bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grain‐scale‐based simulation of granular material
Authors: Bidier Sami , Ehlers Wolfgang 
Published: October 2015

AbstractIn recent years, new developments in experimental mechanics, e. g., particle‐tracking methods using X‐ray micro‐tomography, have provided a new insight into the material behaviour of granular media. The possibility to capture the individual grain displacement and rotation of all particles within a sample provides a new fundament for a reliable numerical simulation of granulates. This is, in particular, the case for deformation localisation in shear zones as they are observed in bi‐ and triaxial compression tests, where the exact thickness of the localised zone as well as the amount of accompanying grain displacements and rotations are measurable in a precise and direct way. In this context, the Discrete‐Element (DE) Method has become a promising and frequently used modelling technique for granular materials. In contrast to macroscopically based continuum‐mechanical approaches, the DE approach treats each particle as a rigid and uncrushably body and is, therefore, defined on a microscopic level of description. This consequently allows a direct comparison with experimental data from grain‐scale tracking methods. In the present contribution, the DE method is applied in order to solve problems of localisation in granular media. Therefore, constitutive inter‐particle contact laws are formulated for forces and torques which are transferred between interacting particles. With a given solution of initial‐boundary‐value problems on the microscale, a computational homogenisation procedure leads to macroscopic quantities purely stemming from microscopic information. Herein, a particle‐centre‐based volume averaging technique leads to macroscopic quantities which correspond to quantities known from micropolar continuum theories. The contribution presents a framework for the homogenisation in all time steps in a fully 3‐dimensional context and discusses the activation of micropolar effects in the localised zone. Furthermore, the admissible size of the chosen Representative Elementary Volume (REV) is addressed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled two‐scale shell model for comb‐like sandwich structures
Authors: Heller Dominik , Gruttmann Friedrich 
Published: October 2015

AbstractIn this work a coupled two‐scale sandwich shell model is proposed, where 4‐node quadrilaterals are employed both on the global and the local scale. The coupled global‐local boundary value problem is derived by means of a variational formulation and ensuing linearization. A numerical simulation is carried out for linear elastic and elasto‐plastic material behavior with small strains.The resulting coupled nonlinear boundary value problem is solved simultaneously in a Newton iteration with incremental load steps. Various types of sandwich models are investigated in the form of uni‐ and bidirectionally stiffened structures. For the unidirectionally stiffened beam, an analytical reference solution is present by means of classical beam theory. In addition, the numerical results of all coupled calculations are compared to full scale shell models, showing very good agreement while significantly reducing the size of occurring system matrices. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental investigation and approximation of the temperature‐dependent stiffness of short‐fiber reinforced polymers
Authors: Kehrer L. , Müller V. , Brylka B. , Böhlke T. 
Published: October 2015

AbstractIn order to predict the effective material properties of a short‐fiber reinforced polymer (SFRP), homogenization of elastic properties with the self‐consistent (SC) scheme and the interaction direct derivative (IDD) method is performed by means of µCT data describing the microstructure of the composite material. Using dynamic mechanical analysis (DMA), the material properties of both, polypropylene and fiber reinforced polypropylene are investigated by tensile tests under thermal load. The measured storage modulus of the matrix material is used as input parameter for the homogenization scheme. The effective properties of SFRP are compared to experimental results from DMA. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multi‐scale modeling of beam‐like structures: A new boundary condition concept for the RVE
Authors: Klarmann Simon , Gruttmann Friedrich 
Published: October 2015

AbstractIn this work a coupled two‐scale beam model using Timoshenko beam elements [1] with finite displacements on the macro scale and fully non‐linear 3D brick elements on the micro scale is proposed. The calculation is carried out with the so‐called FE2 concept. To achieve the coupling between the beam and the brick elements, the algorithm from [2] is adapted.Within the degenerated concept of the Timoshenko beam, the introduction of a pure shear deformation leads to significant problems concerning the equilibrium condition on the micro scale. Applying this deformation mode on the RVE with periodic boundary conditions results in a rigid body rotation. Using linear displacement boundary conditions instead, the wrapping deformation is suppressed on the boundary, leading to a length dependency in the torsional deformation mode. In addition, the shear forces introduce a bending moment, which depends on the length of the RVE and adds spurious normal stresses and a length dependency of the shear stiffness.To overcome these problems, periodic boundary conditions are applied and the displacement assumptions are modified such that the shear deformation is achieved with force pairs on both ends of the RVE. The resulting model leads to length independent results in tension, bending and torsion and a domain which is able to produce a pure shear stress state. Consequently, only this domain of the model should be homogenized which can be accomplished by modifying the variations in the algorithm [2]. The concept is validated by simple linear and non‐linear test problems. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Materials design of elastic properties of multiphase polycrystalline composites using model functions
Authors: Lobos Mauricio , Yuzbasioglu Tunc , Böhlke Thomas 
Published: October 2015

