bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two accuracy improvements on nonuniform transformation field analysis for plasticity coupled to softening
Authors: Ju Xiaozhe , Mahnken Rolf 
Published: October 2016

AbstractA reduced order homogenization scheme for the case of plasticity coupled with softening effects is proposed. This is based on a straightforward extension of the so‐called nonuniform transformation field analysis (NTFA, [2]). Two related new methods, denoted as uneven NTFA and adaptive NTFA accounting for accuracy improvements, are also presented, which are based on the ideas of parameter identification and adaptive modeling, respectively. A complementary numerical study is given. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linking macroscopic deformation processes to microstructure evolution using an FE‐FFT‐based micro‐macro transition and non‐conserved phase‐fields
Authors: Kochmann Julian , Ehle Lisa , Wulfinghoff Stephan , Svendsen Bob , Reese Stefanie 
Published: October 2016

AbstractThe purpose of this work is the multiscale FE‐FFT‐based prediction of macroscopic material behavior, micromechanical fields and bulk microstructure evolution in polycrystalline materials subjected to macroscopic mechanical loading. The macroscopic boundary value problem (BVP) is solved using implicit finite element (FE) methods. In each macroscopic integration point, the microscopic BVP is embedded, the solution of which is found employing fast Fourier transform (FFT), fixed‐point and Green's function methods. The mean material response is determined by the stress‐strain relation at the micro scale or rather the volume average of the micromechanical fields. The evolution of the microstructure is modeled by means of non‐conserved phase‐fields. As an example, the proposed methodology is applied to the modeling of stress‐induced martensitic phase transformations in metal alloys. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improving the convergence behavior of hierarchical atomistic‐to‐continuum multiscale models using stochastic approximation
Authors: Wurm Patrick , Ulz Manfred H. 
Published: October 2016

AbstractThe aim of this work is to provide an improved information exchange in hierarchical atomistic‐to‐continuum models by applying stochastic approximation (SA) methods. A typical hierarchical two‐scale model is chosen and enhanced. Due to very high computational cost, the microscale of this model may not be sufficiently sampled in practical calculations; a problem, which was recently investigated in [1]. As a consequence, the microscale produces noise‐corrupted output due to thermal effects. The thermal noise creates a setting that shows remarkable resemblance to the Robbins‐Monro iteration scheme known from SA. This resemblance justifies the use of two averaging strategies known to improve the convergence behavior of SA schemes under certain, fairly general, conditions. No additional computational cost is introduced by this approach. The proposed strategies implemented in the multiscale model are tested on a numerical example. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of Effective Properties of MMC by Computational Homogenization
Authors: York Duran José L. , Kuhn Charlotte , Müller Ralf 
Published: October 2016

AbstractOn the macrolevel Metal Matrix Composites (MMCs) resemble a homogeneous material. However, on the microlevel they show an inhomogeneous microstructure. This paper will have how heterogeneities affect the overall properties and the behaviour of a material (i. e. the effective properties). This is done using computational homogenization techniques. Finite element (FE) simulations were conducted in ABAQUS in connection with MATLAB, using material parameters for aluminium alloy AA2124 and SiC to develop a representative volume element (RVE) of the MMC AMC217xe. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Transient contraction flow of a nonlinear viscoelastic fluid
Authors: Descher Stefan , Wünsch Olaf 
Published: October 2016

AbstractThe unsteady behavior of a Phan‐Thien‐Tanner fluid in a pressure driven contraction flow is investigated. Calculations are performed using the log‐conformation reformulation and block coupled pressure correction. Studies are carried out for the Deborah number De of the process and the model's extension parameter α. It is shown that for very small and very large De the fluid responds newtonian whereas for moderate De damped oscillations of the volume flux can be observed. The studies for α show that the flow is shear dominant despite the extensional flow character of contractions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A non‐conventional discontinuous Lagrangian for viscous flow
Authors: Scholle Markus , Marner Florian 
Published: October 2016

AbstractAlthough many attempts for finding a variational formulation of Navier‐Stokes equations have been made, a Lagrangian for viscous flow has not been established yet. An auspicious suggestion was made by Scholle [1] by extending Seliger and Whitham's Lagrangian [2] with additional terms ending up with some partial success: on the one hand, the phenomenon ‘viscosity’ occurs in a qualitatively correct manner, on the other hand the equations of motion resulting from the variation of Hamilton's principle differ from Navier‐Stokes equations and therefore, their solutions reveal noticeable quantitative differences to those of Navier‐Stokes equations. In this paper the Lagrangian [1] is modified by applying an innovative idea by Anthony [3], motivated by the reformulation of the Lagrangian in terms of complex fields, which can also be understood as the inversion of Madelungs idea [4] of reformulating the complex Schrödinger's equation into a hydrodynamic form. The prize one has to pay is that the resulting Lagrangian is discontinuous and therefore the mathematical treatment of the related variational problem challenging. Furthermore, an additional parameter, ω0, has to be introduced. However, it is demonstrated that Navier‐Stokes equations are recovered by the limit ω0 → ∞, whereas the case of finite ω0 can be interpreted as a generalization towards non‐equilibrium thermodynamics [3]. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flow‐induced anisotropic viscosity in short fiber reinforced polymers
Authors: Bertóti Róbert , Böhlke Thomas 
Published: October 2016

