bluuebunny/crossref_metadata_2025_split huggingface dataset:
Direct numerical simulation of transition in MHD duct flow
Authors: Krasnov Dmitry , Zikanov Oleg , Thess André , Boeck Thomas 
Published: December 2011

AbstractTransition in the flow of electrically conducting fluid in a square duct with insulating walls is studied by direct numerical simulations. A uniform magnetic field is applied in the transverse direction. Moderate values of the Reynolds (Re = 5000) and Hartmann (Ha = 0 … 30) numbers are considered that correspond to the classical Hartmann & Lazarus [1] experiments. It is shown that the laminarization begins in the Hartmann layers, whereas the sidewall layers remain turbulent. Complete re‐laminarization occurs in the range of R = Re/Ha ≈︁ 220, which is in agreement with the H. & L. experiments. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the analysis of an electronic model for solar cells including energy resolved defect densities
Authors: Glitzky Annegret 
Published: December 2011

AbstractIn this paper we study analytic properties of electronic models for solar cells, which take into account varying, energy resolved densities of defects. We establish energy estimates and the boundedness of weak solutions and give an existence and uniqueness result for weak solutions to the model equations in two space dimensions. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Derivation of effective interface conditions for reaction‐diffusion equations
Authors: Liero Matthias 
Published: December 2011

AbstractWe address the derivation of effective interface conditions for reaction‐diffusion systems. The considered system is defined in a domain containing a thin layer that shrinks to the interface when its thickness ε tends to zero. The evolution of the system can be written in the form of an energy balance involving an energy and a dissipation functional. Using the Mosco convergence of the dual of the dissipation functional for ε → 0 it is possible to do a limit passage in the energy balance and obtain a limit system that describes the evolution on the interface. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence of the fixed pivot technique for continuous Smoluchowski coagulation equation
Authors: Giri Ankik Kumar , Hausenblas Erika 
Published: December 2011

AbstractIn this work, the fixed pivot technique (FPT) [2] is analyzed for nonlinear continuous Smoluchowski coagulation equation on four different types of grids. More importantly, the FPT gives the accuracy of second order for uniform and geometric grids while it reduces the order of accuracy by one on a locally uniform grid. At the end, the scheme is unfortunately zero order accurate on random grids. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A Deterministic Filter for non‐Gaussian State Estimation
Authors: Pajonk Oliver , Rosić Bojana V. , Litvinenko Alexander , Matthies Hermann G. 
Published: December 2011

AbstractThe usual mathematical method to represent uncertain quantities, for example the state of a dynamical system with uncertain initial conditions, are random variables (RVs). In many problems the space of elementary events Ω, on which the RVs are defined as functions of these events, is not concretely accessible, so that the usual idea of a function (e.g. given as a formula) loses much of its meaning. The representation of RVs is therefore often strikingly different from what is used for “normal” functions. With the help of RVs one can formulate Bayesian estimators for the uncertain quantity when additional information (usually noisy, incomplete measurements) becomes available. A common way to derive such an estimator is to use an instance of the projection theorem for Hilbert spaces.In this work we present a linear Bayesian estimation method which results from using a recently popular representation of an RV, the polynomial chaos expansion (PCE), also known as “white noise analysis”. The resulting method is completely deterministic, as well as computationally efficient. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimization of Optimal Power Flow Problems
Authors: Brune Maria , Castaing Laure , Walther Andrea 
Published: December 2011

AbstractOptimal power flow problems arise in the context of the optimization and secure exploitation of electrical power in alternating current (AC) networks. This optimization problem evaluates the flow on each line and to ensure that they are under line thermal limits. To improve the reliability of the power supply, a secure network is necessary, i.e., it has to be able to cope with some contingencies. Nowadays high performance solution methods, that are based on nonlinear programming algorithms, search for an optimal state while considering certain contingencies. According to the number of contingencies the problem size increases linearly. As the base case can already be large‐scaled, the optimization time computation increases quickly. Parallelization seems to be a good way to solve quickly this kind of problem. This paper considers the minimization of an objective function and at least two constraints at each node. This optimization problem is solved by IPOPT, an interior point method, coupled with ADOL‐C, an algorithmic differentiation tool, and MA27, a linear solver. Several results on employed parallelizing strategies will be discussed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical Methods for Parameter Estimation Using Krylov‐Type Techniques
Authors: Kriwet Gregor , Kostina Ekaterina 
Published: December 2011

AbstractIn the paper we consider constrained nonlinear parameter estimation problems. The method of choice to solve such problems is the generalized Gauss‐Newton method. At each iteration of the Gauss‐Newton we solve the linearized parameter estimation problem and compute covariance matrix, necessary for the error assessment of the estimates, using an iterative linear algebra technique, namely LSQR algorithm. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control of hydrothermal waves in a thermocapillary flow using a gradient‐based control strategy
Authors: Muldoon Frank , Kuhlmann Hendrik 
Published: December 2011

