bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimate of the Domain Orientation Distribution Function and the Thermoelastic Properties of Pyrolytic Carbon Based on an Image Processing Technique
Authors: Lin S. , Böhlke T. , Langhoff T.‐A. 
Published: December 2011

AbstractThe microstructure of Pyrolytic Carbon (PyC) can be described as an aggregate of coherent domains with different orientations. The domains exhibit an approximately a hexagonal material symmetry. In order to apply statistical homogenization schemes which predict the thermomechanical properties in terms of the microstructural characteristics, a quantitative description of PyC microstructures based on the domain orientation distribution function (DODF) is introduced in this work. The von‐Mises Fisher distribution is applied for modeling the orientation of the unit normal vectors of the graphene planes. The respective probabilty density function depends on the so‐called concentration parameter κ. The parameter κ is estimated by the set of domain orientations, which can be obtained by applying the image processing technique. This procedure facilitates the estimate of the 2nd order bounds (Hashin‐Shtrikman upper and lower bounds) based on the real microstructure. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Validation of Material Models in Grain Scale Simulation based on EBSD Experimental Data
Authors: Van Tung Phan , Jöchen Katja , Böhlke Thomas 
Published: December 2011

AbstractA crystal plasticity model and a homogenization method are used to analyze the local and global mechanical behavior of a ferritic stainless steel. In the first step the material constants are determined based on tensile tests and used to simulate the local deformation behavior on the grain scale in the second step. For that 2D EBSD data are discretized by finite elements. The computed local grain reorientations of three different BCC slip systems are compared to experimental data at the state of 20% elongation. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical homogenization of composite structures with rhombic fiber arrangements
Authors: Würkner Mathias , Berger Harald , Gabbert Ulrich 
Published: December 2011

AbstractA numerical procedure is developed to determine effective material properties of unidirectional fiber reinforced composites with rhombic fiber arrangements. With the assumption of a periodic micro structure a representative volume element (RVE) is considered, where the phases have isotropic or transversely isotropic material characterizations. The interface between the phases is treated as perfect. The procedure handles the primary non‐rectangular periodicity with homogenization techniques based on finite element models. Due to appropriate boundary conditions applied to the RVE elastic effective coefficients are derived. Six different boundary condition states are required to get all coefficients of the stiffness tensor. Results are listed and compared with other publications and good agreements are shown. Furthermore new results are presented, which exhibit the orthotropic behavior of such composites caused by the rhombic fiber arrangement. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of Highly Viscoelastic Polymer Melts using VF and DEVSS Methods
Authors: Al‐Baldawi Ammar , Wünsch Olaf 
Published: December 2011

AbstractViscoelastic polymer melts are usually modeled with a macro approch. This is done using an anisotropic mobility tensor to generalize the Maxwell model. In recent works the use of micro approches is increasing, e.g. the so‐called POM‐POM model. In this work a frame independent flow type property is introduced in order to help visualizing the elongation and shear regions in a 3D flow. Which in turn helps to choose the right material model, since the model parameters are adjusted with 1D shear flows and the elongation properties are mostly neglected. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupling of the Reynolds Fluid‐Film Equation with the 2D Navier‐Stokes Equations
Authors: Esmaeili L. , Schweizer B. 
Published: December 2011

AbstractThe pressure field in thin fluid films can quite precisely be calculated by Reynolds fluid‐film equation. In some problems, it may be useful to couple thin fluid‐films with general 2D or 3D fluid flows. In the current work, we analyze the fluid flow, pressure and temperature field in a hydrodynamic journal bearing with a rectangular oil groove. Pressure and temperature in the fluid gap are calculated by means of the Reynolds equation and the 2D energy equation. Cavitation effects are taken into account by incorporating a 2‐phase cavitation approach. In order to calculate the velocity and pressure field in the oil groove, the 2D Navier‐Stokes equations are used; the temperature distribution in the oil groove is computed by means of the 2D energy equation. Appropriate coupling conditions for velocity, pressure and temperature are formulated in order to couple the flow in the fluid gap with the flow in the oil groove. Thermal expansion of journal shaft and bearing housing are also taken into account, since the bearing clearance changes with increasing temperature. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear effects due to cavitation in self‐lubricated bearings
Authors: Neacşu Ioana Adina , Scheichl Bernhard , Kluwick Alfred 
Published: December 2011

