bluuebunny/crossref_metadata_2025 huggingface dataset:
A FEM model for lifetime prediction of Ancorsteel1000C in rolling contact fatigue
Authors: Özden U.A. , Giang N.A. , Chen G. , Bezold A. , Broeckmann C.
Published: December 2014

Ancorsteel1000C is commonly used for important components including bearing rollers, gears, connecting rods, wheels and rails; most failures of these components are caused by rolling contact fatigue (RCF). In this study the fatigue damage indicator based on Fatemi‐Socie critical plane were determined in a local hot spot area in finite element (FE) model in case of Hertzian stress with zero slip condition. The simulation results compared with respect to experimental data, which is in good agreement. Therefore, this approach can be implemented as a useful tool for lifetime calculations in RCF in the process of structure fatigue design. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Damage modelling and lifetime prediction of adhesively bonded joints under sustained loading with constant and variable amplitudes
Authors: Kroll Ulrich , Matzenmiller Anton
Published: December 2014

The lifetime of adhesively bonded joints under service loading is predicted by a linear viscoelastic traction–separation model, which is enhanced by an isotropic damage approach. Therefore, a scalar damage variable is defined according to the concept of effective stresses based on the hypothesis of strain equivalence in the framework of continuum damage mechanics. The damage evolution is driven by a specific equivalent stress, adapted for ductile adhesives. Experimental data acknowledge the validity of the proposed model for the lifetime prediction of adhesive joints. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical modelling of the in‐plane compressive behaviour of pile fibres in Spacer Fabric Composites
Authors: Köllner Anton , Völlmecke Christina
Published: December 2014

The mechanical behaviour of Spacer Fabric Composites (SFC) is highly influenced by their pile fibres. Within this work, the in‐plane compressive behaviour of pile fibres in SFC is investigated. An analytical model is developed based on rigid hinged struts. Therefore, a representative part of the continuous fibre is chosen. The bending behaviour and the interaction of the pile fibre with facesheet fibres is modelled using rotational and extension springs respectively. The system proposed is fully defined by three generalized coordinates. The total potential energy of the system is determined and used to obtain information about the deformation behaviour. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical modelling of nonlinear buckling of (de‐)laminated composite struts
Authors: Völlmecke Christina
Published: December 2014

Laminated fibre‐reinforced composites are prone to delamination damage. This interlaminar defect lowers the critical buckling load of a strut and may lead to unstable postbuckling. Thus, the critical load of laminated and delaminated struts are the topic of investigation herein. Small scale experimental investigations were undertaken and comparison is sought with analytical formulations whilst a model for a delaminated strut is introduced. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Passive damping of bridge vibrations by tuned liquid column gas dampers
Authors: Ziegler Franz
Published: December 2014

Sealed tuned liquid column gas dampers, i.e. with a gas spring effect taken into account, TLCGD, are ideally suited to increase the effective structural damping of bridges when vibrating in the critical low frequency band, substituting the classical mechanical damper (TMD). The evident features of TLCGD are no moving mechanical parts, cheap and easy implementation, low maintenance costs and simple modification of the natural frequency (by means of altering the equilibrium gas pressure). Modal tuning in analogy to the classical mechanical damper, TMD, in the design stage is subsequently followed by fine‐tuning in state space, rendering the absorber parameter (frequency and damping) optimal and, when designing smaller units in parallel action, yields the control even more robust. The equilibrium gas‐pressure is the main control parameter to optimize the absorber frequency when the volume of the individual gas vessel above the liquid‐gas interface is properly selected. U‐ or V‐shaped TLCGD with horizontal extension maximized, are proposed to reduce dominating horizontal vibrations of long‐span bridges (including pedestrian bridges), and in the case of the cantilever method of bridge construction to allow the increase of the maximum length of the cantilever, despite of wind‐gusts. An alternate design, VTLCGD provides the control force vertically, and thus counteracts dominating vertical, traffic‐induced vibrations. The horizontal length of the absorber is kept to a minimum. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Galerkin‐based multi‐scale time integration for nonlinear structural dynamics
Authors: Bartelt Matthias , Groß Michael
Published: December 2014

This paper deals with a GALERKIN‐based multi‐scale time integration of a viscoelastic rope model. Using HAMILTON's dynamical formulation, NEWTON's equation of motion as a second‐order partial differential equation is transformed into two coupled first order partial differential equations in time. The considered finite viscoelastic deformations are described by means of a deformation‐like internal variable determined by a first order ordinary differential equation in time. The corresponding multi‐scale time‐integration is based on a PETROV‐GALERKIN approximation of all time evolution equations, leading to a new family of time stepping schemes with different accuracy orders in the state variables. The resulting nonlinear algebraic time evolution equations are solved by a multi‐level NEWTON‐RAPHSON method. Realizing this transient numerical simulation, we also demonstrates a parallelized solution of the viscous evolution equation in CUDA©. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Krylov Subspace Reduced‐Order Modeling Methods for Structural Dynamic Finite Element Systems
Authors: Tegtmeyer Stefanie , Nackenhorst Udo
Published: December 2014

