bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical behavior of a pH‐sensitive hydrogel ring used in a micro‐optical device
Authors: Zalachas Nicolas , Cai Shengqiang , Suo Zhigang , Lapusta Yuri
Published: December 2012

A hydrogel is a polymer network that can absorb a large quantity of solvent and swell due to a physical or chemical stimulus. Hydrogels are more and more used as smart materials in recent micro‐applications. This fact requires the development of adequate models and simulation tools for their large deformation behavior. These models must also predict the onset of instabilities, such as folding or creasing. In this work, we study an interesting application of adaptive optical microsystem using a previously developed theory of inhomogeneous large deformation of a pH‐sensitive hydrogel. The devices function is based on the swelling of a ring made of a pH‐sensitive hydrogel. The latter controls the focal length of the liquid microlens. Our aim is to analyze major design parameters that affect the hydrogel ring behavior and the function of the micro‐optical device. The problem is solved numerically with the finite element commercial software ABAQUS. Various modes of large deformation and the influence of the rings aspect ratio on the behavior of the micro‐device are investigated. Results show that, for relatively short rings, a stable swelling takes place. Rings with a relatively big aspect ratio can have an unstable swelling with the propagation of a creasing instability. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A model of the heat conduction for functionally graded laminate with uniformly distributed micro inclusions
Authors: Wągrowska Monika , Woźniak Czesław , Szlachetka Olga
Published: December 2012

The aim of the contribution is to formulate an asymptotic model of heat conduction for functionally graded two component laminate reinforced by periodically spaced micro inclusions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization of random elastic networks with non‐affine kinematics
Authors: Tkachuk Mykola , Linder Christian
Published: December 2012

This contribution concerns the mechanics of materials with random network microstructures. It develops a general homogenization approach that allows to link the microscopic deformation of fibers in the disordered network with the macroscopic response of the continuous solid. This link is established by a novel micro‐macro relation based on the kinematics of maximal advance paths that constrains the unknown microscopic stretch of fibers with respect to the macroscopic strain. This relation accounts for the topology of the network, in particular, its connectivity and takes for the tetrafunctional networks a clearly interpretable tensorial form. In line with the principle of the minimum averaged free energy the elastic response of the network is obtained by the relaxation of the variable fiber stretch subjected to the kinematic constraint. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local probabilistic homogenization schemes for assessment of material uncertainties in solid foams
Authors: Hohe Jörg , Beckmann Carla
Published: December 2012

The present study is concerned with a numerical scheme for prediction of the effective properties of solid foams considering their uncertainty. The approach is based on an analysis of a large‐scale, statistically representative volume element which is subdivided into small‐scale testing volume elements. Application of a standard homogenization scheme to the testing volume elements together with a stochastic evaluation yields a complete probabilistic characterization of the material which may be used for a random field definition of the material behaviour in a macroscopic effective field analysis of foam structures. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A stochastic homogenization scheme for damaged composites
Authors: Hürkamp André , Nackenhorst Udo
Published: December 2012

A stochastic homogenization scheme for the computation of effective elastic properties for damaged micro‐heterogeneous materials is presented. The statistics is captured by uncertain material properties as well as stochastic interpolation between the upper and lower Hashin‐Shtrikman bounds. The resulting multidimensional stochastic problem is solved via sophisticated Monte Carlo methods and applied to Ultra‐High‐Performance‐Concrete. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Near critical laminar flow past an expansion ramp
Authors: Kluwick Alfred , Braun Stefan , Szeywerth Rene
Published: December 2012

Steady two‐dimensional laminar flows past an expansion ramp are known to exist up to a critical ramp angle in the limit c as the Reynolds number tends to infinity. The theory of viscous‐inviscid interaction combined with a local bifurcation analysis is used to study the evolution of three‐dimensional unsteady perturbations if $|\alpha - \alpha_c| \ll 1$ for both sub‐ and supercritical conditions. Special emphasis is placed on the effects of controlling devices and the phenomenon of bubble bursting. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic description of incipient separation bubble bursting
Authors: Braun Stefan , Scheichl Stefan , Kluwick Alfred
Published: December 2012

