bluuebunny/crossref_metadata_2025 huggingface dataset:
An effective multigrid method for high‐speed flows
Authors: Swanson R. C. , Turkel E. , White J. A.
Published: August 2005

We consider the use of a multigrid method with central differencing to solve the Navier–Stokes equations for high‐speed flows. The time‐dependent form of the equations is integrated with a Runge–Kutta scheme accelerated by local time‐stepping and variable‐coefficient implicit residual smoothing. Of particular importance are the details of the numerical dissipation formulation, especially the switch between the second and fourth difference terms. Solutions are given for two‐dimensional laminar flow over a circular cylinder and a 15‐degree compression ramp.
Recursive filters determined from implicit formulations
Authors: Raymond William H.
Published: August 2005

A numerical procedure is used to identify the relationship between recursive and implicit filters. We find that the implicit filters can each be decomposed into two recursive filters at each grid point location by using Choleski matrix factorization. Specifically, the implicit second‐order sine filter yields the traditional first‐order recursive filter, while we recover the standard second‐order recursive sine filter from its fourth‐order implicit counterpart. This approach thus provides an alternative to traditional methods for calculating the coefficients associated with the recursive sine filters. We also find that we cannot recover the traditional form for the recursive tangent filter from the implicit tangent filter.
Hierarchical method for elliptic problems using wavelet
Authors: Cai Zhiqiang , Weinan E.
Published: August 2005

In this paper we explore the hierarchical structures of wavelets, and use them for solving the linear systems which arise in the discretization of the wavelet–Galerkin method for elliptic problems. It is proved that the condition number of the stiffness matrix with respect to the wavelet bases grows like O(log2 H/h) in two dimensions, and the condition number of the wavelet preconditioning system is bounded by O(log2 H/h) in d dimensions, instead of O(h−2) if the scaling function bases are used.
Variational validation of a membrane finite element with drilling rotations
Authors: Allman D. J.
Published: August 2005

It is shown that a triangular membrane finite element with vertex ‘drilling rotations’ which was developed in earlier publications is, in fact, a correct implementation of a variational principle. The existence of a variational principle is a crucial factor which places the earlier work on a secure theoretical foundation. It implies superior computational characteristics of the finite‐element equations and provides valuable guidance on practical issues such as the consistent treatment of boundary conditions.
Improved finite‐difference solutions of the diffusion equation for heat conduction
Authors: Bhattacharya M. C.
Published: August 2005

A number of improved finite‐difference solutions of explicit form have been reported recently. The choice of a particular solution of these improved explicit forms is dependent on the value of the non‐dimensional time step as well as whether the process involves cooling or heating. The conditions for stable operation are clarified in the paper. Two new improved solutions of implicit forms are also reported in the paper. These new solutions give better accuracy compared to the conventional Crank–Nicolson and pure implicit methods, and have unrestricted stability.
Application of iterative global/local finite‐element analysis. Part 2: Geometrically non‐linear analysis
Authors: Whitcomb John D. , Woo Kyeongsik
Published: August 2005

A geometrically non‐linear global/local technique was developed and tested. This technique uses separate global and local finite‐element models. Iteration is used to enforce equilibrium between the global and local models. The results of this initial study suggest that the technique can be used to reduce both computer memory and CPU requirements.
Consistent concept for line search algorithms in combination with arc‐length constraints
Authors: Schweizerhof Karl
Published: August 2005

A general line search concept is presented, which can be applied for the solution of non‐linear equations in the presence of constraint conditions as in arc‐length methods in a consistent manner.
Matrix filter for correcting experimental data
Authors: Lukasiewicz S.
Published: August 2005

The paper presents a filtering algorithm which corrects the results of measurements of certain physical quantities if any additional information about the measured values is known. The algorithm is very effective in one‐dimensional as well as in two‐dimensional problems where additional constraints are presented in the form of differential equations. For example, this technique can be used to correct the measurements of certain dynamic quantities if some information about motion of examined bodies is known. It can also be used to correct the strain field measurements if the conditions of continuity of strain field are included.
Finite‐element computer simulation of atmospheric convection with anisotropic eddys
Authors: Mann Kenneth J.
Published: August 2005

