bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermo‐mechanically coupled modelling of cellular MgO‐C refractories under thermal shock
Authors: Bleistein Thomas , Jung Anne , Diebels Stefan
Published: October 2016

Refractory materials such as magnesium oxide carbon (MgO‐C) composites are used in the steel‐making industry for furnaces, ladles or oxygen converters. A new class of composites are cellular MgO‐C materials, consisting of carbon foams filled with magnesium oxide and inclusions of gas filled pores. Cellular MgO‐C composites have the advantage of significantly improving the thermo‐mechanical properties [1]. This contribution focuses on the FEM implementation of a fully coupled thermo‐mechanical continuum model. It is based on the theory of porous media (TPM) restricted by a kinematic coupling of the displacement field of all constituents. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A thermo‐mechanical energetic cohesive zone model accounting for Kapitza interfaces
Authors: Esmaeili Ali , Javili Ali , Steinmann Paul
Published: October 2016

The objective of this contribution is to study computational aspects of modeling thermo‐mechanical solids containing mechanically energetic, geometrically non‐coherent Kapitza interfaces under cyclic loading. The interface is termed energetic in the sense that it possesses its own energy, entropy, constitutive relations and dissipation. To date, classical thermo‐mechanical cohesive zone models do not account for elastic interfaces. Therefore we propose a novel interface model that couples the classical cohesive zone formulation to the interface elasticity theory under the Kapitza assumption within a thermo‐mechanical framework. In other words, such an interface model allows for discontinuities in geometry, temperature and normal stress fields, while not permitting a jump in the normal heat flux across the interface. The equations governing a fully non‐linear transient problem are given. In particular, a comparison is made between the results of the classical thermo‐mechanical cohesive zone model and our novel (cohesive + energetic Kapitza) interface formulation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulation of hydraulic fracture of porous materials using the phase‐field modeling approach
Authors: Heider Yousef , Markert Bernd
Published: October 2016

In this contribution, the numerical simulation of hydraulic fracture of fluid‐saturated porous materials is carried out on a continuum‐mechanical scale using the theory of porous media (TPM), extended by a phase‐field modeling (PFM) approach. Following this, behaviors such as crack nucleation and propagation, solid matrix deformation and interstitial‐fluid flow change from Darcy to Stokes‐like flow in the cracked region can be realized. Moreover, permanent changes of the local physics due to occurrence of the crack, such as of the volume fractions and the permeability, are taken into consideration. The mathematical modeling of this problem yields a strongly coupled system of differential algebraic equations (DAE). Thus, special descretization schemes for a stable and efficient solution are needed. To reveal the ability of the proposed model to simulate the important features of hydraulic cracking, a two‐dimensional example using the finite element method is presented. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Flexible C++ Framework for the Efficient Solution of Strongly Coupled Multifield Problems
Authors: König Marcel , Radtke Lars , Düster Alexander
Published: October 2016

Coupled multifield problems occur in a wide variety of engineering applications. Due to the ever increasing available computational ressources, the numerical analysis of multifield phenomena has gained much interest in recent years. Partitioned solution strategies have been demonstrated to be a flexible and efficient way to solve even strongly coupled multifield problems. Major advantages of these approaches are the possibility to use different spatial and temporal discretizations for each of the subproblems and to employ existing, specialized solvers for their solution. In this work, we propose the software framework comana, which incorporates a partitioned solution strategy for the efficient numerical treatment of general multifield problems. Drawing on a highly modular architecture, comana greatly facilitates exchanging solvers and allows to easily implement tuned coupling algorithms. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of seismic attenuation in fluid‐saturated fractured media: An extended view of the Skempton coefficient
Authors: Pollmann Nele , Jänicke Ralf , Renner Jörg , Steeb Holger
Published: October 2016

The interpretation of data from seismic exploration gains from consideration of hydro‐mechanical processes in particular when the waves propagate through fluid‐filled fractured porous rocks. We specifically investigate attenuation processes in porous rock containing complex fracture networks with the main objective to identify effective hydro‐mechanical material properties by computational homogenization. To this end, we generate stochastic fracture ensembles and approximate fractures as ellipses with low aspect ratio (1/100). In other words, the fractures constitute thin and long hydraulic conduits with high permeability. Full periodic boundary conditions are employed on the small scale. We observe a strongly heterogeneous pressure propagation in the fracture network and the surrounding rock. The properties of the macroscopic substitute model are derived by means of a volume averaging technique. We identify a dependence of effective properties on fluid saturation and amount of fractures. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Micromechanics of Electro‐ and Magneto‐active Soft Composites
Authors: Rudykh Stephan
Published: October 2016

