bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stability of stationary states of a quantum energy transport model for semiconductors
Authors: Röhrig Elisa , Pinnau René 
Published: December 2011

AbstractDue to the ongoing miniaturization of devices quantum effects are no longer negligible in semiconductor modeling. Also temperature effects play a role for example when identifying hot spots in devices. QET models, which can be derived via moment method from the Wigner‐BKG model, include both physical features. We analyze the stability of stationary states. Suitable numerical methods and computational results are presented. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational formulations in continuum mechanics
Authors: Scholle Markus 
Published: December 2011

AbstractVariational formulations of the governing equations are of great interest in continuum mechanics: on the one hand a deeper theoretical insight in the respective system is possible, on the other hand variational formulations give rise for the development of semi‐analytical and numerical methods like Ritz' direct method, especially FEM.Despite these benefits, there are many problems in continuum mechanics for which a variational principle is not available. The reason for this is that in contrast to conservative Newtonian mechanics, where the Lagrangian is given as difference between kinetic and potential energy, no generally valid construction rule for the Lagrangian has been established in the past.In this paper a construction rule is developed, on the Galilei‐invariance of the system, leading to a general scheme for Lagrangians the individual analytical form of which is determined by an inverse treatment of Noether's theorem. This procedure is demonstrated for an elastically deforming body. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Short‐Term Prediction of the Sea State Dynamics
Authors: Chabchoub Amin , Hoffmann Norbert P. 
Published: December 2011

AbstractForecasting of the sea level plays a key role to control on‐ and offshore facilities. First, we start with a determinstic time series method based on the state space embedding to determine the vector field of the nonlinear dynamical system and deduce the solution of its corresponding high‐order differential equation. Second, We assume that the sea state is a stochastic process governed by a deterministic part and by noise so that this dynamical system can be modelled by the Langevin equation. We extract the nonlinear dynamical system considering fluctuations directly from a measured time series by estimating the drift vector and the diffusion matrix of the Fokker‐Planck equation. In order to determine the prediction accuracy, the numerical solutions of the deterministic model and the Langevin equation are compared to the data values at future time. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Set‐valued processes induced by parameterised stochastic differential equations with an application to Tuned Mass Dampers
Authors: Schmelzer Bernhard , Oberguggenberger Michael , Adam Christoph 
Published: December 2011

AbstractIn this paper ordinary stochastic differential equations whose coefficients depend on uncertain parameters are considered. An approach is presented how to combine both types of uncertainty (stochastic excitation and parameter uncertainty) leading to set‐valued stochastic processes. The latter serve as a robust representation of solutions of the underlying stochastic differential equations. The mathematical concept is applied to a problem from earthquake engineering, where it is shown how the efficiency of Tuned Mass Dampers can be realistically assessed in the presence of uncertainty. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Isogeometric structural shape optimization using a fictitious energy regularization
Authors: Friederich Jan , Scherer Michael , Steinmann Paul 
Published: December 2011

AbstractIn isogeometric analysis, NURBS basis functions are used as shape functions in an isoparametric finite‐element‐type discretization. Among other advantageous features, this approach is able to provide exact and smooth representations of a broad class of computational domains with curved boundaries. Therefore, this discretization method seems to be especially convenient for computational shape optimization, where a smooth and CAD‐like parametrization of the optimal geometry is desired. Choosing boundary control point coordinates of an isogeometric discretization as design variables, an additional design model can be avoided. However, for a higher number of design variables, typical drawbacks like oscillating boundaries as known from early node‐based shape optimization methods appear. To overcome this problem, we propose to use a fictitious energy regularization: the strain energy of a fictitious deformation, which maps the initial to the optimized domain, is employed as a regularizing term in the optimization problem. Moreover, this deformation is used for efficiently moving the dependent nodes within the domain in each step of the optimization process. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shape optimisation analysing the inner structure of sensitivity matrices
Authors: Gerzen Nikolai , Barthold Franz‐Joseph 
Published: December 2011

AbstractThis contribution deals with sensitivity analysis in nodal based shape optimisation. Sensitivity analysis is one of the most important parts of a structural optimisation algorithm. The efficiency of the algorithm mainly depends on the obtained sensitivity information. The pseudo load and sensitivity matrices which appear in sensitivity analysis are commonly used to derive and to calculate the gradients and the Hessian matrices of objective functions and of constraints. The aim of this contribution is to show that these matrices contain additional useful information which is not used in structural optimisation until now. We demonstrate the opportunities and capabilities of the new information which are obtained by singular value decomposition (SVD) of the pseudo load and sensitivity matrices and by eigenvalue decomposition of the Hessian matrix. Furthermore, we avoid jagged boundaries in shape optimisation by applying a density filtering technique well‐known in topology optimisation. Numerical examples illustrate the advocated theoretical concept. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Re‐visiting structural optimization of the Ziegler pendulum: singularities and exact optimal solutions
Authors: Kirillov Oleg 
Published: December 2011

