Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Numerical Methods and Modeling  (932)
  • Neurologie
  • Theoretische Physik
  • Messtechnik
  • Strömungsmechanik
  • Wiley-Blackwell  (932)
  • Springer  (5)
  • Oxford University Press
  • American Institute of Physics (AIP)
  • 1995-1999  (937)
Collection
Publisher
  • Wiley-Blackwell  (932)
  • Springer  (5)
  • Oxford University Press
  • American Institute of Physics (AIP)
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Der Anaesthesist 48 (1999), S. 630-638 
    ISSN: 1432-055X
    Keywords: Schlüsselwörter Intrakranielle Druckmessung ; Messgenauigkeit ; Intrakranielle Drucksonden ; Messtechnik ; Compliance ; Key words ICP monitoring ; Measurement accuracy ; ICP probes ; Compliance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract Goal: Intracranial pressure (ICP) monitoring has a key role within the neuromonitoring, although ICP does not monitor processes of the central neuron directly and only with delay. One of the important factors in ICP monitoring is measurement accuracy. For a better understanding of ICP probes and their differences, the function and principles of intracranial pressure transducers should be evaluated from a technical point of view. Method: The principles of ICP measurement were analyzed and compared. Practical applications of these principles were examined and examples of different ICP probes were discussed regarding their mode of pressure transformation. The technical advances of ICP monitoring were analyzed. Results: Since LUNDBERG, a variety of different types of transducers has been developed. Ventricular ICP monitoring has been supplemented by extradural and intraparenchymatous probes. An increasing miniaturization of the transducers has emerged. Additionally, fiberoptic systems have been developed. Latest developments include multifunctional ICP probes. So far, the main problem of most types of transducers consists in the inability to assess measurement accuracy of a probe during the period of patient monitoring. Conclusion: ICP probes should be tested better for correct function by the manufacturer prior to sale. External controls of the measurement accuracy should be performed more frequently to ensure constant quality. Future ICP transducers have still to be more cost- effective.
    Notes: Zusammenfassung Fragestellung: Die Messung des intrakraniellen Drucks hat eine Schlüsselstellung innerhalb des Neuromonitorings erhalten, obwohl durch den Hirndruck die eigentlichen metabolischen Prozesse am zentralen Neuron nicht direkt und auch nur zeitlich verzögert registriert werden können. Voraussetzung für eine zuverlässige Hirndruckmessung sind spezifische Eigenschaften von Hirndrucksonden, die im folgenden untersucht werden sollen. Diese sollen dabei aus messtechnischer Sicht analysiert und kategorisiert werden, um ein besseres Verständnis für deren unterschiedliche Funktionsweise und Messeigenschaften zu erhalten. Methodik: Es werden die verschiedenen Messprinzipien, die bislang zur Anwendung kamen, dargelegt. Es wird aufgezeigt, wie diese Prinzipien praktisch genutzt werden. Probleme der Messgenauigkeit werden aus messtechnischer und klinischer Sicht erörtert. Ergebnisse: Es wurden seit Lundberg eine Vielzahl verschiedener Transducertypen entwickelt. Die ventrikuläre Hirndruckmessung wurde ergänzt durch epidurale und intraparenchymatöse Sonden. Eine zunehmende Miniaturisierung der Transducer und eine Verbesserung der Messtechnik hat eingesetzt. Zusätzlich wurden fiberoptische Systeme entwickelt. Neueste Entwicklungen zielen auf Multifunktionssonden ab, die zusätzlich zum intrakraniellen Druck auch die Hirntemperatur und weitere Parameter gleichzeitig messen können. Hauptproblem vieler der bisherigen Sonden ist das Fehlen einer direkten Kontrolle des Messverhaltens während des klinischen Einsatzes. Schlussfolgerungen: Sonden sollten vor Gebrauch vom Hersteller noch besser auf Funktionsfähigkeit überprüft und entsprechend ausgewiesen werden. Externe Kontrollen zur Überprüfung des Messverhaltens von intrakraniellen Drucksonden sollten zusätzlich verstärkt durchgeführt werden, um die Qualitätssicherung zu verbessern. Zukünftige intrakranielle Drucksonden müssen noch kostengünstiger werden.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 0029-5981
    Keywords: boundary element method ; acoustic scattering ; design optimisation ; fluid-structure interaction ; boundary integral equation ; inverse problems ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper a boundary element formulation for the sensitivity analysis of structures immersed in an inviscide fluid and illuminated by harmonic incident plane waves is presented. Also presented is the sensitivity analysis coupled with an optimization procedure for analyses of flaw identification problems. The formulation developed utilizes the boundary integral equation of the Helmholtz equation for the external problem and the Cauchy-Navier equation for the internal elastic problem. The sensitivities are obtained by the implicit differentiation technique. Examples are presented to demonstrate the accuracy of the proposed formulations. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 0029-5981
    Keywords: accuracy of numerical solution ; time-step ; finite element ; finite difference ; time-stepping schemes ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This study presents an experimental approach to estimate time steps that integrate the two-dimensional field equation over a square element within 5 per cent accuracy from the exact solution. The time-step estimates were determined for three finite element, and three finite difference schemes. Comparisons between finite element and finite difference methods and the various time-stepping schemes were conducted. The dynamic time-step estimates are functions of grid size and the smallest eigenvalue of the system of ODEs, λ1. The results indicate that the finite element and finite difference methods generate similar time-step estimates and are at similar accuracy levels. The central difference scheme is superior to the other two schemes as far as the flexibility in allowing larger time step while maintaining the accuracy. The backward difference and the forward difference schemes were very close in their level of accuracy. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 0029-5981
    Keywords: design sensitivity ; semi-analytic ; rigid body motions ; shells ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the recent past inaccuracy problems have been reported that arise when computing shape design sensitivities by the semi-analytical method. Since both the analytical and the global finite-difference method do not show these severe inaccuracies, it has been concluded that these errors are due to the numerical differentiation of the finite-element stiffness matrices, which is inherent in the semi-analytical method. Moreover, it has also been observed that these inaccuracies become especially dominant when relatively large rigid body motions can be identified for individual elements. So far, improvements to the semi-analytical method are focusing on the numerical differentiation of the finite-element stiffness matrices. It is shown in the present paper that the contribution to the design sensitivities corresponding to the rigid body motions can be evaluated by exact differentiation of the rigid body modes. This approach requires only minor programming effort and the additional computing time is very small. As shown by numerical examples, the proposed method eliminates the problem of abnormal errors occurring in the semi-analytical method. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 5
    ISSN: 0029-5981
    Keywords: linear finite element analysis ; geometrically non-linear finite element analysis ; element technology ; shell elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the present contribution we propose a so-called solid-shell concept which incorporates only displacement degrees of freedom. Thus, some major disadvantages of the usually used degenerated shell concept are overcome. These disadvantages are related to boundary conditions - the handling of soft and hard support, the need for special co-ordinate systems at boundaries, the connection with continuum elements - and, in geometrically non-linear analyses, to a complicated update of the rotation vector.First, the kinematics of the so-called solid-shell concept in analogy to the degenerated shell concept are introduced. Then several modifications of the solid-shell concept are proposed to obtain locking-free solid-shell elements, leading also to formulations which allow the use of general three-dimensional material laws and which are also able to represent the normal stresses and strains in thickness direction. Numerical analyses of geometrically linear and non-linear problems are finally performed using solely assumed natural shear strain elements with a linear approximation in in-plane direction.Although some considerations are needed to get comparable boundary conditions in the examples analysed, the solid-shell elements prove to work as good as the degenerated shell elements. The numerical examples show that neither thickness nor shear locking are present even for distorted element shapes. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 6