AbstractThe problem of controlling the hydrothermal waves in a thermocapillary flow is addressed using a gradient based control strategy. The control is a spatially and temporally varying heat flux boundary condition at the free surface. The control which minimizes the hydrothermal waves is found using a conjugate gradient method, where the gradient of the objective function with respect to the control variables is obtained from solving a set of adjoint equations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solution of inverse problems to detect permissible design spaces
Authors: Pannier Stephan , Grossenbacher Kathrin , Liebscher Martin , Graf Wolfgang , Kaliske Michael 
Published: December 2011

AbstractIn many engineering applications, a structural design is determined by way of a multi‐stage design process. Thereby, the information of previous simulations, e.g. sensitivity analysis, should be used for further investigations. In special, the aim is to improve the reliability as early as possible. Therefore, an approach is presented to determine alternative permissible design spaces on the basis of arbitrary point sets. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Two‐sided harmonic subspace extractions for the generalized eigenvalue problem
Authors: Benner Peter , Hochstenbach Michiel , Kürschner Patrick 
Published: December 2011

AbstractOne crucial step of the solution of large‐scale generalized eigenvalue problems with iterative subspace methods, e.g. Arnoldi, Jacobi‐Davidson, is a projection of the original large‐scale problem onto a low dimensional subspaces. Here we investigate two‐sided methods, where approximate eigenvalues together with their right and left eigenvectors of the full‐size problem are extracted from the resulting small eigenproblem. The two‐sided Ritz‐Galerkin projection can be seen as the most basic form of this approach. It usually provides a good convergence towards the extremal eigenvalues of the spectrum. For improving the convergence towards interior eigenvalues, we investigate two approaches based on harmonic subspace extractions for the generalized eigenvalue problem. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The FEAST algorithm for large eigenvalue problems
Authors: Galgon Martin , Krämer Lukas , Lang Bruno 
Published: December 2011

AbstractWe consider the eigensolver named FEAST that was introduced by Polizzi in 2009 [1]. This solver, tailored to the (partial) solution of large sparse (generalized) eigenproblems offers good potential for parallelism and showed good robustness in our experiments. We briefly introduce the algorithm, point out some problems and give two examples. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the Computation of Particular Eigenvectors of Hamiltonian Matrix Pencils
Authors: Benner Peter , Voigt Matthias 
Published: December 2011

AbstractWe discuss a structure‐preserving algorithm for the accurate solution of generalized eigenvalue problems for skew‐Hamiltonian/Hamiltonian matrix pencils λN − ℋ. By embedding the matrix pencil λ𝒩 − ℋ into a skew‐Hamiltonian/Hamiltonian matrix pencil of double size it is possible to avoid the problem of non‐existence of a structured Schur form. For these embedded matrix pencils we can compute a particular condensed form to accurately compute the simple, finite, purely imaginary eigenvalues of λ𝒩 − ℋ. In this paper we describe a new method to compute also the corresponding eigenvectors by using the information contained in the condensed form of the embedded matrix pencils and associated transformation matrices. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive coupling of FEM and BEM: Simple error estimators and convergence
Authors: Aurada Markus , Feischl Michael , Karkulik Michael , Praetorius Dirk 
Published: December 2011

AbstractA posteriori error estimators and adaptive mesh‐refinement have themselves proven to be important tools for scientific computing. For error control in finite element methods (FEM), there is a broad variety of a posteriori error estimators available, and convergence as well as optimality of adaptive FEM is well‐studied in the literature. This is, however, in sharp contrast to the boundary element method (BEM) and to the coupling of FEM and BEM. In our contribution, we present an easy‐to‐implement error estimator for some FEM‐BEM coupling which, to the best of our knowledge, has not been proposed in the literature before. The derived mesh‐refining algorithm provides the first adaptive coupling procedure which is mathematically proven to converge. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical investigation of nanoindentation of viscoelastic polymer layers and parameters re‐identification
Authors: Chen Zhaoyu , Diebels Stefan 
Published: December 2011

AbstractIn the present contribution, we focus on the numerical investigation of nanoindentation of viscoelastic polymer layers using the finite element code ABAQUS®. The time‐dependent behaviour of the viscoelastic layer is modeled with Boltzman hereditary integration based on Prony series. The normal contact between the rigid indenter and the deformable layer are treated numerically as a unilateral non‐penetration constraint problem. The computer‐based numerical optimisation routine is treated by employing the Matrix Laboratory MATLAB® combined with ABAQUS®. The stochastic strategy is used based on principles of biological evolution, i. e. an evolution strategy. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational integrators for electric circuits
Authors: Ober‐Blöbaum Sina , Tao Molei , Owhadi Houman 
Published: December 2011

