bluuebunny/crossref_metadata_2025 huggingface dataset:
Bearing of geometric and material properties to bone strength in bending
Authors: Winter Werner
Published: December 2008

Osteoporosis is characterized by decreasing of bone mass and bone strength with advanced age. For characterization of material properties of bone the volumetric bone mineral density is one of the most important contributing factors to bone strength. Often bending tests of whole bone are used to get information about the state of osteoporosis. From an uniaxial test of a bone specimen it is assumed that an elastic region exists up to initial yield stress and a following hardening region. In bending tests beside material properties geometric properties like shape and cortical thickness appropriate the non‐linear moment‐curvature curve. The aim of this contribution is to show how an elastic‐plastic material law including tensile damage influences the global bending behavior. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic stall measurements on airfoils
Authors: Wolken‐Möhlmann Gerrit , Barth Stephan , Peinke Joachim
Published: December 2008

We present a new method for measuring the lift forces acting on an airfoil segment under dynamic stall conditions. Thereby the pressure distribution over the wind tunnel walls is detected by an adequate number of pressure sensors. The airfoil is rotated by a stepping motor with angular velocities up to 300°/s. Measurements with Reynolds number up to Re = 700 000 can be performed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energy‐momentum conserving integration of parallel manipulators
Authors: Uhlar Stefan , Betsch Peter
Published: December 2008

In the framework of a rotationless formulation for multibody systems, we present an investigation of multibody mechanisms. The benefit of this kind of formulation is the design of energy‐momentum conserving integration schemes, which facilitate a stable numerical integration of differential algebraic equations governing the motion of open‐loop and closed‐loop systems.

We introduce a coordinate augmentation technique for the incorporation of rotational degrees of freedom and subsequently perform a size‐reduction to lower the computational costs and to improve the numerical conditioning [1]. Furthermore the treatment of nonholonomic constraints is addressed [3]. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Chebyshev expansion for the component functions of the almost‐Mathieu operator
Authors: Marrero Jesús C. Abderramán
Published: December 2008

The component functions {Ψn (ε)} (n 2 Z+) from difference Schrödinger operators, can be formulated in a second order linear difference equation. Then the Harper equation, associated to almost‐Mathieu operator, is a prototypical example. Its spectral behavior is amazing. Here, due the cosine coefficient in Harper equation, the component functions are expanded in a Chebyshev series of first kind, Tn (cos 2πθ). It permits us a particular method for the θ variable separation. Thus, component functions can be expressed as an inner product,
equation image
(cos 2πθ) ·
equation image
. A matrix block transference method is applied for the calculation of the vector
equation image
. When θ is integer, {Ψn (ε) is the sum of component from
equation image
. The complete family of Chebyshev Polynomials can be generated, with fit initial conditions. The continuous spectrum is one band with Lebesgue measure equal to 4. When θ is not integer the inner product Ψn can be seen as a perturbation of vector
equation image
on the sum of components from the vector
equation image
. When
equation image
, with p and q coprime, periodic perturbation appears, the connected band from the integer case degenerates in q sub‐bands. When θ is irrational, ergodic perturbation produces that one band spectrum from integer case degenerates to a Cantor set. Lebesgue measure is Lσ = 4(1 – |λ|), 0 < |λ| ≤ 1. In this situation, the series solution becomes critical. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Flow of viscoplastic materials through converging channels
Authors: Alexandrov Sergei , Lyamina Elena , Mishuris Gennady
Published: December 2008

Many classical rigid perfectly/plastic solutions cannot be extended to more complicated rigid plastic materials, such as rigid plastic hardening materials and rigid viscoplastic materials. The present paper reveals sources of this difficulty in the case of flow of rigid viscoplastic material through infinite converging rough wedge‐shaped and axisymmetric channels. Two types of viscoplastic models without strain hardening are considered, with and with no saturation stress. The maximum friction law is adopted at the friction surface. Qualitative features of the solutions are compared to those occurring in compression of a rigid plastic layer between rough, parallel plates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of pressure work on free convection flow along a vertical circular cone with suction and variable surface temperature
Authors: Alim M. A. , Alam Md. M.
Published: December 2008

Free convection laminar flow from a vertical circular cone maintained a variable surface temperature with suction and pressure work effects has been investigated. The governing boundary layer equations are transformed into a non‐dimensional form and the resulting nonlinear system of partial differential equations are reduced to local non‐similarity equations. The governing non‐similarity equations are then solved numerically by implicit finite difference method together with Keller box scheme. Numerical results are presented in terms of velocity and temperature profiles of the fluid as well as the local skin‐friction coefficients and the local heat transfer rate for different values of Prandtl number Pr, suction parameter ξ, temperature gradient parameter n and the pressure work parameter ∈. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strong convergence for large bodies in micromagnetics
Authors: Carstensen Carsten , Praetorius Dirk , Boiger Wolfgang
Published: December 2008