AbstractFor a chosen combination of materials for a multiphase polycrystalline composite, a crystallite orientation distribution function for each phase is formulated as a superposition of analytic central model von Mises‐Fisher functions. The chosen central model functions allow the analytic integration of orientation averages of arbitrarily anisotropic fourth‐order tensors. Based on this result, the first‐order bounds of Voigt and Reuss and the geometric average of the stiffness can be expressed explicitly in closed forms for arbitrarily anisotropic polycrystalline materials and number of phases depending on the volume fractions and the influence of the crystallographic texture of each constituent. These expressions can then be used for the materials design aiming the determination of volume fractions and orientation distribution of selected materials for prescribed effective properties. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on statistically similar RVEs for real microstructures based on different statistical descriptors
Authors: Scheunemann Lisa , Balzani Daniel , Brands Dominik , Schröder Jörg 
Published: October 2015

AbstractA method for constructing statistically similar representative volume elements (SSRVEs) for a real dual‐phase (DP) steel microstructure is presented in this contribution. The advantageous material properties of such kind of steels originate from the interaction of the microstructure constituents of the material on the microscale. In order to capture these effects directly in the material modeling, the FE2 method is a suitable tool, where an RVE representing the microstructure of a material is used in the microscopic boundary value problem, which is solved at each Gauss‐point of the macroscopic boundary value problem. However, RVEs based on real microstructures typically implicate high computational expenses due to the complexity of the underlying microstructure and its discretization. SSRVEs, which have a lower complexity than conventional RVEs but are still able to represent the material, can be used instead. Here, different statistical measures for the construction of SSRVEs and their comparison are the main focus. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polynomial shape functions on the logarithmic space: the LogFE method
Authors: Schröppel Christian , Wackerfuß Jens 
Published: October 2015

AbstractWe extend the Logarithmic finite element method, a novel finite element approach for solving boundary‐value problems proposed in [1], to a complete set of degrees of freedom, i.e. translational and rotational degrees of freedom in three dimensions. In contrast to the standard Ritz‐Galerkin formulation, the shape functions are given on the logarithmic space of the deformation function. Unlike existing formulations based on Lie groups, they may include polynomial functions of arbitrary degree. The method focuses on reducing the low‐frequency components in the error, while minimizing spurious high‐frequency deformations, a characteristic that is particularly advantageous in the context of a multigrid algorithm, in which the method may be used to construct an approximation for the coarse grid. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cascade Continuum Micromechanics Model for the Effective Diffusivity of Porous Materials: Exponential Hierarchy across Cascade Levels
Authors: Timothy Jithender J. , Meschke Günther 
Published: October 2015

AbstractThe effective molecular diffusivity of porous materials such as cementitious, geological or synthetic materials is strongly affected by the complexity of the pore‐space which may span across multiple scales from the nanometer to the sub‐millimeter range. Recently, a semi‐analytical Cascade Continuum Micromechanics (CCM) Model [1,2] was proposed, which allows to compute estimates of the effective diffusivity given the porosity ϕ, the intrinsic diffusivity of molecules in the pore‐fluid D and a complexity parameter n. In contrast to existing micromechanics models, the CCM model is able to predict a physically consistent percolation threshold. In this paper, the classical CCM model is generalized so as to characterize a pore‐volume distribution and its influence on the effective diffusivity at a particular cascade level. The generalized CCM model shows an exponential pore‐volume distribution across cascade levels that is implicitly included in the classical CCM model. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Axisymmetric flow over a backward‐facing step in an annular pipe
Authors: Beladi Behnaz , Kuhlmann Hendrik C. 
Published: October 2015

AbstractThe incompressible flow of a Newtonian fluid over a backward‐facing step is investigated numerically. The geometry is an annular pipe in which the radius of the inner cylinder decreases suddenly. Keeping the radial expansion ratio fixed axisymmetric flows are computed for outlet radius ratios from 0.1 to 1 (ratio of the inner to the outer outlet radius). The Reynolds number at which the flow separates from the outer cylinder decreases as the outlet radius ratio decreases for constant inlet geometry. The growth with Reynolds number of the recirculation zone on the inner outlet cylinder just behind the step is strongly reduced when the recirculation zone on the outer cylinder is established. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extreme event detection in near‐wall turbulence using reflection‐encoded readout of micropillar arrays
Authors: Hegner F. , Mikulich V. , Axtmann B. , Rist U. , Brücker Ch. 
Published: October 2015

