bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation der aktiven Schwingungskontrolle von Fluid‐Struktur Wechselwirkung durch piezoelektrische Materialien
Authors: Sun Peng , Dinkler Dieter , Zilian Andreas 
Published: February 2009

AbstractEin numerisches Modell zur aktiven Kontrolle des dynamischen Verhaltens von Tragwerken unter transienter Windeinwirkung wird vorgestellt. Auf der Oberschicht passiver Tragstrukturen werden piezoelektrische Sensoren und Aktoren appliziert. Die resultierenden adaptierbaren Strukturen sind mit einem Regler gekoppelt. Die Modellierung der elektroelastischen Struktur erfolgt mit der geometrisch nichtlinearen Elastizitätstheorie und der Maxwell–Faraday–Theorie der Elektrostatik. Die Windumströmung der Struktur ist als inkompressibles, Newton'sches Fluid mit den Navier–Stokes–Gleichungen beschrieben. Die Diskretisierung der gekoppelten Modellgleichungen beider Kontinua erfolgt mit finiten Raum–Zeit–Elementen. Zeitliche Änderungen der Zustandsgrößen werden mit dem diskontinuierlichen Galerkin–Verfahren approximiert. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some basic ideas for the reconstruction of statistically similar microstructures for multiscale simulations
Authors: Balzani Daniel , Schröder Jörg 
Published: February 2009

AbstractIn this contribution we propose a method for the generation of statistically similar representative volume elements (RVE's). These RVE's are obtained by assuming that given real microstructures may be represented by periodic ones. Then an optimization problem has to be solved where the side condition of equal spectral density of the real microstructure and the statistically similar RVE is taken into account. First numerical results show that the proposed method works in principle and leads to more efficient direct multiscale simulations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Macroscopic mechanical properties of metal foam in dependence on the inhomogenities of the mesoscale
Authors: Schwarzer Daniel , Vogt Harald , Proppe Carsten 
Published: February 2009

AbstractIn this contribution, a way of simulating the influence of the mesoscopic irregular structure of metal foams on the macroscale is shown. To this end, mesoscopic periodic volume elements of a foam are derived in order to compute the mechanical properties including the effects of inhomogenities like imperfections, irregular structure and varying cell wall thicknesses. With the help of these volume elements, which are analysed via the finite element method, and their varying mechanical properties, a local varying stiffness can be computed and inserted into the macromechanical model. In this way the propagation of uncertainities from the mesoscale to the macroscale can be assessed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
About the projection of kinematical quantities within the FE2‐approach
Authors: Ebinger Tobias , Steeb Holger , Diebels Stefan 
Published: February 2009

AbstractWithin the FE2‐approach strain–like quantities are projected to the boundary of the attached microstructure yielding Dirichlet boundary conditions for the microscopic boundary value problem. By use of the divergence theorem one can show that the projection of gradient information to the boundary of the attached microstructure fulfills the condition that the volumetrical average of the strain–like quantities in the inner of the microstructure is exactly the same as the projected quantity, provided that the microstructure is continous. However, within the Cosserat continuum theory [1] the strain tensor depends directly on the extra rotation and not on the gradient of it. Thus, the projection can not be carried out in the same way as for gradient information. The present approach shows how to circumvent this problem by giving the extra–rotation within the Cosserat continuum theory a strong kinematical interpretation in the form of a displacement field, which shows the same effects as the extra–rotation itself. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Periodic three‐dimensional mesh‐generation for Voronoi tessellations with application to cubic crystal aggregates
Authors: Fritzen Felix , Böhlke Thomas , Schnack Eckart 
Published: February 2009

AbstractWe present a technique for the generation of unstructured periodic spatial discretizations of three–dimensional Voronoi tessellations. These define model microstructures for various polycrystalline aggregates. The elastic properties of cubic crystal aggregates are examined numerically using periodic displacement boundary conditions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical results for an elasto‐plastic Cosserat model with more than one million dof in 3D
Authors: Müller Wolfgang , Neff Patrizio , Wieners Christian 
Published: February 2009

AbstractWe present a finite element implementation of a infinitesimal elasto–plastic Cosserat model allowing for non–symmetric stresses. We use the von Mises yield criterion and restrict plastic effects to the classical elastic response as in the perfect plastic case. We review the nonlinear equations for the weak formulation of the problem. Numerical results are presented for 3D example with more than one million degrees of freedom. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructural behaviour of transversal isotropic material
Authors: Münch Ingo , Neff Patrizio , Wagner Werner 
Published: February 2009