We study the coupled behavior in soft active microstructured materials undergoing large deformations in the presence of an external electric or magnetic field. We focus on the role of the microstructures on the coupled behavior, and examine the phenomenon in the composites with (a) periodic composites with rectangular and hexagonal periodic unit cells, and (b) in composites with the random distributions of active particles embedded in a soft matrix. We show that for these similar microstructures exhibit very different responses in terms of the actuation, and the coupling phenomenon. Next, we consider the macroscopic and microscopic instabilities in the active composites. We show that the external field has a significant influence of the instability phenomena, and can stabilize or destabilize the composites depending on the direction relative to composite geometry. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Advanced FEM for free surface flow with application to landslides
Authors: Schauer Marco , Reinstädler Sven , Dinkler Dieter
Published: October 2016

An advanced space‐time finite element method is presented to investigate movements of landslides and their interaction with flexible structures. The mechanics of liquefied soil is described by Navier‐Stokes‐equations for visco‐plastic non‐newtonian fluid. Likewise the fluid the kinematics of the structure is described by velocities, taking large rotations into account. This leads to a monolithic fluid‐structure interaction approach considering the multi‐field problem as a whole. The discretized model equations are assembled in a single set of algebraic equations, which are solved by applying Newton‐Raphson scheme. Free surface motion of landslide is described by the level‐set method. To reduce computational effort the fragmented finite element method is used, where only active finite elements are evaluated. A pde‐based extrapolation of the velocity‐field is applied to ensure an accurate transport of distance function, which defines the profile in space and time of the free surfaces. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomigration in Sn‐Pb solder bumps: Modelling and simulation
Authors: Schuß Stefan , Hesch Christian , Weinberg Kerstin
Published: October 2016

It is well known a homogeneous binary alloy subjected to a temperature gradient will become inhomogeneous. This decomposition phenomenon is called thermomigration or thermotransport or Soret effect, which is a cross‐effect in irreversible processes between heat conduction and atomic diffusion. In the present contribution we focus on a diffuse interface model for separation processes affected by temperature gradients coupled with a heat diffusion equation in order to describe thermomigration effects caused by joule‐heating. To be specific, we focus on phase separation in solder bumps consisting of tin and lead. Therefore we discuss the modelling of a Gibbs' configurational free energy density as well as the modelling of the chemical mobility, mobility of thermotransport and Dufour coefficient as sufficiently smooth functions in particle concentration and absolute temperature. The resulting set of partial differential equations involves spatial derivatives of fourth order. Consequently, the variational formulation of the problem mandates approximation functions which are at least C1‐continuous. In order to fulfill this requirement a B‐Spline based finite element scheme is provided. One of the main advantages of B‐Splines is the possibility to represent complex geometries exactly. However, it has been shown that especially curved B‐Spline geometries can not be treated in a straight forward manner in finite element analysis. For this reason we demonstrate the implementation of boundary conditions to avoid the arising numerical perturbations. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Coupled simulation in vehicle engineering
Authors: Burger Michael , Schneider Fabio , Steidel Stefan
Published: October 2016

Modern vehicles are highly complex systems consisting of many subsystems in various physical domains, e.g. electric, electronic, hydraulic and control systems that dynamically interact. For any subsystem, there are tailored simulation tools with specifically developed and adapted numerical solvers. In this context, co‐simulation strategies are particularly attractive, where each submodel is solved with appropriate numerical methods. In industrial applications, one is hereby confronted with enormous numerical challenges with respect to efficiency, accuracy and numerical stability – especially in online applications. In this article, we present co‐simulation strategies by means of selected application examples from the field of vehicle engineering. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strongly‐coupled modelling and analysis of energy harvesting devices
Authors: Zilian Andreas , Ravi Srivathsan
Published: October 2016

A monolithic approach is proposed that provides simultaneous modelling and analysis of the harvester, which involves surface‐coupled fluid‐structure interaction, volume‐coupled electro‐ mechanics and a controlling energy harvesting circuit for applications in energy harvesting. A space‐time finite element approximation is used for numerical solution of the weighted residual form of the governing equations of the flow‐driven piezoelectric energy harvesting device. This method enables time‐domain investigation of different types of structures (plate, shells) subject to exterior/interior flow with varying cross sections, material compositions, and attached electrical circuits with respect to the electrical power output generated. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Remarks on coupled multi‐scale simulations and high performance computation
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim
Published: October 2016

To describe material behaviour more precisely than nowadays, tomorrows simulation software will include multi‐scale homogenisation techniques. State of the art are various scale bridging strategies, like FE‐ODE, FE‐Phasefield or FE2‐Method. We are dealing with the FE2‐Method, see [3], [4], which gives us the possibility to take the geometric, discrete micro‐structure of a material into account. Furthermore, it allows to integrate enhanced continuum mechanical models. Here, we are researching on two‐scale approach with poro‐mechanical coupling based on the Theory of Porous Media (TPM), for more details see [1] or [2]. The framework is demanding and need a lot of computational effort. In order to receive industrial recognition, it is necessary to decrease the computation runtime. One way to go is definitely using high performance cluster. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Homogenization of thermomechanical tread‐road contact for the investigation of tire rolling resistance
Authors: Beyer Robert , Nackenhorst Udo
Published: October 2016

