and thus the pressure gain is very sensitive to the position of the excitation. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffraction of water waves by a slotted dual cylindrical caisson breakwater
Authors: Basmat A.
Published: November 2010

The linearized theory of water waves is used to examine the diffraction of incident regular waves by a slotted dual cylindrical caisson breakwater. The breakwater consists of a vertically slotted outer cylinder circumscribing an impermeable inner cylinder. Under the assumption that the wavelength is much greater than its thickness, each panel is replaced by a thin structure and the permeability is modeled by suitable boundary conditions applied on its surface. The mixed boundary‐value problem for the outer cylinder is transformed to dual series relations and the least‐square method is applied to get the forces on the structure and associated diffraction field. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental Evidence for Breather Type Dynamics in Freak Waves
Authors: Chabchoub Amin , Vitanov Nikolay , Hoffmann Norbert
Published: November 2010

Freak or rogue waves on the ocean seemingly appear from nowhere, cause severe damage to ships and offshore structures due to their large crest heights, and disappear at once. Since the Draupner wave measured on New Year's day 1995 finally confirmed the existence of freak waves, different models were developed to describe them. One deterministic model to investigate their occurrence is the nonlinear Schrödinger equation (NLS) describing the nonlinear evolution of wave train envelopes. Due to the modulation instability, also referred to as Benjamin‐Feir instability, strong spatial localization of wave amplitude may arise and breather type solutions are hypothesized to form the dynamical back‐bone of rogue waves. To test this hypothesis, breather type solutions of the NLS are compared to two extreme wave records: the Draupner wave recorded in central North Sea and the Yura wave recorded in the Sea of Japan. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of Dispersion Characteristics of Composites
Authors: Karmazin Alexander , Kirillova Evgenia , Seemann Wolfgang , Syromyatnikov Pavel
Published: November 2010

This numerical study of dispersion characteristics of some symmetric and asymmetric composites modelled as multilayered packets of layers with arbitrary anisotropy of each layer is carried out. The authors introduce a subsidiary boundary problem of three‐dimensional theory of elasticity for the system of partial differential equations describing the harmonic oscillations of the composite excited by a surface load. The authors obtained the curves and surfaces describing slowness of the wave front of Lamb waves propagating with respect to the direction of propagation. The method suggested by the authors of the present article does not impose any restrictions on the type of elastic anisotropy of the layers, their orientations and mutual positions. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient wave propagation in a one dimensional partially saturated poroelastic column
Authors: Li Peng , Schanz Martin
Published: November 2010

Based on the theory of mixtures, a dynamic three phase model for partially saturated poroelasticity is established. This model is applied to a one‐dimensional unsaturated poroelastic column and an analytical solution in the Laplace domain is deduced. By using the Convolution Quadrature Method, the solution in the time domain is obtained. Using some widely distributed porous materials as rock, soil and sediment, the wave propagation behavior in terms of displacement and pore pressure is examined. By neglecting the viscosity of the fluid, assuming very large fluid permeabilities, the second and third compressional waves are identified. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modal‐based fluid structure coupling in room acoustics considering non‐deterministic properties
Authors: Pospiech Martina , Buchschmid Martin , Rentrop Peter , Müller Gerhard
Published: November 2010

Nowadays fluid structure interaction methods gain more and more importance. For room acoustical problems the coupling to realistic boundary conditions, absorbers and reflectors, is still a remaining challenge in the optimization process for the frequency response of the acoustic volume. The following work will present a coupling method based on the Component Mode Synthesis and Hamilton's Principle for the steady state response of linear room acoustic problems. Therein realistic boundaries like absorbers are coupled with the help of their related frequency dependent impedances. For a more physical interpretation uncertain parameters are considered within the input data. Basic possibilistic and probabilistic concepts are applied on benchmark configurations to estimate the variation in frequency response functions from uncertain input data. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Wave‐Based Approach to Adaptively Control Self‐Excited Vibrations in Drill‐Strings
Authors: Kreuzer Edwin , Steidl Michael
Published: November 2010

Due to their small diameter‐to‐length‐ratio, drill‐strings are vulnerable to torsional vibrations. Moreover, the string is exposed to unknown or uncertain time‐variant and nonlinear loads (e.g. friction with falling friction characteristics, contact with the borehole, differential sticking), which can result in severe torsional vibrations and stick‐slip. The control law for the boundary controller at the top drive of the string needs to adapt to those unknown loads in order to stabilize the vibrations. The torsional vibrations of a drill‐string are governed by the wave equation. Analytical solutions and control laws are often based on a separation of the dynamics into a time‐ and a space‐dependent part (modal representation). Here, we decompose the vibrations into two traveling waves according to the D'Alembert solution, using only few measurements along the string. The wave which travels up the string is then compensated by the actuator at the top drive. With this compensation, the upward‐traveling wave is no longer reflected back into the string and vibration energy is absorbed, thus stabilizing the torsional vibrations. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Influence of Multi‐Layered Obstacles on the Wave Scattering Behaviour in TRC
Authors: Weber Wolfgang , Zastrau Bernd W.
Published: November 2010

In this contribution, the influence of the eccentricity of a multi‐layered scatterer to the wave scattering behaviour of Textile Reinforced Concrete is analyzed. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)