bluuebunny/crossref_metadata_2025 huggingface dataset:
A data‐parallel approach to multiblock flow computations
Authors: Sawley M. L. , Tegnér J. K.
Published: November 2005

Multiblock methods are often employed to compute flows in complex geometries. While such methods lend themselves in a natural way to coarse‐grain parallel processing by the distribution of different blocks to different processors, in some situations a fine‐grain data‐parallel implementation may be more appropriate. A study is presented of the resolution of the Euler equations for compressible flow on a block‐structured mesh, illustrating the advantages of the data‐parallel approach. Particular emphasis is placed on a dynamic block management strategy that allows computations to be undertaken only for blocks where useful work is to be performed. In addition, appropriate choices of initial and boundary conditions that enchance solution convergence are presented. Finally, code portability between five different massively parallel computer systems is examined and an analysis of the performance results obtained on different parallel systems is presented.
Mixed explicit/implicit time integration of coupled aeroelastic problems: Three‐field formulation, geometric conservation and distributed solution
Authors: Farhat Charbel , Lesoinne Michel , Maman Nathan
Published: November 2005

A three‐field arbitrary Lagrangian‐Eulerian (ALE) finite element/voluem formulation for coupled transient aeroelastic problems is presented. The description includes a rigorous derivation of a geometric conservation law for flow problems with moving boundaries and unstructured deformable meshes. The solution of the coupled governing equations with a mixed explicit (fluid)/implicit (structure) staggered procedure is discussed with particular reference to accuracy, stability, distributed computing, I/O transfers, subcycling and parallel processing. A general and flexible framework for implementing partitioned solution procedures for coupled aeroelastic problems on heterogeneous and/or parallel computational platforms is described. This framework and the explicit/implicit partitioned procedures are demonstrated with the numerical investigation on an iPSC‐860 massively parallel processor of the instability of flat panels with infinite aspect ratio in supersonic airstreams.
The parallel processing technique applied to the cellular automation method in fluid dynamics simulations
Authors: Inoue Yukihiko , Katsuragi Kazuyuki , Ukai Osamu , Adachi Takeshi
Published: November 2005

This paper describes an efficient parallel algorithm of the cellular automaton (CA) method for microscopic fluid dynamics simulations. The CA method is parallelized with so‐called multispin coding and with one‐dimensional domain decomposition. The parallel CA method has a constant computational load balance and small data transfer between only nearby domains. We have applied the parallel CA method to a large‐scale Poiseuille flow simulation and an immiscible two‐phase flow simulation on a Fujitsu AP1000 with 64 processors.
Three‐step explicit finite element computation of shallow water flows on a massively parallel computer
Authors: Kashiyama Kazuo , Ito Hanae , Behr Marek , Tezduyar Tayfun
Published: November 2005

Massively parallel finite element strategies for large‐scale computations of shallow water flows and contaminant transport are presented. The finite element discretizations, carried out on unstructured grids, are based on a three‐step explicit formulation both for the shallow water equations and for the advection‐diffusion equation governing the contaminant transport. Parallel implementations of these unstructured‐grid‐based formulations are carried out on the Army High Performance Computing Research Center Connection Machine CM‐5. It is demonstrated with numerical examples that the strategies presented are applicable to large‐scale computations of various shallow water flow problems.
Analysis of shear layers based on the lattice gas model
Authors: Yuasa Atsushi , Inamuro Takaji , Adachi Takeshi
Published: November 2005

The ‘two‐colour lattice gas model’ is applied to the analysis of shear layers between two parallel flows with different velocities U1 and U2. Two cases, (a) U1 = 0.4, U2 = 0.2 and (b) U1 = 0.4, U2 = 0.0, are calculated and compared with the theoretical solutions. We obtain good agreement between theory and calculations in the velocity profiles of the shear layers. It is found that this model can simulate complicated physical phenomena of shear layers at the microscopic level.
New numerical schemes based on a criterion for constructing essentially stable and accurate numerical schemes for convection‐dominated equations
Authors: Sakai Katsuhiro
Published: November 2005

In order to obtain stable and accurate numerical solutions for the convection‐dominated steady transport equations, we propose a criterion for constructing numerical schemes for the convection term that the roots of the characteristic equation of the resulting difference equation have poles.

By imposing this criterion on the difference coefficients of the convection term, we construct two numerical schemes for the convection‐dominated equations. One is based on polynomial differencing and the other on locally exact differencing.

