bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical modelling and optimization aspects of soft dielectric actuators
Authors: Klassen Markus , Xu Bai‐Xiang , Müller Ralf 
Published: December 2011

AbstractDielectric elastomer actuators (DEAs) represent a new type of actuator made of electroactive polymers which can undergo large deformations. Some applications for DEAs are: Artificial muscles, haptic feedback, pumps, robotics, deformable surfaces in aerospace, etc. For this reason the numerical modelling and optimization of DEAs represent an active field of research which supports the designing process of these actuators.In this work the basic equations of the electro‐mechanic coupled problem are presented in a first step. Here the Neo‐Hooke and the Yeoh model have been chosen to model the behaviour of a nearly incompressible elastomer. To study optimization aspects, material inclusions in a sandwich type DEA structure have been taken into consideration. Ceramics whit high electric permittivity and air are taken into account to explore the effect of inclusions on the deformation. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A constitutive model for shape memory alloy fibres and its applicability to prestressed composites
Authors: Kohlhaas Benedikt , Klinkel Sven 
Published: December 2011

AbstractThis contribution is concerned with a constitutive model for shape memory fibres. The 1D‐constitutive model accounts for the pseudoplastic and shape memory effect (SME). The macroscopic answer of the material is determined by the evolution from a twinned martensitic lattice into a deformed and detwinned one. On the macroscopic scale these effects are responsible for the upper boundary of the hysteresis which is situated around the origin of the stress‐strain‐diagram. During the phase transition process inelastic strains arise. When the lattice is fully detwinned, a linear elastic branch at the end of the hysteresis is observed. The initial state of the material is recovered by unloading and heating the material subsequently. The constitutive model is derived from the Helmholtz' free energy and fulfils the 2nd law of thermodynamics. For the present model five internal state variables are employed. Two of them are used to describe the inelastic strain and a backstress. The others represent the martensitic volume fraction and are necessary to describe the SME. The latter variables are depending on the deformation state as well as on temperature. A change on temperature goes along with a reduction of the inelastic strain. The model is incorporated in a fibre matrix discretization to prestress the surrounding structure. The boundary value problem is solved for a truss element applying the finite element method. Examples will demonstrate the applicability in engineering structures. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Geometrically Nonlinear Continuum Thermomechanics with Surface Energies Coupled to Diffusion
Authors: McBride Andrew , Steinmann Paul , Javili Ali , Bargmann Swantje 
Published: December 2011

AbstractSurfaces can have a significant influence on the overall response of a continuum body but are often neglected or accounted for in an ad‐hoc manner. This work briefly describes a thermodynamically consistent, nonlinear, continuum thermomechanics formulation which accounts for surface structures and includes the effects of diffusion. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FE2 Modelling of Hybrid Sandwich Composites
Authors: Chambon Cécile , Diebels Stefan 
Published: December 2011

AbstractThis paper presents a procedure to simulate the behaviour of a sandwich composite material. The classical solution to model this kind of structure is the plate theory. Nevertheless, because of the incapacity to take non‐linear material behaviour into account, this method cannot be used to model our problem. Indeed, the sandwich structure contains metallic layers, and their behaviour is elasto‐plastic. For these reasons, a numerical homogenisation will be presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy‐Minimization in Atomic‐to‐Continuum Scale‐Bridging Methods
Authors: Eidel Bernhard , Stukowski Alexander , Schröder Jörg 
Published: December 2011

AbstractThe focus of this contribution is on a novel, improved technique for energy minimization in atomic simulations and its adaption to a variationally consistent formulation of the quasicontinuum (QC) method. The optimization algorithm called FIRE for Fast Inertial Relaxation Engine can be understood as a modification of the Steepest Descent (SD) method, which improves SD by accelerating the system in the direction of the force, making the minimization more aggressive. The performance of FIRE is assessed in a representative example against well‐established optimization methods with respect to efficiency and stability. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale Modeling of Nanocrystalline Materials: A Variational Approach
Authors: El Sayed Tamer , Gürses Ercan 
Published: December 2011

AbstractThis paper presents a variational multi‐scale constitutive model in the finite deformation regime capable of capturing the mechanical behavior of nanocrystalline (nc) fcc metals. The nc‐material is modeled as a two‐phase material consisting of a grain interior (GI) phase and a grain boundary (GB) phase. A rate‐independent isotropic porous plasticity model is employed to describe the GB phase, whereas a crystal‐plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the GI phase. Assuming the rule of mixtures, the overall behavior of a given grain is obtained via volume averaging. The scale transition from a single grain to a polycrystal is achieved by Taylor‐type homogenization. It is shown that the proposed model is able to capture the inverse Hall‐Petch effect. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermo‐Mechanical FE2 Simulation Scheme for Abaqus
Authors: Regener Benjamin , Krempaszky Christian , Werner Ewald , Stockinger Martin 
Published: December 2011