Computational resources can be used more efficiently by introducing reduced‐order models, instead of solving large systems of equations of the original model. In this contribution, the Krylov subspace method, a reduced‐order modeling method, is studied and compared to the modal decomposition for a rubber wheel model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermal stresses in a cylindrical panel with free ends
Authors: Haskul Mehmet , Arslan Eray
Published: December 2014

Elastic stress state of a thick‐walled cylindrical panel, which is subjected to a positive temperature gradient in the radial direction, is investigated under generalized plane strain conditions. In particular, the stress distributions in the panel at the elastic limit according to von Mises' yield criterion are studied. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Extension of the scaled boundary finite element method to geometrical and physical nonlinearity
Authors: Behnke Ronny , Mundil Matthias , Birk Carolin , Kaliske Michael
Published: December 2014

The scaled boundary finite element method (SBFEM) has been used in many fields of engineering to solve the governing equations in bounded and unbounded 2D as well as 3D domains. In solid mechanics, the semi‐analytical solution strategy of the SBFE formulation (numerical in circumferential direction, analytical in radial direction) is based on the assumption of linear elastic material behavior and only small geometrical changes. However, a large group of materials (e.g. rubber) shows geometrical and physical nonlinearity at mechanical loading. In this contribution, the extension of the SBFEM to geometrical and physical nonlinearity is examined. A plane finite element is developed which uses the concept of shape functions constructed by the SBFEM in the framework of a nonlinear finite element analysis. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of Uncertain Inelastic Material Behaviour using the Stochastic Finite Element Method
Authors: Fink Sebastian , Nackenhorst Udo
Published: December 2014

In this work, an approach for computing three‐dimensional structures with random material properties, such as the yield stress, Young's modulus and hardening parameters is proposed. The random material properties are represented as random fields which are realized with the Spectral Representation Method (SPRM). The proposed approach is coupled with Monte Carlo Simulation (MCS) to determine the response statistics of a simple mechanical structure. The numerical results are compared with those obtained from classical Latin Hypercube Sampling (LHS). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SBFEM elements for thin‐walled composite beams with arbitrary layup
Authors: Jung Jonathan Daniel , Becker Wilfried
Published: December 2014

The scaled boundary finite element method (SBFEM) is a semi‐analytical method in which only the boundary is discretized. The results on the boundary are scaled into the domain with respect to a scaling center which must be “visible” from the whole boundary. For beam‐like problems the scaling center can be selected at infinity and only the cross‐section is discretized. Two new elements for thin‐walled beams have been developed on the basis of the first order shear deformation theory. The beam sections are considered to be multilayered laminate plates with arbitrary layup. The arbitrary cross‐section is discretized with beam elements of Timoshenko type. Using the virtual work principle gives the SBFEM equation, which is a system of differential equations of a gyroscopic type. The solution is calculated using the matrix exponential function. The elements have been tested and compared with a finite element model and they give good results. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Active influence on friction contacts in larger objects
Authors: Hammerschmidt Antonia , von Wagner Utz , Kracht Kerstin
Published: December 2014

Ultrasonic vibrations in the micrometer amplitude range have been proven to be capable to influence frictional contacts with respect to decreasing friction coefficients in experiments on small test set‐ups solely loaded by their small weight. The question is, if these effects can also be found in larger objects. This paper shows results of experimental work on applying this effect to larger objects and lager normal loads. Special focus is layed on the contact between the wheel and the rail, while the wheel or the rail being excited by piezoceramics or shakers respectively. To get the largest possible vibration amplitudes, the wheels are designed using FE‐models and are experimentally investigated for optimal actor placing and excitation by modal analysis. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of the hydraulic fluid pipe on the dynamic stability of a shift gearbox
Authors: Jehle Georg , Fidlin Alexander
Published: December 2014

Shift gearboxes are used in vehicle drive trains in order to transmit the driving torque of the motor and to shift between different transmission ratios. Because of the occurrence of sliding friction forces and ‐torques during the shifting period, unwanted vibrations can arise. Several mechanisms which lead to a destabilization of the stationary state in shift gearboxes are conceivable: variable friction coefficient [1], wobbling clutch disc [2], or vibrations because of coupled DoFs due to the helical gearing [3].