The former scheme coincides with the QUICK scheme when the mesh Reynolds number (Rm) is \documentclass{article}\pagestyle{empty}\begin{document}$\mathop \[{\textstyle{{\rm 8} \over {\rm 3}}}\] $\end{document}, which is the critical value for its stability, while it approaches the second‐order upwind scheme as Rm goes to infinity. Hence the former scheme interpolates a stable scheme between the QUICK scheme at Rm = \documentclass{article}\pagestyle{empty}\begin{document}$\mathop \[{\textstyle{{\rm 8} \over {\rm 3}}}\] $\end{document} and the second‐order upwind scheme at Rm = ∞. Numerical solutions with the present new schemes for the one‐dimensional, linear, steady convection‐diffusion equations showed good results.
Modified box schemes for pollutant transport in rivers with dead zones
Authors: Strauber Györgyi
Published: November 2005

Several difference schemes approximating a mathematical model of river pollution are investigated and their truncation error, stability and monotonicity conditions are shown. Based on numerical experiments, the classical six‐point schemes and some new modified box schemes are compared. The latter proved to be not only faster but also more accurate for practically used step lengths.
Aid to Africa: an unfinished agenda
Authors: Addison Tony , Mavrotas George , McGillivray Mark
Published: November 2005

The Millennium Development Goals (MDGs) give aid to Africa a new emphasis. Yet aid flows to Africa have trended downward over the last decade, and as a consequence more Africans now live in poverty. This is especially true of Sub‐Saharan Africa. Any progress towards the main MDG target of halving the number of people living in poverty clearly requires more aid. It also requires a better understanding of what drives aid volumes to Africa and precisely how these flows impact on African economies. This paper examines trends in official aid to Africa, Sub‐Saharan Africa in particular, over the period 1960 to 2002, highlighting falls in aid since the early 1990s. It concludes with consideration of future challenges for aid to Africa. Copyright © 2005 John Wiley & Sons, Ltd.
The facial motor nucleus transcriptional program in response to peripheral nerve injury identifies Hn1 as a regeneration‐associated gene
Authors: Zujovic Violetta , Luo Defang , Baker Henry V. , Lopez M. Cecilia , Miller Kelly R. , Streit Wolfgang J. , Harrison Jeffrey K.
Published: November 2005

Facial nerve axotomy (FNA) is a well‐established experimental model of motoneuron regeneration. After peripheral nerve axotomy, a sequence of events including glial activation and axonal regrowth leads to functional recovery of the afflicted pool of motoneurons. Using microarray analysis we identified an increase in the expression of 60 genes (at a false discovery rate of 0.1, genes were significant P < 0.004) within the facial nucleus as a consequence of nerve injury. In situ hybridization analysis validated the increased expression of many of these axotomy‐induced genes. One specific gene, encoding a unique primary amino acid sequence, termed hemopoietic‐ and neurologic‐expressed sequence‐1 (Hn1), was evaluated more extensively using several additional nerve injury paradigms. Hn1 mRNA was upregulated in injured facial motoneurons in both rats and mice. Sustained upregulation of Hn1 mRNA was evident after nerve resection whereas levels of Hn1 mRNA returned to baseline in animals subjected to nerve crush or nerve transection. Hn1 was also increased in the dorsal motor nucleus and the nucleus ambiguous after vagus nerve axotomy, another regeneration model. No upregulation of Hn1 expression was observed, however, in two nonregeneration models: FNA in newborn rats and rubrospinal tractotomy. Hn1 mRNA was ubiquitous in the developing central nervous system whereas its expression in adult brain was confined to neurons of the hippocampus, cortex and cerebellum. These findings identify Hn1 as a gene associated with nervous system development and nerve regeneration. © 2005 Wiley‐Liss, Inc.
Phosphodiesterase‐Iα/autotaxin (PD‐Iα/ATX): A multifunctional protein involved in central nervous system development and disease
Authors: Dennis Jameel , Nogaroli Luciana , Fuss Babette
Published: November 2005

Phosphodiesterase‐Iα/autotaxin (PD‐Iα/ATX) was originally identified as a cell‐motility‐stimulating factor secreted by a variety of tumor cells. Thus, studies related to its potential functional roles have traditionally focused on tumorigenesis. PD‐Iα/ATX's catalytic activity, initially defined as nucleotide pyrophosphatase/phosphodiesterase, was soon recognized as being necessary for its tumor cell‐motility‐stimulating activity. However, only the discovery of PD‐Iα/ATX's identity with lysophospholipase D, an extracellular enzyme that converts lysophosphatidylcholine into lysophosphatidic acid (LPA) and potentially sphingosylphosphoryl choline into sphingosine 1‐phosphate (S1P), revealed the actual effectors responsible for PD‐Iα/ATX's ascribed motogenic functions, i.e., its catalytic products. PD‐Iα/ATX has also been detected during normal development in a number of tissues, in particular, the central nervous system (CNS), where expression levels are high. Similar to tumor cells, PD‐Iα/ATX‐expressing CNS cells secrete catalytically active PD‐Iα/ATX into the extracellular environment. Thus, it appears reasonable to assume that PD‐Iα/ATX's CNS‐related functions are mediated via lysophospholipid, LPA and potentially S1P, signaling. However, recent studies identified PD‐Iα/ATX as a matricellular protein involved in the modulation of oligodendrocyte–extracellular matrix interactions and oligodendrocyte remodeling. This property of PD‐Iα/ATX was found to be independent of its catalytic activity and to be mediated by a novel functionally active domain. These findings, therefore, uncover PD‐Iα/ATX, at least in the CNS, as a multifunctional protein able to induce complex signaling cascades via distinct structure–function domains. This Mini‐Review describes PD‐Iα/ATX's multifunctional roles in the CNS and discusses their potential contributions to CNS development and pathology. © 2005 Wiley‐Liss, Inc.
Nitrate in vegetables: toxicity, content, intake and EC regulation
Authors: Santamaria Pietro
Published: November 2005