A computer simulation is made of cellular convection in an anisotropic atmosphere in an attempt to more closely approximate the observed values with those obtained from mathematical models. A finite‐element Galerkin technique, with Taylor approximation and Crank–Nicolson, is employed and comparisons are made with the author's earlier finite‐element models of isotropic convection and with finite‐difference models. It is found that postulates from physics on the effect of anisotropy on cellular atmospheric convection, with its increase in the aspect ratio, are well modelled with this finite‐element technique.
A simple time‐step control scheme
Authors: Givoli Dan , Henigsberg Ilan
Published: August 2005

A simple automatic time‐step control procedure is devised for use in implicit one‐step time‐integration schemes. First‐ and second‐order semi‐discrete systems of equations emanating from finite‐element spatial discretization are considered. The varying time‐step interval is controlled by the relative distance between the solution in two consecutive time steps, using the solution update formula of the time integrator under consideration. A model problem involving the vibrations of a membrane is used to demonstrate the performance of the scheme.
Analytic evaluation of singular boundary integrals without CPV
Authors: Lutz Earlin D. , Gray L. J.
Published: August 2005

Boundary integral equations are generally derived by employing a Cauchy Principal Value definition for the singular integral involving the derivative of the Green function. As a consequence, evaluation of this integral requires special attention, and computing the associated ‘solid angle coefficient’ can often pose difficulties. As discussed herein, these problems can be avoided by defining the integral directly, in terms of a limit to the boundary. This approach leads to a straightforward evaluation procedure.
Macro finite element using subdomain integration
Authors: Woo Kyeongsik , Whitcomb John D.
Published: August 2005

For some heterogeneous materials, it is not practical to model the microstructure directly using traditional finite elements. Furthermore, it is not always accurate to use homogenized properties. Macro elements have been developed which permit microstructure within a single element. These macro elements performed well in initial tests.
Locking‐free straight beam element based on curvature
Authors: Lee Pal‐Gap , Sin Hyo‐Chol
Published: August 2005

The formulation of a straight beam element to eliminate the shear locking phenomenon is presented. The element is based on curvature so that the bending energy is fully represented, and the shear strain energy is incorporated into the formulation by the equilibrium equation. Four examples are chosen to verify the concept of the element employed and its capability of the analysis. The solutions obtained reveal that the element describes the behaviour of the straight beam quite exactly and efficiently, showing no locking and that it is also applicable to the analysis of both thin and thick straight beams.
Perturbation method for computing eigenvalue bounds in structural vibration systems with interval parameters
Authors: Chen Su‐Huan , Qiu Ziping , Liu Zhongsheng
Published: August 2005

In this study a perturbation method for computing the upper and lower bounds of eigenvalues of structural vibration systems with interval parameters is presented. The eigenproblem of the uncertain (interval) structure is expressed by equations consisting of the uncertainties. If the uncertainity is small in parameters, the eigensolutions of uncertain structures can be obtained efficiently by the perturbation method presented. A numerical example is given to demonstrate the validity of the method.
High‐order polynomial interpolation in boundary integral equation analysis
Authors: Walker S. P.
Published: August 2005

A sixth‐order polynomial shape function is developed for BIE analysis. The function is applied over only three‐noded elements, but with the support for the function extending over adjacent elements. This avoids the oscillations near the ends of the range which otherwise are characteristic of high‐order polynomial interpolation. Various test problems are explored, and it is shown that results as accurate as those from conventional quadratic elements are obtained with larger nodal spacings, and thus giving the potential for significant reductions in matrix storage requirements and solution times.
Space‐time oriented streamline diffusion methods for non‐linear conservation laws in one dimension
Authors: Hansbo Peter
Published: August 2005

In this paper we consider an explicit finite‐element method, with elements adaptively oriented in space‐time, for the solution of one‐dimensional conservation laws, extending previous work dealing with linear convection‐diffusion and incompressible flow. In particular we consider Burgers' equation and the compressible Euler equations.
Cyclic symmetry in boundary elements
Authors: Ranjbaran A.
Published: August 2005

An efficient algorithm for consideration of axial and cyclic symmetry in the boundary‐element method is presented. The appropriate transformation relationships was derived. The algorithm is then implemented in a boundary element program for the analysis of 2D elastostatic problems. Through analysis of typical problems the validity of the algorithm and its implementation is verified. A high level of accuracy and substantial reduction in computer time and storage was achieved.
Some geometric problems related to fracture‐control in complex structures
Authors: Beakou A. , Touratier M. , Abdi R. El
Published: August 2005