The convexified Landau‐Lifshitz minimisation problem in micromagnetics leads to a degenerate variational problem. Therefore strong convergence of finite element approximations cannot be expected in general. This paper introduces a stabilised finite element discretisation which allows for the strong convergence of the discrete magnetisation fields with reduced convergence order for a uniaxial model problem. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Applications of RBF collocation method to elliptic PDEs in an arbitrary domain by fictitious domain extensions
Authors: Chen Jiahn‐Horng
Published: December 2008

A fictitious domain extension approach is introduced to study elliptic PDE's defined in arbitrary domains by the radial basis function (RBF) collocation method. In this approach, arbitrary physical geometries are extended to domains which are topologically rectangular. The solution domain is also extended to the fictitious area and assumed to satisfy the same governing equation in it and on its extended boundaries. The boundary conditions are still specified on the boundaries of the original physical domain. The problem in the extended domain becomes ill‐posed. However, it can be easily circumvented by the collocation method. We demonstrate that the solution can be directly obtained without domain decompositions and iterations. The new approach is simple, efficient and accurate. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Multimodel control approach for electrohydraulic servo systems
Authors: Hancu Olimpiu , Maties Vistrian , Balan Radu
Published: December 2008

The paper proposes a control design approach based on a multipoint linearization method for linear electro‐hydraulic servo systems. The nonlinear model of servo system is linearized around of operational points and Matlab environment is used to adjust the points distribution based on an errors estimation. These models are used to design an optimal controller which online modifies the feedback control parameters. Simulation and experimental results are provided to show the effectiveness of approach. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
From point cloud data to the continuum model of geometry
Authors: Harrison J.
Published: December 2008

The quantum calculus of [6] gives discrete approximations to continuum models of geometry. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cardiac arrhythmias: dynamics and geometry
Authors: Holden Arun. V. , Benson Alan P. , Halley Graeme
Published: December 2008

Cardiac arrhythmia have been modelled by non‐linear wave process in excitable media. Here we explain the effect of size, geometry and heterogeneity in the heart. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Problems in practical application of high resolution numerical schemes to internal and external tasks of aerodynamics
Authors: Bosniakov S.M. , Vlasenko V.V. , Glazkov S.A. , Jitenev V.K. , Kazhan E.V. , Quest J. , Mikhailov S.V.
Published: December 2008

This report presents numerical method for solution of aerodynamic tasks on the basis of Reynolds Averaged Navier‐Stokes Equations. The method is applied to simulation of flow around aircraft (including engine‐airframe interference) and to description of flowfield in the wind tunnel (WT) with aircraft model inside. To satisfy growing practical requirements both to accuracy of numerical results and to calculation time, zonal approach is proposed: flow regions with small scales of physical phenomena may be described using implicit scheme, and the rest of the flowfield – using explicit scheme. An example of modeling flow in the test section of European Transonic Windtunnel is shown. Unsteady phenomena around WT slotted walls were obtained. Calculations of noise suppressing nozzles with different geometry are considered. Numerical simulation has allowed to improve the nozzle geometry and to provide essential noise suppression. All presented examples confirm the need in further development of effective and accurate algorithms for practical tasks solution. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of tissue anisotropy versus inhomogeneity on the structural behaviour of an elderly human mandible
Authors: Kober C. , Hellmich C. , Erdmann B. , Stübinger S. , Sader R. , Zeilhofer H.‐F.
Published: December 2008

Within the biomechanics of bony organs, individual tissue anisotropy and inhomogeneity are intensively discussed subjects. This paper is dedicated to the impact of a fully anisotropic and inhomogoneous material description on the structural behaviour of an elderly partially edentulous human mandible. Radial, axial, and circumferential trajectories of orthotropic elasticity were reconstructed from kind of inner skeleton derived from the organ's geometry and from coherent structures recognisable from the spatial distribution of the grey values coming from computer tomography (CT). Based on recent micromechanical research driven forward by the second author, CT numbers were transferred into inhomogeneous stiffness tensor components reflecting individual tissue properties. These coefficients were considered as local orthotropic elastic coefficients in reference to coordinate systems formed by the anisotropic trajectories of elasticity. For the sake of a complete anisotropic material description over the whole organ, the tensor components were transformed into a global base frame which allows assembling an overall patient‐specific stiffness matrix. Various sensitivity analysis revealed that the more the anisotropy is considered the more the mandible is spared from loading which indicates kind of mechanical optimality of the mandible with respect to tissue anisotropy. In the opposite, the consideration of individual inhomogeneous tissue properties resulted in intensification of load concentrations due to pathological alterations of the organ which gives rise to the suggestion of self‐energising processes of bone resorption. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Hybrid symbolic‐numeric algorithms for computational convex analysis
Authors: Lucet Yves
Published: December 2008

Computational convex analysis focuses on developing efficient tools to compute fundamental transforms arising in convex analysis. Symbolic computation tools have been developed, and have allowed more insight into the calculation of the Fenchel conjugate and related transforms. When such tools are not applicable e.g. when there is no closed form, fast transform algorithms perform numerical computation efficiently.

