bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the stabilization of tetrahedral finite elements using volume and area bubble functions
Authors: Caylak Ismail , Mahnken Rolf 
Published: August 2008

AbstractIn order to overcome the oscillatory effects of the bi‐linear Galerkin formulation for tetrahedral elements the mixed method of incompatible modes and the mixed method of enhanced strains are reformulated, thus giving both the interpretation of a mixed finite element method with stabilization terms. For nonlinear problems these are nonlinearly dependent on the current deformation state, and therefore are replaced by linearly dependent stabilization terms. The approach becomes most attractive for the numerical implementation, since the use of quantities related to the previous Newton iteration step, typically arising for mixed enhanced elements, is completely avoided. The stabilization matrices for the mixed method of incompatible modes and the mixed method of enhanced strains are obtained with volume and area bubble functions. Cook's membrane problem illustrates successfully the stabilization effect for bi‐linear tetrahedral elements. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Smolyak algorithms based on digital (t, α, d)‐sequences for multivariate integration
Authors: Dick Josef , Leobacher Gunther , Pillichshammer Friedrich 
Published: August 2008

AbstractWe use so‐called (t, α, d)‐sequences and Smolyak's algorithm to construct d × l ‐dimensional integration rules with optimal convergence rates in a suitable function space. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A three‐phase FE‐model for the simulation of partially saturated soils
Authors: Nagel Felix , Meschke Günther 
Published: August 2008

AbstractWhile for many numerical simulations in geotechnics use of a two‐phase model is sufficient, separate consideration of all three phases is mandatory for numerical simulations of partially saturated soils subjected to compressed air. This is a common technique frequently applied for temporary ground support in tunnelling. For the numerical simulation of tunnelling using compressed air, a multiphase model for soft soils is developed, in which the individual constituents of the soil – the soil skeleton, the fluid and the gaseous phase – and their interactions are considered. The three phase model is formulated within the framework of the Theory of Porous Media (TPM), based upon balance equations and constitutive relations for the soil constituents and their mixture. Water is modelled as an incompressible and air as a compressible phase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Representation of the interface conditions of the acoustic transmission problem at a curved contact of heterogeneous media in terms of transmission and reflection operators
Authors: Ayzenberg Milana , Aizenberg Arkady , Pajchel Jan 
Published: August 2008

AbstractWe schematically derive rigorous transmission and reflection operators at a curved interface between heterogeneous acoustic media. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Language technologies for semantic markup in mathematics
Authors: Caprotti Olga 
Published: August 2008

AbstractThe Web Advanced Learning Technologies project showed how, by applying state of the art language technologies to semantic markup of mathematics, it is possible to automatically produce renderings of mathematical content in a variety of languages. The intended application area of this work is that of computer assisted assessment and testing in mathematics where standardized entry examinations for perspective students could be used independently of country and language. A similar multilingual approach can be developed for any situation in which it is possible to identify a specific mathematical jargon. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Phase field simulations on the interaction of ferroelectric domains with point defects
Authors: Schrade D. , Xu B.X. , Müller R. , Gross D. 
Published: August 2008

AbstractOne of the suspected micro‐mechanical mechanisms causing electric fatigue in ferroelectric materials is the hindering and blocking of domain wall movement. These blocking or pinning phenomena are thought to be due to point defects which interact with domain walls and applied external loads. A phase field model employing the spontaneous polarization as an order parameter is used to simulate the inhomogeneous material behavior. The coupled field equations are solved using the Finite Element Method. The influence of a stationary point defect on a domain wall is shown in a numerical simulation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A boundary‐value problem for an infinite elastic strip with a semi‐infinite crack
Authors: Itou Hiromichi , Tani Atusi 
Published: August 2008

AbstractIn this paper we consider a boundary value problem for an infinite elastic strip with a semi‐infinite crack. The mass forces are supposed to be zero; on the crack the free traction boundary conditions are posed. The usage of the plane elastic single and double layer potentials reduces the problem to a system of singular integral equations. It is shown that this system is uniquely solvable in the appropriate Hölder spaces by the Fredholm alternative. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical analysis and adaptive computation for solutions of elliptic problems with randomly perturbed coefficients
Authors: Målqvist Axel , Estep Donald , Tavener Simon 
Published: August 2008

AbstractWe develop a reliable efficient method for computing solutions to the Poisson equation a with randomly perturbed coefficient. We assume the perturbation to be piecewise constant and use a non‐overlapping domain decomposition algorithm, where the domains coincides with regions where the perturbation is constant, to solve the equations. On each sub‐domain we use an truncated Neumann series to approximate the inverse of the local stiffness matrix. By doing so we can solve for all samples simultaneously in a very efficient way. We derive a posteriori error estimates and construct an adaptive algorithm to tune the method parameters automatically. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modelling Ziegler‐Natta polymerization in high‐pressure reactors
Authors: Fasano A. , Mancini A. 
Published: August 2008