AbstractA fully coupled multi‐physics (thermo‐mechanical) multi‐length scale (macro‐micro) finite element based simulation scheme for the commercial FE code Abaqus is introduced. The coupling of scales, initial boundary value problems on the macro‐ and micro‐scale as well as the micro‐scale testing procedure, which completes the consistent loop across the scales, are outlined. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extraction of effective material parameters with application to sandwich structures
Authors: Sehlhorst Hans‐Georg , Düster Alexander , Diebels Stefan , Rank Ernst 
Published: December 2011

AbstractIn this contribution we present a first‐order numerical homogenization approach which allows for extracting effective linear elastic properties of heterogeneous materials. The approach is based on the window or self consistency method where a representative microscopic subdomain is embedded into a window of effective properties. Since these properties are not known in advance they have to be determined iteratively. For the discretization of the micro structures we use the Finite Cell Method, which is a fictitious domain method of higher‐order. It is very well suited for efficiently discretizing complicated geometries stemming, for example, from tomography (CT‐scans). In the numerical examples we will investigate a bending test of a sandwich plate which is composed of a polymeric core with thin faceplates made of Aluminum. Firstly, effective properties of the core are extracted and then applied to a macroscopic numerical model. The numerical results are validated by experiments. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanics model for tortuosity and homogenized diffusion properties of porous materials with distributed micro‐cracks
Authors: Timothy Jithender Jaswant , Meschke Günther 
Published: December 2011

AbstractContinuum micromechanics [2,3] is used to model tortuosity within the context of ion transport to obtain the homogenized diffusivity of intact and micro‐cracked porous materials. A novel cascade homogenization technique to model ion diffusion in porous materials is proposed. A REVuc that represents the porous material is modelled as a spherical pore‐space inclusion in a recursively updated matrix with an initial diffusivity without any tortuosity. A REVc representing the micro‐cracked material is modelled with prolate ellipsoidal inclusions representing micro‐cracks embedded in a porous matrix [4]. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructural driven computational modeling of polymers
Authors: Tkachuk Mykola , Linder Christian 
Published: December 2011

AbstractThe key focus of this work is the polymer microstructure which is the origin of the overall material response. In elastomers random three‐dimensional networks are formed by long macromolecules connected at the cross‐links by vulcanization or permanent entanglements. The mechanical response of these materials is mainly entropic and is related to the number of conformations that flexible polymer chains can attain. The available kinetic theories link the entropy of a single chain to such microscopic quantities as the end‐to‐end distance between the cross‐links or the constraining tube diameter among others. The central issue of micromechanically‐based material modeling is the relation between these quantities and the macroscopic deformation. In this work this connection is established by a network homogenization approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Homogenization of Damage in the Hardened Cement Paste due to Alkali Silica Reaction
Authors: Wu Tao , Temizer İlker , Wriggers Peter 
Published: December 2011

AbstractIn this contribution, the model of the concrete deterioration due to the alkali silica reaction(ASR) at the microscale is set up. Based on a three‐dimensional micro computer‐tomography, a finite‐element mesh is constructed at the micrometer length scale and 3D coupled Chemo‐Themo‐Mechanics model in the hardened cement paste(HCP) and computational homogenization of damage are addressed in this contribution. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Large Eddy Simulations of Swirling Nozzle‐Jet Flow Undergoing Vortex Breakdown
Authors: Luginsland T. , Kleiser L. 
Published: December 2011

AbstractWe developed a numerical setup to simulate swirling jet flow undergoing vortex breakdown. Our simulation code CONCYL solves the compressible Navier‐Stokes equations in cylindrical coordinates using high‐order numerical schemes. A nozzle is included in the computational domain to account for more realistic inflow boundary conditions. Preliminary results of a Re = 5000 compressible swirling jet at Mach number M a = 0.6 with an azimuthal velocity as high as the maximum axial velocity (swirl number S = 1.0) capture the fundamental characteristics of this flow type: At a certain point in time the jet spreads and develops into a conical vortex breakdown. A stagnation point‐flow in the vicinity of the jet axis is clearly visible with the stagnation point located close to the nozzle exit. The stagnation point precesses in time around the jet axis, moving up‐ and downstream. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of mass transfer in thin liquid films on spinning disks using the integral method
Authors: Prieling Doris , Steiner Helfried 
Published: December 2011

AbstractThe present work applies the integral method to analyze the momentum and mass transfer in thin liquid films on spinning disks, with the aim to describe the complex process of wet chemical etching of rotating silicon wafers The obtained results capture very well the essential features of the etching activity on the disk, and are in good agreement with experimental results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On higher order effects in marginally separated flows
Authors: Scheichl Stefan , Kluwick Alfred , Braun Stefan 
Published: December 2011