Nitrate content is an important quality characteristic of vegetables. Vegetable nitrate content is of interest to governments and regulators owing to the possible implications for health and to check that controls on the content are effective. Nitrate itself is relatively non‐toxic but its metabolites may produce a number of health effects. Until recently nitrate was perceived as a purely harmful dietary component which causes infantile methaemoglobinaemia, carcinogenesis and possibly even teratogenesis. Recent research studies suggest that nitrate is actually a key part of our bodies' defences against gastroenteritis. In this review are reported: (1) vegetable classification as a function of nitrate accumulation; (2) vegetable contribution to the total dietary exposure of nitrate; (3) European Commission Regulation No. 563/2002 which sets limits for nitrate in lettuce and spinach; (4) the maximum levels set in some countries for beetroot, cabbage, carrot, celery, endive, Lamb's lettuce, potato, radish and rocket; (5) the results of surveys on the nitrate content of vegetables in Italy and other European countries. Copyright © 2005 Society of Chemical Industry
The Parkinson–Control study: A 1‐year randomized, double‐blind trial comparing piribedil (150 mg/day) with bromocriptine (25 mg/day) in early combination with levodopa in Parkinson's disease
Authors: Castro‐Caldas Alexandre , Delwaide Paul , Jost Wolfgang , Merello Marcelo , Williams Adrian , Lamberti Paolo , Aguilar Miguel , Del Signore Susanna , Cesaro Pierre
Published: November 2005

Dopamine agonists have been recommended as early treatment for Parkinson's disease (PD), alone or combined with levodopa. Piribedil is a non‐ergot selective D2/D3 agonist with α2 antagonist properties shown to be effective in the treatment of PD. This 12‐month international, randomized, double‐blind trial aimed to assess the efficacy of piribedil 150 mg versus bromocriptine 25 mg, in early combination with levodopa in Stage I to III PD patients. Motor efficacy was assessed using the Unified Parkinson's Disease Rating Scale (UPDRS III, Items 18–31) as improvement from baseline. Response rate was defined as a 30% improvement. Among the 425 randomly assigned patients, 178 were also included in a substudy on cognitive follow‐up evaluated by a dysexecutive syndrome oriented battery. A relevant improvement in UPDRS III over the 12‐month study duration was observed both in the piribedil and bromocriptine groups (−7.9 ± 9.7 points from baseline versus −8.0 ± 9.5; not significant [n.s.]) with a response rate of 58.4% and 55.3% (n.s.), respectively. Piribedil and bromocriptine resulted in similar improvement on all UPDRS III subscores. Piribedil patients required less levodopa dose increase than those on bromocriptine. Cognitive performance remained generally unchanged in both groups, with a significant effect of piribedil limited to the Wisconsin Card Sorting Test. An overall good tolerability of piribedil was observed. Early combination of piribedil 150 mg with levodopa resulted in significant long‐term improvement of all motor symptoms in PD patients insufficiently controlled by levodopa alone. Taking into account both efficacy and acceptability in the long‐term, piribedil proved in this bromocriptine controlled study to be an effective and safe treatment for PD. © 2005 Movement Disorder Society
Asymptotic analysis of the quantum Liouville equation
Authors: Steinrück Herbert
Published: November 2005

We present an asymptotic analysis of the quantum Liouville equation with respect to the Planck's constant, which models the temporal evolution of the (quasi)distribution of an ensemble of electrons under the action of a potential. We consider two cases: firstly a smooth potential, and secondly a potential modelled by a δ‐distribution. In both cases the zeroth‐order term behaves classically. In the smooth case the classical Liouville equation is satisfied and in the case for the δ‐potential an interface condition is derived, so that everything is reflected at the potential barrier.
An optimal control problem for the Helmholtz equation in a stratified Shallow ocean
Authors: Xu Yongzhi
Published: November 2005

In this paper we shall consider a kind of optimal control of the Robin problem. First, we discuss the solvability of the Robin problem, which is not uniquely solvable in general. Then we find the representation of the far‐field pattern in terms of the minimal solution to an integral equation. Based on this representation, an optimization problem is discussed and a Galerkin scheme for the solution is presented.
Determination of an unknown function in a parabolic equation with an overspecified condition
Authors: Chadam John M. , Yin Hong‐Ming
Published: November 2005

