bluuebunny/crossref_metadata_2025_split huggingface dataset:
A formal finite element approach for open boundaries in transport and diffusion ground‐water problems
Authors: Padilla Francisco , Leclerc Michel , Villeneuve Jean‐Pierre 
Published: November 2005

AbstractIn the application of the finite element method to diffusion and convection‐dispersion equations over a ground‐water domain, the Galerkin technique was used to incorporate Neumann (or second‐type) and Cauchy (or third‐type) boundary conditions. While mass movement through open boundaries is a priori unknown, these boundaries are usually treated as a zero Neumann condition at some far distance from the domain of interest. Nevertheless, cheaper and better solutions can be obtained if these unknown conditions are adequately incorporated in the weak formulation and in the transient solution schemes (open boundary condition). Theoretical and numerical proofs are given of the equivalences between this approach and a ‘well‐posed’ problem in a semi‐infinite domain with a zero Neumann condition at a boundary placed at infinity. Transport and diffusion equations were applied in one dimension to show the numerical performances and limitations of this procedure for some linear and non‐linear problems. No a priori limitations are foreseen in order to find similar solutions in two or three dimensions. Thus the spatial discretization in the proximity of open boundaries could be drastically reduced to the domain of interest.
Diffusion flame analysis of an afterburner as a function of the air‐fuel ratio
Authors: Chuang Shu‐Hao , Jiang Jiunn‐Shean 
Published: November 2005

AbstractThe diffusion flame of an afterburner as a function of the air‐fuel ratio is analysed by employing the SIMPLE‐C algorithm and the turbulence κ‐κ model. In the present analysis, better combustion efficiency of an afterburner with a slightly fuel‐lean mixture is shown. The velocity, fuel mass fraction, temperature and combustion efficiency distributions of reacting flow in an afterburner with two V‐gutter flameholders as a function of the air–fuel ratio are also discussed and compared. The calculated results in the present analysis can be applied to the fundamental study of reacting flow in an afterburner.
Non‐oscillatory shock‐capturing finite element methods for the one‐dimensional compressible Euler equations
Authors: Yang J. Y. , Lien Fue‐Sang , Hsu Chang‐An 
Published: November 2005

AbstractA class of shock‐capturing Petrov–Galerkin finite element methods that use high‐order non‐oscillatory interpolations is presented for the one‐dimensional compressible Euler equations. Modified eigenvalues which employ total variation diminishing (TVD), total variation bounded (TVB) and essentially non‐oscillatory (ENO) mechanisms are introduced into the weighting functions. A one‐pass Euler explicit transient algorithm with lumped mass matrix is used to integrate the equations. Numerical experiments with Burgers' equation, the Riemann problem and the two‐blast‐wave interaction problem are presented. Results indicate that accurate solutions in smooth regions and sharp and non‐oscillatory solutions at discontinuities are obtainable even for strong shocks.
Solution techniques for the vorticity–streamfunction formulation of two‐dimensional unsteady incompressible flows
Authors: Tezduyar T. E. , Liou J. , Ganjoo D. K. , Behr M. 
Published: November 2005

AbstractA review of our solution techniques for the vorticity–streamfunction formulation of two‐dimensional incompressible flows is presented. While both the viscous and inviscid cases are considered, the derivation of the proper finite element formulations for multiply connected domains is emphasized. In all formulations associated with the vorticity transport equation, the streamline upwind/Petrov–Galerkin method is used. The adaptive implicit–explicit and grouped element‐by‐element solution strategies are employed to maximize the computational efficiency. The solutions obtained in all test cases compare well with solutions from previously published investigations. The convergence and benchmark studies performed in this paper show that the solution techniques presented are accurate, reliable and efficient.
Finite element solution of flow between eccentric cylinders with viscous dissipation
Authors: De Araujo J. H. C. , Ruas V. , Vargas A. S. 
Published: November 2005