    ISSN: 0029-5981
    Keywords: contact ; friction ; complementarity ; Newton's method ; interior point method ; finite elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents two algorithms for solving the discrete, quasi-static, small-displacement, linear elastic, contact problem with Coulomb friction. The algorithms are adoptions of a Newton method for solving B-differentiable equations and an interior point method for solving smooth, constrained equations. For the application of the former method, the contact problem is formulated as a system of B-differentiable equations involving the projection operator onto sets with simple structure; for the application of the latter method, the contact problem is formulated as a system of smooth equations involving complementarity conditions and with the non-negativity of variables treated as constraints. The two algorithms are numerically tested for two-dimensional problems containing up to 100 contact nodes and up to 100 time increments. Results show that at the present stage of development, the Newton method is superior both in robustness and speed. Additional comparison is made with a commercial finite element code. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 7
    ISSN: 0029-5981
    Keywords: secant and tangent stiffness matrices ; structural analysis ; finite element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents a general and straightforward procedure based on the use of the strain energy density for deriving symmetric expressions of the secant and tangent stiffness matrices for finite element analysis of geometrically non-linear structural problems. The analogy with previously proposed methods for deriving secant and tangent matrices is detailed. The simplicity of the approach is shown in an example of application. © 1998 John Wiley & Sons, Ltd.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 0029-5981
    Keywords: incompressible flow ; rotor-stator configurations ; multigrid methods ; parallel computing ; moving grids ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A parallel multigrid finite volume solver for the prediction of unsteady flows in rotor-stator configurations using a moving-grid technique is presented. The numerical solution procedure is based on a second-order finite volume discretization with collocated block-structured grids, an implicit time discretization, a pressure-correction procedure of SIMPLE type, a non-linear multigrid method and a grid partitioning technique for parallelization. For the handling of the rotation and the relative movement of stationary and moving parts of the configuration a splitting technique is employed, which, based on the block structuring, divides the computational domain in a stationary and a rotating part. According to this splitting, the time-dependent flow equations are solved in a stationary and rotating frame of reference, and a special coupling procedure is used for the interfacial blocks. The method is investigated with respect to its accuracy, where special emphasis is given to the influence of different interpolation techniques of pressure-related terms within the non-staggered pressure-correction scheme. As a practical application, the flow in a stirrer configuration with baffles is studied, for which also results concerning the numerical and parallel efficiency of the proposed method are given. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 9
    ISSN: 0029-5981
    Keywords: boundary elements ; Cauchy principal-value integrals ; Hadamard finite part integrals ; Hölder continuity ; relaxed regularization ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Three stages are involved in the formulation of a typical direct boundary element method: derivation of an integral representation; taking a Limit To the Boundary (LTB) so as to obtain an integral equation; and discretization. We examine the second and third stages, focussing on strategies that are intended to permit the relaxation of standard smoothness assumptions. Two such strategies are indicated. The first is the introduction of various apparent or ‘pseudo-LTBs’. The second is ‘relaxed regularization’, in which a regularized integral equation, derived rigorously under certain smoothness assumptions, is used when less smoothness is available. Both strategies are shown to be based on inconsistent reasoning. Nevertheless, reasons are offered for having some confidence in numerical results obtained with certain strategies. Our work is done in two physical contexts, namely two-dimensional potential theory (using functions of a complex variable) and three-dimensional elastostatics. © 1998 John Wiley & Sons, Ltd.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 10
    ISSN: 0029-5981
    Keywords: sensitivity analysis ; singular boundary integral equations ; hypersingular integrals ; boundary element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper investigates the evaluation of the sensitivity, with respect to tangential perturbations of the singular point, of boundary integrals having either weak or strong singularity. Both scalar potential and elastic problems are considered. A proper definition of the derivative of a strongly singular integral with respect to singular point perturbations should accommodate the concomitant perturbation of the vanishing exclusion neighbourhood involved in the limiting process used in the definition of the integral itself. This is done here by esorting to a shape sensitivity approach, considering a particular class of infinitesimal domain perturbations that ‘move’ individual points, and especially the singular point, but leave the initial domain globally unchanged. This somewhat indirect strategy provides a proper mathematical setting for the analysis. Moreover, the resulting sensitivity expressions apply to arbitrary potential-type integrals with densities only subjected to some regularity requirements at the singular point, and thus are applicable to approximate as well as exact BEM solutions. Quite remarkable is the fact that the analysis is applicable when the singular point is located on an edge and simply continuous elements are used. The hypersingular BIE residual function is found to be equal to the derivative of the strongly singular BIE residual when the same values of the boundary variables are substituted in both SBIE and HBIE formulations, with interesting consequences for some error indicator computation strategies. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 11
    ISSN: 0029-5981
    Keywords: earthing grid ; horizontally stratified multilayer earth ; integral equation formulation ; finite element technique ; average potential method ; exponential approximation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a new numerical procedure for analysing earthing grids buried in horizontally stratified multilayer earth. The procedure is very efficient and general. The total number of layers and the total number of metallically disconnected earthing grids are completely arbitrary. A single earthing grid can be positioned in several layers. The procedure is based on an integral equation formulation. Earthing grid conductors are subdivided into segments and the average potential method is used. Efficiency and generality of the computation procedure are based on the successful application of numerical approximations of two kernel functions of the integral expression for the potential distribution within a single layer which is caused by a point current source. Each kernel function of the observed layer is approximated using a linear combination of 15 exponential functions. Extension from the point source to a segment of the earthing grid conductor is done by integrating the potential contribution due to a line of point current sources along the segment axis. This computational procedure gives highly accurate results in a short execution time. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 12
    ISSN: 0029-5981
    Keywords: distributed parallelization ; finite elements ; coarse-grain parallelism ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Parallel simulation of incompressible fluid flows is considered on networks of homogeneous workstations. Coarse-grain parallelization of a Taylor-Galerkin/pressure-correction finite element algorithm are discussed, taking into account network communication costs. The main issues include the parallelization of system assembly, and iterative and direct solvers, that are of common interest to finite element and general numerical computation. The parallelization strategies are implemented on a Sun workstation cluster using the Parallel Virtual Machine (PVM) message passing library. Test results are obtained with a maximum of nineteen workstations and various PVM configurations are exhibited. Parallel efficiency close to ideal has been achieved for some strategies adopted. It is suggested that load balancing may not always be beneficial on distributed platforms with broadcasting communication connection. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 13