In this paper we consider the inverse problems of identifying some space‐dependent unknown coefficients in parabolic equations subject to initial boundary value conditions along with an overspecified condition at the final time t = T. We use the overspecified information to transform the problems into non‐linear parabolic equations involving a functional of the solution with respect to the time variable. This transformation allows us to establish existence theorems for these inverse problems by employing the Schauder fixed‐point theorem.
Advective estimates
Authors: Lohéac Jean‐Pierre
Published: November 2005

Consider the partial differential equation: wt + bw + a· ∇w = g in ℝn × [0, T] (x1 <0) and if the function a1 is positive, then, in the left half‐space, the solution w is an O (ν) for small Viscosity ν.
On the mathematical foundations of hyperthermia therapy
Authors: Kremer Jüurgen , Louis Alfred K.
Published: November 2005

Hyperthermia is an aid to standard cancer therapy. The aim is to heat up a tumour region inside the patient's body with the help of microwave radiation. The microwayes are generated by some suitable antenna array. Here we investigate the control properties of such antenna configurations and determine their resolution capabilities. We will define the hyperthermia operator, which can produce every field of any antenna array up to any degree of accuracy. We shall see that this operator is compact and we are able to compute a singular system under general assumptions explicitly. This, together with a detailed knowledge of the decay of the singular values, constitutes the tools with which we treat the previously stated problems. We examine the propagation of microwave radiation in homogeneous media and then carry over the results obtained to the case of inhomogeneous media.
Mathematical problems of liquid crystal flows
Authors: Calderer M. Carme
Published: November 2005

This article deals with flow phenomena in liquid crystal materials. The model that I analyse is that due to Ericksen for liquid crystals with variable degree of orientation. One of the goals is understanding the role of the order parameter in the model. I examine the multiplicity of solutions, phases, that occur in shear flow regimes and analyse their stability under physically realistic conditions. In particular, I show that ellipticity of the linearized system of governing equations is a consequence of the Clausius–Duhem inequality.
On stationary flow of asymmetric fluids with diffusion
Authors: Krzyżanowski Piotr
Published: November 2005

We prove existence and uniqueness theorems for weak solutions of equations describing stationary isothermic motion of a mixture of two viscous incompressible fluids with asymmetric stress tensor, in a bounded subset of ℝ3. The model of the flow we consider here assumes that some of coefficients characterizing isotropic properties of the fluid equal zero.
Inverse scattering from an open arc
Authors: Kress Rainer
Published: November 2005

A Newton method is presented for the approximate solution of the inverse problem to determine the shape of a sound‐soft or perfectly conducting arc from a knowledge of the far‐field pattern for the scattering of time‐harmonic plane waves. Fréchet differentiability with respect to the boundary is shown for the far‐field operator, which for a fixed incident wave maps the boundary arc onto the far‐field pattern of the scattered wave. For the sake of completeness, the first part of the paper gives a short outline on the corresponding direct problem via an integral equation method including the numerical solution.
On the bending of plates with transverse shear deformation and mixed periodic boundary conditions
Authors: Constanda Christian , Lobo Miguel , Pérez Eugenia
Published: November 2005

The method of matched asymptotic expansions is used to find a homogenized problem whose solution is an approximation to the solution of a mixed periodic boundary value problem in the theory of bending of thin elastic plates. A critical size for the fixed parts of the boundary is found such that the boundary condition of the homogenized problem is an intermediate case between that for the clamped edge plate and that for the free boundary plate.
On some second‐order non‐linear systems of a hyperbolic‐parabolic type
Authors: Chrzȩszczyk Andrzej
Published: November 2005

We consider local solutions to the Cauchy problem for a class of non‐linear hyperbolic‐parabolic systems generalizing the systems of elasticity and thermoelasticity. Our main purpose is to relax the usual regularity requirements to include the nonclassical solutions into considerations.
A method of computing numerically integrated stiffness matrices
Authors: Gupta Ajaya K. , Mohraz Bijan
Published: November 2005

A method of formulating and computing numerically integrated stiffness matrices is presented. Through a better organization of the formulation which is easily achieved by the use of index notation, the computations for integrating and evaluating the element stiffness matrix are substantially reduced. For cases in which the terms of the material property tensor are not functions of position co‐ordinates (elastic isotropic and anisotropic materials), a further reduction in computation is achieved by multiplying the material property‐tensor after the numerical integration has been carried out.
Elastic‐plastic analysis of Saint‐Venant torsion problem by a hybrid stress model
Authors: Yamada Y. , Nakagiri S. , Takatsuka K.
Published: November 2005

An application of the finite element method to inelastic analysis of the Saint‐Venant torsion problem, using a triangular element formulated on the basis of the hybrid stress approach, is described. The stress field in the element is defined by a stress function which is assumed to vary linearly within the element. The warping function on the element boundary is also defined by a linear expression. Numerical results indicate that the method gives an accurate stress solution and is appropriate to the elastic‐plastic analysis of bars of arbitrary cross‐section which may include multiply connected regions. It is further shown that such phenomena as planar orthogonal plastic anisotropy, strain‐hardening and unloading of relevant twisted bar can be treated in a unified manner.
A finite element, linear programming methods for the limit analysis of thin plates
Authors: Faccioli E. , Vitiello E.
Published: November 2005

Finite elements having linear moment distributions and use of linearized yield criteria allow one to determine lower bounds to the collapse load of thin plates as solutions of linear programs.