A homogenization framework for the stochastic average meso‐scale tread‐road interaction with emphasis on macro‐scale rolling resistance calculations is presented in this contribution. This framework accounts for large scale, high‐frequency penetration of tread rubber by the highest asperities as well as for the nonlinear thermo‐viscoelastic material behavior of this tread rubber in the regime of finite strains. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Computational Homogenization of Transient Diffusion Problems
Authors: Kaessmair Stefan , Steinmann Paul
Published: October 2016

In this contribution, we address the computational treatment of transient diffusion problems with heterogeneous microstructures using first‐order homogenization. There, we treat two different cases, firstly, when the transient part at the microscale can be neglected due to the vanishingly small size of the representative volume element (RVE) and secondly, when no steady state is reached at the microscale. This is the case when dealing with a relaxed version of the scale separation condition. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structural optimisation of multiscale problems based on variational sensitivity analysis
Authors: Kijanski Wojciech , Barthold Franz‐Joseph
Published: October 2016

The contribution presents the essential steps for the extension of the well‐known FE2 method by elements from variational design sensitivity analysis. The derived sensitivity information for a given structure can be used to suggest improved designs using methods for structural optimisation with objective functions, constraints and design variables on multiple scales. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational Homogenisation using Reduced‐Order Modelling applied to Hyperelasticity
Authors: Soldner Dominic , Brands Benjamin , Zabihyan Reza , Steinmann Paul , Mergheim Julia
Published: October 2016

Within this study nonlinear reduced‐order modelling for hyperelastic material is applied for the boundary value problem on the micro‐scale which arises in the context of computational homogenisation. This involves the Proper Orthogonal Decomposition and the Discrete Empirical Interpolation Method for the nonlinear term. Considered error measures are the errors of the displacement field, the averaged stresses and the effective elasticity tensor. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling the effective permeability of microcracked materials using continuum and lattice micromechanics
Authors: Timothy Jithender J. , Meschke Günther
Published: October 2016

Using the framework of the mean‐field homogenization method, we propose a continuum and a lattice version of the cascade micromechanics model for the estimation of the effective permeability of microcracked materials. Estimates for the critical microcrack density below which the REV becomes effectively impermeable are derived for both the continuum and the lattice idealizations. A validation example that compares model predictions with direct numerical simulations for the effective permeability as a function of the microcrack volume fraction is provided. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerische Strömungsanalyse und Optimierung von Kraftwerksbuchten bei Laufwasserkraftanlagen
Authors: Ostermann Lars , Seidel Christian
Published: October 2016

Für den wasserbaulichen Entwurf von Wasserkraftanlagen und ihre strömungsmechanische Optimierung werden neben dem rein auf Erfahrungswerten basierenden Entwurf vor allem experimentelle Untersuchungen am physikalischen Teilmodell oder Vollmodell im Wasserbaulabor eingesetzt. Strömungsmechanische Untersuchungen mit Hilfe numerischer Strömungsprogramme auf der Basis von 2D‐ und 3D‐Verfahren kommen teilweise zum Einsatz und stellen eine sinnvolle Ergänzung zu den experimentellen Verfahren dar. Für die Optimierung von Wasserkraftanlagen bieten sich schnelle numerische Lösungsverfahren an, die die Untersuchung einer größeren Anzahl von Optimierungsparametern und Strömungszuständen ermöglicht. Bei den 2D‐Verfahren eignen sich besonders Flachwassergleichungsbasierte Verfahren, da für diese Verfahren auf Grund ihrer weitverbreiteten Anwendung bei der Untersuchung strömungsmechanischer Fragestellungen im Wasserbau eine Vielzahl von Erfahrungswerten vorliegt, die häufig durch Insitu‐Messungen verifiziert sind. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of the regularity of the sediment bed on bed‐load transport
Authors: Jain Ramandeep , Vowinckel Bernhard , Fröhlich Jochen
Published: October 2016

The present study analyzes the impact of regularly arranged sediment bed on the particle clustering by introducing an artificial non‐uniformity in the particle packing. Two simulations only differing in their sediment bed configuration are reported with the non‐uniform roughness created through a random vertical displacement of the fixed particles constituting the rough wall. It is found that the irregular roughness enhances particle clustering as well as bed‐load transport compared to the case of uniform roughness. As a result the statistics of disperse and continuous phase are markedly different. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Enhanced mass transfer in micro‐capillary two‐phase flow
Authors: Lakshmanan Peter , Ehrhard Peter
Published: October 2016