In the design of members with flaws, it is necessary to keep the stress intensity factor K of any sharp crack below the fracture toughness Kcr of the materials. Stress‐intensity factor equations for the more common basic specimen geometries and various loading conditions are available in the literature. The application of these equations to complex structures involves geometric problems such as the identification of the outline of each member and the sizing of the equivalent specimen for each flaw. The paper gives a response to such difficulties.
Use of central‐difference operators for solution of singularly perturbed problems
Authors: Hegarty Alan F. , Miller John J. H. , O'Riordan Eugene , Shishkin G. I.
Published: August 2005

Singularly perturbed second‐order elliptic equations with boundary layers are considered. These may be considered as model problems for the advection of some quantity such as heat or a pollutant in a flow field or as linear approximations to the Navier‐Stokes equations for fluid flow. Numerical methods composed of central‐difference operators on special piece‐wise‐uniform meshes are constructed for the above problems. Numerical results are obtained which show that these methods give approximate solutions with error estimates that are independent of the singular perturbation parameter. An open theoretical problem is posed.
A simulation of free‐surface electrohydrodynamic flow
Authors: Kaiser Kenneth L. , Kaiser Mark J. , Weeks Walter L.
Published: August 2005

Theoretical and experimental analysis of free‐surface electrohydrodynamic flow is fragmented and incomplete. Simulation studies of this phenomenon are further limited by the inherent complexities in the modelling process. In this note a mathematical model is developed to analyse free‐surface electrohydrodynamic flow in two dimensions, and preliminary results of the simulation are described. The configurations examined include electrified conducting surfaces, the dielectrophoretic forces, and a conducting jet. The simulation is compared with analytical results in the first two investigations and is shown to be quite accurate. In the last simulation it is demonstrated that in the initial formation of a conducting jet, a 10 per cent increase in applied voltage results in about a 10 per cent increase in fluid velocity.
Instability, chaos, and growth and decay of energy of time‐stepping schemes for non‐linear dynamic equations
Authors: Xie Y. M. , Steven G. P.
Published: August 2005

In this paper we present numerical experiments made to investigate the behaviour of the Newmark time‐stepping scheme applied to non‐linear dynamic systems. Our attention is focused on the instability and chaos in the Newmark scheme when it is applied to the equation ü + P(u) = 0, representing a non‐linear elastic spring. Some unusual modes of behaviour, which are of substantial interest, have been observed. In the first case, a stable but chaotic solution is found. In the second case, while a stable solution is obtained with a certain time step, an unstable solution is found by decreasing the time step. In the third case, instability is triggered by neglecting the initial acceleration. A simple modification of the Newmark scheme is proposed which keeps the energy constant for the equation ü + P(u) = 0 and thereby guarantees unconditional stability. Numerical examples in support of such an energy‐conserving scheme are presented.
Efficient refinement/derefinement algorithm of nested meshes to solve evolution problems
Authors: Ferragut L. , Montenegro R. , Plaza A.
Published: August 2005

An adaptive refinement/derefinement algorithm of nested meshes is presented. Some definitions are introduced. The main properties of the derefinement algorithm are remarked upon and its efficiency is shown through two numerical examples: a time‐dependent convection‐diffusion problems with dominant convection and a quasistationary problem.
Effect of finite‐element mesh topology on simulating mechanical breakdown in solids
Authors: Cox Simon J. D. , Paterson Lincoln
Published: August 2005

Fracture in heterogeous solids can be simulated with finite elements. We compare simulations of mechanical breakdown using meshes based on two types of geometrical elements: quadrilaterals and hexagons. The different co‐ordination of the meshes leads to important differences in the load‐carrying geometry close to failure. Hexagonal elements give a better representation of failure in brittle solids, whereas quadrilateral elements have a resemblance to fibrous solids.
Stochastic boundary‐element methods applied to 3D elastic problems and reliability of structural strength
Authors: Weidong Wen
Published: August 2005

The stochastic boundary‐element method (SBEM) is developed in this paper for 3D elastic problems and reliability analysis of structural components. The integral equations of BEM are derived partially by random variables, and the integral equations of SBEM are established. Considering the applied loads and the limitation of material strength to be a Gauss distribution, the numerical results in this paper show good agreement with those obtained from Monte Carlo simulation and theoretical solutions.
On the large time behaviour of transient dynamic kernels for two‐dimensional wave scattering
Authors: Ness J. K. , Rudolphi T. J.
Published: August 2005