The latter effect results in translational oscillations in axial and radial direction of the clutch disc. It was observed that damping forces influence the boundary of the region of stability in the parameter space ‐ though it is not entirely clear where such forces originate from. For this reason, in this work the effect of the fluid of the hydraulic actuation of the clutch system is analyzed. The fluid pipe is situated in the center of the gear unit input shaft and forces the fluid to oscillate when the system becomes unstable. In return, the fluid implies shear stress and pressure on the adjacent mechanical parts (shaft, pressure plates). The analysis of the stationary state of the coupled system reveals a clear effect of fluid properties on the stability: both the mass density and the kinematic viscosity are able to change the location of the border between stable and instable regions in the parameter space. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Arclength Continuation Methods for the Investigation of Non‐linear Oscillating Systems with the Concept of Non‐linear Normal Modes
Authors: Jerschl Martin , Willner Kai
Published: December 2014

Non‐linear normal modes (NNMs) can be considered as a non‐linear analogon to the description of linear systems with linear normal modes (LNMs). The definition of NNMs can be found in [1]. Small systems with a low number of degrees of freedom and non‐linear couplings (cubic springs) are investigated here. With increasing energy in the system the progressive non‐linearity leads to a hardening effect. One typical dynamical property of non‐linear systems is the frequency‐energy dependency of the resulting oscillations. A good graphic illustration is to plot such a dependency in a so called frequency‐energy plot (FEP). A NNM branch can be calculated by a numerical continuation method with starting at low energy level in a quasi linear regime and increasing the energy and reducing the period of the oscillation iteratively. Thereby a branch is a family of NNM oscillations with qualitatively equal motion properties [2]. In non‐linear systems internal resonances and other phenomena can occur. Several tongues can bifurcate from a NNM branch. Therefore ordinary continuation methods may fail at such bifurcation points. Here a predictor‐corrector‐method is used and different corrector algorithms are discussed for the branch continuation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilization of the radial equilibrium of a tethered satellite with respect to out‐of‐plane initial perturbations
Authors: Steindl Alois
Published: December 2014

We investigate the stabilization of the radial equilibrium of a tethered satellite by tension control, if both in‐plane and out‐of‐plane deviations from the vertical position are taken into account. While in‐plane perturbations can be eliminated in finite time, the length rate change of the tether acts as parametric control on the out‐of‐plane deviations. Therefore the control becomes less effective, if the perturbation decreases.

In order to improve the convergence we investigate the optimal control problem assuming no costs for the applied tension force but restricting the control force to a finite interval. For tether cconfigurations close to the vertical target position this approach yields a solution with singular control, which leads to a faster decay of the deviations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter study of a multi‐body friction oscillator
Authors: de Payrebrune Kristin M. , Kröger Matthias
Published: December 2014

In many technical applications sliding contacts with multiple contact points or engagements exist, like between seals and rough surfaces, between grinding wheel and workpiece, or between granular material and storage box. In a simplified way these contacts can be represented by a friction oscillator with multiple bodies. The behavior of the friction oscillator with one body is already well known. However only few studies exist on the behavior of a friction oscillator with multiple bodies. In this study especially the dynamical behavior depending on the number of bodies, the friction characteristic and the velocity of the belt has been investigated. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conceptual Difficulties in Plasticity including the Gradient of one Scalar Plastic Field Variable
Authors: Wulfinghoff Stephan , Bayerschen Eric , Böhlke Thomas
Published: December 2014

This article discusses a conceptual problem of gradient plasticity theories including a scalar plastic field variable, the Laplacian of which enters the yield criterion. Since the plastic field variable is assumed a scalar, it contains no information on the direction of the plastic flow. The work at hand demonstrates that even arbitrarily small perturbations can determine the direction of the plastic deformation in many formulations, which is considered an unphysical behavior. In this sense, the solution is not stable with respect to the boundary conditions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual‐mixed finite element analysis of crystalline sub‐micron gold
Authors: Konchakova Natalia , Husser Edgar , Bargmann Swantje
Published: December 2014

An extended crystal plasticity model is applied to crystalline sub‐micron gold in order to study the mechanical response. Numerical results for different crystal sizes are presented and discussed. The governing equations are discretized and, subsequently, solved via a dual‐mixed finite element formulation [1, 2]. The evolution equation of the dislocation density is taken as a global field relation additionally to the balance of linear momentum, whereas the flow rule is solved locally at the Gauß point level [3,4]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A general finite plasticity model with a smooth elastic‐plastic transition and isotropic hardening. A finite element formulation and numerical verification
Authors: Jabareen Mahmood
Published: December 2014

