bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical shakedown analysis of axisymmetric sandwich shells: An upper bound formulation
Authors: Morelle Patrick 
Published: August 2005

AbstractShakedown analysis of axisymmetric elastic–perfectly plastic sandwich shells is performed here using a new upper bound formulation based on a special form of Koiter's theorem concerning piecewise linearized yield surfaces. Starting from finite element techniques and the Tresca sandwich yield condition, shakedown analysis is reduced to a linear programming problem which is solved by a powerful simplex algorithm. Numerical results are given for a number of examples and a comparison is made with a previously computed lower bound formulation.
Elastic‐plastic state of torispherical heads
Authors: Varga L. , Gara P. , Kollar Gy. 
Published: August 2005

AbstractThe value of the permissible pressure in torispherical heads is usually judged from the size of the permanent deformations after the first load cycle. The difficulty always lies in the determination of the maximum permanent strain caused by the pressure, as the strain depends on the changes of the elastic‐plastic state. The elastic‐plastic state of the heads can be, for example, found and well followed by the finite element method. Values obtained in this way are naturally valid only for the case examined. However, by extending the numerical investigations and by appropriately processing and evaluating the results certain regularities and generalizations can be recognized. On this basis certain approximations can be made, leading to a very simple and reliable calculation process.
Optimum load time history for non‐linear analysis using dynamic relaxation
Authors: Řeřicha Petr 
Published: August 2005

AbstractA modification of the dynamic relaxation method is proposed which facilitates static analysis of non‐linear problems. Continuous loading in time is adopted instead of the ordinary step function of time. Inertia and damping forces arising during the loading process are kept at a minimum using an optimum load time history. This results from the stationary condition of an appropriate functional. The equation of motion is included as a subsidiary condition. Continuous load—deflection curves can be obtained. An incremental solution is avoided. Application of the method is extremely simple. Existing programs based on explicit time integration schemes can be easily adapted for it. Sample solutions are presented.
A turbulence model for buoyant and combusting flows
Authors: Spalding D. Brian 
Published: August 2005

AbstractIt is argued that ‘sifting’ phenomena, in which fragments of fluid subjected to larger body forces move through those subjected to smaller body forces, are prevalent in turbulent flows, and that they can be simulated by means of mathematical methods which have been developed for two‐phase flows.A connection with Prandtl's mixing‐length theory is established; and it is deduced from the success of that theory for shear flows that there must exist a source term in the normal‐to‐wall‐velocity equations which is proportional to the gradient of along‐the‐wall velocity. This term is then included in the two‐fluid‐model equations.Solutions of the equations are presented for a turbulent Couette flow in which the heating of one of the walls and the presence of a gravitational field can cause ‘sifting’ phenomena to become dominant. The friction and heat‐transfer coefficients, and the profiles of velocity and temperature, are computed and discussed, for flows both with and without buoyancy influences.
Three‐dimensional transient thermo‐elastic analyses by the BIE method
Authors: Chaudouet A. 
Published: August 2005

AbstractThe proposed method is the direct boundary integral equation (BIE) method applied to three‐dimensional transient heat transfer analyses and to corresponding elastostatic analyses under thermal loading. The mechanical and thermal problems are decoupled. For those not familiar with the BIE method, a short survey of the basic principles is given to help them understand the mathematical treatment, which is performed in the frame of distribution theory. The tempered elementary solution of the transient heat transfer problem contains time and space variables. The numerical treatment of the thermal equation is performed analytically with respect to time and numerically with respect to space in the same way as for steady state equations. Great care is paid to space integration in order to compute the values of the kernels precisely enough on the surface and inside the volume. The computational treatments of both problems are realized in such a way as to minimize computing time. Differences between transient and steady state analyses, on the one hand, and between elastostatic analyses with and without thermal loading, on the other, are emphasized. Finally, an analytical example shows the good behaviour of the proposed method to solve singular thermal problems and an industrial example shows the accuracy of the results obtained by using the BIE method to solve three‐dimensional thermo‐elastic problems.
A finite element method for free and forced convection heat transfer
Authors: Schnipke Rita J. , Rice James G. 
Published: August 2005

AbstractA new finite element method is presented. This new method contains several novel features including a streamline upwind formulation for the advection terms and equal order interpolations for all variables: velocities, pressure, temperature and other fluid properties. This new formulation uses an iterative solution method greatly reducing the computer storage requirements. The validity of the new finite element method was tested on both a natural convection problem, a thermally driven cavity, and a forced convection problem, a heated cylinder in cross‐flow. The predicted results compared favourably with a benchmark solution for the cavity and an empirical correlation for the cylinder in cross‐flow.
Numerical models for the thermo‐mechanical evolution of Atlantic‐type continental margins
Authors: Cloetingh S. A. P. L. , Wisse G. 
Published: August 2005

