bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamic Behaviour of Very Large Floating Structures (VLFS) in Waves
Authors: König Marcel , Ferreira González Daniel , Abdel‐Maksoud Moustafa , Düster Alexander
Published: December 2014

An effective way to solve multiphysics scenarios in general and fluid‐structure interaction problems in particular is to rely on a partitioned solution approach, which allows for the use of different discretisation schemes and specialised solvers for each of the individual subdomains. A coupling interface, which manages the transfer of the field quantities between the solvers, has been developed and successfully applied to a great variety of coupled problems. Different predictor and relaxation techniques have been implemented to stabilize the solution algorithm and accelerate its convergence. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bounds and an isotropically self‐consistent singular approximation of the linear elastic properties of cubic crystal aggregates for application in materials design
Authors: Lobos Mauricio , Böhlke Thomas
Published: December 2014

For crystal aggregates, the orientation distribution of single crystals affects the anisotropic linear elastic properties. In the singular approximation for cubic materials, this influence is reflected by a fourth‐order texture coefficient. From this approximation, the statistical bounds of Voigt, Reuss and Hashin‐Shtrikman, and an isotropically self‐consistent singular approximation can be obtained. Here, an approximation is called isotropically self‐consistent, if, for a vanishing texture, it results in the isotropic self‐consistent approximation. The isotropically self‐consistent singular approximation has the following advantages: i) it lies between the bounds of Voigt, Reuss and Hashin‐Shtrikman, ii) it offers a useful approximation of the effective material behavior of textured anisotropic polycrystals, and iii) it can be used for material design purposes tailoring anisotropic properties mainly depending on the crystallographic texture. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparison of Statistical Descriptors for the Construction of Statistically Similar RVEs
Authors: Scheunemann Lisa , Balzani Daniel , Brands Dominik , Schröder Jörg
Published: December 2014

A method for the construction of three‐dimensional statistically similar representative volume elements (SSRVEs) is presented. Since the beneficial material properties of microheterogeneous materials originate in the microstructure, its incorporation in material modeling is desired. The FE2 method is a suitable tool to accomplish this step. Applying this method, a microscopic boundary value problem, given by a representative volume element (RVE) is attached to every integration point of the macroscale. Such RVEs taken from real microstructures exhibit a high level of complexity, thus raise computational costs. The use of a SSRVE with lower complexity is able to decrease these costs. Here, different statistical measures are compared in view of the performance in the SSRVE construction procedure. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asphalt concrete: From µCT scans towards multiscale modelling of effective properties
Authors: Schüler Thorsten , Jänicke Ralf , Steeb Holger
Published: December 2014

This paper will give a short overview about the geometrical aspects in asphalt concrete and especially the creation of artificial microstructures on the basis of informations taken from µCT scans. Informations such as volume fraction or particle size distribution are the foundation for the artificial microstructures. The generation is executed on the basis of a Voronoi diagram with an option for weighting, shrinking and pseudo‐rotation of the particles. The microstructures are generated in a periodic manner to ensure periodic boundary conditions for all later numerical analyses. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local probabilistic homogenization schemes for assessment of material uncertainties in solid foams
Authors: Hohe Jörg , Paul Hanna , Beckmann Carla
Published: December 2014

The present study is concerned with a probabilistic model for prediction of the uncertainties in the effective material response of long fiber reinforced thermoplastic materials. The model is based on a simple elasticity model using the rules of mixture together with an ensemble averaging procedure. Assuming the scatter band width of local fiber orientation angle and the local fiber density as random variables, a probabilistic model is obtained. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An accelerated simulation method of medium density wood fiber boards
Authors: Sliseris Janis , Andrä Heiko , Kabel Matthias
Published: December 2014

An accelerated micro‐scale simulation method for the prediction of the stiffness of medium density fiber boards is proposed with the aim to increase the speed of the coupled micro‐macro simulation and to study the influence of fiber orientation on material properties. The stiffness is interpolated between loads in a n‐dimensional simplex figure, which is constructed in a macroscopic strain, temperature, moisture, time and other load. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary value driven approach to computational homogenization
Authors: Fleischhauer Robert , Kaliske Michael
Published: December 2014

A novel approach to computational homogenization methods for the analysis of heterogeneous structures with large length scale differences between their micro‐ and macroscale is presented. The boundary value driven approach to homogenization (BVDH) is efficient and reliable compared to existing multi‐scale frameworks and the limit cases of homogenization, respectively. Furthermore, the proposed approach is applicable to multi‐physical problems such as thermomechanical analysis. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computation of effective non‐linear inelastic properties of magnetostrictive composites
Authors: Labusch Matthias , Keip Marc‐André , Kiefer Björn , Schröder Jörg
Published: December 2014