The appearance of short laminar separation bubbles in high Reynolds number (Re) wall bounded flows due to appropriate adverse pressure gradient conditions is usually associated with minor effects on global flow properties (e.g. lift force). However, localized reverse flow regions are known to react very sensitively to perturbations and in further consequence may trigger the laminar‐turbulent transition process or even cause global separation. The present investigation of marginally separated boundary layer flows is based on an asymptotic approach Re → ∞. Special emphasis is placed on solutions of the corresponding model equations which blow up within finite time indicating the ejection of a vortical structure and the emergence of shorter spatio‐temporal scales reminiscent of the early transition scenario (‘ bubble bursting’ ). Within the framework of marginal separation theory, an alternative adjoint operator method is used to formulate evolution equations governing the viscous‐inviscid interaction process in leading and higher order correction required for the study of later stages of the flow development. Their blow up structure specifies the initial condition of and the match to the subsequent triple deck stage. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulating of a pressing process of a viscoelastic polymer melt
Authors: Al‐Baldawi Ammar , Wünsch Olaf
Published: December 2012

A well known and often used method to obtain anisotropic polymer films is the so‐called pressing process. Here, films are squeezed under high temperatures, pressure and deformation rates. To simulate such a process, the polymeric matrix is treated as a non‐Newtonian, viscoelastic melt. The modeling of such melts is done with the anisotropic molecule movement tensor generalization of the Maxwell Model for high deformation rates. The viscoelastic flow simulations are done with DEVSS stabilization techniques and an ALE based dynamic mesh Method. In this work we present simulations in order to show the difference between classical approaches using a generalized Newtonian viscosity to model the melt and the used viscoelastic models. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Separation of magnetic particles in channel flows by BEM
Authors: Ravnik Jure , Hriberšek Matjaž , Vogel Franziska , Steinmann Paul
Published: December 2012

In‐line separation of suspensions can become difficult in case of particles with comparable values of densities. For flows in micro devices in such cases gravitational settling is inefficient, and other separation techniques must be applied. In case of magneto active particles, the action of Kelvin magnetic force in a non‐uniform magnetic field could be used in order to achieve a higher degree of particles separation. The contribution therefore deals with Euler‐Lagrangian formulation of dilute two‐phase flows. The Boundary element based computational algorithm solves the incompressible Navier‐Stokes equations written in velocity‐vorticity formulation. The non‐uniform magnetic field is defined analytically for the case of a set of long thin wires. The particle trajectories are computed by applying the 4th order Runge‐Kutta method. The computed test case consists of a narrow channel with laminar flow of suspension under Re = 1 − 10. Particle trajectories under the influence of a non‐uniform magnetic field are computed for the case of magnetite and aluminium particles suspended in water. The efficiency of separation on basis of particle trajectories for different values of Re number and magnetic field strength is performed, clearly indicating superior separation of magneto active particles. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Gas exchange of almost leak‐tight display cases
Authors: Strecha Johannes , Steinrück Herbert
Published: December 2012

A gas exchange model based on diffusion and stack pressure driven convection for display cases will be discussed and evaluated experimentally. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flow over back‐facing step in a narrow channel
Authors: Uruba Václav , Jonáš Pavel
Published: December 2012

Flow structure behind the backward facing step in a narrow channel was studied in details. The step height was 25% of the channel width. The structure of the region just behind the step forming the back‐flow region is studied in details using stereo PIV technique. Time‐mean 3D structures behind the step are evaluated and shown in the paper. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Free energy budgets in viscoelastic natural convection
Authors: De Angelis Elisabetta
Published: December 2012

It has been known for a long time that the introduction of a small amount of polymer additives could significantly reduce friction drag in wall‐bounded turbulent flows [1]. However, in the last years also the effect of polymers on turbulent thermal convection has drawn attention with controversial results. In this context, aim of this contribution is the presentation of the mathematical model for the study of natural convection between parallel walls in a dilute polymer solution. The discussion here will be also extended to the description of the kinetic and free energy balances in this flow. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐Phase Flow in Single‐Screw Extruders
Authors: Lübke Martin , Wünsch Olaf
Published: December 2012

This work concerns numerical simulation of free‐surface flows of highly viscous liquids in single‐screw extruders.The numerical treatment of a partially filled extruder is a challenging task due to the complex geometry and the large differences in density and viscosity between the two phases, e.g. polymer melt and air. Furthermore, the rotation of the screw leads to a continuous renewing of the free‐surface. For this purpose the Volume of Fluid (VOF) method is used. First a simplified two‐dimensional model of a single‐screw extruder is considered. Good agreement is obtained between the numerical results and experimental data. Finally, the three dimensional free‐surface flow in a partially filled single‐screw extruder with dynamic mesh motion is presented. In addition, the power characteristics of a conveying screw element with varying degree of filling is discussed. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical study of a liquid/liquid slug flow in a micro‐reactor
Authors: Dittmar Ina , Ehrhard Peter
Published: December 2012

