bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration elimination in cable‐stayed footbridges and bridges
Authors: Pakos Wojciech , Wójcicki Zbigniew , Grosel Jacek
Published: August 2008

In this paper, the problems of eliminating vibration in cable stayed footbridges and bridges by dynamically steering the tension in cables during construction vibration are considered. A physical and a mathematical model of cable stayed footbridges and bridges has been formulated. A damping model has been selected on the basis of an analysis of vibrations due to periodic excitation. Standard computer software and the author's own program, both leaning on Finite Element Method (FEM), have been used to analyze the eigenproblem and the forced vibration of bridges. On the basis of the formulated theory an efficient algorithm of forced vibration reduction analysis was established. The reduction is achieved by dynamically steering the tension in cables. A sensitivity analysis has been used. An example has been provided. The theory presented takes into account the new method in the elimination of vibration in cable stayed bridges and footbridges. It can therefore be applied to dynamic analysis of modern cable stayed bridges with typical structure systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of LQR techniques to the adaptive control of quasilinear parabolic PDEs
Authors: Saak Jens , Benner Peter
Published: August 2008

LQR problems for linear parabolic PDEs have been studied in detail in the literature for the past 3 to 4 decades. The solvability of feedback control problems for a large class of problems is well understood. In recent years numerical methods for the approximation of the corresponding Riccati operators have been developed. These methods are able to calculate the feedback operator directly and thus can compute the solutions to linear problems efficiently. Here we study the applicability of such techniques to the control of quasilinear equations via local linearization in an adaptive control setting. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic crack propagation in a 2D elastic body. The out‐of plane case
Authors: Sändig A.‐M. , Lalegname A. , Nicaise S.
Published: August 2008

We discuss the propagation of a running crack under shear waves in a rigorous mathematical way for a simplified model. This model is described by two coupled equations in the actual configuration: a two‐dimensional scalar wave equation in a cracked bounded domain and an ordinary differential equation derived from an energy balance law. The unknowns are the displacement fields u = u (y, t) and the one‐dimensional crack tip trajectory h = h (t). We handle both equations separately, assuming at first that the crack position is known. Existence and uniqueness of strong solutions of the wave equation are studied and the crack‐tip singularities are derived under the assumption that the crack is straight and moves tangentially. Using an energy balance law and the crack tip behaviour of the displacement fields we finally arrive at an ordinary differential equation for h (t), called equation of motion for the crack tip. We demonstrate the crack‐tip motion with corresponding nonuniformly crack speed by numerical simulations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Control and stability analysis of a turbocharged Diesel engine using singular perturbation methods
Authors: Seyrkammer Hannes , Schlacher Kurt
Published: August 2008

The control of the air path of a diesel engine with a variable geometry turbocharger and exhaust gas recirculation can be improved significantly by nonlinear methods. The control objective is to supply an amount of fresh air by the compressor and to achieve a desired pressure in the intake manifold in the neighborhood of an operating point of the engine. The mathematical model of the air path is split into a slow and a fast part. For the proposed controller, asymptotic stability of the closed loop system in the sense of Lyapunov is guaranteed by the use of singular perturbation methods. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On high intensity ultrasound focusing by optimal acoustic lens design
Authors: Veljović Slobodan , Kaltenbacher Barbara
Published: August 2008

Shape optimization of an acoustic lens is considered. The problem comes from the usage of ultrasound in medical treatment of kidney stones. Since it can be assumed that no topology changes take place and only small geometry modifications have to be taken into account, we can work with gradient type optimization methods on a parameterization of the lens shape. For this purpose, the lens is parameterized by cubic splines and as a first step, the linear wave equation with jumping coefficients is used to represent wave propagation through the entire domain consisting of the fluid region (i.e., the human tissue) and the lens region. I.e. our model consists of the equation utt – c2Δu = 0, where the speed of sound c is piecewise constant taking different values inside and outside of the lens. The cost functional is of tracking type to achieve an acoustic pressure distribution that exhibits a point focus at the desired location and has low amplitudes elsewhere. A sensitivity analysis is performed whose results are used in the numerical computations based on gradient methods using adjoint techniques for efficient gradient evaluation. Numerical results are presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Spacecraft insertion on unstable periodic orbits for formation flight applications
Authors: Villac Benjamin F.
Published: August 2008

Recent interest in formation flight near the libration points opens the question of precise spacecraft insertion along a nominal orbit. While current approaches emphasize the station‐keeping and (re)configuration of such formations, we propose a dynamical mechanism for spacecraft insertion and servicing in formation flight based on the concept of stable fibration. Practical considerations due to finite targeting accuracy are briefly considered via a numerical experiment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics of surfactant‐covered drops in linear flows
Authors: Vlahovska Petia M.
Published: August 2008