AbstractStructural optimization of non‐conservative systems with respect to stability criteria is a research area with important applications in fluid‐structure interactions, friction‐induced instabilities, and civil engineering. In contrast to optimization of conservative systems where rigorously proven optimal solutions in buckling problems have been found, for non‐conservative optimization problems only numerically optimized designs were reported. The proof of optimality in the non‐conservative optimization problems is a mathematical challenge related to multiple eigenvalues, singularities on the stability domain, and non‐convexity of the merit functional. We present a study of the optimal mass distribution in a classical Ziegler's pendulum where local and global extrema can be found explicitly. In particular, for the undamped case, the two maxima of the critical flutter load correspond to a vanishing mass either in a joint or at the free end of the pendulum; in the minimum, the ratio of the masses is equal to the ratio of the stiffness coefficients. The role of the singularities on the stability boundary in the optimization is highlighted and extension to the damped case as well as to the case of higher degrees of freedom is discussed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multiobjective optimization with expensive objectives applied to a thermodynamic material design problem
Authors: Pieper Martin 
Published: December 2011

AbstractIn many technical optimization problems, simulations of physical processes determine the objective function. Usually the runtime for these simulations is larger than a few minutes. Therefore a coupling with favorable optimization algorithms is not practicable. A promising solution is to work with different, simplified physical models, with reduced simulation time. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A structural optimization approach for passanger car tires with consideration of uncertainties
Authors: Serafinska Aleksandra , Graf Wolfgang , Kaliske Michael 
Published: December 2011

AbstractIn order to support the design process of passenger car tires, a multi‐objective optimization approach based on Finite Element Analysis (FEA) can be utilized. Providing a reliable and high quality design requires the consideration of data uncertainty within the optimization process. This uncertainty is caused predominantly by instable production conditions of tire components as well as incomplete information concerning e.g. loading. In order to capture the state of information which is indeed available in such engineering applications, an uncertainty model, which enables modelling fragmentary or dubious information as well as mathematical formulation of expert specifications and evaluations has to be applied. The presented requirements are fulfilled by the uncertainty model fuzziness. Therefore, an approach of multi‐objective optimization with consideration of fuzzy quantities was developed. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grid transfer operators for multigrid methods
Authors: Donatelli Marco 
Published: December 2011

AbstractLocal Fourier analysis (LFA) is a classical tool for proving convergence theorems for multigrid methods (MGMs). Analogously, the symbols of the involved matrices are studied to prove convergence results for MGMs for Toeplitz matrices. We show that in the case of elliptic partial differential equations (PDEs) with constant coefficients, the two different approaches lead to an equivalent optimality condition. We argue that the analysis for Toeplitz matrices is an algebraic generalization of the LFA which allows to deal not only with differential problems but also, e.g., with integral problems. A class of grid transfer operators related to the B‐spline's refinement equation is discussed as well. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On optimal step‐length gradient eigensolvers
Authors: Neymeyr Klaus 
Published: December 2011

AbstractGradient iterations for the minimization of the Rayleigh quotient are robust and (with a proper preconditioning) fast iterations to compute approximations of the smallest eigenvalue of a self‐adjoint elliptic partial differential operator. Up to now sharp convergence estimates were only known for the basic fixed‐step size preconditioned gradient iteration (also called preconditioned inverse iteration). Recently sharp convergence estimates have been proved for optimal step size (preconditioned) gradient iterations. These new estimates are compared with previous results. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical simulation of (nearly) incompressible material, using adaptive mixed finite element method
Authors: Balg Martina , Meyer Arnd 
Published: December 2011

AbstractIn this paper we present a way to numerically simulate large deformations of incompressible material and the corresponding hydrostatic pressure by using a mixed, adaptive finite element method (FEM). Starting from the system of differential equations we will derive the weak nonlinear formulation, which can be solved with a Newton's method. In every iteration step this will lead to a saddle point problem. By using Taylor Hood finite elements we will obtain a discrete, indefinite problem, which can be handled with the Bramble Pasciak conjugate gradient method. Finally we give a numerical example. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
hp‐TDG/IPDG for Parabolic Obstacle Problems
Authors: Banz Lothar , Stephan Ernst P. 
Published: December 2011