The great advantages of micro–reactors are associated with an extremely high surface–to–volume ratio. Hence, micro–reactors permit promising operating conditions, such as almost perfect heat or mass transfer. The hydrodynamics of a liquid/liquid slug flow in a micro–channel is characterized by complex vortex structures in both the disperse and the continuous phase. The disperse phase, in our investigations, is not wetting the walls and, thus, a thin film of the continuous phase persists between the disperse phase and the wall. Due to this phenomenon, a relative movement between disperse and continuous phase is possible and, indeed, observed. Understanding of these complex phenomena allows for a control of the hydrodynamics, and thus, to tailor the heat and mass transport in a desired manner. To study the physics of this complex liquid/liquid system, a modified level–set method in conjunction with an immersed–boundary formulation is engaged. The mesh resolution represents a challenge, as the spatial resolution has to resolve the thin film between the disperse phase and the wall adequately. All simulations are implemented within the software OpenFOAM. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical study of the primary breakup of a plane liquid sheet with co‐flowing air streams
Authors: Kannan Suresh kumar , Peters Bernhard
Published: December 2012

The objective of this study is to model the primary breakup of a plane liquid sheet emerging from an air‐blast nozzle. In the present work the interface compression scheme proposed by OpenCFD Ltd. [1] has been used to capture the interface between the liquid and gas. A One‐equation subgrid scale (sgs) turbulent energy transport model attributed to Yoshizawa [2] is used for modeling the effects of turbulence. The set up case selected for this study is based on the experiments carried out by Mitra [3]. The 2D simulations performed in this study predict the breakup length of the plane liquid sheet in good agreement with the experimental data. Future work will involve, performing 3D simulations of the plane liquid sheet generated by the air‐blast nozzle and performing comparisons of the resulting droplet characteristics with the experimental data. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ALE‐FEM For Two‐Phase Flows With Insoluble Surfactants
Authors: Hahn Andreas , Tobiska Lutz
Published: December 2012

We present a finite element method for the flow of two immiscible incompressible fluids in two and three dimensions. Thereby the presence of surface active agents (surfactants) on the interface is allowed, which alter the surface tension. The model consists of the incompressible Navier‐Stokes equations for velocity and pressure and a convection‐diffusion equation on the interface for the distribution of the surfactant. A moving grid technique is applied to track the interface, on that account a Arbitrary‐Lagrangian‐Eulerian (ALE) formulation of the Navier‐Stokes equation is used. The surface tension force is incorporated directly by making use of the Laplace‐Beltrami operator technique [1]. Furthermore, we use a finite element method for the convection‐diffusion equation on the moving hypersurface. In order to get a high accurate method the interface, velocity, pressure, and the surfactant concentration are approximated by isoparametric finite elements. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the coupling of compressible and incompressible regions
Authors: Boger Markus , Jaegle Felix , Klein Rupert , Munz Claus‐Dieter
Published: December 2012

This contribution deals with the coupling of compressible to incompressible flow regions in one space dimension. Iterative coupling procedures based on jump conditions across the interface have been derived. They couple the solution of a half Riemann problem on the compressible side to the analytical solution of the incompressible side. For the incompressible equations, the pressure is split into a thermodynamic background and a hydrodynamic part. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical computation of dispersion relations in wave guides
Authors: Gravenkamp Hauke , Song Chongmin , Prager Jens
Published: December 2012

In this paper a numerical approach, based on the Scaled Boundary Finite Element Method (SBFEM), is described to obtain dispersion relations for propagating modes in wave guides. While the formulation is developed for plate structures, it can easily be extended to wave guides with arbitrary cross‐section. The cross‐section is discretized in the Finite Element sense while all equations remain analytical in the direction of propagation. The wave numbers of all propagating modes are obtained as the solutions of a standard eigenvalue problem. The group velocities can be calculated accurately as the eigenvalue derivatives. The use of higher‐order elements drastically increases the efficiency and accuracy of the computation. This approach can be used for wave guides with arbitrary distribution of material parameters. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dispersion in Cylindrical Waveguides with Uncertain Parameters
Authors: Schaal Christoph , Krautter Miriam , Hanss Michael
Published: December 2012

In order to localize cracks in cylindrical structures using guided waves, precise knowledge of the wave speeds is crucial. Instead of basing calculations on crisp parameters, for this Structural Health Monitoring application, uncertainty in parameters is handled by representing parameters as fuzzy numbers and applying the Transformation Method. For calculating dispersion curves, the Waveguide Finite Element Method is used for each parameter set. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inter‐wire Coupling Model Development for Health Monitoring of Cable Structures
Authors: Higgins Natalie , Schaal Christoph
Published: December 2012

