bluuebunny/crossref_metadata_2025_split huggingface dataset:
Material modelling of a sheet‐layered lamination stack by homogenization
Authors: Baloglu Maximilian Volkan , Willner Kai 
Published: October 2016

AbstractIn electrical machines, sheet‐layered lamination stacks play an important role for the mechanical behavior of the system. Especially the interlayer between individual sheets and their interaction have a severe influence on the structure. In the context of performance and computational effort, it is desirable to avoid a full FE simulation of a lamination stack with every single sheet. Therefore, homogenization techniques are presented to identify a transversely isotropic surrogate material model, while Zero‐Thickness elements are utilized during this process to cover the interplay of single sheets. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A homogenisation strategy for micromorphic continua based on particle mechanics
Authors: Bidier Sami , Ehlers Wolfgang 
Published: October 2016

AbstractMaterials with a granular microstructure frequently fail in narrow zones due to strain localisation. Examplarily, one may look at the shear‐zone development in dry sand during bi‐ and triaxial loading, where grains in the shear‐zone exhibit large displacements and rotations. Furthermore, localisation is also observed in materials, where the microstructure consists of grains and a binding material, such as for example metal‐casting moulds. Here, sand grains are bound together via a polyurethan‐based material and macroscopic material failure originates from the deformation and breakage of the binder material. Within a continuum‐based modelling approach, these microstructural effects can be accounted for by the consideration of an additional microcontinuum at each material point of the macroscopic body. These extended continuum theories, such as the micromorphic continua and its micropolar and microstrain sub‐formulations, assume a characteristic microcontinuum deformation on a lower scale and have been successfully applied in the field of granular media. Exemplarily, in the framework of a micropolar continua, it is possible to contact forces to stresses and couple stresses via an appropriate homogenisation technique. This method includes the introduction of a Representative Elementary Volume (REV) on the mesoscale situated between the particle and the continuum scale. In this contribution, a homogenisation strategy based on a particle‐centre‐based REV definition is presented that is generally valid for micromorphic and micropolar continua. Therefore, a grain‐binder microstructure is investigated, where particle rotations contribute to the micropolar part, while binder deformations yield the additional macromorphic character. Numerical examples are given, where results from discrete‐element simulations are locally averaged and show the individual activation of the microcontinuum characteristics in the localised zones. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The heterogeneous multiscale finite element method FE‐HMM for the homogenization of linear elastic solids
Authors: Eidel Bernhard , Fischer Andreas 
Published: October 2016

AbstractThe objective of the present paper is a formulation of the Heterogeneous Multiscale Finite Element Method (FE‐HMM) for the homogenization of linear elastic solids in a geometrical linear frame, and doing so, for the first time, of a vector‐valued field problem. The macro stiffness is estimated by stiffness sampling on heterogeneous microdomains in terms of a modified quadrature formula, which implies an equivalence of energy densities of the microscale with the macroscale. Existing a‐priori estimates are assessed and used for optimal micro‐macro refinement strategies in the H1‐norm and the L2‐norm. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mean field homogenization and experimental investigation of short and long fiber reinforced polymers
Authors: Kehrer Loredana , Pinter Pascal , Böhlke Thomas 
Published: October 2016

AbstractThe effective elastic material properties of short fiber reinforced polypropylen are determined by means of the self‐consistent (SC) method and the interaction direct derivative (IDD) method. In order to account for thermoelastic effective material properties, a Hashin‐Shtrikman (HS) based two‐step homogenization method with variable reference stiffness is used. The influence of the reference stiffness, dependent on a scalar parameter is investigated. Information on the microstructure are derived by computed tomography scans (µCT) and considered within the homogenization schemes. Thermomechanical properties of a long fiber reinforced polymer (LFRP) and a short fiber reinforced polymer (SFRP) are obtained by means of dynamic mechanical analysis (DMA). Simulation results for SFRP are compared to experimental results. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale simulation for description of rubber friction
Authors: Lang Ronny , Falk Korbinian , Kaliske Michael 
Published: October 2016

AbstractThe interaction between tire and road generates the transferable forces, which are necessary for driving dynamics and safety. These forces are based on friction between rubber material and pavement surface and depend on the roughness of the pavement, the slip velocity, the contact pressure and the temperature. Based on the finite element method, the friction coefficient is calculated by numerical simulation. The roughness of the pavement surface is described by the height difference correlation function (HDCF), which allows partitioning into different length scales. This multiscale approach is suitable to understand and to evaluate friction phenomena. These phenomena are hysteresis friction based on dissipation inside the rubber material and adhesion friction, which describes the direct bonding between two materials. Given, that the material parameters of rubber highly depend on temperature and the frictional dissipation leads to a warming of the rubber, the provision for these effects is necessary for a realistic desciption of friction. The method allows an understanding of friction phenomena on the micro‐scale like the real contact area or the microscopic contact pressure. Also, the temperature distribution inside the tire cross‐section can be illustrated. The resulting coefficient of friction is validated by experimental data based on linear friction tests and compared to analytical solutions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Logarithmic finite element method in a multigrid setting
Authors: Schröppel Christian , Wackerfuß Jens 
Published: October 2016