Surfactants modify interfacial properties and significantly affect drop behavior in flow. We study the dynamics of a drop, which is covered with a monolayer of insoluble surfactant, in linear viscous flows, both unbounded and in the presence of a wall. The effect of viscosity contrast is included. Analytical results in a form of expansions for weak flows and high viscosity drops are developed. Numerical results with three‐dimensional boundary integral simulations are used to explore large deformations. The results show that surfactant generally enhances drop deformation, certainly under small‐deformation conditions. The steady‐state drop shape and surfactant distribution are independent of viscosity contrast in straining flows (e.g. hyperbolic, axisymmetric strain). The drop shape and surfactant distribution are insensitive to viscosity contrast under small deformation conditions for any linear flow; the effect of the rotational component at higher‐order. The theory quantifies the effect of surfactant on drop migration away from a bounding wall as well as the rheology of dilute emulsions. It predicts non‐Newtonian features such as shear thinning viscosity and normal stress. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
State‐constrained optimal control problem with radiation interface conditions
Authors: Meyer Christian , Yousept I.
Published: August 2008

A state‐constrained optimal control problem arising in the context of sublimation crystal growth is considered. The presence of pointwise state‐constraints and nonlocal radiation interface conditions constitutes the major issue of this problem. A regularity result of the state is presented that allows to derive the optimality condition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficient smoothing of Crank‐Nicolson method for pricing barrier options under stochastic volatility
Authors: Yousuf M.
Published: August 2008

Most of the option pricing problems have nonsmooth payoff. In barrier options certain aspects of the option are triggered if the asset price becomes too high or too low. Standard smoothing schemes used to solve problems with nonsmooth payoff do not work well for the barrier option because a discontinuity is introduced in the time domain each time a barrier is applied. An improved smoothing strategy is introduced for smoothing the A ‐stable Cranck‐Nicolson scheme at each time when a barrier is applied. A partial differential equation (PDE) approach is utilized for the evaluation of complex option pricing models under stochastic volatility which brings major mathematical and computational challenges for estimation and stability of the estimates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Simulations of swelling media by weakly fulfilled Dirichlet boundary conditions
Authors: Acartürk Ayhan , Ehlers Wolfgang
Published: August 2008

Charged hydrated porous media, which are found in biomechanics as well as in geomechanics, have the capability to change their volume under varying chemical conditions of the environment. In this contribution, these materials are modelled in the framework of the thermodynamically consistent Theory of Porous Media (TPM).

The underlying model consists of four constituents, a charged solid and an aqueous solution composed of water and the ions of dissolved salt. The solid is modelled by a finite elasticity law accounting for the multiphasic micro structure, whereas the fluid is considered as a viscous Newton ian fluid. One finally ends up with four balance relations, the volume balance of the fluid, the concentration balance of the cations, the momentum balance and the balance of charges of the overall mixture.

The resulting set of partial differential equations is solved within the framework of the FEM. Therefore, the weak forms are derived and the resulting set of equations for the primary variables pore pressure p, cation concentration cm and solid displacement uS is implemented into the FE tool PANDAS. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Grid filter models for large‐eddy simulation
Authors: Bouffanais Roland , Habisreutinger Marc‐A. , Deville Michel O.
Published: August 2008

A new interpretation of approximate deconvolution models (ADM) when used with implicit filtering as a way to approximate the projective grid filter is given. Consequently, a new category of subgrid models, the grid filter models (GFM) is defined. ADM appear as a particular case of GFM since only approximate deconvolution is achieved. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel approach using parallel Kalman filters in time and frequency estimation
Authors: Jarlemark Per , Emardson Ragne
Published: August 2008

In the present information based knowledge society, accurate knowledge of time and frequency plays a fundamental role. For many applications, real time estimates of the clocks time and frequency error are required. We have developed a novel approach for estimating time and frequency errors based on an assembly of clocks of varying quality. By using parallel Kalman filters we utilize all available measurements in the estimation. As these measurements are available with different delays, the Kalman filter produces estimates of different quality. One filtermay produce real‐time estimates while another filter waits for delayed measurements. When new information becomes available, the parallel Kalman filters exchange information in order to keep the state matrices updated with the most recent information. In Kalman filtering, accurate modelling of the measurement system is fundamental. All the contributing clocks, as well as the time transfer methods, are modelled as stochastic processes. By using this methodology and by correctly modelling the contributing clocks, we obtain minimum mean square error estimators (MMSE) of the time and frequency errors of a specific clock at every epoch. In addition, we also determine the uncertainty of each time and frequency error estimate. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Covariance analysis for active vehicle suspensions
Authors: Schiehlen Werner , Fehr Jörg , Jung Kim Yun
Published: August 2008