    ISSN: 0029-5981
    Keywords: equivalent domain integral ; integrals of Legendre polynomials ; S-functions ; divergence theorem ; mixed mode ; decomposition method ; limit value ; error prediction ; selective p-distribution ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new path-independent contour integral formula is presented to estimate the crack-tip integral parameter, J-value, for two-dimensional cracked elastic bodies which may quantify the severity of the crack-tip stress fields. The conventional J-integral method based on a line integral has been converted to an equivalent area or domain integral (EDI) by the divergence theorem. It is noted that the EDI method is very attractive because all the quantities necessary for computation of domain integrals are readily available in a finite element analysis. The details and its implementation are extended to the p-version FE model with hierarchic elements using integrals of Legendre polynomials. By decomposing the displacement field obtained from the p-version finite element analysis into symmetric and antisymmetric displacement fields with respect to the crack line, the Mode-I and Mode-II non-dimensional stress intensity factors can be determined by using the decomposition method. The example problems for validating the proposed techniques are centrally oblique cracked plates under tensile loading. The numerical results associated with the variation of oblique angles show very good agreement with the existing solutions. Also, the selective distribution of polynomial orders and the corner elements for automatic mesh generation are applied to improve the numerical solution in this paper. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 25 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 14
    ISSN: 0029-5981
    Keywords: inverse problem ; boundary element method ; transient conduction problem ; conjugate gradient method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A Boundary Element Method (BEM)-based inverse algorithm utilizing the iterative regularization method, i.e. the conjugate gradient method (CGM), is used to solve the Inverse Heat Conduction Problem (IHCP) of estimating the unknown transient boundary temperatures in a multi-dimensional domain with arbitrary geometry. The results obtained by the CGM are compared with that obtained by the standard Regularization Method (RM).The error estimation based on the statistical analysis is derived from the formulation of the RM. A 99 per cent confidence bound is thus obtained. Finally, the effects of the measurement errors to the inverse solutions are discussed.Results show that the advantages of applying the CGM in the inverse calculations lie in that (i) the major difficulties in choosing a suitable quadratic norm, determining a proper regularization order and determining the optimal smoothing (or regularization) coefficient in the RM are avoided and (ii) it is less sensitive to the measurement errors, i.e. more accurate solutions are obtained. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 15
    ISSN: 0029-5981
    Keywords: 2-D magnetic field analysis ; vector hysteresis model ; complementary principles ; FE-FD discretization ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The main purpose of this paper is to incorporate a refined hysteresis model, viz., a vector Preisach model, in 2-D magnetic field computations. Two complementary formulations, based either on the scalar or on the vector potential, are considered. The governing Maxwell equations are rewritten in a suitable way, that allows to take into account the proper magnetic material parameters and, moreover, to pass to a variational formulation. The variational problems are solved numerically by a Finite Element approximation, using a quadratic mesh, followed by a time discretization method based upon a modified Cranck-Nicholson algorithm. Finally, the effectiveness of the presented mathematical tools have been confirmed by several numerical experiments, comparing the complementarity of the two procedures. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 16
    ISSN: 0029-5981
    Keywords: crack ; superposition ; stress intensity factor ; boundary elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper reviews some recent developments in superposition methods for calculating linear elastic stress intensity factors and eigenvalues for cracks and notches, presents some new results for pairs of edge cracks and provides new insights into the nature of the errors in these processes. The procedure requires a numerical solution to the full cracked problem and a second solution on the same mesh using the known form of the singularity in an infinite region. This is equivalent to the well-known Subtraction of Singularity (SST) method. The advantages of this procedure over conventional SST are: (1) no modifications need to be made to a standard computer program; (2) multiple crack tips may be analysed without the difficulty of unknown rigid body displacements at the crack tips; (3) solutions with different boundary conditions on the same mesh may be obtained simply in one step by re-using one singular field solution; The singular crack tip field may also be studied independently leading to estimates of the eigenvalues and some insight into mesh-induced errors. The additional computational cost of a two-step procedure is minimal since the solution matrix from step one may be re-used with a new right-hand side. Numerical experiments using the boundary element method demonstrate the accuracy and simplicity of the superposition approach for notches, simple cracks, mixed-mode cracks, two edge cracks of different lengths and eigenvalues under various boundary conditions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 17
    ISSN: 0029-5981
    Keywords: finite deformation ; thermo-elastoviscoplasticity ; generalized standard materials ; finite elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Technological forming processes of thermo-elastoviscoplastic solids are numerically simulated via finite elements based on an appropriate theoretical framework. Departing from the local balance laws of linear momentum and internal energy, the constitutive behaviour is introduced via the concept of ‘generalized standard materials (gsm)’, where a thermodynamic potential and a dissipation potential are the only two scalar quantities needed. They are expressed in invariants of symmetric mixed-variant tensors, respectively. Then the dissipation term evolves from the thermodynamic potential in a very natural way as well as the evolution equations for the internal variables emanate from the dissipation potential. An Eulerian setting is used.The numerical solution (of the non-linear coupled thermomechanical problem) is carried out via ‘displacement and assumed enhanced displacement-gradient’-based finite ring-elements in an ‘isentropic’ mechanical phase and via ‘temperature’-based finite ring-elements in an isogeometrical thermal phase and a global Newton-Raphson iterative method in both phases, respectively. The coupled consistent tangent moduli are carefully derived. Numerical results of the thermally triggered necking of a circular bar and of the impact of a copper rod on a rigid wall are given. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: elastodynamics ; boundary elements ; higher order ; analytical integration ; multi-domain ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general higher-order formulation for the time domain elastodynamic direct boundary element method is presented for computing the transient displacements and stresses in multiply connected two-dimensional solids. The displacement and traction interpolation functions are linear in time and quadratic in space. All integrations are analytical, and are expressed in terms of twelve basic recurring integrals. Causality is ensured by integrating only over the dynamically active parts of each element, and the algorithm presented is time-marching and implicit. The use of analytical integrations allows both unbounded and bounded domain problems to be solved without having to introduce special enclosing elements. All of these improved features allow for a formulation that is very efficient and accurate. The stability and accuracy of the elastodynamic boundary element algorithm is demonstrated by solving several example problems and comparing the results with available analytical and numerical solutions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 19
