bluuebunny/crossref_metadata_2025 huggingface dataset:
Superconvergence recovery technique and a posteriori error estimators
Authors: Zhu J. Z. , Zienkiewicz O. C.
Published: November 2005

A new superconvergence recovery technique for finite element solutions is presented and discussed for one dimensional problems. By using the recovery technique a posteriori error estimators in both energy norm and maximum norm are presented for finite elements of any order. The relation between the postprocessing and residual types of energy norm error estimators has also been demonstrated.
Petrov‐Galerkin finite element model for compressible flows
Authors: Brueckner Frank P. , Heinrich Juan C.
Published: November 2005

A Petrov‐Galerkin method for the solution of the compressible Euler and Navier‐Stokes equations is presented. It is based on the introduction of an anisotropic blancing diffusion in the direction of the local direction of propagation of the scalar variables. The local direction in which the anisotropic diffusion is introduced is uniquely determined, and the magnitude of the balancing diffusion is automatically calculated locally using a criterion that is optimal for one‐dimensional transport equations.

The algorithm has been implemented using four‐noded bilinear elements with forward Euler and second‐order Runge‐Kutta methods of integration in time. Several applications are presented and show the stability and approximation properties of the method.
Trust region methods for structural optimization using exact second order sensitivity
Authors: Sunar M. , Belegundu A. D.
Published: November 2005

The performance of multiplier algorithms for structural optimization has been significantly improved by using trust regions. The trust regions are constructed using analytical second order sensitivity, and within this region, the augmented Lagrangian ϕ is minimized subject to bounds. Evaluation of first and second derivatives of ϕ by the adjoint method does not require derivations of individual (implicit) constraint functions, which makes the method economical. Eight test problems are considered and a vast improvement over previously used multiplier algorithms has been noted. Also, the algorithm is robust with respect to scaling, input parameters and starting designs.
Direct evaluation of singular integrals in elastoplastic analysis by the boundary element method
Authors: Lu Shan , Ye T. Q.
Published: November 2005

This paper presents a new method for the direct and accurate evaluation of strongly singular integrals in the sense of Cauchy principal values and weakly singular integrals over quadratic boundary elements in three‐dimensional stress analysis and quadratic internal cells in two‐dimensional elastoplastic analysis by the boundary element method. A quadratic triangle polar co‐ordinate transformation technique is applied to reduce the order of singularity of the singular integrals. Next, a form of Stokes' theorem is introduced in order to remove the singularity in the Cauchy principal value integrals; therefore, the evaluation of these integrals can be carried out by standard Gaussian quadrature. Numerical examples of 2‐D elastoplastic problems and a 3‐D elastic problem show the effectiveness and efficiency of the method.
The finite element solution of elliptical systems on a data parallel computer
Authors: Hutchinson Scott , Hensel Edward , Castillo Steven , Dalton Kim
Published: November 2005

A study is conducted of the finite element solution of elliptic partial differential equations on a data parallel computer. A nodal assembly technique is introduced which maps a single node to a single processor. The system of equations is first assembled and then solved in parallel using a conjugate gradient algorithm for unsymmetric, non‐positive definite systems. Using this technique and a massively parallel machine, problems in excess of 100k nodes are solved.

Results of electromagnetic scattering, governed by the 2‐d scalar Helmholtz equation, are presented for both an infinite cylinder and an airfoil cross‐section. Solutions are demonstrated for a wide range of object sizes. A summary of performance data is given for a set of test problems.
A hierarchical approach to automatic finite element mesh generation
Authors: Yuen M. M. F. , Tan S. T. , Hung K. Y.
Published: November 2005

A point‐based two‐stage hierarchical method for automatic finite element mesh generation from a solid model is presented.

Given the solid model of a component and the required nodal density distribution, nodes are generated according to the hierarchy—vertex, edge, face and solid. At the vertices, nodes are established naturally. Nodes on the edges, faces and inside the solid model are generated by recursive subdivision. The nodes are then connected to form a valid and well‐conditioned finite element mesh of tetrahedron elements using modified Delaunay Triangulation. Checks are conducted to ensure the compatibility of geometry and topology between the solid model and the mesh.
A numerical approach for determining weight functions in fracture mechanics
Authors: Beghini M. , Bertini L. , Vitale E.
Published: November 2005

The paper deals with the development of a numerical method for determining Weight Functions in two‐dimensional problems. After a short review of some recent numerical techniques an original approach is presented. The method is based on Finite Element calculations with coarse meshes and on the knowledge of some values of the Stress Intensity Factor for one reference loading condition. The validity of the method is demonstrated for a theoretical case and its accuracy and suitability are discussed with reference to practical applications.
An adaptive finite element method for transient compressible flows with moving boundaries
Authors: Probert E. J. , Hassan O. , Morgan K. , Peraire J.
Published: November 2005