However, computing the composition of several transforms is difficult to achieve with fast transform algorithms, which is the case for the recently introduced proximal average operator. We consider the class of piecewise linear‐quadratic functions which, being closed under the most relevant operations in convex analysis, allows the robust and efficient numerical computation of compositions of transforms like the proximal average. The algorithms presented are hybrid symbolic‐numeric: they first compute a piecewise linear‐quadratic approximation of the function, and then manipulate the approximation symbolically. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Thermomechanical behavior of pseudoelastic NiTi shape memory alloys
Authors: Luig Patrick , Grabe Christian , Bruhns Otto
Published: December 2008

The thermomechanical behavior of polycrystalline Ni‐rich pseudoelastic NiTi shape memory alloys is analyzed. Special focus is on regions within the stress strain diagram which are regarded as linear elastic in common phenomenological material models, i.e. the region between zero stress and the beginning of the pseudoelastic plateau as well as the region within the hysteresis. In both cases, severe temperature changes can be observed. A possible explanation for this effect is twofold: On the one hand, it might be explained by the presence of an R‐phase transformation. On the other hand, unstructured martensite of the B19' phase may form. However, the assumption of a purely thermo‐elastic material behavior in those regions does not seem to hold true in general. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of differential Riccati equations arising in optimal control for parabolic PDEs
Authors: Mena Hermann , Benner Peter
Published: December 2008

The numerical treatment of linear‐quadratic regulator problems on finite time horizons for parabolic partial differential equations requires the solution of large‐scale differential Riccati equations (DREs). Typically the coefficient matrices of the resulting DRE have a given structure (e.g. sparse, symmetric or low rank). Here we discuss numerical methods for solving DREs capable of exploiting this structure. These methods are based on a matrix‐valued implementation of the BDF methods. The crucial question of suitable stepsize and order selection strategies is also addressed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Robust a‐posteriori error control of Cahn‐Hilliard type equations with elasticity
Authors: Bartels Sören , Müller Rüdiger
Published: December 2008

Phase separation of an initially homogeneous mixture into two different phases can be modeled on a mesoscopic scale by the Cahn‐Hilliard equation. The interface thickness between the pure phases enters as a small parameter γ into this mass conserving fourth order semilinear parabolic equation. Numerical analysis is well established for a fixed parameter size, but error estimates depend exponentially on γ–1 and thus become useless if γ → 0. We consider the case, that elastic stresses due to a lattice misfit become important and the equation has to be coupled to a system of linear elasticity. Applications include e. g. the simulation of Sn‐Cu alloys for the production of lead free solder or Ni‐Al alloys used for rotor blade surfaces. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An iterative optimum‐optimorum theory for the design of a globally optimal shape
Authors: Nastase A.
Published: December 2008

In some previous papers, the author has developed the optimum‐optimorum theory, which solves an enlarged variational problem with free boundaries, inside of a class of flying configurations (FCs), defined by some chosen common properties. This optimization strategy was used by the author for the inviscid, aerodynamical, global optimal design of three models, namely, Adela, a delta wing alone and of two fully‐integrated wing‐fuselage FCs, namely, Fadet I and Fadet II, which have all high values of L/D (lift to drag). A further enlargement of the optimization strategy is developed here, in form of an iterative optimum‐optimorum theory, which uses the inviscid global optimized FC's shape as first step of iteration and the own developed reinforced Navier‐Stokes solutions up the first computational checking and up the second step of iteration. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Combining modeling, simulation, optimization and analysis under a unique framework
Authors: Serna S. Pena , Stork A.
Published: December 2008

The virtual engineering design process is based on several phases and every phase is supported by special concepts, representations and tools. This process is complex and the transition and communication between phases is difficult because of conversions and transformations. Embodiment is the phase, which more time requires, in order to produce a definitive layout from the concept, hence, we are designing and developing a unique framework where the embodiment phase can be performed, integrated and combined without transformations and conversions. This approach will support the engineers with advanced techniques on modeling meshes, conceptual simulations and real time optimization. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sensitivity analysis for indirect measurement and profile reconstruction in scatterometry
Authors: Groß Hermann , Rathsfeld Andreas
Published: December 2008