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: transient dynamics ; direct integration ; subcycling ; diffusion problems ; structural dynamics ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Subcycling algorithms which employ multiple timesteps have been previously proposed for explicit direct integration of first- and second-order systems of equations arising in finite element analysis, as well as for integration using explicit/implicit partitions of a model. The author has recently extended this work to implicit/implicit multi-timestep partitions of both first- and second-order systems. In this paper, improved algorithms for multi-timestep implicit integration are introduced, that overcome some weaknesses of those proposed previously. In particular, in the second-order case, improved stability is obtained. Some of the energy conservation properties of the Newmark family of algorithms are shown to be preserved in the new multi-timestep extensions of the Newmark method. In the first-order case, the generalized trapezoidal rule is extended to multiple timesteps, in a simple way that permits an implicit/implicit partition. Explicit special cases of the present algorithms exist. These are compared to algorithms proposed previously. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 20
    ISSN: 0029-5981
    Keywords: flexible multibody dynamics ; finite rotation ; beam finite elements ; variational principles ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general finite element formulation is presented for dynamic analysis of spatial elastic beams, for small strains, in a multi-body configuration. The tangent maps associated to the finite rotation vector are used to compute the tangent matrices used to integrate implicitly the equations of motion in descriptor form. A corotational method and a mixed variational method are used to compute the tangent stiffness matrix. The tangent constraint matrices are obtained using consistent linearization of the constraint equations. The tangent inertia matrices, including the gyroscopic and centrifugal terms, are also obtained by using the tangent maps of rotation. The numerical examples analyzed in this paper include: dynamic analysis of flexible beam structures and multi-flexible body systems with open and closed kinematic loops. A comparison with the previous results in the literature shows a very good performance in terms of time integration step and number of elements used. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 21
    ISSN: 0029-5981
    Keywords: variational elements method ; multipole expansion ; acoustic radiation ; variational formulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The acoustic radiation of general structures with Neumann's boundary condition using Variational Boundary Element Method (VBEM) is considered. The classical numerical implementation of the VBEM suffers from the computation cost associated with double surface integration. To alleviate this limitation, a novel acceleration method is proposed. The method is based on the expansion of the cross influence matrices in terms of multipoles using the expansion of the Green's function in terms of spherical Bessel functions. Since the resulting multipoles are not dependent on the elements locations, large computation time savings are achieved. Moreover, it is shown that by accounting for the monopole, dipole and quadrupole terms in the multipole expansion, the classical convergence criteria usually used in boundary element guarantee convergence of the proposed method. Several numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 22
    ISSN: 0029-5981
    Keywords: inverse problems ; adjoint equations ; solidification ; natural convection ; design optimization ; uniformity in casting products ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a finite element algorithm based on the adjoint method for the design of a certain class of solidification processes. In particular, the paper addresses the design of directional solidification processes for pure materials such that a desired freezing front heat flux and growth velocity are achieved. This is the first time that an infinite-dimensional continuum adjoint formulation is obtained and implemented for the solution of such inverse/design problems with moving boundaries and Boussinesq incompressible flow.The present design problem belongs to a category of inverse problems in which one is looking for the unknown conditions in part of the boundary, while overspecified boundary conditions are supplied in another part of the boundary (here the freezing interface). The solidification design problem is mathematically posed as a whole time-domain optimization problem. The gradient of the cost functional is calculated using the solution of an appropriately defined continuous adjoint problem. The minimization process is realized by the conjugate gradient method via the solutions of the direct, adjoint and sensitivity sub-problems.The proposed methodology is demonstrated with the solidification of an initially superheated liquid aluminum confined in a square mold. The non-uniformity in the casting product in the direction of gravity due to the existence of natural convection in the melt is emphasized. The inverse design problem is then posed as finding the appropriate spatial-temporal variations of the boundary heat flux on the vertical mold walls that can eliminate or reduce the effects of convection on the freezing interface heat fluxes and growth velocity. The numerical example demonstrates the accuracy and convergence of the adjoint formulation. Finally, open related research design problems are discussed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 23
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: hybrid-Trefftz stress elements ; gradient-dependent elastoplasticity ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The stress model of the hybrid finite element formulation is applied to the analysis of quasi-static, gradient-dependent elastoplastic structural problems. The finite element approximation consists in the direct estimate of the stress and plastic multiplier fields in the domain of the element and of the displacements and plastic multiplier gradients on its boundary. The finite element equations are derived directly from the relevant fundamental structural conditions, namely equilibrium, compatibility, elasticity and gradient-dependent plasticity. The finite element solving system for the finite step incremental analysis is encoded as a recursive sequence of symmetric parametric linear complementarity problems (SPLCP). The sequence of SPLCP is solved using a direct extension of the restricted basis linear programming algorithm. The implementation of the formulation and of the algorithm is illustrated with numerical applications. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 24
    ISSN: 0029-5981
    Keywords: inverse problem ; incompressible ; shape design ; seal design ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a formulation for incorporating quasi-incompressibility in inverse design problems for finite elastostatics where deformed configurations and Cauchy tractions are known. In the recent paper of Govindjee and Mihalic [1996, Comput. Methods Appl. Mech. Engng., 136, 47-57.] a method for solving this class of inverse problems was presented for compressible materials; here we extend this work to the important case of nearly incompressible materials. A displacement-pressure mixed formulation is combined with a penalty method to enforce the quasi-incompressible constraint without locking. Numerical examples are presented and compared to known solutions; further examples present practical applications of this research to active problems in elastomeric component design. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 25
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: curved beam element ; hybrid-mixed formulation ; nodeless degrees of freedom ; field-consistency ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The purpose of this work is to show the successful use of nodeless degrees of freedom in developing a highly accurate, locking free hybrid-mixed C0 curved beam element. In the performance evaluation process of the present field-consistent higher-order element, the effect of field consistency and the role of higher-order interpolation on both displacement-type and hybrid-mixed-type elements are carefully examined. Several benchmark tests confirm the superior behaviour of the present element. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 26
    ISSN: 0029-5981
    Keywords: domain decomposition ; multipoint constraints ; numerical scalability ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We consider the iterative solution by a class of substructuring methods of the large-scale systems of equations arising from the finite element discretization of structural models with an arbitrary set of linear multipoint constraints. We present a methodology for generalizing to such problems numerically scalable substructure based iterative solvers, without interfering with their formulations and their well-established local and global preconditioners. We apply this methodology to the FETI method, and show that the resulting algorithm is numerically scalable with respect to both the substructure and problem sizes. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 27