AbstractWe discuss and simulate transversal isotropic material under tension loading. The preferential direction of the material is inclined under 45 degrees to the direction of the tensile resultant. In this configuration the deformation of a rectangular test specimen differ from the behaviour of isotropic material in the way, that beside Poissons effect additional displacement appear perpendicular to the tension direction. In classical continuum theories, this transverse deformations describe a typical S–shape. By using a non–local continuum theory, the effect of microstructural orientation is incorporated into the numerical model. Then, it depends on a phenomenological parameter of inner structure whether the energetically favoured configuration is classical or contains microstructural behaviour. In the second case, the transverse deformation is not described by the typical S–shape, but with higher forms of it. A simple experimental model will show the connection between the inner structure of the material and the rotational parameters within the non–local continuum theory. It is evident, that these parameters are responsible for the non–classical behaviour and give the possibility to find energetically favoured solutions. The results of the finite–element–analyses can help to understand constitutive parameters for the non–local continuum theory and to apply it to other specimens. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Continuum‐Atomistic Coupling based on Computational Homogenization
Authors: Ricker Sarah , Mergheim Julia , Menzel Andreas , Steinmann Paul 
Published: February 2009

AbstractThe objective of this work is the extension of the classical computational homogenization scheme for continuous micro–structures to the homogenization of atomistic systems. The atomistic setting is simulated by applying the so–called atomistic finite element method. In particular the influence of atomistic defects onto the macroscopic material behavior is highlighted. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical homogenization of foam‐like structures based on the FE2‐approach
Authors: Sehlhorst Hans‐Georg , Jänicke Ralf , Düster Alexander , Rank Ernst , Steeb Holger , Diebels Stefan 
Published: February 2009

AbstractThe computation of foam–like structures is still a topic of research. There are two basic approaches: the microscopic model where the foam–like structure is entirely resolved by a discretization (e.g. with Timoshenko beams) on a micro level, and the macroscopic approach which is based on a higher order continuum theory. A combination of both of them is the FE2‐approach where the mechanical parameters of the macroscopic scale are obtained by solving a Dirichlet boundary value problem for a representative microstructure at each integration point.In this contribution, we present a two–dimensional geometrically nonlinear FE2‐framework of first order (classical continuum theories on both scales) where the microstructures are discretized by continuum finite elements based on the p‐version.The p‐version elements have turned out to be highly efficient for many problems in structural mechanics. Further, a continuum–based approach affords two additional advantages: the formulation of geometrical and material nonlinearities is easier, and there is no problem when dealing with thicker beam–like structures.In our numerical example we will investigate a simple macroscopic shear test. Both the macroscopic load displacement behavior and the evolving anisotropy of the microstructures will be discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
3‐D Modeling of Shock‐induced Precursor Decomposition and Nano‐Particle Growth
Authors: Al‐Hasan N.S. , Schnerr G.H. 
Published: February 2009

AbstractIn the ongoing joint project “Gasdynamically induced nano–particles” (PAK 75/1) a novel method of gas–phase synthesis of nano–particles is being developed [1]. This project is supported by the Deutsche Forschungsgemeinschaft (DFG), the pilotfacility is erected in collaboration with Evonik Degussa, Hanau, Germany. The key features of the new method are the static temperature increase across a stationary shock to provide ignition conditions of the precursor and the subsequent gasdynamic quenching of the particle growth when the desired particle diameter of 10−8m is reached. In this work the decomposition of the precursor, the reactive heat release and the particle growth are coupled with the 3–D transonic flow inside the particle reactor. The simulation results show the effect of shock/boundary layer interactions on the decomposition reaction as well as the effects of the reactive heat release on the shock location and the resulting particle size distribution. The Reynolds number at the shock location is Rex=9·106, the boundary layer thickness is δ=2.2 mm and the pre–shock Mach number is M=1.58. The complex transonic reactive flow within the particle reactor requires a high mesh resolution to resolve the local details of the internal flow problem. In addition, an efficient particle model is required. The formation and growth of the particles are modeled by three separate reactions. The primary reaction is the decomposition of the precursor and the production of monomers. It is modeled by a one step reaction described by an Arrhenius equation. The secondary reaction, the formation of critical nuclei is in our case negligible, because of the high supersaturation ratio of the order of 103 instantly after the primary reaction, where the monomers are already critical nuclei. The tertiary reaction is the particle growth by surface condensation, coagulation and single–aggregation. To simulate the particle growth we apply a local monodisperse bimodal formulation. Thereby, the monodisperse model of Kruis et al. [2] is extended by an additional discrete monodisperse mode for the critical nuclei. This method describes the local particle size due to turbulent mixing, coagulation and coalescence. The coagulation starts in the Knudsen regime Kn ≫ 1 and reaches the continuum regime with particle diameters of the order of 10−8m and a mean free path of the same order of magnitude. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Solution of Turbine Cascade Flow by Two Equations, EARSM and Bypass Transition Turbulence Models
Authors: Fořt J. , Dobeš J. , Fürst J. , Halama J. , Kozel K. , Louda P. , Příhoda J. 
Published: February 2009