AbstractThe commonly used flow models for fiber reinforced polymers often neglect the flow induced mechanical anisotropy of the suspension. With an increasing fiber volume fraction, this plays, however, an important role. There are some models which count on this effect, they are, however, phenomenological and require a fitted model parameter. In this paper, a micromechanically based constitutive law is proposed which considers the flow induced anisotropic viscosity of the fiber suspension. The introduced viscosity tensor can handle arbitrary anisotropy of the fluid‐fiber mixture depending on the actual fiber orientation distribution. A homogenization method for unidirectional structures in contribution with orientation averaging is used to determine the effective viscosity tensor. The motion of rigid ellipsoidal fibers induced by the flow of the matrix material is described by Jeffery's equation. A numerical implementation of the introduced model is applied to representative flow modes. The calculated stress values are analyzed in transient and stationary flow cases. They show a less pronounced anisotropic viscous behaviour in every investigated case compared to the results obtained by the use of the Dinh‐Armstrong constitutive law. The reason for the qualitative difference is that the presented model depends on the complete orientation information, while the other one is linear in the fourth‐order fiber orientation tensor. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and Simulation of Food Foams
Authors: Gladbach Katharina , Delgado Antonio , Rauh Cornelia 
Published: October 2016

AbstractThe rheological behaviour of protein solutions containing bubbles at rest, but particularly during fluid mechanical transport is not sufficiently investigated yet. Protein foams have a great importance in food production because of their special sensory properties. A suspension that contains bubbles in a Newtonian liquid exhibits inherently a complex rheological behaviour, such as elastic effects, a shear‐ and time‐dependent viscosity and normal stress differences. The deformation state of the bubbles in a suspension subjected to a steady shear is a function of the gas volume fraction ϕ and the capillary number NCa. In the present article, material equations for protein solutions with gas volume fractions ϕ ≤ 0.75 and small bubble deformations, i. e. NCa ≪ 1, are analysed and further developed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Void dynamics in lead‐free Sn‐Ag‐Cu solder joints
Authors: Werner Marek , Reppel Thomas , Weinberg Kerstin 
Published: October 2016

AbstractAs a result of thermal and mechanical loading of Sn‐Ag‐Cu solder joints pores, flaws and voids may nucleate and grow. Such void nucleation is studied here by means of a phase‐field approach which accounts for the decomposition of the solder into phases described by its concentration c. In this investigation, the void growth results from boundary inward flux only, effects due to grain size and interstitials are not involved, cf. [1].The free energy functional is approximated by a second order Taylor expansion and thus composed of a bulk free energy density and a Ginzburg‐type gradient term. The bulk free energy density ϕ follows a classical Ginzburg‐Landau double‐well potential. The gradient‐energy coefficient κ depends on ϕ and is calculated similar to [2]. Experimental data have been adapted for the modeling of the temporal evolution of the concentration of voids located on a square domain in 2D. The simulation is based on a B‐spline finite element analysis. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From CAA to CFD
Authors: Akkermans R.A.D. , Bernicke P. , Ewert R. , Dierke J. 
Published: October 2016

AbstractIn this contribution, an application of a computational aeroacoustic code as a hybrid Zonal LES tool is presented. The here used hybrid approach is based on a novel implementation of the Non‐Linear Perturbation Equations extended with fluctuating viscous terms, denoted as “Overset” since a perturbation analysis is performed on top of a background flow. The extension to LES is demonstrated with isotropic decaying turbulence, where the expected temporal decay and scaling of the reference DNS data is recovered with the LES employing a classical Smagorinsky model. Furthermore, a conceptual approach is presented that describes the investigation of sound sources with application to trailing‐edge noise. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Drag reduction via wall‐normal oscillations in turbulent flat plate boundary layer flow at very high Reynolds number
Authors: Albers Marian , Meysonnat Pascal S. , Schröder Wolfgang 
Published: October 2016

AbstractThe effects of wall‐normal single point oscillations in turbulent boundary layers at very high Reynolds number are investigated by numerical simulation. The impact on the friction drag and on the turbulent structures is analyzed. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bayesian calibration of model coefficients for a simulation of flow over porous material involving SVM classification
Authors: Friedman Noémi , Kumar Pradeep , Zander Elmar , Matthies Hermann G. 
Published: October 2016

