bluuebunny/crossref_metadata_2025_split huggingface dataset:
Boundary element method analysis of stationary thermoelasticity problems in non‐homogeneous media
Authors: Sládek J. , Sládek V. , Markechová I. 
Published: October 2005

AbstractThis paper presents an advanced BEM formulation for the solution of stationary problems of thermoelasticity taking into consideration the thermally induced non‐homogeneity. An iterative scheme is used to determine the displacement fields because the formulation contains a domain‐type integral with displacements. As compared with the existing BEM formulation, this one does not contain a domain integral of the temperature field and, furthermore, the integral representation of stresses is written in the regularized from. Consequently, all the integrals can be computed numerically by using the regular Gaussian quadrature.
Finite elements with displacement interpolated embedded localization lines insensitive to mesh size and distortions
Authors: Dvorkin Eduardo N. , Cuitiño Alberto M. , Gioia Gustavo 
Published: October 2005

AbstractA new finite element formulation aimed at the solution of problems involving strain localization is presented. The proposed formulation incorporates displacement interpolated embedded localization lines. Results are shown to converge to an ‘exact solution’ when the mesh is refined and also to be quite insensitive to mesh distortions.
A stable alternating direction method for simulating multi‐dimensional solidification problems
Authors: Mampaey F. 
Published: October 2005

AbstractApplication of the Alternating Direction Implicit (ADI) method to study solidification problems reveals some drawbacks. At the interface between different‐materials, temperature oscillations may be recorded at the simulation start which eventually may cause instability. The problems originate from the explicit temperature calculation. Shortcomings may be eliminated by substituting the explicit temperature calculation by an implicit one which is carried out on a limited number of adjacent elements. Results of real solidification problems show that the modified method behaves better than the original ADI method. The new procedure, which is formulated in terms of the finite volume method, eliminates the occurrence of physically incorrect temperature calculations and oscillations initially present in the vicinity of the interface between different materials. When applied to the three‐dimensional solidification problem of the sand coated die, simulation results are in good agreement with experimental data.
Specifications of boundary conditions for Reissner/Mindlin plate bending finite elements
Authors: Häggblad Bo , Bathe Klaus‐Järgen 
Published: October 2005

AbstractPlate bending finite elements based on the Reissner/Mindlin theory offer improved possibilities to pursue reliable finite element analyses. The physical behaviour near the boundary can be modelled in a realistic manner and inherent limitations in the Kirchhoff plate bending elements when modelling curved boundaries can easily be avoided. However, the boundary conditions used are crucial for the quality of the solution. We identify the part of the Reissner/Mindlin solution that controls the boundary layer and examine the behaviour near smooth edges and corners. The presence of boundary layers of different strengths for different sets of boundary conditions is noted. For a corner with soft simply supported edges the boundary layer removes the singular behaviour of Kirchhoff type from the stress resultants. We demonstrate the theoretical results by some numerical studies on simple plate structures which are discretized by an accurate, higher‐order plate element. The results provide guidance in choosing efficient meshes and appropriate boundary conditions in finite element analyses.
Rates of change of closed‐loop eigenvalues and eigenvectors of actively controlled structures
Authors: Pan T. S. , Rao S. S. , Venkayya V. B. 
Published: October 2005

AbstractThe sensitivity of the closed‐loop eigenvalues and eigenvectors of actively controlled flexible structures with distinct eigenvalues is considered. The sensitivity information is essential in the optimization of large space structures with stability/performance robustness, closed‐loop eigenvalues or damping ratios treated as objective or constraint functions. The efficiency of the analytical expressions derived for the rates of change of the closed‐loop eigenvalues with respect to structural design variables is demonstrated through two numerical examples. The utility of the sensitivity of the closed‐loop eigenvalues and eigenvectors in evaluating the derivatives of the stability and performance robustness indices is also indicated and illustrated through numerical examples.
An elliptical growth model of forest fire fronts and its numerical solution
Authors: Richards Gwynfor D. 
Published: October 2005

AbstractA system of differential equations that describe the growth of a forest fire front in time for variable fuel, weather and topographical conditions is derived. The system is first order, non‐linear and contains parameters that can be obtained from forestry data. A finite difference solution is presented, together with its inherent problems and their solution. Results are presented for a variety of situations that include variable fuel, wind and fire breaks. It is found that the equations and their solution efficiently produce simulations for complex problems.
Compatible description of tool surfaces and FEM meshes for analysing sheet forming operations
Authors: Keum Y. T. , Nakamachi E. , Wagoner R. H. , Lee J. K. 
Published: October 2005