AbstractWe present a study of some mechanical aspects of the polymerization processes named after the names of the Nobel laureates (1963) Karl W. Ziegler and Giulio Natta.Using the ideas of [1] as a starting point, we formulate a mathematical model encompassing the mechanical behavior of the polymer while it grows around the nanometric catalytic particles. As a basis we use the theory of [5]. The full model is exposed in [3]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparison of static optimization criteria for resolving the 3D muscle redundancy problem during human gait
Authors: Ou Ye , Kecskeméthy Andrés 
Published: August 2008

AbstractIn this paper, different approaches of static optimization for predicting muscle forces during human walking are investigated. In order to better reflect the true mechanics of the human body, a three‐dimensional musculoskeletal model of a single leg is developed. The joint moments generated by muscles during walking are computed from inverse dynamics. The muscle force is estimated by different optimization criteria, each satisfying the moment constraints at all joints and the lower and upper muscle force constraints. Several polynomial and non‐polynomial criteria frequently used in literature are studied. Then the results obtained from these calculations are compared with each other. This paper provides an overview of the effects of different optimization criteria on the 3D muscle force distribution problem during human walking. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Modeling and simulation of population balances in particulate systems
Authors: Qamar Shamsul 
Published: August 2008

AbstractThis article focuses on the modeling and simulation of population balance equations (PBEs) for simultaneous growth, nucleation and aggregation processes. Two numerical method are proposed for this purpose. The first method combines the method of characteristics (MOC) for growth process with a finite volume scheme (FVS) for aggregation process. The second method uses a high resolution finite volume scheme to solve the resulting PBEs. The numerical results show that both methods give accurate results. However, the first method is more efficient and accurate as compared to the second method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of high‐order discretization schemes for the DNS of compressible swirling mixing layers
Authors: Müller S.B. , Kleiser L. 
Published: August 2008

AbstractWe report on results of highly accurate Direct Numerical Simulations (DNS) solving the Navier‐Stokes equations in cylindrical coordinates. The DNS code computes a compressible swirling mixing layer at Mach number Ma = 0.8. We present two simulations differing in the spatial discretization schemes for the convective terms. On the same grid, comparisons of flow simulations using different discretization schemes for otherwise identical conditions can be performed quantitatively and improve the understanding of the effects of numerical errors and in particular numerical dissipation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effective matrix formalism for singularity analysis of differential equations and new intergrable system in nonlinear elasticity
Authors: Novozhilova L.S. , Urazhdin S.V. 
Published: August 2008

AbstractWe introduce a simple matrix formalism for Taylor series and generalized Laurent series that can be used for implementing the Taylor method for nonlinear ODEs and singularity analysis of differential equations. Advantages of this approach over conventional techniques are shown on model examples. Surprisingly, the same formalism can be used for proving C‐integrability of a 3D model in nonlinear elasticity. An alternative proof is obtained by using similarity between the model in nonlinear elasticity and the classic Pohlmeier‐Lund‐Regge model from high energy physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Interior point methods specialized to optimal pump operation costs of water distribution networks
Authors: Lima Aline , Oliveira Aurelio 
Published: August 2008

AbstractIn the water distribution problem the loss is important and the objective function must consider it combined with pump costs. The problem becomes complex because the loss in each branch is as a nonlinear function of water outflow. The objective of this work consists in solving the water distribution problem using interior point methods and to exploit the particular structure of the problem and the specific matrix sparse pattern of the of the resulting linear systems. The interior point methods show to be robust, achieving fast convergence in all instances tested. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Bridging scales: An attempt to incorporate cellular responses within a three‐dimensional FEM model of active muscle contraction
Authors: Röhrle O. , Davidson J.B. , Kim J.H.K. , Pullan A.J. 
Published: August 2008

AbstractA mathematical model of the cellular responses of skeletal muscles has been integrated within a three‐dimensional biomechanical Finite Element (FEM) model. The FEM model is based on a tri‐cubic Hermite Finite Element discretisation of the governing equations of finite elasticity theory and a transversely isotropic constitutive law. To incorporate the cellular information, homogenised values of key physiological parameters, e.g. the pre‐ and post‐power stroke concentration of crossbridge attachments, are computed at the Gauss points of the FEMintegration scheme. These values are then used to modify the stress tensor in such a way that it resembles the contractile response. The advantages of such an improved three‐dimensional FEM model are far reaching. These models can be used, for example, to investigate and study local muscle contraction, muscle recruitment patterns, force generation, or fatigue response of skeletal muscles. As an illustrative example, one twitch of the tibialis anterior, in which 25% of the muscle fibres are excited by a nerve stimulus, is simulated. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal control of a large PDAE molten carbonate fuel cell model
Authors: Rund Armin , Sternberg Kati , Pesch Hans Josef , Chudej Kurt 
Published: August 2008