AbstractA method is presented which uses the intensity‐based encoding of deflection of micropillars to detect criticical events in near‐wall turbulence. The pillars are tailored to respond only to the streamwise or the spanwise component of the wall‐shear stress with larger deflection. Light reflected from the side‐walls of these structures is used to dected certain events in the flow that run along the wall. Examples are given for defined disturbances in a planar Couette flow. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Receptivity and non‐uniqueness of turbulent boundary layer flows
Authors: Scheichl Bernhard 
Published: October 2015

AbstractThe classical theory of firmly attached time‐mean turbulent boundary layers, exhibiting fully developed broadband turbulence, in the limit of large Reynolds numbers, Re, is extended in two ways, where the focus lies on their stability and receptivity. At first, the description of non‐unique equilibrium flows having a so‐called moderately large velocity deficit is generalised as weak spanwise variations and unsteadiness is taken into account. Here the time period of filtering the flow tends to infinity such that conventional Reynolds averaging is obtained as Re → ∞. Secondly, the method of matched asymptotic expansions is supplemented with a suitable multiple‐scales approach so as to capture the global effect of pronounced surface waviness on the time‐mean velocity profile of the boundary layer in a self‐consistent manner in terms of a memory decaying exponentially from the surface. Remarkably, the results of the asymptotic analysis are qualitatively independent of any turbulence closure. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High‐Reynolds‐number effects on turbulent scalings in compressible channel flow
Authors: Modesti Davide , Bernardini Matteo , Pirozzoli Sergio 
Published: October 2015

AbstractThe effect of the Reynolds number in a supersonic isothermal channel flow is studied using a direct numerical simulation (DNS). The bulk Mach number based on the wall temperature is 1.5, and the bulk Reynolds number is increased up to Reτ ≈︁ 1000. The use of van Driest velocity transformation in the presence of heated walls has been questioned due to the poor accuracy at low Reynolds number. For this reason alternative transformations of the velocity profile and turbulence statistics have been proposed, as, for instance, semi‐local scalings. We show that the van Driest transformation recovers its accuracy as the Reynolds number is increased. The Reynolds stresses collapse on the incompressible ones, when properly scaled with density, and very good agreement with the incompressible stresses is found in the outer layer. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic solutions of an extended Korteweg–de Vries equation describing solitary waves with weak or strong downstream decay in turbulent open‐channel flow
Authors: Müllner Markus , Schneider Wilhelm 
Published: October 2015

AbstractSolitary waves in turbulent open‐channel flow over a strip of enlarged bottom roughness are considered. Slightly supercritical, fully developed flow far upstream and downstream is assumed. An analysis by Schneider [1] yielded an extended Korteweg–de Vries equation that is solved in the present paper by matched asymptotic expansions up to second order. Solutions for the surface elevation and the location of the wave crest are given. It is shown that a minimum enlargement of the bottom roughness is required for the stationary wave to exist. The surface elevation exhibits either a weak downstream decay, i.e. a shallow ‘tail’, or, if the enlargement of the bottom roughness equals an eigenvalue, the strong decay of the classical soliton solution. Numerical results available for the latter case [2] are in very good agreement with the present analytical solution. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coarse‐Grid‐CFD for the Thermal Hydraulic Investigation of Rod‐Bundles
Authors: Viellieber Mathias , Class Andreas 
Published: October 2015

AbstractA nuclear reactor core, that is a few meters in height and diameter is composed of hundreds of fuel assemblies which are again composed of tenth of fuel rods with a diameter of about 10 mm. The relevant length scales for a Computational Fluid Dynamics (CFD) simulations range from the sub millimetre range, relevant for the sub channels up to several meters. Describing such a multi‐scale situation with CFD is extremely challenging and the traditional approach is to use integral methods. These are sub channel and sub assembly analyses codes requiring closure by empirical and experimental correlations. A CFD simulation of a complete nuclear reactor set up resolving all relevant scales requires exceedingly large computational resources. However, in many cases there exists repetitive geometrical assemblies and flow patterns. Based on this observation the general approach of creating a parametrized model for a single segment and composing many of these reduced models to obtain the entire reactor simulation becomes feasible. With the Coarse‐Grid‐CFD (CGCFD) ( [1], [2]), we propose to replace the experimental or empirical input with proper CFD data. Application of the methodology starts with a detailed, well‐resolved, and verified CFD simulation of a single representative segment. From this simulation we extract in tabular form so‐called volumetric forces which upon parametrization is assigned to all coarse cells. Repeating the fine simulation for multiple flow conditions parametrized data can be obtained or interpolated for all occurring conditions to the desired degree of accuracy. Note, that parametrized data is used to close an otherwise strongly under‐resolved, coarsely meshed model of a complete reactor set up. Implementation of volumetric forces are the method of choice to account for effects as long as dominant transport is still distinguishable on the coarse mesh. In cases where smaller scale effects become relevant the Anisotrop Porosity Formulation (APF) allows capturing transport phenomena occurring on the same or slightly smaller scale compared to the coarse mesh resolution. Within this work we present results of several fuel assemblies, that were investigated with our methodology. In particular, we show Coarse‐Grid‐CFD simulations including a 127 pin LBE cooled wire wrapped fuel assembly. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and simulation of mobile jet agitator for a biogas plant
Authors: Alimi Aria , Wünsch Olaf 
Published: October 2015