The present paper focuses on the determination of effective magneto‐mechanical properties of magnetostrictive composite materials in consideration of their microscopic morphologies. For this purpose, a homogenization procedure involving a two‐scale transition is applied, where representative volume elements (
${\cal RVE}$
s) on the microscopic level are used. In order to obtain characteristic non‐linear and hysteretic magnetization and magnetostrictive strain curves, we implemented a dissipative material model into the homogenization framework. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Guaranteed bounds on homogenized periodic media by FFT‐based Galerkin method
Authors: Vondřejc Jaroslav , Zeman Jan , Marek Ivo
Published: December 2014

An FFT‐based method, introduced by Moulinec and Suquet [1] in 1994, is an effective alternative to conventional Finite Element Method (FEM) for numerical homogenization of periodic media. Here, we summarize the recent variational reformulation and discretizations by Vondřejc et al. [2–6], which are based on conforming Galerkin approximations with trigonometric polynomials as basis functions. This insight, naturally leading to guaranteed bounds on homogenized matrix, opens a wide area of further investigations, which are also briefly discussed here. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Buckling Analysis of Carbon Nanotubes – Application of a concurrent atomistic‐continuum multiscale approach
Authors: Hollerer Stefan
Published: December 2014

In this work, a concurrent atomistic‐continuum multiscale approach is applied in order to analyse the buckling behaviour of carbon nanotubes. In particular, the bridging domain method that is grounded on an overlapping domain partitioning scheme with an energy‐based blending of the subdomains is used. The atomistic subdomain is modelled by means of a molecular statics approach and the continuum subdomain is handled using the finite element method. Outcomes of numerical simulations of defective single‐walled carbon nanotubes under bending load are presented. More specifically, the impact of variably located Stone‐Wales defects on the buckling behaviour of a nanotube is studied using the concurrent multiscale approach. The results of the multiscale model are validated against a full atomistic molecular statics simulation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Molecular dynamics and finite elements: an approach to couple different worlds
Authors: Pfaller Sebastian , Possart Gunnar , Steinmann Paul
Published: December 2014

The procedure proposed here couples a continuum with a particle region by introducing an overlapping bridging domain where both regions exchange information. Beyond existing methods, the particle region is computed by Molecular Dynamics (MD) at finite temperature, using a code that has been developed by our co‐workers of the Theoretical Physical Chemistry Group at TU Darmstadt. It is also used in the wide field of physical chemistry for various approaches. In contrast to MD procedures employing periodic boundary conditions (PBC), stochastic boundary conditions (SBC) allow for the definition of static anchor points. These additional artificial particles are coupled to the continuum part and serve as information transmitter. The continuum is treated classically by the Finite Element Method (FEM) which has been adapted based on the Arlequin and the bridging domain method. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Localisation in granular media: Particle approach, homogenisation and continuum modelling
Authors: Bidier Sami , Ehlers Wolfgang
Published: December 2014

The individual motion of grains in granular material has a strong influence on the macroscopic material behaviour, which is in particular the case for the phenomena of strain localisation in shear zones and justifies the need for techniques that incorporate a micro‐macro transition. In this contribution, granular media are investigated in three steps. Firstly, a microscopic particle‐based modelling is set up, where individual grains are considered as rigid uncrushable particles while their motion is obtained through Newton's equations of state. The inter‐particle contact forces are thereby determined via constitutive contact‐force formulations, which have to account for the envisaged material behaviour. The second step is the homogenisation of the obtained particle's displacements and contact forces through a particle‐centre‐based strategy towards continuum quantities. Therefore, Representative Elementary Volumes (REV) are introduced on the mesoscale and the specific construction of the REV boundary leads to the understanding of granular media as a micropolar continuum. Finally, in order to verify the homogenisation strategy, a continuum based micropolar model is applied to model localisation phenomena and a comparative study of the results is carried out in a qualitative way. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A non‐affine micro‐sphere formulation for electroactive polymers
Authors: Thylander Sara , Menzel Andreas , Ristinmaa Matti
Published: December 2014

With the capability to convert electrical energy into mechanical energy, electroactive polymers (EAP) continuously find new and more advanced applications. Their ability to considerably change in size and shape together with low cost and weight makes them suitable for technological applications in robotics and biomimetics as actuators and sensors. A dielectric actuator, one of the most common applications of EAP, consists of a soft elastomer sandwiched between two electrodes. Common for elastomeric material is a viscous response and associated time dependence on both electric and mechanical behaviour. In this work, an electromechanically coupled micro‐sphere formulation for nonlinear electroelasticity formerly proposed by the authors is further extended and includes non‐affine deformation measurements as well as viscous effects. Also, a finite element simulation of a cylindrical specimen and calibration of mechanical parameters have been performed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling advanced high‐strength steels based on direct micro‐macro calculations
Authors: Gandhi Ashutosh , Balzani Daniel , Schröder Jörg
Published: December 2014