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: strut ; initial imperfection ; post-buckling analysis ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Computational procedure has been presented for the post-buckling analysis of a strut with initial imperfection when subjected to progressive end shortening. Polynomial expression in very general form is used to simulate the actual initial imperfection, while the deformations are expressed by suitable trigonometric series. Geometric non-linearity is introduced into the strain-displacement relations in a manner that is consistent with the von Karman assumptions. Non-linear equilibrium equations are solved by a Newton-Raphson procedure. Results are presented for cases with symmetric and non-symmetric initial imperfection. Good comparison with other solutions and experimental results is obtained in all applications. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 28
    ISSN: 0029-5981
    Keywords: soil-pore fluid interaction ; staggered solution ; finite elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new class of unconditionally stable staggered implicit-implicit time-stepping algorithms for coupled soil-pore fluid dynamic problems is presented. The proposed schemes are stabilized with a pressure correction method and the staggered procedure introduced earlier by the second author is a simplified case of the new algorithms. The stabilized procedure is efficient in numerical time domain analysis of soil-pore fluid interaction occurring in earthquake and consolidation problems. Several examples of linear and non-linear problems demonstrate the stability and accuracy of the proposed numerical solution algorithms. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 29
    ISSN: 0029-5981
    Keywords: sensitivity analysis ; structural optimization ; truss structures ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new approach to structural sensitivity analysis based on the so-called virtual distortion method is presented. The proposed methodology enables the calculation of derivatives for elastic as well as elasto-plastic structures on the basis of knowledge of current strains, permanent plastic deformations and influence matrix, describing interactions between a chosen member and the entire structure. The analytical basis as well as numerical verification of the concept is demonstrated. Advantages of the proposed approach, in the sense of numerical cost, are summarized in conclusions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 30
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: finite element method ; variational inequalities ; contact problems ; heuristic algorithms ; nondifferential optimization methods ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This article is devoted to the development of a new heuristic algorithm for the solution of the general variational inequality arising in frictional contact problems. The existing algorithms devised for the treatment of the variational inequality representing frictional contact rely on the decomposition of the physical problem into two sub-problems which are then solved iteratively. In addition, the penalty function method and/or the regularization techniques are typically used in the solution of these reduced sub-problems. These techniques introduce user-defined parameters which could influence the convergence and accuracy of the solution. The new method presented in this article overcomes these difficulties by providing a solution for the general variational inequality without decomposition into sub-problems. This is accomplished using a new heuristic algorithm which utilizes mathematical programming techniques, and thus avoids the use of penalty or regularization methods. The versatility and reliability of the developed algorithm were demonstrated through implementation to the case of frictional contact of an elastic hollow cylinder with a rigid foundation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 31
    ISSN: 0029-5981
    Keywords: three-dimensional conduction heat transfer ; special boundary integral formulation ; Design Sensitivity Analysis (DSA) ; Direct Differentiation Approach (DDA) ; optimization ; CONMIN algorithm ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In some steady heat conduction problems in special geometries which consist of a closely spaced surface and circular holes in an infinite domain, thermal system designers may want to optimize the configuration of circular holes in terms of their radii and locations to achieve the goal of uniform temperature distribution over a closely spaced surface. In this paper, an efficient optimization procedure for this kind of problem is proposed utilizing (i) the special boundary element analysis, (ii) the corresponding design sensitivity analysis and (iii) the CONMIN algorithm. Three sample problems were solved to demonstrate the efficiency and the usefulness of the proposed optimization procedure. Some industrial engineering examples of such problems can be found in the injection molding process, the compression molding process, and so on. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: warping ; bimoment ; Vlasov's thin-walled beam ; block stiffness matrix ; finite element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new finite element for the analysis of thin-walled open beams with an arbitrary cross section is presented. Combining Timoshenko beam theory and Vlasov thin-walled beam theory, the derived element includes both flexural shear deformations and warping deformations caused by the bimoment. By adopting an orthogonal Cartesian co-ordinate system, one can obviate the ad hoc introduction of St. Venant stiffness. The derived block stiffness matrix is comparable but more general than the one given by earlier researchers. The versatility and accuracy of the new element are demonstrated by comparing the numerical results with the classical solutions or other numerical results available in the literature. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: moving boundary ; numerical quench back ; discretization errors ; accuracy and convergence ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: One of the most important thermofluid processes encountered in internally cooled superconducting magnets is that of quenching. Numerical simulation of the quench propagation involves accurately modelling a moving boundary layer at the quench front. Due to the highly non-linear nature of the quench process, slightest numerical errors can rapidly grow to unacceptable limits. The quench propagation in such a non-converged solution exhibits a very rapid propagation velocity which resembles a ‘quenchback’ effect. Hence, the term ‘Numerical Quenchback’ is used to characterize a numerically unstable solution of the governing quench model. This paper presents the underlying physical phenomena that causes a numerical discretization scheme to have error terms that increase exponentially with time, causing the numerical quenchback effect. Specifically, by analytically solving the equivalent differential equation of the numerical scheme, we are able to obtain closed-form relations for the error terms associated with the propagation velocity. This allows us to define error criteria on the space and time steps used in the simulation. The reliability of the error criteria is proven by detailed convergence studies of the quench process. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 34
    ISSN: 0029-5981
    Keywords: boundary integral equations ; Fredholm integral equations ; circulant preconditioners ; preconditioned conjugate gradient method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, we consider solving potential equations by the boundary integral equation approach. The equations so derived are Fredholm integral equations of the first kind and are known to be ill-conditioned. Their discretized matrices are dense and have condition numbers growing like O(n) where n is the matrix size. We propose to solve the equations by the preconditioned conjugate gradient method with circulant integral operators as preconditioners. These are convolution operators with periodic kernels and hence can be inverted efficiently by using fast Fourier transforms. We prove that the preconditioned systems are well conditioned, and hence the convergence rate of the method is linear. Numerical results for two types of regions are given to illustrate the fast convergence. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 35