AbstractWe have developed a versatile finite element approach to analyse stresses and displacements induced in thermally thinned and thickened geological structures. Material and geometric non‐linearities form an important aspect of the finite element simulation. The changes in geometry are incorporated by a multipoint constraint procedure. The method takes into account temperature‐dependent variations in rheological properties of the medium, including the presence of a brittle–ductile transition. We illustrate the application of the method for specific geophysical problems associated with the temperature history of the earth's crust at continental margins of the Atlantic type.
Pulverized coal conversion in downflow gasifier
Authors: Phuoc T. X. , Durbetaki P. 
Published: August 2005

AbstractThe behaviour of coal particles undergoing pyrolysis in a downflow reactor is modelled in two dimensions using integral approximation. The governing equations are solved numerically by marching procedures using Adams–Moulton and Romberg integration methods. The conversion of coal particles is studied in terms of chemical kinetics, hydrodynamic flow of volatiles and the heat transfer mechanism at the interface. The conversion increases with decreasing velocity, solid loading, particle diameter and total pressure. Owing to large amounts of gas production, the influence of pyrolysis on the gas‐particle heat transfer and drag coefficients becomes important at large particle diameters. For particle diameters less than 100 μm, such influence is minimal.
Numerical simulation in precision castings
Authors: Hamar R. 
Published: August 2005

AbstractMicroporosities often appear during the solidification of foundry pieces. They result from the volume contraction of the alloy during its solidification. Thermal transfers between alloy and mould check the solidification. They are estimated by a finite volume method, including specific calculation of the mould filling‐up, the alloy solidification and the resulting feeding of the mould.The calculation uses a geometrical enmeshment of the whole mould, generating numerous elements of different sizes. From the experimental fluid flow measurement, the mould filling‐up may be described step by step by the computer, as can the initial thermal transfer. Thermal transfers are related to the solidification enthalpic release obtained from quantitative differential thermal analysis. They are also related to the fluid flow induced by solidification shrinkage.Such a calculation leads to the location of the microporosities, from which pressure drops can be estimated during solidification.
Mixing and solidification of a turbulent liquid jet in a co‐flowing stream
Authors: Enright P. G. , Katgerman L. , Ludwig J. C. , Rogers S. 
Published: August 2005

AbstractA mathematical model has been developed to quantify the effects of process conditions during turbulent solidification and mixing of a liquid metal jet in a confined co‐flowing molten metal stream.The modelling has been split into three parts. First, a single phase model with no latent heat effects to consider the solidification potential. Secondly, a two phase model where the second phase is comprised of solid particles which solidify during mixing of the two streams. Thirdly, a two phase model where the second phase consists of the inner jet, which is assumed to break up into droplets of given size, and solid particles are allowed to form by solidification within the droplets.The results show that the thermal history (solidification path) of the solid phase formed is affected by latent heat and particle size, which implies that solidification, nucleation and jet fragmentation events should be included dynamically to ensure realistic predictions.
On the extrusion of visco‐elastic fluids subject to viscous heating
Authors: Milthorpe J. F. , Tanner R. I. 
Published: August 2005

AbstractThe die‐swell occurring during the extrusion of a visco‐elastic fluid has been extensively examined in recent years, both experimentally and numerically. These investigations have been mainly confined to isothermal flows. If the material is initially relatively cool, however, viscous heating may lead to proportionally large changes in temperature and material properties, with significant effects on die‐swell. An iterative computational model is presented which describes the flow of Maxwell and Oldroyed fluids subject to the effect of temperature gradients induced by viscous heating and thermal boundary conditions. Predictions are presented for extrusion from both slit and axisymmetric dies.
The method of moving asymptotes—a new method for structural optimization
Authors: Svanberg Krister 
Published: August 2005

AbstractA new method for non‐linear programming in general and structural optimization in particular is presented. In each step of the iterative process, a strictly convex approximating subproblem is generated and solved. The generation of these subproblems is controlled by so called ‘moving asymptotes’, which may both stabilize and speed up the convergence of the general process.
Treatment of material discontinuities in finite element computations
Authors: Mackinnon R. J. , Carey G. F. 
Published: August 2005

AbstractWe consider finite element analysis of problems with discontinuous material coefficients. For applications in which the material interface crosses an element, we develop special elements with an embedded flux constraint at the interface. This new procedure is compared with the standard finite element method with interface coincident with the element boundary and with an existing method proposed by Steven.1 Supporting numerical studies are conducted and rates of convergence for the solution and interface flux are examined. Some local superconvergence behaviour is observed.
Finite element solution of three‐dimensional incompressible fluid flow problems by a preconditioned conjugate residual method
Authors: Robichaud Michel P. , Tanguy Philippe A. 
Published: August 2005