AbstractIn this contribution the identification of the model coefficients of a novel turbulent flow model over porous media is concerned. The flow is modeled with a volume and Reynolds averaged compressible Navier‐Stokes equations approach. The main focus of this contribution is to calibrate the model coefficients starting from expert prior knowledge by incorporating DNS data of the velocity field and the Reynolds stresses. For the inverse problem general Polynomial Chaos Expansions (gPCE) based surrogate model was used. To avoid the identification of nonphysical coefficient setups, these parametric regions were filtered out by identifying a decision boundary by the support vector machine binary classification. The machinery of the Markov Chain Monte Carlo (MCMC) was used for the data assimilation combined with a nonlinear Minimum Mean Square Estimator (MMSE) for speeding up the convergence of the random walk of the MCMC. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal Experimental Design to Identify the Average Stress‐Strain Response in Short Fiber‐Reinforced Plastics
Authors: Ospald Felix , Herzog Roland 
Published: October 2016

AbstractWe show how to use optimal experimental design methods for the parameter identification of short fiber reinforced plastic (SFRP) materials. The experimental data is given by computer simulations of representative volume elements (RVE) of the SFRP material. The experiments are designed such that a minimal number of RVE simulations is required and that the model response attains a minimal variance for a class of strains and fiber orientations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stochastic upscaling of heterogeneous materials
Authors: Sarfaraz Muhammad Sadiq , Rosić Bojana , Matthies Hermann G. 
Published: October 2016

AbstractWe propose a probabilistic strategy to upscale the material spatial variability from fine to coarse scale. To implement this idea in a numerical framework, we consider the coarse‐scale as stochastic, i. e. its material properties are considered uncertain and modeled as random variables/fields. Numerical examples are shown to demonstrate the applicability of proposed approach. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An impulse control approach for optimal maintenance scheduling of a gas turbine
Authors: Gröger Michael 
Published: October 2016

AbstractToday gas turbine outages are determined by one global life counter and deterministic life times. In the future the gas turbine will be equipped with multiple life counters for outage determination. Therefore we present an impulse control approach which takes the probabilistic nature of the damage mechanism into account to calculate an optimized maintenance schedule. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling, simulation and optimization of an elastic structure under moving loads
Authors: Kimmerle Sven‐Joachim 
Published: October 2016

AbstractWe consider an elastic structure that is subject to moving loads representing e.g. heavy trucks on a bridge or a trolley on a crane beam. A model for the quasi‐static mechanical behaviour of the structure is derived, yielding a coupled problem involving partial differential equations (PDE) and ordinary differential equations (ODE). The problem is simulated numerically and validated by comparison with a standard formula used in engineering. We derive an optimal policy for passing over potentially fragile bridges. In general, our problem class leads to optimal control problems subject to coupled ODE and PDE. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The One‐Shot Method in SU2
Authors: Kusch Lisa , Gauger Nicolas R. 
Published: October 2016

AbstractFor PDE‐constrained optimization tasks the one‐shot approach is well‐suited. The solution of the state equation is augmented with an adjoint solver to provide approximate reduced derivatives that can be used in an optimization iteration to change the design. In this paper different one‐shot strategies for SU2 are implemented and tested for aerodynamic shape optimization in the open‐source multi‐physics package SU2 to extend the choice of optimization algorithms. These include the application of the one‐shot approach when considering additional constraints apart from the state equation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Frequency based preconditioning and smoothing for shape optimization
Authors: Kusch Jonas , Gauger Nicolas R. , Müller Siegfried , Schmidt Stephan 
Published: October 2016

AbstractIn this paper, we present a smoothing technique which can be understood as a Quasi‐Newton method. The idea of this preconditioner is that it approximates the symbol of the inverse Hessian, which has smoothing behavior. This symbol is derived analytically for the Stokes equations and investigated numerically for a flow with a Reynolds number of 80. The resulting symbol is then approximated by differential operators, which will lead to a method similar to Sobolev Smoothing. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An efficient optimization method for mechanical shells considering cut‐outs
Authors: Dienemann Robert , Schumacher Axel 
Published: October 2016

AbstractIn this contribution an optimization method for shell structures is presented. This method was developed in order to perform a simultaneous optimization of the shape and position of the mid surface and a topology optimization to introduce cut‐outs. A topology optimization method for continuum structures is combined with a manufacturing constraint for deep drawable sheet metals. It is shown, how more than a million design variables can be handled efficiently using a mathematical optimization algorithm for the design update and the finite element method for the structural simulation. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Using Local Spectral Information in Domain Decomposition Methods – A Brief Overview in a Nutshell
Authors: Klawonn Axel , Kühn Martin , Rheinbach Oliver 
Published: October 2016