The method is quite general and rigorously meets the requirement of the lower bound theorem of limit analysis for concentrated or line load distributions. Ways of treating distributed surface loads are also discussed and tested.

Actual bounds are computed for a variety of plate problems governed by Tresca yield criterion and compared with previous solution obtained from higher order stress elements and non‐linear optimization techniques. The comparison shows that the present method can yield accurate bounds with considerably shorter computer times and relatively small number of elements. Additional tests show that numerical convergence to the limit loads is assured by suitable refinement of the mesh pattern.
Design parameter variation and structural response
Authors: Romstad K. M. , Hutchinson J. R. , Runge K. H.
Published: November 2005

A general power series method is developed to aid in obtaining changes in the response variable due to changes in design parameters. The approach is considered for eigenvalue problems and systems of simultaneous equations which may represent static, dynamic and stability response problems. Particular emphasis is placed upon the eigenvalue problem and techniques for improving the calculations form the power series are suggested utilizing modified Rayleigh quotient expressions. Each of the methods proposed is treated computationally by the formulation of a finite element solution of column elastic stability. Investigations of solution accuracy versus percentage variation in element stiffness, whether the method underestimates or overestimates the changes, and the required number of eigenvalue solutions are presented.
The finite element method in domains with curved boundaries
Authors: Zlámal Miloš
Published: November 2005

For boundary value problems of the second order in two variables, there are proposed elements suitable for use along the curved part of the boundary. Numerical results show a considerable improvement of accuracy.
Stability criteria for explicit finite difference solutions of the parabolic diffusion equation with non‐linear boundary conditions
Authors: Milton James L. , Goss William P.
Published: November 2005

The criteria for stability of the explicit finite difference solution of the one‐dimensional, transient, conduction heat transfer problem with both radiant and convection heat transfer at the boundaries are considered in this paper. These criteria are governed by an inequality set from a functional relationship between the newly calculated and the old temperature at each node.

From the node with the most stringent criteria, it is shown that setting the coefficient of the old temperature equal to zero in the governing difference equation is not sufficient for a general criterion. On the other hand, setting the derivative of the new temperature with respect to the old temperature equal to zero in the governing difference equation presents a simple, straightforward technique for obtaining a sufficient condition for a stable system. It is further shown that the second law of thermodynamics, written in explicit finite difference form, does present a necessary criterion for stability. However, the second law, because it is in the form of an inequality, does not present as simple a criterion as the derivative method does.

The specific problem studied is a finite thickness slab, initially at a uniform temperature, but instantaneously subjected to both radiation and convection on its two surfaces. Temperature profiles were calculated on a digital computer and are presented in dimensionless graphical form over a range of five dimensionless parameters. A plot that relates stability to the maximum time‐step size for the entire range of practical conditions of radiation numbers is also presented.
Optimized prestressing by linear programming
Authors: Kirsch Uri
Published: November 2005

The problem of optimizing the prestressing force and the tendon configuration for an indeterminate prestressed structure with prescribed cross‐sectional dimensions is formulated in linear programming form, The structure is subjected to multiple load conditions and constraints are related to the structural behaviour and to the tendon configuration.

It is shown that the number of behaviour constraints at each point in the structure can be reduced, as they represent parallel hyperplanes in the design space. Necessary conditions for feasible solutions are derived. The method based on transformation of the design variables, is suitable for beams, frames, grids and plates. Its application is illustrated for the case of a prestressed bridge.
Comparison of some penalty function based optimization procedures for the synthesis of a planar truss
Authors: De Silva B. M. E. , Grant G. N. C.
Published: November 2005

The present investigation examines the multibar truss optimization problem in the context of a general class of unconstrained optimization procedures in conjunction with various types of penalty function transformations. Specifically, the problem is transformed into a series of unconstrained minimization problems using the penalty function techniques of Heaviside and SUMT. These are solved using the methods of Rosenbrock (orthogonal directions), Powell (conjugate directions) and Nelder–Mead (Simplex). This resulted in many cases in substantial improvements being recorded over previously reported data. The paper includes a comparative study of the synthesis based on these procedures.
Transient shell response by numerical time integration
Authors: Krieg Raymond D. , Key Samuel W.
Published: November 2005

In using the finite element method to compute a transient response, two choices must be made. First, some form of mass matrix must be decided upon. Either the consistent mass matrix prescribed by the finite element method can be employed or some form of diagonal mass matrix may be introduced. Secondly, some particular time integration procedure must be adopted. The procedures available divide themselves into two classes: the conditionally stable explicit schemes and the unconditionally or conditionally stable implicit schemes. The choices should be guided by both economy and accuracy. Using exact discrete solutions compared to the exact solutions of the differential equations, the results of these choices are displayed. Concrete examples of well‐matched methods, as well as ill‐matched methods, are identified and demonstrated. In particular, the diagonal mass matrix and the explicit central difference time integration method are shown to be a good combination in terms of accuracy and economy.
The efficient finite element analysis of rectangular and skew laminated plates
Authors: Kolář V. , Němec I.
Published: November 2005