In this paper the covariance analysis will be extended to active suspension systems with skyhook dampers. The covariance matrix of the entire vehicle system follows from an algebraic equation, the so‐called Ljapunov matrix equation, and no integrations are required. An essential prerequisite of the covariance analysis is a white noise input process. This can always be provided by modelling the random vehicle excitation by means of a shape filter. Performance criteria are presented and appropriate design parameters are found by optimization. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An optimised sparse grid combination technique for eigenproblems
Authors: Garcke Jochen
Published: August 2008

We introduce the optimised sparse grid combination technique for the numerical solution of d ‐dimensional eigenproblems on sparse grids. We present numerical results for the stationary Schrödinger equation in the case of hydrogen. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A parameter‐choice method that exploits residual information
Authors: Hansen Per Christian , Kilmer Misha E.
Published: August 2008

Most algorithms for choosing the regularization parameter in a discrete ill‐posed problem are based on the norm of the residual vector. In this work we propose a different approach that seeks to use all the information available in the residual vector, and we show how to use statistical tools and fast Fourier transforms to extract this information efficiently. This approach leads to a computationally inexpensive parameter‐choice rule based on the normalized cumulative periodogram, which is particularly suited for large‐scale problems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Curvilinear airfoil optimization of extremal drag force in hydro‐aerodynamics
Authors: Lupu Mircea , Scheiber Ernest
Published: August 2008

Direct and inverse boundary value problems are solved and the solution of an optimization problem is obtained analytically in the case of some nonlinear integral functionals. The plane potential flow of an inviscid fluid is considered in the absence of mass forces (Hyp). The flow – unlimited jet – encounters a symmetrical curvilinear obstacle (the Helmholtz scheme).

For inverse problems there are derived singular integral equations and the movement is obtained in the auxiliary canonical half plane. Next, an optimization problem is solved analytically. The design of the optimal airfoil is performed. The drag coefficient and other geometrical parameters are computed in the case of a given distribution of the velocity on the profile. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Shape‐matching and classification using structural descriptors
Authors: Marini Simone
Published: August 2008

Technological improvements related to object acquisition, visualisation and modelling, have caused a considerable growth of the number of 3D models in digital form. Digital 3D models are now available in large databases of shapes, ranging from unstructured repositories, like the web, to specialised catalogues used in engineering and simulation. In this panorama it is clear that methods for the retrieval and automatic classification of 3D content will play a crucial role in the development of efficient applications for the organisation and filtering of 3D data.

In this paper, a methodology based on the coupling of geometric and structural information will be discussed for the global and partial matching of 3D shapes and for their automatic classification. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Direct reconstruction of complex refractive index distribution from boundary measurements
Authors: Nandakumaran A. K. , Varma Hari M. , Mohan Vasu R.
Published: August 2008

We obtain the reconstruction of the refractive index distribution of body based on the intensity and normal derivative of the intensity measurements. The Helmholtz equation is inverted either directly or indirectly through repeated implementation of the forward operator and its adjoint, for recovering the complex refractive index distribution. We do not adopt the procedure of recovery of phase (normally required for complete knowledge distribution). We derive certain sensitivity relations which is used for the easy computation of the Jacobian. Our procedure successfully reconstructs the real and imaginary parts of the complex refractive index from the measurement of the two data types derived from the complex amplitude at the boundary. Our other interest is the reconstruction of the spectroscopic variations of optical absorption coefficients and visco‐elastic properties of a tissue which is extremely useful in diagnostic medicines. The research is on progress and some results are available. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Voltage amplification transfer function analysis of the operational amplifier in the negative capacitance circuits for vibration control with piezoceramics
Authors: Oleskiewicz Robert , Neubauer Marcus , Krzyzynski Tomasz
Published: August 2008

Piezo elements due to their ability of converting mechanical energy into electrical energy and vice versa can be found in numerous mechanical vibration damping and absorbing applications. A desired effect may be customized by an external impedance shunt branch connected to the plates of the piezo element. The negative capacitance connected in serial with the passive shunt significantly improves the damping and absorbing performance of such systems. Negative capacitance circuit is built of an impedance converter realized by the operational amplifier. Since the amplifiers are not the ideal elements, the performance of the proposed systems is limited. This is due to the maximum voltages and currents that the operational amplifiers are able to generate. This effect causes instabilities and limits the operational area of the impedance converter. In the paper, the amplification transfer function of the non‐ideal operational amplifier in the negative impedance converter is studied, and the necessary modification with the additional passive elements is proposed. The influence of the certain imperfections in the design, and its improvements are shown on the system consisting of the 1DOF mechanical oscillator, and a shunted piezo element. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strong tractability of multivariate integration of arbitrary order
Authors: Dick Josef , Pillichshammer Friedrich
Published: August 2008

