bluuebunny/crossref_metadata_2025 huggingface dataset:
Single‐ and multiscale aspects of the modeling of curing polymers
Authors: Bartels Alexander , Klinge Sandra , Hackl Klaus , Steinmann Paul
Published: December 2012

Within this contribution, the focus is placed on the simulation of the isochoric behavior of polymers during the curing process. To this end, a model based on the assumption of free energy in the form of a convolution integral is applied. Since this allows the implementation of the time‐dependent material parameters, the free energy is interpreted as the total accumulated energy. Different from this, the strain energy is related to the current state of deformation and used to define the temporary stiffness. In order to avoid volume locking effects typical of isochoric materials, the free energy is furthermore split into a volumetric and a deviatoric part. A multifield description depending on the displacements, volume change and hydrostatic pressure is introduced as well. The model is implemented within a single‐ and multiscale FE program and used to simulate the behavior of homogeneous and microheterogeneous polymers. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermoviscoplasticity deduced from enhanced rheological models
Authors: Bröcker Christoph , Matzenmiller Anton
Published: December 2012

A new ideal body is proposed for representing isotropic hardening. Hence, a rheological model of thermoviscoplasticity may be assembled with linear isotropic and kinematic hardening and nonlinear strain rate sensitivity. The related constitutive equations including the yield function and the flow rule are directly deduced from the kinematics and the stress equilibrium of the rheological network and result in a well‐known model. Based on the free energy of the rheological network, the equation of heat conduction is obtained with the dissipative heat source term, driven by plastic deformations. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the finite strain deformation and initial anisotropy of amorphous thermoplastic polymers
Authors: Hempel Philipp , Seelig Thomas
Published: December 2012

This work deals with modeling the mechanical behavior of thermoplastic polymers in the finite strain regime over a wide range of temperatures. Thereby, special emphasis is put on the incorporation of an initial anisotropy in terms of “frozen‐in” molecular orientation which results from a preceding manufacturing process. A computational example is discussed which considers an injection molded plate undergoing inhomogeneous deformation (buckling) during re‐heating. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanical modeling of bainitic phase transformation
Authors: Schneidt Andreas , Antretter Thomas , Mahnken Rolf
Published: December 2012

We develop a micromechanical material model for phase transformation from austenite to bainite for a polycrystalline low alloys steel. In this material (e.g. 51CrV4) the phase changes from austenite to perlite‐ferrite, bainite or martensite, respectively. This work is concerned with phase transformation between austenite and n‐bainite variants in differently orientated grains. The characteristic features of bainite formation are the combination of time‐dependent transformation kinetics and lattice shearing in the microstructure. These effects are considered on the microscale and transferred to the polycrystalline macroscale by means of homogenisation of stochastically orientated grains. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A model for martensitic microstructure, its geometry and interface effects
Authors: Goodarzi Mehdi , Hackl Klaus
Published: December 2012

In line with our formerly presented continuum micromechanical model [4,5] of the laminate microstructure of martensite, we here modify and reformulate the model to further its simplicity and clarity. The basic postulates are slightly altered. However, the approach remains the same, namely the kinematic assumption of nearly‐planar laminate geometry put into an energy minimization framework with proper ansatzes of twin‐interface and boundary energies. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On consistent tangent operator derivation and comparative study of rubber‐like material models at finite strains
Authors: Hossain Mokarram , Steinmann Paul
Published: December 2012

Rubber‐like materials can deform largely and non‐linearly upon loading and return to the initial configuration when the load is removed. Such rubber elasticity is achieved due to very flexible long chain molecules and a three‐dimensional network structure that is formed via cross‐linking or entanglements between molecules. Over the years, to model the mechanical behaviour of such randomly‐oriented micro‐structure, several phenomenological and micro‐mechanically motivated network models for nearly incompressible hyperelastic polymeric materials have been proposed in the literature. For comparison of all selected models in reproducing the well‐known Treloar data, the analytical expressions for the three homogeneous defomation modes, i.e. uniaxial tension, equibiaxial tension and pure shear have been derived and the performances of the models are analysed. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
All‐electron calculations with finite elements
Authors: Schauer Volker , Linder Christian
Published: December 2012

The Kohn‐Sham equations resemble a nonlinear eigenvalue problem for the determination of the electronic structure of an atomic system, where the electrons are exposed to an effective potential, accounting for the Coulomb and quantum mechanical interactions between the particles. The effectiveness of the potential requires an iterative solution procedure, until self‐consistency is reached. This work illustrates the implementation of the self consistent field algorithm based on nested finite elements spaces and analyzes its properties in the case of all‐electron calculations on atoms as large as the noble gas Xenon. All‐electron calculations have maximal requirements onto the numerical basis, as it must be able to represent all the orthogonal electronic wavefunctions simultaneously together with the electrostatic potential, showing singularities at the positions of the atoms. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear dynamics of the dielectric elastomer actuator
Authors: Xu Bai‐Xiang , Mueller Ralf , Klassen Markus , Gross Dietmar
Published: December 2012