Various solutions of laminated plates by the finite element method are analysed. An efficient solution of skew (or rectangular) laminated plates with small effect of σz and ϵz stress and strain components is developed. It can be used with an arbitrary number of layer elements (sub‐elements) in different plate elements. Some remarks to the possible modification of solution are presented. Numerical examples with a short discussion and conclusions complete the paper.
Analysis of plates on elastic foundations
Authors: Carpenter W. C.
Published: November 2005

The modification required to provide plate on elastic foundation analysis capability with existing finite element algorithms is presented. As shown by an example, the modification is applicable to configurations with varying ratios of plate to foundation stiffness.
On the generalization of equicofactor matrices
Authors: Kardestuncer H.
Published: November 2005

Eguicofactor properties of the entities occurring in electric networks and discrete elastic systems extend beyond the present definition of such entities. For instance, the zero‐sum property of these matrices is, in fact, a particular version of a broader definition. The generalization is accomplished in using higher order submatrices as opposed to scalars (submatrices of order 1) in the present literature.
Rate of convergence for the iterative approach in elastic‐plastic analysis of continua
Authors: Yamamoto Yoshiyuki
Published: November 2005

In connection with the finite element method, the iterative approach has been commonly used for the analysis of elastic‐plastic continua. The rate of convergence of iteration is investigated in the present paper; it depends largely upon the ratio of tangent modulus to Young's modulus, accuracy of the first guess for the exact solution and occurrence of unloading. In the case of finite displacements the rate of convergence is closely related to the stability characteristics of the continua in the sense of Shanley.
On finite element integration in natural co‐ordinates
Authors: Eisenberg Martin A. , Malvern Lawrence E.
Published: November 2005

Integration formulas for polynomial expressions in terms of natural co‐ordinates are extensively quoted without proof in standard references on finite element theory. A derivation of these relations is presented and their application is extended to non‐integral exponents.
Fluid‐structure dynamic interaction and wave forces. An introduction to numerical treatment
Authors: Zienkiewicz O. C. , Bettess P.
Published: November 2005

The paper presents an introduction to two general approaches used in the soluation of coupled structures and fluid systems in which effects of large scale flow are excluded. In the first approach, the Lagrangian, the fluid is simply treated as a ‘solid’ with a negligible shear modulus. In the second method, Eulerian, a single pressure variable is used in the fluid.

The numerical problems posed, discretization methods used and possible simplifications are discussed.
A displacement method for the analysis of vibrations of coupled fluid‐structure systems
Authors: Hamdi Mohamed Ali , Ousset Yves , Verchery Georges
Published: November 2005

A variational principle in terms of displacements in the fluid and the structure with a penalty for irrotationality of displacement in the fluid is developed for the analysis of harmonic vibrations of ideal compressible fluid and elastic structure systems. Its Discretization by the finite element method leads to an algebraic eigenvalue problem with a positive definite symmetric banded matrix. Numerical examples obtained for pure acoustic cases and coupled cases show the efficiency of the method.
Optimum design of prestressed concrete slabs using primal geometric programming
Authors: Ramamurthy S.
Published: November 2005

Prestressed concrete members, because of the use of high strength materials and the efficient disposition of tensile forces, need considerably less material. This and other advantages, however, are offset by the high unit costs of materials and the associated specialized labour. Thus, it is important to make the most of the savings in materials through the application of optimum design procedure. Among the available optimization techniques, generalized geometric progamming (GGP) is ideally suited because the design equations of prestressed concrete members are expressible in the form of polynomials. Using the GGP, in this study, a set of minimum prestress force designs are obtained for various depths of one‐way slab. From the data thus obtained a minimum cost design procedure is explained. Moreover, the need for supplementary non‐prestressed reinforcement to obtain economical designs for depths of slab beyond a certain depth is also shown.
On the efficient time integration of systems of second‐order equations arising in structural dynamics
Authors: Enright W. H.
Published: November 2005

Fixed stepsize low‐order methods are the most widely used technique for solving the second‐order initial value problems that arise in structural dynamics. In this paper we shall describe the special stability difficulty that arises with this class of problem and we will outline how variable stepsize techniques can cope with this difficulty and result in efficient numerical methods.
Large deflections and large‐amplitude free vibrations of straight and curved beams
Authors: Reddy J. N. , Singh I. R.
Published: November 2005