A description is given of an adaptive finite element method for the simulation of two dimensional compressible flows with moving boundaries. The method is implemented on an unstructured triangular grid and the mesh adaptation is achieved by local grid regeneration, using an error estimation procedure coupled to an automatic triangular mesh generator. Two numerical examples are included to illustrate the numerical performance of the method.
Finite element analysis of heat transfer and flow problems using adaptive remeshing including application to solidification problems
Authors: Lewis R. W. , Huang H. C. , Usmani A. S. , Cross J. T.
Published: November 2005

An error estimation technique for adaptive finite element analysis of heat conduction problems is described. The performance of this technique is demonstrated using a two‐dimensional steady‐state linear benchmark problem with a known analytical solution. A transient non‐linear heat conduction problem involving solidification is then solved as a typical practical application. Some preliminary investigations for error indicators in flow problems are presented.
Paving: A new approach to automated quadrilateral mesh generation
Authors: Blacker Ted D. , Stephenson Michael B.
Published: November 2005

This paper presents a new mesh generation technique, paving, which meshes arbitrary 2‐D geometries with an all‐quadrilateral mesh. Paving allows varying element size distributions on the boundary as well as the interior of a region. The generated mesh is well formed (i.e. nearly square elements, elements perpendicular to boundaries, etc.) and geometrically pleasing (i.e. mesh contours tend to follow geometric contours of the boundary). In this paper we describe the theory behind this algorithmic/heuristic technique, evaluate the performance of the approach and present examples of automatically generated meshes.
Bounds on eigenvalues of finite element systems
Authors: Lin Jerry I.
Published: November 2005

Bounds on eigenvalues of various finite element systems are analysed by using an element eigenvalue theorem together with the Global Eigenvalue Theorem. Both two dimensional continuum dynamics and heat conduction problems are considered. These bounds provide stable time steps for explict time integration schemes. A reduced eigenproblem at element quadrature point level, with all zero eigenvalues suppressed, is also presented in this paper. The simplified eigenproblem results in simple formulas for calculating the eigenvalues.
The Lanczos algorithm applied to unsymmetric generalized eigenvalue problem
Authors: Rajakumar C. , Rogers C. R.
Published: November 2005

Application of the two‐sided Lanczos recursion to the unsymmetric generalized eigenvalue problem is presented. The system matrices are real and unsymmetric. Therefore, the recursions are performed in real arithmetic and complex arithmetic is employed in the QR algorithm used to extract the eigenvalues of the transformed tridiagonal matrix. The biorthonormal transformation of the unsymmetric generalized eigenvalue problem is considered in detail with appropriate proofs presented in Appendices. Issues relating to the computer implementation of the unsymmetric generalized eigenvalue problem are discussed. The example problems solved demonstrate the working of the algorithm in extracting the complex and/or real eignevalues of an unsymmetric system of matrices. Also, the algorithm is applied to extract a few of the eigenvalues of a large fluid‐structure interaction problem, and the results are compared with the eigenfrequencies extracted by an unsymmetric subspace iteration procedure presented in the literature.
A boundary integral equation method for an inverse problem related to crack detection
Authors: Nishimura N. , Kobayashi S.
Published: November 2005

This paper discusses an application of a boundary integral equation method (BIEM) to an inverse problem of determining the shape and the location of cracks by boundary measurements. Suppose that a given body contains an interior crack, the shape and the location of which are unknown. On the exterior boundary of this body one carries out measurements which are interpreted mathematically as prescribing Dirichlet data and measuring the corresponding Neumann data, or vice versa, for a field governed by Laplace's equation. The inverse problem considered here attempts to determine the geometry of the crack from these experimental data. We propose to solve this problem by minimizing the error of a certain boundary integral equation (BIE). The process of this minimization, however, is shown to require solutions of certain are proposed. Several 2D and 3D numerical examples are given in order to test the performance of the present method.
Dynamics of flexible multibody systems using cartesian co‐ordinates and large displacement theory
Authors: Avello Alejo , de Jalón Javier García , Bayo Eduardo
Published: November 2005

A formulation for the dynamic analysis of flexible systems, composed of slender bodies that can be accurately modelled by beams is presented in this paper. A new set of state variables, composed of Cartesian co‐ordinates of points and unit vectors, is introduced to define the beam with respect to an inertial frame. A non‐linear Timoshenko beam finite element capable of handling finite displacements with small linear elastic strains is developed. This allows relative displacements between material points of a single beam to be arbitrarily large. Since deformations are not explicit variables, there is no need to define a moving reference frame attached to each flexible body. Instead, deformations are obtained through a displacement‐deformation relation based on finite‐displacement beam theory. The differential equations of motion are obtained using the Lagrange equations. A symmetric, constant and sparse mass matrix is obtained in the inertial frame. Constraints are introduced with a penalty formulation and the resulting set of ordinary differential equations is integrated with Newmark's family of methods. The whole formulation is extremely simple and the results demonstrate the capabilities and efficiency of the proposed method for dynamic simulation, even when relative displacements are finite in a single beam or coupling effects are significant.
Modelling and control of flexible robots
Authors: Chedmail P. , Aoustin Y. , Chevallereau Ch.
Published: November 2005

