bluuebunny/crossref_metadata_2025_split huggingface dataset:
A coupled phase‐field model for ductile fracture in crystal plasticity
Authors: Hernandez Padilla Carlos Alberto , Markert Bernd 
Published: December 2014

AbstractThe objective of this work is to present a simplified, nonetheless representative first stage of a phenomenological model to predict the crack evolution of ductile fracture in single crystals. The proposed numerical approach is carried out by merging a conventional well‐ stablished elasto‐plastic crystal plasticity model and a well‐known phase‐field model (PFM) modified to predict ductile fracture. A two‐dymensional initial boundary‐value problem of ductile fracture is introduced considering a single crystal Nickel‐base superalloy material. the model is implemented into the finite element context subjected to a one‐dimensional tension test (displacement‐controlled). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constitutive relation for the mass transfer during a gas‐liquid phase transition in porous media
Authors: Häberle Kai , Ehlers Wolfgang 
Published: December 2014

AbstractThe transition between two different phases of a substance is an everyday process, which is encountered amongst others in the geomechanical field, for example, in CO2 storage. The transition from the liquid to the gaseous phase and vice versa crosses the so‐called two‐phase region, where both phases coexist for specific temperature and pressure conditions. In this context, two mass‐balance equations are defined for both fluid phases, respectively. These two equations are coupled by the mass‐production term, which describes the mass transfer between the two phases during phase transition. A great variety of models exist to describe phase transition processes in zero dimensional systems, e. g., batch reactors. However, only a few articles can be found, where phase changes inside a porous medium are discussed. An approach to the latter case can be based on the well‐founded, continuum‐mechanical Theory of Porous Media (TPM), which allows to describe multi‐phasic flow inside a deformable porous medium. By evaluating the entropy inequality, a constitutive relation for the mass production term can be derived. This term compares to the two‐film theory, the standard model for the description of mass transfer in a two‐phase system. Adapting this relation to porous media leads to a mass transfer coefficient, which represents the kinetic behaviour of the molecules of the substance under consideration and the influence of the solid porous material on the phase transition process. For lack of experimental data, the mass transfer coefficient will be composed of the transfer coefficient from classical thermodynamics and geometrical information of the porous‐media structure. The thermodynamical behaviour of the fluid is described by, e. g., the Redlich‐Kwong‐Soave equation of state. Simulations conducted with either changing temperature or pressure boundary conditions are compared with simulations, where only one mass balance is used for both fluid phases and the mass transition is only visible by the jump in density. This allows for the verification of the derived constitutive relation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Study on Mixed Finite Element Formulations Applied to Diffusion Problems
Authors: Kaessmair Stefan , Javili Ali , Steinmann Paul 
Published: December 2014

AbstractThe objective of this contribution is to study various mixed finite element schemes applied to classical and non‐classical diffusion problems. The Fickean diffusion is considered using a three‐field formulation where the concentration gradient and the diffusive flux are additionally chosen as independent variables. Furthermore, the non‐classical diffusion model given by the Cahn–Hilliard equation is discussed where mixed finite elements are used to cast the fourth‐order PDE into two second‐order PDEs. A penalized version of a mixed formulation for the underlying second gradient model is given by specific micromorphic models. Another approach is a classical second order splitting method. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dependence of the aeroelastic stability of a slender U‐beam on the realized flow pattern
Authors: Strecha Johannes , Steinrück Herbert 
Published: December 2014

AbstractWe investigate the aeroelastic behaviour of a slender U‐beam in cross‐flow. Two distinct, time periodic flow patterns are observed in simulations of the flow around this beam. Its aeroelastic properties depend on the realized flow pattern, especially so for low reduced velocities: One flow pattern leads to pronounced torsional vortex‐induced vibrations. No such vibrations could be observed under the other flow pattern. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the effective elasticity tensor of a folded sandwich core
Authors: Massow Holger , Becker Wilfried 
Published: December 2014

AbstractThis document describes the homogenization of a folded sandwich core. By using a numerical homogenization concept the components of the elasticity tensor of the foldcore continuum are determined. The foldcore exhibits an effective orthotropic behaviour with the particularity that it can be auxetic. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The heterogeneous multiscale method as a framework for coupling the finite element method and molecular dynamics
Authors: Ulz Manfred H. 
Published: December 2014