AbstractIf the angle of attack α of a slender airfoil reaches a critical value αs flow separation is known to occur at the upper s surface. Further increase of α initially leads to the formation of a short laminar separation bubble which has an extremely weak influence on the external flow field – a phenomenon known as marginal separation – but then rather rapidly causes a severe change of the flow behaviour, leading to leading edge stall. According to the asymptotic theory of marginal separation holding in the limit of large Reynolds numbers Re, the flow in the neighbourhood of the separation bubble is governed by an integro‐differential equation. This so‐called interaction equation contains a single controlling parameter which relates the angle of attack to the Reynolds number, with a value Γs corresponding to αs. Some recent results concerning higher order s s corrections to this theory and their effect on the stability of steady solutions will be presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of Thermal Stratification on the Stability of Ekman‐Couette‐Flow
Authors: Withalm Martin , Hoffmann Norbert P. 
Published: December 2011

AbstractThe Ekman‐Couette‐System consists of two infinitely extended plates which are sheared in opposite directions over a fluid and are additionally rotated about their normal axis. In the case of angular velocities which tend to zero, the system becomes the classical Couette‐System, whereas for high angular velocities the boundary layers of the upper and lower plate are separated and represent Ekman boundary layers. For both limit cases the influence of thermal stratification on the stability of the base flow has been a subject of research for some time, but not so for moderate angular velocities. This was the motivation for doing a linear stability analysis for that case, including both stable and unstable stratification for a Prandtl number equal to unity. The results show, that as expected, stable stratification is suppressing the emergence of stationary as well as Type I‐ and Type II‐shear‐instabilities, while unstable stratification is supporting them. For unstable stratification, the system can also become unstable to a convection instability with all its properties known from other systems, except for that their orientation angle is not coincidental but determined due to the influence of the shear and Coriolis forces. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nitsche‐XFEM for a transport problem in two‐phase incompressible flows
Authors: Lehrenfeld Christoph 
Published: December 2011

AbstractWe consider the transport of a dissolved species in a divergence‐free immiscible incompressible two‐phase flow modeled by a convection diffusion equation. The so‐called Henry interface condition leads to a jump condition for the concentration at the interface between the two phases. This discontinuity of the solution render the numerical solution on unfitted meshes difficult. Furthermore time discretization on moving interfaces and handling typically convection dominant situations makes the overall problem delicate. We propose a numerical method using extended finite elements and a Nitsche‐type technique combined with streamline diffusion stabilization. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Viscous linear instability of a sheared liquid‐gas interface ‐ Effect of a velocity deficit near the interface
Authors: Otto Thomas , Boeck Thomas , Rossi Maurice 
Published: December 2011

AbstractThe 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 different asymptotic velocities and a velocity deficit near the interface. We examine the influence of the velocity deficit on the spatial growth rates of two competing modes originating from the Kelvin‐Helmholtz and viscosity contrast mechanisms. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical study of liquid/liquid slug flow in a capillary microreactor
Authors: Dittmar Ina , Ehrhard Peter 
Published: December 2011

AbstractThe great advantage of microreactors is associated with an extremely large surface‐to‐volume ratio. Hence, microreactors permit promising operating conditions, such as almost‐perfect heat or mass transfer. This, of course, requires that the hydrodynamics is well understood. The hydrodynamics of a liquid/liquid slug flow in a micro‐capillary is characterized by a complex vortex structure in both the disperse and the continuous phase. The disperse phase, in our investigations, is not wetting the walls and, thus, a thin film of the continuous phase persist between the disperse phase and the wall. Due to this phenomenon, a relative movement between disperse and continuous phase is possible and, indeed, observed. Understanding of these complex phenomena allows for a control of the hydrodynamics, and thus, to tailor the heat and mass transport in a desired manner.Apparently, several effects influence the hydrodynamics. The main dimensionless groups are a Reynolds number, a Capillary number, and the ratio of viscosities and densities of both phases. To study the physics of this complex two‐liquid system, a modified level‐set method in conjunction with an immersed‐boundary formulation is engaged. Presently, the simulations are time‐dependent and axially‐symmetric in nature. The mesh resolution represents a challenge, as the spatial resolution has to resolve the thin film between the disperse phase and the wall adequately. All simulations are implemented within the software OpenFOAM. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Instable Waves between Rough Elastic Bodies in Sliding Contact
Authors: Graf Matthias , Ostermeyer Georg‐Peter 
Published: December 2011