The object of this paper is to present a study on the modelling and control of flexible robots by using a knowledge based control design approach. We first develop an appropriate model of such a mechanical system in the case of open loop robot structures. We use a total Lagrangian formulation. After discretization, the degrees of freedom are the joint variables and the elastic degrees of freedom of each link. The elastic motions are referred to the rigid configuration of the considered link. The control law is obtained by using a non‐linear decoupling technique which is applied to the joint variables. A second control loop performs an active damping of the elastic motions: it is based on the linearized model and uses the LQR method. This approach has been experimented with a two flexible links robot. The results demonstrate its feasibility. Further developments mainly concern theoretical aspects on the robustness of these control laws, the identification of the model parameters and the choice of other appropriate modelling techniques.
Direct determination of periodic solutions of the dynamical equations of flexible mechanisms and manipulators
Authors: Meijaard J. P.
Published: November 2005

A method based on finite elements, characterized by generalized strains as functions of the nodal co‐ordinates, is the basis for the computer program SPACAR for the kinematic and dynamic analysis of flexible multibody systems. This program allows also the evaluation of the linearized dynamical equations, which makes possible the implementation of a method for the direct determination of stationary and periodic solutions and of a continuation method for these solutions if some parameter is varied. As an illustration, these methods are applied to a Duffing equation, a double pendulum and a slider‐crank mechanism with an elastic connecting rod.
Shell theory versus degeneration—a comparison in large rotation finite element analysis
Authors: Buechter Norbert , Ramm Ekkehard
Published: November 2005

The first part of this study addresses the controversy ‘degenerated solid approach’ versus ‘shell theory’. It is shown that both formulations differ only in the kind of discretization if they are based on the same mechanical assumptions. In particular for degenerated shell elements different versions of explicit integration across the thickness are discussed. Among these are the approximation ‘Jacobian across the thickness is constant’, proven to be too restrictive, and the series expansion of the inverse Jacobian which turns out to be unnecessary although it leads to equations of the same order as those of a ‘best first approximation’ of a shell theory.

The second part deals with the description of large rotations. It is demonstrated for problems formulated in three components of a rotation vector that a straightforward derivation results in a symmetric tangent stiffness matrix. However, a modified version is also added leading to an unsymmetric matrix already discussed in the literature. For shell problems with only two rotational variables both formulations coincide.
A universal method for including shear deformation in thin plate elements
Authors: Yuqiu Long , Fei Xi
Published: November 2005

A universal method which can be used to generalize thin plate elements to thick ones without adding any extra degree of freedom (DOF) is presented in this paper. To illustrate this method, a rectangular moderately thick plate element with 12 DOF is constructed on the basis of the well known thin plate ACM element. The element can be used in the analysis of both thin and thick plates. Shear locking is avoided.
A simplified analysis of plate structures using Trefftz‐functions
Authors: Hochard Ch. , Proslier L.
Published: November 2005

This paper presents a method for a quick evaluation of stresses and displacements in a plate structure for elastostatic problems. First, an approximation is built from the mathematical structure of the solutions for starshaped domains, which is representative of long wavelength effects. Second, a variational formulation consistent with this approximation is proposed. Finally, two alternative procedures for coupling adjacent domains are demonstrated.
On a highly robust spurious‐mode filtering method for uniformly reduced‐integrated shell elements
Authors: Vu‐quoc L. , Hoff C.
Published: November 2005

In structural elements that allow shear deformation, uniformly reduced integration is used to avoid shear and membrane locking. The spurious modes of an underintegrated stiffness matrix can be filtered using perturbation methods. Although finite elements with perturbed stiffness show very good results, the displacements still conceal a component of spurious modes, albeit with very small magnitude depending on the perturbation factor. To desensitize the numerical results completely from the perturbation factor, a projection of the applied force is proposed to complement the perturbation of the stiffness such that spurious modes are not excited, thus providing robustness to the filtering of spurious modes. The proposed methodology is general in nature, but is applied in this paper to a 9‐node shell element with uniformly reduced integration as an illustration. The perturbation of the stiffness matrix and the projection of the force vector are performed at the element level, avoiding expensive local‐global transformations. As a consequence of the force projection, the perturbation factor for the stiffness can be arbitrarily small, and the element yields accurate results for a wide range of shell thickness.
Computation of MPD flows and comparison with experimental results
Authors: Sleziona P. C. , Auweter‐Kurtz M. , Schrade H. O.
Published: November 2005