AbstractImplementation of the 3‐D finite element method (FEM) of sheet forming operations has proceeded slowly. In particular, describing the arbitrary tool surfaces in an accurate and smooth manner, with well behaved first and second derivatives, has been a major obstacle. A new geometric method, suitable for representing any rigid tool surface, has been developed and shown to be superior to the usual schemes. The new method relies on the described tool surface for position data only. The spatial derivatives are obtained by considering only the sheet mesh nodal positions. This new scheme has been implemented with a rigid‐viscoplastic FEM program using general surface descriptions based on B‐splines and linear inter‐polation. Analytic representations of a hemispherical and rounded square punch were also compared. the comparisons show that the proposed method offers several advantages over other general formulations.1. The new representation is the proper one for formulating the equilibrium condition. Alternate forms can produce spurious results.2. The proposed method introduces inherently smooth surface derivatives that improve numerical stability, even with crude surface resolution. Suitable test problems show covergence with the new method far past the divergence points of the simulations using the standard general surface description.3. The method is reasonably efficient, with a time penalty of approximately 30–50 per cent (unoptimized) with respect to analytic surface descriptions.
An automatic remeshing technique for finite element simulation of forming processes
Authors: Habraken A. M. , Cescotto S. 
Published: October 2005

AbstractAn automatic remeshing scheme has been developed to enable finite element simulation of complicated forming processes. In order to avoid the tedious procedures of interrupting the analysis, performing rediscretization, mapping of current state variables and preparing the new set of boundary conditions, a fully automatic remeshing method is described. The different steps of this method are presented with the help of one industrial example.
An adaptive remeshing technique for non‐Newtonian fluid flow
Authors: Dannelongue H. H. , Tanguy P. A. 
Published: October 2005

AbstractAn unstructured mesh generator is integrated in a finite element solver for the adaptive solution of non‐Newtonian fluid flows. An a posteriori error estimate for the equations of motion is presented and is shown to behave according to theoretical convergence rates. The estimate is used to drive the refinement process, and the resulting iterative remeshing algorithm leads to reduction of the error level in the case of an axisymmetric contraction. Original data structures used to speed‐up remeshing and interpolation between unstructured grids are also presented.
Numerical analysis of polymer injection moulding process using finite element method with marker particles
Authors: Matsuhiro Itaru , Shiojima Takeo , Shimazaki Yoji , Daiguji Hisaaki 
Published: October 2005

AbstractA numerical method for analysing an axisymmetric injection moulding process is presented. A consistent approximation to pressure is applied for a penalty function formulation of Galerkin's finite element method. To analyse the moving free surface and visualize the transient flow pattern, marker particles are introduced. An axisymmetric abrupt cavity, which is filled with a generalized Newtonian fluid, is solved to verify the scheme. As a practical example problem, the transient flow through moulds of a memory disc is analysed.
Computer aided simulation of metal flows in non‐axisymmetric extrusions through bridge dies
Authors: Kiuchi Manabu , Hoshino Michihiko 
Published: October 2005

AbstractA computer aided simulation technique based on the upper bound theorem is developed in order to analyse three‐dimensional metal flows of workpieces in various extrusion processes. The developed method is applied to simulations of forward extrusions of tubes through bridge dies. The effects of die geometry on extrusion pressure, geometries of dead zone and plastic zone and three‐dimensional flow of workpiece are calculated. The results are compared with experimental measurments and fairly good agreement between them is found.
Elastic‐viscoplastic implicit formulation for finite element simulation of complex sheet forming processes
Authors: Saran Michal J. , Samuelsson Alf 
Published: October 2005

AbstractA formulation for numerical simulation of complex forming processes with generally shaped tools is developed. Special attention is drawn to the accuracy, efficiency and robustness. An incremental displacement approach based on Lagrangian formulation as well as an elastic‐viscoplastic material model with Hill's cross‐anisotropy, power law hardening and strain rate sensitivity are assumed. An implicit integration of the constitutive equations is derived. Frictional contact conditions yield additional constraint relations which, together with equilibrium equations, form the basis for derivation of the consistent tangent matrix. To further increase efficiency and accuracy, application of the adaptive remeshing procedures for sheet forming is investigated. The performance of the proposed algorithm is shown by comparison of the numerical results with the analytical solution for an in‐plane stretching test and with the experimental measurements from 3‐D sheet forming pressings where materials, radius and wall dimensions used are similar to those from industrial applications.
On numerical modelling of hot rolling of metals
Authors: Too J. J. M. 
Published: October 2005

AbstractA transient, thermomechanical model, METFORM, based on viscoplasticity and heat and mass transport theories has been developed specifically for the prediction of the flow behaviour of metals during hot rolling. The coupling of metal flow, heat transport and microstructural changes is discussed and a framework to account for the coupling behaviour is formulated. The model is partially verified by experiments and is applied to the hot strip mill roughing process, with the focus of interest on skid mark effects and related difficulties frequently observed in hot rolling. Methods for overcoming these difficulties are proposed based on the results obtained from the model. The coupling between microstructure development and the variations of local strain, strain gradient and temperature is confirmed by the predicted strain/strain gradients and micrographs obtained from a hot rolling experiment.
Numerical simulation of the superplastic forming of thin sheet components using the finite element method
Authors: Bonet J. , Wood R. D. , Wargadipura A. H. S. 
Published: October 2005