This paper is concerned with the large‐deflection (bending and free vibration)analysis of thin elastic curved beams by conventional and mixed finite element methods. The conventional finite element method is based on the total potential energy expression, whereas the mixed method is based on a Reissner‐type variational statement and involves the bending moments and deflections as primary dependent variables. Incremental and direct formulations are presented for both methods. The nonlinearity is included in the numerical method via an iterative procedure (i.e. the in‐plane force due to the large deflection is not treated as constant but included under the integral in the energy expression). In the case of vibrations, the transverse shear and rotary inertia effects are also included. A number of numerical examples of beams with various edge conditions are analysed for deflections and natural frequencies, and the results are compared with those reported in the literature.
An error indicator for the generalized eigenvalue problem using the hierarchical finite element method
Authors: Friberg P. O.
Published: November 2005

The hierarchical concept applied to eigenvalue problems is considered. An error indicator is derived from the pertinent Rayleigh quotient. The indicator serves as an estimation ‘a posteriori’ of the relative change in an eigenvalue for a hierarchical refinement. A numerical example is included.
Derivation of geometrically nonlinear finite shell elements via tensor notation
Authors: Harte R. , Eckstein U.
Published: November 2005

To develop geometrically nonlinear, doubly curved finite shell elements the basic equations of nonlinear shell theories have to be transferred into the finite element model. As these equations in general are written in tensor notation, their implementation into the finite element matrix formulation requires considerable effort. The present paper will demonstrate how to derive the nonlinear element matrices directly from the incrementally formulated nonlinear shell equations using a tensor‐oriented procedure. This enables the numerical realization of all structural responses, e.g. the calculation of pre‐ and post‐buckling branches in snap‐through analysis and especially in bifurcation analysis, including the detection of critical points and the consideration of geometric imperfections. To avoid loss of accuracy care is taken for a realistic computation of the geometric properties as well as of the external loads. Finally, the developed family of shell elements will be presented and its efficiency will be demonstrated by some applications to linear and geometrically nonlinear structural phenomena.
Shape design sensitivity analysis for non‐linear anisotropic heat conducting solids and shape optimization by the BEM
Authors: Meric R. A.
Published: November 2005

Shape design sensitivity analysis (SDSA) expressions have been derived for non‐linear anisotropic heat conducting solid bodies by following the material derivative concept and adjoint variable method of optimal shape design given in the literature. The variation of a general integral functional has been described in terms of primary and adjoint quantities evaluated at the varying boundaries. As an example problem in shape optimization, optimal outer boundary profiles of an orthotropic solid body are obtained by the boundary element method (BEM), after reformulating the SDSA equations in a form which is most suitable for the BEM.
An element‐by‐element method for heat conduction CAE including composite problems
Authors: Buratynski Edward K.
Published: November 2005

Mechanical computer aided engineering (CAE) implies large finite element problems due to the geometric complexity of the ‘true’ 3D designs. Application of the standard finite element technique is not practical for such problems because the direct solution of the global matrix equations is too costly. This paper considers the element‐by‐element implicit algorithm for the CAE application of transient heat conduction. The direct solution is avoided by an operator splitting or approximate factorization technique. This results in both the execution time and storage requirements for each time step being linearly proportional to the number of elements while retaining unconditional stability. However, the approximate factorization introduces additional truncation error and incorrect jump conditions at material interfaces. Detailed analyses and numerical experiments are carried out in one dimension to assess the nature and mechanism of these inaccuracies. A three dimensional implementation is then compared with one dimensional results. The need for an additional predictor–corrector element‐by‐element algorithm for 3D composite problems is also presented.
Ill‐Conditioned equations in kinematics and dynamics of machines
Authors: Park Taewon , Haug Edward J.
Published: November 2005

During mechanical system kinematic and dynamic analysis, linear and non‐linear algebraic equations must be solved. Algebraic equations are often ill‐conditioned, due either to physical singularities or large numerical errors, in which case solutions may have large errors or analysis methods may fail. Causes of ill‐conditioned problems are studied and illustrated with examples. Ill‐conditioned matrices and matrix condition numbers are discussed and an efficient and reliable indicator of ill‐conditioned matrices is suggested. In constrained kinematic and dynamic analysis, equations are solved repetitively, so symbolic factorization is used. The ill‐conditioning problem due to symbolic factorization is discussed and methods of detecting ill‐conditioning are suggested. Three examples are studied to demonstrate the effectiveness and use of condition numbers and ill‐conditioned system detection methods.
A numerical study of laminar and turbulent flows in a two‐dimensional bend with or without a guide vane
Authors: Kotb N. A. E. , Mokhtarzadeh‐Dehghan M. R. , Ward‐Smith A. J.
Published: November 2005

A numerical study of the flow in a two‐dimensional 90° circular‐arc bend is presented. The study is based on the solution of the governing equations using a finite volume technique. Both laminar and turbulent flows are considered. Particular attention is given to the occurrence and size of the separation regions and, in this respect, the effects of Reynolds number and bend radius to height ratio are discussed. The study includes the effect of a guide vane, placed in the bend, on the flow characteristics. It is shown that the emerging velocity distribution is more uniform than that associated with flow in a bend without a guide vane. The presence of a guide vane is shown to suppress the formation of regions of flow separation. Comparisons are made between the effects on the flow of two different designs of guide vane.
Accuracy of a class of concurrent algorithms for transient finite element analysis
Authors: Ortiz Michael , Nour‐Omid Bahram , Sotelino Elisa D.
Published: November 2005