AbstractThe Logarithmic finite element (“LogFE”) method is a novel finite element approach for solving boundary‐value problems proposed in [1]. In contrast to the standard Ritz‐Galerkin formulation, the shape functions are given on the logarithmic space of the deformation function, which is obtained by the exponentiation of the linear combination of the shape functions given by the degrees of freedom.Unlike many existing multigrid formulations, the LogFE method allows for a very smooth interpolation between nodal values on the coarse grid. It can thus avoid problems with regard to locking and convergence that appear in multigrid applications using only linear interpolation, especially for larger corsening factors.We illustrate the use of the LogFE method as a coarse grid algorithm, in conjunction with an atomistic finite element method on the fine grid, for calculating the mechanical response of super carbon nanotubes. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of multiscale methods for time‐harmonic Maxwell's equations
Authors: Henning Patrick , Ohlberger Mario , Verfürth Barbara 
Published: October 2016

AbstractWe shortly revisit the Heterogeneous Multiscale Method (HMM) for the time‐harmonic Maxwell's equations in locally periodic media as introduced in [1]. The optimal a priori bounds in the H(curl) and H−1 norm predicted theoretically are justified by a numerical example in this contribution. The setting consists of a periodic inverse permeability, inspired by [2], and as reference solution a computation on a fine (well‐resolved) grid is used. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the initial phase of the triple deck stage in marginally separated flows
Authors: Braun Stefan , Scheichl Stefan 
Published: October 2016

AbstractThe method of matched asymptotic expansions is used to investigate marginally separated boundary layer flows (laminar or alternatively transitional separation bubbles) at high Reynolds numbers. Typical examples include, among others, the flow past slender airfoils at small to moderate angels of attack and channel flows with suction. As is well‐known, classical (hierarchical) boundary layer computations usually break down under the action of an adverse pressure gradient on the flow, a scenario associated with the appearance of the Goldstein separation singularity. If, however, the parameter controlling the strength of the pressure gradient (the angle of attack or the relative suction rate in the examples mentioned above) is adjusted accordingly, the application of a local viscous‐inviscid interaction strategy is capable of describing localized boundary layer separation. Moreover, taking into account unsteady effects and flow control devices allows the investigation of the conditions leading to forced or self‐sustained vortex generation and the subsequent evolution process culminating in bubble bursting. Within the asymptotic formulation of this stage bubble bursting is associated with the formation of finite time singularities in the solution of the underlying equations and a corresponding break down. The distinct blow‐up structure gives rise to a fully non‐linear triple deck interaction stage featuring shorter spatio‐temporal scales characteristic of the successive vortex evolution process. The paper will focus on the numerical treatment of the initial phase of the latter stage. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hartmann duct flow at moderate magnetic Reynolds numbers
Authors: Bandaru Vinodh , Boeck Thomas , Schumacher Jörg 
Published: October 2016

AbstractThe application of a uniform external magnetic field on the turbulent duct flow of an electrically conducting fluid leads to several interesting changes in the structure and the mean charateristics of the flow. This is fairly well understood from the existing studies of duct flows in the low magnetic Reynolds number (Rm) limit. In this paper, we present the results for magnetohydrodynamic duct flow at moderate Rm obtained from direct numerical simulations (DNS). Several differences are observed to occur in this case as compared to low Rm flows, such as increased Hartmann layer thickness and enhanced large scale turbulence in the core region of the duct cross‐section due to partial expulsion of magnetic flux. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Statistical characteristics and time autocorrelation coefficients of the turbulent swirl flow in pipe
Authors: Čantrak Đorđe , Janković Novica , Ilić Dejan 
Published: October 2016

AbstractIn this paper is presented experimental investigation of the turbulent swirl flow in pipe generated by three axial fans of various geometries. One of these fans (model ZP) generates Rankine swirl, while other two, industrial fans, produce mainly solid body circumferential velocity profile. One‐component laser Doppler anemometry (LDA) is employed in this research. Downstream transformations of the non‐dimensional time‐averaged velocity profiles are analyzed. Distributions of turbulence levels are discussed for all three fans in both measuring sections, as well as statistical moments of higher orders for fluctuations in the axial, radial and circumferential directions. Applied correlation theory revealed turbulence structure and its statistical nature. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of isotropic and anisotropic subgrid scale models in Large Eddy Simulations of a backward‐facing step and square duct flow
Authors: Temme Nils , Niemann Martin , Fröhlich Jochen 
Published: October 2016