An essential feature of the transient dynamic kernels for any time domain boundary integral equation is that they decay towards the static kernels for large time increments. The purpose of the paper is to show that the kernels of Mansur and Brebbia (1982), which are expressed in the form of generalized mathematical functions, do exhibit the correct decay property in contradiction to the claims of Israil and Banerjee (1990). Mansur and Brebbia express the fundamental solution wave discontinuity in terms of the generalized functions H(t) and δ(t), the Heaviside and Dirac delta functions, but do not explicitly demonstrate the required long time behaviour. In the 1990 paper the temporal discontinuity of the kernels is expressed by conventional functions in two time regimes and is shown to possess the correct long time behaviour, while it is claimed that the kernels in the 1982 paper do not. It is shown here that, assuming either constant or linear variation in time, usage of the generalized functions in the fundamental solution does yield the static fundamental solution for large time steps, as expected.
Reliable Delaunay‐based mesh generation and mesh improvement
Authors: Boender Edwin
Published: August 2005

The paper describes a method for generating triangulations of two‐dimensional domains. Firstly, a description is given of a reliable algorithm that creates a constrained Delaunay triangulation for a multiply‐connected planer domain, without performing any explicit visibility computations. Then, several techniques to improve an existing triangulation are discussed. It turned out that a new variant of mesh relaxation was most effective in improving an existing triangulation. Several examples are included to illustrate the method's overall behaviour.
Two‐dimensional adaptive quadrilateral mesh generation
Authors: Chen Ke
Published: August 2005

In the paper we address the problem of 2D adaptive quadrilateral mesh generation by using the variational principles. We first find the variational integral which generates the known grid system of curve‐by‐curve error equidistributions. We then use the same intergral to generate a new adaptive grid system which is superior to the known system in that the new system produces smoother meshes. Moreover, the new integral may be combined linearly with existing smoothness control integrals to yield more robust adaptive grid systems. Numerical results and comparisons are reported.
A note on the treatment of frictionless contact between non‐smooth surfaces in fully non‐linear problems
Authors: Laursen T. A. , Govindjee S.
Published: August 2005

An approach is presented for the formulation of the unilateral contact constraint in the presence of contact surface discontinuities. Such discontinuities may be due to physical corners on the surfaces of contacting bodies, or may be introduced by a discretization process (e.g. finite elements). It is asserted that a strong analogy exists between this problem and the one describing inelastic evolution in the presence of a discontinuous yield surface. This analogy is exploited to produce an effective treatment of the frictionless corner problem, complete with an effective augmented Lagrangian implementation for accurate constraint enforcement.
Numerical solution to a stochastic interception problem
Authors: Reuter Gerhard W.
Published: August 2005

A finite difference scheme is derived to solve for the probability density that a moving point, whose velocity is continually pertubed by Gaussian white noise, reaches a given target within a given time period. The numerical scheme is applied to the problem of finding the probability that two moving spheres collide.
An optimized implementation of the Newmark/Newton‐Raphson algorithm for the time integration of non‐linear problems
Authors: Jacob Breno Pinheiro , Ebecken Nelson Francisco Favilla
Published: August 2005

The paper describes an optimized computational implementation of a basic ‘building block’ for non‐linear structural dynamic analysis programs: the combination of the modified Newton‐Raphson iterative technique with an implicit time integration operator (in this case a member of the Newmark family), working in an incremental‐‐iterative formulation for the equations of motion. The objective of this implementation is to attain improved computational efficiency, regarding both CPU time and memory requirements. The basic formulation and derivation are presented, along with the implementation details; the positive aspects related to the computational optimization are highlighted.
Solution of the differential Riccati equation using the transmission line modelling (TLM) technique
Authors: Woolfson M. S. , Hui S. Y. R.
Published: August 2005

In this communication, the application of the transmission line modelling (TLM) technique to the solution of the differential Riccati equation is described. A comparison is made between the TLM, fourth‐order Runge‐Kutta and the first‐order Gear methods, for the case where one is applying the Kalman filter to the estimation of a voltage in a passive analogue circuit. In the particular example studied, the state equation is second‐order. It is found that, when the system is underdamped, the fourth‐order Runge‐Kutta method has the best performance, followed by the TLM method. When the system is overdamped and stiff, the TLM method yields results that are closest to the analytical solution. Finally, a discussion is presented of the effects of errors in the TLM solution of the Riccati equation on the accuracy of the solution to the continuous Kalman filter estimation equation.
Transverse shear correction factors for laminates in cylindrical bending
Authors: Laitinen M. , Lahtinen H. , Sjölind S.‐G.
Published: August 2005