Advanced high strength steels have immense commercial applicability today owing to the good combination of strength and ductility they offer. These properties mainly result from interactions of micro‐heterogeneities leading to a complex macroscopic material behavior. One of these steels is the Dual Phase (DP) steel which has a microstructure consisting of two phases: ferrite (matrix material) and martensite (inclusion material). This paper proposes a technique to model the post‐production situation of these steels, which is characterized by distributed material properties as well as eigenstresses. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and numerical investigation of paperboard creasing
Authors: Li Yujun , Simon Jaan‐Willem , Reese Stefanie
Published: December 2014

Laminated paperboard is widely used in packaging products. It usually consists of multiple layers bonded to each other by starch or adhesion. The indentation of fold lines (creasing) plays a crucial role during the whole converting process. It is important to control delamination and other damage effects to arrive at commercial cartons with high quality. Thus, the aim of this study is to describe the material behavior of a laminated paperboard during the creasing process. The paperboard was considered as a laminate of three different layers, and each was modeled separately with an anisotropic elastic‐plastic material model while a cohesive zone approach described the opening behavior in between. The initial yielding was given by the Hill's 48 yield criterion, while the isotropic strain hardening was described by a power law hardening function. To calibrate the material parameters, a sequence of tensile and compression tests was conducted for each layer in different directions to account for the material's anisotropy. Finally, the creasing process was investigated using a two‐dimensional plane strain finite element model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Patterned turbulence and relaminarization in MHD pipe and duct flows
Authors: Krasnov Dmitry , Zikanov Oleg , Boeck Thomas
Published: December 2014

We present results of a numerical analysis of relaminarization processes in MHD duct and pipe flows. It is motivated by Julius Hartmann's classical experiments on flows of mercury in pipes and ducts under the influence of magnetic fields. The simulations, conducted both in periodic and non‐periodic settings, provide a first detailed view of flow structures that have not been experimentally accessible. The main novelty of the analysis is very long (tens to hundreds of hydraulic diameters) computational domains that allows to discover new flow regimes with localized turbulent spots near the side walls parallel to the magnetic field. The computed critical parameters for transition as well as the friction coefficients are in good agreement with Hartmann's data. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Examples of the Re‐number effect on the transitional flat plate boundary layers
Authors: Antoš Pavel , Jonáš Pavel , Procházka Pavel , Uruba Václav
Published: December 2014

Dimensionless mean flow characteristics and the location of the transitional region were investigated of flat plate boundary layers (smooth surface or covered by sandpaper 60 grit) at the external flow velocities about 5 m/s, 10 m/s and 14 m/s and with turbulence levels either natural (less than 0.003) or gained by a grid across the flow (FST level 0.03 at the leading edge). Preliminary comparison of the received results with those previously published [1] is presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A study of truly incompressible and weakly compressible Smoothed Particle Hydrodynamics methods to model incompressible flows with free surfaces
Authors: Beck Florian , Hirschler Manuel , Niecken Ulrich , Eberhard Peter
Published: December 2014

The Smoothed Particle Hydrodynamics (SPH) method is a meshless discretization method for solving, e.g., the Navier‐Stokes equations. By now, it is used for hydraulic problems as well as for solid bodies. In general, there are two distinguishable approaches for incompressible fluid flows. One is called weakly compressible SPH (WCSPH) and the other is called truly incompressible SPH (ISPH). The main difference between these two approaches is the way of pressure evaluation. In WCSPH, a state equation is used, while in ISPH the pressure Poisson equation is solved. Each approach has its advantages as well as its disadvantages, for example the complexity of the numerical algorithm for WCSPH is smaller than for ISPH, but the pressure field is more accurate for ISPH.

In this work, two representative examples are studied. The simulations were performed with two different codes, one developed at the Institute of Engineering and Computational Mechanics and one at the Institute of Chemical Process Engineering. It is the aim of this work to show some properties of WCSPH and ISPH as well as to compare two different implementations that, in detail, are very complex. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational Formulations for Viscous Flow
Authors: Scholle Markus
Published: December 2014

For physical systems, the dynamics of which is formulated within the framework of Lagrange formalism the dynamics is completely defined by only one function, namely the Lagrangian. As well‐known the whole conservative Newtonian mechanics has been successfully embedded into this methodical concept. Different from this, in continuum theories many open questions remain up to date, especially when considering dissipative processes. The viscous flow of a fluid, given by the Navier‐Stokes equations is a typical example for this. In this contribution a special approach for finding a Lagrangian for viscous flow is suggested and discussed. The equations of motion resulting from the respective Lagrangian are compared to the Navier‐Stokes equations and differences are discussed. For a simple flow example their solution is compared to the one resulting from Navier‐Stokes equations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micro diffuser flow modeling for cold gas propulsion systems
Authors: Groll Rodion
Published: December 2014

The use of highly diluted and hypersonic gas flow is in the scope of application of cold gas thrusters for space applications. Satellites and small spacecrafts are navigated to their orbital trajectory with these nozzles. Inside these propulsion systems high density gradients are dominating the efficiency and the thrust steering behavior of the propulsion systems.