Process design of multi‐phase unit operations on the micro‐scale relies on the detailed knowledge of the hydrodynamics and mass transfer of discrete disperse fluid particles. The present work examines gas bubbles in micro‐capillaries. For the case of bubbles rising in vertical capillary, the hydrodynamics and concentration fields are determined over a wide field of parameters (Re, Sc, dbubble/dcapillary) using a combination of level‐set and body‐fitted mesh methods. Drag coefficients and Sherwood numbers are computed from the results and can be used to derive empirical correlations for each parameter and mode of operation. These correlations allow for the individual optimization of the mass transfer process in micro‐capillaries. The results are compared to experimental data and available correlations in literature with generally good agreement. It can be shown that mass transfer can be enhanced by using small geometries like micro‐capillaries. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerische Modellierung der Freispiegelströmung am Beispiel eines Kreissegmentschützes
Authors: Schippke Hans‐Henning , Seidel Christian , Dinkler Dieter
Published: October 2016

Es wird ein Berechnungsmodell vorgestellt mit dem eine numerische Analyse der Überströmung von Verschlussorganen möglich ist. Der Arbeitsschwerpunkt liegt auf der Untersuchung der Stabilität des Lösungsverfahren unter Berücksichtigung der zu wählenden komplexen Randbedingungen sowie der physikalischen und numerischen Parameter. Die Güte der dabei gewonnen Ergebnisse wird mit experimentellen Untersuchungen abgeglichen. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the flow around Glauert‐Goldschmied body in the narrow channel and separation control strategy
Authors: Procházka Pavel , Uruba Václav
Published: October 2016

Previously, there was tested a wire dielectric barrier discharge (DBD) plasma actuator to generate sufficiently strong ionic wind to affect freely developed boundary layer in the narrow channel. This paper will report about next step – to installation of actuator inside a streamlined body. The experiment will take place inside perspex rectangular (250 × 100 mm) channel and main task is to find the appropriate place for actuator fitting for three different flow regimes. Hence, the separation point and recirculation area will be investigated via PIV anemometry for base case and for active flow control methods (e.g. plasma actuator) as well as frequency spectrum of the flow will be evaluated to describe the nature of the flow. The measurement plane will be perpendicular to the bottom of the channel and in longitudinal level. These essential information will be used for actuator design, actuator embedding and to tune actuator frequency in order to suppress the recirculation area as much as possible. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On Hahn polynomial expansion of a continuous function of bounded variation
Authors: Goertz René
Published: October 2016

We consider the well‐known method of least squares (cf., e.g., [1, p. 217]) on an equidistant grid with N + 1 nodes on the interval [−1, 1]. We investigate the following problem: For which ratio N/n, do we have pointwise convergence of the least square operator LSNn : C[−1,[1][→[Pn? To solve this problem we investigate the relation between the Jacobi polynomials Pα,βk (cf., e.g., [2, p. 216]) and the Hahn polynomials Qk (·; α, β, N) (cf., e.g., [2, p. 204]). In particular, we present the following result: Let f ∈ {g ∈ C1[−1, 1] : g′∈ BV [−1, 1]} and let (Nn)n be a sequence of natural numbers with n4/Nn → 0. Then the least square method LSNn [f] converges for each x ∈ [−1, 1]. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the calculation of Topological Derivatives considering an exemplary nonlinear material model
Authors: Weider Katrin , Schumacher Axel
Published: October 2016

In this contribution, a new approach for dealing with material nonlinearities in structural optimization is presented. The method combines the advantage of the calculation of the Topological Derivatives in elasticity problems with the use of meta‐modelling for capturing complex correlations. For an exemplary nonlinear material model, the calculation of the Topological Derivative and the resulting difference to the linear elastic material model is shown. An academic example shows the difference between the linear and the nonlinear material model. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Global Convergence of the Jacobi Method
Authors: Hari Vjeran , Begović Kovač Erna
Published: October 2016

The paper is concerned with the global convergence of the Jacobi method for symmetric matrices under a special class of cyclic pivot strategies. That class generalizes the well‐known class of serial strategies. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dual‐primal isogeometric tearing and interconnecting solvers for multipatch continuous and discontinuous Galerkin IgA equations
Authors: Hofer Christoph , Langer Ulrich
Published: October 2016

We present results regarding fast and robust solvers for equations arising from continuous and discontinuous Galerkin discretization of heterogeneous diffusion problems in the context of Isogeometric Analysis. The solvers considered belong to the class of non‐overlapping domain decomposition methods which use tearing and interconnection strategies. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multisymplectic variational integrators for PDEs of geometrically exact beam dynamics using algorithmic differentiation
Authors: Leitz Thomas , Leyendecker Sigrid
Published: October 2016

For the simulation of geometrically exact beam dynamics [4], a multisymplectic Lie‐group variational integrator [3] is derived. Based on the implementation of the discrete Lagrangian, algorithmic differentiation is used in the computation of both, the discrete Euler‐Lagrange equations, and the Jacobi matrix needed for the Newton‐Raphson iteration. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Discontinuous Galerkin Method for Fractional Differential Equations
Authors: Franz Sebastian , Rubisch Johanna
Published: October 2016

We investigate the numerical treatment of fractional derivatives using a discontinuous Galerkin approach. We consider fractional differential equations in one dimension.