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: Newmark method ; complex-time-steps ; time-step integration method ; higher-order algorithms ; excitation modification ; parallel algorithms ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper, unconditionally stable higher-order accurate time-step integration algorithms with controllable numerical dissipation are presented. The algorithms are based on the Newmark method with complex time steps. The ultimate spectral radius (μ), the sub-step locations (βj) and the weighting factors (αj) are the algorithmic parameters. For an algorithm that is (2n-1)th order accurate, the sub-step locations which may be complex, are shown to be the roots of an nth degree polynomial. The polynomial is given explicitly in terms of n and μ. The weighting factors are then obtained by solving a system of n simultaneous equations. It is further shown that the order of accuracy is increased by one for the non-dissipative algorithms with μ=1. The stability properties of the present algorithms are studied. It is shown that if the ultimate spectral radius is set between -1 and 1, the eigenvalues of the numerical amplification matrix are complex with magnitude less than or equal to unity. The algorithms are therefore unconditionally C-stable. When the ultimate spectral radius is set to 0 or 1, the algorithms are found to be equivalent to the first sub-diagonal and diagonal Padé approximations, respectively. The present algorithms are more general as the numerical dissipation is controllable and are very suitable for parallel computers. The accuracy of the excitation responses is found to be enhanced by the present complex-time-step procedure. To maintain high-order accuracy, the excitation may need some modifications. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 36
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: object oriented programming ; tensor analysis ; constitutive driver programming ; finite element programming ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a novel programming tool, nDarray, which is designed using an Object Oriented Paradigm (OOP) and implemented in the C++ programming language. Finite element equations, represented in terms of multidimensional tensors are easily manipulated and programmed. The usual matrix form of the finite element equations are traditionally coded in FORTRAN, which makes it difficult to build and maintain complex program systems. Multidimensional data systems and their implementation details are seldom transparent and thus not easily dealt with and usually avoided. On the other hand, OOP together with efficient programming in C++ allows building new concrete data types, namely tensors of any order, thus hiding the lower level implementation details. These concrete data types prove to be quite useful in implementing complicated tensorial formulae associated with the numerical solution of various elastic and elastoplastic problems in solid mechanics. They permit implementing complex nonlinear continuum mechanics theories in an orderly manner. Ease of use and the immediacy of the nDarray programming tool in constitutive driver programming and in building finite element classes will be shown. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 37
    ISSN: 0029-5981
    Keywords: fluid-structure interaction ; porous medium ; symmetric finite element equations ; weighted residual formulation ; noise and vibration transmission ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A weak solution of the coupled, acoustic-elastic, wave propagation problem for a flexible porous material is proposed for a 3-D continuum. Symmetry in the matrix equations; with respect to both volume, i.e. ‘porous frame’-‘pore fluid’, and surface, i.e. ‘porous frame/pore fluid’-‘non-porous media’, fluid-structure interaction; is ensured with only five unknowns per node; fluid pore pressure, fluid-displacement potential and three Cartesian components of the porous frame displacement field. Taking Biot's general theory as starting point, the discretized form of the equations is derived from a weighted residual statement, using a standard Galerkin approximation and iso-parametric interpolation of the dependent variables. The coupling integrals appearing along the boundary of the porous medium are derived for a number of different surface conditions.The primary application of the proposed symmetric 3-D finite element formulation is modelling of noise transmission in typical transportation vehicles, such as aircraft, cars, etc., where porous materials are used for both temperature and noise insulation purposes. As an example of an application of the implemented finite elements, the noise transmission through a double panel with porous filling and different boundary conditions at the two panel boundaries are analysed. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 38
    ISSN: 0029-5981
    Keywords: Free-front tracking ; volume of fluid method ; Hele-Shaw method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: With free surface flow problems the position of the free front at a particular time step needs to be predicted. When simulating the flow of hot molten polymer in injection moulds this position is essential for the prediction of the position of the weld lines on the final product. Weld lines are important in that they indicate positions of diminished strength and spoil the aesthetics of the product. A code using a finite volume approach on the thin gap Hele-Shaw flow equations to simulate the filling stage of the injection moulding process has been developed which requires a suitable algorithm for the free-front tracking. The Volume of Fluid (VOF) method was implemented in this study for the tracking of the free front. The discretization and various formulations of the VOF equation are presented as well as the results obtained. The impact on the existing equations is also investigated as well as the development of a packing routine that is used to eliminate the diffusive nature of the VOF equation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 39
    ISSN: 0029-5981
    Keywords: finite elements ; boundary integral equations ; Dirichlet-to-Neumann mapping ; error estimates ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The application of the uncoupling of boundary integral and finite element methods to solve exterior boundary value problems in R2 yields a weak formulation that contains only one boundary term. This is the so-called uncoupling term, which is determined by the boundary integral operator of the single-layer potential acting on a circle centered at the origin. The purpose of this paper is to provide a suitable formula, which combines analytical and numerical methods, to approximately integrate the uncoupling term to any exacteness. Our method provides sharper error estimates than the one that uses Truncated Infinite Fourier Series (TIFE). As a model we consider the exterior Dirichlet problem for the Laplacian, and use linear finite elements for the corresponding Galerkin scheme. Some numerical experiments are also presented. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 40
    ISSN: 0029-5981
    Keywords: elastic membrane ; finite membrane elements ; potential flow ; QCM vortex lattice ; aerodynamical and structural interaction ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Methods for the calculation of potential flow around thin bodies are well known and can be found in several publications. According to these publications the vortex lattice method (VLM) combined with the quasi-continuous-method (QCM) is most effective for membrane-like bodies with no aerodynamical thickness. The possible flow around edges of a membrane causes singularities which are considered using a cosine-spaced vortex lattice. The structural membrane analysis with the finite element method (FEM) is also well known and has been applied to several problems of engineering. If the same mesh is used for both methods it is easy to combine the QCM and the FEM. However, a cosine-spaced FE-mesh makes no sense because it is not FEM problem-orientated. Therefore, until now, equidistant or nearly equidistant vortex lattices have been used to calculate the interacting flow and structure. They also cause unacceptable errors because they are not optimal for the VLM problem.This paper describes a new method to reduce the errors of combined calculations of flow and structure. A FEM problem-orientated mesh out of improved finite elements is combined with a cosine-spaced vortex lattice. The method is called quasi-continuous-continuous (QCC) because the discrete forces of the VLM are transformed into a continuous membrane load. A set of numerical examples shows the excellent numerical performance of the QCC and the reduction of errors. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 41
    ISSN: 0029-5981
    Keywords: infinite elements ; unbounded domains ; acoustics ; finite element methods ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A novel approach to the development of infinite element formulations for exterior problems of time-harmonic acoustics is presented. This approach is based on a functional which provides a general framework for domain-based computation of exterior problems. Special cases include non-reflecting boundary conditions (such as the DtN method). A prominent feature of this formulation is the lack of integration over the unbounded domain, simplifying the task of discretization. The original formulation is generalized to account for derivative discontinuities across infinite element boundaries, typical of standard infinite element approximations. Continuity between finite elements and infinite elements is enforced weakly, precluding compatibility requirements. Various infinite element approximations for two-dimensional configurations with circular interfaces are presented. Implementation requirements are relatively simple. Numerical results demonstrate the good performance of this scheme. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 42