Structural Health Monitoring (SHM) allows the integrity of a system to be monitored in situ, detecting weaknesses as they form. Due to the waveguide nature of cylindrical structures, ultrasonic waves can be used to detect defects in cables over large distances. Considering that common power line cables consist of several individual wires, a straightforward energy‐based approach is chosen to simplify the model development. The purpose of this investigation is to extend the current coupling model to include n wires and to verify this model for a seven‐wire cable, experimentally. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of Mode Conversion at Defects in Rope Structures using Ultrasonic Waves
Authors: Bischoff Stefan , Gaul Lothar
Published: December 2012

Ultrasonic waves travel in rope structures over long distances as guided waves, allowing for effective health monitoring. In order to localize and characterize defects, an exact knowledge of the propagation, reflection, and transmission properties of the ultrasonic waves is required. These properties can be obtained using the Finite Element Method by modeling a segment of the periodic waveguide with a periodicity condition. The solution of the corresponding eigenvalue problem leads to all propagating modes of the waveguide as well as locally generated evanescent modes. The Boundary Element Method (BEM) is used in combination with the Finite Element Method for characterizing the wave propagation. The mode conversion at discontinuities, such as cracks or notches, can be subsequently described by reflection and transmission coefficients. The simulation results are the corresponding coefficients as a function of frequency and enable the selection of adequate modes for an effective defect detection. Additionally, it is demonstrated that along with the localization of cracks, conclusions about the crack geometry can be made with the help of reflection and transmission coefficients. The reliability and numerical accuracy of the simulation results are verfied by comparison with experimental findings. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microscale Investigations of Highfrequency Wave Propagation Through Highly Porous Media
Authors: Uribe David , Saenger Erik , Jänicke Ralf , Steeb Holger , Ruiz Oscar
Published: December 2012

Wave propagation in highly porous materials has a well established theoretical background. Still there are parameters which require complex laboratory experimentation in order to find numerical values. This paper presents an effective method to calculate the tortuosity of aluminum foam using numerical simulations. The work flow begins with the acquisition of the foam geometry by means of a micro‐CT scanner and further image segmentation and analysis. The elastodynamic wave propagation equation is solved using a velocity‐stress rotated staggered finite‐difference technique. The effective wave velocities are calculated and using the fluid and, aluminum effective properties, the tortuosity is determined. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rotation‐Symmetric Referencebodys For Energy Efficient Flow Around Bodies
Authors: Quarti Michael , Gottlieb Andreas , Bühler Karl , Kachel Gerhard
Published: December 2012

Topology optimization is used to optimize problems of flow around bodies and problems of guided flow. Within the context of research, optimization criteria are developed to increase the energy efficiency of these problems [1] [2] [3] [4] [5]. In order to evaluate the new criteria in respect to the increasing of energy efficiency, reference bodies for different Reynolds numbers in combination with given design space limitations are needed. Therefore, an optimal body at Reynolds number against 0 was analytically determined by Bourot [6]. At higher Reynolds numbers, in the range of laminar and turbulent flows, no analytical solution is known. Accordingly, reference bodies are calculated by CFD calculations at three technical relevant Reynolds numbers (1.000, 32.000, 100.000) in combination with parameter optimization. The cross section of the bodies is described by a parameterized model.

To get the optimal body, a parameter optimization based on a “brute force”; algorithm is used to optimize with regard to the friction loss and pressure loss in order to minimize the total loss (cd‐value). The result is an optimal parameter constellation, depending on the Reynolds number. Within the results, it is possible to develop the optimal geometries. The identified characteristics of the flow field around these bodies are used as base for new optimization criteria. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilization of Laminar Boundary‐Layer Flow using Dielectric Barrier Discharge Plasma Actuators
Authors: Duchmann Alexander , Vieira Débora , Grundmann Sven , Tropea Cameron
Published: December 2012

A numerical method is developed to study the stabilizing effect of dielectric barrier discharge plasma actuators on laminar boundary‐layer flow. A finite difference approach based on a Keller box discretization is chosen to solve the Falkner‐Skan transformed boundary‐layer equations. The fluid dynamic effect of the flow‐control device is implemented as a body‐force field, derived quantitatively from previous measurements using particle image velocimetry. The resulting laminar boundary‐layer flow is compared to experimental wind tunnel measurements and the effect on hydrodynamic stability is investigated in the framework of linear stability theory. A good agreement between experimentally acquired and numerically predicted transition locations based on an empirical function is obtained, rendering the numerical scheme valuable as a design tool for DBD based flow control applications. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the flow resistance of wide surface structures
Authors: Daschiel Gertraud , Baier Tobias , Saal Jürgen , Frohnapfel Bettina
Published: December 2012