As potential material for artificial muscles and haptic displays, dielectric elastomer provides large deformations with lower cost and high efficiency. The material behaves nonlinearly in both the kinematics and the constitutive relation. In this work, the nonlinear equation of motion for a dielectric elastomer actuator with a sandwich structure under constant electric potential is derived from the energy conservation condition. The equation of motion is numerically solved, and the results are discussed. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A flexible multi‐physics coupling interface for partitioned solution approaches
Authors: Brändli Silvan , Düster Alexander
Published: December 2012

A common way of solving multi‐physics problems is the use of a partitioned approach. To this end specialized solvers are utilized for the different subproblems and linked via a common communication interface. In this paper a communication interface is presented, which is capable of dealing with different kind of coupled problems. The subproblems may be discretized separately and linked either through a common boundary or by a common volume region.

In order to stabilize and to accelerate the implicit coupling iteration different relaxation techniques and predictor methods are implemented. Finally, the coupling interface is applied to a well‐known fluid‐structure interaction (FSI) benchmark. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Freezing and Thawing Processes with Capillary Effects in fluid filled porous media
Authors: Bloßfeld Wolfgang Moritz , Bluhm Joachim , Ricken Tim
Published: December 2012

In this contribution, a macroscopic quadruple model for the simulation of freezing and thawing processes in fluid filled porous media is presented. The main focus lies on the description of the distribution of fluid and ice pressure as well as solid deformation before, during and after the ice formation in consideration of energetic and capillary effects. Furthermore, the porosity change of the porous material is considered, i.e., the variation of permeability during ice formation will be simulated. The illustrated results of numerical examples will be presented to demonstrate the practical application of the model. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acceleration of partitioned coupling schemes for problems of thermoelasticity
Authors: Erbts Patrick , Düster Alexander
Published: December 2012

A partitioned coupling scheme for problems of thermo‐elasticity at finite strains is presented. The coupling between the mechanical and thermal field is one of the most important multi‐physics problem. Typically two different strategies are used to find an accurate solution for both fields: Partitioned or staggered coupling schemes, in which the mechanics and heat transfer is treated as a single field problem, or a monolithic solution of the full problem. Monolithic formulations have the drawback of a non‐symmetric system which may lead to extremely large computational costs. Because partitioned schemes avoid this problem and allow for numerical formulations which are more flexible, we consider a staggered coupling algorithm which decouples the mechanical and the thermal field into partitioned symmetric sub‐problems by means of an isothermal operator‐split. In order to stabilize and to accelerate the convergence of the partitioned scheme, two different methods are employed: dynamic relaxation and a reduced order model quasi‐Newton method. A numerical simulation of a quasi‐static problem is presented investigating the performance of accelerated coupling schemes. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantifying diffusion for an ultrasonic wire bonding process by applying the theory of material forces
Authors: Sbeiti Mohamad , Müller Wolfgang H. , Schneider‐Ramelow Martin , Geissler Ute , Schmitz Stefan
Published: December 2012

Ultrasonic wire bonding is a method applied in electronic packaging to fabricate interconnections between two devices at ambient temperature. In order to investigate the material diffusion during this process, the occurring thermal and mechanical mechanisms at and around the interface of the formed bond were studied by means of coupled thermo‐mechanical FE simulations. Within the framework of material forces the local jump of the Eshelby tensor was compared with the thickness of the formed intermetallic phase for various bonding parameters. This allows us to predict an effective diffusion constant which takes temperature and mechanical driving forces into account. After this relation has been established a subsequent objective of our investigations is to optimize the growth of the Au8Al3 intermetallic phase in terms of bonding parameters. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase transition in methane oxidation layers – a coupled FE multiphase description
Authors: Sindern Andrea , Ricken Tim , Bluhm Joachim , Denecke Martin , Schmidt Torsten C.
Published: December 2012

Worldwide, the most common sites of waste disposal are landfills. After solid waste is deposited in a landfill, physical, chemical, and biological processes ensue and modify the waste. Due to these reactions, landfill gas is produced inside the landfill body and effuses into the atmosphere at the outer layer. These processes create environmentally harmful landfill pollutants (methane (CH4)) and carbon dioxide (CO2)). The impact of methane on the greenhouse effect is about 20 times higher than that of carbon dioxide.

WorldwideIn order to estimate potential environmental risk of the landfill, a second important phenomenon has to be taken into account: the bacterial methane conversion in the porous cover layer which significantly reduces the amount of methane emitted into the atmosphere. Subsequently, the metabolism of different methanotrophic bacteria converts methane and oxygen into carbon dioxide, water, and biomass.