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: flow control ; numerical solution of Navier-Stokes equation ; Karhunen-Loève Galerkin procedure ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new method of solving the Navier-Stokes equations efficiently by reducing their number of modes is proposed in the present paper. It is based on the Karhunen-Loève decomposition which is a technique of obtaining empirical eigenfunctions from the experimental or numerical data of a system. Employing these empirical eigenfunctions as basis functions of a Galerkin procedure, one can a priori limit the function space considered to the smallest linear subspace that is sufficient to describe the observed phenomena, and consequently reduce the Navier-Stokes equation defined on a complicated geometry to a set of ordinary differential equations with a minimum degree of freedom. The present algorithm is well suited for the problems of flow control or optimization, where one has to compute the flow field repeatedly using the Navier-Stokes equation but one can also estimate the approximate solution space of the flow field based on the range of control variables. The low-dimensional dynamic model of viscous fluid flow derived by the present method is shown to produce accurate flow fields at a drastically reduced computational cost when compared with the finite difference solution of the Navier-Stokes equation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 43
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: meshless ; projections ; approximation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A technique for incorporating discontinuities in derivatives into meshless methods is presented. The technique enriches the approximation by adding special shape functions that contain discontinuities in derivatives. The special shape functions have compact support which results in banded matrix equations. The technique is described in element-free Galerkin context, but is easily applicable to other meshless methods and projections. Numerical results for problems in one and two dimensions are reported. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 44
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    ISSN: 0029-5981
    Keywords: unbounded domain ; wave equation ; steady ; transient ; finite element ; infinite element ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a family of axisymmetric, spheroidal ‘wave envelope’ elements for modelling exterior wave problems. They are of variable radial order and can be used to represent steady and transient wave fields. The formulation is presented for the axisymmetric case using elements which are based on oblate and prolate spheroidal geometries. These offer the prospect of reduced dimensionality - in comparison to conventional, spherically formulated elements - when used to represent wave fields in the vicinity of slender or flat objects. Conjugated weighting functions are used to give frequency-independent acoustic ‘mass’, ‘stiffness’ and ‘damping’ matrices. This facilitates a simple extension of the method to transient problems. The effectiveness and accuracy of the method is demonstrated by a comparison of computed and analytic solutions for sound fields generated by a rigid sphere in steady harmonic oscillation, by a rigid sphere excited from rest, and by a circular plate vibrating in a plane baffle. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 45
    ISSN: 0029-5981
    Keywords: structural dynamics ; damping ; discrete elements ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Algorithmic aspects of energy dissipation mechanisms of dynamic structural systems in conjunction with central difference time integration method are investigated and damping proportional to M(M-1K)m (where K is the stiffness matrix, M is the mass matrix and m is a damping parameter) is proposed. Detailed algorithms for M(M-1K)m proportional damping for the central difference time integration method are presented together with stability criteria and numerical test problems. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 46
    ISSN: 0029-5981
    Keywords: Cosserat continuum theory ; rigid-plastic FEM ; powder compaction ; microscopic rotation ; couple stress ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The effect of microscopic rotation of powder particles in compaction is included in the rigid-plastic finite element method on the basis of the Cosserat continuum theory. In the Cosserat continuum theory, couple stress induced from the microscopic rotation is introduced, and the equilibrium equations of moment for the couple stress are solved simultaneously with those of force. A yield criterion for the Cosserat porous continuum is proposed by taking the effect of the couple stress into consideration, and constitutive equations for the rigid-plastic porous material are derived from the yield criterion on the basis of the associated flow rule. The equilibrium equations of force and moment for the Cosserat continuum are formulated by the use of the Galerkin method. The effect of microscopic rotation of powder particles in plane-strain closed-die compaction is examined. In addition, the calculated result is compared with that for the conventional continuum without the microscopic rotation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 47
    ISSN: 0029-5981
    Keywords: turbulent transition ; turbulence modelling ; Navier-Stokes equation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper describes a novel approach in simulating laminar to turbulent transition by using two-equation models. The Total Stresses Limitation (TSL) concept is used to make the two-equation model capable of predicting high-Reynolds-number transitional flow. In order to handle the transition triggered by laminar separation at a low Reynolds number location, which commonly occurs in high speed flow, a sensor is introduced to detect separation and trigger transition in the separated zone. Test cases include the classical flat-plate turbulent boundary flow, and low-pressure turbine cascade flows at design and off-design conditions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 48
    ISSN: 0029-5981
    Keywords: compliant ; collapsible ; stenotic ; free moving ; Navier-Stokes ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Cardiovascular illness is most commonly caused by a constriction, called a stenosis. A non-linear mathematical model with a free moving boundary was introduced to study viscous flow in tapered elastic tubes with axisymmetric constrictions subject to a prescribed pressure drop and a uniform external pressure. An iterative numerical scheme using a boundary iteration method was developed to solve the model. Effects of stenosis severity and stiffness, pressure drop, external pressure and stiffness of the vessel wall on the flow and wall motion were evaluated. It was found that stenosis severity, pressure drop and external pressure played more dominant roles than tube wall stiffness and stenosis stiffness perturbation. Tubes with 71 and 78 per cent stenoses showed two areas of negative transmural pressure and complex contraction-expansion-contraction wall motion patterns. Two types of tube diameter contraction and negative transmural pressure were observed, one was just distal to the stenosis and the other was near the outlet of the tube. Experiments using stenotic silicone tubes were conducted to quantify the tube law and verify the predicted pressure-flow relationship. The agreement between the numerical results and experimental measurements is better than that from a previous model which assumed periodicity of the tube and imposed different pressure conditions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 49
    ISSN: 0029-5981
    Keywords: Reissner's plate theory ; Winkler foundation ; boundary element method ; fundamental solutions ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper the application of the boundary element method to thick plates resting on a Winkler foundation is presented. The Reissner plate bending theory is used to model the plate behaviour. The Winkler foundation model is represented by continuous springs which are directly incorporated into the governing differential equation. The fundamental solutions are constructed using operator decoupling technique. These fundamental solutions represent three different cases depending on the problem constants. The explicit forms of the boundary and internal point kernels are given in all cases. Quadratic isoparametric boundary elements are used to model the plate boundary. Several examples are presented to demonstrate the accuracy of the present formulation. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 50
    ISSN: 0029-5981