The accuracy of a new class of concurrent, procedures for transient finite element analysis is examined. A phase error analysis is carried out which shows that wave retardation leading to unacceptable loss of accuracy may occur if a Courant condition based on the dimensions of the subdomains is violated. Numerical tests suggest that this Courant condition is conservative for typical structural applications and may lead to a marked increase in accuracy as the number of subdomains is increased. Theoretical speed‐up ratios are derived which suggest that the algorithms under consideration can be expected to exhibit a performance superior to that of globally implicit methods when implemented on parallel machines.
Sensitivity analysis and shape optimization of axisymmetric structures
Authors: Cheu Tsu‐Chien
Published: November 2005

An efficient method is developed for sensitivity analysis in shape optimization of axisymmetric structures. The technique of isoparametric mapping is used to generate the finite element mesh from a small set of master elements and master nodes. Co‐ordinates of selected master nodes are used as design variables. Shape function values of master elements at derived finite element nodes obtained during the isoparametric mapping process are utilized to calculate the gradients of weight and response of the structures with respect to the design variables. Analytic formulations of the gradients are developed for sensitivity analysis of axisymmetric structures. An optimization procedure using a sequential linear programming method is applied to effectively utilize the calculated gradients. Numerical examples of optimum design of disks subject to thermo‐mechanical loadings are presented.
Frictionless geometrically non‐linear contact using quadratic programming
Authors: Johnson A. R. , Quigley C. J.
Published: November 2005

The successive quadratic programming (SQP) method is used with the finite element method (FEM) to solve frictionless geometrically non‐linear contact problems involving large deformations of the elastica in the presence of flat rigid walls. To formulate the SQP problems, the potential energy (PE) is expanded in a Taylor series of second order in displacement increments about a configuration near a contact solution. The SQP problems consist of minimizing the Taylor expansion of the PE subject to the inequality constraints which represent contact. The quadratic programming (QP) method is made part of a Newton–Raphson (NR) search in which the QP corrections are made when a NR step does not satisfy the constraints. A revised simplex method developed by Rusin is used to solve the QP problems. The elastica is modelled with a total Lagrangian FEM developed by Fried. Solutions are obtained for the end loaded buckled elastica in point contact with a rigid wall and for a uniformly loaded elastica in regional contact with a rigid wall. The problems are also solved using a penalty method. The results obtained for the point contact problem are compared to an analytical solution. Calculations were made to obtain numerical information on maximum load step size and the number of inverse operations required for each load step. Cases in which the elastica stiffened substantially as a result of the initiation of contact are also discussed.
The FDM in arbitrary curvilinear co‐ordinates—formulation, numerical approach and applications
Authors: Tworzydlo Wlodzimierz W.
Published: November 2005

The basic concept, formulation and numerical application of a fully automatic version of the finite difference method (FDM) on a two‐dimensional manifold embedded in three‐dimensional Euclidean space are presented. This version of the FDM was developed in order to enable automatic solution of problems formulated in arbitrary curvilinear co‐ordinate systems in terms of covariant derivatives (e.g. shell equations).

In the classical version of the FDM all operations in the curvilinear co‐ordinates (the derivation of base vectors, curvature tensors and so on) have to be performed manually. The goal of the present work was to transfer this job to a computer, in order to minimize the user's effort during the numerical formulation of the physical problem. The relevant version of the fully automatized program FIDAMF, based on the FDM on arbitrary irregular grids,1,2 has been worked out. This code performs automatically all stages of the numerical analysis, starting from the mesh generation and approximation of the shape of the manifold, through computation of necessary objects on this manifold, to the solution of linear or non‐linear problems formulated in terms of covariant derivatives.

The method has been extended to the analysis of problems in which the co‐ordinate system changes during the computation (e.g. the analysis of large deformations in the convectional description). This version of the curvilinear FDM was applied to the analysis of large deformations of hyperelastic membrane shells.

The approach and the numerical routines, although used here with the FDM, can be combined with any other approximation method, in particular the finite element method.
Approximate direct‐search minimax circuit optimization
Authors: Sussman‐Fort Stephen E.
Published: November 2005

A direct‐search optimization strategy, involving pattern‐searches, pattern‐moves and a simplex algorithm, has been applied to a number of frequency‐domain circuit problems. We show that an approximate minimax result can be obtained with our simple approach, which includes using a modified minimax error function. In the examples attempted, the method comes quite close to the accuracy, if not the efficiency, of true minimax optimizers, and yields an accuracy as good as or better than a least‐pth (p = 10) gradient optimizer. The method is broadly appropriate wherever it is difficult or inconvenient to calculate the gradients required for conventional minimax optimization.