AbstractSelf‐lubricating bearings are journal bearings having a porous network which acts as a reservoir of fluid. Impregnation is done once, and is enough to sustain life‐time lubrication. Our concern in this type of application is with the phenomena of fluid film cavitation under th.e assumption of purely hydrodynamic lubrication. In this sense we solve a modified Reynolds equation numerically, including a refinement of the pressure‐density relation, and iteratively couple the result in terms of pressure with Darcy's law for flows through porous media. The resulting method resorts to a simulated‐annealing strategy, which properly accounts for the nonlinearity due to the presence of cavitation and the density variations inside the cavitation region, together with the continuous phase change from the the fully liquid regime. Most importantly, it is found both analytically and numerically that recondensation is associated with the occurrence of density jumps. The numerical results provide an accurate description of the pressure and density distributions. Also, statements concerning existence and essential properties of the solutions can be made for both the sintered and a massive bearing (uncoupled case). The most interesting limiting case studied thoroughly is the one for which the eccentricity ε is quite high (ε → 1−), corresponding to highly loaded bearings, which captures the bounds of applicability of the present approach. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary element method based algorithm for simulation of fluid flow in 3D
Authors: Ravnik Jure , Škerget Leopold 
Published: December 2011

AbstractA boundary element method based numerical scheme that solves the velocity‐vorticity formulation of Navier‐Stokes equation is presented. The developed method is validated and used to simulate laminar viscous flow coupled with heat transfer in 3D. Benchmark test cases were use to determine the validity of the method. Flow around a hotstrip is presented as a test case. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Mixed Convection Flow past a Horizontal Plate in a Channel: Wake ‐ Potential Flow Interaction
Authors: Steinrück Herbert 
Published: December 2011

AbstractThe mixed convection flow past a horizontal plate in a horizontal channel in a distinguished limit of large Reynolds and Grashof numbers is considered. An interaction problem between the wake and the potential flow is formulated and analyzed. It turns out that stationary solutions exist only if a suitable defined interaction parameter is below a critical value. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity Studies of Large Eddy Simulations of Combustion Systems with an Unstructured Implicit Solver
Authors: Aschmoneit Kai , Kuenne Guido , Janicka Johannes 
Published: December 2011

AbstractIsothermal as well as reacting turbulent flows are investigated by means of LES with the implicit, unstructured code PRECISE‐UNS. Primarily, the swirl burner configuration TECFLAM is simulated isothermal. Calculations with different time step sizes are taken out to examine the influence of the Courant number on the LES solution. In addition, the impact of the spatial resolution is investigated. Next, the jet diffusion flame configuration Sandia Flame D is calculated with the Flamelet Generated Manifold (FGM) approach. Mean profiles of the velocity components, mixture fraction and temperature as well as their variances are compared to experimental data. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamical structure of the turbulent boundary layer on rough surface
Authors: Uruba Václav , Jonáš Pavel , Hladík Ondřej 
Published: December 2011

AbstractThe experiments on structure of turbulent boundary layer on the plane rough wall without pressure gradient are presented. Sand roughness of the wall is considered. Measurements are carried out using Time‐Resolved PIV technique in planes parallel and perpendicular to the wall. The results on rough wall are compared with the base case of boundary layer on smooth wall. Hairpin vortices have been detected. Topology and typical size of those structures substantially differ in the cases in question. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulations of acoustic emissions due to offshore‐pile installation
Authors: Henke Sascha , Milatz Marius , Grabe Jürgen 
Published: December 2011

AbstractThe use of renewable energy is growing due to economic reasons and a spreading sense of ecology. One possible source for renewable energy is wind energy. It is predicted that the number of offshore wind parks will be increasing within the next ten years. The foundation piles of offshore wind power plants are normally installed by impact driving. This leads to an emission of acoustic noise which possibly influences or even damages the sense of hearing of marine mammals like seals and whales.In this contribution the propagation of acoustic waves in air and water due to pile driving is investigated using the finite element method (FEM) with an explicit time integration scheme. In the analyses a mass representing the pile hammer falls on an elastically modeled offshore monopile. The surrounding media is varied between air and water in order to investigate the acoustic emissions due to the pile driving process with respect to the medium. The numerical results are compared to measurements which can be found in literature to verify the numerical models. Furthermore, as a practical example the numerical model can be used in order to simulate noise reduction techniques such as the bubble curtain. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact and Damage Localisation of Carbon‐Fibre‐Reinforced Plastic Plates
Authors: Ungethuem Andy , Lammering Rolf 
Published: December 2011

AbstractDue to increasing usage of light weight structures and carbon‐fibre‐reinforced plastics well‐known procedures for the examination of components inefficient in terms of efforts or costs. Therefore, the development of a complementary system is suggested which allows for detecting damaging events and damages in a structure. A new wave migration model enables to determine the location of an impact for non‐isotropic plates. The method is based on the wave propagation after an impact. Piezo‐electric sensors capture the strain caused by the propagating wave. The evaluation and processing of the signals of at least four sensors allow for the calculation of the impact location from the runtime of the signals. In the case of non‐isotropic material the shape of the wave front has to be known for the structure under investigation, for example experimentally due to measurement and monitoring of the wave propagation by a Laservibrometer or analytically by calculating the propagation speed of bending waves. On the same basis damage localisation in anisotropic carbon‐fibre‐reinforced plastic plates is possible. Considerations to signal analysis using wavelet transformation are presented and both models are validated experimentally. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Virtual test facilities for building acoustic predictions using FEM
Authors: Wulkau Meike , Langer Sabine 
Published: December 2011