WorldwideTo model this highly complex and coupled problem we used the well‐known theory of porous media to obtain a thermodynamically consistent description which in turn leads to a fully‐coupled finite element (FE) calculation concept. The theoretical and numerical framework will be presented in order to describe the coupled processes occurring during the phase transition by bacterial activity in the methane oxidation layer. The model analyzes the relevant gas concentrations of methane, carbon dioxide, oxygen, and nitrogen as well as the driving phenomena of production, diffusion, and convection. Based on a model predicting gas production in landfills, see [1], a multiphase continuum approach for landfill cover layers is presented. In order to validate the model, we compare numerical simulations with experimental data. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Domain Decomposition Solvers for Some Fluid‐Structure Interaction Problems
Authors: Langer Ulrich , Yang Huidong
Published: December 2012

In this note, we present some of our recent work on domain decomposition solvers for the fluid‐structure interaction problems with nearly incompressible and anisotropic elasticity models. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Macroscopic modelling of the selective beam melting process
Authors: Riedlbauer Daniel , Mergheim Julia , McBride Andrew , Steinmann Paul
Published: December 2012

The present contribution is concerned with the macroscopic modelling of the selective beam melting process by using finite elements. In this context the objective is to detail a continuum model to describe the process. Furthermore two different solution approaches are applied to the model and compared in terms of performance. An adaptive mesh refinement strategy is also demonstrated to increase the quality of the solution in the vicinity of the beam. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Modeling and Simulations of Dielectric Elastomer Actuators for Thin Structures
Authors: Zwecker Sandro , Klinkel Sven
Published: December 2012

The contribution is concerned with a finite element formulation that deals with thin structures made from dielectric elastomer material. For that a special solid shell formulation, which uses eight nodes per element and four degrees of freedom (three displacements and one for the electric potential) per node, is presented. It is based on a Hu‐Washizu mixed variational principle using six independent fields: displacements, electric potential, strains, electric field, mechanical stresses, and dielectric displacements. In recent years structures made from dielectric elastomers have been investigated by many researchers. This interest is caused by the ability of such devices to efficiently transform electric energy into mechanical work at inexpensive cost of production. The efficiency increases with a higher area to thickness ratio, thus the need to accurately simulate thin structures is well‐founded. On the other hand a 3d description of the constitutive behavior is necessary to capture all nonlinear effects arising from the material. Thus a 3d constitutive law with respect to the electro‐mechanical coupling incorporated in a finite element solid shell formulation is presented. Some examples demonstrate how it deals with finite strains and large deformations of thin structures by applying electrical loading conditions. The analyzed devices respond with elongation, bending, or buckling, depending on the mode of activation. The electrically induced buckling can be utilized to obtain large deformations. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of dense fluid‐particle flows using computational fluid dynamics (CFD) and discrete element method (DEM)
Authors: Iqbal Naveed , Rauh Cornelia , Delgado Antonio
Published: December 2012

Discrete Element Method (DEM) has been successfully coupled with Computational Fluid Dynamics (CFD) in the framework of OpenFOAM an open source CFD simulation code. In the current study, at first the model is validated with the simple test case of spherical particle comparing the results with the analytical solution. Then the simulation of a gaseous fluidized bed is considered. The coupled mass and momentum balance equations are used to calculate the flow behavior, particle fluidization and bubble formation. The dimensions of the simulation domain are similar to Link et al. (2005) but with different stiffness of particles. The higher velocity of gaseous fluid relative to particles entering through a jet causes the particles to fluidize. The particles behavior, fluidization, bubble formation and the velocity vectors of particles show a good agreement with the literature. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of organic binder decomposition and combined seepage‐ and diffusive transport of the gaseous reaction products through a porous green body during thermal debinding of ceramic parts.
Authors: Schmidt Ingo , Riedel Hermann , Svoboda Jiři
Published: December 2012

This article presents a model which describes the chemical decomposition of organic binders, the combined Maxwell‐Stefan and Knudsen diffusion and the seepage flow of multiple gaseous reaction products through a porous body and the implementation of the model into a finite element framework. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element methods for problems with solid‐liquid‐solid phase transitions and free melt surface
Authors: Jahn Mischa , Luttmann Andreas , Schmidt Alfred , Paul Jordi
Published: December 2012

Modeling and computation of a process with solid‐liquid‐solid phase transitions and a free capillary surface is discussed. The main components of the model are heat conduction, a free melt surface, a moving phase boundary, and its coupling with the Navier‐Stokes equations. We present two different approaches for handling the phase transitions by applying in a FE method, namely an energy conservation based approach, and a sharp interface approach with moving mesh. By combining both methods, we benefit from the advantages of the respective approach. The methods are applied to a problem where material is accumulated by melting the tip of thin steel wires using laser heating. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Modeling Aspects of Dielectric Elastomer Actuators
Authors: Müller Ralf , Klassen Markus , Xu Baixiang
Published: December 2012

In modern actuator technology dielectric elastomers are considered as new materials to realize smart actuators which are known as dielectric elastomer actuators (DEAs). In comparison to piezoceramics actuators, DEAs offer the possibility to achieve large deformations with low actuation forces. This property motivates the implementation as artificial muscles since the deformation‐force behavior is similar. Other application fields are pumps, deformable surfaces in aerospace, robotics and haptic feedback.