Micro flows in the transient regime between free molecular flow and continuous flow are not able to be computed with trustworthy results by using a continuous model with no‐slip boundary conditions. Therefore boundary slip‐velocity models are used for modeling the reduced wall shear stress. Molecular shear stresses decrease the molecular mean velocity near the wall. With a Knudsen number depending slip‐velocity model the effective shear stress is computed by the mean gradient of the velocity profile near the wall.

In the present study a trans‐sonic nozzle flow is computed by using a calibrated velocity slip model what depends on the Knudsen number. The Knudsen numbers are lower the Kn=1 at the nozzle neck of the propulsion system. The results are compared with simulation results of a uniform channel flow and computations of the corresponding no‐slip approach. The differences in the hypersonic region are following discussed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Premixed Turbulent Combustion in a Gas Engine using the Immersed Boundary Method and a Level Set Flame Model
Authors: Bruzzese Christian , Class Andreas , Bruder Ingmar , Bronner Yvan
Published: December 2014

An efficient simulation approach for turbulent flame brush propagation is a level set formulation closed by the turbulent flame speed. A formulation of the level set equation with the corresponding treatment of the turbulent mass burning rate that is compatible with standard Finite Volume discretization schemes available in computational fluid dynamics codes is employed. In order to simplify and to speed up the meshing process in complicated geometries (here in gas engines) the immersed boundary method in a continuous formulation, where the forces replacing the boundaries are introduced in the momentum conservation equations before discretization, is employed. In our contribution, aspects of the numerical implementation of the level set flame model combined with the immersed boundary formulation in OpenFOAM are presented. First representative simulation results of a homogeneous methane/air mixture combustion in a simplified engine geometry are shown. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of a multi‐component Eulerian approach to capture interface evolution and vorticity generation in compressible multiphase flow
Authors: Nowakowski Andrzej F. , Nicolleau Franck C.G.A.
Published: December 2014

The hyperbolic Eularian model is used as a mathematical framework for compressible multiphase flows. The formulation was obtained after an averaging process of the single phase Navier‐Stokes equations. The closure of multi‐component system leads to the volume fraction equation containing a non‐conservative term and a pressure equilibrium condition. As a result the model equations cannot be written in a conservative form. To solve the equations a finite volume Godunov type computational approach is developed which uses an approximate Riemann solver combined with a numerical scheme to tackle the non‐conservative terms. The approach accounts for pressure non‐equilibrium. It enables resolving interfaces separating compressible fluids and captures the baroclinic source of vorticity generation. The computations are performed for various initial conditions and compared with theoretical and experimental data for a shock‐bubble interaction problem. The investigated cases include acoustic wave transmission through isolated bubbles of helium and krypton. The numerical results illustrate the characteristic features of the evolving interfaces. The impulsively generated flow perturbations are dominated by the reflection and refraction of the shock and by the vorticity generation within the media. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experiments on the spreading of silicone oil droplets on horizontal rotating plates
Authors: Blank Mirja , Ehrhard Peter
Published: December 2014

The spreading of liquid films is involved in many coating processes, e.g. in the spin‐coating process. To achieve a high quality of the coating, the spreading liquid layer should be thin and homogeneous. Instabilities at the wetting front may lead to an inhomogeneous thickness of the coating layer and to uncoated areas. In this article the spreading of perfectly‐wetting silicone oil droplets with viscosity of 100 mPa s on rotating glass plates is discussed. A Schlieren system is set up to observe the wetted area and a traversed chromatic confocal distance sensor is used to measure the contour of the droplet. The experimental data are presented and compared to an analytical model which is derived from lubrication theory and valid for thin liquid layers. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Investigation of the Free‐Surface Flow within an Annulus
Authors: Gundlach Janto , Lübke Martin , Wünsch Olaf
Published: December 2014

This study describes the free‐surface flow of a highly viscous liquid between two concentric cylinders. In the process the morphology of the phase boundary is determined using a straight volume of fluid approach. Due to large differences in viscosity the gaseous phase is considered as vacuum. The numerical results of free‐surface flow measures are compared to previous calculations and experimental values. The investigation shows that the used two‐phase method is well‐suited to predict the location and shape of the interface. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The flow of vapors through porous ceramic membranes consisting of several layers
Authors: Loimer Thomas , Uchytil Petr , Reznickova Jirina
Published: December 2014