A number of approaches for finite deformation elastoplasticity with different classes of kinematic decomposition have been published in the literature (e.g. additive split of the Lagrange strain, multiplicative split of the deformation gradient, additive split of the rate of deformation, etc.). In the present work, a general theoretical framework for modeling a smooth elastic inelastic transition for large deformations of rate independent elastic‐plastic and rate dependent elastic‐viscoplastic materials has been proposed. It is well known that in classical rate independent elastic‐plastic models the transition from the elastic regime to the plastic regime is rather sharp, while in the present model this transition is smooth and both rate independent and rate dependent models are characterized by overstress. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Macroscopic modeling of material interfaces based on atomistic descriptions
Authors: Sievers Christian , Clausmeyer Till , Mosler Jörn
Published: December 2014

The effective macroscopic properties of a broad variety of different materials are defined by the properties of the involved material interfaces. Grain boundaries in polycrystals represent a well‐known example. However, in contrast to classical bulk materials, the mechanical properties of material interfaces can oftentimes not be identified in a straightforward manner. In this paper, a multiscale framework is presented which allows to compute macroscopic properties of material interfaces based on molecular dynamics. The key idea of the elaborated multiscale framework is the coupling of an RVE associated with the atomistic scale to an RVE based on a continuum mechanics description by means of the principle of energy equivalence. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct evaluation of limit states of heterogeneous materials under cyclic thermo‐mechanical loadings
Authors: Chen Min , Hachemi Abdelkader , Markert Bernd
Published: December 2014

Classical shakedown theorems and their extensions to various material models rest on the temperature‐independent coefficients. In this paper, the lower‐bound of direct methods is extended to the application on the heterogeneous materials with temperature dependent yield strength and elastic modulus. Moreover, a numerical platform is developed, which makes the practical application more convenient and efficient. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Failure in anisotropic nonwoven materials at finite deformation
Authors: Raina Arun , Linder Christian
Published: December 2014

The current work proposes a finite deformation strong discontinuity approach based modeling of failure in anisotropic materials with reorientation based micromechanical network model for the bulk response. These materials consist of randomly cross‐linked one dimensional filaments at their microstructure which undergo non‐affine deformation as well as reorientation upon loading before undergoing complete failure. The computationally efficient strong discontinuity approach allows to capture the failure kinematics by introducing a local problem where a strong discontinuity exists, thereby leading to an enhanced deformation gradient. A precise evaluation of the bulk response is done by homogenizing the physical microscopic response of constituent filaments where reorientation is introduced with an initial straightening effect of fiber undulations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient Simulation of Short Fibre Reinforced Composites
Authors: Meyer Arnd , Springer Rolf
Published: December 2014

Lightweight structures become more and more important and one great class within these structures are parts produced by injection moulding. To improve the mechanical properties of these parts short fibers are injected within the molten plastics. Now a way to describe these properties without knowing the fibre orientation exactly is needed. We show an intuitive way, how mechanical properties of short fibre reinforced composites for linear thermoelasticity can be described and show the relation to other approaches. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the transformation equations for the shock and polynomial Equations of State in hydrocodes
Authors: Esteban Beatriz , Gebbeken Norbert
Published: December 2014

This paper compares two sets of equations that can be employed to transform the parameters of the shock Equation of State into those of the polynomial Equation of State used in hydrocodes. The first set is taken from literature, whilst the second set is derived by the authors, which can be seen as a correction to the first set of equations. Furthermore, the consequences on the numerical simulations of using the corrected set of equations is discussed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical calculation of the tangent stiffness matrix in materials modeling
Authors: Meier Felix , Schwarz Cornelia , Werner Ewald
Published: December 2014

The Finite Element Method in the field of materials modeling is closely connected to the tangent stiffness matrix of the constitutive law. This so called Jacobian matrix is required at each time increment and describes the local material behavior. It assigns a stress increment to a strain increment and is of fundamental importance for the numerical determination of the equilibrium state. For increasingly sophisticated material models the tangent stiffness matrix can be derived analytically only with great effort, if at all. Numerical methods are therefore widely used for its calculation. We present our method to calculate the tangent stiffness matrix for the logarithmic strain measure. The approach is compared with other commonly used procedures. A significant increase in accuracy can be achieved with the proposed method. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter identification for rubber materials with artificial higher dimensional data
Authors: Mahnken Rolf , Nörenberg Nicole
Published: December 2014

In general, laboratory test render only a limited number of experimental data. Consequently, the prediction of material behaviour becomes a difficult task and, moreover, a statistical analysis with a statistically based approach is almost impossible. As a remedy to increase the number of data, artificial data are generated by stochastic simulation. As a consequence an arbitrary number of data is available and the process of parameter identification can be analysed statistically. Here, the special challenge is the consideration of spatial and inhomogeneous problems. In this work artificial data are generated for a elastomer strip with hole under tension. The inhomogeneous stress/strain fields are optically measured with an Aramis/GOM system and have to be fitted to a stochastic model in order to generate artificial data. B‐Splines are applied to fit the geometry of the test specimen and the measured data in space as well as in time. Parameter identifications applied and the resulting material parameters are statistically analysed. In the example, a statistical analysis of an Ogden model is performed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐affine strain measures for continuum models of network materials
Authors: Ehret Alexander E. , Ogden Ray W. , Mazza Edoardo
Published: December 2014