The present work introduces the fundamental concepts to describe the electromechanical coupling in the concept of continuum mechanics for finite deformations.

As a benchmark a 3D sandwich actuator setup is taken into account to analyze the mechanical compression stability of the elastomer structure, see [1, 2]. This structure is also considered to study the influence of inhomogeneities in the deformation behavior. For this purpose piezoceramic and air inclusions are considered in the finite element mesh.

As a last numerical example an elastomer tube with three pairs of electrodes is simulated numerically to motivate the use of dielectric elastomers as peristaltic pumps. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Invariance of Parrinello‐Rahman molecular dynamics and its relation to continuum mechanics
Authors: Ulz Manfred H.
Published: December 2012

Parrinello‐Rahman molecular dynamics has proved to be a reliable technique for the investigation of phase transitions in solids. This type of molecular dynamics may lead to a proper description of the atomistic scale in multi‐scale analysis of engineering problems. However, the employed Lagrangian is proposed without a derivation and lacks invariance under modular transformations. A re‐interpretation of the Lagrangian in terms of continuum mechanics was recently developed. The new formulation is derived in a consistent physical manner and only quantities native to continuum mechanics are incorporated into this Lagrangian. Based on this recent continuum‐related derivation, the invariance of the new Lagrangian under modular transformations is investigated. The implication that the obtained dynamics is invariant to the chosen unit cell corroborates with results in solid state physics and is a mandatory requirement for the suitability of multi‐scale analysis. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical aspects on computational homogenization of epoxy/glass composites
Authors: Fleischhauer Robert , Dal Hüsnü , Kaliske Michael
Published: December 2012

Numerical aspects of two‐scale modeling of epoxy/glass composites are presented. The homogenization process is carried out under consideration of periodic boundary constraints (PBC) of the representative volume element (RVE) due to the periodic structure of glassfiber reinforced epoxy systems. The introduction of artificial constraints for computing macro‐stresses and macro‐moduli is presented by giving the modified algorithmic treatment of a two‐scale approach using PBC. The proposed algorithm is applied to an ISO 527 epoxy/glass test specimen. The results of computations considering or not considering interphases and interfaces within the composite are compared. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Construction of Statistically Similar RVEs for 3D Microstructures
Authors: Scheunemann Lisa , Balzani Daniel , Brands Dominik , Schröder Jörg
Published: December 2012

This contribution presents a method to construct three‐dimensional Statistically Similar RVEs (SSRVEs) for the simulation of dual phase steel (DP steel). Since the microstructure of DP steel strongly influences the overall material properties, it should be incorporated in numerical calculations. For this purpose the FE2 method can be applied and for an efficient computation SSRVEs with a reduced complexity compared to the real microstructure have to be defined, which still represent the mechanical response of the material accurately. The construction method is based on the minimization of a least‐square functional considering suitable statistical measures describing the inclusion morphology of a given real microstructure. The mechanical response of the SSRVEs is compared to the response of the real microstructure in virtual mechanical tests. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tolerance modelling of heat conduction in bidirectional graded thin walled cellular structures
Authors: Baron Eugeniusz , Czarnecka Sylwia
Published: December 2012

The aim of this contribution is to present a new method of formulation of simplified model of skeletonal structures. The exact description of the heat conduction leads to PDEs with highly oscillating and discontinuous coefficients. We would like to obtain the simplified models of the tolerance type which is described by PDEs with smooth coefficients. As a method of modelling we used the tolerance averaging. This method could be treated as a certain generalization of the well known homogenization method. However, it is not basis on the limit passage from the microstructure size to zero. This method makes it possible to analyze the effect of microstructure size on the overall i.e. macroscopic behavior of the composite structure. Instead of limit passage, we introduce here the concept of tolerance parameter. Using this concept we could define the slowly varying functions [1], [2]. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale Modeling for the Simulation of Damage Processes at Refractory Materials under Thermal Shock
Authors: Henneberg Dimitri , Ricoeur Andreas
Published: December 2012

