bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite element simulation of nonlinear magnetoelectric coupling and damage behaviour in multiferroic composites
Authors: Avakian Artjom , Ricoeur Andreas
Published: March 2018

In this paper, the constitutive modelling of nonlinear multifield behavior as well as the finite element implementation are presented. Nonlinear material models describing the magneto‐ferroelectric or electro‐ferromagnetic behaviors are presented. Both physically and phenomenologically motivated constitutive models have been developed for the numerical calculation of principally different nonlinear magnetostrictive behaviors. Further, the nonlinear ferroelectric behavior is based on a physically motivated constitutive model. On this basis, the polarization in the ferroelectric and magnetization in the ferromagnetic and magnetostrictive phases, respectively, are simulated and the resulting effects analyzed. Additionally, the ferroelectric model accounts for damage due to microcrack growth. Numerical simulations focus on the calculation of magnetoelectric coupling and on the prediction of local domain orientations as well as damage processes going along with the poling process, thus supplying information on favorable electric‐magnetic loading sequences. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling of the deformation‐dependent fluid flow in the fibrous gas diffusion layer of fuel cells
Authors: Chaaban Mohamad , Heider Yousef , Markert Bernd
Published: March 2018

The following contribution presents a numerical model for the description of the compression of gas diffusion layers (GDL) of polymer electrolyte membrane fuel cells (PEMFC). Proceeding from a macroscopic multiphasic modelling approach for porous materials, the work below instills the neo‐Hookean material law of finite deformations within the framework of the theory of porous media (TPM). Subsequently, the alteration in the deformation‐dependent intrinsic permeability is computed as an evaluation criteria of the effect of compression on the performance of the GDL. In furtherance of the affected transport property, a modified intrinsic permeability function is presented and validated to fit the profile of compression. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical methods for the modeling of the magnetization vector in multiferroic heterostructures
Authors: Dornisch Wolfgang , Schrade David , Wolf Jana , Müller Ralf
Published: March 2018

Multiferroic heterostructures are commonly used to obtain electro‐magnetic coupling effects. Thereby, the ferroelectric layer is used to control the magnetization in the ferromagnetic layer. The coupling between the layers is obtained by the mechanical coupling between the layers, which have well‐defined interfaces. Within this contribution we use phase field models to define the polarization and magnetization in the ferroelectric and ferromagnetic layers, respectively. A coupling between polarization/magnetization and strains in each layer in combination with coherent deformations at the interface yields an electromagnetic coupling within the entire heterostructure. Numerical formulations for the interpolation of the polarization vector are well‐defined in the literature. However, the establishment of a consistent numerical formulation for the ferromagnetic layer, where the length of the magnetization vector has to be constant, remains a difficult task. We propose a new numerical approach for the consistent treatment of the ferromagnetic layer and provide numerical simulations which illustrate the electromagnetic coupling effect. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled phase transformation and solute diffusion model for bainitic transformation
Authors: Düsing Martin , Mahnken Rolf
Published: March 2018

In materials science one distinguishes between upper and lower bainite, where both microstructures develop due to different diffusion processes. In this work we describe these different mechanisms with a new diffusion model coupled to a multiphase‐field equation. Numerical examples demonstrate the expected behavior. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modal Substructuring of Geometrically Nonlinear Plates
Authors: Karamooz Mahdiabadi Morteza , Buchmann Erhard , Rixen Daniel Jean
Published: March 2018

This work considers model reduction of geometrically nonlinear finite element (FE) model of a plate structure developed in a commercial FE package. The structure is first divided into smaller substructures. Since there is normally no access to the nonlinear stiffness tensors in FE packages, a non‐intrusive method is used in this paper to reduce the order of each substructure separately. In order to generate the nonlinear reduced order model (NLROM), the reduced substructures are assembled using the coupling procedure of the Component Mode Synthesis (CMS) method. As a linear basis, truncated free and fixed interface modes are used here to check the efficiency of the developed NLROM based on them. A plate structure subjected to large deflections is considered in this study to implement the substructuring method. For the sake of validation, Nonlinear Normal Modes (NNMs) are employed to check the convergence of NLROMs in a broadband frequency range. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiphysics of Tribocontacts
Authors: Ostermeyer Georg‐Peter , Bräuer Günter , Merlis Joshua , Kaestner Peter , Kipp Christian
Published: March 2018

The complex processes involved in the dry friction between two bodies are not yet fully understood. Towards an improved understanding of the associated tribological phenomena, the authors combine their skills and expertise in the respective fields of tribological experimentation, modeling, and simulation, as well as topological and chemical surface analyses. The aim of this research is more accurate predictions of the tribological behavior of minimal friction material mixtures. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model order reduction for thermomechanical problems including radiation
Authors: Rother Stephan , Beitelschmidt Michael
Published: March 2018