To control the design and manufacturing of lithographic masks a fast and non‐destructive measurement technique is needed. In scatterometry the mask is illuminated by plane waves from various directions, the scattered light is measured, and the geometry of the mask surface is reconstructed from the measured data. The quality of reconstruction surely depends on the angles of incidence, on the wave lengths and/or the number of propagating scattered wave modes. Optimizing the conditioning of some Jacobian matrices, we develop a sensitivity analysis to find an optimal measurement configuration for scatterometry. Our first important test geometry is a simple periodic line‐space structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Numerical solution of the dynamic problem of the elasticity theory in arbitrary shaped plane domain
Authors: Ribacova Galina
Published: December 2008

The numerical method for solving the dynamical problems of the theory of elasticity in two‐dimensional arbitrary shaped regions is proposed. The developed method consists of two main stages. The first one deals with the numerical grid generation. The method for creating the regular two dimensional grids based on equations of longitudinal plate deformation is presented. The last problem is solved numerically by means of finite difference method with the posterior using of the iteration process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
SPSA for oil‐parameter estimation and reservoir management
Authors: Rodriguez A. , Klie H , Wheeler M.
Published: December 2008

In this paper we implement and test the Simultaneous Perturbation Stochastic Approximation method (SPSA) in order to perform parameter estimation or history matching in reservoir simulation. The SPSA algorithm allows the determination of descent directions with very few forward model evaluations no matter the number of parameters. We test this approach for the estimation of transmissibilities for a single‐phase flow problem in very heterogeneous environments. The global properties of SPSA allow the determination of reasonable good inverse solutions which is demonstrated through numerical experiments. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Contact area of solid bodies: calculations compared to measured results
Authors: Sick J.‐H. , Ostermeyer G.‐P.
Published: December 2008

A novel attempt is made to directly measure the contact area of solid bodies by relating it to the electrical contact resistance. This method was used by F. P. Bowden and D. Tabor in the 1930s already. We confined the setup by use of low conductive thin film coatings. This way it is possible to point out the influence of contact area in contrast to incidental contaminations. By use of wear resistant coatings it will be possible to measure the contact area in sliding contacts as well. New measurements and calculations are compared with the original setup and model for contact resistance and contact area, respectively. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal design of a 2 DOF parallel robot
Authors: Stan S.‐D. , Maties V. , Balan R.
Published: December 2008

This paper is aimed at presenting a study on the optimization of the Biglide mini parallel robot, which comprises two‐degree‐of‐freedom (DOF) mini parallel robots with constant struts. The robot workspace is characterized and the inverse kinematics equation is obtained. In the paper, design optimization is implemented with Genetic Algorithms (GA) for optimization considering transmission quality index and workspace. Here, intended to show the advantages of using the GA, we applied it to a multicriteria optimization problem of 2 DOF mini parallel robot. Genetic algorithms (GA) are so far generally the best and most robust kind of evolutionary algorithms. A GA has a number of advantages. It can quickly scan a vast solution set. Bad proposals do not affect the end solution negatively as they are simply discarded. The obtained results have shown that the use of GA in such kind of optimization problem enhances the quality of the optimization outcome, providing a better and more realistic support for the decision maker. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Diffusion‐wave phenomena
Authors: Stojanović Mirjana , Gorenflo Rudolf
Published: December 2008

We announce the forthcoming papers [4] and [5] in which we prove the existence and the uniqueness, find properties, asymptotic and regularity of the solution to diffusion‐wave phenomena. We give explicit solutions for 1, 2, …, n ‐term time fractional diffusion‐wave equations. For the distributed order equation and for the equation with n‐term time fractional derivatives, we prove that the first fundamental solution is always a probability density for x ∈ R. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inversion‐based trajectory planning for the heat equation with temperature‐dependent parameters and radiation boundary conditions
Authors: Utz Tilman , Meurer Thomas , Wild Daniel , Kugi Andreas
Published: December 2008

This contribution is concerned with the trajectory planning for the nonlinear heat equation with radiation boundary conditions (BCs). For this, the infinite‐dimensional model is spatially discretized using finite differences. The discretized finite‐dimensional model serves as a basis for a flatness‐based feedforward control design. In the case of constant physical parameters, it is shown that the thus obtained feedforward controller converges to the feedforward controller for the original infinite‐dimensional problem in the limit as the discretization step size tends to zero. In the case of temperature‐dependent parameters, simulation results illustrate the convergence behavior. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid optimization approach for automated parameter estimation problems
Authors: Argáez M. , Klie H. , Quintero C. , Velázquez L. , Wheeler M.
Published: December 2008