We show the existence of digitally‐shifted polynomial lattice rules which achieve strong tractability results for Sobolev spaces of arbitrary high smoothness. The convergence rate is shown to be best possible up to a given degree of smoothness of the integrand. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic expansion of highly conductive thin sheets
Authors: Schmidt Kersten , Tordeux Sébastien
Published: August 2008

Sensitive measurement and control equipment are protected from disturbing electromagnetic fields by thin shielding sheets. Alternatively to discretisation of the sheets, the electromagnetic fields are modeled only in the surrounding of the layer taking them into account with the so called Generalised Impedance Boundary Conditions.

We study the shielding effect by means of the model problem of a diffusion equation with additional dissipation in the curved thin sheet. We use the asymptotic expansion techniques to derive a limit problem, when the thickness of the sheet ε tends to zero, as well as the models for contribution to the solution of higher order in ε. These problems are posed in limit area of vanishing ε with condition for the jump of the solution and it's normal derivative, which avoid to mesh the computational domain, even locally, at the scale of ε.

We derive the problems for arbitrary order and show their existence and uniqueness. Numerical experiments for the problems up to second order show the asymptotic convergence of the solution of right order in mean of the thickness parameter ε. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid coupling interface method for elliptic complex interface problems
Authors: Chern I‐Liang , Shu Yu‐Chen
Published: August 2008

We propose a coupling interface method (CIM) under Cartesian grid for solving elliptic complex interface problems in arbitrary d dimensions, where the coefficients, the source terms, and the solutions may be discontinuous or singular across the interfaces. It consists of a first‐order version (CIM1) and a second‐order version (CIM2). In one dimension, this finite difference method at a grid point adjacent to the interface is derived based on piecewise linear (CIM1) or quadratic (CIM2) approximation of the solution and two jump conditions. The method is extended to high dimensions through a dimensionby‐dimension approach. To connect information from each dimension, a coupled equation for the principal derivatives is derived through the jump conditions in each coordinate direction. For CIM2, one‐side interpolation for cross derivatives is need. This coupling approach reduces number of grid point in the finite difference stencil. The hybrid method uses CIM1 or CIM2 adaptly for complex interface. Numerical tests demonstrate that CIM1 and CIM2 are respectively first order and second order in the maximal norm with less error as compared with other methods. In addition, the hybrid CIM can solve complex interface problems in two and three dimensions. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quadrature formulae with multiple nodes and a maximal trigonometric degree of exactness
Authors: Milovanović Gradimir V. , Cvetković Aleksandar S. , Stanić Marija P.
Published: August 2008

In this paper we consider interpolatory quadrature formulae with multiple nodes that have the maximal trigonometric degree of exactness. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis of shear bands in solids by means of computational homogenization
Authors: Stanković L. , Mosler J.
Published: August 2008

A novel fully three–dimensional framework for the numerical analysis of shear bands in solids undergoing large deformations is presented. The effect of micro shear bands on the macroscopic material response is computed by means of a homogenization strategy. More precisely, a strain–driven approach which complies well with displacement–driven finite element formulations is adopted. The proposed implementation is based on periodic boundary conditions for the micro–scale. Details about the implementation of the resulting constraints into a three–dimensional framework are discussed. The shear bands occurring at the micro–scale are modeled by a cohesive zone law, i.e., the tangential component of the traction vector governs the relative shear sliding displacement. This law is embedded into a Strong Discontinuity Approach (SDA). To account for realistic sliding modes, multiple shear bands are allowed to form and propagate in each finite element. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of a mean shear on the spectrum of passive scalar fluctuations
Authors: Celani A. , Cencini M. , Vergassola M. , Villermaux E. , Vincenzi D.
Published: August 2008

The form of the spectrum of passive scalar fluctuations in the inertial–convective range is investigated. In the presence of a mean shear, there exists a critical wave number kc. At wave numbers greater than kc, the mean shear does not influence the spectrum of scalar fluctuations and the Obukhov–Corrsin prediction holds. At wave numbers smaller than kc, the mean shear dominates and the spectrum is less steep. These predictions are based on the study of Lagrangian dynamics of fluid particles and account for the experimental observations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dissipative solitons and their interactions
Authors: Akhmediev N. , Soto‐Crespo J. M. , Grelu Ph.
Published: August 2008