AbstractMolten carbonate fuel cells are well suited for stationary power production and heat supply. In order to enhance service life time, hot spots, resp. high temperature gradients inside the fuel cell have to be avoided. In conflict with that, there is the desire to achieve faster load changes while temperature gradients stay small. For the first time, optimal fast load changes have been computed numerically. The dimensionless model is based on the description of physical and chemical phenomena. The numerical procedure is based on a method of lines approach via spatial discretization and the solution of the resulting very large scale optimal control problem s.t. a differential‐algebraic equation system by a nonlinear programming approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Subset selection for parameter estimation in an HIV model
Authors: Fink Martin , Attarian Adam , Tran Hien 
Published: August 2008

AbstractThis paper discusses methodologies for subset selection for nonlinear least squares parameter estimation. In particular, we will present approaches for partitioning the parameter space into well‐conditioned and ill‐conditioned subsets. The algorithms are applied to a simplified mathematical model of the physiologic response of the human immunodeficiency virus (HIV) in humans. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Physics‐based preconditioners for solving PDEs on highly heterogeneous media
Authors: Aksoylu Burak , Klie Hector 
Published: August 2008

AbstractEigenvalues of smallest magnitude become a major bottleneck for iterative solvers especially when the underlying physical properties have severe contrasts. These contrasts are commonly found in many applications such as composite materials, geological rock properties, and thermal and electrical conductivity. The main objective of this work is to construct a method as algebraic as possible that could efficiently exploit the connectivity of highly heterogeneous media in the solution of diffusion operators. We propose an algebraic way of separating binary‐like systems according to a given threshold into high‐ and low‐conductivity regimes of coefficient size O (m) and O (1), respectively where m ≫ 1. The condition number of the linear system depends both on the mesh size and the coefficient size m. For our purposes, we address only the m dependence since the condition number of the linear system is mainly governed by the high‐conductivity subblock. Thus, the proposed strategy is inspired by capturing the relevant physics governing the problem. Based on the algebraic construction, a two‐stage preconditioning strategy is developed as follows: (1) a first stage that comprises approximation to the components of the solution associated to small eigenvalues and, (2) a second stage that deals with the remaining solution components with a deflation strategy (if ever needed). The deflation strategies are based on computing near invariant subspaces corresponding to smallest eigenvalues and deflating them by the use of recycled the Krylov subspaces. More detail on the proposed preconditioners can be found in [1]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High order boundary integral methods forMaxwell's equations using Microlocal Discretization and Fast Multipole Methods
Authors: Darrigrand E. , Gatard L. , Mer‐Nkonga K. 
Published: August 2008

AbstractAn efficient method to solve time harmonic Maxwell's equations in exterior domain for high frequencies is obtained by using the integral formulation of Després combined with a coupling method (MLFMD) based on the Microlocal Discretization method (MD) and the Multi‐Level Fast Multipole Method (MLFMM) [1]. In this paper, we consider curved finite elements of higher order in the MLFMD method. Moreover, we improve the MLFMD method by sparsifying the translation matrix of the MLFMM, which involves privileged directions in that application. This improvement leads to a significant reduction of the algorithm complexity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
FEM‐BEM coupling for elasto‐plastic analysis: automatic adaptive generation of the FEM and BEM zones of discretization
Authors: Elleithy W. 
Published: August 2008

AbstractIn this paper, we present the concept and implementation issues of an adaptive FEM‐BEM coupling method for two – dimensional elasto‐plastic analysis. Considerable attention is devoted to the generation and progressive adaption of the FEM and BEM discretizations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Computational micro‐macro transitions at large strains for curvilinear physical directions
Authors: Grytz Rafael , Meschke Günther 
Published: August 2008

