bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of jointed structures using zero thickness interface elements
Authors: Geisler Johannes , Willner Kai 
Published: August 2008

AbstractAn important contribution to global damping of mechanical devices is structural damping due tomicroslip effects with friction in joint interfaces. In order to investigate the mechanical behaviour in these contact interfaces numerically, a contact element in the context of Finite Element Method (FEM) is presented. The suggested element is an isoparametric zero thickness element which is well suited for the present problem because the contact area is known and only small relative displacements occur. Arbitrary linear or nonlinear constitutive contact models for normal and tangential contact behaviour can be implemented. Using a proper parametrisation of the contact area, it is possible to apply the element in contact interfaces lying arbitrarily in space and in interfaces discretized with distorted elements. This method is described before a numerical example is compared with experimental results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of extrusion of aluminum alloys
Authors: Kayser Tobias , Parvizian Farhad , Hortig Christian , Svendsen Bob 
Published: August 2008

AbstractThe purpose of this work is the modeling and simulation of the material behavior of aluminum alloys during extrusion, cooling and metal forming processes. In particular, the alloys of the 6000 series (Al‐Mg‐Si) and 7000 series (Al‐Zn‐Mg) are relevant here. Under the corresponding conditions, their behavior is controlled mainly by dynamic recovery during the extrusion and static recrystallization during cooling. The current material model is based on the role of the energy stored in the material during extrusion as the driving force for microstructural evolution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Reciprocity in material space
Authors: Kienzler Reinhold 
Published: August 2008

AbstractIn Newtonian mechanics, reciprocity relations of Betti and Maxwell are useful tools in the analysis of engineering problems. Similar reciprocity relations have been established recently in Eshelbian Mechanics. In this contribution, a defect‐interaction problem is investigated and various aspects of reciprocity are studied. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamics and family of equilibria in a population kinetics model with cosymmetry
Authors: Kovaleva Ekaterina S. , Tsybulin Vyacheslav G. , Frischmuth Kurt 
Published: August 2008

AbstractWe study dynamics in the population kinetics model which is given by the system of nonlinear parabolic equations with cosymmetry property. The cosymmetry implies the emergence of continuous families of steady states with variable spectrum of stability. Different scenarios of evolution of families of equilibria and nonstationary regimes are analyzed numerically by a finite‐difference scheme which respects the cosymmetry property. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐equilibrium gas‐liquid transition model
Authors: Librovich Bronislav V. , Nowakowski Andrzej F. , Chaer Issa , Tassou Savvas 
Published: August 2008

AbstractA new rigorous mathematical model for evaporation/condensation, including boiling, has been proposed. A problem of phase transition and in particular evaporation/condensation is one of the most acute problems of modern technology with numerous applications in industry, such as: in refrigeration, distillation in chemical industry. It is very common to use equilibrium evaporation model, which assumes that concentrations of species in the gas phase is always at saturated condition. Such kind of approach can lead to significant errors, resulting in negative concentrations in complex computer simulations. In this work two analytical solution of simplified differential‐algebraic system have been obtained. One of them was deduced using assumption that the process is isothermal and gas volume fraction is constant. In the second solution the assumption about gas volume fraction has been removed. The code for numerical solution of differential‐algebraic system, using conservative scheme, has been developed. It was designed to solve both systems of equations with boiling and without. Numerical calculations of ammonia‐water system with various initial conditions, which correspond to evaporation and/or condensation of both components, have been performed. It has been shown that, although system quickly evolves to quasi equilibrium state (the differences between current and equilibrium concentrations are small) it is necessary to use non‐equilibrium evaporation model, to calculate accurately evaporation/condensation rates, and consequently all other dependent variables. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Automated solution of differential equations
Authors: Logg Anders 
Published: August 2008

AbstractDifferential equations are solved routinely by large computer programs, but the solution process is rarely automated. Each equation requires a different program and each such program requires a considerable amount of work to develop and maintain.The FEniCS project provides a set of tools that automate important aspects of the solution process, ultimately aiming at a complete automation of computational mathematical modeling, including the automation of discretization, discrete solution, error control, modeling and optimization. A key component of FEniCS is the FEniCS Form Compiler (FFC), which automates the discretization of differential equations by taking as input a variational problem in mathematical notation and generating highly efficient optimized low‐level code for the evaluation of the corresponding discrete operator. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vibration elimination in cable‐stayed footbridges and bridges
Authors: Pakos Wojciech , Wójcicki Zbigniew , Grosel Jacek 
Published: August 2008

AbstractIn 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

AbstractLQR 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

AbstractWe 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

AbstractThe 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

AbstractShape 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

AbstractRecent 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

AbstractSurfactants 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

AbstractA 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

AbstractMost 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

AbstractCharged 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

AbstractA 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

AbstractIn 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

AbstractIn 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

AbstractWe 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

AbstractMost 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

AbstractDirect 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

AbstractTechnological 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

AbstractWe 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)