AbstractThis work deals with numerical solution of transonic flow in turbine cascades. We compare results achieved by SST, TNT and EARSM turbulence models and we also present results achieved by two equations turbulence model with an algebraic bypass transition model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Symmetry group analysis and similarity solutions of the CBS equation in (2+1) dimensions
Authors: Gandarias1 M.L. , Bruzon1 M.S. 
Published: February 2009

AbstractWe consider the (2+1)—dimensional integrable Calogero—Bogoyavlenskii—Schiff (CBS) written in a potential form. By using classical Lie symmetries, we consider travelling‐wave reductions with variable velocity depending on the form of an arbitrary function. The corresponding solutions of the (2+1)‐dimensional equation involve arbitrary smooth functions. Consequently the solutions exhibit a rich variety of qualitative behaviours. Indeed by making adequate choices for the arbitrary functions, we exhibit solitary waves and bound states. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermodynamics / turbulence analogy modelling dissipating molecular gas flows for high Knudsen numbers
Authors: Groll R. , Rath H. J. 
Published: February 2009

AbstractModelling micro channel flows momentum and heat diffusion / convection are recent parameters modelling the molecule velocity distribution. Macroscopic models describe velocity and energy / enthalpie with integrals of mass increments. Using microscopic models motion and forces of a molecular flow have to be computed by models of physical properties, whose are described by statistical power moments of the molecule velocity. Therefore dilute flows have to be investigated in small channels with a mean free path length of molecules higher than the channel width of the the micro channel itself (λ0≥H0). Modelling this process by a continuous flow the boundary conditions have to be modified (e.g. [6]). The present model uses the statistical approximation of the molecule velocity distribution to simulate the behaviour of this discrete flow with a weighted averaged molecule velocity ∼ξi, its standard deviation σ and the characterisic molecule collision rate z. The number density N per volume V near one position is used for the weighting factor averaging method describing the mean molecule velocity. The present model is validated computing Poiseuille and Couette flows with different Knudsen numbers. Showing the advantages of the present model the simulation results are compared with simulation results of the wall–distance depending diffusivity model of Lockerby and Reese [4] and BGK results of a Lattice–Boltzmann simulation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical experiments on flow control of near wall turbulence
Authors: Lammers Peter , Jovanovic Jovan , Delgado Antonio 
Published: February 2009

AbstractIn this paper we demonstrate by means of direct numerical simulations (DNS) of channel flow with surface structuring or modified boundary conditions how turbulence can be controlled by influencing the anisotropy state of near wall turbulence. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐dimensional turbulent boundary layer on wind turbine blades
Authors: Dumitrescu Horia , Cardos Vladimir 
Published: February 2009

AbstractThe momentum integral technique for predicting the boundary–layer growth in three–dimensional flow has been extended to include the entrainment equation as the closure model. Special attention has been devoted to those terms in the differential equations that change the boundary–layer structure from that of cvasi two–dimensional steady flow, at outboard locations, to a tree–dimensional flow pattern. It is concluded that the stall is delayed due to the boundary–layer reattachment at inboard sections in conjunction with the onset of a spanwise vortex like structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct numerical simulation of single gas bubbles in pure and contaminated liquids
Authors: Lakshmanan Peter , Ehrhard Peter 
Published: February 2009

AbstractDisperse gas bubbles play an important role in many industrial applications. Knowing the rising velocity, the interfacial area, or the critical size for break–up or coalescence in different systems can be crucial for the process design. Hence, knowing the fundamental behaviour of a single bubble appears mandatory for the examination of bubble swarms and for the Euler–Lagrange or Euler–Euler modelling of disperse systems. In the present work a level–set–based volume–tracking method is implemented into the CFD–code OpenFOAM to follow the free interface of a single bubble. The volume–tracking method is coupled with a transport model for surfactants on the interface, including adsorption and desorption processes. The dependency of surface tension on the local surfactant concentration on the interface is modelled by a non–linear (Langmuir) equation of state. Marangoni forces, resulting from surface tension gradients, are included. The rise of a single air bubble (i) in pure water and (ii) in the presence of surfactants of different strengths is simulated. The results show good agreement with available correlations from literature. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling of local particle accumulation in disperse flows with kinematic singularities
Authors: Lebedeva N.A. , Osiptsov A.N. 
Published: February 2009

