bluuebunny/crossref_metadata_2025_split huggingface dataset:
A constitutive model for a high alloyed cast CrMnNi TRIP‐steel
Authors: Prüger Stefan , Kuna Meinhard 
Published: December 2011

AbstractThe macroscopic material model, proposed by Papatriantafillou [1], is adopted to describe the rate dependent flow behaviour and the temperature and stress state dependent γ‐α′ phase transformation of a newly developed cast TRIP‐steel. Simple test of the implemented model revealed that the evolution of the martensite volume fraction is not predicted correctly in case of inelastic deformation and subsequent unloading. Therefore, we present an improved model for the γ‐α′ phase transformation and show that these predictions are due to the choice of the corresponding thermodynamical driving force. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of different distortional hardening models suitable for the analysis of magnesium
Authors: Shi Baodong , Mosler Joern 
Published: December 2011

AbstractHCP metals such as magnesium are characterized by a strong interplay between dislocation slip and deformation‐induced twinning. These micromechanical processes result in a complex macroscopic behavior. More precisely, in addition to classical isotropic and kinematic hardening, the shape of the macroscopic yield function changes during deformation as well. This effect which is frequently referred to as distortional hardening is particularly pronounced in case of non‐radial loading paths typical for most forming processes. Consequently, a physically sound distortional hardening is of utmost importance for several technically relevant applications. In the present contribution, three different of such enhanced hardening models are critically analyzed. Focus is on the modeling of magnesium. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the simulation of nonlinear hardening in metallic materials using the concept of representative directions
Authors: Shutov Alexey , Freund Michael , Ihlemann Jörn 
Published: December 2011

AbstractWe generalize a uniaxial model of finite strain viscoplasticity using the concept of representative directions. As a result, a new phenomenological material model is obtained, which can describe the mechanical behavior under arbitrary loading conditions. The original uniaxial model takes the nonlinear isotropic and kinematic hardening into account, but it does not cover the distortional hardening. We show that the isotropic and kinematic hardening is completely retained during the process of generalization. Moreover, the distortional hardening effects are naturally induced by the concept. The resulting material model is validated by a comparison with real experimental data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary value problems of steady vibrations in the theory of thermoelasticity with microtemperatures
Authors: Svanadze Merab 
Published: December 2011

AbstractIn this paper the linear theory of steady vibrations of thermoelasticity with microtemperatures for isotropic solids with microstructure is considered. The uniqueness and existence theorems of solutions of the internal and external second boundary value problems (BVPs) by means of the boundary integral method (potential method) and the theory of singular integral equations are proved. The existence of eigenfrequencies of the internal homogeneous BVP of steady vibrations is studied. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of the mixed time partitioning methods in relation to the size of time step
Authors: Gawronska Elzbieta , Sczygiol Norbert 
Published: December 2011

AbstractIn this paper we focus on stability of a mixed time partitioning methods in relation to time step size which is using in numerical modelling of two‐component alloys solidification. We present the numerical integration methods to solve solidification problems in a fast and accurate way. Our approach exploits the fact that physical processes inside a mould are of different nature than those in a solidifying cast. As a result different time steps can be used to run computations within both sub‐domains. Because processes that are modeled in the cast sub‐domain are more dynamic they require very fine‐grained time step. On the other hand a heat transfer within the mould sub‐domain is less intense, and thus coarse‐grained step is sufficient to guarantee desired precision of computations. We propose using a fixed time step in the cast and its integer multiple in other parts of mould. We use one‐step explicit and implicit time integration Θ schemes. These time integration schemes are applied to equations obtained after spatial discretization. The implicit scheme is unconditionally stable, but stability of the explicit scheme depends on the size of time step. Critical time step size can be determined on the basis of eigenvalues of the amplification matrix that depend on the material properties, size and type of the finite element. In this work we present the manner of determining the critical time step and its affect on the course of numerical simulation of solidification. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct numerical simulation of particles in a fluid interacting with a wall
Authors: Lechner Christiane , Kuhlmann Hendrik C. 
Published: December 2011