We present a hybrid optimization approach for solving automated parameter estimation models. The hybrid approach is based on the coupling of the Simultaneous Perturbation Stochastic Approximation (SPSA) [1] and a Newton‐Krylov Interior‐Point method (NKIP) [2] via a surrogate model. The global method SPSA performs a stochastic search to find target regions with low function values. Next, we generate a surrogate model based on the points of regions on which the local method NKIP algorithm is applied for finding an optimal solution. We illustrate the behavior of the hybrid optimization algorithm on one testcase. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Projection acceleration of Krylov solvers
Authors: Vuik C. , Tang J.M. , Nabben R.
Published: December 2008

In many applications it appears that the initial convergence of preconditioned Krylov solvers is slow. The reason for this is that a number of small eigenvalues are present. After these bad eigenvector components are approximated, the fast superlinear convergence sets in. A way to have fast convergence from the start is to remove these components by a projection. In this paper we give a comparison of some of these projection operators. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive detection of distribution changes in medical information systems
Authors: Xue Xinjian Jack
Published: December 2008

The number of messages received by a medical information system was modelled as the signal in a stochastic process. Algorithms were developed for detecting changes of mean and variance and reporting the changes of status from normal to abnormal (upward edge), and vice verse (downward edge) under the assumption that the signal was distributed independently and normally in a series of time intervals. System tests have shown that the performance of the fault detecting and reporting in non‐holiday days is generally satisfactory for all laboratory data feeds. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Exploiting statistical properties of wavelet coefficient for face detection and recognition
Authors: Al‐Jawad Naseer
Published: December 2008

Wavelet transforms (WT) are widely accepted as an essential tool for image processing and analysis. Image and video compression, image watermarking, content‐base image retrieval, face recognition, texture analysis, and image feature extraction are all but few examples. It provides an alternative tool for short time analysis of quasi‐stationary signals, such as speech and image signals, in contrast to the traditional short‐time Fourier transform. The Discrete Wavelet Transform (DWT) is a special case of the WT, which provides a compact representation of a signal in the time and frequency domain. In particular, wavelet transforms are capable of representing smooth patterns as well anomalies (e.g. edges and sharp corners) in images. We are focusing here on using wavelet transforms statistical properties for facial feature detection, which allows us to extract the image facial feature/edges easily. Wavelet sub‐bands segmentation method been developed and used to clean up the non‐significant wavelet coefficients in wavelet sub‐band (k) based on the (k‐1) sub‐band. Moreover, erosion which is considered as one of the fundamental operation in morphological image processing, been used to reduce the unwanted edges in certain directions. For face detection, face template profiles been built for both the face and the eyes for different wavelet sub‐band levels to achieve better computational performance, these profiles used to match the extracted profiles from the wavelet domain of the input image using the Dynamic Time Warping technique DTW. The DTW smallest distance allows identifying the face and the eyes location. The performance of face features distances and ratio has been also tested for face verification purposes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Structure formation and phase behaviour in ferrofluid monolayers: theory and computer simulations
Authors: Cerdà Juan J. , Kantorovich Sofia , Holm Christian
Published: December 2008

In order to investigate the peculiarities brought by the quasi‐2D geometry into the aggregation processes in ferrofluids, a combination of density functional theory (DFT), and molecular dynamics (MD) simulations is presented. The microstructure formation and the phase behaviour of monodisperse ferrofluid monolayers is studied. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A ranking for the nodes of directed graphs based on game theory (Poster Presentation)
Authors: Amer Rafael , Giménez José Miguel , Magãna Antonio
Published: December 2008

We introduce a value that allows us to emphasize the importance of each player in a cooperative game when the cooperation possibilities are limited according to the links of an oriented network. The proposed concept of accessibility tries to conjugate the marginal contributions of each node as a game player with the cooperation geometry imposed by the directed graph that models the network. As a consequence, it is possible to offer a ranking for the nodes of directed graphs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Out‐of‐plane displacement measurement near the crack tip during a crack propagation: Validation of a 3D formulation for a specimen in PMMA loaded in mode I.
Authors: Hédan S. , Valle V. , Cottron M. , Brémand F.
Published: December 2008