The possibility of skin‐friction drag reduction in channel flows due to surface structures is investigated numerically. In this context, surface structures with a high width to height ratio compared to the typical dimensions of riblets are studied in the laminar as well as in the turbulent flow regime. In general, it is found that a reduction of the flow resistance is possible in both flow regimes. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Turbulent Flow with Embedded Vortical Structures Induced by Vortex Generators in a Cascade
Authors: Soucková Natálie , Uruba Václav
Published: December 2012

Presented work is the next step after several experimental examinations of vortex generator influence on a flow separation occurring on a model of the NACA 63A421 airfoil with deflected simple flap. In this stage of research the vortices produced by vortex generators (VGs) were studied using Particle Image Velocimetry technique (PIV) and numerical simulations. Vane type VGs with two spacings among VGs pairs in straight channel with turbulent flow were tested. The average velocity flow field, peak of vorticity and circulation decay downstream of VGs were evaluated. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On an asymptotic upper‐convected Maxwell model for a viscoelastic jet
Authors: Lorenz Maike , Marheineke Nicole , Wegener Raimund
Published: December 2012

In this work we present a strict systematic derivation of a one‐dimensional upper convected Maxwell model (UCM) for the dynamics of a curved viscoelastic jet using asymptotic analysis in the slenderness ratio of the jet. The model does not pose any restrictions on shape and motion of the center‐line or the velocity profile. Numerical results are shown for stationary gravitational fiber spinning. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Non‐linear Characteristics Evaluation of Vibratory Tool and Terrain Interaction for Embankment Works
Authors: Debeleac Carmen , Nastac Silviu
Published: December 2012

The complete and correct identification and evaluation of proper characteristics of terrain for embankment works is the frame idea of this analysis. The study began from the necessity of vibratory working tools utilization for different construction jobs. Mainly, the simple dynamic calculus is used for estimation of proper parameters values for this kind of works. It supposes a linear characteristic of the material in interaction with vibrating tool and it estimates the domain of working parameters. But instrumental tests reveal that the terrain has a non‐linear characteristic and the dynamic behaviour acquires deviation from theoretical estimations. An identification procedure followed by a correct and complete evaluation of the non‐linear parameters gives the necessary information for a practical case. Available mathematical models require a lot of initial values for characteristic parameters, but changing the case changes the values. A complex model which needs only initial tuning offers a proper solution to simulate, estimate, evaluate and analyze the interactions between the vibratory tools of construction equipments and the terrain. Non‐linear static and dynamic characteristics are the basic model defined properties. Elastic, dissipative and plastic rheological components were included into the main model. Partial concluding remarks have shown a good approximation between numerical results and experiments. The results of this study are very useful for vibratory equipment designing and correct exploitation, check of Regulations conformity for construction technologies, and oldies equipments maintenance. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Brownian dynamics of rigid body by fluctuating hydrodynamic equations
Authors: Pandey Anamika , Klar Axel , Tiwari Sudarshan
Published: December 2012

In this work, Brownian dynamics of rigid body in an incompressible fluid with fluctuating hydrodynamic equations is presented. To demonstrate the Brownian motion of rigid body, fluctuating hydrodynamic equations have been coupled with equations of motion of rigid body. Thermal fluctuation is included in the fluid equations via random stress terms unlike the random terms in the conventional Brownian dynamics type approach. Calculation of random stress terms in the fluid is easier in comparison to the random terms in the particle motion. Direct numerical simulation for the Brownian motion of rigid body with a meshfree framework is analysed. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Using the Elements of Manufacturing Systems Management in the Calculation of the Implementation of a Serial‐Modular Industrial Robot within a Flexible Work Cell Designed for Special Applications
Authors: Rizescu Alexandru Marius , Petrişor Silviu Mihai
Published: December 2012

In this paper, the authors propose a basic design of a flexible work cell with a parallel organization, destined for the spot welding of AAV carcasses. The cell is serviced by three industrial TTR robots that perform spot welding operations on the carcasses flowing on the conveyor belt to each of the robots performing this operation. This paper presents economic issues on the value of the robots comprised by the system, the calculus of the entire FWC value, the determination of the FWC static configuration, and evaluates the overall profitability of the cell using elements pertaining to the mathematical game theory and the graph theory, as well. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical optimisation of process parameters for combined quasi‐static and impulse forming
Authors: Rozgić Marco , Taebi Farhad , Stiemer Marcus
Published: December 2012

Mathematical optimisation of technological forming processes requires expensive simulations to evaluate objective function and constraint values as well as their derivative and Hessian informations. Therefore numerical linearisation methods like the finite difference method or the BFGS‐update are necessary. In this work the effects of these approximation techniques are studied. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter identification based on multiple inhomogeneous experiments of practical relevance
Authors: Schellenberg Dirk , Juhre Daniel , Ihlemann Jörn
Published: December 2012