The most common definitions, the Riemann‐Liouville and Caputo derivatives, as well as a third definition are considered. Different types of initial condition statements are investigated for the extended discontinuous Galerkin method.

We obtain numerical results on the order of convergence in the L2 and H1 norms. We compare the classical discontinuous Galerkin method with our adapted approach and show results for the different types of fractional derivatives.

Further work was carried out on parabolic differential equations with fractional time derivatives, which is to be published cf. [2]. A keystone in the further research is the development of analytical tools for theoretical convergence results. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adjoint‐Based Optimal Boundary Control of a Stefan Problem System Fully Coupled with Navier‐Stokes Equations
Authors: Baran Björn , Heiland Jan
Published: October 2016

Free boundary and moving boundary problems, that can be used to model crystal growth or the solidification and melting of pure materials, receive growing attention in science and technology. The optimal control of these problems appear even more interesting since certain desired shapes of the boundaries improve, e.g., the material quality in the case of crystal growth. We consider the so called two‐phase Stefan problem that models a solid and a liquid phase separated by a moving interface.

In the work presented, we take a sharp interface model approach and define a quadratic tracking‐type cost functional that penalizes the deviation of the interface from the desired state at a final time as well as the control costs. Following the “optimize‐then‐discretize” paradigm, we formulate a first order optimality system using the formal Lagrange approach and derive the adjoint PDE system that provides the needed gradient of the cost functional.

By means of an example setup of a container with an in‐ and outflow of water and a cooling unit at the bottom, we illustrate how the derived formulations can be used to achieve a desired interface between the solid and the fluid phase by controlling the flow at the inlet. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification and Tracking‐Control for an Optomechatronical Image Derotator Using Neural Networks
Authors: Altmann Bettina , Rohloff Benjamin , Pape Christian , Reithmeier Eduard
Published: October 2016

In this paper an optomechatronical image derotator is used for vibration measurements on rotating objects. First of all, the concept of the derotator is explained and it is shown that the phase position and the rotational velocity of the derotator and the measurement object have to be aligned. Therefore, a highly dynamic tracking‐control is needed. Considering the nonlinear friction of the synchronous motor, a model of the system which considers this non‐linearity is evolved. This is accomplished by using neural networks for the approximation of the friction term. In this case General Regression Neural Networks (GRNN) are used for the learning algorithm. Moreover, the system's parameters, eg. the friction term and the inertia, are identified based on the nonlinear model. Then a feedback control is designed by using the controllable canonical form through feedback linearization. Finally, the results of vibration measurements on a rotating blisk using the nonlinear control concept for the derotator are shown. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Unimodular completion and direct flat representation in the context of differential flatness
Authors: Fritzsche Klemens , Knoll Carsten , Franke Matthias , Röbenack Klaus
Published: October 2016

Despite its significance in nonlinear controller design, the verification of the property of differential flatness and the identification of so‐called flat outputs is a continuing research topic. However, the difficulty of both verification and identification heavily depends on the representation of the system. This contribution shows that flatness may be a far less complicated matter, depending on the choice of coordinates. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The Newton‐Kleinman method for the optimal control of stable weakly regular linear systems
Authors: Massoudi Arash , Reis Timo
Published: October 2016

We give an algorithm to find the approximate solution of the linear‐quadratic optimal control problem for stable weakly regular linear systems. This algorithm can be understood as a generalization of the Newton‐Kleinman method known from the finite‐dimensional theory. The central characteristic of our approach is the possibility to solve problems with unbounded control and observation operators, which is motivated by partial differential equations with boundary control and observation. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control concepts for a parallel manipulator with flexible links
Authors: Morlock Merlin , Burkhardt Markus , Seifried Robert
Published: October 2016

Light‐weight robots are advantageous considering the low energy consumption and the low material cost. However, in light‐weight structures significant oscillations can occur which make the control very challenging. Objective of this research is end‐effector trajectory tracking of a parallel manipulator with flexible links. Hereby, only the manipulator's drives are used, and no additional actuation on the flexible bodies is considered. For accurate trajectory tracking, feedforward control of the manipulator is used based on inverse dynamics and servo‐constraints, combined with feedback control of the drive positions. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Higher order variational integrators in optimal control theory
Authors: Ober‐Blöbaum Sina
Published: October 2016