AbstractA new algorithm for the solution of the three‐dimensional Navier–Stokes equation using the mixed formulation and an incomplete factorization technique is presented. The linear system obtained at each modified Newton–Raphson iteration is solved by the preconditioned conjugate residual method (PCR) using an out‐of‐core incomplete LU factorization as preconditioning. This factorization is performed on a matrix stored by a new static storage method called the packed skyline method. The performance of the proposed algorithm is assessed for the wall‐driven cubic cavity problem using the Q −P1 enriched element.
Numerical tests for assessing finite element model convergence
Authors: Verma A. , Melosh R. J. 
Published: August 2005

AbstractNew requirements for finite element model convergence are defined. It is shown that the presence of constant strain states in an element is not sufficient to guarantee convergence.Numerical tests are proposed to assess convergence, direction of convergence, monotonicity of convergence, convergence rate and monotonicity of convergence rate. The proposed tests are mathematically stronger and more general than existing tests.
Trefftz method: Fitting boundary conditions
Authors: Zieliński A. P. , Herrera I. 
Published: August 2005

AbstractThe paper presents various ways of fitting the boundary conditions in the T‐complete functions method. The authors point out the distinct advantages of the orthogonal collocation in comparison to the equidistant collocation and the integral fit. The convergence of the Collatz error measures and the conditioning of the solution matrices are investigated in detail.
The uniqueness characteristics of mixed finite element methods in linear elasticity
Authors: Boot J. C. 
Published: August 2005

AbstractHaving established the non‐uniqueness, in general, of quadratic–linear functionals in elasticity, the investigative work on this topic is reviewed, whence it is noted that there is no existing formal approach for the identification of either the causes of singular solutions or suitable remedial measures that might ensure their elimination. A comparison of the weighted averages obtained from the single field and Reissner's principles is then used to identify a higher order uniqueness criterion for the latter. A detailed consideration of the application of the new condition to the arch equations demonstrates how and why singular solutions can be obtained, and thence how suitable forms of remedial action can often be identified. Finally, several other classes of problem are briefly investigated in order to show how the criterion can be used to explain the full range of known behaviour of the mixed methods.
A self‐adaptive co‐ordinate transformation for efficient numerical evaluation of general boundary element integrals
Authors: Telles J. C. F. 
Published: August 2005

AbstractAlmost all general purpose boundary element computer packages include a curved geometry modelling capability. Thus, numerical quadrature schemes play an important role in the efficiency of programming the technique. The present work discusses this problem in detail and introduces efficient means of computing singular or nearly singular integrals currently found in two‐dimensional, axisymmetric and three‐dimensional applications. Emphasis is given to a new third degree polynomial transformation which was found greatly to improve the accuracy of Gaussian quadrature scheme's within the near‐singularity range. The procedure can easily be implemented into existing BE codes and presents the important feature of being self‐adaptive, i.e. it produces a variable lumping of the Gauss stations toward the singularity, depending on the minimum distance from the source point to the element. The self‐adaptiveness of the scheme also makes it inactive when not useful (large source distances) which makes it very safe for general usage.
A hybrid BEM model
Authors: Schnack E. 
Published: August 2005

AbstractThe hybrid stress method is very successful for stress concentration problems.1–7 Especially for problems of fracture mechanics, procedures can be found that work efficiently for two‐ and three‐dimensional problems. The rate of convergence with this method, evidently, is higher than that with conventional FE models. The BEM procedure, too, works more efficiently, but shows some essential disadvantages against the FEM, such as that for the direct method no symmetric positive definite matrix can be found and that there occur numerical problems at corners.8,9 This happens also when BEM and FEM are even coupled commonly.10–12. In the following, a hybrid BEM model will be described which combines the advantages of both the FEM and the BEM. It will be shown in this paper that BEM is very successful in formulating finite element functions for the hybrid assumed stress method.
A numerical method for dynamic analysis of a general cross‐section rod under combined loads
Authors: Nagaya Kosuke , Goto Tetsuro , Sasaki Toyonori , Ikai Shigeo 
Published: August 2005

AbstractThis paper is concerned with a method for obtaining stresses in a rod of arbitrary cross‐section subjected to combined loads of bending, shearing and torsion which are the complicated functions of time. In the first step, the analysis derives the bending moment, shearing force and torsional moment by use of a combination method of the Laplace transformation and Fourier series expansion. The transient stresses are obtained based on the two‐dimensional theory of elasticity, but in which the Fourier expansion collocation procedure is applied to deal with the complex boundary shape of the cross‐section. To affirm the validity of this analysis, experimental tests are also carried out for an oval rod subjected to the three combined transient loads.
Norm methods and partial weighting in multicriterion optimization of structures
Authors: Koski Juhani , Silvennoinen Risto 
Published: August 2005