Thermal field problems including heat exchange by radiation lead to nonlinear system equations with a high number of inputs and outputs as radiation heat fluxes correspond to the fourth power of the temperature and thermal loads are distributed over the whole surface. In an alternative approach presented here, radiation is defined as a part of the load vector. Thus, the system matrices are constant. Furthermore, loads changing synchronously during operation are grouped into one column of the input matrix and load vector snapshots are used to consider the radiation heat fluxes. Hence, the Krylov Subspace Method can be applied to significantly reduce the system dimension and the computation times allowing transient thermal parameter studies. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerische Simulation der Freispiegelströmung in einem Wasserrad
Authors: Schippke Hans‐Henning , Seidel Christian , Dinkler Dieter
Published: March 2018

Es wird ein Berechnungsmodell für 2‐Fluid‐Strömungen mit drehendem Starrkörper vorgestellt, mit dem eine numerische Analyse der Strömungsvorgänge innerhalb von Schaufelwasserrädern möglich ist. Mit dem vorgestellten Berechnungsmodell erfolgt die erstmalige numerische Untersuchung der bei Schaufelwasserrädern auftretenden Strömungsvorgänge. Dabei werden die wesentlichen Punkte im Rahmen der numerischen Umsetzung eingehend diskutiert und die gewonnenen Ergebnisse anhand experimenteller Daten auf ihre physikalische Plausibilität hin überprüft. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A polarisation based approach to model strain dependent electrostatic pressure of dielectric elastomer actuators
Authors: Schlögl Tristan , Leyendecker Sigrid
Published: March 2018

A wide‐spread lumped parameter model describing the electrostatic pressure is presented by Pelrine et. al. in 1998 [1]. In Pelrine's model, the electrostatic pressure is affected by the relative permittivity of the material, also known as dielectric constant. However, many researchers found that the dielectric constant of DEAs is not constant at all, but decreasing with increasing pre‐stretch of the material. In this work, an alternative modelling approach is presented, explaining the stretch dependent actuation pressure. It is shown that this new model fits experimental data found in literature quite well. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of electro‐chemomechanical behavior of ionic polymer‐metal composites within the framework of the Theory of Porous Media
Authors: Serdas Serdar , Bluhm Joachim , Schröder Jörg
Published: March 2018

Ionic polymer‐metal composites (IPMCs) serve as electro‐mechanical transducers for actuator and sensor applications, see [1]. Typically, they are sandwiched between two impermeable electrodes comprising the polymer network, the liquid, the fixed anions and the mobile cations. The actuation mechanism takes place by applying an electric potential (voltage) and the mobile cations move towards the cathode. Due to the relocation of the cations (electrostatic and ionic forces), a deformation of the IPMC can be observed. In contrast, the sensing mechanism is performed by applying a mechanical load yielding to a concentration redistribution and generating an electrical potential inside the IPMC. In Leichsenring [2], a parametric study has been carried out for the description of an IPMC. Therein, the Theory of Porous Media (TPM) was used, see [3], while the motion of the liquid and the cations were restricted. In the present contribution, the actuation and sensing behavior of an IPMC is presented within the framework of the TPM, see [5]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Large‐Deformation Phase‐Field Approach for the Modeling of Magneto‐Sensitive Elastomers
Authors: Sridhar Ashish , Keip Marc‐André , Miehe Christian
Published: March 2018

Magneto‐sensitive materials show magneto‐mechanical coupled response and are thus of increasing interest in the recent age of smart functional materials. Ferromagnetic particles suspended in an elastomeric matrix show realignment under the influence of an external applied field, in turn causing large deformations of the substrate material. The magneto‐mechanical coupling in this case is governed by the magnetic properties of the inclusion and the mechancial properties of the matrix. The magnetic phenomenon in ferromagnetic materials is governed by the formation and evolution of domains on the micro scale. A better understanding of the behavior of these particles under the influence of an external applied field is required to accurately predict the behavior of such materials. In this context it is of particular importance to model the macro scopic magneto‐mechanically coupled behavior based on the micro‐magnetic domain evolution. The key aspect of this work is to develop a large‐deformation micro‐magnetic model that can accurately capture the microscopic response of such materials. Rigorous exploitation of appropriate rate‐type variational principles and consequent incremental variational principles directly give us field equations including the time evolution equation of the magnetization, which acts as the order parameter in our formulation. The theory presented here is the continuation of the work presented in [1, 7] for small deformations. A summary of magneto‐mechanical theories spanning over multiple scales has been presented in [4]. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Microstructural influence on macroscopic response regarding fluid flow through porous media applying TPM2‐Method
Authors: Bartel Florian , Ricken Tim , Schröder Jörg , Bluhm Joachim
Published: March 2018