AbstractWe develop a code to be applied in the context of the cleaning of wafer surfaces by hydrodynamic forces. Our goal is to study the detachment of (submicron) particles, exposed to a shear flow, from a wall by means of direct numerical simulation. The particles are treated as rigid bodies fully interacting with the fluid.To simulate moving particles in the fluid we implement an immersed boundary method with direct forcing into OpenFOAM. The particle‐wall interaction is treated with a soft contact model. As first simple examples we study the elastic normal impact of a cylinder onto a wall as well as the onset of sliding of a cylinder pressed to a horizontal wall by gravity under a time‐depended drag force. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Finite element solution of the Kohn‐Sham equations
Authors: Schauer Volker , Linder Christian 
Published: December 2011

AbstractMany properties of condensed matter as for example electric conductivity, magnetism as well as the mechanical response upon external excitations are determined by the electronic structure of the material. Its evaluation represents a coupled, quantum mechanical many body problem, consisting of the positively charged atomic cores and the negatively charged, fermionic electrons. By the Hohenberg‐Kohn theorem a method was established to calculate the ground state electron density through a density functional. Then the Kohn‐Sham equations resemble a nonlinear, single electron problem with an effective potential, accounting for the Coulomb interactions between the particles as well as for quantum mechanical effects. They can be solved within a self consistent field procedure. In this work a real space formulation for the calculation of the electronic structure in the context of density functional theory is shown. In a first step a finite element based solution algorithm for the Kohn‐Sham equations is developed, based upon which the electron density is obtained in a non‐periodic setting. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Reconstruction and Computation of Dual‐Phase Steel Microstructures Based on 3D EBSD Data
Authors: Brands Dominik , Schröder Jörg , Balzani Daniel , Dmitrieva Olga , Raabe Dierk 
Published: December 2011

AbstractIn this contribution we reconstruct the three dimensional microstructure of a dual‐phase steel based on the tomographic experimental data provided by the 3D electron backscatter diffraction (3D EBSD) method. The cross sections of the resulting microstructure are compared to the 2D reconstruction, which are obtained directly from the 3D EBSD data. We also perform FE‐simulations based on these geometries and observe comparable results in 2D and 3D. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hybrid Micro‐Macro‐Modeling of Evolving Anisotropies and Length Scales in Finite Plasticity of Polycrystals
Authors: Frankenreiter Ilona , Rosato Daniele , Miehe Christian 
Published: December 2011

AbstractThe paper focuses on an efficient multiscale approach to the description of evolving anisotropies in polycrystals. The predictive description of complex overall effects needs multiscale methods, taking into account basic ingredients of the material microstructure by model‐inherent scale‐bridging techniques. Straightforward homogenization‐based multiscale methods, such as FEM2 type two‐scale bridgings, are too time consuming for the solution of real engineering problems. A computationally manageable approach is provided by hybrid micro‐macro‐modeling techniques, which combine a purely macroscopic modeling with selected microstructural bridging techniques. Of particular importance are crystal reorientation mechanisms, which cause texture‐based anisotropies at the macroscale. The coupling is realized by homogenization‐based definitions of macroscopic structural tensors, which account for the evolving orientation texture. A crucial aspect is the combination of this hybrid texture modeling with further anisotropy effects, caused by dislocation‐structures. They are mainly responsible for hardening effects related to changes of the strain path. Furthermore, a particular account is taken on size effects and length scales by embedding the hybrid modeling technique into an extended theory of gradient‐plasticity. This results in a computationally efficient hybrid two‐scale model for polycrystalline plasticity, whose capability is demonstrated by means of representative benchmarks. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effective elastic properties of 3D polypropylene microstructures of an injection moulded plate via different homogenization schemes
Authors: Laschet Gottfried , Baranowski Thomas , Kashko Tanya , Arping Tim 
Published: December 2011