Existing procedures to identify material parameters are based on experiments with simple specimens. Additionally, the load distribution is approximately homogeneous. But there are only few feasible experiments which produce homogeneous or almost homogeneous load distributions. Furthermore, deviations from homogeneity and their consequences cannot be avoided, but are often ignored. We present a solution algorithm which takes several different experimental results into account. Thereby, the experiments are performed on specimens which respond with inhomogeneous distributions of strains and stresses. The restriction to homogeneous loads is not necessary. Thus, it is possible to use different measured data of multiple load cases on one and the same test specimen. The component‐oriented design of the specimen permits to consider the specific properties of product groups, the load types and the effect of the manufacturing process on the final material properties already during the identification process. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interpolation‐based solution of a nonlinear eigenvalue problem in fluid‐structure interaction
Authors: Effenberger Cedric , Kressner Daniel , Steinbach Olaf , Unger Gerhard
Published: December 2012

A nonlinear eigenvalue problem arising from a coupled finite element/boundary element approach for fluid‐structure interaction is considered. We propose an approach based on polynomial interpolation and linearization for its numerical solution. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of Buckingham Π‐theorem to asymmetric plate rolling processes
Authors: Münker Tobias , Anders Denis , Weinberg Kerstin
Published: December 2012

Rolling under asymmetrical conditions such as temperature gradients within the material, difference of the circumferential velocity of the rolls and different friction coefficients cause the rolled slab to bend towards the direction of one of the rolls. In general this effect is undesired, since it hinders the further material transport and is a potential danger for the machine components in the proceeding processes. Unfortunately the essential mechanisms and the sensitivity of the influencing parameters in asymmetric rolling are still not comprehended sufficiently. Here a novel approach is presented in order to gain an enhanced insight into the front‐end bending phenomenon. To this end Buckingham Π‐theorem is applied to recover dimensionless coefficients describing the state of the roll gap and enable a reduction of the number of calculations in the required parametric studies. These parametric studies have been performed applying a finite element model considering elasto‐plastic material behaviour and the boundary conditions applied to the slab in the roll gap. The dimensionless quantity taking into account the slab's curvature is thoroughly investigated in terms of the other dimensionless system parameters. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of the Finite Pointset Method (FPM) to the kinetic BGK model
Authors: Kobert Maria , Kuhnert Joerg , Klar Axel
Published: December 2012

The BGK model of rarefied gas dynamics [1] is solved numerically by using the Finite Pointset Method (FPM) [2], which is a particle method developed at the ITWM Kaiserslautern. For the implementation a semilagrangian scheme [3] is used. Numerical results are shown on the example of a Shock tube problem for different Knudsen numbers. The solutions are compared to the solutions of exact Euler in the case of small Knudsen numbers and to DSMC solutions for higher Knudsen numbers. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Reduced Basis Method for Time‐Harmonic Maxwell's Equations
Authors: Benner Peter , Heß Martin
Published: December 2012

The Reduced Basis Method (RBM) generates low‐order models of parametrized PDEs to allow for efficient evaluation of the input‐output behaviour in many‐query and real‐time contexts. The RBM approach is decomposed into a time‐consuming offline‐phase, which generates a surrogate model and an online phase, which performs fast parameter evaluations. Rigorous and sharp a posteriori error estimators play a crucial role in the greedy process to generate the surrogate model and give bounds to the output quantities in the online phase.

We show the theoretical framework in which the Reduced Basis Method is applied to Maxwell's equations arising from semiconductor interconnect structures and present first numerical results for model reduction in frequency domain. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Algebraic graph theory and its applications for mesh generation
Authors: Schröppel Christian , Wackerfuß Jens
Published: December 2012

Mesh generation is an important step in many numerical methods. The authors present a novel approach to mesh generation, based on algebraic graph theory, that can be used to systematically construct configurations exhibiting multiple hierarchies and complex symmetry characteristics. The mesh is expressed as a hierarchically symmetric graph that preserves both the hierarchical structure as well as the symmetry characteristics of such configurations. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite volume element method for simulating secondary settling tanks
Authors: Bürger Raimund , Ruiz‐Baier Ricardo , Torres Héctor
Published: December 2012

This contribution summarizes a new finite volume element (FVE) method as a unified scheme for coupled sedimentation‐flow problems in secondary settling tanks in wastewater treatment. The model is two‐dimensional in an axisymmetric setting. A new numerical example is presented. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A finite element method for a noncoercive elliptic problem with Neumann boundary conditions
Authors: Kavaliou Klim , Tobiska Lutz
Published: December 2012