A brittle damage model based on multiscale considerations and homogenisation procedures is presented. Cell models are developed as RVE including different microstructural features. The material laws themselves are formulated on the continuum level. Local failure occurs if the damage variable reaches a critical value. For simple configurations of the microstructure, the relation between stress, strain und temperature is derived from analytical considerations. In order to properly model the thermo‐mechanical coupling, the temperature‐dependence of material constants is taken into account. Fracture and damage mechanical approaches are combined using different techniques. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microscopical investigation of wave propagation phenomena in residual saturated porous media
Authors: Kurzeja Patrick S. , Steeb Holger
Published: December 2012

Wave propagation is used in many fields for measurement and characterization. Corresponding multiphase models usually use a continuous approach. Nevertheless, systems like wetted rocks may be saturated residually in certain situations. In such cases, one fluid is distributed as clusters, each different in size and shape. One single, continuous phase cannot account for a variety of fluid clusters, either disconnected from each other or connected only about thin liquid films. Therefore, we present a model that considers a heterogeneous distribution of disconnected fluid clusters in the form of harmonic oscillators. These oscillators are described and distinguished by their mass, damping and eigenfrequency. Hence, the model allows to characterize different clusters and includes an additional damping mechanism due to oscillations of the fluid clusters. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cosserat Parameter Identification within the Frame of the Discrete Element Method
Authors: Wessels Nicola , Hackl Klaus
Published: December 2012

One of the main challenges using the Discrete Element Method is that there is no direct compliance to the well known continuum parameters such as elastic moduli. In this article we show how homogenization procedures using representative volume elements composed of discrete particles lead to Cosserat continua.

Simulating a shear test with discrete elements it becomes obvious, that the evolving microstructure is mainly composed of contact chains that form triangles and quadrilaterals. For these contact chains we set up contact energies in normal and shear directions and combine those to derive the effective energy of the material. By comparison of this energy to a Cosserat energy we can derive formulas for the Lamé and Cosserat parameters. They are now only dependent on the interaction energies and radii of the particles. To show the validity of our assumptions and derivations we present some discrete element simulations of shear tests. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotics for thin elastic fibers in unilateral contact
Authors: Bare Zoufine , Orlik Julia
Published: December 2012

What is the contact condition in a 1D beam‐model and is it possible to obtain the frictional moments and forces from the 3D traction? If it is possible does the cross‐section of the beams influence these values? These questions motivate to study the dimension reduction of a 3D contact problem for beams. This paper is a continuation of [1]. In [1] the asymptotic dimension reduction of a Robin‐type elasticity boundary value problem was presented. In this work the explicit relation between a 3D contact problem and a 3D Robin‐type elasticity boundary value problem are established and the 1D equations derived in [1] are interpreted as 1D contact conditions, further some numerical examples are shown. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical and Numerical Modelling of the Safe Turn Manoeuvres of Agricultural Aircraft
Authors: Rašuo Boško
Published: December 2012

In this paper, a theoretical study of the turn manoeuvre of an agricultural aircraft is presented. The manoeuvre with changeable altitude is analyzed, together with the effect of the load factors on the turn manoeuvre characteristics during the field‐treating flights. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Preliminary results of the conditional analysis of wall friction during laminar‐turbulent transition of a rough wall boundary layer
Authors: Jonáš Pavel , Hladík Ondrej , Mazur Oton , Uruba Václav
Published: December 2012

The conditional analysis of the instantaneous wall friction is applied on time records made in transitional boundary layers originating on smooth surface or surface covered by sand paper (grits 60) under turbulent free stream. The applied intermittency analysis of measurement allowed the evaluations of turbulent and non‐turbulent zone averages. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Unsteady convective diffusion of a solute in a Hagen‐Poiseuille flow through a tube with permeable wall
Authors: Dumitrache Alexandru , Frunzulica Florin
Published: December 2012

Influence of Interphase Mass Transfer (IMT) on the unsteady convective diffusion in a fluid flow through a tube surrounded by a porous medium is examined against the background of no IMT. The three coefficients namely exchange coefficient, convection coefficient, and dispersion coefficient are evaluated asymptotically at large‐time. The exchange coefficient exists due to IMT. All‐time analysis is made analytically when there is no IMT. The mean concentration distribution is measured at a point inside and outside the slug. The peak of mean concentration is higher than that of pure convection and it is further enhanced with increase of porous parameter. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Exact Navier‐Stokes Solution for Three‐Dimensional, Spanwise‐Homogeneous Boundary Layers
Authors: John Michael O. , Obrist Dominik , Kleiser Leonhard
Published: December 2012