AbstractVariational integrators are symplectic‐momentum preserving integrators that are based on a discrete variational formulation of the underlying system. So far, variational integrators have been mainly developed and used for a wide variety of mechanical systems. In this work, we develop a variational integrator for the simulation of electric circuits. An appropriate variational formulation is presented to model the circuit from which the equations of motion are derived. Finally, a corresponding time‐discrete variational formulation provides an iteration scheme for the simulation of the electric circuit. In this way, a variational integrator is constructed that gains several advantages. A comparison to standard integration techniques shows that even for simple LCR circuits a better long‐time energy behavior and frequency preservation can be obtained. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sliding Mode Control of a Remotely Operated Underwater Vehicle with Adaptive Fuzzy Dead‐Zone Compensation
Authors: Bessa Wallace M. , Kreuzer Edwin 
Published: December 2011

AbstractDue to the great technological improvement obtained in the last decades, it became possible to use robotic vehicles for underwater exploration. During the execution of a certain task with a remotely operated underwater vehicle, the operator needs to monitor and control a number of parameters. If some of these parameters, as for instance position and attitude, could be controlled automatically, the teleoperation of the vehicle can be enormously facilitated. Based on experimental tests, it was verified that marine thrusters can exhibit dead‐zone nonlinearities. This work describes the development of a variable structure control strategy for an underwater vehicle with a thrust system subject to dead‐zone input. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State Reconstruction in Higher Dimensional PDEs with Spatially Varying Parameters
Authors: Jadachowski Lukas , Meurer Thomas , Kugi Andreas 
Published: December 2011

AbstractThe state estimation problem is considered for a diffusion‐reaction system with spatially varying parameters defined on a 3‐dimensional rectangular domain with the measured output being restricted to a single surface. For this, a backstepping‐based observer design is applied, which enables to obtain the observer gains such that the observer error dynamics decays exponentially in the L2‐norm. At first, an idealized system output restricted to a single surface is assumed as an available measurement. Secondly, in view of a practical realization of the proposed observer, the idealized system output is reconstructed from a set of finite‐dimensional measurements. The observer error convergence and the applicability of the proposed approach are evaluated by means of numerical simulations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model Order Reduction and Error Estimation for the Parameter‐Dependent Eddy Current Equation
Authors: Jung Nadine 
Published: December 2011

AbstractIn design optimization many simulations are performed of the same physical phenomena. Using model order reduction methods these physical phenomena can be efficiently computed for various geometries, but there is an error compared to the full order solution. This error is estimated by error estimators in different norms. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Invariance Entropy
Authors: Kawan Christoph 
Published: December 2011

AbstractIn this paper, the concept of invariance entropy for continuous‐time control systems is introduced. This quantity measures the minimal data rate necessary to render a compact subset of the state space invariant by a coder‐controller device. Invariance entropy is an intrinsic quantity of the open‐loop system and shares several properties with the classical entropy quantities in the field of dynamical systems. Some of these properties, in particular relations to Lyapunov exponents, are pointed out. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Integrated design and optimization of a complex nonlinear hybrid electric powertrain including simulations in time domain
Authors: Marx Matthias , Sacher Oliver , Söffker Dirk 
Published: December 2011

AbstractThis paper deals with the design and optimization of hybrid electric powertrains. Therefore basic relations of the behavior of hybrid electric powertrain systems and the controller design are introduced. Based on models of typical hybrid electric system components principal optimization approaches with respect to performance parameters like efficiency, availability, lifetime, etc. are shown. Hereby an optimization algorithm based on a global optimization technique is applied. Using the example of a fuel cell based hybrid electric powertrain system the approaches are introduced and compared to each using time‐domain simulations integrated in optimization algorithms. The results show that both approaches are appropriate to design the system as well as the controllers. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Feedforward Control for a Non‐Uniform Euler‐Bernoulli Beam
Authors: Meurer Thomas , Schröck Johannes , Kugi Andreas 
Published: December 2011

AbstractFlatness‐based motion planning is considered for an Euler‐Bernoulli beam with viscous damping by introducing a systematic spectral approach, which is based on the Riesz spectral properties of the system operator. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Frequency compensation for a class of DAE's arising in electrical circuits
Authors: Hennig Eckhard , Krauße Dominik , Schäfer Eric , Sommer Ralf , Trunk Carsten , Winkler Henrik 
Published: December 2011