Higher order variational integrators are analyzed and applied to optimal control problems posed with mechanical systems. First, we derive two different kinds of high order variational integrators based on different dimensions of the underlying approximation space. While the first well‐known integrator is equivalent to a symplectic partitioned Runge‐Kutta method, the second integrator, denoted as symplectic Galerkin integrator, yields a method which in general, cannot be written as a standard symplectic Runge‐Kutta scheme [1]. Furthermore, we use these integrators for the discretization of optimal control problems. By analyzing the adjoint systems of the optimal control problem and its discretized counterpart, we prove that for these particular integrators optimization and discretization commute [2]. This property guarantees that the accuracy is preserved for the adjoint system which is also referred to as the Covector Mapping Principle. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stabilization of switched DAEs via fast switching
Authors: Trenn Stephan
Published: October 2016

Switched differential algebraic equations (switched DAEs) can model dynamical systems with state constraints together with sudden structural changes (switches). These switches may lead to induced jumps and can destabilize the system even in the case that each mode is stable. However, the opposite effect is also possible; in particular, the question of finding a stabilizing switching signal is of interest. Two approaches are presented how to stabilize a switched DAE via fast switching. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cascadic Multigrid in a Spectral‐Element Context
Authors: Huismann Immo , Stiller Jörg , Fröhlich Jochen
Published: October 2016

Current research in computational fluid dynamics focuses on high‐order methods, which offer a significant reduction of the computational effort for a given error bound. In low‐order methods optimal complexity solvers for elliptic equations, e.g. the Helmholtz equation, are readily available, but for high‐order methods these are still an area of research. This work evaluates the effectiveness of the Cascadic Multigrid Method in the context of spectral elements, comparing it to a standard Krylov subspace solver. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Circular proofs for the modal mu‐calculus
Authors: Afshari Bahareh , Leigh Graham E.
Published: October 2016

Inspired by Stirling's tableau proofs [4] we introduce a finite, cut‐free sound and complete sequent calculus for the modal mu‐calculus. Proofs in this system are finite trees in which leaves are either axioms or assumptions that are discharged by a specific rule of the calculus. The discharge rules provide a way to unfold assumptions motivating the name circular proofs. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dimer models and Grassmannian cluster categories
Authors: Baur Karin
Published: October 2016

A dimer model can be defined as a quiver embedded into a surface in such a way that the complement is a disjoint union of disks with oriented boundaries. Such models can also be considered in the case of a surface with boundary. The Postnikov diagrams used by J. Scott to describe the cluster structure of the homogeneous coordinate ring of the Grassmannian give rise to dimer models on a disk in this sense. We associate a natural algebra to such a dimer model. This algebra is a modified version of the corresponding Jacobian algebra, taking the boundary into account. Taking the sum of the idempotents corresponding to boundary vertices, we obtain an idempotent subalgebra, which we call the boundary algebra. We show that it is independent of the choice of dimer model and coincides with an algebra that B. Jensen, A. King and X. Su have used to model the cluster structure of the homogeneous coordinate ring of the Grassmannian categorically. This reports on joint work with A. King (Bath) and R. Marsh (Leeds) and with D. Bogdanic (Graz). (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards modelling skeletal muscle growth and adaptation
Authors: Altan Ekin , Zöllner Alexander , Avcı Okan , Röhrle Oliver
Published: October 2016

Despite an increasing interest in modelling skeletal muscles adaptation, models that address the phenomena within a continuum‐mechanical framework using muscle‐specific material models are rare in literature. This work focuses on modelling one form of skeletal musle adaptation, namely sarcomerogenesis. Sarcomerogenesis occurs when a given stretch is sustained over a period of time and the number of basic contractile units, which are the sarcomeres, increase.

To model sarcomerogenesis within a continuum‐mechanical setting, the growth framework based on a multiplicative split of the total deformation gradient is employed. An evolution equation that describes sarcomerogenesis is used and incorporated in a transversally isotropic material model that accounts for a skeletal muscle's active force production capabilities. The material tangent modulus is derived and implemented within the finite‐element analysis software. Using this model, one sees that increased number of sarcomeres results in a decreased force response of the muscle tissue over time. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the modelling of finite growth considering the mechanics of cell division
Authors: Bolea Albero Antonio , Böl Markus
Published: October 2016

Mitotic cells grow in volume and divide themselves into two identical cells producing at macroscopic scale a volume expansion in living bodies. Due to inhomogeneous distributions of the growth factors, growth occurs at different rates and directions. Focusing into the direction of growth, some living bodies alter their growing behaviour influenced by mechanical loads. If loads appear during the growth process, cell division is reorientated following the main direction of the elastic deformations. Therefore, new cells will be created in this direction while relaxing the stress state of the body at the same time. In this work, we present a modelling approach for growing bodies which change their growth direction depending on mechanical loads. The model is implemented into a finite element framework to be an useful tool for predicting morphological changes in growing bodies. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐Infrastructure Real‐Time Embedded Control via Variational Integrators
Authors: Schultz Jarvis , Murphey Todd
Published: October 2016