We consider a noncoercive convection‐diffusion problem with Neumann boundary conditions appearing in modeling of magnetic fluid seals. The associated operator has a non‐trivial one‐dimensional kernel spanned by a positive function. A discretization is proposed preserving these properties. Optimal error estimates in the H1‐norm are based on a discrete stability result. Numerical results confirm the theoretical predictions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase lag analysis of variational integrators using interpolation techniques
Authors: Kosmas O.T. , Leyendecker Sigrid
Published: December 2012

In the present work we derive higher order variational integrators and combine them with phase lag properties for the numerical integration of systems with oscillatory solutions. The discrete Lagrangian in any time interval is defined as a weighted sum of the evaluation of the continuous Lagrangian at intermediate time nodes. The expressions used for configurations and velocities use linear interpolation, cubic spline interpolation or interpolation via trigonometric functions. The new methods depend on a frequency, which needs to be chosen appropriately. Results show that the energy error of the integration method is decreased for good frequency estimates. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Derivation of an adjoint high‐Reynolds number model for thermally driven flows
Authors: Lincke Anne , Stück Arthur , Rung Thomas
Published: December 2012

This paper presents a high‐Reynolds number (high‐Re) approach to the adjoint Navier‐Stokes‐Fourier equations based upon modified high‐Re boundary conditions for buoyancy‐driven flows. For reasons of efficiency, the computational framework adheres to the continuous adjoint method using a frozen‐turbulence assumption. Opposed to the state of the art, the present model uses a high‐Re model for the primal equations and a high‐Re model for the adjoint equations. The adjoint high‐Re model can easily be implemented and be used for flow problems where wall functions are needed. The impact of this approach is an improved consistency of primal and adjoint equations which leads to stable and realistic shape optimisation results for industrial flows. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Approach to Shape Optimization with State Constraints
Authors: Leithäuser Christian , Feßler Robert , Pinnau René
Published: December 2012

We introduce a new approach to solve shape optimization problems with state constraints. The problem is reformulated on a fixed reference domain using conformal pull‐back. The shape dependence is then hidden in the conformal parameter. The problem is discretized using FEM and solved as an NLP. Finally the optimal shape can be reconstructed from the optimal conformal parameter. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multilevel optimization for PDAE‐constrained optimal control problems with pointwise constraints on control and state
Authors: Clever Debora , Lang Jens
Published: December 2012

We have developed a fully adaptive optimization environment suitable to solve complex optimal control problems restricted by partial differential algebraic equations (PDAEs) and pointwise constraints on the control [1, 2]. This contribution is devoted to the inclusion of pointwise constraints on the state within the optimization environment. To this end we first give a brief introduction into the architecture of the environment and the inclusion of pointwise constraints on the state by Moreau‐Yosida regularization. Then, we test the new tool by applying it to an optimal boundary control problem for the cooling of hot glass down to room temperature, modeled by radiative heat transfer and semi‐transparent boundary conditions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
POD and CVT Galerkin reduced‐order modeling of the flow around a cylinder
Authors: Ullmann Sebastian , Lang Jens
Published: December 2012

Reduced‐order models are applied to the laminar vortex‐shedding flow around a circular cylinder. The models rely on approximations of the solutions in the space spanned by a set of POD or CVT reduced basis vectors, which are computed from snapshots of a numerical solution. To enable the computation of drag and lift forces, the modeling of the velocity and pressure is realized via a one‐way coupling. A comparison of the results of the CVT and POD reduced‐order models is presented. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Zero crossings in the step response of linear time‐delay systems
Authors: Damm Tobias , Muhirwa Luc N.
Published: December 2012

Relations between zeros of the transfer function and properties of the step response are quite well‐known for linear time‐invariant systems. In this paper we provide new derivations of some of these results about zero crossings which immediately allow a generalization to systems with time‐delay. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Approach for Parameter Identification in Distributed Parameter Systems
Authors: Knüppel Torsten , Woittennek Frank
Published: December 2012

Identification of physical parameters in systems modelled by linear partial differential equations (p.d.e.) from lumped measurements is considered. The problem is solved by means of an alternative formulation of the boundary value problem as convolutional system. The approach allows for the identification even in the presence of non‐homogeneous initial conditions. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Orbital stabilization of a class of underactuated mechanical systems
Authors: Knoll Carsten , Röbenack Klaus
Published: December 2012

Typically, the aim of a controller is to stabilize an equilibrium or a reference trajectory. For underactuated mechanical systems this objective might not be achievable because of the occurance of limit cycles due to discontinuous effects like actuator backlash or Coulomb friction. Therefore, an alternative approach is to explicitly impose a stable periodic orbit on the system by a suited controller. This way at least amplitude, frequency and settling time can be influenced directly. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computationally efficient receding horizon trajectory tracking control for a tubular reactor example
Authors: Utz Tilman , Graichen Knut
Published: December 2012