AbstractMethods for generating Pareto optimal solutions to a multicriterion optimization problem are considered. The norm methods based on the scalarization of the original multicriterion problem by using the l‐norm are discussed in a unified form and a parametrization suitable for different interactive design systems is suggested. In addition, an alternative approach which, instead of scalarization, reduces the dimension of the multicriterion problem is proposed. This is called the partial weighting method and it can beinterpreted as a generalization of the traditional scalarization technique where the weighted sum of the criteria is used as the objective function. The first of these two approaches (norm method) is very flexible from a designer's point of view and it can be applied also in non‐convex cases to the determination of the Pareto optimal set whereas the latter (partial weighting method) is especially suitable for problems where the number of criteria is large. Throughout the article several illustrative truss examples are presented to augment the scanty collection of multicriterion problems treated in the literature of optimum structural design.
An efficient quadrilateral element for plate bending analysis
Authors: Saleeb A. F. , Chang T. Y. 
Published: August 2005

AbstractA simple, shear flexible, quadrilateral plate element is developed based on the Hellinger/Reissner mixed variational principle with independently assumed displacement and stress fields. The crucial point of the selection of appropriate stress parameters is emphasized in the formulation. For this purpose, a set of guidelines is formulated based on the following considerations: (i) suppression of all kinematic deformation modes, (ii) the element has a favourable value for the constraint index in the thin plate limit, (iii) element properties are frame‐invariant. For computer implementation the components of the element stiffness matrix are evaluated analytically using the symbolic manipulation package MACSYMA. The effectiveness and practical usefulness of the proposed element are demonstrated by the numerical results of a variety of problems involving thin and moderately thick plates under different loading and support conditions.
Multi‐objective optimization of fuzzy structural systems
Authors: Rao S. S. 
Published: August 2005

AbstractIt is recognized that there exists a vast amount of fuzzy information in both the objective and constraint functions of the optimum design of structures. Since most practical structural design problems involve several, often conflicting, objectives to be considered, a multi‐objective fuzzy programming method is outlined in this work. The fuzzy constraints define a fuzzy feasible domain in the design space and each of the fuzzy objective functions defines the optimum solution by a fuzzy set of points. A method of solving a fuzzy multi‐objective structural optimization problem using ordinary single‐objective programming techniques is presented. The computational approach is illustrated with two numerical examples.
Stability convergence and accuracy of the DuFort and Frankel difference diagram approximating a class of non‐linear parabolic field equations
Authors: Wiak Sławomir 
Published: August 2005

AbstractThe paper presents a method of calculation for the transient electromagnetic field in a steel rotor screen of a superconducting generator. Using the difference method, the spatial–temporal distributions of the electromagnetic field have been calculated as a result of solving the non‐linear partial differential equation for the vector potential A (in space Ω(r, θ,t)). For the difference diagram the conditions of stability and convergence have been determined.
Residual flow procedure for sea water intrusion in unconfined aquifers
Authors: Sugio S. , Desai C. S. 
Published: August 2005

AbstractA simplified procedure is presented for the analysis of sea water intrusion in unconfined aquifers. It involves the finite element method with a residual flow procedure which combines transformation of the salt water zone into the fresh water zone that has the same pressure distribution as that of the salt water. This procedure avoids simultaneous solutions of governing differential equations for both flow and mass transport. Numerical results are compared with laboratory observations.
Finite element analysis of quasi‐prismatic bodies using Chebyshev polynomials
Authors: Vijayakar Sandeep M. , Busby Henry R. , Houser Donald R. 
Published: August 2005

AbstractA new kind of finite element is presented in this paper which is designed to work efficiently for bodies that are either prismatic or ‘quasi‐prismatic’ in shape. Quasi‐prismatic shapes are those which can be obtained from prismatic shapes by mere distortion. The element which is formulated in this paper may be coupled with other types of three‐dimensional elements to allow the modelling of structures which are only partially prismatic or which have prismatic shapes within them. The element allows for a variety of boundary conditions, yet yields meshes which are easy to generate. The performance of this element is evaluated by numerical experiments that compare its results with analytical solutions for a thick cylinder problem and a curved beam problem. The element has also been demonstrated on a turbine blade model.
A plane hybrid element with rotational d.o.f. and adjustable stiffness
Authors: Cook Robert D. 
Published: August 2005

AbstractA simple formulation of a nine d.o.f plane triangle is achieved by the assumed‐stress hybrid approach. The element has two translations and the rotation about a normal to the plane as d.o.f. at each node. Performance of the element is shown to be good. A device for softening overly‐stiff elements is found to be effective and is suggested as a widely applicable method of improving the behaviour of hybrid elements. A particularly simple form of the element, herein called the CST Hybrid, appears to be the best performer.