This paper presents a discrete time receding horizon control scheme that leverages the numerical properties of a variational integrator to facilitate real‐time control generation on an embedded system. The variational integrator employed is well‐suited to classical estimation and control algorithms, e.g. LQR, extended Kalman filters, and particle filters. The structure‐preserving properties of this variational integrator lead to increased performance of estimation and control routines, especially in low‐bandwidth applications. Several experimental examples are presented that illustrate the features of this receding horizon control scheme when leveraging the desirable numerical properties of the variational integrator. © 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flow structures and heat transfer characteristics in arrays of submerged laminar impinging jets
Authors: Rohlfs W. , Bieber M. , Ehrenpreis C. , Jörg J. , Sabelberg E. , Kneer R.
Published: October 2016

This study summarizes the scaling behavior of single laminar submerged jets with circular and planar cross sections. Unified correlations for the stagnation zone heat transfer of both configurations, based on the dominant dimensionless numbers, are presented. In technical applications, impinging jets are often applied in jet array configurations. Compared to single jet impingement, jet‐to‐jet interaction can have a substantial influence on local heat transfer. A distinct pattern of the heat transfer coefficient was observed experimentally. Numerical simulations revealed two counter‐rotating vortices in the interaction zone between two jets to be the causing mechanism of this pattern. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
swMATH – next steps
Authors: Chrapary Hagen
Published: October 2016

Mathematical software is of increasing importance in teaching activities, research, industry and daily life. But searching and finding information about relevant mathematical software is a non‐trivial task. swMATH [1] is a new and comprehensive information service on mathematical software and mathematical research data. It contains information on nearly 13.000 software packages with more than 120.000 references to scientific articles citing the software. It offers free access to information on software in all mathematical subjects from large general purpose systems to small packages and includes benchmarks, languages, data sets, and web services, too. The paper starts with a short description of our approach and addresses some open problems for the further development. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Novel extracellular polymeric substances produced by Cupriavidus necator IPT 027 grown on glucose and crude glycerol originated from biodiesel
Authors: Ribeiro Paulo Leonardo Lima , Campos Márcio Inomata , Druzian Janice Izabel
Published: October 2016

The aim of this study was to evaluate the production and properties of novel extracellular polymeric substances (EPS) from glucose (EPS 1) and crude glycerol (CG) from castor beans oil (EPS 2). Cupriavidus necator IPT 027 cultivated with glucose and CG (35 °C, 150 rpm, 72 hr, pH 7, shaker) produced approximately 1.60 ± 0.01 and 2.83 ± 0.02 g l−1 EPS, respectively, with high‐molecular weight (3.89 × 105 and 1.89 × 107 Da) and constituted of different functional groups such as uronic acid, monosaccharides (glucose, mannose, arabinose, and fucose) and primary amine group. The composition of the fermentable substrate influenced the melting temperature (221.11 and 230.18 °C), crystallinity (34.36% and 37.11%), degradation temperature (255.06 and 296.62 °C) and morphology. EPS showed pseudoplastic non‐Newtonian fluid behavior in the aqueous solutions, presenting potential applicability biotechnological and industrial mainly in food industry as emulsifiers and biosurfactants. This is the first study on the production and characterization of EPS obtained by C. necator IPT 027 in culture with glucose and CG. Copyright © 2016 John Wiley & Sons, Ltd.
High temperature surface neutralization process with random copolymers for block copolymer self‐assembly
Authors: Sparnacci Katia , Antonioli Diego , Perego Michele , Giammaria Tommaso Jacopo , Seguini Gabriele , Ferrarese Lupi Federico , Zuccheri Giampaolo , Gianotti Valentina , Laus Michele
Published: October 2016

Hydroxyl terminated poly(styrene‐r‐methyl methacrylate) (P(S‐r‐MMA)) random copolymers (RCPs), with molecular weight (Mn) spanning from 1700 to 69 000 g mol−1 and equal styrene unit content, were grafted at different temperatures onto a silicon oxide surface and subsequently used to study the orientation of nanodomains with respect to the substrate, in cylinder forming polystyrene‐b‐poly(methyl methacrylate) (PS‐b‐PMMA) block copolymer thin films. When the grafting temperature increases from 250 to 310 °C, a substantial increase in the grafting rate is observed. In addition, an increase in the surface neutralization efficiency occurs thus resulting in an increase in the robustness of the surface neutralization step. These data revealed that the neutralization of the substrate is the result of a complex interplay between RCP film characteristics and underlying substrate properties that can be finely tuned by properly adjusting the temperature of the grafting process. © 2016 Society of Chemical Industry
Unravelling Malaria Antigen Binding to Antibody‐Gold Nanoparticle Conjugates
Authors: Cavadas Miguel A. S. , Monopoli Marco P. , Cunha Cláudia Sá e , Prudêncio Miguel , Pereira Eulália , Lynch Iseult , Dawson Kenneth A. , Franco Ricardo
Published: October 2016