The plane stagnation flow onto (Hiemenz boundary layer, HBL) and the asymptotic suction boundary layer flow over a flat wall (ASBL) are two boundary layer flows for which the incompressible Navier‐Stokes equations are amenable to exact similarity solutions. The Hiemenz solution has been extended to swept Hiemenz flows by superposition of a third, spanwise‐homogeneous sweep velocity. This solution becomes singular as the chordwise, tangential base flow component vanishes. In this limit, the homogeneous ASBL solution is valid, which however cannot describe the swept Hiemenz flow, because it does not contain any chordwise velocity. This work presents a generalized three‐dimensional similarity solution which describes three‐dimensional spanwise homogeneously impinging boundary layers at arbitrary wall‐normal suction velocities, using a rescaled similarity coordinate. The HBL and the ASBL are shown to be two limits of this solution. Further extensions consist of oblique impingement or different boundary suction directions, such as slip or stretching walls. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical and experimental investigation of thermal convection in an inclined narrow gap
Authors: Sommer Oliver , Heiland Hans Georg , Wozniak Günter
Published: December 2012

The knowledge of the fluid behaviour in inclined cavities is of fundamental importance as far as heat and mass transfer are concerned. The interest in this subject is particularly increasing due to the rapid process in micro technologies. We therefore studied the flow‐ and temperature field of such flows numerically as well as experimentally using CFD and PIV/T, respectively. We present and discuss the numerical and experimental results of our investigations and explain the applied techniques. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Investigation of the Separate Flow and Stall‐delay for Horizontal‐Axis Wind Turbine
Authors: Frunzulica Florin , Mahu Razvan , Dumitrescu Horia
Published: December 2012

The flow characteristics and stall delay phenomenon of a stall regulated wind turbine rotor due to blade rotation in steady state non‐yawed conditions are investigated. An incompressible Reynolds‐averaged Navier‐Stokes solver is applied to carry out the separate flow cases at high wind speeds from 11 m/s to 25 m/s with an interval of 2 m/s. The objective of the present research effort is to validate a first‐principles based approach for modeling horizontal axis wind turbines (HAWT) under stalled flow conditions using NREL/Phase VI rotor data. The computational results are compared with the predicted values derived by a new stall‐delay model and blade element momentum (BEM) method. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cauchy Problems and Breakdown in the Theory of Marginally Separated Flows
Authors: Aigner Mario J. , Braun Stefan
Published: December 2012

Flow separation can be viewed as one of the trigger events of laminar‐turbulent boundary layer transition. Thus, intensive investigations have been carried out as to when and how laminar boundary layers break down. In the special case of marginal separation, i.e. the formation of short laminar separation bubbles, high Reynolds number asymptotic theory yields integro‐differential equations governing the essential flow behavior. We will present further considerations of associated initial value problems (IVPs) in planar and three‐dimensional flow cases regarding the general ill‐posedness. As for regularization methods, higher order asymptotic terms comprising the streamline curvature in the boundary layer region are taken into account rendering the hence modified problem well‐posed, which can be seen from the dispersion relation and numerical solutions of the full problem. Even though the regularized IVPs admit limiting steady states in their time evolution, the phenomenon of finite time blow‐up, which can be interpreted as “bubble bursting”, is still present for certain initial conditions. The inevitable breakdown of the asymptotic description leads to the emergence of a new asymptotic structure of shorter spatio‐temporal scales associated with the unique self‐similar blow‐up structure. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Internal Flow Analysis for Slow Moving Small Droplets in Contact with Hydrophobic Surfaces
Authors: Rasool Raheel , A. Sauer Roger , Osman Muhammad
Published: December 2012

Internal fluid flow behavior for slow moving small droplets in contact with hydrophobic surfaces is analyzed. The shape of the droplet is first computed using the Young‐Laplace equation. For this purpose a Finite Element (FE) model [1], in which contact constraints are enforced through Penalty and Augmented Lagrange Multiplier methods, is used. The flow field within the droplet is then analyzed using the Stokes flow model, considering a de‐coupled approach. Similar to the membrane deformation model, the formulation for the flow analysis is also expressed in the framework of FE analysis. Both, stabilized (Pressure Stabilizing/Petrov‐Galerkin PSPG) and Galerkin FE formulations are considered. The motion of the fluid inside the droplet is governed by the slip condition enforced on the membrane of the droplet. Numerical examples for droplets rolling steadily are presented. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic Mode Decomposition for Swirling Jet Flow Undergoing Vortex Breakdown
Authors: Luginsland Tobias , Kleiser Leonhard
Published: December 2012

Swirling jets undergoing vortex breakdown occur in many technical applications, e.g. vortex burners, turbines and jet engines. At the stage of vortex breakdown the flow is dominated by a conical shear layer and a large recirculation zone around the jet axis. We performed Large‐Eddy Simulations (LES) of compressible swirling jet flows at Re=5000, Ma=0.6 in the high swirl number regime (S=1). A nozzle is included in our computational setup to account for more realistic inflow conditions. The obtained velocity fields are analyzed by means of temporal and spatial dynamic mode decomposition (DMD) to get further insight into the characteristic structures dominating the flow. We present eigenvalue spectra for the case under consideration and discuss the stability behaviour in time and space. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Multiscale Approach of Turbulent Premixed Flames treated as a Gasdynamic Discontinuity
Authors: Strein Sabine , Bruzzese Christian , Class Andreas G.
Published: December 2012