For several years, experimental investigations with magnetoplasmadynamic (MPD) thrusters have been conducted at the Institute for Space Systems (IRS). In order to achieve a better understanding of these thrusters, numerical procedures to calculate these MPD accelerators have been applied. A theoretical model for the calculation of the current, electron temperature and flow distribution in self‐field MPD thrusters has been developed. The extended Ohm's law has been applied to calculate the current contour lines, the electron energy equation is taken to calculate the electron temperature distribution and a two‐dimensional flow code is used to obtain the velocity, pressure and heavy particles temperature distributions. With both temperature distributions, a thermal non‐equilibrium in the plasma flow is obtained. The gas dynamic equations are solved by a finite volume code EUFLEX, which was transformed to cylindrical co‐ordinates and extended for the implementation of j × B and heat source terms. The electromagnetic discharge equation and the electron energy equation are transformed into curvilinear co‐ordinates and solved for the steady phase by a modified Gauss–Seidel algorithm. A comparison of the numerical and experimental results for different currents is presented and discussed.
A BEM approach to model heat flow during crystallization
Authors: Erhun Mehmet , Advani Suresh G.
Published: November 2005

In most polymer processing applications such as injection moulding, fibre spinning and extrusion, crystallization plays an important role. The energy flow at the solid‐liquid interface during crystallization controls the kinetics and subsequently influences the morphology of the transforming material. Our approach is based on the classical phase‐change problem. The governing transient heat conduction equations in the liquid and the solid domains are solved using a boundary element method (BEM) with a time dependent fundamental solution to determine the temperature distribution. The boundary energy equation is used to predict the movement of the front. The crystallization kinetics are introduced through a mathematical model based on the cooling rate of a hypothetical control volume in the solid (crystalline) domain and the changes in the crystallinity are expressed in terms of the varying interface temperature. First, we verified the BEM formulation and implementation by comparing the results of two examples with an analytical and a finite difference method in one‐dimension. Next, we investigated the effects of the crystallization kinetics by allowing the interface temperature to vary during the crystallization process. The results show that the crystallization front movement is slowed considerably when the kinetics are taken into account. Also, depending on the cooling rate and the parameters in the kinetics model, there may be undercooling during the process.
The multiple reciprocity method applied to thermal stress problems
Authors: Neves A. C. , Brebbia C. A.
Published: November 2005

In this paper, the multiple reciprocity boundary element method is applied to transform domain integrals due to thermal loadings into equivalent boundary integrals. The resulting formulation is restricted to two‐dimensional elastic and isotropic materials with any steady‐state temperature distribution, including internal heat generation. Several numerical examples are presented to validate the formulation and demonstrate the accuracy of the method.
Efficient and reliable accelerated constant stiffness algorithms for the solution of non‐linear problems
Authors: Chen Chang‐New
Published: November 2005

The paper relates to a secant‐relation‐based acceleration method used to improve the modified Newton‐Raphson scheme in which the constant stiffness matrix formed at the first iteration step is adopted to make incremental predictions for all iteration steps. An accelerator defined by minimizing a certain globally defined system error is used to scale the incremental response vector obtained by the modified Newton‐Raphson prediction in iteratively updating the response vector. The performance of acceleration is dependent on the method used to evaluate the system error. A consistent approach of evaluating the system error leads to obtaining a consistent accelerator. Another approach evaluates the system error less consistently, which results in obtaining a less consistent accelerator. Numerical results of non‐linear finite element analyses will be presented to show the effectiveness of this approach and to demonstrate the conclusion made by theoretical investigation regarding the convergency performances of the two accelerators proposed.
The C° structural finite elements reformulated
Authors: Briassoulis D.
Published: November 2005

A new formulation was recently proposed by the present author aimed at removing the shear and membrane locking mechanisms from the C° structural elements. The performance achieved was shown to be excellent, completely eliminating all locking problems. In some cases of C° plate and shell element applications; however, the proposed formulation was shown to yield flexible (softer than expected) models. Analysis of this behaviour revealed the presence of an internal moment redistribution mechanism with the classical formulation. The absence of this mechanism from the new formulation was found to be responsible for the potential introduction of softening effects in the elastic finite element models. In the present paper, the internal moment redistribution effect is examined analytically and the key component responsible for its development is isolated. The new formulation, as originally proposed for the C° structural elements, is modified so that the internal moment redistribution mechanism is retained, yet, with all locking mechanisms being rejected. The proposed formulation has been subjected recently to extensive numerical investigation with excellent results.
Inverse stefan problem: Tracking of the interface position from measurements on the solid phase
Authors: Bénard C. , Afshari A.
Published: November 2005

This study presents a sequential algorithm for the identification of the position s of the moving boundary of a variable one‐dimensional or two‐dimensional domain from discrete measurements, temperatures and fluxes, collected at the fixed boundary. The inverse problem is solved by minimization, with respect to s, of a penalized output least square criterion defined on a sliding time horizon of length τ. At every time step, several iterations are performed to estimate the unknown s. Each iteration consists in a guess of s, a computation of the corresponding value of the output y (direct model) and the criterion J, and a step towards a new estimation of s. The impact of the different parameters, space and time discretization intervals, regularization coefficient, dimension of the unknown parameter s, length of the observation horizon, choice of the observed output (temperature or flux) and choice of the direct model is thoroughly analysed for an analytical test case.
The conjugate formulation of a radiation induced transient natural convection boundary layer
Authors: Li Xianming , Durbetaki Pandeli
Published: November 2005