The fundamental aim of this study is the determination zone of the 3D effects and the transient one at the vicinity of the crack tip during a crack propagation in brittle materials (PMMA) using an optical method (Michelson interferometer). With the obtained interferograms, we can extract the phase (thus the relief) by using a new numerical approach based on the principle of images correlation between real fringes and virtual fringes. Different dynamic tests are realized by a plate loaded in mode I under a constant loading. We compare the obtained data with the two‐dimensional theory of Westergaard (plane stress hypothesis) [1]. With the divergence is established, we propose a new 3D formulation, based on a formulation employed for static crack, which takes into account 3D and transient effects. For the static cracks, the 3D effects relate to a presence of the state of three‐dimensional stresses. However in dynamics, the transient effects appear and are related to the crack propagation velocity. The 3D effects and transient effects lead to results equivalent to experimental ones in terms of displacement but are completely different to results given by the two‐dimensional theory near the crack tip. It is possible to quantify the zone when the plane stress hypothesis is not valid according to the crack propagation speed V. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Andronov–Hopf bifurcation and group symmetry for differential equations non‐resolved under derivative
Authors: Loginov Boris , Makeev Oleg , Konopleva Irina , Rousak Yu.
Published: December 2008

For the differential equations in Banach spaces non‐resolved under derivative on the base of general theorem about group symmetry inheritance by relevant A.M. Lyapounov and E. Schmidt branching equations the possibilities of the reduction (dimension lowering) of the potential type branching equations are studied. As corollaries the results about general form of branching equations with rotational symmetries for evolution equation with degenerate Fredholm operator at the derivative are established. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Automatic adaptation of an integration formula in thickness direction for solid‐shell elements
Authors: Michaloudis Georgios , Schweizerhof Karl
Published: December 2008

In the simulation of shell problems in which plastic stresses in thickness direction are developed, the necessity of a more accurate integration through thickness using more integration points e.g. Gauss points becomes obvious, often increasing respectively the computational time and effort. A new algorithm is proposed for the automatic adaptation of the integration formula in thickness direction during the computation. Simple engineering criteria are found to define the time‐point and the regions to increase the number of integration points. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A coupled MD–FE approach for contact at microscopic length–scales (Poster Presentation)
Authors: Helmich Tobias , Nackenhorst Udo
Published: December 2008

Contact at very tiny length–scales is characterized by atomic force interaction. A technical application of interest is the atomic force microscope (AFM). A coupled molecular dynamics (MD) – finite element (FE) approach is outlined to tackle the multi–scale problem by numerical simulation. Guidelines for the spatial discretization are derived from convergence studies. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Adaptive numerical simulation of intracellular calcium dynamics
Authors: Nagaiah Chamakuri , Warnecke Gerald , Rüdiger Sten , Falcke Martin
Published: December 2008

We present the adaptive numerical simulation of intracellular calcium dynamics. The dynamics of intracellular calcium is determined by the liberation and uptake by cellular stores as well as reactions with buffers. This process is characterized by the existence of multiple length scales. The modeling of diffusion, binding and membrane transport of calcium ions in cells leads to a system of reaction‐diffusion equations. We used piecewise linear finite elements for the spatial discretization and time discretization by a linearly implicit Runge‐Kutta scheme. In our description the dynamics of IP3‐controlled channels remains discrete and stochastic. The strongly localized temporal behavior due to the on‐off behavior of channels as well as their spatial localization is treated by an adaptive numerical method. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Applications of graph theory
Authors: Pirzada S.
Published: December 2008

Graph theory is rapidly moving into the mainstream of mathematics mainly because of its applications in diverse fields. In this paper, we discuss certain ways of applying graph theoretical techniques to solve various problems and present the review of some of the applications. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A multiscale method for parameter estimation in reservoir simulation
Authors: Rodriguez A. , Klie H. , Wheeler M.
Published: December 2008

We consider a multiscale approach to the problem of parameter estimation or history matching in reservoir simulation. To do this, we look at the problem upscaling as the most important component of the proposed method. For upscaling we suggest a global approach which seeks to minimize the misfit between fine scale and coarse scale simulations and then used the Simultaneous Perturbation Stochastic Approximation (SPSA) method to deal with the minimization process. The essential idea of multiscale history matching comsists of constructing a coarsening sequence of models, so that each one of them minimizes the misfit between preditctions and observations. Then, the cosarsest model is downscaled one step into the sequence and used as an initial guess for the next step of refinement. The process is repeated until no improvement is observed in the solution. Numerical experiment indicate that this approach produces consistent results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A doubly optimal stopping of a risk process (Poster Presentation)
Authors: Karpowicz Anna , Szajowski Krzysztof
Published: December 2008

Problems which lead to an optimal stopping of a risk process are considered. Let an insurance company be endowed with an initial capital a > 0, receive insurance premiums and pay out successive claims. The losses occur according to renewal process. At any moment the company may broaden or narrow down the offer, what entails the change of the parameters. These changes concern the rate of income, the intensity of renewal process and the distribution of claims. The model of the risk process with two types of claims stream is considered. After the change the management wants to know the moment of the maximal value of the capital assets. Our goal is to find two optimal stopping times: the best moment of change the parameters and the moment of maximal value of the capital assets. A dynamic programming method to calculate the expected capital at that times is used. Based on the model which combine two types of risk the model of reinsurance with two firms is formulated. In this case the aim is to find for the firms the equilibrium strategy. The equilibrium is constructed in class of strategies driven by their risks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Toward a solution to the high Weissenberg number problem
Authors: Trebotich David
Published: December 2008