The flow of a vapor through a porous ceramic membrane is investigated. The membrane consists of several layers and is asymmetric with respect to the flow direction. The flow process is modeled accounting for capillary condensation, for the capillary pressure at liquid menisci, and for the temperature difference between the upstream and the downstream side of the membrane due to the Joule‐Thomson effect, which induces a transfer of heat in downstream direction. Condensation may occur in various parts of the membrane. Condensation has a large influence on the mass flux through the membrane. The mass flux in one flow direction through the membrane may be a few times larger than the mass flux in the other flow direction. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the sonic composites subjected to severe acoustic loads
Authors: Ilie Ruxandra , Ioan Rodica , Brişan Cornel
Published: December 2014

Transformation acoustics opens a new avenue towards the fabrication of a new class of sonic composites with scatterers made of auxetic materials embedded in the epoxy matrix. The design of the acoustic scatterers is based on the property of Helmoltz equations to be invariant under coordinate transformations, i.e. a specific spatial compression is equivalent to a variation of the material parameters in the original space. In this paper, the noise suppression for a wide full band‐gap of frequencies is discussed for spherical shell scatterers made of auxetic materials. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approach for Adaptive Sound Power Minimization of Elemental Sources in Theory and Experiments
Authors: Krause Uli , Sachau Delf
Published: December 2014

Low frequency noise is a major issue in future aircraft with counter rotating open rotor engines. Passive noise treatments are bulky and heavy at these low frequencies. That is why active approaches are considered. The well known concept of destructive interference is used by state of the art active noise cancellation methods. The active systems are located closely to the noise source to cancel it. The microphones used for pressure minimization are in the near sound field of the noise source where active and reactive sound intensity are present. The pressure based concept is minimizing just the potential part of the acoustic energy. A new approach is proposed in this paper. It minimizes directly the net flow of acoustic energy that is transmitted into an interior. Simulation results showed that a proper estimation of acoustic power output is achieved by measuring sound intensity at a single point directly on the central axis of each secondary source. The innovative energy based active control approach (TASPM) has also successfully been validated in a laboratory environment. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of defects to the band‐gaps generation
Authors: Munteanu Ligia , Popescu Mihaela
Published: December 2014

Effect of defects to the band‐gaps generation in sonic composites is investigated in this paper. Acoustic scatterers are composed by piezoceramic hollow spheres of functionally graded materials. Defects are vacancies or foreign interstitial atoms which are supported by the interfaces between the hollow spheres and the matrix. The presence of defects in sonic composites is related to the generation of localized modes in the vicinity of the point defect with a significant evanescent behavior of the waves outside the defect point. As result, the full band‐gap is wider than in the case of no defects. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Uncertainty Analysis for Crack Detection in Cylindrical Waveguides
Authors: Schaal Christoph , Hanss Michael
Published: December 2014

Cable structures usually consist of several individual wires, where each wire acts as a waveguide, guiding waves over long distances. The influence of uncertainty on a crack detection algorithm based on the Hilbert transform is investigated in this work. Not only is vagueness in calculated group velocities considered, but also imprecision in the algorithm's parameters. Moreover, the validity and robustness of the considered algorithm with applied uncertainty is discussed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of drying and wetting on the wave propagation in partially saturated soils
Authors: Albers Bettina
Published: December 2014

The propagation of sound waves in Del Monte sand filled by an air‐water mixture is studied by a linear model. Even if it does not include an operator to describe the hysteresis of the capillary pressure curve, hysteresis is accounted for: the wave analysis is performed for the two limit cases of main drying and main wetting. In the van Genuchten law both drying and wetting data are applied. Four waves appear: one transversal wave and three longitudinal waves. For the waves driven mainly by the skeleton it could be expected that the influence of consideration of the hysteresis in the capillary pressure curve is negligible. In contrast, the numerical results for the waves driven by the pore fluids exhibit a smaller influence than expected. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Frequency‐dependent properties of multiphase materials: origins, needs, and effective use in geophysics and modern synthetic materials.
Authors: Kurzeja Patrick S. , Steeb Holger
Published: December 2014

Dynamic processes in multiphase materials, e.g., fluid‐filled sandstones or bones, are described by models that include frequency‐dependent properties. The origin of such properties is introduced as an averaged representation of frequency‐dependent microscale motions. In addition to classical frequency‐dependence of fluid flow, the influence of weak, high‐porosity materials and fluid‐fluid interfaces is discussed. The relevant characteristic numbers are contrasted and specific situations are demonstrated, in which frequency dependence has to be considered or not. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damping of water hammer oscillations – comparison of 3D CFD and 1D calculations using two selected models for pipe friction
Authors: Riedelmeier Stefan , Becker Stefan , Schlücker Eberhard
Published: December 2014