AbstractSuperplastic forming is a manufacturing process whereby titanium or aluminium sheet is blow formed into a die to produce very light and strong aerospace components. Of crucial importance is the prediction of the final thickness distribution and the pressure cycle necessary to maintain superplasticity. This paper discusses a finite element based solution to these problems and presents examples for typical components including diffusion bonding effects.
Applications of a self‐adaptive algorithm to non‐linear finite element analysis
Authors: Lee Sang H. , Hsieh Steve S. 
Published: October 2005

AbstractA self‐adaptive algorithm has been developed and implemented for the implicit time integration of non‐linear finite element analysis. In this algorithm, a proper time increment for the next time step is estimated based on the deformation pattern at the preceding step. The iteration process for the equalibrium employs expeditious methods such as quasi‐Newton updates and line searches as well as an adaptive stiffness matrix update strategy for efficiency. Convergence difficulties induced from inadequate prediction of step size or the change in non‐linearities are tackled by the bisection method. These procedures were also successfully applied to static problems by ignoring the damping and the inertia forces. The objective of this paper is to demonstrate the applicability and the effectiveness of the adaptive algorithm in a wide spectrum of non‐linear problems. Six example problems are illustrated, some of which are rather novel. As demonstrated in this paper, the self‐adaptive algorithm implemented in MSC/NASTRAN is proving to be versatile, accurate and efficient.
Derivatives of tangential stiffness matrices for equilibrium path descriptions
Authors: Eriksson Anders 
Published: October 2005

AbstractThe paper describes how several procedures, based on expressions from analytical elastic stability theory, are introduced as numerical tools in a general Finite Element program for geometrically non‐linear structural analysis. Especially is discussed how derivatives of the tangential stiffness matrix can be utilized in several contexts in the solution algorithm. These include improved predictions for the step‐wise solution of equilibrium states, identification of critical points and accurate descriptions of initial post‐bifurcation behaviour.For two plane beam and bar elements, formulations have been developed giving analytical expressions for these derivatives. The corresponding numerical approximations, needed in other element types, are also discussed. The paper discusses the relative efficiency of higher order predictions in relation to these different element types and different solution strategies. Some numerical examples, showing different types of behaviour, are analysed and discussed.
Physical shape functions in finite element analysis of moderately thick plates
Authors: Gilewski Wojciech , Gomuliński Andrzej 
Published: October 2005

AbstractA new rectangular finite element for moderately thick plates is presented. The element is based on the concept of physical shape functions, i.e. functions which contain in themselves physical and geometrical properties of the element. The analytic formulae of stiffness, geometric stiffness and mass matrices are presented for isotropic material. The element is free from locking and zero energy modes not corresponding to rigid body motions.Several examples are presented for static, initial stability and free vibration problems.
Automatic quadrilateral/triangular free‐form mesh generation for planar regions
Authors: Sezer Levent , Zeid Ibrahim 
Published: October 2005

AbstractAutomation of finite element mesh generation holds great benefits for mechanical product development and analysis. In addition to freeing engineers from mundane tasks, automation of mesh generation reduces product cycle design and eliminates human‐related errors. Most of the existing mesh generation methods are either semi‐automatic or require specific topological information. A fully automatic free‐form mesh generation method is described in this paper to alleviate some of these problems. The method is capable of meshing singly or multiply connected convex/concave planar regions. These regions can be viewed as crosssectional areas of 2 1/2 D objects analysed as plane stress, plane strain or axisymmetric stress problems. In addition to being fully automatic, the method produces quadrilateral or triangular elements with aspect rations near one. Moreover, it does not require any topological constraints on the regions to be meshed; i.e. it provides free‐form mesh generation. The input to the method includes the region's boundary curves, the element size and the mesh grading information. The method begins by decomposing the planar region to be meshed into convex subregions. Each subregion is meshed by first generating nodes on its boundaries using the input element size. The boundary nodes are then offset to mesh the subregion. The resulting meshes are merged together to form the final mesh. The paper describes the method in detail, algorithms developed to implement it and sample numerical examples. Results on parametric studies of the method performance are also discussed.
Multiplier methods for engineering optimization
Authors: Arora J. S. , Chahande A. I. , Paeng J. K. 
Published: October 2005