Coupled soliton pairs in nonlinear dissipative systems can exist in various forms. They can be stationary, or they can pulsate periodically, quasi‐periodically or chaotically, as is the case for single solitons. Each type is stable in the sense that a given bound state exists in the same form inde.nitely. Single solitons can be perfectly stable for a given set of parameters. However, this does not mean that a bound state formed from them is either stationary or stable. Moreover, their relations can be highly complicated. Such is the life of dissipative solitons. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Conditional Lagrange derivative and its application
Authors: Béda Peter B. , Béda Gyula
Published: August 2008

Our paper aims to show what to do in material modeling for an inelastic body. The method we use is based on the virtual work σ ′δε and on the variation of some function W with respect to the strain tensor. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic analysis of porous materials: Numerical modeling with a space‐time FEM
Authors: Chen Z. , Steeb H. , Diebels S.
Published: August 2008

In the current work, we investigate the dynamic analysis of a two‐phase porous material using the space‐time discontinuous Galerkin method. The physical model is based on the Theory of Porous Media (TPM). The finite element approximation consists of continuous approximations in space but discontinuous ones in time. The continuity condition between the adjacent time intervals is weakly enforced by the upwind flux treatment. No artificial penalty function is involved. Moreover, the Embedded Velocity Integration technique is applied to reduce the second‐order equation in time into a first order one without introducing an additional constraint. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A sequential Monte Carlo algorithm for solving BSDEs
Authors: Gobet Emmanuel , Labart Céline
Published: August 2008

We present and analyze a numerical algorithm for solving BSDEs based on Picard iterations and on a sequential control variate method. Its convergence is geometric. Moreover, our algorithm provides a regular solution w.r.t. time and space. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modified Landweber tterations in a multilevel setting applied to the determination of nonlinear material parameters in piezoelectricity
Authors: Lahmer Tom
Published: August 2008

An efficient solution of the inverse problem of identifying nonlinear dependencies in hyperbolic systems of PDEs, here piezoelectric material parameter curves, is the aim of this work. The dominant material tensor entries in the coupled field equations which describe the electromechanical interplay are approximated by functions depending on the physical field quantities electric field or mechanical stress. In order to solve this nonlinear and ill‐posed problem of parameter curve identification efficiently, modified Landweber iterations (steepest descent and minimal error) will be studied. A multilevel approach is expedient due to the discretization of the unknown parameter curves and high computational efforts solving the forward problem (transient, nonlinear FEM computations). Theoretical investigations concerning convergence and regularization properties of the methods in a multilevel scenario will be presented, along with numerical results from an example in piezoelectricity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A mathematical approach to biological invasive processes
Authors: Liţcanu Gabriela
Published: August 2008

In this note we deal with a mathematical model arising in biology. The result presented here concerns the asymptotic analysis of one‐dimensional travelling wavefront solutions for this model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A note on the error growth in the numerical integration of periodic orbits
Authors: Calvo M. , Laburta M.P. , Montijano J.I. , Rández L.
Published: August 2008

The aim of this note is to extend the analysis of B. Cano and J. M. Sanz‐Serna [2] on the global error behaviour of general one step methods in the numerical integration of a periodic orbit to the case that such a periodic orbit can be embedded into a family of periodic orbits. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Automatic differentiation for portable process systems models
Authors: Petera Monika
Published: August 2008

The development of complicated mathematical models in process systems engineering requires a lot of human effort. The high development cost of complex models can be reduced by reusing submodels created by other modelers. The exchange of ready‐to‐use components requires a common standardized data format. CapeML is an XML‐based meta language defined for describing equation‐based models in process system engineering. This domain specific language provides a convenient level of abstraction to which auxiliary code transformations can be applied. Automatic differentiation is a semantic transformation of programs that describe mathematical functions. It applies the chain rule of differential calculus and generates a new program that additionally calculates the derivatives of the underlying function. ADiCape is an XSLT‐based tool for automatic augmentation of CapeML models with the derivative information. A platform‐independent CapeML representation of a model together with additional code to calculate derivatives is available in a bundle and can be reused by the engineers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Rate‐dependent incremental variational formulation of ferroelectricity
Authors: Rosato Daniele , Miehe Christian
Published: August 2008

The paper presents continuous and discrete variational formulations for the treatment of the non‐linear response of piezoceramics under electrical loading. The point of departure is a general internal variable formulation that determines the hysteretic response of the material as a generalized standard medium in terms of an energy storage and a rate–dependent dissipation function. Consistent with this type of standard dissipative continua, we develop an incremental variational formulation of the coupled electromechanical boundary value problem. We specify the variational formulation for a setting based on a smooth rate–dependent dissipation function which governs the hysteretic response. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Scaling limits of magnetic forces between two bodies
Authors: Schlömerkemper Anja , Schmidt Bernd
Published: August 2008