The vertical surface of a non‐reactive semi‐infinite solid is suddenly heated by a radiative heat flux source. The surface temperature increases and a thermal wave penetrates the solid. At the same time, the hot surface heats the neighbouring air, which begins to move upward under the influence of gravity. The events in both domains are closely connected and the compressible fluid in the boundary layer establishes a hydrodynamic and thermal coupling. Such coupling and the non‐linearity in this problem require a special solution approach. A numerical technique was selected, which is based on the finite control volume method developed by Patankar and Spalding. The Patankar–Spalding method was modified to accommodate both the solid domain and the gas phase domain simultaneously. The conjugate formulation for the transient combined solid phase and gaseous boundary layer was investigated. It was found that the new conjugate method provided reliable solutions to the current problem. Furthermore, the analysis revealed that the time required for the surface temperature to attain a specified value was inversely proportional to the square of the radiative heat flux.
Implementation of a lamina‐based constitutive relationship for analysing thick composites
Authors: Zywicz Edward
Published: November 2005

The finite element implementation of a lamina‐based elastic constitutive relation appropriate for describing the three‐dimensional (3‐D) behaviour of fibre composite laminated media is presented. Unconstrained by the two‐dimensional restrictions accompanying plate and shell theories, this approach resolves the macro 3‐D deformation fields found in 'thick' laminated or filament wound composites without requiring each lamina to be individually discretized to assign material properties. In rectangular isoparametric solid elements where laminae locally parallel an element 'face', the implementation represents 'exactly' the elastic laminate behaviour by replacing the discrete lamina stiffnesses with continuous polynomial moduli functions. Attributable directly to the lamina constitutive relationship used, appropriate for fibre‐dominated material systems, the implementation automatically preserves interlaminar continuity of tractions and displacements within each element for laminates assembled from a single lamina type. The order of the effective moduli functions is determined by the element kinematics and by requiring identical net mid‐surface elemental forces and moments. In general, this representation substantially reduces the number of stored variables and through‐thickness integrations required, and allows 'exact' integration by higher‐order Gaussian quadrature. Additionally a single element may span any portion or number of laminae, thus allowing nearly arbitrary meshing and solution resolution. Several numerical examples using 3‐D 8‐node isoparametric solid elements demonstrate the approach's convergence and overall behaviour.
Use of boundary element method for the determination of tool shape in electrochemical machining
Authors: Das Shuvra , Mitra Ambar K.
Published: November 2005

The problem of cathode shape determination for a given anode shape in electrochemical machining is considered. An algorithm based on the boundary integral equation technique and non‐linear optimization for this inverse problem is developed. The additional flux condition at the anode is used as the constraint in this ill‐posed problem. Through an iterative process, the shape of the cathode is determined by minimizing a functional. The algorithm is tested on two examples. It is shown that the algorithm is consistently superior compared to published numerical techniques based on the embedding method or the method of the lines.
reduction of equilibrium, compatibility and flexibility matrices, in the force method
Authors: Pellegrino S. , Kwan A. S. K. , Van Heerden T. F.
Published: November 2005

This paper develops analytical expressions and numerical for reducing the structural matrices which are used in the Force Method of structural analysis. Two simple examples illustrate the calculations for pin‐jointed trusses.

Two advanced applications, a beam cross consisting of two coplanar beams which are linked by a shear connector, and an equilibrium linear‐stress finite element, are also presented.
Some theoretical aspects in computational analysis of adhesive lap joints
Authors: Destuynder P. , Michavila F. , Santos A. , Ousset Y.
Published: November 2005

This paper is devoted to the numerical analysis of bidimensional bonded lap joints. For this purpose, the stress singularities occurring at the intersections of the adherend‐adhesive interfaces with the free edges are first investigated and a method for computing both the order and the intensity factor of these singularities is described briefly. After that, a simplified model, in which the adhesive domain is reduced to a line, is derived by using an asymptotic expansion method. Then, assuming that the assembly debonding is produced by a macro‐crack propagation in the adhesive, the associated energy release rate is computed. Finally, a homogenization technique is used in order to take into account a preliminary adhesive damage consisting of periodic micro‐cracks. Some numerical results are presented.
How to recognize the order of infinitesimal mechanisms: A numerical approach
Authors: Salerno Ginevra
Published: November 2005