AbstractThe most important characteristic in building acoustics is the transmission loss which describes the insulation performance of a separating component. This quantity is defined by the ratio of inclined sound power to transmitted power. The transmission loss is usually measured in costly experimental set‐ups of either real size facilities or down scaled test models. In order to reduce the effort and to gain further insight into the complex behavior of wave propagation in coupled structure‐fluid systems, virtual test facilities using numerical methods (FEM) are established. An appropriate determination of the reverberation time is essential for obtaining good quality simulations. The results of the simulated transmission loss are presented and compared with common analytical prediction methods based on the transfer matrix method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Formation of crystalline bubble structure in wet metal foams
Authors: Heitkam Sascha , Fröhlich Jochen 
Published: December 2011

AbstractSmall monodispersed bubbles form regular patterns when they agglomerate. Many experimental investigations revealed a preference of f.c.c. packing against h.c.p. packing in these structures, that could not yet be explained. In the present work this feature is reproduced numerically and analyzed. It is shown that drainage from layers above causes the preference. By investigating the transient crystal growth and packing rearrangement a mechanism is found that reduces the stability of h.c.p. packing and explains the phenomenom. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Singularities on the boundaries of magnetorotational instabilities and scaling laws
Authors: Kirillov Oleg , Stefani Frank 
Published: December 2011

AbstractIn the theory of magnetorotational instability and its modern extensions such as the helical MRI, non‐trivial scaling laws between the critical parameters are observed. In case of the standard MRI it is well known that the Reynolds and Hartmann numbers are scaled as Re ∼ Ha2 while for the helical MRI Re ∼ Ha3. What is less known is that the thresholds of SMRI and HMRI plotted as surfaces in the space of parameters, possess singularities that determine the scaling laws. Moreover, the two paradoxes of SMRI and HMRI in the limits of infinite and zero magnetic Prandtl number (Pm), respectively, sharply correspond to the singularities on the instability thresholds. In either case, it is the local Plücker conoid structure that explains the non‐uniqueness of the critical Rossby number, and its crucial dependence on the Lundquist number. For HMRI, we have found an extension of the former Liu limit Roc ≃ −0.828 (valid for Lu = 0) to a somewhat higher value Ro ≃ −0.802 at Lu = 0.618 which is, however, still below the Kepler value. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation of the vortex train using plasma barrier discharge actuator
Authors: Procházka Pavel , Uruba Václav 
Published: December 2011

AbstractThe plasma actuator is used to generate periodical train of vortices moving along the surface. For generation the high‐frequency high‐voltage AC is used forming more‐or‐less steady wall‐jet‐like flow by the dielectric barrier discharge or corona discharge. Low‐frequency modulation of the supply voltage is applied to generate vortices. Parameters of the vortex train are studied as function of the generator setting using TR‐PIV technique. The generated flow patterns are to be applied for control of a boundary layer. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Korn's inequality for incompatible tensor fields
Authors: Neff Patrizio , Pauly Dirk , Witsch Karl‐Josef 
Published: December 2011

AbstractWe prove a Korn‐type inequality for bounded Lipschitz domains in $\Omega {\rm ~in~}{\rm I\!R}^3$ and non‐symmetric square integrable tensor fields $P : \Omega \to {\rm I\!R}^{3\times 3}$ having square integrable rotation ${\rm Curl~}P : \Omega \to {\rm I\!R}^{3\times 3}$. For skew‐symmetric P or compatible $P =\nabla\;v$ our estimate reduces to non‐standard variants of Poincaré's or Korn's first inequality, respectively, for which our new estimate can be viewed as a common generalized version. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Global existence result for rate‐independent processes in viscous solids with heat transfer
Authors: Paoli Laetitia , Petrov Adrien 
Published: December 2011

AbstractThis note deals with three‐dimensional models for rate‐independent processes describing materials undergoing phase transformations with heat transfer. The problem is formulated within the framework of generalized standard solids by the coupling of the momentum equilibrium equation and the flow rule with the heat transfer equation. The existence of a global solution for this thermodynamically consistent problem is obtained by using a fixed‐point argument combined with global energy estimates. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Class of Evolutionary Problems with an Application to Acoustic Waves with Impedance Type Boundary Conditions.
Authors: Picard Rainer 
Published: December 2011