Mindlin‐type plate and shell finite elements are the most widely used ones in the analysis of laminated composite structures. In the commercially available finite element programs, the transverse shear correction factors for these elements are usually the same as for structures made of isotropic materials. In the paper the shear correction factors are determined using energy principles for general laminates in cylindrical bending. Results for various materials and laminates are presented.
An independent refinement and integration procedure in multiregion finite element analysis
Authors: Krishnamurthy T. , Raju I. S.
Published: August 2005

An independent refinement and integration procedure is developed to couple together independently modelled (global and local) regions in a single analysis. The finite element models can have different levels of refinement and the nodes along the interface between them need not coincide with one another. A spline interpolation function that satisfies the linear isotropic plate‐bending differential equation is used to relate the local model interface nodal displacements to the global model interface displacements. The proposed independent refinement and integration procedure is validated by applying it to problems involving in‐plane and out‐of‐plane deformations.
The variationally correct rate of convergence for a two‐noded beam element, or why residual bending flexibility correction is an extravariational trick
Authors: Prathap G.
Published: August 2005

In this paper I re‐examine the mechanics of the residual bending flexibility correction and show that it is an extravariational trick.
On the solution of second‐order post‐buckling fields
Authors: Kouhia R. , Menken C. M.
Published: August 2005

Second‐order post‐buckling fields emanate from the solutions of a constrained minimization problem. Two iterative solution algorithms for this specific type of constrained problem are described. A classical augmented Lagrangian algorithm is compared with a simpler one utilizing the specific feature of the initial post‐buckling analysis. Numerical examples of prismatic plate‐type structures are presented.
An efficient data structure for the advancing‐front triangular mesh generation technique
Authors: Kwok W. , Haghighi K. , Kang E.
Published: August 2005

A new approach is presented to optimize the search, deletion and insertion operations in the advancing‐front triangular grid generation technique. This approach is based on the heap, hash table and linked list data structures. The basic idea is to use different data structures for different operations. When the front is updated after forming an element, a hash table with doubly linked lists is used to speed up searching, deleting, and inserting operations. On the other hand, a heap is used to select the shortest side for constructing each new element. Therefore, there is a need for two copies of the generation front: one is stored in the hash table with doubly linked lists, and the other one in the heap. For each element generated, this approach is able to search for a side to be removed from the front in a constant time on average, and delete and insert a side from and into the front in O(logN) time on average, where N is the number of sides in the front. The technique is also capable of searching and selecting the shortest side from the front for creating a new element in O(1) time. Several examples are included to demonstrate the performance of the approach.
Direct application of constraints to symmetric algebraic systems
Authors: Schreyer H. L. , Parsons D. A.
Published: August 2005

Constraints arise naturally in the context of rigid inclusions, incompressibility, inextensible fibres and deformed finite elements. Typical methods for handling constraints in the governing matrix equation include Lagrange multipliers, penalty weights and elimination of variables. Each procedure has a particular undesirable feature. Proposed here is an approach in which each constraint is handled directly and sequentially through a modification of the rows and columns of the governing matrix and force vector. Positive definiteness, symmetry and the dimensions of the matrix remain unchanged. Elementary examples involving both the static and dynamic response of a bar are given to illustrate the procedure.
Transonic flow computations using streamfunction and potential function
Authors: Zhang S. , Barron R. M. , An C.‐F.
Published: August 2005

A new formulation is proposed for two dimensional transonic potential flow calculations. The present approach takes advantage of both streamfunction and potential function formulations. A modified form of the partial differential equations and simplified boundary conditions are derived. Numerical examples show that a reliable method has been developed, capable of calculating highly transonic potential flows.
Boundary layers in uniform and variable thickness plates with rectangular and curved planforms using the finite strip method
Authors: Hinton E. , Selman A. , Al‐Khamis M.
Published: August 2005

The Mindlinn‐Reissner finite strip method is used to study in a qualitative manner boundary layer effects_in uniform and variable‐thickness plates with rectangular and curved planforms.
The method of fundamental solutions for non‐linear thermal explosions
Authors: Chen C. S.
Published: August 2005