Water hammer calculations are important for power plants, drinking water systems and procedural facilities. In most cases, the piping systems are very big and the probability of a resonance between a part of the piping system and a hydraulic oscillation resulting from water hammer is very high. The limiting factors for the amplitudes of the structural stresses and strains are the structural and hydraulic damping. In general, one‐dimensional codes based on the method of characteristics with quasi‐steady friction models are used to calculate the hydraulic system. This results in too small damping of the pressure oscillation and thus in an overestimation of the structural loads. Two models from the literature for a more physical reproduction of the fluid damping using one‐dimensional codes are presented and compared with a quasi‐steady pipe friction model. Additionally, a three‐dimensional computational fluid dynamics simulation of a water hammer oscillation in a small pipe section including a 90°‐bend was carried out. A comparison of the results of the three‐dimensional simulation and the one‐dimensional calculations with regard to the pressure and friction velocity distributions was performed, the performance of the models was evaluated and the limits of validity were identified. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of acoustic parameters in flow fields using OpenFOAM
Authors: Schmalz Jan , Kowalczyk Wojciech
Published: December 2014

In the present paper a Computational Aero Acoustics approach based on Lighthill's and Curle's Acoustic Analogies was implemented in OpenFOAM 2.1.1. The novel developed OpenFOAM application solvers acousticFoam and acousticRhoFoam can be used for transient incompressible and compressible simulations respectively. The CAA approach takes High Performance Computing environment into account and realize the computation of flow and acoustic fields within the acoustical near field on one mesh only. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Kinematic‐wave analysis of particle settling in tube centrifuges
Authors: Anestis Georg , Schneider Wilhelm
Published: December 2014

The kinematic‐wave theory of particle settling in tube centrifuges is subject to controversy. G. Anestis and W. Schneider [1] made the common assumption that the flow in a rotating tube of large length/diameter ratio can be treated in one‐dimensional approximation. Their results have been found in agreement with measurements [2], [3]. However, M. Ungarish [4] performed an analysis of the two‐dimensional settling process in the limit of vanishing particle concentration and obtained results that are not in accord with the one‐dimensional flow approximation, irrespective of the length/diameter ratio. It is the aim of the present investigation to gain a better understanding of the process. According to this analysis, quasi‐one‐dimensional kinematic waves are embedded in a two‐dimensional bulk flow that is governed by the boundary conditions at the walls of the tube. The results are compared with those of the one‐dimensional flow approximation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Three‐Dimensional Green's Function for a Layered Isotropic Half‐space
Authors: Chen Lin , Butenweg Christoph , Klinkel Sven
Published: December 2014

A numerical approach to calculate the Green's function for a layered half space is presented. It is based on the precise integration method (PIM), which is an efficient and accurate numerical method for the solution of one order ordinary differential equations. In the numerical implementation, the layered half space is divided into numerous mini‐layers; and the dual vector form of the wave motion equation is introduced to combine two adjacent mini‐layers/layers. The advantages of the proposed algorithm are: (a) it overcomes the exponent overflow generally encountered with employing the transfer matrix method; (b) it avoids solving the intractable transcendental functions in the stiffness matrix method and the huge matrix calculation in the thin layer method; (c) it imposes no limit to the thickness of layered strata and ensures convergence at high‐frequency range. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient simulation of wave propagation in heterogeneous materials
Authors: Joulaian Meysam , Duczek Sascha , Gabbert Ulrich , Düster Alexander
Published: December 2014

In this contribution we explain the core idea of the recently proposed spectral cell method, which combines a fictitious domain approach with finite elements of high order and noticeably relieves the burden of mesh generation. Moreover, it employs mass lumping techniques and significantly reduces the computational expenditure. Our studies show that the spectral cell method leads to similar results yet with less computational effort as compared to standard techniques. These properties turn the method to a viable tool for the wave propagation analysis of structures that obey a complicated geometry. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wave propagation and band gaps in homogenized phononic plates — modelling by spectral decomposition
Authors: Rohan Eduard , Cimrman Robert , Miara Bernadette
Published: December 2014

The paper deals with analysis of the elastic waves in the Reissner‐Mindlin type of plates formed by strongly heterogeneous structures. The homogenized plate model involves frequency‐dependent mass coefficients associated with the plate cross‐section rotations and the plate deflections. Intervals of frequencies called band gaps exist for which these coefficients constituting a mass matrix can be negative, so that certain wave modes cannot propagate. A spectral decomposition based method is proposed which is suitable to compute the plate response for an external loading by periodic forces with frequencies in range of the band gaps. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An efficient line search technique and its application to adjoint topology optimisation
Authors: Gerdes Anne , Hinze Michael , Rung Thomas
Published: December 2014