AbstractBiological tissues such as those involved in the eye, heart, veins or arteries are heterogeneous on one or another spatial scale and can undergo very large elastic strains. Frequently, these tissues are characterized by shell‐like structures at the macroscopic scale and the physical material directions follow curvilinear paths. We consider a homogenized macro‐continuum formulated in curvilinear convective coordinates with locally attached representative micro‐structures. Micro‐structures attached to different macroscopic points are assumed to be rotated counterparts according to the curvilinear path of the physical material directions at the macro‐scale. The solution of such multi‐scale problems according to the computational homogenization scheme [1, 2, 3] would need a different RVE at each macroscopic point. The goal of this paper is to use the same initial RVE at each macroscopic point by generalizing the computational homogenization scheme to a formulation considering different physical spaces at the micro‐ and macro‐scale. The deformation and the reference frame of the micro‐structure are assumed to be coupled with the local deformation and the local reference frame at the corresponding point of the macrocontinuum. For a consistent formulation of micro‐macro transitions physical reference directions are defined on both scales, where the macroscopic one follows a curvilinear path. To formulate the generalized micro‐macro transitions in absolute tensor notation the operations scale‐up and scale‐down are introduced. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical implementation of seismic wavefield operators via path integrals
Authors: Lamoureux Michael P. , Margrave Gary F. 
Published: August 2008

AbstractThe seismic imaging problem centers around mathematical and numerical techniques to create an accurate image of the earth's subsurface, using recorded data from geophones that capture reflected seismic waves. Using a path integral approach, a wavefield extrapolater can be expressed as a limit of depth‐sliced path steps through a variable velocity medium. An image is created from the correlation between upward and downward going waves. We report on the mathematical issues that arise in implementing numerical algorithms based on the path integral approach, in particular convergence, stability, and accuracy. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A few typical delamination patterns of compressed thin films
Authors: Pham V.D. , Gruttmann F. 
Published: August 2008

AbstractIn this paper we consider compressed flat thin films on rigid substrates. Residual compressive stresses arising e.g. from temperature loading are the driving quantities of the irreversible delamination process. A Reissner–Mindlin shell formulation is used as a model for the thin film, since small geometrical imperfections are considered to initiate buckling. For the interface we postulate the existence of a cohesive free energy as a function of the opening displacement vector and internal variables. The irreversible delamination process is described using a cohesive law of exponential type, where the parameters depend on the combination of the modes I, II and III. In order to analyse the delamination process exactly we use the energy criterion of the steady‐state growth. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Implementing Taylor models arithmetic with floating‐point arithmetic
Authors: Revol Nathalie 
Published: August 2008

AbstractThe implementation of Taylor models arithmetic may use floating‐point arithmetic to benefit from the speed of the floatingpoint implementation. The issue is then to take into account the roundoff errors. Here, we assume that the floating‐point arithmetic is compliant with the IEEE‐754 standard. We show how to get tight bounds of the roundoff errors, and more generally how to get high accuracy for the coefficients as well as for the bounds on the roundoff errors
A new level‐set technique for the crack‐detection problem
Authors: Alvarez Diego , Dorn Oliver , Moscoso Miguel 
Published: August 2008

AbstractWe present a new technique for recovering key characteristics of defects such as snake‐like cracks from boundary electrical measurements. We propose a shape‐based reconstruction algorithm adapting the level set techniques to the situation of modelling very thin shapes. Two level set functions are employed: the first one models the location and form of the crack, and the second one models its length and connectivity. Two Hamilton‐Jacobi type equations are derived to describe the evolution laws for these two level set functions in order to minimize the least squares data misfit. Numerical experiments in 2D show the efficiency of this method for reconstructing disconnected cracks in the presence of measurement noise. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The 3D asymptote generalization of MetaPost Bézier interpolation
Authors: Bowman John C. 
Published: August 2008

AbstractThe descriptive vector graphics language Asymptote provides for the typesetting of mathematical figures a capability analogous to what TEX provides for typesetting equations. Labels are typeset with TEX, for professional quality and overall document consistency, and the simplex linear programming method is used to solve overall size constraint issues between fixed‐sized and scalable objects. Asymptote's three‐dimensional generalization of the spline interpolation algorithms of Hobby (Discrete and Computational Geometry 1, 1986) is shape invariant under three‐dimensional affine transformations and reduces in the planar case to Hobby's prescription. By using recursive refinement to add additional Bézier control points, one can then efficiently approximate a perspective‐invariant nonuniform rational B‐spline. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Boundary optimal flow control with state constraints
Authors: de los Reyes Juan Carlos , Yousept Irwin 
Published: August 2008

AbstractThe numerical solution of the Dirichlet boundary optimal control problem of the Navier‐Stokes equations in presence of pointwise state constraints is investigated. A Moreau‐Yosida regularization of the problem is proposed to obtain regular multipliers. Optimality conditions are derived and the convergence of the regularized solutions towards the original one is presented. The paper ends with a numerical experiment. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)