AbstractThe mechanical properties of a polypropylene (PP) part depend on its morphology and degree of crystallinity. To evaluate its effective elastic behaviour two upscaling schemes are developed and compared. In the 1st method the spherulites are assumed to be isotropic and vary linearly with the spherulite diameter. In the 2nd one, the homogenization is performed successively on two scales. At the nanoscale, the bilamina of amorphous and crystalline phases is homogenized. Then, at the microscale, a 3D radial distribution of effective bilamina is homogenized. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear stability characteristics of the pressure‐gradient driven flow between walls in a rotating system under the influence of the Coriolis force
Authors: Khan Muhammad Ijaz , Vasanta Ram Venkatesa 
Published: December 2011

AbstractThe paper addresses the question of the disturbance propagation when the plane channel flow on a rotating system is under the influence of the Coriolis force. The problem is approached through the method of Stewartson and Stuart (1971) to handle bifurcation characteristics. It starts from solving the linear (eigenvalue) problem and extends the same to handle growing distubances in the vicinity of the neutral surface. Solution for the problem addressed over the range of flow parameters characterised by the dominant physical mechanism affecting transition, viz. the Tollmien‐Schlichting mechanism or the Coriolis force mechanism, will be presented.. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A mixed least‐squares formulation of the Navier‐Stokes equations for incompressible Newtonian fluid flow
Authors: Schwarz Alexander , Schröder Jörg 
Published: December 2011

AbstractThe goal of this contribution is the numerical simulation of Newtonian fluid flow. In order to solve the governing incompressible Navier‐Stokes equations, a mixed finite element based on a least‐squares formulation is presented. We derive a div‐grad first‐order system resulting in a three‐field approach with stresses, velocities, and pressure as unknowns, see e.g. Cai et al. [1], which is the basis for the associated minimization problem. Finally, a numerical example is presented to show the applicability and performance of the considered formulation. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inflow Treatment for the Simulation of Subsonic Jets with Turbulent Nozzle Boundary Layers
Authors: Bühler S. , Kleiser L. 
Published: December 2011

AbstractThe state of the boundary layer at the nozzle exit of a circular nozzle‐jet configuration has an important influence on the development of the shear layer and the emitted sound. Of special interest is the acoustic near‐field obtained when the nozzle exit boundary layer is fully turbulent. The turbulent inflow generation and the inflow boundary treatment are important issues to be addressed. We use the Synthetic Eddy Method (SEM) to generate a turbulent inflow which reproduces mean flow and Reynolds stress profiles of specified reference data. The spatially and temporally varying synthetic fluctuations are imposed in the simulation by a forcing term added to the governing equations which is active in a small region downstream of the inflow boundary. This forcing in combination with characteristic boundary conditions allows for passing of upstream‐propagating acoustic waves and avoids an uncontrolled drift of mean‐flow quantities. We employ this inflow boundary treatment for a subsonic nozzle‐jet flow simulation at a Reynolds number of ∼ 9500 and Mach number of 0.9. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermocapillary flow on a gas‐liquid surface under normal and reduced gravity
Authors: Heiland Hans Georg , Schade Klaus‐Peter , Wozniak Günter 
Published: December 2011

AbstractThe aim of the present work is the study of the thermocapillary flow phenomenon at 1‐g, μ‐g conditions and the transition between 1‐g and μ‐g. The experimental results were observed with a novel high speed imaging system using a combination of a monochrome high speed CCD camera and a liquid crystal tunable filter. The flow velocity and the temperature patterns could be measured simultaneously from the seeded thermochromic liquid crystals, which change colour depending on their temperature. We investigated the thermocapillary flow with an experimental setup, where a bubble is positioned in a liquid matrix under a heated wall. The µ‐g experiments were conducted in the drop tower of the ZARM‐Institute of the University of Bremen. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficiency of a DC magnetic field used for braking the flow within a continuous casting mould
Authors: Miao Xincheng , Timmel Klaus , Eckert Sven , Lucas Dirk , Gerbth Gunter 
Published: December 2011