A multiscale approach describing a turbulent flame as a gasdynamic discontinuity [1] on each scale is proposed. The methodology becomes attractive if simulations on individual scales are implemented in a very efficient way. Simulations in a 2D rectangular box with an artificial turbulence field exploiting a robust phase‐field/level‐set method fit this purpose. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integral analysis of the flow dynamics and mass transfer in a wavy liquid film on a spinning disk
Authors: Prieling Doris , Steiner Helfried , Brenn Günter
Published: December 2012

In the present work the complex process of diffusion‐controlled wet chemical etching of a rotating silicon wafer is analyzed in the framework of an unsteady integral boundary layer approximation. The obtained results reproduce the waviness and the associated enhancement of the mass transfer in the wavy region, and are in good agreement with experimental findings. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Iso‐surface Computation in 3D using a graph‐theoretical Approach
Authors: Ali Abdulaziz , Bothe Dieter
Published: December 2012

The existing combinatorial methods for iso‐surface computation are efficient for pure visualization purposes, but it is known that the resulting iso‐surfaces can have holes, and topological problems like missing or wrong connectivity can appear. To avoid such problems, we introduce a graph‐theoretical method for the computation of iso‐surfaces on cuboid meshes in ℝ3. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Lamb wave interaction with defects in laminated plates by SEM
Authors: Asmus Andreas , Lammering Rolf
Published: December 2012

For the simulation of the interaction of elastic waves in CFRP Plates with inhomogeneities and defects the spectral finite element method (SEM) is under investigation. The SEM uses high‐order shape functions which are composed of Lagrange polynomials with nodes at the Gauss‐Lobatto quadrature (GLq) points. In this way we obtain a diagonal mass matrix which makes an explicit time scheme more efficient. In a numerical example based on the first order shear deformation theory (FSDT) a computation by FEAP of an interaction with an inhomogeneity is presented. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Acoustical Performance of Concreted Wood Fiber Materials
Authors: Lumei Calin , Arghir Mariana , Tot Alin‐Cosmin
Published: December 2012

In this paper, an inverse acoustical characterization for determination of porosity, flow resistivity, tortuosity and other parameters of a concreted wood material was proposed. Sound absorption measurements for a concreted wood fiber material were made in an impedance tube. Four acoustical models from literature were briefly described. Each model was fitted to the experimental data in order to compute their unknown parameters. Using a least‐square method, the experimental data (sound absorption coefficient) was used to optimize the acoustical models by best‐fitting the unknown parameters. The results of this paper show that the presented technique leads to reliable estimates of the physical parameters of the material. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulations of Pile Integrity Tests Using a Coupled FEM SBFEM Approach
Authors: Schauer Marco , Langer Sabine
Published: December 2012

Piles are widely used to build a proper foundation for various buildings. The pile's quality in situ can be tested by a so called pile integrity test. In order to apply this test, an acceleration sensor is attached to the pile's head which than receives an impulse. Due to this impulse a p‐wave runs through the pile. The major part of this wave is reflected from the pile's toe and is measured by the attached acceleration sensor on top of the pile. This yields an acceleration‐time plot which has to be analysed to determine the pile's condition.

Sometimes the interpretation of these plots is difficult, specially when the cross‐section of the pile is changing or is influenced by the surrounding soil. For a better understanding of this kind of measurements, numerical simulations can be performed. For these simulations a coupled finite element method (FEM) and scaled boundary finite element method (SBFEM) approach is used. This approach satisfies Sommerfeld's radiation condition and allows simulating an infinite half‐space. This ensures that the applied impulse will not to be reflected at the artificial boundary which is introduced by the boundary of the numerical discretisation. The coupled approach proposed here requires discretisation of a small domain only in contrast to a purely FEM‐based approach. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Design of Device for Determination of the Sound Absorbtion Coefficient
Authors: Tot Alin‐Cosmin , Arghir Mariana
Published: December 2012

This paper presents a constructive variant of acoustic impedance tube used to determine the coefficient of sound absorption materials. This alternative design brings a contribution in terms of the number of microphones mounted on the tube impedance control of acoustic vibration generator, with the calibration system of microphones mounted on the device. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determining of Velocity Fields During Real and Experimental Simulated Beer Fermentations by UDV and LDA
Authors: Böttcher Kai , Meironke Heiko
Published: December 2012

Beer fermentation is a very complex process, especially in the fluid‐mechanical and the biochemical point of view. Our aim is to optimize the fermentation by flow control, which requires quantities of data. The applied velocity measuring techniques should be non‐invasive to ensure that neither the flow nor the fermentation in the green beer gets influenced. Therefore, an Ultrasonic Doppler Velocimetry (UDV) system is used to determine velocity fields with 128 measuring points. It works in the turbid fluid with the existing yeast cells as tracer particles and can be applied easily to the industrial scale.