AbstractThe present paper employs the anisotropic explicit algebraic subgrid‐stress model (EASM), proposed by Marstorp et al. J. Fluid. Mech. 639, 403 ‐ 432 (2009), developed in the spirit of an earlier explicit algebraic RANS‐model for statistical closures. The EASM in its elementary, computationally efficient non‐dynamic version is used for Large Eddy Simulation of three‐dimensional flows over a backward‐facing step at a bulk Reynolds number of 4805 and a square duct at 2205. Its performance is assessed by comparison with experimental data and an own Direct Numerical Simulation. Furthermore, a set of eddy‐viscosity models, including the recent σ‐model, is employed for comparison. Various statistical quantities are evaluated to assess the respective performance of the different models showing, that the anisotropic EASM compares favorably to the other models. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
New explicit algebraic stress model for three‐dimensional turbulent flows
Authors: Vigdorovich Igor , Foysi Holger 
Published: October 2016

AbstractAn explicit algebraic turbulent‐stress model is built in the framework of so‐called Rodi's weak‐equilibrium approximation, which, taking into account the known model representations for the pressure‐strain‐rate correlation and turbulence‐dissipation rate, reduces the differential equations for the Reynolds‐tensor components to a system of quasi‐linear algebraic equations for the five independent components of the anisotropy tensor B. We propose an original method for solving this quasi‐linear system. The tensor in question B is sought in the form of an expansion in a tensorial basis formed from the mean strain and rotation rate tensors which contains only five elements. The expansion's coefficients are functions of five simultaneous invariants of these tensors. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A semi‐implicit multi‐fluid SPH algorithm suitable for GPU
Authors: Fürstenau Jan‐Philipp , Avci Bircan , Wriggers Peter 
Published: October 2016

AbstractMulti‐fluid flows are a common problem in process and naval engineering. In this paper an incompressible Smoothed Particle Hydrodynamics (SPH) algorithm is presented, to solve multi‐fluid flows with high density ratios (≤ 1000). The results of the Rayleigh‐Taylor instability and the rising bubble test case are compared with the results obtained by a weakly compressible SPH algorithm with respect to the results obtained by grid‐based solvers. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of mass transfer in liquid/liquid slug flow
Authors: Heckmann Christian , Ehrhard Peter 
Published: October 2016

AbstractThe mass transport for a liquid/liquid extraction system is examined using a numerical concept following the idea of the interface‐tracking method. Separate, body‐fitted, static computational domains are arranged around an imported steady‐state interface topology. The domains are coupled at the free interface to capture the behaviour of the conjugated system. The steady‐state hydrodynamics are the basis for the simulation of the transient mass transport, which is calculated as a passive scalar concentration or one‐way coupling. The investigation is restricted to the extraction from the disperse to the continuous phase. Simulation results for an extraction from the disperse to the continuous phase show that most of the mass is transferred through the wall‐film region into the continuous phase. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tangential Homology for Defect Detection in the Time of Flight Diffraction Method (TOFD)
Authors: Cuenca Jose F. , Iske Armin , Labud Patrick A. , Nemitz Oliver 
Published: October 2016

AbstractUltrasonic non‐destructive testing (NDT) techniques are widely used in industry to evaluate properties of a component, material or system without causing any damage. The time of flight diffraction method (TOFD) is regarded as a valuable procedure for the detection of welding defects. We propose an innovative concept for NDT relying on tangential homology. The novel technique allows us to analyze topological properties of manifolds from discrete data. This in turn provides an automated classification of TOFD defects which does not require any interactions with a human operator. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal adaptation of acoustic black holes by evolutionary optimization algorithms
Authors: Rothe Sebastian , Ghaffari Mejlej Vahid , Langer Sabine C. , Vietor Thomas 
Published: October 2016

AbstractThe interest of engineers is focusing increasingly on a reduced sound radiation of constructions. In particular, structures with a large surface, such as cabin linings of airplanes as well as a roof or a bottom plate of cars, tend to be good acoustic radiators and lead to an annoyance of passengers. As countermeasures, often complex and time consuming design changes or expensive active measures are used. In many cases, a more elegant and cheaper option is to improve the acoustic properties by using passive measures. Acoustic black holes are an innovative passive method which combine two advantages: A material reduction by improving acoustic properties is performed.The main idea is to guide and to focus acoustically critical bending waves by a specific wall thickness diminution. Through targeted local damping placement in the middle of an acoustic black hole, a structure can be globally damped in a very efficient way. The efficiency depends on the position and size of the acoustic black holes [1]. Finding the optimal size and position on the structure is therefore an important challenge.This paper introduces a new strategy to find an optimal position of acoustic black holes to reduce the sound radiation of plane structures by using evolutionary optimization algorithms. Numerical calculations are exemplarily shown on a rectangular plate. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Elastic Wave Propagation in Soft Microstructured Composites Undergoing Finite Deformations
Authors: Galich Pavel , Slesarenko Viacheslav , Rudykh Stephan 
Published: October 2016