    Keywords: refined triangular discrete Kirchhoff plate element ; C1-continuity requirement ; natural frequency of vibration ; critical load of buckling ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A refined triangular discrete Kirchhoff thin plate bending element RDKT which can be used to improve the original triangular discrete Kirchhoff thin plate bending element DKT is presented. In order to improve the accuracy of the analysis a simple explicit expression of a refined constant strain matrix with an adjustable constant can be introduced into its formulation. The new element displacement function can be used to formulate a mass matrix called combined mass matrix for calculation of the natural frequency and in the same way a combined geometric stiffness matrix can be obtained for buckling analysis. Numerical examples are presented to show that the present methods indeed, can improve the accuracy of thin plate bending, vibration and buckling analysis. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 51
    ISSN: 0029-5981
    Keywords: viscous flow ; boundary element ; indirect formulation ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the present work, we propose an indirect boundary-only integral equation approach for the numerical solution of the Navier-Stokes system of equations in a three-dimensional flow cavity. The formulation is based on an indirect integral representational formula for the permanent Stokes equations, and the use of a particular solution of a nonhomogeneous Stokes system of equations in order to obtain in an iterative way the corresponding complete solution of the problem. Previous boundary-only integral equation approaches to the present problem, using direct boundary elements formulations, result in a series of matrix multiplications that make these approaches computationally costly. Due to the use of an indirect formulation, the present approach is free from those matrix multiplications. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 52
    ISSN: 0029-5981
    Keywords: shape optimization ; sensitivity analysis ; non-linear arch ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A shape optimization method for geometrically non-linear structural mechanics based on a sensitivity gradient is proposed. This gradient is computed by means of an adjoint state equation and the structure is analysed with a total Lagrangian formulation. This classical method is well understood for regular cases, but standard equations have to be modified for limit points and simple bifurcation points. These modifications introduce numerical problems which occur at limit points. Numerical systems are very stiff and the quadratic convergence of Newton-Raphson algorithm vanishes, then higher-order derivatives have to be computed with respect to state variables. A geometrically non-linear curved arch is implemented with a finite element method via a formal calculus approach. Thickness and/or shape for differentiable costs under linear and non-linear constraints are optimized. Numerical results are given for linear and non-linear examples and are compared with analytic solutions. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 53
    ISSN: 0029-5981
    Keywords: structural dynamics ; time integration ; weighted residuals ; implicit procedure ; unconditional stability ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An unconditionally stable single-step implicit algorithm for the integration of the equations of motion arising in structural dynamics is presented. Within a time step, the displacement for a single degree of freedom system is approximated by a function which is cubic in time. The four coefficients of the cubic are chosen to satisfy the two initial conditions and two weighted integral equations. By considering general weight functions, six additional coefficients arise. In a series of steps, these coefficients are selected to (i) maximize algebraic accuracy by matching terms of Taylor's expansions of exact and approximate solutions, (ii) ensure unconditional stability and (iii) optimize numerical conditioning of the equations in a limiting case. Equations required to implement the procedure are presented. The method as presented has no algorithmic damping of higher modes, although it is indicated how this may be achieved. The error in period elongation obtained using the proposed method is shown to be far less than using alternative procedures. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 54
    ISSN: 0029-5981
    Keywords: unsymmetric sparse matrices ; frontal solver ; direct methods ; finite elements ; BLAS ; computational kernels ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We consider the implementation of a frontal code for the solution of large sparse unsymmetric linear systems on a high-performance computer where data must be in the cache before arithmetic operations can be performed on it. In particular, we show how we can modify the frontal solution algorithm to enhance the proportion of arithmetic operations performed using Level 3 BLAS thus enabling better reuse of data in the cache. We illustrate the effects of this on Silicon Graphics Power Challenge machines using problems which arise in real engineering and industrial applications. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 55
    ISSN: 0029-5981
    Keywords: neural networks ; training ; constitutive models ; non-linear ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new method, termed autoprogressive training, for training neural networks to learn complex stress-strain behaviour of materials using global load-deflection response measured in a structural test is described. The richness of the constitutive information that is generally implicitly contained in the results of structural tests may in many cases make it possible to train a neural network material model from only a small number of such tests, thus overcoming one of the perceived limitations of a neural network approach to modelling of material behaviour; namely, that a voluminous amount of material test data is required. The method uses the partially-trained neural network in a central way in an iterative non-linear finite element analysis of the test specimen in order to extract approximate, but gradually improving, stress-strain information with which to train the neural network.An example is presented in which a simple neural network constitutive model of a T300/976 graphite/epoxy unidirectional lamina is trained, using the load-deflection response recorded during a destructive compressive test of a [(±45)6]S laminated structural plate containing an open hole. The results of a subsequent forward analysis are also presented, in which the trained material model is used to simulate the response of a compressively loaded [(±30)6]S structural laminate containing an open hole. Avenues for further improvement of the neural network model are also suggested.The proposed autoprogressive algorithm appears to have wide application in the general area of Non-Destructive Evaluation (NDE) and damage detection. Most NDE experiments can be viewed as structural tests and the proposed methodology can be used to determine certain damage indices, similar to the way in which constitutive models are determined. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 56
    ISSN: 0029-5981
    Keywords: boundary element method ; stiffened panels ; repair patches ; fracture mechanics ; damage tolerance ; stress intensity factors ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper presents a formulation based on the Dual Boundary Element Method and on the Dual Reciprocity Method for the analysis of thin cracked metal sheets to which thin metal patches and stiffeners are adhesively bonded.The stiffened cracked sheet is modelled with the Dual Boundary Element Method. Adhesive shear stresses are modelled as action-reaction body forces exchanged by the sheet and patches. The Dual Reciprocity Method is used to avoid the discretization of the patches attachment domain into internal cells.Several examples are presented to demonstrate the efficiency and robustness of the method developed. The examples include sheets with embedded or edge cracks, stiffened or not, to which single or double patches are adhesively bonded. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 57
    ISSN: 0029-5981
    Keywords: elastoplastic analysis ; boundary element method ; fracture mechanics ; dual boundary element method ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this paper a general boundary element formulation for the three-dimensional elastoplastic analysis of cracked bodies is presented. The non-linear formulation is based on the Dual Boundary Element Method. The continuity requirements of the field variables are fulfilled by a discretization strategy that incorporates continuous, semi-discontinuous and discontinuous boundary elements as well as continuous and semi-discontinuous domain cells. Suitable integration procedures are used for the accurate integration of the Cauchy surface and volume integrals. The explicit version of the initial strain formulation is used to satisfy the non-linearity. Several examples are presented to demonstrate the application of the proposed method. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    Signatur Availability
    BibTip Others were also interested in ...
  • 58
    ISSN: 0029-5981
    Keywords: parallel computing ; finite elements ; substructures ; Engineering ; Numerical Methods and Modeling