We present results of a numerical study of high Weissenberg number flows using the method of Trebotich, Colella and Miller, J. Comput. Phys. vol. 205 (2005). We consider benchmark viscoelastic flow of an Oldroyd‐B fluid in four to one sudden contractions for We = 1, 10, Re = 1. We conclude that (i) underlying wave behavior in the solution for flows at critical and supercritical elastic Mach number prevents the solution from reaching a steady‐state; and (ii) high resolution is needed to resolve structure in the solution downstream from the re‐entrant corner in order to determine convergence. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Leaving and reaching the moon from a libration point orbit
Authors: Alessi E.M. , Gómez G. , Masdemont J.J.
Published: December 2008

We represent the Earth–Moon system as a Circular Restricted Three–Body Problem and we look for trajectories which allow the departure from the lunar surface and which might have played a role in the formation of impact craters. We take advantage of the central and hyperbolic invariant manifolds which exist in the neighbourhood of the collinear equilibrium points L1 and L2. Different types of semi–analytical and numerical methodologies are exploited. The most meaningful results are pointed out. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Surface melting and effective anchoring in nematics
Authors: Biscari Paolo , Turzi Stefano
Published: December 2008

We study the equilibrium configuration of a nematic liquid crystal bounded by a rough surface. If ξ and η are, respectively, the nematic coherence length and the characteristic wavelength of the roughness, we show that in both limiting cases ξ ≪ η and η ≪ ξ the wrinkling of the surface induces a nontrivial structure in the equilibrium solution which may be interpreted in terms of an effective weak anchoring potential. We also determine how the effective surface extrapolation length is related to the microscopic anchoring parameters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
An Iterative method for solving fractional differential equations
Authors: Daftardar‐Gejji Varsha , Bhalekar Sachin
Published: December 2008

In the present paper non‐linear, time fractional advection partial differential equation has been solved using the new iterative method presented by Daftardar‐Gejji and Jafari [1]. The results are compared with those obtained by Adomian decomposition and Homotopy perturbation methods. It is demonstrated that the new iterative method gives the best approximation among these. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Force control of a fluidic muscle driven parallel platform
Authors: Singh Mahendra Dhanu , Liem Kusnadi , Neumann Rüdiger , Kecskeméthy Andrés
Published: December 2008

In this paper a new method for the force control of a parallel platform consisting of six fluidic‐muscles of type RRPS is presented. Fluidic muscles require that the gas model as well as the rubber nonlinearities are included in the control scheme. Moreover, the control law for the gas flow in the proportional directional control valve in 3/3‐way function needs to be taken into account. The present paper describes the basic dynamic models as well as testbed results for the existing fluidic‐muscle parallel platform “HexaSpine” [3]. Here each leg is equipped with a force sensor, a pressure sensor and a magnetostrictive position encoder. The control scheme for the platform comprises six control loops for the six operated actuators with a model based force control each. It is shown that the aforementioned control scheme leads to a stable force control of the platform driven by fluidic muscles. As an application, the device will be employed in fields of biomechanics, as well as in general environments requiring physical simulation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Some creative properties of the 2D and 3D lattice distributed interconnected chaotic oscillators and neuronal networks
Authors: Gontar Vladimir
Published: December 2008

Mathematical modeling and computer simulations of brain creativity & consciousness, artificial intelligence, mathematical imaging are the areas of research where the networks of interconnected oscillators playing an important role. Here we are presenting novel approach for mathematical modeling of brain creativity in a form of 2D symmetrical colored artistic patterns (ornaments) and 3D patterning. It was shown that special networks of chaotic oscillators simulated by the difference equations (discrete logistic equation, Henon equations and discrete chemical reactions basic equations [1]) possess creative patterns within their chaotic regimes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Vortical flow in thermo‐acoustic devices
Authors: Ishigaki Masahiro , Kuzuu Kazuto , Adachi Shizuko , Ishii Katsuya
Published: December 2008

Taconis oscillation in a closed long tube with large thermal gradient is studied by numerical calculation of the 2D compressible Navier‐Stokes equations. The both ends of tube are hot (T = TH), and the center of side wall is cold (T = TC). We analyze the pressure amplitude pamp and the time averaged temperature Tm in the closed tube. pamp is almost homogenous in the tube cross section, however, Tm is not homogenous in the central cold region. We also observe two steady states at the same temperature ratio θ = TH/TC. It is important to analyze the effects of the boundary layer in this cold region on Taconis oscillations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Non‐polynomials spline methods for solving a fourth‐order parabolic equation
Authors: Khan Arshad
Published: December 2008