AbstractHierarchical two‐scale methods are computationally very powerful as there is no direct coupling between the macro‐ and microscale. Such schemes develop first a microscale model under macroscopic constraints, then the macroscopic constitutive laws are found by averaging over the microscale. The heterogeneous multiscale method (HMM) is a general top‐down approach for the design of multiscale algorithms. While this method is mainly used for concurrent coupling schemes in the literature, the proposed methodology also applies to a hierarchical coupling. This contribution discusses a hierarchical two‐scale setting based on the heterogeneous multi‐scale method for quasi‐static problems: the macroscale is treated by continuum mechanics and the finite element method and the microscale is treated by statistical mechanics and molecular dynamics. Our investigation focuses on an optimised coupling of solvers on the macro‐ and microscale which yields a significant decrease in computational time with no associated loss in accuracy. In particular, the number of time steps used for the molecular dynamics simulation is adjusted at each iteration of the macroscopic solver. A numerical example demonstrates the performance of the model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale modeling of continuous fiber and fabric reinforced rubber components
Authors: Achenbach Volker , Baaser Herbert 
Published: December 2014

AbstractFabric or continuous fiber reinforced rubber components (e.g. tires, air springs, industrial hoses, conveyor belts or membranes) are underlying high deformations in application and show a complex, nonlinear material behavior. A particular challenge depicts the simulation of these composites. In this contribution we show the identification of the stress and strain distributions by using an uncoupled multiscale modeling method, see [1]. Within this method, two representation levels are described: One, the meso level, where all constituents of the composite are shown in a discrete manner by a representative volume element (RVE) and secondly, the macro level, where the structural behavior of the component is defined by a smeared anisotropic hyperelastic constitutive law. Uncoupled means that the RVE does not drive the macroscopic material behavior directly as in a coupled approach, where a RVE boundary value problem has to be solved at every integration point of the macro level. Thus an uncoupled approach leads to a tremendous reduction in numerical effort because the boundary value problem of a RVE just has to be solved at a point of interest, see [1]. However, the uncoupled scale transition has to fulfill the HILL–MANDEL condition of energetic equivalence of both scales. We show the calibration of material parameters for a given constitutive model for fiber reinforced rubber by fitting experimental data on the macro level. Additionally, we demonstrate the determination of effective properties of the yarns. Finally, we compare the energies of both scales in terms of compliance with the HILL–MANDEL condition by using the example of a biaxial loaded sample and discuss the consequences for the mesoscopic level. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermo‐mechanical homogenisation – application to HVOF thermal‐sprayed WC‐Co coatings
Authors: Berthelsen Rolf , Denzer Ralf , Menzel Andreas 
Published: December 2014

AbstractHard material coatings are widely employed as wear protection for highly engrossed surfaces. For example, coatings consisting of tungsten carbide (WC) and cobalt (Co) are used for sheet metal forming tools. A relatively cost‐efficient coating technique is the high velocity oxygen fuel (HVOF) thermal spraying process which, as a trade‐off, induces a large amount of energy into the heterogeneous coating and the substrate. Hence, this leads to a complex transient, thermomechanically coupled problem. In order to predict the residual stresses during the quenching procedure, a two scale finite element framework is established wherein the scale bridging is performed by application of two different homogenisation approaches. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A spotlike edge state in plane Poiseuille flow
Authors: Zammert Stefan , Eckhardt Bruno 
Published: December 2014

AbstractWe study the laminar turbulent boundary in plane Poiseuille flow at Re = 1400 and 2180 using the technique of edge tracking. For large computational domains the attracting state in the laminar‐turbulent boundary is localized in spanwise and streamwise direction and chaotic. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and Simulation of Degassing Process
Authors: Alimi Aria , Lübke Martin , Wünsch Olaf 
Published: December 2014

AbstractThis work deals with the modelling and simulation of a degassing process mainly used for extruders in polymer industry. The numerical simulations are done with finite‐volume method using OpenFOAM for a 2D single screw extruder. The material parameters have been all chosen for a PDMS‐Pentane polymer mixture so that the results could be compared with the available experiments already performed for this mixture [1]. In addition to experiments, the numerical results will be compared with an analytical solution derived from Danckwerts' model [2][3]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bio‐inspired propulsion: Downstream travelling wave motion of a surface with finite & infinite extension
Authors: Müllner Markus 
Published: December 2014

AbstractThe thrust force on a surface that performs a fish‐like travelling wave motion downstream to an oncoming flow is discussed. Unsteady potential flow, with vortex shedding from the trailing edge, is known to explain the generation of thrust. Contrarily, fish swimming has been related to the flow over an infinitely extended surface. To interlink both problems, the potential flow over the surface of finite length is considered in the limit of high wave numbers. It turns out that the leading order, space‐periodic pressure does not contribute to thrust. Thus, the perturbation pressure is essential for propulsion. Besides, laminar flow is considered in the space‐periodic setting. The present results reveal – in contrast to literature – that the surface force is always drag. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of reattachment region behind backward‐facing step in a narrow channel
Authors: Uruba Václav 
Published: December 2014