A numerical method based on the method of fundamental solutions, thin plate spine interpolation and monotone iteration is devised to find the minimal solution of the steady‐state blow‐up problem. The method of fundamental solutions requires neither domain nor boundary discretization and results in high accuracy and efficiency. For illustration, critical values of the Frank‐Kamenetskii parameter are given for different geometrical boundaries in the two‐dimensional case.
Proper eigenvalue solution for the transient response of multidimensional heat transfer systems
Authors: Callarotti Roberto C.
Published: August 2005

We present a new procedure for the numerical calculation of the transient response of systems characterized by partial differential equations in several space variables and time. The procedure is based on: (i) spatially discretizing the system, (ii) deriving an equivalent circuit for each volume element, (iii) applying a time Laplace transformation and obtaining an admittance matrix, (iv) writing the expressions for the Laplace transforms of the desired variables according to Cramer's determinant rule, (v) interpreting the determinants as generalized eigenvalue problems, (vi) obtaining the proper eigenvalues of the system (poles and zeros), and (vii) finding the time‐dependent solutions by ‘trivial’ inverse Laplace transformations. Although the procedure proposed applies to many partial differential equations (fluid flow in porous media, conductive heat transfer with convection, pressure tests in oil wells, electrical conduction, etc.), in the paper we illustrate the procedure in detail for a conduction heat transfer system (nine nodes). The procedure presented is much more efficient numerically than the direct numerical integration (in space and time) of the ruling PDE, or than solutions which require ‘standard’ numerical inverse Laplace transformation after matrix inversion.
Solution of unbounded domain problems using elliptic artificial boundaries
Authors: Ben‐Porat Gil , Givoli Dan
Published: August 2005

Exact non‐local boundary conditions are derived and used on an artificial boundary to solve the two‐dimensional Laplace and Helmholtz equations in an unbounded domain. The artificial boundary is chosen to be an ellipse, as opposed to previous works which employed circular boundaries. The use of elliptic artificial boundaries enables one to enclose slender obstacles very efficiently, especially in the case of Laplace's equation.
A fully spectral solution method for parabolic equations
Authors: Kumar K. N. Kiran , Eswaran V.
Published: August 2005

A comparison is made between the performance of the (aliased) Chebȳshev collocation method (CM) and the more recent Galerkin collocation method (GCM), which is a least‐squares collocation method, in solving the laminar, incompressible, steady boundary‐layer equations, which are parabolic in nature. An iterative procedure based on the preconditioned residual minimization method has been used. It is shown that the GCM is superior to the CM on several counts. Unlike the CM, the GCM minimizes the residual uniformly over the entire domain. The global accuracy of the solution is found to be higher in the GCM, at lower grid resolutions. The method also achieves much higher convergence rates. Unlike in the collocation method, the final residual values obtained in the GCM are good indicators of the level of accuracy achieved in the solution. It is highly likely that these results will be repeatable in other systems of parabolic partial differential equations.
Computational Methods in Coupled Electron–Ion Monte Carlo Simulations
Authors: Pierleoni Carlo , Ceperley David M.
Published: August 2005

In the last few years, we have been developing a Monte Carlo simulation method to cope with systems of many electrons and ions in the Born–Oppenheimer approximation: the coupled electron–ion Monte Carlo method (CEIMC). Electronic properties in CEIMC are computed by quantum Monte Carlo rather than by density functional theory (DFT) based techniques. CEIMC can, in principle, overcome some of the limitations of the present DFT‐based ab initio dynamical methods. The new method has recently been applied to high‐pressure metallic hydrogen. Herein, we present a new sampling algorithm that we have developed in the framework of the reptation quantum Monte Carlo method chosen to sample the electronic degrees of freedom, thereby improving its efficiency. Moreover, we show herein that, at least for the case of metallic hydrogen, variational estimates of the electronic energies lead to an accurate sampling of the proton degrees of freedom.
Time interval gating for analysis of cell function using flow cytometry
Authors: Durack Gary , Lawler Gretchen , Kelley Steve , Ragheb Kathy , Roth R. A. , Ganey P. , Robinson J. Paul
Published: August 2005