In this paper a fourth‐order variable coefficient parabolic partial differential equation, that governs the behaviour of a vibrating beam, is solved by using a three level method based on non‐polynomial quintic spline in space and finite difference discretization in time. We also obtain two new high accuracy schemes of O (k4, h6) and O (k4, h8) and two new schemes which are analogues of Jain's formula for the non‐homogeneous case. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the vibration behavior of the DOBSON SPACE TELESCOPE
Authors: Kracht K. , Wagner U. von , Segert T.
Published: December 2008

The paper gives an overview about the results of modal analysis for the deployment structure of a lab model of the DOBSON SPACE TELESCOPE. The data of the modal analysis of the unfolded structure has been used to simulate the mechanical vibrations of the telescope forced by operating conditions.

Furthermore the vibration response of the folded structure during launch conditions, which has been simulated by a shaker, has been examined. All results show that the aluminium model of the DOBSON SPACE TELESCOPE would be ready for service referring to the aspect of mechanical vibrations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Application of operator splitting in the solution of reaction‐diffusion equations
Authors: Ladics Tamas
Published: December 2008

Operator splitting is a widely used method in the numerical solution of partial differential equations. A comparison of the different splitting techniques in the solution of 1 and 2 dimensional reaction‐diffusion equations is made. The process of the solution is a composition of certain splitting procedure and a given numerical method. We study the interaction between the different splitting procedures and different numerical schemes. The order of the convergence of this composed method is calculated. The error of the approximate solution is characterized as a funct ion of the applied splitting and numerical scheme. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Real options in biodiversity conservation
Authors: Leroux Anke D. , Martin L. , Goeschl Timo
Published: December 2008

The literature on optimal conversion defines rules that determine the rate at which land is irreversibly moved out of conservation into production. This paper explores the implications on these rules of allowing for a feedback between conversion decisions and the stochasticity of conservation benefits, using the well‐known ecological mechanism of extinction debt as an illustration. This yields a model with a controlled‐diffusion process at its core that is solved using a real‐options approach and that leads to the conventional conversion rule as a special case. Calibrating the model to a specific case (Costa Rica), the paper demonstrates the presence of an augmented quasi‐option value depending on the strength of the feedback. This results in quantifiable changes in land values and the amount of conservation. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Constraint isomorphism and correction algorithms for violations
Authors: Munakata Toshinori , Fadlalla Adam
Published: December 2008

When a problem can be characterized by different parameter sets, constraints imposed on one parameter set must be consistent with, or isomorphic to, constraints imposed on other parameter sets. When mapping among the parameter sets is not so visibly obvious, one might overlook consistency violations, which have occurred in the past. This paper examines such violations and possible correction algorithms. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The CONV method for pricing options
Authors: Lord R. , Fang F. , Bervoets F. , Oosterlee C.W.
Published: December 2008

In this paper, we discuss a convolution based method, the CONV method, for pricing options with early‐exercise features, in which the asset prices are modeled by Lévy processes. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analytical and numerical solutions of a generalized hyperbolic non‐Newtonian fluid flow
Authors: Pakdemirli M. , Sarı P. , Solmaz B.
Published: December 2008

Generalized hyperbolic non‐Newtonian fluid model first proposed by Al‐Zahrani [1] is considered. The model was successfully applied to some drilling fluids with better performance in relating shear stress and velocity gradient compared to power‐law and Hershel‐Bulkley model. Special flow geometries namely pipe flow, parallel plate flow and flow between two rotating cylinders are treated. For the first two cases, analytical solutions of velocity profiles in the form of integrals are presented. For the flow between two rotating cylinders, the differential equation is solved by Runge‐Kutta method combined with shooting. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ground‐based measurement of ash distribution in volcanic plumes
Authors: Phillips Jeremy C. , Yamamoto Hiroko , Watson I. Matthew , Bluth Gregg J.S.
Published: December 2008

Measurement of ash particle distribution within volcanic eruption plumes is important for volcanic hazard prediction, but is difficult because of the inherent danger and inaccessibility of volcanoes, and the three‐dimensional time‐dependent dynamics of turbulent eruption plumes. A combined study using a novel UV camera coupled with classical analysis of the dynamics of finite‐volume buoyant plumes has been used to develop a detection algorithm for ground‐based volcanic ash monitoring. The method provides the capability to observe and measure the internal structure of the plume, and processes occurring during plume rise, including concentration of ash over time into the plume ‘head’, increased ash at the plume edges during early formation and dilution at the top of the plume head as entrainment of surrounding air occurs. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)