For the adjoint topology optimisation of a fluid‐dynamic cost functional we apply an Armijo step length selection rule in the gradient descent algorithm. To reduce the computational effort for evaluating the cost functional value in the step length prediction, the function evaluation step is performed on a coarse mesh. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Lorentz force flow meter for application at blast furnaces: design and calibration
Authors: Hernández Daniel , Karcher Christian , Thess André
Published: December 2014

A reference Lorentz force flow meter (LFF) has been developed to measure molten steel mass flow at the end of the runner of an experimental blast furnace. It works according to the principles of Lorentz force velocimetry [1] in which a static magnetic field interacts with a liquid metal stream. The magnetic field lines are generated by an arrangement of permanent magnets and penetrate the entire cross‐section of the flow generating eddy currents and a total Lorentz force inside the melt. This force is proportional to the mass flow of the liquid metal and owing Newton's third law, there is a counter force of the same magnitude acting on the magnet system which is connected to a load cell. For accurate flow rate measurements, a “dry and wet calibration” of the LFF needs to be performed [2]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the influence of plasma DBD actuator on the flow in a rectangular channel
Authors: Procházka Pavel , Uruba Václav
Published: December 2014

Previously, the vortical structures generated by plasma DBD actuator working in unsteady regime were investigated in detail. The generalized model describing the behaviour of these vortices in dependency on input power parameters was introduced. This paper should reveal how the wall‐jet‐like‐flow generated by that actuator will affect the developed flow in a rectangular channel with cross‐section dimension of 250 × 100 mm. The actuator is considered in spanwise configuration where the induced flow has the same or opposite orientation as the main flow. The flow control will be tested both for steady regime and for unsteady regime. The dynamic of that complex phenomenon will be studied and results in qualitatively and quantitatively meaning will be presented. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Feedback Stabilization of an Oscillating Vertical Cylinder by POD Reduced‐Order Model
Authors: Tissot Gilles , Cordier Laurent , Noack Bernd R.
Published: December 2014

The objective of this paper is to demonstrate the use of Reduced‐Order Models (ROM) based on Proper Orthogonal Decomposition (POD) to stabilize by vertical oscillations the flow over a circular cylinder at a Reynolds number equal to 60. Since in Fluid‐Structure Interaction, the POD algorithm cannot be applied directly, we then implement the fictitious domain method of [1] where the solid domain is treated as a fluid undergoing an additional constraint. The POD‐ROM is classically obtained by projecting the Navier‐Stokes equations on a small number of POD modes. The cylinder movement is then enforced in the POD‐ROM through the introduction of Lagrange multipliers. A Linear Quadratic Regulator framework is used to determine the optimal control law, in our case the vertical velocity of the cylinder, such that the flow is stabilized. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Stokes resolvent equations in 2d exterior domains
Authors: Varnhorn Werner
Published: December 2014

With methods of hydrodynamical potential theory we construct a solution of the Stokes resolvent equations in 2d exterior domains with C1,α‐boundaries, 0 < α ≤ 1. The resulting system of boundary integral equations is uniquely solvable for small resolvent parameter λ and allows the limiting procedure λ → 0. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal estimates on free boundary propagation in thin‐film flow
Authors: Fischer Julian
Published: December 2014

We present a method for the derivation of lower bounds on free boundary propagation for the thin‐film equation, one of the most prominent examples of a higher‐order degenerate parabolic equation. In particular, we obtain sufficient conditions for instantaneous forward motion of the free boundary, upper bounds on waiting times, as well as lower bounds on asymptotic propagation rates. Our estimates coincide (up to a constant factor) with the previously known reverse bounds and are therefore optimal. To the best of our knowledge, these results constitute the first lower bounds on free boundary propagation for any higher‐order degenerate parabolic equation. Our technique is based on new monotonicity formulas for solutions to the thin‐film equation which involve weighted entropies with singular weight functions. It turns out that our method is not restricted to the thin‐film equation, but also applicable to other higher‐order parabolic equations like quantum drift‐diffusion equations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The NLS and FWI approximation make wrong predictions for the water wave problem in case of small surface tension
Authors: Sunny Danish Ali , Schneider Guido , Zimmermann Dominik
Published: December 2014

In has been shown in [5] that the NLS approximation makes wrong predictions for the water wave problem in case of small surface tension. We explain that the ideas used in [5] allow to show a similar result for the FWI approximation, too. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Shape and Material Nonlinearities Influences about the Internal Thermal Dissipation for Elastomer‐Based Vibration Isolators
Authors: Nastac Silviu , Debeleac Carmen
Published: December 2014