Based on stretch averaging, two non‐affine strain measures for materials with random network microstructure are suggested. The first concept provides a scaling between affine and non‐affine behaviour that is predefined by the network functionality. The second approach applies to fibres that experience strong reorientation upon macroscopic deformation of the network. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled phase‐field model for ductile fracture in crystal plasticity
Authors: Hernandez Padilla Carlos Alberto , Markert Bernd
Published: December 2014

The objective of this work is to present a simplified, nonetheless representative first stage of a phenomenological model to predict the crack evolution of ductile fracture in single crystals. The proposed numerical approach is carried out by merging a conventional well‐ stablished elasto‐plastic crystal plasticity model and a well‐known phase‐field model (PFM) modified to predict ductile fracture. A two‐dymensional initial boundary‐value problem of ductile fracture is introduced considering a single crystal Nickel‐base superalloy material. the model is implemented into the finite element context subjected to a one‐dimensional tension test (displacement‐controlled). (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constitutive relation for the mass transfer during a gas‐liquid phase transition in porous media
Authors: Häberle Kai , Ehlers Wolfgang
Published: December 2014

The transition between two different phases of a substance is an everyday process, which is encountered amongst others in the geomechanical field, for example, in CO2 storage. The transition from the liquid to the gaseous phase and vice versa crosses the so‐called two‐phase region, where both phases coexist for specific temperature and pressure conditions. In this context, two mass‐balance equations are defined for both fluid phases, respectively. These two equations are coupled by the mass‐production term, which describes the mass transfer between the two phases during phase transition. A great variety of models exist to describe phase transition processes in zero dimensional systems, e. g., batch reactors. However, only a few articles can be found, where phase changes inside a porous medium are discussed. An approach to the latter case can be based on the well‐founded, continuum‐mechanical Theory of Porous Media (TPM), which allows to describe multi‐phasic flow inside a deformable porous medium. By evaluating the entropy inequality, a constitutive relation for the mass production term can be derived. This term compares to the two‐film theory, the standard model for the description of mass transfer in a two‐phase system. Adapting this relation to porous media leads to a mass transfer coefficient, which represents the kinetic behaviour of the molecules of the substance under consideration and the influence of the solid porous material on the phase transition process. For lack of experimental data, the mass transfer coefficient will be composed of the transfer coefficient from classical thermodynamics and geometrical information of the porous‐media structure. The thermodynamical behaviour of the fluid is described by, e. g., the Redlich‐Kwong‐Soave equation of state. Simulations conducted with either changing temperature or pressure boundary conditions are compared with simulations, where only one mass balance is used for both fluid phases and the mass transition is only visible by the jump in density. This allows for the verification of the derived constitutive relation. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Study on Mixed Finite Element Formulations Applied to Diffusion Problems
Authors: Kaessmair Stefan , Javili Ali , Steinmann Paul
Published: December 2014

The objective of this contribution is to study various mixed finite element schemes applied to classical and non‐classical diffusion problems. The Fickean diffusion is considered using a three‐field formulation where the concentration gradient and the diffusive flux are additionally chosen as independent variables. Furthermore, the non‐classical diffusion model given by the Cahn–Hilliard equation is discussed where mixed finite elements are used to cast the fourth‐order PDE into two second‐order PDEs. A penalized version of a mixed formulation for the underlying second gradient model is given by specific micromorphic models. Another approach is a classical second order splitting method. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dependence of the aeroelastic stability of a slender U‐beam on the realized flow pattern
Authors: Strecha Johannes , Steinrück Herbert
Published: December 2014

We investigate the aeroelastic behaviour of a slender U‐beam in cross‐flow. Two distinct, time periodic flow patterns are observed in simulations of the flow around this beam. Its aeroelastic properties depend on the realized flow pattern, especially so for low reduced velocities: One flow pattern leads to pronounced torsional vortex‐induced vibrations. No such vibrations could be observed under the other flow pattern. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Determination of the effective elasticity tensor of a folded sandwich core
Authors: Massow Holger , Becker Wilfried
Published: December 2014

This document describes the homogenization of a folded sandwich core. By using a numerical homogenization concept the components of the elasticity tensor of the foldcore continuum are determined. The foldcore exhibits an effective orthotropic behaviour with the particularity that it can be auxetic. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The heterogeneous multiscale method as a framework for coupling the finite element method and molecular dynamics
Authors: Ulz Manfred H.
Published: December 2014