We propose a method which significantly shortens the time required for both the collection and analysis of data derived from multiple sample, flow cytometric kinetic assays. We have defined the term Time Interval Gating (TIG) to describe this method. TIG effectively allows one flow cytometer to concurrently monitor several samples over the course of a kinetic assay. Data for all samples are stored in a single FCS 2.0 compatible listmode data file which we refer to as the TIG data file. TIG is adaptable to most commerical flow cytometers. Standard listmode analysis software can be used to analyze the TIG data files and correlate any combination of tubes and/or time intervals from the assay. Results for the entire assay can be displayed on a single two parameter plot. This paper describes how TIG is applied to neutrophil oxidative burst measurement using a standard EPICS Elite flow cytometer. In this assay, 11 samples were each monitored for 30 min to identify the extent to which volatile organic chemicals (VOCs) inhibited the oxidation of DCFH in stimulated neutrophils. TIG makes the oxidative burst assay practical for high volume screening by reducing the overall flow cytometer and analysis time required by a factor of ten. In addition, TIG provides an organized approach to managing data acquisition on instruments equipped with automated sampling systems.
Natural killer function in flow cytometry: Identification of human lymphoid subsets able to bind to the NK sensitive target K562
Authors: Vitale M. , Zamai L. , Neri L. M. , Manzoli L. , Facchini A. , Papa S.
Published: August 2005

NK cells are a phenotypically, morphologically and functionally heterogeneous population. This has led to the current thought that the non‐MHC restricted cytotoxity is a cellular function that can be associated to different phenotypes. The recognition of the target cell and the conjugate formation is always the first step that eventually leads to the lysis of target. Characterization of the phenotypical pattern of the cells able to bind to K562 targets is the purpose of this study. A multiparametric flow cytometry binding assay has been employed to identify the different K562‐bound lymphocyte subsets. In particular, cells that coexpress the CD16 and CD8 antigens (CD16+8dim+) showed a significantly higher binding capacity than their CD16+8− counterpart. Moreover, the highest binding values have been found in cells that did not express the CD16 antigen at all, but still expressed the CD8dim antigen, such as the small CD8dim+3+ population. These data show that, the NK lytic function being dependent on binding, minor subpopulations must be considered among effector cells, which might correspond to different lytic activities. None of the previously published methodologies that analyze conjugates by flow cytometry or fluorescence microscopy were able to measure the binding capacity of small, double stained, lymphocyte subsets.
Amphotericin B susceptibility testing of Candida species by flow cytometry
Authors: O'Gorman Maurice R. G. , Hopfer Roy L.
Published: August 2005

We have developed an 8 hr flow cytometry (FCM) method for assessing susceptibility of yeasts to amphotericin B (AmpB). The method detects both high‐level and relative‐resistance to the drug. Variables found to affect fluorescence of control and AmpB treated cells included pH, presence of glucose, incubation conditions, concentration and length of exposure to both AmpB and ethidium bromide (ETBR), and the degree of resistance to AmpB. The FCM method was optimized based on increased red fluorescence intensity (RF), decreased forward angle light scatter (FALS), and a negative gating technique. A dose response was seen between 0.1 and 10 μg AmpB/ml for the susceptible control strain. Greater than 50% of cells from all susceptible strains tested transfer into the negative gate when exposed to 2.5 μg Amp B/ml while fewer than 5% of cells of the highly resistant C. tropicalis (ATCC 28707) are affected at concentrations up to 20μg/ml. This method may provide a more accurate assessment of Amp B susceptibility than conventional tube dilution methods.
Subsidence above volumetric and waterdrive gas reservoirs
Authors: Schrefler B. A. , Lewis R. W. , Majorana C.
Published: August 2005

A fully coupled consolidation model has been developed for the simulation of the surface subsidence above gas reservoirs. The model is based on the Biot Theory and the material balance equation for hydrocarbon reservoirs. The model is extremely versatile and can handle such complex situations as vertical cross‐sections where several gas reservoirs and aquifers are exploited at different levels. Computer runs were used to generate several reservoir formation profiles and the surface subsidence bowl for a variety of conditions. These results indicate the importance of various parameters which are disregarded in proelasticity models.
Projection conditions on the vorticity in viscous incompressible flows
Authors: Quartapelle L. , Valz‐Gris F.
Published: August 2005

The problem of establishing appropriate conditions for the vorticity transport equation is considered. It is shown that, in viscous incompressible flows, the boundary conditions on the velocity imply conditions of an integral type on the vorticity. These conditions determine a projection of the vorticity field on the linear manifold of the harmonic vector fields. Some computational consequences of the above result in two‐dimensional calculations by means of the nonprimitive variables, stream function and vorticity, are examined. As an example of the application of the discrete analogue of the projection conditions, numerical solutions of the driven cavity problem are reported.
Effect of open boundary condition on numerical simulation of three‐dimensional hydrothermal behavior of Biscayne Bay, Florida
Authors: Sengupta Subrata , Miller H. P. , Lee Samuel S.
Published: August 2005

A three‐dimensional time dependent free‐surface model has been used to simulate the velocity and temperature distributions in Biscayne Bay, an estuarine basin in South Florida. Comparisons with tide gauge data and airborne infrared temperature data have been made. Analyses of three‐dimensional velocity structure, phase relationships of velocity with depth and horizontal location have been conducted.