AbstractFor second‐order elliptic partial differential equations large discontinuities in the coefficients yield ill‐conditioned stiffness matrices. The convergence of domain decomposition methods (DDM) can be improved by incorporating (numerically computed) local eigenvectors into the coarse space. Different adaptive coarse spaces for DDM have been constructed and used successfully. For two‐level Schwarz, FETI‐1 and BDD methods, adaptive coarse spaces with a rigorous theoretical basis are known for 2D and 3D. Although successfully in use for almost a decade, a theory for adaptive coarse spaces for FETI‐DP and BDDC was lacking. While the problem was recently settled for 2D, the estimate for the 3D adaptive algorithm required improved coarse spaces. We give an brief overview of the literature, i. e., the different known approaches, and show numerical results for a specific adaptive FETI‐DP method in 3D, where the condition number bound could only recently be proven. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ℋ‐matrix techniques for approximating large covariance matrices and estimating its parameters
Authors: Litvinenko Alexander , Genton Marc , Sun Ying , Keyes David 
Published: October 2016

AbstractIn this work the task is to use the available measurements to estimate unknown hyper‐parameters (variance, smoothness parameter and covariance length) of the covariance function. We do it by maximizing the joint log‐likelihood function. This is a non‐convex and non‐linear problem. To overcome cubic complexity in linear algebra, we approximate the discretised covariance function in the hierarchical (ℋ‐) matrix format. The ℋ‐matrix format has a log‐linear computational cost and storage O(knlogn), where rank k is a small integer. On each iteration step of the optimization procedure the covariance matrix itself, its determinant and its Cholesky decomposition are recomputed within ℋ‐matrix format. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A non symmetric FVM‐BEM coupling method
Authors: Erath Christoph , Of Günther , Sayas Francisco‐Javier 
Published: October 2016

AbstractWe consider the prototype model for flow and transport of a concentration in porous media in an interior domain and couple it with a diffusion process in the corresponding unbounded exterior domain. To guarantee mass conservation and stability with respect to dominating convection also for a discrete solution we introduce a non symmetric coupling of the vertex‐centered finite volume method (FVM) and the boundary element method (BEM). BEM approximates the unbounded exterior problem which avoids truncation of the domain. One can also interpret that the (unbounded) exterior problem “replaces” the boundary conditions of the interior problem. We aim to provide a first rigorous analysis of the discrete system for different model parameters; existence and uniqueness, convergence, and a priori estimates. Numerical examples illustrate the strength of the chosen method which is computational cheaper than the previous three field FVM‐BEM couplings. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive FEM for NURBS Surface Shells
Authors: Weise Michael 
Published: October 2016

AbstractThe application of shell theories in the finite element method (FEM) requires a description of the shell midsurface geometry and its derivatives. Modern computer aided design software uses non‐uniform rational B‐splines (NURBS) for geometry description. We give some insights on how to implement adaptive FEM for NURBS surface Naghdi shells. A speciality is the incorporation of tangential vectors with continuous directions, but jumping lengths. Such vectors may occur when NURBS surfaces are combined. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Snapshot location for POD in control of a linear heat equation
Authors: Alla Alessandro , Gräßle Carmen , Hinze Michael 
Published: October 2016

AbstractIn the present work, we study the approximation of a distributed optimal control problem for a linear heat equation with model order reduction based on Proper Orthogonal Decomposition (POD‐MOR). We show that snapshot location for control problems is crucial in model reduction. For the determination of the time instances (snapshot locations) we utilize an a‐posteriori error control concept which is based on a reformulation of the optimality system of the underlying optimal control problem as a second order in time and fourth order in space elliptic system. Finally, we present a numerical test to illustrate our approach. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
How not to discretize the control
Authors: Wachsmuth Daniel , Wachsmuth Gerd 
Published: October 2016

AbstractIn this short note, we address the discretization of optimal control problems with higher order polynomials. We develop a necessary and sufficient condition to ensure that weak limits of discrete feasible controls are feasible for the original problem. We show by means of a simple counterexample that a naive discretization by higher order polynomials can lead to non‐feasible limits of sequences of discrete solutions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Air Flow in Model Room
Authors: Ćoćić Aleksandar , Brajović Mladen , Lečić Milan 
Published: October 2016

AbstractEfficient, and appropriate indoor air environment is important issue in building design. Air flow patterns which are formed in the room are mainly depended on its geometrical parameters. Investigation of flow patterns are performed on a relatively simple geometry of model room, with a small obstacle (partition) in it. There are several interesting flow phenomena which are present in the model room: flow through sudden geometry expansion, stagnation flow with lateral boundaries, flow over the obstacle, etc. Since the air velocities are low, it is assumed that flow is incompressible. Numerical calculations of these patterns have been done using RANS modeling approach. For all calculations an extended version of open‐source CFD software OpenFOAM was used. Several turbulence models have been used for RANS approach, with special attention on their performance in capturing unsteady flow phenomena. Comparison of obtained numerical results and available experimental results for mean velocities shown good agreement. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)