AbstractA computational study of viscous flow between two eccentrically rotating cylinders is presented in which the effect of viscous dissipation is taken into account. The space discretization is based on piecewise linear finite elements with velocity stabilization, while the method of characteristics is used for time integration. Numerical results illustrate the efficiency of the adopted approach.
Algebraic grid generation for complex geometries
Authors: Shih T. I‐P. , Bailey R. T. , Nguyen H. L. , Roelke R. J. 
Published: November 2005

AbstractAn efficient computer programme called GRID2D/3D has been developed to generate single and composite grid systems within geometrically complex two‐ and three‐dimensional (2D and 3D) spatial domains that can deform with time. GRID2D/3D generates single grid systems by using algebraic grid generation methods based on transfinite interpolation. The distribution of grid points within the spatial domain is controlled by stretching functions and grid lines can intersect boundaries of the spatial domain orthogonally. GRID2D/3D generates composite grid systems by patching together two or more single grid systems. The patching can be discontinuous or continuous. For 2D spatial domains the boundary curves are constructed by using either cubic or tension spline interpolation. For 3D spatial domains the boundary surfaces are constructed by using a new technique, developed in this study, referred to as 3D bidirectional Hermite interpolation.
A study of upstream‐weighted high‐order differencing for approximation to flow convection
Authors: Tsui Yeng‐Yung 
Published: November 2005

AbstractThis paper is concerned with a number of upstream‐weighted second‐ and third‐order difference schemes. Also considered are the conventional upwind and central difference schemes for comparison. It commences with a general difference equation which unifies all the given first‐, second‐ and third‐order schemes. The various schemes are evaluated through the use of the general equation. The unboundedness and accuracy of the solutions by the difference schemes are assessed via various analyses: examination of the coefficients of the difference equation, Taylor series truncation error analysis, study of the upstream connection to numerical diffusion, single‐cell analysis. Finally, the difference schemes are tested on one‐ and two‐dimensional model problems. It is shown that the high‐order schemes suffer less from the problem of numerical diffusion than the first‐order upwind difference scheme. However, unboundedness cannot be avoided in the solutions by these schemes. Among them the linear upwind difference scheme presents the best compromise between numerical diffusion and solution unboundedness.
To the boundary and back—a numerical study
Authors: Karni S. 
Published: November 2005

AbstractThis study identifies the key parameters upon which energy absorption at artificial boundaries depends. A thorough numerical study is presented, of typical reflections from open computational boundaries, for problems governed by hyperbolic systems of equations. The emphasis is on systems, where it is often the combination of all boundary procedures that determine the quality of boundary treatment. We study dissipative numerical models which have so far not been analysed to the same extent as non‐dissipative models and employ a Law‐Wendroff‐type scheme as a prototype. While it is widely accepted that dissipative models tend to give fewer problems than non‐dissipative ones, we show a variety of cases where substantial reflections do occur even in ID and quasi‐ID set‐ups, where theory predicts best results. This can partly be explained by the vanishing of dissipation in the far field. Group velocity analysis, justifiable on the grounds of weak dissipation, predicts a pathological behaviour which is confirmed by numerical experiments. We demonstrate strong focusing of asymptotic errors generated at the artificial boundary. Internal reflections due to slowly expanding grids are shown for non‐linear systems. The need for high‐frequency boundary conditions naturally arises and combined low‐high‐frequency boundary recipes following Higdon, Vichnevetsky and Pariser are adapted to systems and tested. Partial cures are also discussed, mainly in terms of pointing out their theoretically limited potential.
Prediction of flow over helically ribbed surfaces
Authors: Henry F. S. , Collins M. W. 
Published: November 2005

AbstractFully developed, steady flow through an annulus with a multistart, helical‐ribbed inner cylinder is numerically predicted and compared with available data. To facilitate comparison, the transverse‐ribbed case is included. It is predicted that substantial differences exist between turbulent flow over helical ribs and that over transverse ribs. The predictions clarify the experimental finding that helical‐ribbed cylinders can be expected to have better pressure drop and heat transfer characteristics than transverse‐ribbed cylinders. For this work the AERE Harwell code FLOW3D Release 2 was used.
Diffusion flame analysis of twin plane jets via a kinetic theory approach
Authors: Chuang Shu‐Hao , Hong Zuu‐Chang 
Published: November 2005