AbstractWe present a mixed hp‐FE time DG method combined with an interior penalty DG method for parabolic obstacle problems. The discrete Lagragian multiplier set is spanned by basis functions which are biorthogonal to the basis functions of the primal variable. This allows us to write the discrete mixed problem as a problem of finding the root of a strongly semi‐smooth function. In turn, this problem is solved by a locally Q‐quadratic converging semi‐smooth Newton method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Convergence of adaptive FEM for elliptic obstacle problems
Authors: Feischl Michael , Page Marcus , Praetorius Dirk 
Published: December 2011

AbstractWe treat the convergence of adaptive lowest‐order FEM for some elliptic obstacle problem with affine obstacle. For error estimation, we use a residual error estimator which is an extended version of the estimator from [2] and additionally controls the data oscillations. The main result states that an appropriately weighted sum of energy error, edge residuals, and data oscillations satisfies a contraction property that leads to convergence. In addition, we discuss the generalization to the case of inhomogeneous Dirichlet data and non‐affine obstacles χ ∈ H2(Ω) for which similar results are obtained. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Identification of Starshape Constant Conductivity Inclusion from Boundary Measurement
Authors: Garnadi Agah D. 
Published: December 2011

AbstractThe problem of determining the interface separating a starshape support of constant conductivity inclusion from boundary measurement data of a solution of the corresponding PDEs is considered. An equivalent statement as a nonlinear integral equation is obtained. The problem is implemented using Fourier method. Numerical experiment based on simplified iteratively regularized Gauss‐Newton method (sIRGNM) is presented. MSC classes: 31A25, 35R30, 65N21. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled FEM/DG approach for the simulation of cavitating micro foams
Authors: Kopecz Stefan , Meister Andreas , Wünsch Olaf 
Published: December 2011

AbstractWe consider difficulties which arise during our simulations of cavitating micro foams. The compatibility of velocity and transport, satisfaction of a maximum principle and generalization of an incompressible Navier‐Stokes solver. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fully conservative, skew‐symmetric finite difference schemes for compressible flows on distorted grids
Authors: Reiss Julius , Sesterhenn Jörn 
Published: December 2011

AbstractWe present a fully conservative finite difference scheme for the compressible Navier‐Stokes equations. Due to its skew‐symmetry in the momentum equation it is possible to have no physical or artificial damping. Therefore it is especially suited for simulations of configurations where perfect conservation is needed along with low damping. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Lie splitting on polygonal domains
Authors: Ostermann Alexander , Schratz Katharina , Spielberger Georg 
Published: December 2011

AbstractIn this short note, we discuss the convergence properties of splitting methods for the time integration of parabolic evolution equations. Through numerical experiments we show that the Lie splitting method suffers from an order reduction on non‐convex polygonal domains. An in‐depth study of the local error allows us to explain this behavior and to understand the improved convergence properties of a related scheme, the Douglas‐Rachford method. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An optimization of a Mindlin‐Timoshenko beam with a dynamic contact on the boundary
Authors: Bock Igor 
Published: December 2011

AbstractWe deal with the optimal control problem governed by a hyperbolic variational inequality describing the perpendicular vibrations of a Mindlin‐Timoshenko beam clamped on the left end with a rigid obstacle at the right end. A variable thickness of a beam plays the role of a control parameter. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Variational design sensitivity analysis of dual problems with applications to error analysis
Authors: Materna Daniel , Barthold Franz‐Joseph 
Published: December 2011

AbstractDual or adjoint solutions play an important role in many fields which deal with local quantities of interest. This contribution is concerned with a novel approach for the sensitivity of the dual solution itself, i.e. we investigate the change in the dual solution at a deformed configuration of the material body due to changes in the design of the body. We consider a general variational framework and present the application of the proposed approach to the prediction of changes in the quantity of interest as well as error analysis for the truncation error of classical first‐order sensitivity relations. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On ℋ︁2‐model reduction of linear parameter‐varying systems
Authors: Benner Peter , Breiten Tobias 
Published: December 2011

AbstractIn this paper, we will discuss an advantageous relation between a special class of linear parameter‐varying systems and bilinear control systems. This will automatically lead to parameter‐preserving model reduction techniques. Furthermore, we review a recently introduced interpolation‐based ℋ2‐framework for bilinear control systems. By means of a numerical example, the efficiency of the new method will be underlined. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Controllability properties and prediction‐free control of linear systems with incommensurate delays
Authors: Gehring Nicole , Rudolph Joachim , Woittennek Frank 
Published: December 2011