AbstractMost sliding bodies are not perfectly flat, but show a rough surface topography or tribological layer. This paper analyses a sliding system consisting of two elastic bodies with continuous contact and steady sliding. Surface topographies are taken into account by an inertia film on one of the sliding surfaces. A linear model is developed that allows an analytical solution. As a typical tribological system, the contact between pad and disc in a brake system is discussed. It can be shown that unstable elastic waves travel through the contact between both bodies. This instability is opened only when a tribological layer on the brake pad is taken into account. This microscopic excitation can cause a loss of stability of the entire (brake) system. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐dimensional ultrasound Doppler velocimeter for velocity field measurements of liquid metal flows
Authors: Franke Sven , Fischer Andreas , Büttner Lars , Czarske Jürgen , Räbiger Dirk , Eckert Sven 
Published: December 2011

AbstractWe present a novel fluid flow measurement system based on the pulsed‐wave ultrasound Doppler velocimetry being able to determine two‐dimensional velocity fields. It applies for the measurement of unsteady liquid metal flows driven by electromagnetic forces concerning the research field of magnetohydrodynamics. The application of advanced processing techniques enable high data acquisition rates and concurrently a high spatial resolution facilitating to resolve transient liquid metal flow structures which could not been acquired so far. An experimental setup utilizing liquid metal in a cubic vessel exposed to a stationary rotating magnetic field was used to validate the reliability of the measurement system. The swirling fluid motion in its horizontal section could be resolved into a velocity field grid of 24 × 24 vectors while achieving frame rates of about 30 fps. Results from a further study driving liquid metal in a cylindrical vessel by a pulsed rotating magnetic field are presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of two‐dimensional turbulent wall jet on a coanda surface
Authors: Florin Frunzulica , Alexandru Dumitrache , Octavian Preotu , Horia Dumitrescu 
Published: December 2011

AbstractThe Coanda effect that is the tendency of a fluid jet to stay attached to an adjacent curved surface that is very well shaped has been employed to improve the performance of various devices. The main objective of this paper is to investigate ways of keeping the flow attached to a larger length of a Coanda surface. There are considered two possibilities: one passive, which uses a slot that connects the low pressure and high pressure points on the Coanda surface and an active one, based on the principle of synthetic jet, created through an orifice located near the point of detachment of the jet. Reynolds averaged Navier‐Stokes simulations (RANS) with shear stress transport k‐ω (SST model) of Menter have been used to compute the two‐dimensional turbulent wall jet. The numerical results are presented for the two methods considered. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Study of Creeping Liquid Metal Flow in the Presence of a Permanent Magnet
Authors: Pulugundla Gautam , Karcher Christian 
Published: December 2011

AbstractIn this paper, we present the numerical study of interaction of a liquid metal flow with a small permanent magnet. Such an analysis is of fundamental interest for applications involving Lorentz Force Velocimetry (LFV). As a canonical problem, we consider the flow of liquid metal in the creeping flow regime (Re=0.01) through a square duct with electrically insulating walls. For this setup, we perform magnetohydrodynamic (MHD) simulations by coupling the commercial finite volume solver FLUENT and finite element solver COMSOL Multiphysics. Parametric analyses are performed at different relative positions of the permanent magnet with respect to the duct and with different magnetisation directions. The analyses provide good reference results for qualitative understanding of MHD flows exposed to non‐uniform magnetic fields. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laminar magnetohydrodynamic duct flow in the presence of a magnetic dipole
Authors: Tympel Saskia , Krasnov Dmitry , Boeck Thomas , Schumacher Jörg 
Published: December 2011

AbstractWe study magnetohydrodynamic flow of a liquid metal in a straight duct. The magnetic field is produced by an exterior magnetic dipole. This basic configuration is of fundamental interest for Lorentz force velocimetry (LFV), where the Lorentz force opposing the relative motion of conducting medium and magnetic field is measured to determine the flow velocity. The Lorentz force acts in equal strength but opposite direction on the flow as well as on the dipole. We are interested in the dependence of the velocity on the flow rate and on strength of the magnetic field as well as on geometric parameters such as distance and position of the dipole relative to the duct. To this end, we perform numerical simulations with an accurate finite‐difference method in the limit of small magnetic Reynolds number, whereby the induced magnetic field is assumed to be small compared with the external applied field. The hydrodynamic Reynolds number is also assumed to be small so that the flow remains laminar. The simulations allow us to quantify the magnetic obstacle effect as a potential complication for local flow measurement with LFV. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Euler‐Bernoulli Beam with Boundary Control: Stability and FEM
Authors: Miletic Maja , Arnold Anton 
Published: December 2011

AbstractWe consider a model for the time evolution of a piezoelectric cantilever with tip mass. With appropriately shaped actuator and sensor electrodes, boundary control is applied and a passivity based feedback controller is designed to include damping into the system. Assuming that the cantilever can be modeled by the Euler‐Bernoulli beam equation, we obtain a coupled PDE‐ODE system. First we discuss its dissipativity, and its asymptotic but non‐exponential stability. Next we derive a FEM using piecewise cubic Hermitian shape functions that is still dissipative. This is illustrated on a numerical simulation. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)