Thanks to the advancements in the digital era we are able to capture naturally grown and artificially manufactured microstructures with various scanning devices like CT and MRT and can transfer the digital image data to finite element models. In addition, there has been a permanent improvement in the quality of additive reproduction technology. Looking at the biomedical industry producing organic parts, porous materials saturated with fluids play an important role. For this reason, we also have to develop appropriate simulation technology providing a description for porous materials regarding the underlying microstructure. This contribution presents a numerical experiment for the flow through a porous body with different underlying microstructures applying the TPM2‐Method. The different macroscopic behavior for the displacements, pressure distribution, and volumetric fluid flow for an isotropic and two differently orientated anisotropic microstructures are shown in section 3. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational inelasticity for loading conditions on multiple time scales by adaptive step size control
Authors: Gote Ajinkya , Eidel Bernhard
Published: March 2018

This contribution proposes an algorithm based on adaptive step size control for the simulation of inelastic solids and structures undergoing loading conditions at multiple time scales. Adaptivity in time integration of viscoelastic constitutive laws is directed by an refinement indicator which is constructed from integrators of different order, here a fourth‐order Runge‐Kutta (RK) method and linear Backward‐Euler. The key novel aspect is that by virtue of an recently established consistency condition the higher order methods, p ≥ 2, can achieve their full nominal order without fulfilling the weak form of balance of linear momentum in the RK stages, but only at the end of the time interval. A representative numerical example illustrates the performance of the present adaptive method and underpins the computational savings compared with uniform time step sizes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparison of mean field homogenization schemes for short fiber reinforced thermoplastics
Authors: Hessman Patrick Arthur , Hornberger Kurt
Published: March 2018

Different mean field homogenization methods are applied to a short glass fiber reinforced polybutylene terephthalate. The different models' predictions for the anisotropic effective elastic properties are assessed and compared to experimental data from tensile tests. Additionally, the estimation of fiber stresses and the influence of the fiber length distribution is studied. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Error‐controlled homogenization for a class of linear elastic composite problems
Authors: Ju Xiaozhe , Mahnken Rolf
Published: March 2018

The research field of model adaptivity is well established, aiming at adaptive selection of mathematical models from a well defined class of models (model hierarchy) to achieve a preset level of accuracy, see e.g. [4, 5]. The present work addresses its application to a class of linear elastic composite problems. In order to adaptively control both macro model and macro discretization errors, we present a coupled adaptive scheme, which is driven by a goal‐oriented error estimator based on duality techniques. For efficient computation of the dual solution, we make use of a patch‐based recovery technique proposed in [6]. As a possibility for model adaptivity, we propose a model hierarchy based on the classical bounding theories [2, 3], which is established in a natural and theoretically consistent manner, without combination of different methods using a priori knowledge. For illustration, a numerical example is presented. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An adaptive approach for modeling a fiber‐matrix composite with the FE2 method
Authors: Praster Maximilian , Klinkel Sven
Published: March 2018

In materials with a complicated microstructre [1], the macroscopic material behaviour is unknown. In this work a Fiber‐Matrix composite is considered with elasto‐plastic fibers. A homogenization of the microscale leads to the macroscopic material properties. In the present work, this is realized in the frame of a FE2 formulation. It combines two nested finite element simulations. On the macroscale, the boundary value problem is modelled by finite elements, at each integration point a second finite element simulation on the microscale is employed to calculate the stress response and the material tangent modulus. One huge disadvantage of the approach is the high computational effort. Certainly, an accompanying homogenization is not necessary if the material behaves linear elastic. This motivates the present approach to deal with an adaptive scheme. An indicator, which makes use of the different boundary conditions (BC) of the BVP on microscale, is suggested. The homogenization with the Dirichlet BC overestimates the material tangent modulus whereas the Neumann BC underestimates the modulus [2]. The idea for an adaptive modeling is to use both of the BCs during the loading process of the macrostructure. Starting initially with the Neumann BC leads to an overestimation of the displacement response and thus the strain state of the boundary value problem on the macroscale. An accompanying homogenization is performed after the strain reaches a limit strain. Dirichlet BCs are employed for the accompanying homogenization. Some numerical examples demonstrate the capability of the presented method. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Investigation of stress‐velocity LSFEMs for the incompressible Navier‐Stokes equations
Authors: Nisters Carina , Schwarz Alexander , Schröder Jörg
Published: March 2018

In this contribution three mixed least‐squares finite element methods (LSFEMs) for the incompressible Navier‐Stokes equations are investigated with respect to accuracy and efficiency. The well‐known stress‐velocity‐pressure formulation is the basis for two further div‐grad least‐squares formulations in terms of stresses and velocities (SV). Advantage of the SV formulations is a system with a smaller matrix size due to a reduction of the degrees of freedom. The least‐squares finite element formulations, which are investigated in this contribution, base on the incompressible stationary Navier‐Stokes equations. The first formulation under consideration is the stress‐velocity‐pressure formulation according to [1]. Secondly, an extended stress‐velocity formulation with an additional residual is derived based on the findings in [1] and [5]. The third formulation is a pressure reduced stress‐velocity formulation based on a condensation scheme. Therefore, the pressure is interpolated discontinuously, and eliminated on the discrete level without the need for any matrix inverting. The modified lid‐driven cavity boundary value problem, is investigated for the Reynolds number Re = 1000 for all three formulations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Experimental and asymptotic investigation of a rotary wave in a cylindrical container
Authors: Steinrück Herbert , Maly Anton
Published: March 2018