We report on a study of the magnetic force between two rigid bodies in the continuum limit starting from atomistic dipoledipole interactions for various micro‐ and macroscopic distance regimes, cf. [A. Schlömerkemper, B. Schmidt, Discrete‐tocontinuum limits of magnetic forces in dependence on the distance between bodies, MPI MIS Preprint 29, 2007]. For bodies that are far apart in atomic units classical formulae for magnetic forces are recovered, while for bodies whose distance is comparable to the atomistic lattice spacing a new term that explicitly depends on the atomistic distance and the underlying crystal lattice structure is obtained. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐Reynolds boundary driven cavity flows in a thin liquid shell
Authors: Sznitman J. , Rösgen T.
Published: August 2008

Low‐Reynolds recirculating cavity flows are traditionally generated from lid‐driven boundary motion at a solid‐fluid interface or result from shear flow over an opening. Such flows are typically described by the equations of creeping motion, where viscous forces are dominant. We illustrate using Particle Image Velocimetry (PIV) an original family of boundary‐driven cavity flows occurring, in contrast to classic configurations, at a liquid‐gas interface: thermally‐induced Marangoni flows in a thin liquid shell generate forced, steady‐state recirculating flows inside the cavity. Forcing relies on viscous mechanisms at the boundary but resulting flow patterns are, however, inviscid. Here, the inviscid equations of fluid motion are not used as an approximation, but rather come as a result from the solution of the creeping motion equations in the region inside the sphere. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A new shallow water model, by asymptotic analysis, with linear dependence on depth
Authors: Rodríguez José M. , Taboada‐Vázquez Raquel
Published: August 2008

In this paper, we study Euler equations in a domain with small depth. With this aim, we introduce a small a‐dimensional parameter ε related to the depth and we use asymptotic analysis to study what happens when ε becomes small. In this way we obtain a shallow water model that considers the possibility of a non‐constant bottom and the horizontal velocity components depend on z if the vorticity is not zero. The new model is able to calculate exactly the solutions to Euler equations that are linear in z, whereas the classic model just obtains the average velocities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Stability of reduced electric arc models
Authors: Torrilhon Manuel
Published: August 2008

An energy equation coupled to the eddy‐current Maxwell equations with nonlinear material coefficients gives a reduced electric arc model with interesting existence and stability behaviour. Applications are arcs in industrial plasma flows. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Learning multiresolution schemes for compression of images
Authors: Yáñez D. F. , Aràndiga F. , Cohen A.
Published: August 2008

We introduce a new type of multiresolution based on the Harten's framework using learning theory. This changes the point of view of the classical multiresolution analysis and it transforms an approximation problem in a learning problem opening great possibilities. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Locomotion based on the control of the shape of magnetic fluid surfaces and of magnetizable media
Authors: Zimmermann K. , Naletova V.A. , Zeidis I. , Turkov V.A. , Böhm V. , Kolev E. , Popp J.
Published: August 2008

The realization of locomotion based on the deformation of a free surface of a magnetic fluid layer in a traveling magnetic field is studied. A plane flow of an incompressible viscous magnetic fluid layer on a horizontal surface in a nonuniform magnetic field and a plane two‐layers flow of incompressible viscous magnetic fluids between two parallel solid planes in a magnetic field is considered. Also the flow of an incompressible viscous magnetic fluid layer on a cylinder in a nonuniform magnetic field is an object of investigation. The deformation and the motion of a body made by a magnetizable polymer in an alternating magnetic field are experimentally studied. The cylindrical body (worm) which is located in a cylindrical tube is analyzed. These effects can be used in designing autonomous mobile robots without a hard cover. Such robots can be employed in clinical practice and biological investigations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exact equations for smoothed Wigner transforms and homogenization of wave propagation
Authors: Athanassoulis A. G. , Politis K. S.
Published: August 2008

The Wigner transform (WT) is a quadratic transform that takes an oscillatory function u (x): ℝn ↦ ℂd to a phase‐space density W (x, k) = W [u ](x, k): ℝ2n ↦ ℂd ×d , resolving it over an additional set of 'wavenumber' variables. The WT and its variations have been heavily used in quantum mechanics, semiconductors, homogenization of wave equations, timefrequency analysis, signal processing, pseudodifferential operators etc.