Conjugates formed by antibody adsorption to gold nanoparticles (AuNP) have found extensive utilization in immunoassays due to the high surface area and interesting optical and electronic properties of the nanomaterials. Nevertheless, the mechanism of formation of antibody‐AuNP conjugates and their antigen binding characteristics have not been sufficiently explored in terms of specificity and consequent clinical applicability. Dynamic light scattering and related techniques have been successfully employed to detect antigen binding to antibody‐AuNP complexes. Here, a range of different techniques from the bionanotechnology realm have been applied to obtain a detailed picture of a competitive immunoassay for malaria antigen detection, based on fluorescence‐quenching by AuNPs. Both agarose gel electrophoresis and differential centrifugal sedimentation (DCS) analyses provide binding constants in the same order of magnitude, for antibody binding to AuNP and for antigen binding to antibody‐AuNP conjugates. Both techniques are also able to reveal inhibition of antigen binding in the presence of a major blood plasma protein, transferrin (via competitive binding). DCS is further used to show inhibition of the binding of the antigen in the presence of human plasma, a realistic testing condition, of high relevance to the implementation of immunoassays at the clinical level.
Order and Defects in Ceramic Semiconductor Nanoparticle Superstructures as a Function of Polydispersity and Aspect Ratio
Authors: Gerigk Melanie , Bahner Jochen , Kollek Tom , Helfrich Stefan , Rosenberg Rose , Cölfen Helmut , Polarz Sebastian
Published: October 2016

The supreme aim of nanoparticle‐based materials is to achieve new properties extending over the features of individual constituents. The emergence of cooperativity necessitates precise positioning and orientation of nanoparticle ensembles. Thus, it is important to understand and learn how to control self‐assembly processes of nanoparticles. Besides shape, the structural uniformity plays a key role for ordering in superstructures. Therefore, it is challenging to synthesize nanorods with narrow polydispersity. An analysis of the systematic variation of aspect ratio and polydispersity is missing. A series of zinc oxide nanorods is presented and it is shown that their formation resembles step‐polymerization with an amorphous precursor state as a monomer and polar ZnO particles as entities capable of growing. The width of nanorods is kept constant (15 nm) and the length is varied between 20 and 100 nm, as well as improving the polydispersity of the nanorod length from 36% to 10%. Best samples have been achieved by post‐preparative treatment using gradient centrifugation. A method has been developed for semiquantitative evaluation of orientational order. Ordering in structures formed by quasispherical particles is always low despite low polydispersity. For rod‐like nanoparticles with increasing aspect ratio, superstructure order depends on the occurrence of different defects, which correlate differently to nanoparticle polydispersity.
Risk Assessment of Sea Dumped Conventional Munitions
Authors: Voie Øyvind A. , Mariussen Espen
Published: October 2016

Energetic compounds from dumped ammunition are toxic to aquatic organisms. Leakage of ammunition residues will occur when the bombshells are broken and the energetic compounds come into contact with water. The munitions compounds have a complex behavior in the environment, particularly in the sediment‐water phase, and the calculation of safety levels are dependent on choice of methodology. Estimated sediment quality benchmark levels combined with multi‐increment sampling strategy provide the most proper tool for performing ecological risk assessment at a dump site. Dumped munitions may be located in areas, where shellfish, invertebrates, and benthic or pelagic fish are consumed by humans. A monitoring program for early warning of potential contaminants in the vicinity of fish farms could be conducted by passive samplers for explosives. Further development of both sample procedures and analytical methods to increase the quality of the chemical analyses are encouraged.
The UK Ministry of Defence Project Orientated Environmental Management System (POEMS)
Authors: Galante Erick , Temple Tracey , Ladyman Melissa , Gill Philip P.
Published: October 2016

The Project Orientated Environmental Management System (POEMS) is the UK Ministry of Defence (MoD) bespoke environmental management system for the acquisition and use of equipment. The full implementation of a site‐specific environmental management system is challenging for the MoD because there are many permanent MoD sites with transient populations, frequently changing site activities and diverse types of equipment. Nevertheless, MoD policy requires that all sites are covered by an environmental management system. POEMS is based on international standards ISO14001 and ISO14040, which focus on environmental management systems and life cycle assessment, respectively. The primary aim of POEMS is to identify and manage any environmental aspects (causes) and impacts (effects) by scrutinising MoD equipment and activities during acquisition, operation and disposal. This is achieved by drawing up a priority list of activities associated with the equipment based on anticipated environmental impact scores, resulting in an environmental management plan that spans the life cycle of the equipment and any corresponding activities. This article describes the POEMS procedure for both experts and non‐experts, and demonstrates the implementation of POEMS using a 105‐mm artillery round as a theoretical case study. The results anticipated at each stage of the POEMS procedure are discussed in detail, and the documentation necessary to verify the correct application of POEMS is demonstrated.