Hierarchical two‐scale methods are computationally very powerful as there is no direct coupling between the macro‐ and microscale. Such schemes develop first a microscale model under macroscopic constraints, then the macroscopic constitutive laws are found by averaging over the microscale. The heterogeneous multiscale method (HMM) is a general top‐down approach for the design of multiscale algorithms. While this method is mainly used for concurrent coupling schemes in the literature, the proposed methodology also applies to a hierarchical coupling. This contribution discusses a hierarchical two‐scale setting based on the heterogeneous multi‐scale method for quasi‐static problems: the macroscale is treated by continuum mechanics and the finite element method and the microscale is treated by statistical mechanics and molecular dynamics. Our investigation focuses on an optimised coupling of solvers on the macro‐ and microscale which yields a significant decrease in computational time with no associated loss in accuracy. In particular, the number of time steps used for the molecular dynamics simulation is adjusted at each iteration of the macroscopic solver. A numerical example demonstrates the performance of the model. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiscale modeling of continuous fiber and fabric reinforced rubber components
Authors: Achenbach Volker , Baaser Herbert
Published: December 2014

Fabric or continuous fiber reinforced rubber components (e.g. tires, air springs, industrial hoses, conveyor belts or membranes) are underlying high deformations in application and show a complex, nonlinear material behavior. A particular challenge depicts the simulation of these composites. In this contribution we show the identification of the stress and strain distributions by using an uncoupled multiscale modeling method, see [1]. Within this method, two representation levels are described: One, the meso level, where all constituents of the composite are shown in a discrete manner by a representative volume element (RVE) and secondly, the macro level, where the structural behavior of the component is defined by a smeared anisotropic hyperelastic constitutive law. Uncoupled means that the RVE does not drive the macroscopic material behavior directly as in a coupled approach, where a RVE boundary value problem has to be solved at every integration point of the macro level. Thus an uncoupled approach leads to a tremendous reduction in numerical effort because the boundary value problem of a RVE just has to be solved at a point of interest, see [1]. However, the uncoupled scale transition has to fulfill the HILL–MANDEL condition of energetic equivalence of both scales. We show the calibration of material parameters for a given constitutive model for fiber reinforced rubber by fitting experimental data on the macro level. Additionally, we demonstrate the determination of effective properties of the yarns. Finally, we compare the energies of both scales in terms of compliance with the HILL–MANDEL condition by using the example of a biaxial loaded sample and discuss the consequences for the mesoscopic level. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermo‐mechanical homogenisation – application to HVOF thermal‐sprayed WC‐Co coatings
Authors: Berthelsen Rolf , Denzer Ralf , Menzel Andreas
Published: December 2014

Hard material coatings are widely employed as wear protection for highly engrossed surfaces. For example, coatings consisting of tungsten carbide (WC) and cobalt (Co) are used for sheet metal forming tools. A relatively cost‐efficient coating technique is the high velocity oxygen fuel (HVOF) thermal spraying process which, as a trade‐off, induces a large amount of energy into the heterogeneous coating and the substrate. Hence, this leads to a complex transient, thermomechanically coupled problem. In order to predict the residual stresses during the quenching procedure, a two scale finite element framework is established wherein the scale bridging is performed by application of two different homogenisation approaches. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A spotlike edge state in plane Poiseuille flow
Authors: Zammert Stefan , Eckhardt Bruno
Published: December 2014

We study the laminar turbulent boundary in plane Poiseuille flow at Re = 1400 and 2180 using the technique of edge tracking. For large computational domains the attracting state in the laminar‐turbulent boundary is localized in spanwise and streamwise direction and chaotic. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and Simulation of Degassing Process
Authors: Alimi Aria , Lübke Martin , Wünsch Olaf
Published: December 2014

This work deals with the modelling and simulation of a degassing process mainly used for extruders in polymer industry. The numerical simulations are done with finite‐volume method using OpenFOAM for a 2D single screw extruder. The material parameters have been all chosen for a PDMS‐Pentane polymer mixture so that the results could be compared with the available experiments already performed for this mixture [1]. In addition to experiments, the numerical results will be compared with an analytical solution derived from Danckwerts' model [2][3]. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bio‐inspired propulsion: Downstream travelling wave motion of a surface with finite & infinite extension
Authors: Müllner Markus
Published: December 2014