Structures presenting kinematical inderterminacy are usually called mechanisms. This paper is entirely concerned with assemblies which reveal themselves to be mechanisms at a null value of the load. Among them a first distinction is made between infinitesimal and finite ones, the former being characterized by one or several directions of lower (but not zero) stiffness, whereas the latter show at least one finite admissible displacement for which none of the bars undergoes any elongation. Moreover, there exists the possibility to make a further distinction among the infinitesimal mechanisms, according to which is the order of the stiffness along the direction considered above. The way of evaluating this order is to perform a local analysis of the strain energy of the assembly, once the displacement field is parametrized in terms of a suitable parameter. By means of a finite element technique, this analysis can be easily performed through the numerical approach presented in this report.
Creep deformation structural analysis using an efficient numerical algorithm
Authors: Whirley Robert G. , Henshall Gregory A.
Published: November 2005

This paper presents a fast numerical algorithm for the implementation of material models for creep into finite element codes. First, an overview of existing algorithms for transient and steady‐state creep is given. Next, a new formulation is presented which reduces the constitutive integration to the solution of a scalar non‐linear algebraic equation. A solution is shown to exist without the need for subincrementation. Details of the numerical algorithm are then discussed. The paper closes with several numerical examples which illustrate the speed, robustness and accuracy of the proposed procedure as implemented in the Lawrence Livermore National Laboratory finite element codes NIKE2D and NIKE3D.
The use of orthogonal projections to handle constraints with applications to incompressible four‐node quadrilateral elements
Authors: Hueck Ulrich , Schreyer Howard L.
Published: November 2005

Linear equality multipoint constraint conditions define a vector space which is used to construct an orthogonal projection operator. Another orthogonal projection operator follows from the complement to the constrained vector space. A procedure is developed in which these operators are used in a systematic fashion to solve a set of algebraic equations subject to a set of multipoint constraints. In addition to elementary examples to illustrate the procedure, a problem associated with an incompressible, isotropic, elastic material is solved using four‐node quadrilateral finite elements. The method of orthogonal projections provides the insight to show that, with the application of the incompressibility constraint, convergence is obtained for any arbitrary value of Poisson's ratio chosen sufficiently far from the value of one‐half, which is the value normally associated with incompressibility. The bending performance of the incompressible four‐node quadrilateral can be adjusted with artificial values of Poisson's ratio. The result is that calculations are performed with full numerical quadrature of the element, and mesh locking, hourglass instabilities and subsequent modifications to the element stiffness matrix are avoided.
A multigrid method for the generalized symmetric eigenvalue problem: Part II—performance evaluation
Authors: Hwang T. , Parsons I. D.
Published: November 2005

The behaviour of the multigrid method is studied by solving some simple test problems. Optimum choices for some of the parameters are discussed, together with effective techniques for solving the coarse mesh correction equation. The effects of ill‐conditioning on the performance of the algorithm are examined. In particular, thin shells and non‐uniform meshes are observed to slow convergence. The solution of practical, large scale problems demonstrates the utility and speed of the proposed multigrid method. For example, the first 10 eigensolutions of a stiffened plate problem with 193 536 degrees‐of‐freedom were computed in 1.6 CPU hours using 42 Mbytes of memory on a Convex C240.
Seismic response analysis of alluvial valley with two dipping layers by a boundary element‐finite element coupling method
Authors: Abe Kazuhisa , Yoshida Yutaka
Published: November 2005

A coupling process of time‐domain boundary element method and finite element method is constituted for analysis of the dynamic response of an alluvial valley. Since the characteristics of these two methods are different from each other, the time increment of the boundary element method is set to be an integer multiple of the finite element method, and a combination of a linear interpolation of boundary element equations at two successive time steps with a finite element equation is proposed. Using this procedure, responses of alluvial valleys with two dipping layers are analysed for a vertically incident SV wave, and influence of the lower layer on these responses is investigated. It is found that the presence of the additional lower layer affects not only the reflected waves but also the surface waves. Furthermore, when an outcropping lower layer exists at the basin edges, the valley suffers an amplification of motion and an extreme increase in strains. These results show that a small difference in the layer at the basin edge is significant in analysing dynamic responses of an alluvial valley.
Boundary element analysis of thin plates internally bounded by rigid patches
Authors: Hartley Gilbert A. , Abdel‐Akher Ahmed , Chen Peilei
Published: November 2005

Procedures are described for modelling a structural system consisting of thin Kirchhoff plates with internal patch areas capable of displacing as rigid flat surfaces. The physical prototype for these patches could be interconnection points for one‐dimensional frame type elements of various shapes and layout, rigidly connected at these finite size 'joints' in the plate. The numerical procedure for modelling the thin plate is the Direct Boundary Element Method (DBEM) and a simple overview of this procedure is provided. Potential trouble spots, of which the user should be aware, are described.