Rotary gravity waves in a partially filled vertical cylindrical container excited by a rotating disc at the top of the cylinder are investigated. Analytical results for the growth rate of the waves are reported. Moreover, the development of the wave is shown in an experiment. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lamb wave resonance transmission through a system of deep notches in a plate‐like waveguide
Authors: Glushkov Evgeny , Glushkova Natalia , Eremin Artem , Lammering Rolf
Published: March 2018

The results of theoretical and experimental investigation into resonance phenomena accompanying guided wave propagation in a metallic plate with a finite regular system of rectangular deep notches are presented. While the expected intensification of wave blocking by a system of notches comparing to the case of a single defect is confirmed, the resonance transmission at the predicted frequencies within these forming stop bands is also observed. Noticeable motion localization in the waveguide area between the notches at these frequencies is visualized with experimental surface B‐scans. Their patterns coincide with the theoretical predictions obtained on the basis of a semi‐analytical computer model for the notched infinite plate. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generation of surface waves through friction: FEM investigation
Authors: Graf Matthias
Published: March 2018

Sliding friction between two bodies can generate elastic vibration. This study uses a finite‐element model comprising an elastic body sliding against a flat rigid surface with constant coefficient of friction. For the elastic body a structured topography is taken into account. The model shows traveling surface waves, which depend on the asperities of the sliding surface. It can be shown that the surface structure and its inertia are the cause for elastic waves in the contact region. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Existence of minimisers for nonlinear strain‐gradient elastoplasticity with finite or infinite cross‐hardening
Authors: Anguige Keith
Published: March 2018

Consideration is given to the existence of minimisers for a family of variational models of finite‐strain single‐crystal elastoplasticity with infinite cross‐hardening. The non‐convex cross‐hardening condition on the plastic slip necessitates the use of special analytical tools, in particular the combination of the div‐curl Lemma with a slip‐exclusion Lemma of Conti & Ortiz [1], if one wishes to prove existence for physically reasonable parameters. A regularised model with a cross‐hardening matrix is also briefly discussed ‐ existence of minimisers for this model also follows by a div‐curl argument, at least if one goes over to the case of linearised elasticity. Moreover, in this case one can also prove that the regularised model Γ‐converges to the infinite‐cross‐hardening model as the hardening matrix becomes unboundedly large. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrothermal Description of Organic Semiconductor Devices by p(x)‐Laplace Thermistor Models
Authors: Fuhrmann Jürgen , Glitzky Annegret , Liero Matthias
Published: March 2018

We consider a p(x)‐Laplace thermistor model for electrothermal effects in organic semiconductor devices and propose a hybrid finite‐volume/finite‐element scheme which is combined with path‐following methods to find a numerical solution. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Material‐based process‐chain optimization in metal forming
Authors: Morand Lukas , Pagenkopf Jan , Helm Dirk
Published: March 2018

The characteristics of a manufacturing product are influenced by a variety of different factors, such as the material properties of the base product. The prediction of properties that give optimal results in metal forming applications is a complex task but of high interest for the manufacturer. To realize such a prediction scheme, the process chain is split up into individual process steps and for each of them an inverse modeling is required. The specific aim of this work is to present an approach for the inverse problem formulation of a process step and to solve it using methods of machine learning. Moreover, the challenges that often arise due to the ill‐posed nature of inverse problems will be discussed. The main focus is on the crystallographic texture of metals, which strongly affects the deformation behavior during a process step and highly influences the characteristics of the final product. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure‐exploiting polynomial chaos for uncertain optimal control problems with sparse derivative generation
Authors: Bergner Lilli , Kirches Christian
Published: March 2018

We present advances in structure‐exploiting non‐intrusive polynomial chaos methods for the numerical solution of nonlinear optimal control problems with parametric uncertainties. In particular, we make use of the special structure induced by the spectral projection to reuse model derivatives and exploit sparsity information leading to a fast automatic sensitivity generation. This greatly reduces the computational effort of Newton‐type methods for the solution of the resulting high‐dimensional surrogate problem. The results are complemented by a complexity comparison and a numerical case study. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Makroskopische Modelle zur Untersuchung der Dynamik von Schaumstrukturen
Authors: Kancheva Elena Vladimirova , Ams Alfons
Published: March 2018