AbstractThe aim of the study is to model the formation of local particle accumulation zones near several typical kinematic singularities. The flows considered are: (i) a steady two–dimensional flow with localized vorticity of the Kelvin cat's eye type (vortex in a mixing layer), (ii) a steady axisymmetric flow formed by a vortex filament normal to a plane in viscous fluid (simple model of tornado), (iii) a neighbourhood of a zero acceleration point in two–dimensional unsteady (harmonic) flow. From parametric numerical calculations, we investigated the inertial mechanisms of forming local particle accumulation zones and found the threshold values of governing parameters separating qualitatively different particle velocity and density patterns. In particular, it is shown that the zero–acceleration point can either “attract” or “scatter” the particles. Zones of concentrated vorticity are typically devoid of particles. In the tornado–like flow, an axisymmetric “cup‐shaped” particle accumulation region is formed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Advances in Numerical Prediction of Extrusion Tools used for Fabrication of Rubber Profiles
Authors: Müllner Herbert W. , Wieczorek André , Fidi Wolfgang , Eberhardsteiner Josef 
Published: February 2009

AbstractThis contribution is focussed on numerical simulations of realistic extrusion tools of rubber profiles. The underlying material parameters provided by material characterization procedure which is based on capillary–experiments in combined with die swell measurements. The simulations were performed with the CFD program POLYFLOW under usage of an inverse calculation approach. The validation of these simulations is performed by comparison predicted andf measured dimensions of the already fabricated tools. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spatial Instability Of Two‐Phase Mixing Layers
Authors: Otto Thomas , Rossi Maurice , Boeck Thomas 
Published: February 2009

AbstractThe initial stage of liquid atomization by a fast gas stream is considered by means of spatial stability analysis of two–phase shear layers. We solve the viscous linear stability problem for parallel flow modelled by error–function profiles. The unstable modes known from temporal theory are recovered in the convectively unstable case for fluid properties close to the air/water system. The most unstable wavelength depends only weakly on the absolute velocity relative to the laboratory system. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the effects of compressibility in marginally separated flows
Authors: Scheichl Stefan , Kluwick Alfred 
Published: February 2009

AbstractIf the angle of attack α of a slender airfoil reaches a critical value αs flow separation is known to occur at the upper surface. Further increase of α initially leads to the formation of a short laminar separation bubble which has an extremely weak influence on the external flow field — a phenomenon known as marginal separation — but then rather rapidly causes a severe change of the flow behaviour (leading edge stall). According to the asymptotic theory of marginal separation holding in the limit of large Reynolds numbers t→∞ the flow in the neighbourhood of the separation bubble is governed by an integro–differential equation exhibiting a single controlling parameter Γ which relates the angle of attack to the Reynolds number, with a value Γs corresponding to αs. Numerical investigations have shown that solutions to this equation exist up to a critical value Γc>Γs only and this has been taken as an indication that a substantial change of the flow field must take place if Γ exceeds Γc. In the case of unsteady three–dimensional perturbations of a two–dimensional steady marginally separated boundary layer in the limit Γ→Γc, the (generalized form of the) integro–differential equation reduces to a nonlinear diffusion equation of Fisher type. This asymptotic description serves as a basis for the investigations concerning compressibility effects, also in respect of the mechanism through which the hydromechanic motion inside the boundary layer could be transformed into aerodynamic sound. A modified interaction equation is obtained, which in addition to Γ, contains the Mach number at the point of separation as a second controlling parameter. The unsteady changes of the boundary layer displacement thickness in the limit ΔΓ=Γc−Γ→0, again governed by Fisher's equation, then are identified to act as a quadrupole source for sound radiation. The most surprising outcome is the fact that in the three–dimensional case, the second derivative with respect to the lateral direction contained in the Fisher equation changes its sign and becomes negative if the Mach number exceeds a certain value. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of Thermal Convection in an Inclined Narrow Cavity
Authors: Wu J. , Rubes D. , Heiland H.G. , Wozniak G. 
Published: February 2009

AbstractIn order to adapt to the rapid progress in fabricating and utilizing micro electromechanical systems, the investigation of the fluid behaviour in small volumes is of fundamental importance as far as heat and mass transfer are concerned. After the experimental exploration in a small vertical gap with a temperature gradient [1], subsequently the investigation of thermal convection in an inclined narrow cavity is followed experimentally. The gap volume is 6 × 24 × 17 mm3 with a width of 6 mm. Liquid crystal tracer particles are used for measuring the temperature and velocity distribution of the fluid. The measurement results are presented and discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Aerodynamic and aeroacoustic phenomena due to non‐uniform flow of wind turbines
Authors: Dumitrache Alexandru , Dumitrescu Horia , Cardos Vladimir 
Published: February 2009

AbstractStall control and pitch control are the most commonly used methods of regulating power. However, through the opportunities presented by the flexible (or teetered) hub of a two–bladed teetered rotor one can also utilize yaw control to regulate power. This is achieved by adjusting the capture area of the rotor disk relative to the prevailing wind direction. This paper presents the aerodynamic and aeroacoustic results obtained from theoretical models for a rotor when is yawed to the undisturbed flow. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)