The WT however has a fundamental difficulty: WTs exhibit artifacts, collectively known as ‘interference terms’, and can be arbitrarily more complicated than the original wavefunction. A very successful, well established way to go around this is using the Wigner measures (WMs), a semiclassical approximation to the WT. We propose a different approach, namely smoothing the WT with an appropriate kernel. Such smoothed WTs (SWTs) have been used with great success in signal processing. They have not been used in the treatment of PDEs, a fundamental obstacle being the lack of exact equations governing their evolution. We present the machinery which allows the coarse‐scale reformulation of a broad class of wave problems in terms of the SWT, along with numerical experiments which clearly show the validity and applicability of the method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetostrictive actuation of a smart beam with hysteretic material behaviour
Authors: Bossong Heiko , Schmidt Rüdiger
Published: August 2008

Magnetostrictive materials can be used as actuators in smart structures technology. The relation between induced strain and the applied magnetic field is nonlinear and shows hysteretic behaviour. Thus the magnetomechanical coupling coefficient is not constant and should be defined as a function of strain or magnetic field in computations.

In this study the hysteresis of a mechanically unconstrained actuator is determined using the Michelson interferometry. The hysteretic behaviour is modelled phenomenologically by a Preisach model. Using these experimental data for the modelling of an active structure with embedded magnetostrictive actuators, the actual coupling coefficient can be determined utilising the Preisach model. With this procedure the actuation strain of an embedded actuator, including the physical nonlinearities, can be calculated using the material characteristics obtained with an unconstrained actuator. For the determination of the actual coupling coefficient a strain‐ and field‐dependent approach is used.

For an experimental validation of the method outlined above, a magnetostrictive actuator is characterised experimentally and then applied to a cantilever aluminium beam. Then, the tip displacement of the actuated beam is measured with a laser triangulation sensor and compared with the numerical results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of internal parametric and kinematic excitation on nonlinear gearbox vibration
Authors: Byrtus Miroslav , Zeman Vladimír
Published: August 2008

This paper deals with mathematical modelling of nonlinear vibration of large rotating shaft systems with gears and rollingelement bearings. Gearing and bearing couplings bring into the system nonlinear phenomena like impact motions due to the possibility of the mesh interruption. The motion of the system is influenced by the internal kinematic excitation in gearing and by the parametric excitation caused by periodic change of number of teeth in gear meshing. The influence of simultaneous internal kinematic and parametric excitation is investigated in dependence on revolutions of the driving shaft of a test‐gearbox. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
BepiColombo gravitational capture and the elliptic restricted three‐body problem
Authors: Campagnola Stefano , Lo Martin
Published: August 2008

This paper shows how the BepiColombo trajectory near Mercury follows the invariant manifolds to its final capture. The BepiColombo gravitational capture provides several recovery opportunities at nominal conditions and was designed by exploring the solution space entirely, without knowledge of the invariant manifolds. In this work we reproduced the trajectory in the model of the elliptic restricted three body‐ problem (due to the high eccentricity of Mercury's orbit) and showed that it does follow the manifolds. Consequently we envision that manifolds should be used to give insight on the solution space, speeding up the design and optimization process and there by saving cost. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Approximate implicitization and recursive surface intersection algorithms
Authors: Dokken Tor
Published: August 2008

Most published work on intersection algorithms for Computer Aided Design (CAD) systems addresses transversal intersections [1], situations where the surface normals of the surfaces intersected are well separated along all intersection curves. For transversal intersections the divide and conquer strategy of recursive subdivision, Sinha's theorem [2] and the convex hull property of NonUniform Rational B‐Spline surfaces (NURBS) efficiently identify all intersection branches. However, in singular or near singular intersections, situations where the surfaces are parallel or near parallel in an intersection region, along an intersection curve or in an intersection point, even deep levels of subdivision will frequently not sort out the intersection topology. The paper will focus on the novel approach of Approximate Implicitization to address these challenges. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel quasicontinuum method for the seamless transition from atomistic to continumm length scales and its application to nanoindentation of single‐crystalline materials
Authors: Eidel Bernhard , Stukowski Alex
Published: August 2008

We propose a novel fully nonlocal quasicontinuum (QC) approach which is based on two approximation steps, (i) the coarsegraining via kinematic constraints and (ii) the sampling of the energy in clusters along with summation rules. The present approach is closely related to the framework in [1] where forces instead of the energy is subject to sampling. Here, we show that only energy sampling strictly preserves the symmetry of atomic interactions whereas force sampling generally does not. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic instabilities in biological membranes
Authors: Campelo F. , Hernández‐Machado A.
Published: August 2008

A phase‐field model for dealing with the elastic bending energies is studied in the context of dynamic instabilities in membranes. We use it to study curvature‐driven pearling instability in vesicles induced by the anchorage of amphophilic polymers on the membrane. Within this model, we obtain the morphological changes reported in the experimental literature. The formation of a homogeneous pearled structure is achieved by consequent pearling of an initial cylindrical tube from the tip. For high enough concentration of anchors, we show theoretically that the homogeneous pearled shape is energetically less favorable than an inhomogeneous one, with a large sphere connected to an array of smaller spheres. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A novel two‐factor forecasting model for fuzzy time series
Authors: Li Sheng‐Tun , Lin Su‐Yu , Cheng Yi‐Chung
Published: August 2008