AbstractDiffusion flame solutions of twin plane jets based on a turbulent kinetic theory due to Chung and a Green function method by Hong are presented. The chemical reaction between fuel and oxidizer is assumed to be one‐step, one‐direction and infinitely fast. The solutions are obtained by direct integration over a constructed probability density function in velocity space. The probability density functions of reactants in transverse velocity space, species mass fraction distributions, turbulent transport of momentum and heat, temperature distributions and flame structure are also considered in this paper. The diffusion flame phenomena of the twin plane jets show that the interaction between the two jets is a dominant factor.
A numerical method for subcritical and supercritical open channel flow calculation
Authors: Soulis Johannes Vassiliou 
Published: November 2005

AbstractA marching finite volume method is presented for the calculation of two‐dimensional, subcritical and supercritical, steady open channel flow including the usually neglected terms of slope and bottom friction. The channel flow will be assumed to be homogeneous, incompressible, two‐dimensional and viscous with wind and Coriolis forces neglected. A hydrostatic pressure distribution is assumed throughout the flow field. The numerical technique used is a combination of the finite element and finite difference methods. A transformation is introduced through which quadrilaterals in the physical domain are mapped into squares in the computational domain. The governing system of PDEs is thus transformed into an equivalent system applied over a square grid network. Comparisons with other numerical solutions as well as with measurements for various open channel configurations show that the proposed approach is a comparatively accurate, reliable and fast technique.
Boundary linear integral method for compressible potential flows
Authors: Fang Z. , Paraschivoiu I. 
Published: November 2005

AbstractA boundary linear integral method based on Green function theory has been developed to solve the full potential equation for subsonic and transonic flows. In this integral method, potential values in the flow region are determined by potential values represented by boundary integrals and a volume integral. The boundary potential values are obtained by implementing the boundary integrals along boundary segments where a linear potential relation is assumed. The volume integral is evaluated in a grid generated by finite element discretization. The volume integral is evaluated only outside the body. Therefore there is no extra boundary treatment required for evaluation of the volume integral. The source term is assumed to be constant in an element integral volume. The volume integral needs to be evaluated only once and can be stored in computer memory for further usage.
Prediction of wake in a curved duct
Authors: Narasimhan J. L. , Ramjee V. , Diwakar Philip M. , Tulapurkara E. G. 
Published: November 2005

AbstractExperimental data on the development of an aerofoil wake in a curved stream are compared with calculations based on the k‐ε model of turbulence with standard constants and with the model constant Cμ dependent on the local curvature. The mean velocity profile is asymmetric, the half‐width of the wake is more on the inner side of the curved duct than on the outer side, and the turbulent shear stress decreases rapidly on the outer side. The standard k‐ε model is able to satisfactorily reproduce this behaviour. Making Cμ dependent on the local radius improves the agreement on the inner side but slightly worsens it on the outer side.
A finite element formulation for laminar flow of a fluid with microstructure
Authors: Hogan H. A. , Henriksen M. 
Published: November 2005

AbstractA finite element formulation for the steady laminar flow of an incompressible fluid with microstructure has been developed. The particular fluids considered are commonly known as micropolar fluids, in which case suspended particulate microstructures are modelled by an ‘extended’ continuum formulation. The particle microspin is a new kinematic variable which is independent of the classical vorticity vector and thereby allows relative rotation between particles and the surrounding fluid. This formulation also gives rise to couple stresses in addition to classical force or traction stresses. The finite element formulation utilizes a variational approach and imposes conservation of mass through a penalty function. A general boundary condition for microspin has been incorporated whereby microspin at a solid boundary is constrained to be proportional to the fluid vorticity. The proportionality constant in this case can vary from zero to unity. Sample solutions are presented for fully developed flow through a straight tube and compared with an analytical solution. Results are also generated for flow through a constricted tube and compared with a Newtonian fluid solution.
Strategies for parallelizing a Navier‐Stokes code on the intel touchstone machines
Authors: Häuser Jochem , Williams Roy 
Published: November 2005