Die Dynamik offenporiger Schaumstrukturen wird diskutiert. Messungen realer Schaumstrukturen werden mit Computertomographen (CT) durchgeführt und anschließend über Korrelations‐ und Spektralanalyse statistisch ausgewertet. Für weißes Rauschen als Anregung des Modellschaums werden die Zeitlösungen und Autoleistungsdichtespektren berechnet und simuliert. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Comparison of Markov Chain Methods for Reliability Estimation
Authors: Proppe Carsten
Published: March 2018

Two Markov chain Monte Carlo simulation methods for reliability estimation, subset simulation and the moving particles algorithm, are compared based on theoretical arguments and test cases. The differences in the efficiency between both algorithms are rather small. They seem to be well suited for off‐the‐shelf reliability estimations, but with a different setting for the most important parameters (proposal density and initial sample size). (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Hankel‐type norm of a random mass‐spring‐damper system
Authors: Pulch Roland
Published: March 2018

We consider linear dynamical systems including random variables for an uncertainty quantification. A quantity of interest is expanded into a series with orthogonal basis polynomials. We investigate a Hankel‐type norm of a truncated series. An approximation of this norm can be obtained by a quadrature formula, which implies a larger weakly coupled system. We present results of numerical computations using sparse grid quadratures in the case of a mass‐spring‐damper system. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Topology and material orientation optimization based on evolution equations
Authors: Jantos Dustin Roman , Junker Philipp , Hackl Klaus
Published: March 2018

Many modern high‐performance materials have inherent anisotropic elastic properties and its local material orientation can be considered to be an additional design variable for the topology optimization [1–3]. We extend our previous model for topology optimization with variational controlled growth [4–6] for linear elastic anisotropic materials, for which the material orientation is introduced as an additional design variable. We solve the optimization problem purely with the principles of thermodynamics by minimizing the Gibbs energy. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive multiscale methods for elliptic PDEs
Authors: Bauer Maximilian
Published: March 2018

This paper deals with the numerical solution of elliptic partial differential equations with an adaptive multiscale algorithm, which uses symmetric collocation and radial basis functions. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Notes on a novel finite element for anisotropy at large strains
Authors: Viebahn Nils , Schröder Jörg , Wriggers Peter , Balzani Daniel
Published: March 2018

A locking phenomenon can be observed in the case of anisotropic elasticity, due to high stiffness in preferred directions. In this contribution we propose a formulation with the goal to overcome this locking problem. We apply a Simplified Kinematic for the Anisotropic part of the free‐energy by means of a constant approximation of the right Cauchy‐Green tensor. For the tested boundary value problem the SKA‐element performs excellent and behaves extremely robust. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Towards Riccati‐Feedback Control of Complex Flows with Moving Interfaces
Authors: Baran Björn , Benner Peter , Heiland Jan , Saak Jens
Published: March 2018

Problems featuring moving interfaces appear in many applications. They can model solidification and melting of pure materials, crystal growth and other multi‐phase problems. The control of the moving interface enables to, for example, influence production processes and, thus, the product material quality.

We consider the two‐phase Stefan problem that models a solid and a liquid phase separated by the moving interface. In the liquid phase, the heat distribution is characterized by a convection‐diffusion equation. The fluid flow in the liquid phase is described by the Navier–Stokes equations which introduces a differential algebraic structure to the system. The interface movement is coupled with the temperature through the Stefan condition, which adds additional algebraic constraints. Our formulation uses a sharp interface representation and we define a quadratic tracking‐type cost functional as a target of a control input.

We compute an open loop optimal control for the Stefan problem using an adjoint system. For a feedback representation, we linearize the system about the trajectory defined by the open loop control. This results in a linear‐quadratic regulator problem, for which we formulate the differential Riccati equation with time varying coefficients. This Riccati equation defines the corresponding feedback gain.

Further, we present the feedback formulation that takes into account the structure and the differential algebraic components of the problem. Also, we discuss how the complexities that come, for example, with mesh movements, can be handled in a feedback setting. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Parameter estimation with model order reduction and global measurements
Authors: Lukassen Axel Ariaan , Kiehl Martin
Published: March 2018

We present a new method for parameter estimation for elliptic partial differential equations. Parameter estimation requires the evaluation of the partial differential equation for many different parameter sets. Therefore, model order reduction is reasonable. Model order reduction is composed of an offline phase and an online phase. In the offline phase the reduced model is constructed using snapshots. In this paper we use the given measurement as only snapshot. Hence, the computational costs of the offline phase are reduced. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimality Conditions for Switching Operator Differential Equations
Authors: Rüffler Fabian , Hante Falk M.
Published: March 2018