The thrust force on a surface that performs a fish‐like travelling wave motion downstream to an oncoming flow is discussed. Unsteady potential flow, with vortex shedding from the trailing edge, is known to explain the generation of thrust. Contrarily, fish swimming has been related to the flow over an infinitely extended surface. To interlink both problems, the potential flow over the surface of finite length is considered in the limit of high wave numbers. It turns out that the leading order, space‐periodic pressure does not contribute to thrust. Thus, the perturbation pressure is essential for propulsion. Besides, laminar flow is considered in the space‐periodic setting. The present results reveal – in contrast to literature – that the surface force is always drag. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of reattachment region behind backward‐facing step in a narrow channel
Authors: Uruba Václav
Published: December 2014

Dynamics of the flow reattachment behind the backward‐facing step in a narrow channel is studied experimentally using the PIV technique. Reattachment region is detected by statistical characteristics of the flow velocity close to the channel bottom. Two methods of reattachment definition are applied. The reattachment region structure and extent is shown. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of round jets with nozzle‐dependent inflow conditions using the k−ε turbulence model
Authors: Reinhardt Yvonne , Kleiser Leonhard
Published: December 2014

In view of the “round jet initial condition anomaly”, discussed in literature, we investigate the effect of inflow conditions resulting from the use of different nozzle geometries to form the jet. RANS simulations in the framework of OpenFOAM using the k − ε turbulence model are performed. As the standard model coefficient Cε1 = 1.44 is known to overpredict spreading rates for round jets, a value of Cε1 = 1.6 was recommended for this case already in the 1970's. While this works well for jets issuing from long pipes, it does not give satisfactory results for other nozzle geometries. To overcome this deficiency while keeping the k − ε model, we suggest modified coefficients Cε1 based on profiles of mean flow and turbulence at the nozzle exit. We determine optimal values of Cε1 for three different nozzle geometries, and test them at various Reynolds numbers. Good agreement with experimental data is obtained. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the benefits of ODT‐based stochastic turbulence modeling
Authors: Schmidt Heiko , Glawe Christoph , Jozefik Zoltan , Meiselbach Falko T. , Kerstein Alan R.
Published: December 2014

We summarize the group's progress in applying, analyzing, and improving ODT and ODT‐based stochastic turbulence models like ODTLES. Compared to DNS these models span a wider range of scales while compared to RANS/LES (i) the molecular effects are retained and (ii) no assumption of scale separation is made. In this regard ODTLES has more properties of DNS than of standard LES. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical study of a particle separation method based on the Segré‐Silberberg effect
Authors: Fischer Maximilian , Ehrhard Peter
Published: December 2014

Particles that are placed in a laminar pipe flow rotate and migrate transversally to a radial equilibrium position. This so called Segré‐Silberberg effect is used in a new method for size separation of particles. The particles to be separated are placed in a pipe flow and subsequently enter an expansion chamber, where the flow is split and the particles are divided into two fractions. This paper reports the results of two‐dimensional Euler‐Lagrange simulations of the motion of neutrally‐buoyant particles inside the expansion chamber. The simulation results agree well with experimental data on the separation and show that the Saffman force has a significant impact onto the particle trajectories. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solutions of an extended Korteweg‐de Vries equation describing solitary waves in turbulent open‐channel flow
Authors: Jurisits Richard
Published: December 2014

Solitary waves in two‐dimensional, turbulent open‐channel flow are considered. In an asymptotic analysis given in [1], assuming a bottom roughness that is varying along the channel bed, an extended Korteweg‐de Vries (KdV) equation was derived to describe the surface elevation of the wave. We adopted this equation and solved it numerically as a coupled boundary‐value eigenvalue problem, obtaining results for stationary and transient wave solutions as well as for the eigenvalue, which corresponds to distinct values of the bottom friction coefficient. While the numerical solutions as compared to the asymptotic solutions in [1] agree well in the stationary case, there were major differences found in the transient solutions. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigations of Passive Flow Control Devices for Vertical Axis Wind Turbines
Authors: Frunzulică Florin , Dumitrache Alexandru , Dumitrescu Horia
Published: December 2014

The purpose of these investigations is to study the possibilities to improve performances of a typical vertical axis wind turbines (VAWT), of Darrieus‐type, using passive devices (mounted “on” or “inside” the blades of VAWT) to control dynamic flow separation (dynamic stall phenomenon). The passive devices considered for investigations are the Gurney flap, the slot or thin channel, and the turbulence promoters. Studies are performed numerically using computational fluid dynamics and where it is possible the results are compared with existent experimental or numerical data. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Risk assessment for crosswind stability of vehicles on exposed sites
Authors: Proppe Carsten , Zhang Xiaoyu
Published: December 2014