AbstractThe purpose of this paper is to predict the efficiency of the Navier‐Stokes code NSS* which will run on an MIMD architecture parallel machine. Computations are performed using a three‐dimensional overlapping structured multiblock grid. Each processor works with some of these blocks and exchanges data across the boundaries of the blocks. The efficiency of such a code depends on the number of grid points per processor, the amount of computation per grid point and the amount of communication per boundary point. In this paper we estimate these quantities for NSS* and present measurements of communication times for two parallel machines, the Intel Touchstone Delta machine and an Intel iPSC/860 machine, consisting of 520 and 64 Intel i860 processors respectively. The peak performance of the Delta machine is 32 Gflop. Secondly it is shown how, starting from a seven‐block grid of about 5000 000 points for the Hermes space plane, a mesh of 512 equally sized blocks is constructed retaining the original topology. This example demonstrates that multiblock grids provide sufficient control over both the number and size of blocks. Therefore it will be possible to simulate realistic configurations on massively parallel systems with a specified number of processors while achieving good quality load balancing.
Euler solutions for self‐generated rotor blade‐vortex interactions
Authors: Hassan A. A. , Tung C. , Sankar L. N. 
Published: November 2005

AbstractA finite‐difference procedure has been developed for the prediction of three‐dimensional rotor blade‐vortex interactions. The interaction velocity field was obtained through a non‐linear superposition of the rotor flow field, computed using the unsteady three‐dimensional Euler equations, and the embedded vortex wake flow field, computed using the law of Biot‐Savart. In the Euler model, near wake rotational effects were simulated using the surface velocity ‘transpiration’ approach. As a result, a modified surface boundary condition was prescribed and enforced at each time step of the computations to satisfy the tangency boundary condition. For supercritical interactions using an upstream‐generated vortex, accuracy of the numerical results were found to rely on the user‐specified vortex core radius and vortex strength. For the more general self‐generated subcritical interactions, vortex wake trajectories were computed using the lifting‐line helicopter/rotor trim code CAMRAD. For these interactions, accuracy of the results were found to rely heavily on the CAMRAD‐predicted vortex strength, vortex orientation with respect to the blade, and to a large extent on the user‐specified vortex core radius. Results for the one‐seventh scale model OLS rotor and for a non‐lifting rectangular blade having a NACA0012 section are presented. Comparisons with the experimental windtunnel data are also made.
A split operator scheme for ocean wave simulation
Authors: Li Chi Wai 
Published: November 2005

AbstractA coupled discrete spectral model was developed for the prediction of ocean waves by solving the energy conservation equation of the two‐dimensional wave spectrum. The model includes the dispersion correction terms in the governing equation to account for the dispersive effect due to the frequency‐dependent velocities of waves. A split operator scheme is used to deal with the numerical problems arising from different terms of the governing equation. The advection terms are solved by the proven accurate minimax characteristics method to avoid excessive numerical damping or oscillations. The dispersion correction terms are solved by central differencing. The source and sink terms are solved by a quasi‐second‐order explicit scheme with limitation on energy growth per time step to allow the use of a large time step. The model was verified by ideal test cases and wave‐hindcasting studies under typhoon conditions in the South China Sea near Hong Kong.
Numerical solution of the viscous stability equations for low‐speed reacting flows
Authors: Mahalingam Shankar 
Published: November 2005

AbstractThe governing equations required to analyse the linear (viscous) stability of low‐speed reacting flows are derived and a solution method based on initial value problems is described. The algorithm accurately reproduces the neutral stability curve for a non‐reacting viscous shear layer, thus providing partial validation. The results for premixed and non‐premixed flames in planar shear layers are presented and discussed.
A PC‐based system for modelling of convection in enclosures on the basis of the Navier‐Stokes equations
Authors: Ermakov M. K. , Gryaznov V. L. , Nikitin S. A. , Pavlovsky D. S. , Polezhaev V. I. 
Published: November 2005