We consider optimal switching of hybrid abstract evolution equations. The framework includes switching semilinear partial differential equations of parabolic or hyperbolic type, discontinuous state resets, switching costs and allows switching of the principle parts of the equations. We present adjoint‐based formulae for the gradient of the cost functional with respect to position and number of switching time points that lead to first order necessary conditions. Moreover, we discuss an alternate‐direction approach for implementing descent methods. As an application we consider optimal open/close‐switching of valves and on/off‐switching control of compressors in a gas network modelled by a graph with simplified euler equations on edges and suitable coupling conditions at nodes. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of Multi‐Parametric Quadratic Programming to Simulation of Deflected Wires in a Wire Saw
Authors: Treyer Daniel , Gaulocher Sebastian , Niederberger Stefan , Rafael Helge , Ams Alfons
Published: March 2018

In the wire sawing process, a silicon brick is fed into a moving wire web, thus deflecting the wires. By considering static deflections only, the wire displacement and the contact forces between wire and brick may be computed by minimizing the potential energy of the wire, which introduces a constrained quadratic optimization problem. In a time‐domain simulation, the continuously changing contour inside the kerf requires the optimization problem to be solved recurringly. This work aims at reducing the optimization‐related computational effort by applying multi‐parametric quadratic programming. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational integrators for open‐loop and closed‐loop optimal control of mechanical systems
Authors: Flaßkamp Kathrin , Murphey Todd D. , Büskens Christof
Published: March 2018

Mechanical systems have structural properties, e.g. symplecticity, symmetry, and a specific energy behavior, which get lost in standard integration methods. Therefore, symplectic integration methods are used in simulation and control of mechanical systems. This paper combines two methods of the class of structure‐preserving control methods, namely a recently developed feedback control method and open loop optimal control based on variational integrator discretization. The combination is applied to the benchmark example of a cart pendulum system. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An operator based notation of the Lagrange equations for systems with non‐material boundary conditions
Authors: Franze Andreas
Published: March 2018

Problems with non‐material boundary conditions are very important in many applications of continuum mechanics: for example rolling contact, calenders, breaking disks, band saws and belts. This paper deals with the LAGRANGE‐equation for non‐material boundary conditions. Such boundary conditions can be described by non‐material control volumes that cannot be assigned for one and only one set of particles over time.

To define these volumes, a fictitious body is used. Within the scope of this paper several configurations are introduced for the definition of the location of the original and fictitious particles. With the help of the used operator notation it is possible to demonstrate a consistent representation of derivative operators and assign operators as well as entities to their configurations.

On this basis, the LAGRANGE‐equation is derived for material and non‐material control volumes in the EULERIAN and LAGRANGIAN representation. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling a heavy rope using redundant coordinates
Authors: Gerbet Daniel , Rudolph Joachim
Published: March 2018

A generalized Lagrange formalism using redundant coordinates can be applied to systems with distributed parameters. This is illustrated through an example of a heavy rope. The resulting mathematical model for the rope in three‐dimensional space is singularity‐free, at the expense of redundant coordinates constrained by nonlinear equations. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of a running gear with IRWs on curved tracks for a robust control development
Authors: Grether Gustav
Published: March 2018

As a major task of the DLR‐internal project “Next Generation Train”, robust state feedback control with gain scheduling was sucessfully applied to guide the experimental running gear with independently rotating wheels (IRWs) at a 1:5 scaled roller rig, see [1]. However, the adaptation of the control structure to the 1:1 multibody model requires to additionally consider the properties of curved tracks. For that reason, an analytical model of a running gear with IRWs is deduced using Euler‐Lagrange‐equations and taking superelevation and track curvature into account. Furthermore, the complexity of the system is reduced to allow for a robust feedback control synthesis and feed‐forward control including model inversion. Finally, the model is discussed and a first approach for a feed‐forward control in transition curves is shown. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy‐optimal swing‐up of an electromechanically actuated pendulum
Authors: Kern Dominik , Groß Michael
Published: March 2018

A control strategy for swinging up a planar pendulum, from its hanging to its upright position, is presented. Its hinge is actuated by a DC‐motor. In contrast to frequently used models of torque control, the DC‐motor is included as RLC circuits of stator and armature in this paper. The armature voltage is used as input signal, while the stator current is fixed. By passing the horizontal position there is a local loss of controllability, as the motor torque vanishes there. Hamilton's principle is applied and discretized by a variational integrator (VI) in order to compute the optimal feed‐forward control. Thus, the resulting optimal control problem is transferred into a finite‐dimensional optimization problem, and solved by sequential quadratic programming (SQP) methods. The cost function to be minimized is the consumed electrical energy needed to swing up the pendulum in fixed time. In addition to the feed‐forward control (offline), feed‐back control (online) is added in order to stabilize the swing‐up and the upright position. This feedback‐controller is designed as linear‐quadratic regulator (LQR) for the linearization around the nominal trajectory. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear Pressure Control of a Switched Hydraulic System
Authors: Schröders Simon , Fidlin Alexander
Published: March 2018