AbstractThe continuous casting technology provides about 90 percent of the world steel production. The application of DC magnetic fields in form of so‐called electromagnetic brakes is considered for an effective flow control with substantial capabilities to improve the product quality or to enhance the productivity of the process. The main effect of the DC magnetic field is supposed to result in a uniform reduction of the maximum velocities in the discharging jet from the submerged entry nozzle and to damp violent turbulent fluctuations. However, the electromagnetic braking of such highly turbulent and complex flows is complicated phenomenon and has not been understood fully until now. We present numerical and experimental investigations focusing on the fluid flow in the continuous casting mould under the influence of a transverse magnetic field. Numerical calculations were performed using the software package CFX with an implemented RANS‐SST turbulence model. the non‐isotropic nature of the MHD turbulence was taken into account by specific modifications of the turbulence model. Corresponding experimental investigations were carried out at the mock‐up LIMMCAST at HZDR. The comparison between our numerical calculations and the experimental results display a very well agreement. An important outcome of this study is the feature that the magnetic field does not provide a continuous reduction of the velocity fluctuations at the nozzle port. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase resolved measurements of the statistical flow behavior of a backward‐facing step flow controlled by a sinusoidal Lorentz‐force
Authors: Neumann Mathias , Büttner Lars , Weier Tom , Czarske Jürgen 
Published: December 2011

AbstractIn order to gain deeper inside into the behavior of a Lorentz‐force controlled flow behind a backward‐facing step, measurements with a laser Doppler velocity profile sensor were undertaken. By varying the frequency of the sinusoidal Lorentz‐force the influence on the turbulence statistics was studied. Moreover, phase resolved measurement data is presented. The results confirm the characteristic frequency determined on basis of the momentum thickness beforehand. The aim of this study is to understand the influence of the different incitation signals and to reduce the reattachment length. The statistical results show a dependency of the turbulence degree on the excitation frequency as well as a deformation of the flow profile behind the step. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Divergence of a thin elongated plate in supersonic gas flow
Authors: Boris Loginov , Tatyana Badokina , Youri Rousak 
Published: December 2011

AbstractBuckled forms of a thin elastic flexible elongated plate lying on elastic base in supersonic gas flow are computed by bifurcation theory methods. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Selection of minimizers for one‐dimensional Ginzburg‐Landau functional with 3‐well potential by singular lower‐order term
Authors: Raguž Andrija 
Published: December 2011

AbstractWe consider a variant of the Ginzburg‐Landau type functional in one dimension with 3‐well potential, penalized by lower‐order term which has singularity in one of the zeros of the potential function. Based on the approach developed in the paper G. Alberti, S. Muller: A new approach to variational problems with multiple scales, Comm. Pure Appl. Math. 54, 761‐825 (2001), we obtain Gamma‐convergence and provide description of the minimizers as small parameter epsilon tends to zero. We show that introduction of singular lower‐order term results in appropriate selection of the minimizers. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Explicit solution of the boundary value problem of the theory of thermoelasticity with microtemperatures for elastic circle
Authors: Tsagareli Ivane , Svanadze Maia M. 
Published: December 2011

AbstractIn this paper we solve explicitly, by means of absolutely and uniformly convergent series, the 2D boundary value problem (BVP) of statics of the linear theory of thermoelasticity with microtemperatures for an elastic circle. The uniqueness theorem of the internal BVP is proved. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A time optimal control problem for the collision‐free robot motion planning
Authors: Landry Chantal , Gerdts Matthias , Henrion René , Hömberg Dietmar 
Published: December 2011