AbstractA PC‐based system for modelling of convection in enclosures on the basis of the Navier‐Stokes equations is described and a number of test results are given. New examples of mixed convection in a square chamber and thermal convection in ordinary and porous (isotropic and anisotropic) vertical layers are presented which may be of interest in civil and building engineering.
Grid generation for 2D flow problems
Authors: Taniguchi Takeo , Holz Klaus‐Peter , Ohta Chikashi 
Published: November 2005

AbstractA grid generation method is proposed for an arbitrary two‐dimensional domain. The method, based on the Delaunay triangulation, is modified so that it can be used as a grid generator for an arbitrary two‐dimensional area with complex boundary geometry. Input data for the method are the co‐ordinates of all nodes and the ordering of nodes on each boundary. Its efficiency is examined through a number of actual problems, and a numerical experiment clarifies that the grid generation requires a CPU time which is proportional to the number of nodes.
Computation of incompressible viscous flows by the third‐order upwind finite element method
Authors: Kondo Norio , Tosaka Nobuyoshi , Nishimura Toshio 
Published: November 2005

AbstractA third‐order upwind finite element scheme is presented for numerical solutions of incompressible viscous flow problems. In order to achieve the third‐order upwind approximation for only the convection term in the Navier‐Stokes equations, a simplified Petrov‐Galerkin formulation in which a modified weighting function is expressed by the sum of a standard weighting function and its second and third spatial derivatives is employed. The mixed method is also employed in the formulation so that a discretization with high‐order accuracy in space is carried out by the use of linear elements. Because a truncation error caused by the third‐order upwind approximation is smaller than that of a first‐order upwind scheme, it is expected that the third‐order upwind scheme will greatly improve the numerical solutions of the Navier‐Stokes equations. Numerical results in one and two dimensions are presented to illustrate the effectiveness of the proposed scheme.
A flux‐based modified method of characteristics
Authors: Roache Patrick J. 
Published: November 2005

AbstractA flux‐based modified method of characteristics (MMOC) methodology in 1D is described which has the following properties: unconditional stability (though explicit), exact answers for integer CFL (Courant) numbers, completely conservative (locally and globally) and able to utilize various flux limiters and various characteristic‐ (trajectory‐) tracking algorithms. The use of characteristics based on cell‐wise constant characteristic velocities results in considerable code simplification, and Van Leer's MUSCL is an accurate and cost‐effective flux limiter. For CFL≥1 the flux limiter is applied only to the non‐integer part of CFL, whereas the integer part is exact for constant velocities; therefore accuracy improves with larger CFL. It is not a cheap algorithm, although explicit, because the operation count per time step increases with the integer part of CFL, but it is much more accurate than the commonly used implicit upstream differencing. This flux‐based MMOC method is well suited for groundwater flow calculations in which large local Courant numbers arise owing to grid clustering.
Calculation of turbulent combustion of propane in furnaces
Authors: Bai X. S. , Fuchs L. 
Published: November 2005

AbstractAn evaluation of some numerical methods for turbulent reacting flows in furnace‐like geometries is carried out. The Reynolds averaged Navier–Stokes equations and the two‐equation k–ϵ model together with either finite‐rate or infinite‐rate reaction models are solved numerically. Either single‐ or multiple‐step reactions together with the ‘eddy dissipation concept’ (EDC) are used to model reacting flows with finite reaction rates. The numerical scheme is finite difference based, together with a multi‐grid method and a local grid refinement technique. These methods have been used to calculate the combustion of propane in a single‐ and multiple‐burner configurations. In the former case, the sensitivity of the solution to variations in some model parameters (determining the reaction rate) and numerical parameters (mesh spacing) has been studied. It is noted that different dependent variables exhibit different levels of sensitivity to the variation in model parameters. Thus, calibration and validation of models for reacting flows require that one compares the most sensitive variables. For engineering purposes, on the other hand, one may calibrate and validate models with respect to the most relevant variables. Our conclusion is that since sensitivity of the temperature distribution is relatively mild, one can still use EDC‐like methods in engineering applications where details of the temperature field are of minor importance.