Hydraulic power transmission is often used in a variety of technical applications. Due to the nonlinear and often non smooth behaviour of some hydraulic components concerning their volume flow characteristics, the development of control strategies for hydraulic systems is challenging. Most developed control strategies base on linearized models, allowing only local operation in the environment of certain operating points. In this contribution, a nonlinear control strategy, based on the feedback linearization technique, allowing a global compensation of the nonlinearities [2], is developed for a minimal hydraulic circuit consisting of a pressure regulation valve, a vane pump and an ideal consumer. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Impact of Quantisation on Consistency of DMPC in Street Traffic with Dynamic Priority Rules
Authors: Sprodowski Tobias , Pannek Jürgen
Published: March 2018

Distributed systems typically require communication to steer the overall system to a reference or target state and keep it there. We consider an intersection scenario as a spacial set with vehicles as multi‐agents with individual initial and target conditions. Utilising a Distributed Model Predictive Control scheme (DMPC), in every time step each vehicle solves an finite horizon optimal control problem. The resulting optimal state trajectory is projected onto a quantisation of the spatial set and the quantised trajectories are broadcasted to the other vehicles to ensure collision avoidance. The quantisation is mainly motivated to reduce the necessary communication effort among the agents. Here, we introduce prediction coherence as difference of two predictions in two successive time steps. We numerically explore the idea to utilise prediction coherence to derive a lower bound for the communication requirements among the vehicles. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Image Compression with the Region Based Easy Path Wavelet Transform
Authors: Budinich Renato
Published: March 2018

We review the Region Based Easy Path Wavelet Transform method in the context of image compression and how it can be used to encode a Region of Interest in the image with higher quality than the complementary region. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fast Low‐Rank Empirical Cross Gramians
Authors: Himpe Christian , Leibner Tobias , Rave Stephan , Saak Jens
Published: March 2018

The cross Gramian matrix encodes the input‐output coherence of linear control systems and is used in projection‐based model reduction. The empirical cross Gramian is a data‐driven variant of the cross Gramian which also extends to nonlinear systems. A drawback of the empirical cross Gramian for large‐scale systems is its full order and dense structure; yet, it may be computed column‐wise. Using the hierarchical approximate proper orthogonal decomposition (HAPOD), this partial computability can be exploited to obtain a truncated projection for model order reduction without assembling a full cross Gramian. (© 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exome sequencing reveals the genetic landscape and frequent inactivation of PCDHB3 in Chinese rectal cancers
Authors: Ye Wen , Ling Shaoping , Liu Ran‐Yi , Pan Zhi‐Zhong , Wang Gaoyuan , Gao Shijuan , Wu Jiangxue , Cao Lihua , Dong Lili , Li Yingchang , Zhou Yi , Du Wuying , Meng Xiangqi , Chen Jinna , Guan Xinyuan , He Yulong , Pan Changchuan , Zheng XF Steven , Lu Xuemei , Chen Shuai , Huang Wenlin
Published: March 2018

Colorectal cancer (CRC) is the third most common cancer worldwide, with more than 1.3 million new cases and 690 000 deaths each year. In China, the incidence of CRC has increased dramatically due to dietary and lifestyle changes, to become the fifth leading cause of cancer‐related death. Here, we performed whole‐exome sequencing in 50 rectal cancer cases among the Chinese population as part of the International Cancer Genome Consortium research project. Frequently mutated genes and enriched pathways were identified. Moreover, a previously unreported gene, PCDHB3, was found frequently mutated in 5.19% cases. Additionally, PCDHB3 expression was found decreased in 81.6% of CRC tissues and all eight CRC cell lines tested. Low expression and cytoplasmic localization of PCDHB3 predict poor prognosis in advanced CRC. Copy number decrease and/or CpG island hypermethylation contributes to the pervasive decreased expression of PCDHB3. PCDHB3 inhibits CRC cell proliferation, migration, and epithelial–mesenchymal transition. The tumor‐suppressive effects of PCDHB3 are partially due to inhibition of NF‐κB transcriptional activity through K63 deubiquitination of p50 at lysine 244/252, which increases the binding affinity of inactive p50 homodimer to κB DNA, resulting in competitive inhibition of the transcription of NF‐κB target genes by p65 dimers. Our study identified PCDHB3 as a novel tumor suppressor in CRC via inhibition of the NF‐κB pathway, and its expression and localization may serve as prognostic markers for advanced CRC. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
Interaction of cationic antimicrobial peptides from Australian frogs with lipid membranes
Authors: Zhu Shiying , Sani Marc‐Antoine , Separovic Frances
Published: March 2018