AbstractDynamics of the flow reattachment behind the backward‐facing step in a narrow channel is studied experimentally using the PIV technique. Reattachment region is detected by statistical characteristics of the flow velocity close to the channel bottom. Two methods of reattachment definition are applied. The reattachment region structure and extent is shown. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of round jets with nozzle‐dependent inflow conditions using the k−ε turbulence model
Authors: Reinhardt Yvonne , Kleiser Leonhard 
Published: December 2014

AbstractIn view of the “round jet initial condition anomaly”, discussed in literature, we investigate the effect of inflow conditions resulting from the use of different nozzle geometries to form the jet. RANS simulations in the framework of OpenFOAM using the k − ε turbulence model are performed. As the standard model coefficient Cε1 = 1.44 is known to overpredict spreading rates for round jets, a value of Cε1 = 1.6 was recommended for this case already in the 1970's. While this works well for jets issuing from long pipes, it does not give satisfactory results for other nozzle geometries. To overcome this deficiency while keeping the k − ε model, we suggest modified coefficients Cε1 based on profiles of mean flow and turbulence at the nozzle exit. We determine optimal values of Cε1 for three different nozzle geometries, and test them at various Reynolds numbers. Good agreement with experimental data is obtained. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the benefits of ODT‐based stochastic turbulence modeling
Authors: Schmidt Heiko , Glawe Christoph , Jozefik Zoltan , Meiselbach Falko T. , Kerstein Alan R. 
Published: December 2014

AbstractWe summarize the group's progress in applying, analyzing, and improving ODT and ODT‐based stochastic turbulence models like ODTLES. Compared to DNS these models span a wider range of scales while compared to RANS/LES (i) the molecular effects are retained and (ii) no assumption of scale separation is made. In this regard ODTLES has more properties of DNS than of standard LES. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical study of a particle separation method based on the Segré‐Silberberg effect
Authors: Fischer Maximilian , Ehrhard Peter 
Published: December 2014

AbstractParticles that are placed in a laminar pipe flow rotate and migrate transversally to a radial equilibrium position. This so called Segré‐Silberberg effect is used in a new method for size separation of particles. The particles to be separated are placed in a pipe flow and subsequently enter an expansion chamber, where the flow is split and the particles are divided into two fractions. This paper reports the results of two‐dimensional Euler‐Lagrange simulations of the motion of neutrally‐buoyant particles inside the expansion chamber. The simulation results agree well with experimental data on the separation and show that the Saffman force has a significant impact onto the particle trajectories. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solutions of an extended Korteweg‐de Vries equation describing solitary waves in turbulent open‐channel flow
Authors: Jurisits Richard 
Published: December 2014

AbstractSolitary waves in two‐dimensional, turbulent open‐channel flow are considered. In an asymptotic analysis given in [1], assuming a bottom roughness that is varying along the channel bed, an extended Korteweg‐de Vries (KdV) equation was derived to describe the surface elevation of the wave. We adopted this equation and solved it numerically as a coupled boundary‐value eigenvalue problem, obtaining results for stationary and transient wave solutions as well as for the eigenvalue, which corresponds to distinct values of the bottom friction coefficient. While the numerical solutions as compared to the asymptotic solutions in [1] agree well in the stationary case, there were major differences found in the transient solutions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations of Passive Flow Control Devices for Vertical Axis Wind Turbines
Authors: Frunzulică Florin , Dumitrache Alexandru , Dumitrescu Horia 
Published: December 2014

AbstractThe purpose of these investigations is to study the possibilities to improve performances of a typical vertical axis wind turbines (VAWT), of Darrieus‐type, using passive devices (mounted “on” or “inside” the blades of VAWT) to control dynamic flow separation (dynamic stall phenomenon). The passive devices considered for investigations are the Gurney flap, the slot or thin channel, and the turbulence promoters. Studies are performed numerically using computational fluid dynamics and where it is possible the results are compared with existent experimental or numerical data. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Risk assessment for crosswind stability of vehicles on exposed sites
Authors: Proppe Carsten , Zhang Xiaoyu 
Published: December 2014

AbstractThe main purpose of this paper is to provide a reliable evaluation for the crosswind stability of different road vehicles in a realistic physical scenario. Unlike existing approaches, we analyze the wind‐vehicle system by probabilistic methods. The aerodynamic coefficients together with the gust parameters are considered as random variables. In addition, on‐site measured wind data are used to calibrate the gust model. As the excitation of the vehicle is a stochastic process, risk analyses have to be carried out and failure probabilities are computed. Based on the failure probabilities, guidelines for speed limitations or traffic restrictions can be developed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of Approximation Models for Solving Kinetic Equations
Authors: Ahmedov Bahodir , Herty Michael , Frank Martin 
Published: December 2014