The paper will be of interest to structural engineers for analysis of frames having both plate and simple frame elements, for example, building frames; and also to researchers seeking the greater detail that this refined procedure can provide. As a practical tool, the methods described are computationally competitive with existing procedures, including the more rugged approaches used by building structural engineers for dynamic and torsional analysis.
An enthalpy control‐volume—unstructured‐mesh (cv—um) algorithm for solidification by conduction only
Authors: Chow P. , Cross M.
Published: November 2005

Recently, control volume methods have been developed for fluid flow and heat transfer on unstructured meshes. This approach has been extended here to implement the enthalpy based solidification algorithm on an unstructured mesh. A range of two‐dimensional test problems are solved using triangular and quadrilateral cells (or elements). The accuracy of the CV–UM algorithms compare favourably with the structured‐mesh algorithm, though the former algorithms require 1.5–3 times as much CPU as the latter. This overhead is associated with the extra work caused by the unstructuredness of the mesh; the number of sweeps to achieve convergence is roughly comparable for all algorithms. The CV–UM algorithms should perform well on complex geometry problems and, therefore, show potential to be a productive technique in casting solidification analysis.
Three‐dimensional fracture simulation with a single‐domain, direct boundary element formulation
Authors: Martha Luiz F. , Gray L. J. , Ingraffea A. R.
Published: November 2005

An efficient hypersingular boundary integral equation method for three‐dimensional fracture mechanics was presented in a previous paper. The details of the numerical implementation of this method are further discussed herein. In particular, an algorithm for achieving the required differentiability of the crack surface displacement function is discussed. To illustrate the utility of the method, computational results for several strongly interacting multiple‐crack geometries are presented. The calculated stress intensity factors are in excellent agreement with those obtained by an approximate analytical method due to Kachanov and Laures.
Free‐radical polymerization of styrene with p‐nitrobenzyl triphenyl phosphonium ylide as an initiator
Authors: Prajapati Kiran , Varshney Anuradha
Published: November 2005

The free‐radical polymerization of styrene with p‐nitrobenzyl triphenyl phosphonium ylide as an initiator in dioxane at 80 ± 1 °C in a dilatometer under a nitrogen atmosphere for 150 min resulted in a syndiotactic polymer, as evidenced by IR, 1H NMR, and 13C NMR spectroscopy. A 1H NMR spectrum showed methylene protons as triplets; 13C NMR signals of the phenyl ipso carbons were used for the determination of the tacticity. The system followed ideal kinetics. Gel permeation chromatography data were used evaluate the weight‐average molecular weight. The overall activation energy was 47 kJ/mol. Electron spin resonance spectroscopy confirmed the initiation by the phenyl radical obtained by the dissociation of the ylide and the free‐radical mode of polymerization. Differential scanning calorimetry studies showed the glass‐transition temperature of the polymer to be 342 K. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6524–6533, 2005
Synthesis and crosslinking reaction of poly(thiourethane)s having a siloxane moiety in the side chain
Authors: Uenishi Kazuya , Sudo Atsushi , Endo Takeshi
Published: November 2005

Poly(thiourethane)s having a siloxane moiety in the side chain were synthesized with a 5‐membered cyclic dithiocarbonate (DTC) having a siloxane group as a building block. The synthetic pathway consisted of (1) an addition reaction of the DTC with diamines and (2) polyaddition reactions of the resulting dithiols with diisocyanates. The siloxane moiety in the polymer side chain underwent a self‐condensation reaction upon exposure to moisture, and this led to a successful crosslinking reaction of the poly(thiourethane). The crosslinking on a silicate surface was accompanied by condensation between the siloxane side chain of the polymer and the silanol group on the surface, giving the corresponding surface that was permanently coated with the crosslinked polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6492–6502, 2005
Oxidation polymerization of a charge‐transfer complex of 2,6‐bis(2‐thienyl)‐1,4‐dithiafulvene with 7,7,8,8‐tetracyanoquinodimethane
Authors: Gelover‐Santiago Adriana , Naka Kensuke , Chujo Yoshiki
Published: November 2005

A π‐conjugated poly(α‐dithienylen‐dithiafulvene) (2) was obtained by the oxidation polymerization of 2,6‐bis(2‐thienyl)‐1,4‐dithiafulvene (1) as a dithiafulvene monomer derived from 4‐(2‐thienyl)‐1,2,3‐thiadiazole. When a solution of 1 in CHCl3 was added to a stirred solution of FeCl3 in CHCl3, only the low‐molecular‐weight product 2 was obtained. The mixture was stirred for 15 h with an N2 flow. The polymerization at higher temperatures resulted in polymers with large insoluble fractions. A higher molecular weight polymer was obtained by the oxidation polymerization of a charge‐transfer complex of 1 with 7,7,8,8‐tetracyanoquinodimethane (compound 3). In contrast to 2, polymer 4 was readily soluble in dimethyl sulfoxide, dimethylformamide, and acetone and partially soluble in tetrahydrofuran and methanol and had a larger molecular weight (peak top molecular weight = 37,000). The conductivity of polymer 4 was 3 orders of magnitude larger than that of polymer 2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6592–6598, 2005
Improvement of the thermal stability of cluster‐crosslinked polystyrene and poly(methyl methacrylate) by optimization of the polymerization conditions
Authors: Gao Yu , Kogler Franz Rene , Schubert Ulrich
Published: November 2005