AbstractFor linear delay systems with incommensurate (lumped) delays necessary and sufficient conditions for the freeness of the system over the ring of entire functions in ${\rm I\!\!\!C}(s)[e^{-\tau_1 s},\ldots,e^{-\tau_r s}]$ are given. In contrast to the commensurate case the ring does not have the Bézout property. Therefore, additional criteria are needed involving also special properties of pure delay systems. Based on these results a prediction‐free flatness‐based control is designed for a system of two vibrating strings with a point mass and single boundary input. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Trajectory Planning for a Non‐Flat Mechanical System Using Time‐Reversal Symmetry
Authors: Knoll Carsten , Röbenack Klaus 
Published: December 2011

AbstractSome mechanical systems have a special discrete symmetry property associated with the inversion of the direction of the time flow. This "time‐reversal symmetry" allows one to construct solutions of the equations of motion from other known solutions. In the present contribution we examine to which systems this property can be applied. Furthermore, we demonstrate how it can be used to determine an open loop control for equilibrium point transition by solving a stabilization problem in the negative time direction. As a non‐flat mechanical example the popular pole‐cart system is considered. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Advanced Control Design for Wind Turbines
Authors: Liu Yan , Susilo Martinus , Söffker Dirk 
Published: December 2011

AbstractIn this contribution, the concept of a general design platform for control system of wind turbines is proposed. Different models of wind turbine systems are summarized, a novel control strategy for wind turbine control is proposed as a general platform for control system design. Simulation results are presented demonstrating the success of the proposed control method based on one of the chosen models for the design platform. A benchmark model (NREL) is chosen for the platform in order to adjust the control system design. Finally, the design process of control system based on the general platform is given and explained. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Online powermanagement optimization of a fuel cell‐based hybrid electric powertrain
Authors: Marx Matthias , Söffker Dirk 
Published: December 2011

AbstractIn this paper an online optimization approach of the powermanagement of a fuel cell‐based hybrid electric powertrain system is desribed. Therefore two online optimization algorithms of the powermanagement control parameters are introduced and compared experimentally. The first one deals with parameters rating the performance of the system with respect to efficiency, availability, and lifetime. Using a pre‐defined load profile the optimal parameters can be determined for a given powermanagement. The second approach is based on the statistical properties of a predicted and online‐updated measured load profile defining the actual load profile characteristics. Depending on this load profile and with the knowledge of the design parameters of the system appropriate adaptive powermanagement parameters are determined. It becomes clear that the performance of the system with respect to the mentioned system properties can be improved by these approaches. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Model Predictive Control for Heating Ventilating and Air Conditioning Systems
Authors: Rehrl Jakob , Horn Martin 
Published: December 2011

AbstractIn heating ventilating and air conditioning (hvac) systems, model predictive control (mpc) is rarely used up to now. However, the following properties of hvac systems make mpc a well suited control methodology: the plant is a multiple input, multiple output system and its inputs are constrained – both in their value and in their rate of change. Moreover, several disturbances acting on the plant like varying outdoor air temperature or outdoor humidity can be measured. Furthermore, time constants are relatively large which makes it easy to perform the required optimization of the mpc strategy in time. This contribution presents the application of mpc to a real world hvac system. The considered hvac system consists of standard industrial components. The core components of the system are water‐to‐air heat exchangers, both for heating and for cooling purposes as well as a steam humidifier. Hence, air temperature and air humidity can be varied with the help of the investigated hvac system. The derivation of the plant model based on thermodynamic relations is presented as well as the application of the mpc strategy to the real world system. The plant contains some nonlinear elements which have to be dealt with when applying the mpc strategy. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Feedforward Design and Optimality Aspects for the Control of Mechatronic Systems
Authors: Stadlmayr Richard , Gahleitner Reinhard 
Published: December 2011

AbstractThis paper considers the tracking controller design for a mechatronic handling system. The presented approach is based on Port‐Hamiltonian systems and it achieves good tracking as well as good disturbance rejection based on a polynomial approach. A PBC controller stabilizes the trajectory and the feedforward part has to fulfill the given limitations and the time optimality. This approach avoids the solution of a boundary value problem and a real‐time integration of the internal dynamics. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Missing Point Estimation for steady aerodynamic applications
Authors: Vendl Alexander , Faßbender Heike 
Published: December 2011

AbstractModel reduction in aerodynamic applications usually makes use of Proper Orthogonal Decomposition (POD). In this work a POD‐based method, called Missing Point Estimation (MPE), will be applied to steady state flows with variation of the flow parameter angle of attack. The basic idea of MPE is to select a subset of the computational grid points (control volumes) and limit the governing equations to these. Subsequently, the remaining equations are projected onto the POD subspace. This approach has the advantage that the nonlinear right hand side of the governing equations has to be evaluated only for some selected points (control volumes) which makes the MPE faster than classical Galerkin projection. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)