For the validation of CFD‐codes and the better understanding of measurements and flow processes, model fluids are used. They can be adapted to real fluid properties like density and viscosity and allow measurements with Laser Doppler Anemometry (LDA). Another advantage over the real fluid is their fixed composition, which leads to negligible natural variations. All experiments are performed in a 270 litre fermenter. Besides the real process, measurements through optical access points and the simulation of fermentations with CO2 and heat emission are enabled. Eight individually controllable cooling zones are used as thermal actors. Resulting changes in boundary conditions induce temperature gradients and hence allow to control the flow inside the tank.

This work deals with the experimental set‐up and the results on the one hand and a comparison between real and simulated fermentations on the other hand. Special attention is given to investigations of the multi‐phase flow inside the vessel and the effects of changing constraints. The usability of UDV measurement techniques is the key benefit in this case, because it can be used in green beer and model fluids and does not influence the flow. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Turbulent drag reduction at moderate Reynolds numbers via spanwise velocity waves
Authors: Gatti Davide , Quadrio Maurizio
Published: December 2012

The question whether large turbulent drag reduction can be achieved at the high values of Re typical of applications is addressed. Answering such question, either by experiments or DNS, is obviously challenging. For DNS, the problem lies in the tremendous increase of the computational cost with Re, that has to be appreciated in view of the need of carrying out an entire parametric study at every Re, owing to the unknown location of the optimal forcing parameters.

In this paper we limit ourselves to considering an open‐loop technique based on spanwise forcing, the streamwise‐traveling waves introduced by [1], and explore via Direct Numerical Simulations (DNS) how the drag reduction varies when the friction Reynolds number is increased from Reτ = 200 to Reτ = 2000. To achieve high Re while keeping the computational cost affordable, computational domains of reduced size are employed. We adopted special care to interpret results that are indeed still box‐size dependent, as well as strategies to compute the random errors and give the results an error bar.

Our results indicate that still R = 0.29 can be obtained at Reτ = 2000 in the partial region of the parameter space studied. The maximum R is found to decrease as R ˜ Reτ−0.22 in the Reynolds range investigated. As most important outcome, we find that the sensitivity of R to Re becomes smaller when far from the low‐Re optimum parameters: in this region, we suggest R ˜ Reτ−0.08. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐sinusoidal wall oscillation for drag reduction
Authors: Cimarelli Andrea , Frohnapfel Bettina , Hasegawa Yosuke , De Angelis Elisabetta , Quadrio Maurizio
Published: December 2012

The drag reducing properties of wall flows under non‐sinusoidal oscillations are analyzed in the present work. The dependency of the drag reduction rate, R, and of the power spent to move the walls, Pin, with respect the shape of the wall motion are investigated. This preliminary work highlights a significant role of the oscillation shape for turbulence control suggesting more research efforts in the field with possible repercussions for practical applications. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Distortion of liquid metal flow in a square duct due to the influence of a magnetic point dipole
Authors: Tympel Saskia , Krasnov Dmitry , Boeck Thomas , Schumacher Jörg
Published: December 2012

We consider liquid metal flow in a square duct with electrically insulating walls under the influence of a magnetic point dipole using three‐dimensional direct numerical simulations with a finite‐difference method. The dipole acts as a magnetic obstacle. The Lorentz force on the magnet is sensitive to the velocity distribution that is influenced by the magnetic field. The flow transformation by an inhomogeneous local magnetic field is essential for obtaining velocity information from the measured forces. In this paper we present a numerical simulation of a spatially developing flow in a duct with laminar inflow and periodic boundary conditions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electromagnetic interaction of a conducting cylinder with a magnetic dipole caused by steady rotation
Authors: Engert Sonja , Boeck Thomas , Thess André
Published: December 2012

The motion of a conductor in a magnetic field induces eddy currents whose interaction with the field produces Lorentz forces opposing the motion. One can determine the velocity of the conductor from the force on the magnet system since the latter is equal but opposite to the Lorentz force on the conductor. This contactless method is known as Lorentz force velocimetry (LFV). We study an idealized configuration of LFV, i.e. a rotating solid cylinder interacting with a point dipole. The understanding of parameter influences in this setup can be helpful for more realistic configurations. We use a purely kinematic approach appropriate for low magnetic Reynolds numbers. Numerical results for small and large distances between dipole and cylinder have been obtained with the commercial software COMSOL Multiphysics. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)