Cationic antimicrobial peptides (AMPs) from Australian frogs have been extensively studied as alternatives to traditional antibiotics. Solid‐state NMR is used to characterize their effect on lipid bilayers, which are the primary target, but correlation with in vivo situations is tentative in view of the complex effects of changes in sample conditions (such as pH, temperature, lipid composition or peptide concentration). We have used 31P and 2H solid‐state NMR and a range of biophysical techniques to study the impact of the AMPs, maculatin 1.1, caerin 1.1, aurein 1.2, kalata B1, and Chex‐Arg20, on membranes that mimic those of E. coli and S. aureus bacteria and red blood cell membranes. Overall, the length of AMPs affects peptide‐membrane interaction but also their conformations are important. While lipid composition plays a critical role in modulating AMP structure and function, electrostatic interactions are not sufficient to explain their specific activity and interactions with other membrane components need to be considered. Although in an early stage of development, in‐cell NMR of labelled peptides in live bacteria, rather than model membrane studies, may provide new insights into bactericidal mechanisms of AMPs.
Herbicide resistance evolution can be tamed by diversity in irrigated Australian cotton: a multi‐species, multi‐herbicide modelling approach
Authors: Thornby David , Werth Jeff , Hereward James , Keenan Michelle , Chauhan Bhagirath S
Published: March 2018

BACKGROUND

Because herbicide resistance evolves in very large populations over periods of many years, modelling is an important tool for investigating the dynamics of the problem. The Diversity model tracks the simultaneous evolution of resistance to multiple herbicides, using multiple genetic pathways, in several weed species at once. Tracking multiple species and simultaneous resistances is an important development in resistance modelling. We used the Diversity model to test weed management strategies for new cropping cotton varieties with multiple herbicide tolerances (‘triple‐stacked’ varieties), in an Australian context.

RESULTS

The diversity required for long‐term control of three key weeds in Australian cotton goes beyond using three herbicides, especially where there is already a substantial background of existing resistance to one or more of these herbicides. Assuming some glyphosate resistance is already present, simulations showed that glyphosate‐resistant summer grass populations reach 20 000 seeds m−2 within 12 years using the triple‐stack herbicides (glyphosate, glufosinate and dicamba) and a minimum of other tactics. Adding three pre‐emergent modes of action plus cultivation to the system effectively controls glyphosate‐resistant grasses for over 30 years. In conditions where resistance genes are as frequent as 1 in 100, however, highly fecund weeds such as Conyza bonariensis are hard to control beyond 15 years even with very highly diverse management.

CONCLUSIONS

Stacked herbicide tolerances in new crop varieties offers potential for increased herbicide diversity, but existing glyphosate‐resistant weed populations need substantial extra management beyond what a glyphosate/glufosinate/dicamba resistance stack provides. More diverse systems can provide robust management over 30 years in the absence of very high levels of background resistance to other herbicides. © 2018 Society of Chemical Industry
High‐Performance Solution‐Processed IGZO Thin‐Film Transistors with Al2O3/BN Composite Dielectrics Fabricated at Low Temperature
Authors: Yu Byoung‐Soo , Ha Tae‐Jun
Published: March 2018

Recently, solution‐process technologies have attracted significant amounts of attention with regard to fabrication costs, and capable of large‐area deposition for various electronic devices and circuitry. In particular, solution‐processed composite dielectrics have been thoroughly investigated in an effort to improve device performance of thin‐film transistors (TFTs). Here, solution‐processed indium‐gallium‐zinc‐oxide (IGZO) TFTs with solution‐processed aluminum oxide (Al2O3) and boron nitride (BN) composite films are reported which can be fabricated at low temperature. By optimizing the process conditions of Al2O3/BN composite dielectrics, the field‐effect mobility of an IGZO TFT is increased by a factor of 3, relative to that of pristine Al2O3 dielectrics. This is a result of the improved dielectric characteristics of solution‐processed Al2O3 films owing to the reduced density of the defect states. Characterization using transmittance, X‐ray photoelectron spectroscopy and direct‐current electrical measurements conclusively demonstrate that IGZO‐TFTs fabricated with energy electronically excited by microwave absorption exhibit competitive device performance with those fabricated with energy thermally activated by thermal heating at 400 °C.
A nestable, multigrid‐friendly grid on a sphere for global spectral models based on Clenshaw–Curtis quadrature
Authors: Hotta Daisuke , Ujiie Masashi
Published: March 2018

A new grid system on a sphere is proposed which allows for straightforward implementation of both spherical‐harmonics‐based spectral methods and gridpoint‐based multigrid methods. The latitudinal gridpoints in the new grid are equidistant and spectral transforms in the latitudinal direction are performed using Clenshaw–Curtis quadrature. The spectral transforms with this new grid and quadrature are shown to be exact within machine precision provided that the grid truncation is such that there are at least 2N + 1 latitudinal gridpoints for the total truncation wavenumber of N. The new grid and quadrature is implemented and tested on a shallow‐water equations model and the hydrostatic dry dynamical core of the global NWP model JMA‐GSM. The integration results obtained with the new quadrature are shown to be almost identical to those obtained with the conventional Gaussian quadrature on a Gaussian grid. Only minor code changes are required to adapt any Gaussian‐based spectral models to employ the proposed quadrature.