The study of fuzzy time series has increasingly attracted much attention due to its salient capabilities of tackling vague and incomplete data. A variety of forecasting models have devoted to improving forecasting accuracy, however, the issue of partitioning intervals has rarely been investigated. Recently, we proposed a novel deterministic forecasting model to eliminate the major overhead of determining the k‐order issue in high‐order models. This paper presents a continued work with focusing on handling the interval partitioning issue by applying the fuzzy c‐means technology, which can take the distribution of data points into account and produce unequal‐sized intervals. In addition, the forecasting model is extended to allow process twofactor problems. The accuracy superiority of the proposed model is demonstrated by conducting two empirical experiments and comparison to other existing models. The reliability of the forecasting model is further justified by using a Monte Carlo simulation and box plots. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Active control of working machines seat suspension aimed at health protection against vibration
Authors: Maciejewski Igor
Published: August 2008

The paper presents the model and simulation of passive and active earth‐moving machines seat suspension. The object of the simulation is the visco‐elastic passive seat suspension with an air‐spring, hydraulic shock‐absorber and scissors guidance mechanism. Passive seat suspension amplifies the vibration amplitude at low frequency range of excitation signal (the resonance effect). In order to help the working machines operators against vibration, the active system with different control strategies is elaborated. Active system improves significantly the behavior of the seat suspension at low frequency excitation, with the most effectiveness obtained for the resonance frequency. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling and simulation of fibrous biological tissues via discrete homogenization methods
Authors: Caillerie Denis , Milišić Vuk , Mourad Ayman , Raoult Annie
Published: August 2008

Thanks to their geometrical organization at the cell level, soft biological tissues can be modelled from the mechanical point of view as multidimensional networks of elastic bars. The length of the bars is supposed to be small with respect to the size of the macroscopic medium. We introduce a detailed description of the overall structure accounting both for the tensions due to the bars and for the moments between pairs of bars. Using quasi‐periodicity hypotheses, we apply a discrete homogenization technique, [1]. We derive a continuous homogenized mechanical law in the large transformation setting. We describe the basic principles of this approach that was first introduced in the cardiac modelling context in [2]. In a last step we present its implementation in a finite element framework. We comment some aspects of our numerical results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal treatment planning in radiotherapy based on Boltzmann transport calculations
Authors: Schäfer M. , Frank M. , Herty M.
Published: August 2008

A Boltzmann transport model for dose calculation in radiation therapy is considered. We formulate an optimal control problem for the desired dose. We prove existence and uniqueness of a minimizer. Based on this model we derive optimality conditions. The PN discretization in angle of the full model is considered. We show that the PN approximation of the optimality system is in fact the optimality system of the PN approximation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Granular materials: Parameter identification and modelling of localisation problems
Authors: Avci O. , Ehlers W.
Published: August 2008

The prediction of landsliding requires an exact knowledge of the mechanical behaviour of granular materials. This kind of materials, e. g., sand, have a very complex deformation behaviour, which depend on the stress state and on the loading history. In this work, the deformation behaviour of the solid skeleton is characterised via homogeneous triaxial tests on dry sand specimens. Additionally, an appropriate elasto‐plastic material law to describe the solid skeleton in the frame of Theory of Porous Media (TPM) is used, which is implemented in the FE tool PANDAS. Furthermore, a single‐surface yield criterion with isotropic hardening, which limits the elastic domain, and a non‐associated plastic flow are employed.

The determination of the material parameters of the linear elasticity law as well as the single‐surface yield criterion are based on test data of triaxial experiments. The material parameters are identified using a derivative‐based optimisation method (donlp2), which is coupled with PANDAS. Finally, a simulation of a benchmark test is presented to show shear band localisation effects, where the material behaviour is described by a triphasic porous media model based on the TPM, where the constituents are a deformable solid skeleton and two pore fluids, water and air. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An augmented LDG method for linear diffusion problems
Authors: Barrios Tomás P. , Bustinza Rommel
Published: August 2008

In this note we present a review of a stabilized discontinuous Galerkin method for elliptic problems in the plane with mixed boundary conditions. The stabilized scheme is obtained by adding suitable Galerkin least‐squares terms. The corresponding unique solvability and optimal rates of convergence, with respect to the h –version, are established by applying the wellknown Lax‐Milgram theorem, avoiding therefore the introduction of any lifting operator for the analysis. Furthermore, we include a reliable and efficient (up to high order terms) a posteriori error estimator. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)