AbstractA time optimal control problem for the computation of the fastest collision‐free trajectory of a robot surrounded by obstacles is presented. The dynamics of the robot is governed by ordinary differential equations. To build the collision avoidance criterion, the robot and the obstacles are represented as finite unions of convex polyhedra. Each polyhedron is described by a system of linear inequalities. This description combined with linear programming arguments allows us to include the collision avoidance as linear state constraints in the optimal control problem. The resulting system is then solved by a sequential quadratic programming method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Differentiable evaluation of objective functions in sampling design with variance‐covariance matrices
Authors: Mommer Mario S. , Sommer Andreas , Schlöder Johannes P. , Bock H. Georg 
Published: December 2011

AbstractIn this short note we consider the differentiable evaluation of the objective function of the sampling design optimization problem based on the inverse of the Fisher information matrix, and where the integer design variables have been converted into real variables using a relaxation technique. To ensure differentiability and cover the full range of the variables, and thus improve the convergence behavior of derivative‐based optimization algorithms, we propose applying a Cholesky decomposition on the Fisher information matrix, but using a special higher precision floating point arithmetic to ensure stability. While each evalu‐ation of the functional becomes slower, the algorithm is much simpler, amenable to be used with automatic differentiation directly, and can be shown to be very stable. For many practical situations, this is a valuable trade‐off. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetric Exchange of Variables and Stepwise Regression Methods
Authors: Niessner Herbert 
Published: December 2011

AbstractA step in Gauss‐Jordan elimination may be seen as exchanging a dependent variable for an independent one. If at the same time one of them changes sign a symmetric system matrix remains symmetric with the pivot reversing sign [2]. This variant can efficiently be exploited inverting symmetric positive definite matrices but also for obtaining a most complete set of relevant statistical quantities in stepwise regression via normal equations proposed by Efroymson 1960 and improved by Breaux 1968. We compare this method with numerically more stable ones applying orthogonal transformations, in particular that of Eldéen 1972 using Householder transformations and that of Gragg‐LeVeque‐Trangenstein 1979 using modified Gram‐Schmidt. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergent geometric integrator for the Landau‐Lifshitz‐Gilbert equation in micromagnetics
Authors: Goldenits Petra , Praetorius Dirk , Suess Dieter 
Published: December 2011

AbstractWe consider a lowest‐order finite element scheme for the Landau‐Lifshitz‐Gilbert equation (LLG) which describes the dynamics of micromagnetism. In contrast to previous works, we examine LLG with a total magnetic field which is induced by several physical phenomena described in terms of exchange energy, anisotropy energy, magnetostatic energy, and Zeeman energy. In our numerical scheme, the highest‐order term which stems from the exchange energy, is treated implicitly, whereas the remaining energy contributions are computed explicitly. Therefore, only one sparse linear system has to be solved per time‐step. The proposed scheme is unconditionally convergent to a global weak solution of LLG. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Total Variation Diminishing Implicit Runge‐Kutta Methods for Dissipative Advection‐Diffusion Problems in Astrophysics
Authors: Happenhofer Natalie , Koch Othmar , Kupka Friedrich , Zaussinger Florian 
Published: December 2011

AbstractWe investigate the properties of dissipative full discretizations for the equations of motion associated with models of flow and radiative transport inside stars. We derive dissipative space discretizations and demonstrate that together with specially adapted total‐variation‐diminishing (TVD) or strongly stable Runge‐Kutta time discretizations with adaptive step‐size control this yields reliable and efficient integrators for the underlying high‐dimensional nonlinear evolution equations. For the most general problem class, fully implicit SDIRK methods are demonstrated to be competitive when compared to popular explicit Runge‐Kutta schemes as the additional effort for the solution of the associated nonlinear equations is compensated by the larger step‐sizes admissible for strong stability and dissipativity. For the parameter regime associated with semiconvection we can use partitioned IMEX Runge‐Kutta schemes, where the solution of the implicit part can be reduced to the solution of an elliptic problem. This yields a significant gain in performance as compared to either fully implicit or explicit time integrators. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)