The polymerization conditions for polystyrene and poly(methyl methacrylate) crosslinked by 0.5 mol % of the cluster Zr6O4(OH)4(methacrylate)12 were optimized by applying a step polymerization procedure. The onset of thermal decomposition was thus increased up to about 50° for polystyrene and about 110° for poly(methyl methacrylate). The increase in thermal stability correlated with a higher char yield. The glass transition temperatures were also increased by about 15°. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6586–6591, 2005
Crystallization, mechanical, and fracture behaviors of spherical alumina‐filled polypropylene nanocomposites
Authors: Zhao Hongxia , Li Robert K. Y.
Published: November 2005

The objectives of this paper are to study the crystallization behavior and fracture characteristics of spherical alumina (Al2O3) nanoparticle‐filled polypropylene (PP) composites. Nanocomposites containing 1.5–5.0 wt % of the Al2O3 nanoparticles (pretreated with silane coupling agent) were prepared for this investigation. Wide angle X‐ray diffraction (WAXD) results show that a small amount of β‐crystal of PP forms after adding the Al2O3 nanoparticles. According to differential scanning calorimetric (DSC) and optical microscopy (OM) measurements, the Al2O3 nanoparticles make PP spherulite size reduced and crystallization temperature of PP enhanced, by acting as effective nucleating agents. However, there are no obvious differences in the crystallinity for the virgin PP and the Al2O3/PP nanocomposites. Tensile test shows that both the Young's modulus and the yield strength of the Al2O3/PP nanocomposites increase with the particle content increasing, suggesting that the interfacial interaction between the nanoparticles and PP matrix is relatively strong. Under quasi‐static loading rate, the fracture toughness (KIC) of the Al2O3/PP nanocomposites was found to be insensitive to nanoparticle content. Under impact loading rate, the Izod impact strength and the impact fracture toughness (Gc) indicate that the impact fracture toughness increases initially with the addition of 1.5 wt % of the Al2O3 nanofillers into the PP matrix. However, with the further addition of up to 3.0 and 5.0 wt % nanoparticles, both the Izod impact strength and impact Gc change very little. By observing the single‐edge‐double‐notch (SEDN) specimens with optical microscopy after four point bending (4PB) tests, it was found that numerous crazes and microcracks form around the subcritical crack tip, indicating that crazing and microcracking are the dominant fracture mechanisms. Scanning electron microscopy (SEM) observation confirms this result. In addition, when the strain rate of 4PB tests was increased, some wave‐like branches were formed along the fractured edge for the Al2O3/PP nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3652–3664, 2005
Nanoclay‐induced morphology development in chaotic mixing of immiscible polymers
Authors: Dharaiya Dhawal P. , Jana Sadhan C.
Published: November 2005

This study investigated the role of layered silicate clay on morphology development in chaotic mixing of two immiscible polymers, polypropylene (PP) and polyamide 6 (PA6). The study showed that clay particles helped to produce droplets of much smaller size and with narrower size distribution due to their direct influence on the breakup of PP domains. In the experiments, a small quantity of organically modified layered silicate clay was initially mixed in PP and the mixture was blended with PA6 in a chaotic mixer. All morphological forms, such as lamellas, fibrils, and droplets were seen as in the case with no clay. The clay particles reduced interfacial tension between PP and PA6 phases. As a consequence, the PP domains sustained lamellar and fibrillar forms, and thin fibrils were formed. These thin fibrils in turn broke rapidly into smaller droplets. It was also found that a large fraction of clay particles migrated into PA6 phase and contained intercalated PA6 chains in their galleries. These results indicate that clay particles did not participate in compatibilization in this system. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3638–3651, 2005
Peroxisome Proliferator‐Activated Receptors: Potential Therapeutic Targets in Lung Disease?
Authors: Denning Gerene M. , Stoll Lynn L.
Published: November 2005

The peroxisome proliferator‐activated receptors (PPARs) are a family of nuclear hormone receptors that play central roles in lipid and glucose homeostasis, cellular differentiation, and the immune/inflammatory response. Growing evidence indicates that changes in expression and activation of PPARs likely modulate conditions as diverse as diabetes, atherosclerosis, cancer, asthma, Parkinson's disease, and Alzheimer's disease. Activation of these receptors by natural or pharmacologic ligands leads to both gene‐dependent and gene‐independent effects that alter the expression of a wide array of proteins. In the lung, PPARs are expressed by alveolar macrophages, as well as by epithelial, endothelial, and smooth muscle cells. Studies both in vitro and in vivo suggest that PPAR ligands may have anti‐inflammatory effects in asthma, pulmonary sarcoidosis, and pulmonary alveolar proteinosis, as well as antiproliferative and antiangiogenic effects in epithelial lung cancers. Further studies to understand the contribution of these receptors to health and disease will be important for determining whether they represent a promising target for therapeutic intervention. Pediatr Pulmonol. © 2005 Wiley‐Liss, Inc.