AbstractWe consider the propagation of elastic waves in soft composite materials undergoing large deformations. The analysis is performed in terms of small amplitude motions superimposed on a deformed state. By consideration of 2D periodic laminates and 3D fiber composites, we find that an applied deformation influences the elastic waves through the change in the microstructure, and through the change in the local material properties. These effects can be significantly amplified by the deformation induced elastic instability phenomenon leading to microstructure transformations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation and analysis of turbulent MHD channel flow with a streamwise magnetic field
Authors: Krasnov Dmitry , Boeck Thomas 
Published: October 2016

AbstractWe perform large‐eddy simulations of turbulent MHD channel flow with a streamwise magnetic field using a pseudo spectral method. The streamwise magnetic field leads to turbulent drag reduction due to the selective Joule damping of certain flow structures. Near the walls, the turbulent mean velocity profile retains the logarithmic layer but the von Karman constant decreases with increasing magnetic field strength. In the outer region, the flow is characterized by persistent streaky structures of large streamwise extent, which lead to a rather flat mean velocity profile. In addition, the streamwise velocity fluctuations develop a pronounced second peak upon increasing the magnetic induction as well as a second logarithmic layer that increases in steepness. We find that Prandtl's classical mixing‐length model with a variable Kármán constant can describe the modified logarithmic layer reasonably accurately in a wide range of Reynolds and Hartmann numbers. However, the flow modification near the center of the channel is not properly captured by this approach. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of the behavior of thin flexible membranes in interaction with a fluid domain
Authors: Makaremi Masouleh M. , Wozniak G. 
Published: October 2016

AbstractWith the increasing concern over massive damage ensuing from flood, the application of flood protection systems has aroused growing interest. As part of an interdisciplinary project regarding the development of a temporary installable textile protective system against flood, we study, how the thin flexible membrane behaves in interaction with a fluid domain numerically and experimentally. The numerical research was carried out by means of the FV solver available in Star CCM+ based on both morphing motion model and on the basis of overset mesh and morphing motion model, with the help of a FEM solver available in Abaqus and finally through FSI Star CCM+ and Abaqus Co‐Simulation (interconnection between FV solver for fluid domain analysis and FEM solver for solid domain analysis). A key challenge facing us was the implementation of proper damping models to address the problem with oscillation of the membrane. We have examined, how the change in water level affects the behavior of the thin flexible membrane. A comparable physical validation with respect to experimental model has been achieved through numerical analysis. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Drag reduction via spanwise transversal traveling waves of smooth and structured surfaces
Authors: Meysonnat Pascal S. , Schröder Wolfgang 
Published: October 2016

AbstractThe turbulent wall‐shear stress can be influenced through passive and active means. The effect of combining active and passive methods is briefly analyzed using transversal traveling waves for the active method and riblets at an optimum spacing as a passive method. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Active Flow Control Implemented in a Multi‐Stage High‐Speed Axial Compressor
Authors: Schwerdt Lutz , Siemann Jan , Seume Joerg R. 
Published: October 2016

AbstractThe decrease of fuel consumption is a main objective in the development of modern aircraft engines and heavy‐duty gas turbines. Especially at off‐design conditions, one promising approach to suppress flow losses and to increase the efficiency of the compressor is Active Flow Control (AFC) by aspiration or injection. Aerodynamically, the compressor flow of a gas turbine responds more sensitively to volatile flow conditions than the turbine flow because of the positive pressure gradient in a compressor achieved by flow deceleration. In a decelerating flow, particularly at off‐design operating conditions, the compressor flow tends to separate from the blade surfaces. This flow separation causes unstable operating conditions inside the flow path resulting in low overall engine efficiency. Thus it is obvious that counter‐measures against increased flow losses at off‐design operation should be concentrated on the compressor. Considering industrial objectives, both the performance increase and the operating range enhancement are subjects of current compressor research, as is a reduction of vanes or even entire stages. While a reduced vane count reduces cost, even greater benefits can be gained if entire stages could be eliminated and thus the number of rotor discs reduced, which further reduces cost along with reducing the length of the rotor which could also improve rotor dynamics. For all of these purposes, different AFC approaches were implemented in a four stage axial compressor (4AV) and were experimentally examined. This paper presents an overview of the past and ongoing AFC research at the Institute of Turbomachinery and Fluid Dynamics (TFD). (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)