This study deals with nonlinear internal dissipation inside the vibration isolators based on elastomeric composites. Due to the thermal influences on mechanical characteristics occurs during the regular exploitation regime, both conservative and dissipative components have affected and the main parameters continuously change. Beside the nonlinear behaviour of the assembly containing the isolator device, these changes also affects the thermodynamic regime inside the elastomeric material. The isolator shape also affects the internal thermal dissipation state. This complex behaviour implies nonlinear mathematical models, which have to be able to simulate the realistic viscous and elastic characteristics of such composites subjected to dynamic loads. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some properties of asymptotic energy of a class of functionals of Ginzburg‐Landau type endowed with generalized lower‐order oscillatory term in one dimension
Authors: Raguž Andrija
Published: December 2014

We consider a generalization of the functional of Ginzburg‐Landau type studied in the paper A. Raguž: A note on calculation of asymptotic energy for Ginzburg‐Landau functional with externally imposed lower‐order oscillatory term in one dimension, Boll. Un. Mat. Ital. (8)10‐B, 1125‐1142 (2007), whereby the oscillatory term a(ε−βs) (where a ∈ L1per(0, 1) and β > 0) is replaced by a(ρεs) (where limε−→0 ρε = +∞). We describe how the expression for the rescaled asymptotic energy of such class of functionals depends on the properties of the sequence (ρε). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of heat transfer characteristics in energy piles
Authors: Zhou Long , Masood Rao , Jovicic Vojislav , Zbogar‐Rasic Ana , Kempe Victor , Delgado Antonio
Published: December 2014

Single energy pile is studied numerically by both commercial code (CFX 13.0) and open‐source software (OpenFOAM). Both fluid and solid domains are simulated. The temperature distribution in the soil and fluid shows the consistency of the two software. Because of the high computational cost for the simulation of multiple piles, a simplification approach is proposed. The fluid temperatures are updated by iterative analytical calculation while the soil temperatures are simulated by conductive heat transfer equation using OpenFOAM. By this effort, the computation of the whole energy pile system is feasible. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some recent results on a free boundary problem for microelectromechanical systems
Authors: Escher Joachim , Laurençot Philippe , Walker Christoph
Published: December 2014

The mathematical modeling of idealized microelectromechanical systems leads to a nonlinear singular elliptic‐parabolic free boundary problem involving non‐smooth domains and depending on a parameter λ reflecting the applied voltage across the device. Recent results derived in [1,4] are presented which confirm physically important and expected features: For small λ there is (at least) one stable stationary solution and solutions to the evolution equation exist globally in time, while for large λ no stationary solution exists and the evolution equation has no global solution. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stopping Distance from Observations by Stepwise Regression
Authors: Niessner Herbert
Published: December 2014

In a regression equation with many terms stepwise regression allows to pick out significant terms and to exclude insignificant ones. This can be used to solve rank deficient equation systems. Yet significance is not condition. There is a rather simple method for stepwise regression starting from extended normal equations proposed by Efroymson 1960 [1] and improved by Breaux 1968 [2]. Numerically more stable methods apply orthogonal transformations (Eldén 1972 [3], Gragg‐LeVeque‐Trangenstein 1979 [4]). If symmetry is properly made use of [2, 5] the method of Efroymson is the most efficient one with respect to computing time. But reasonable results are obtained only if the terms in the regression equation are physically justified. This illustrates the search for a formula of the stopping distance derived from observations, an exercise given in [9], a book widely used on some universities. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the solution of the Fokker‐Planck equation on infinite domains using problem‐specific orthonormal basis functions in a Galerkin‐type method
Authors: Lentz Lukas , Martens Wolfram
Published: December 2014

Abstract: The dynamical behavior of a mechanical system under random excitation can be described by its probability density function (PDF). The PDF can be determined by random sampling or directly computed as the solution of the corresponding FOKKER‐PLANCK equation (FPE). Since the class of FPE with known exact solution is very small, the solution is mostly approximated by numerical methods including finite elements, finite differences or other types of local discretization methods that are best suited for finite domains. Whilst this restriction can be desired for some models, the domain needs to be unbounded in the general case. The authors present a method of calculating a semi‐analytical approximate solution for the stationary FPE over an unbounded domain using a GALERKIN‐type method. The utilization of a problem‐specific orthonormal basis for the ansatz‐space ensures that only a small number of improper integrals needs to be computed. In fact, these computations are inexpensive and can be performed prior to the more costly algorithm that constructs the system of linear equations. The computation of the specific basis and its properties are discussed in detail. In order to demonstrate the method and its application on technical systems, the PDF for a nonlinear bistable magneto‐piezo‐electric energy harvester is calculated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)