AbstractThis work deals with the modeling and simulation of mixture process in a biogas plant. This mixing process involves a closed pumping procedure, which pumps the constituents of the biogas plant using jet agitators inside the tank. For this purpose, an experimental model has been designed and built in reduced scale to study the mixture process. Furthermore, this process has been simulated numerically. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of mass transfer at free liquid/liquid interfaces
Authors: Heckmann Christian , Lakshmanan Peter , Ehrhard Peter 
Published: October 2015

AbstractA numerical scheme for the simulation of mass transfer processes at free liquid/liquid interfaces using the interface tracking method is presented. Due to comparable diffusion coefficients in liquid/liquid systems, the mass transfer resistance in both phases is relevant for the entire transient mass transfer process. Exemplary, the extraction process from a free rising spherical droplet of constant shape is used. The presented approach can be used in general for any multiphase steady‐state mass transfer system. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Polymer Devolatilization in a Rotating Apparatus
Authors: Hirschfeld Stefan , Hermann Lutz , Wünsch Olaf 
Published: October 2015

AbstractDevolatilization is an important unit operation in polymer processing, that is often performed in rotating devices. This work is concerned with the experimental study of film degassing in a simple rotating apparatus with a blade agitator. The experimental setup and procedure are presented. The results are evaluated with the surface renewal theory which is also known as penetration theory. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gas bubbles in micro capillaries – hydrodynamics and mass transfer
Authors: Lakshmanan Peter , Ehrhard Peter 
Published: October 2015

AbstractProcess design of multi‐phase unit operations on the micro‐scale relies on the detailed knowledge of the hydrodynamics and mass transfer behavior of discrete disperse fluid particles. The present work examines the hydrodynamics and mass transfer of gas bubbles in vertical capillaries. The hydrodynamic behavior of a single bubble in a capillary including is examined numerically using a modified level‐set method [1]. Additionally, the influence of surface‐active contaminations (‘surfactants’) and the resulting Marangoni effects are taken into account [2]. This enables the differentiation between bubbles with a mobile, i.e. clean, interface and those with a immobile, i.e. contaminated, interface. Based on the hydrodynamics, the mass transfer is examined. In the present work, mass transfer is from the bubble into the bulk fluid. By using a very high mesh resolution, the local concentration field in and around the gas bubble can be resolved, which gives access to the local mass transfer. Results are in good agreement available correlations from literature. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Modeling of Laser‐Induced Cavitation Bubbles with a Finite Volume Method
Authors: Lechner Christiane , Koch Max , Reuter Fabian , Köhler Karsten , Mettin Robert , Lauterborn Werner 
Published: October 2015

AbstractWe report on the numerical modeling of laser‐induced cavitation bubbles with the finite volume method using the open source software package OpenFOAM. The numerical model is validated by comparison to experimental data for the two cases of a bubble collapsing under normal ambient conditions in an unbounded liquid as well as close to a solid wall. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A circulating gravity wave in a cylindrical tank
Authors: Steinrück Herbert , Gusner Lorenz 
Published: October 2015

AbstractA circular cylindrical vertical tank is partially filled with a liquid (Water) and a gas (air) above it. The top lid of the container rotates around the cylinder axis and induces a flow in the gas and the liquid. Above a critical rotational speed a large amplitude circulating gravity wave forms. The two phase flow problem will be reduced to a free surface single phase flow problem and the critical parameters, when the axis‐symmetric flow becomes unstable with respect to the circulating gravity wave will be determined. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐destructive testing of porous media by means of sound wave analysis
Authors: Albers Bettina 
Published: October 2015

AbstractThe theoretical investigation of sound waves in porous materials is motivated by the possible construction of non‐destructive testing methods. Here, geotechnical applications are of interest where low frequencies from zero to 100 Hz occur but also systems with higher frequency ranges may be tested non‐invasively. Examples are concrete and other construction materials, road surfaces and pavements (some MHz), biological materials like bones and soft tissues, e.g. the surface of the heart (up to 3 MHz) right up to surface coatings by nanomaterials (approximately 100 MHz). (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)