AbstractWe consider the problem of cancer treatment using radiation therapy. A deterministic Boltzmann equation is considered as the particle transport model. The PN system of moment equations is derived using angular discretization of the transport equation. This PN system is solved using StaRMAP [3]. An optimization problem to get the desired particle distribution is formulated and solved using adjoint equations. The algorithm is validated with several simulations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of the Velocity Field of 2D and 3D Tunnel Models with Frequency Domain Full Waveform Inversion
Authors: Musayev Khayal , Hackl Klaus , Baitsch Matthias 
Published: December 2014

AbstractFull Waveform Inversion (FWI see [1]) has capability to identify the velocity field of a domain with a good precision. Its power comes from the fact that this approach does not only try to fit travel times of waves, but it tries to fit the whole seismogram. This work is about the application of acoustic full waveform inversion to 2D and 3D tunnel models. The necessary boundary conditions are applied to the models and the acoustic equation is solved by higher‐order Finite Elements Method. The Conjugate Gradient (CG) method is utilized to minimize the misfit function. The results were verified with synthetic models. The synthetic tunnel models contain few bodies with different shapes and locations. Starting from a homogeneous velocity field, the synthetic model is sought over iterations. To avoid the ill‐posedness, the locations and numbers of the source and receiver points have to be successfully chosen. Apart from this, the frequency set has also to be carefully constructed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Design space exploration based on variational sensitivity analysis
Authors: Gerzen Nikolai , Barthold Franz‐Joseph 
Published: December 2014

AbstractThis contribution deals with variational sensitivity analysis of a non‐linear solid shell in context of shape optimisation. A technique to explore the structural design is outlined. It is based on the analytical derivation and efficient computation of the Fréchet derivatives of the state functions with respect to the full space of all possible design parameters. This overhead of sensitivity information is examined by a principal component analysis (PCA) in order to detect design changes with major and minor influence on the structural response, the objectives and constraints. This knowledge enables the engineers to understand and improve structural optimisation models and to detect possible numerical defects in the early stage. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparing Optimization Algorithms for Shape Optimization of Extrusion Dies
Authors: Siegbert Roland , Kitschke Johannes , Djelassi Hatim , Behr Marek , Elgeti Stefanie 
Published: December 2014

AbstractThe classical approach to extrusion die design relies heavily on the experience of the die designer; Especially the designer's ability to create an initial die design from a product design, the designer's constructional knowledge and performance during the running‐in trials. Furthermore, the relative unpredictability of the running‐in trials combined with the additional resource usage introduce uncertainties and delays in the time‐to‐market of a given product. To lower these delays and resource usage, extrusion die design can benefit greatly from numerical shape optimization. In this application, however, plastics melts pose a difficult obstacle, due to their rather unintuitive and nonlinear behavior. These properties complicate the numerical optimization process, which mimics running‐in trials and relies on a minimal number of optimization iterations. As part of the Cluster of Excellence Integrative Production Technologies for High‐Wage Countries at the RWTH Aachen University, an effort is made to shorten the manual running‐in process by the means of numerical shape optimization. Using an in‐house numerical shape optimization framework, a set of optimization algorithms, consisting of global, derivative‐free and gradient‐based optimizers, are evaluated with respect to the best die quality and a minimal number of optimization iterations. This evaluation is an important step on the way to include more computationally intensive material models into the optimization framework and identify the best possible optimization strategy for the numerical design of extrusion dies. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarks on different strategies for sensitivity analysis of multiscale problems in structural optimisation
Authors: Kijanski Wojciech , Barthold Franz‐Joseph 
Published: December 2014

AbstractThe adjustment of properties of materials to special requirements plays a more and more important role in engineering applications. Thus, the question about design and optimisation of materials arises. In this contribution some basic and necessary aspects for the treatment of structural optimisation problems in terms of multiscale modelling are given. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
How long does it take to consensus in the Hegselmann‐Krause model?
Authors: Kurz Sascha 
Published: December 2014

AbstractHegselmann and Krause introduced a discrete‐time model of opinion dynamics with agents having limit confidence. It is well known that the dynamics reaches a stable state in a polynomial number of time steps. However, the gap between the known lower and upper bounds for the worst case is still immense. In this paper exact values for the maximum time, needed to reach consensus or to discover that consensus is impossible, are determined using an integer linear programming approach. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)