AbstractMultiplier methods used to solve the constrained engineering optimization problem are described. These methods solve the problem by minimizing a sequence of unconstrained problems defined using the cost and constraint functions. The methods, proposed in 1969, have been determined to be quite robust, although not as efficient as other algorithms. They can be more effective for some engineering applications, such as optimum design and control of large scale dynamic systems. Since 1969 several modifications and extensions of the methods have been developed. Therefore, it is important to review the theory and computational procedures of these methods so that more efficient and effective ones can be developed for engineering applications. Recent methods that are similar to the multiplier methods are also discussed. These are continuous multiplier update, exact penalty and exponential penalty methods.
Dynamic analysis and computer simulation of variable‐mass multi‐rigid‐body systems
Authors: McPhee J. J. , Dubey R. N. 
Published: October 2005

AbstractIn this paper we present a general procedure for analysing the motion of a multi‐rigid‐body system that is capturing and/or ejecting mass. The motivations for this work are given in the introductory section, followed by a description of the mathematical model we have used to represent a variable‐mass system. Using a control volume approach, the differential equations of motion are derived in vector‐dyadic form. The non‐linear scalar components of these equations have been encoded into a Fortran‐77 program that uses a fourth‐order Runge‐Kutta algorithm to compute a numerical solution for the motion of a given physical system; we describe the development of this simulation program and its use of the conformal rotation vector to represent orientations. An application of the program to the dynamic analysis of a specific variable‐mass problem is presented, and a comparison of the numerical results to an analytical solution is used to assess the accuracy of the software. In the concluding section, the advantages and limitations of the underlying formulation are discussed.
An approach to dynamics and control of orbiting flexible structures
Authors: Modi V. J. , Suleman A. , Ng A. C. , Morita Y. 
Published: October 2005

AbstractA relatively general formulation for studying the dynamics of an arbitrary spacecraft with interconnected flexible bodies is developed accounting for thermal deflection, transient system inertias, shift in the centre of mass, shear deformations, rotary inertias and geometric non‐linearities. The computer implementation has been carried out through symbolic manipulation of the equations of motion. Versatility of the formulation is indicated through application to problems of contemporary interest.
Systematic construction of equations of motion for rigid‐flexible multibody systems containing open and closed kinematic loops
Authors: Nikravesh Parviz E. , Ambrosio Jorge A. C. 
Published: October 2005

AbstractA systematic method for formulating the equations of motion for multibody systems containing rigid and flexible bodies is presented. The method of using joint co‐ordinates to derive the minimum number of equations of motion is utilized for rigid bodies and the finite element method is employed for flexible bodies. The equations of motion for flexible bodies are simplified into several steps using (a) a lumped mass assumption, (b) static condensation and (c) modal superposition. The combined rigid and flexible body formulation can be used to simulate dynamic response in a variety of applications such as ride handling, rollover and the crash analysis of vehicles, space structures, and biomechanical problems.
Dynamic analysis of spatial flexible multibody systems using joint co‐ordinates
Authors: Pereira M. S. , Proença P. L. 
Published: October 2005

AbstractThis paper presents a systematic method for deriving the minimum number of equations of motion for spatial flexible multibody systems. Relative kinematics are developed using relative joint co‐ordinates and relative joint velocities to formulate a minimum number of equations of motion. The present method takes advantage of the simplicity of the absolute co‐ordinate formulation and computational efficiency of the relative joint co‐ordinate formulation. The system equations of motion are first formulated in terms of a coupled set of absolute reference co‐ordinates and elastic modal co‐ordinates. These equations are transformed to the joint co‐ordinate space by use of a velocity transformation matrix including the elastic modal velocities. A computer algorithm is proposed and extended to closed loop mechanisms. One example of a flexible vehicle is presented and the results are discussed to illustrate the computational efficiency of the method.
Effects of softening in elastic‐plastic structural dynamics
Authors: Maier G. , Perego U. 
Published: October 2005

AbstractSoftening, understood as unstable behaviour of material or structural components, is considered herein for its possible consequences on the overall behaviour of discrete dynamic models of elastic–plastic beam structures, in the absence of geometric effects. It is shown that multiplicity of incremental solutions (response bifurcations) and manifestations of overall instability may occur. The bifurcated responses may exhibit different scenarios for the same excitation: e.g. shakedown or local damage up to failure. An insight into and criteria for such occurrences are achieved by formulating the rate and the finite increment problem as linear complementarity problems. Period doubling and deterministic chaos under harmonic excitation are observed when reversible (holonomic) softening behaviour is assumed. The strong sensitivity of the phenomena investigated with respect to the choice of the structural model is pointed out. The findings are elucidated by illustrative examples.
Second order approximations in structural genesis and shape finding
Authors: Mlejnek H. P. , Jehle U. , Schirrmacher R. 
Published: October 2005

AbstractThe introduction of second order sensitivities to behaviour approximation in structural optimization is applied and investigated. Numerical computation of second derivatives is considered and evaluated. Two approaches in shape optimization are involved, namely shape finding by moving boundaries and shape genesis by distributing mass in a specified design domain. A series of examples is engaged to work out the benefits of second order information in both the above fields.