AbstractStructured perturbations of regular pencils of the form $sE-A,E,A \in {\rm I\!R}^{n\times n},\; s \in {\rm I\!\!\!C}$, are considered which model the addition of a capacitance c in an electrical circuit in order to improve the frequency response. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control Strategy of Hardware‐in‐the‐Loop Simulator EPOS 2.0 for Autonomous Docking Verification
Authors: Zebenay Melak , Lampariello Roberto , Boge Toralf , Krenn Rainer 
Published: December 2011

AbstractThis paper briefly describes the hybrid simulator system called European Proximity Operation Simulator (EPOS 2.0) and the development of the hardware‐in‐the‐loop (HIL) docking simulation concept. A critical requirement for the docking simulation of this HIL simulator is that the 6‐DOF robots in the loop have to exactly mimic the dynamic response of the two satellites during a contact operation. The main challenges to meet this requirement are in the stiffness of the robots, which is unlike that of the satellites, as well as the time delay in the HIL simulator. The paper mainly presents the impedance parameter identification concept for matching the impedance between the satellites impact model and the EPOS robots. Finally it presents the preliminary results and future work. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multivariate Interpolation with Fundamental Splines of Fractional Order
Authors: Forster Brigitte , Massopust Peter 
Published: December 2011

AbstractFractional B‐splines Bσ, σ ≥ 1, are piecewise polynomials of fractional degree that interpolate the classical Schoenberg splines $B_n, n \in {\rm I\!N}$, with respect to the degree. As the Schoenberg splines of order ≥ 3, they in general do not satisfy the interpolation property $B_\sigma(n-k) = \delta_{n,k},n,k \in {\rm Z\!\!Z}$. However, the application of the interpolation filter $1/\sum_{k\in{\rm Z\!\!Z}} \hat{B}_{\sigma}(\omega-2 \pi k)$—if well‐defined—in the frequency domain yields a fundamental spline of fractional order that does satisfy the interpolation property. We extend these result via ridge functions to multivariate fractional B‐splines. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Uncertainties Quantification and Data Compression in numerical Aerodynamics
Authors: Litvinenko Alexander , Matthies Hermann G. 
Published: December 2011

AbstractWe research how uncertainties in the angle of attack, in the Mach number and in the geometry of the airfoil propagate in the solution (pressure, density, velocity etc). To compute different statistical functionals of the solution we build a low‐rank response surface. The building algorithm is working on the fly, is based on the QR‐decomposition, has drastically reduced memory requirements and linear complexity. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic simulation of particle‐filled hollow spheres
Authors: Steinle Tobias , Vrabec Jadran , Walther Andrea 
Published: December 2011

AbstractWe are simulating a new lightweight material that could potentially be used in several technical applications, such as machine casings to rapidly damp vibrations, reducing wear and tear. This is achieved by employing embedded hollow spheres that are filled with a granular material, such as a ceramic powder. Energy is dissipated via friction caused by the interaction of particles with each other and with the sphere wall. The present dynamic simulation is based on a leapfrog algorithm, a time integration method used in molecular dynamics. Modifications, such as reflecting boundary conditions, are introduced to adapt the scheme to the field of granular materials. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Linear fractional transformations of Stieltjes functions
Authors: Behrndt Jussi , Hassi Seppo , de Snoo Henk , Wietsma Rudi , Winkler Henrik 
Published: December 2011

AbstractLinear fractional transformations of Stieltjes (and inverse Stieljes) functions, which appear naturally in the extension theory of nonnegative symmetric operators with defect one in Hilbert spaces, are investigated. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear process machine interaction in tool grinding
Authors: de Payrebrune Kristin M. , Kröger Matthias 
Published: December 2011

AbstractThe manufacturing of high performance cutting tools, like drills and chamfers, is done by a deep grinding process. This tool grinding process shows nonlinear relations between predefined process parameters, as cutting depth, feed speed and cutting speed, and the process characteristics, as process forces, surface properties and stability. Within an interdisciplinary research project a process model is built up to represent the process machine interaction and to predict process forces, deformation of the workpiece and geometry errors caused by this deformation. In this paper, the process model and the coupling of the included submodules will be described. The focus is thereby on the explanation of the contact module and the implementation in the dynamical model. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational mechanics‐based modeling of size‐dependent hardening in polycrystals
Authors: Bargmann Swantje , Ekh Magnus 
Published: December 2011

AbstractIt has been well‐known for a number of years that the macroscopic material response of polycrystalline metals is influenced by the size and morphology of grains. Different size effects may occur, one of which is the Hall‐Petch effect. The key aim of this contribution is the computational modeling of grain‐size‐dependent hardening in polycrystals using a microstructural approach. Here, the focus is on the influence of the microscopic grain boundary conditions on the simulation results. In particular, micro‐flexible boundary conditions are discussed and compared to micro‐hard and micro‐free assumptions. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)