The main purpose of this paper is to provide a reliable evaluation for the crosswind stability of different road vehicles in a realistic physical scenario. Unlike existing approaches, we analyze the wind‐vehicle system by probabilistic methods. The aerodynamic coefficients together with the gust parameters are considered as random variables. In addition, on‐site measured wind data are used to calibrate the gust model. As the excitation of the vehicle is a stochastic process, risk analyses have to be carried out and failure probabilities are computed. Based on the failure probabilities, guidelines for speed limitations or traffic restrictions can be developed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of Approximation Models for Solving Kinetic Equations
Authors: Ahmedov Bahodir , Herty Michael , Frank Martin
Published: December 2014

We consider the problem of cancer treatment using radiation therapy. A deterministic Boltzmann equation is considered as the particle transport model. The PN system of moment equations is derived using angular discretization of the transport equation. This PN system is solved using StaRMAP [3]. An optimization problem to get the desired particle distribution is formulated and solved using adjoint equations. The algorithm is validated with several simulations. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of the Velocity Field of 2D and 3D Tunnel Models with Frequency Domain Full Waveform Inversion
Authors: Musayev Khayal , Hackl Klaus , Baitsch Matthias
Published: December 2014

Full Waveform Inversion (FWI see [1]) has capability to identify the velocity field of a domain with a good precision. Its power comes from the fact that this approach does not only try to fit travel times of waves, but it tries to fit the whole seismogram. This work is about the application of acoustic full waveform inversion to 2D and 3D tunnel models. The necessary boundary conditions are applied to the models and the acoustic equation is solved by higher‐order Finite Elements Method. The Conjugate Gradient (CG) method is utilized to minimize the misfit function. The results were verified with synthetic models. The synthetic tunnel models contain few bodies with different shapes and locations. Starting from a homogeneous velocity field, the synthetic model is sought over iterations. To avoid the ill‐posedness, the locations and numbers of the source and receiver points have to be successfully chosen. Apart from this, the frequency set has also to be carefully constructed. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Design space exploration based on variational sensitivity analysis
Authors: Gerzen Nikolai , Barthold Franz‐Joseph
Published: December 2014

This contribution deals with variational sensitivity analysis of a non‐linear solid shell in context of shape optimisation. A technique to explore the structural design is outlined. It is based on the analytical derivation and efficient computation of the Fréchet derivatives of the state functions with respect to the full space of all possible design parameters. This overhead of sensitivity information is examined by a principal component analysis (PCA) in order to detect design changes with major and minor influence on the structural response, the objectives and constraints. This knowledge enables the engineers to understand and improve structural optimisation models and to detect possible numerical defects in the early stage. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Comparing Optimization Algorithms for Shape Optimization of Extrusion Dies
Authors: Siegbert Roland , Kitschke Johannes , Djelassi Hatim , Behr Marek , Elgeti Stefanie
Published: December 2014

The classical approach to extrusion die design relies heavily on the experience of the die designer; Especially the designer's ability to create an initial die design from a product design, the designer's constructional knowledge and performance during the running‐in trials. Furthermore, the relative unpredictability of the running‐in trials combined with the additional resource usage introduce uncertainties and delays in the time‐to‐market of a given product. To lower these delays and resource usage, extrusion die design can benefit greatly from numerical shape optimization. In this application, however, plastics melts pose a difficult obstacle, due to their rather unintuitive and nonlinear behavior. These properties complicate the numerical optimization process, which mimics running‐in trials and relies on a minimal number of optimization iterations. As part of the Cluster of Excellence Integrative Production Technologies for High‐Wage Countries at the RWTH Aachen University, an effort is made to shorten the manual running‐in process by the means of numerical shape optimization. Using an in‐house numerical shape optimization framework, a set of optimization algorithms, consisting of global, derivative‐free and gradient‐based optimizers, are evaluated with respect to the best die quality and a minimal number of optimization iterations. This evaluation is an important step on the way to include more computationally intensive material models into the optimization framework and identify the best possible optimization strategy for the numerical design of extrusion dies. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarks on different strategies for sensitivity analysis of multiscale problems in structural optimisation
Authors: Kijanski Wojciech , Barthold Franz‐Joseph
Published: December 2014

The adjustment of properties of materials to special requirements plays a more and more important role in engineering applications. Thus, the question about design and optimisation of materials arises. In this contribution some basic and necessary aspects for the treatment of structural optimisation problems in terms of multiscale modelling are given. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
How long does it take to consensus in the Hegselmann‐Krause model?
Authors: Kurz Sascha
Published: December 2014

Hegselmann and Krause introduced a discrete‐time model of opinion dynamics with agents having limit confidence. It is well known that the dynamics reaches a stable state in a polynomial number of time steps. However, the gap between the known lower and upper bounds for the worst case is still immense. In this paper exact values for the maximum time, needed to reach consensus or to discover that consensus is impossible, are determined using an integer linear programming approach. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)