AbstractA well‐posedness result for a time‐shift invariant class of evolutionary operator equations is considered and exemplified by an application to an impedance type initial boundary value problem for the system of linear acoustics. The problem class allows for memory effects in the domain as well as on the domain boundary. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topology and Geometry Optimization of Branched Sheet Metal Products
Authors: Göllner Thea , Günther Ute , Hess Wolfgang , Martin Alexander , Ulbrich Stefan 
Published: December 2011

AbstractIn order to optimize branched sheet metal profiles consisting of several chambers, decisions concerning topology and geometry have to be made. This leads to a problem entailing discrete and nonlinear features. We describe an integrated approach combining both aspects. The underlying idea is to use a branch‐and‐bound algorithm. In each node of the branch‐and‐bound tree, a nonlinear optimization problem has to be solved. We describe how the branch‐and‐bound tree is constructed, i.e., how the topology decision can be classified in a meaningful way. Moreover, we explain how to approach the nonlinear optimization problem arising in the nodes of the tree. We conclude by presenting a numerical example. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimum Experimental Design for Nonlinear Process Models
Authors: Körkel Stefan 
Published: December 2011

AbstractIn order to validate nonlinear dynamic process models, parameters have to be estimated from experimental data. The method of nonlinear optimum experimental design can improve the statistical reliability of parameter estimates drastically. This article discusses the problem formulation, numerical solution approaches and application strategies for nonlinear experimental design optimization problems. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State‐constrained optimization for identification of small inclusions
Authors: Kovtunenko Victor A. 
Published: December 2011

AbstractThe inverse problem of identification of small geometric objects (defects, inclusions) of unknown topological properties is under the investigation. This problem is treated within the state‐constrained optimization framework. Using topological sensitivity analysis and methods of singular perturbations, a proper approximation by the asymptotic model is justified rigorously. The underlying parametric optimization problem is solved semi‐analytically by a variational calculus. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards optimal Runge‐Kutta smoothers for multigrid methods for unsteady flow problems
Authors: Birken Philipp 
Published: December 2011

AbstractWe consider Runge‐Kutta smoothers in a dual time stepping multigrid method for unsteady flow problems. These smoothers are easily parallelizable and Jacobian‐free, making them very attractive for 3D calculations. Existing methods have been designed for steady flows, leading to slow convergence for unsteady problems. Here we determine the free parameters of the smoother to provide optimal damping for high frequency components for the unsteady linear advection equation. This is compared with an RK smoother designed for steady state problems, as commonly used in CFD codes. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rational multistep methods via modified φj‐functions
Authors: Auzinger Winfried , Łapińska Magdalena 
Published: December 2011

AbstractA class of rational multistep methods, in particular of Adams‐Padé type, is designed via rational modification of the φj‐functions inherent in exponential integrators. Convergence properties and implementation issues are discussed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Simulation of the Boltzmann Equation: Deterministic vs. Monte Carlo Schemes
Authors: Babovsky Hans 
Published: December 2011

AbstractKinetic Lattice Group Models [1] provide a valuable tool for the numerical simulation of the Boltzmann equation. Here we introduce a Monte Carlo version of these. With this we have the unique opportunity to compare deterministic versions with Monte Carlo versions of the same model. We introduce the system and discuss some results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence and quasi‐optimality of adaptive FEM with inhomogeneous Dirichlet data
Authors: Feischl Michael , Page Marcus , Praetorius Dirk 
Published: December 2011

AbstractWe consider an adaptive mesh‐refining algorithm for a lowest‐order finite element method (AFEM). Contrary to prior works, where the Poisson equation with homogeneous Dirichlet data is analyzed, our focus is on the case of inhomogeneous Dirichlet data g ≠ 0. As is usually done in practice, we use nodal interpolation to discretize g. Besides convergence of AFEM, which is proven by means of an appropriate contraction quantity, we also discuss quasi‐optimality of the proposed algorithm. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of transversely isotropic material using adaptive FEM
Authors: Meyer Arnd , Weise Michael 
Published: December 2011

AbstractLightweight construction plays an important role in the global task to save energy. A common approach to reduce the weight of structures is the use of composite materials like fibre reinforced polymers (FRP). FRP can be characterised by transversely isotropic material behaviour, a special case of anisotropy. In our arcticle we present the necessary efforts to include such material behaviour into an existing adaptive FEM code. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual weighted residual method for optimal control of hyperbolic equations of second order
Authors: Kröner Axel 
Published: December 2011

AbstractIn this paper the dual weighted residual method for optimal control problems of hyperbolic equations of second order is considered. The state equation is written as a first order system in time and a posteriori error estimates separating the influences of time, space, and control discretization are derived to obtain a better accurancy of the discrete solution. A numerical example for optimal control of a nonlinear wave equation is presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)