Flatness‐based feedforward control and receding horizon trajectory tracking control can be combined within a two‐degrees‐of‐freedom (2dof) control scheme to obtain robust trajectory tracking for nonlinear systems. The key to a computationally efficient solution of the optimization problem underlying the receding horizon control is the linearization of the time‐variant tracking error dynamics such that the nonlinear optimal control problem may be replaced by a linear‐quadratic formulation. The approach is demonstrated for setpoint transitions of a nonlinear boundary‐controlled parabolic partial differential equation (PDE), which is semi‐discretized for the control design using finite differences on the spatial derivatives. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of transmission line parameters using algebraic methods
Authors: Gehring Nicole , Rudolph Joachim , Stauch Christian
Published: December 2012

An algebraic approach to parameter identification for transmission lines using boundary measurements is suggested. The class of systems under consideration can be modelled by means of linear partial differential equations (p.d.e.s). It includes examples from different technological domains such as the telegrapher's equations or models for fluid transmission lines. The main idea of the approach presented is to generate a set of equations involving only boundary measurements and parameters in such a way that they can easily be interpreted in the time domain. To this end, the system's p.d.e.s are written in terms of o.d.e.s (ordinary differential equations) using Mikusiński's operational calculus. The proposed identification method is illustrated considering a fluid transmission line model with laminar flow and frequency dependent viscous friction. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some remarks concerning differential flatness and tangent systems
Authors: Franke Matthias , Röbenack Klaus
Published: December 2012

The flatness properties of a nonlinear dynamical control system are completely characterized by its tangent approximation. The flat output of the nonlinear system can be obtained (at least from a theoretical point of view) by solving an integrability problem for the flat outputs of the tangent system. In the present contribution, this approach is used to easily obtain flatness conditions for two special classes of systems, namely systems with one input and systems with one input less than states. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximation of scattered data using the lifting scheme
Authors: Stahl Dominik , Damm Tobias
Published: December 2012

In this note we briefly explain a method to approximate scattered data. One major task here is to solve a least squares problem. Demanding that at least constant scattered data is approximated correctly, implies the use of Tikhonov regularizations satisfying a simple constraint. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the dynamic behaviour of fluid‐saturated soil within the framework of elasto‐plasticity
Authors: Schenke Maik , Markert Bernd , Ehlers Wolfgang
Published: December 2012

Phenomena related to porous media dynamics, such as wave propagation and liquefaction, are encountered in many engineering applications, especially, in geomechanics and earthquake engineering. Drawing our attention to fluid‐saturated granular materials with heterogeneous microstructures, the modelling is carried out within a continuum‐mechanical framework by exploiting the well‐established macroscopic Theory of Porous Media (TPM) together with thermodynamically consistent constitutive equations. In this regard, the solid skeleton of the soil is described as an elasto‐plastic material. The underlying equations are discretised and implemented into the coupled porous‐media finite‐element solver PANDAS and linked to the commercial finite‐element package Abaqus through a general interface. This coupling allows the definition of complex intial‐boundary‐value problems through Abaqus, thereby using the state‐of‐the‐art material models of PANDAS. In order to get a detailed understanding of the behaviour of the underlying soil model under dynamic loading conditions, a cyclic torsion test is numerically investigated. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flow Modeling in Rock Fracture for Long Time Simulation of Geothermal Reservoirs
Authors: Ostermeyer Georg‐Peter , Srisupattarawanit Tarin
Published: December 2012

The exploitation of geothermal power is an energy source with great potential for the future. But the exploration and development of deep geothermal energy is connected with high cost and risk, these require a reliable numerical prediction. The analysis of geothermal reservoir is usually interested in long time physical properties (e.g. 50–100 years). Typical CFD simulation tool could be used somehow, but the computational effort may be limited due to incompatibility of small scale heterogeneities. Here we developed flow modeling in rock fracture, which describe the different characteristic flow in different dimension. The fluid flow in tube is described by one dimensional flow (1D flow), while flow in rock fracture is modeled as two dimensional flow (2D flow) on fracture plane. The 1D flow in tube and 2D flows in fracture are coupled to represent three dimensional flows in reservoirs. The solution of coupling system (1D and 2D flow) is obtained by iterative procedure, while the flow inside 2D fracture is calculated by cellular automaton. This algorithm is relatively fast for calculating flow inside rock fracture, especially for long time behavior of 3D–geothermal reservoir. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)