One of the major concerns with three‐dimensional models is the specification of conditions at open‐boundaries, since it is rare that complete time dependent variations of variables at these boundaries are available. Two sets of approximate boundary conditions at the Biscayne Bay‐Atlantic Ocean interface have been used for computations. It was found that specification of averaged surface height variation at open boundaries yield significantly better results than specification of estimated values of velocity.
The implementation of normal and/or tangential boundary conditions in finite element codes for incompressible fluid flow
Authors: Engelman M. S. , Sani R. L. , Gresho P. M.
Published: August 2005

Various techniques for implementing normal and/or tangential boundary conditions in finite element codes are reviewed. The principle of global conservation of mass is used to define a unique direction for the outward pointing normal vector at any node on an irregular boundary of a domain containing an incompressible fluid. This information permits the consistent and unambiguous application of essential or natural boundary conditions (or any combination thereof) on the domain boundary regardless of boundary shape or orientation with respect to the co‐ordinate directions in both two and three dimensions. Several numerical examples are presented which demonstrate the effectiveness of the recommended technique.
Longshore boundary conditions for numerical wave models
Authors: Austin D. Ian , Bettess Peter
Published: August 2005

The problem of truncating nearshore finite element wave models is addressed. Incorrect treatment of the artificial boundaries of the model will cause spurious wave reflections. Three methods for dealing with these boundaries: application of constraints, use of the Smith condition and longshore dampers, are proposed. Numerical results show the dampers to be the best method.
Numerical solution of subsonic and transonic cascade flows
Authors: Habashi W. G. , Kotiuga P. L.
Published: August 2005

In this work a study of the application of the finite element method to transonic flows in axial turbomachines is undertaken.

Solution techniques capable of accurately predicting flows from the incompressible regime up to the establishment of shocks in the transonic regime are presented. In the subsonic and shockless transonic regimes a local linearization method capable of very rapid convergence is used. In the full transonic regime the artificial compressibility method is employed to exclude downstream influences in the supersonic regions. The two approaches can be combined in a unified package and appropriate switches introduced to select the relevant method in any flow regime.
A survey of some second‐order difference schemes for the steady‐state convection–diffusion equation
Authors: Gupta Murli M.
Published: August 2005

This paper presents a survey of several finite difference schemes for the steady‐state convection–diffusion equation in one and two dimensions. Most difference schemes have O(h2) truncation error. The behaviour of these schemes on a one‐dimensional model problem is analysed in detail, especially for the case when convection dominates diffusion. It is concluded that none of these schemes is universally second order. One recently proposed scheme is found to yield highly inaccurate solutions for the case of practical interest, i.e. when convection dominates diffusion. Extensions to two and threedimensions are also discussed.
Numerical simulation of liquefied fuel spills: I. Instantaneous release into a confined area
Authors: Brandeis Julius , Kansa Edward J.
Published: August 2005

The shallow‐water equations in radial symmetry are solved numerically to simulate the collapse of a cylindrical liquid column into an area surrounded by a concentric dike. The following three subcases of this problem are considered: a liquid column collapsing onto a layer of the same liquid, a liquid column collapsing onto a solid surface, and a column of lighter liquid collapsing onto a heavier liquid (i.e. liquefied natural gas (LNG) spilled onto water). The results for the three categories are compared and the differences and similarities between them are analysed.
Numerical simulation of liquefied fuel spills: II. Instantaneous and continuous LNG spills on an unconfined water surface
Authors: Brandeis Julius , Ermak Donald L.
Published: August 2005

A simple numerical model based on the shallow water equations in radial symmetry is used to simulate both instantaneous and continuous spills of liquefied natural gas (LNG) onto a water surface. Using the computed results, a study is made of the similarities and differences in the pool structure resulting from the two types of spills. For instantaneous spills a relation linear on a logarithmic plot is suggested between the maximum pool size and the spill volume. The effects of shear forces and surface cohesivity on the evolution of the spill are also examined.
A frontal method based solution of the quasi‐three‐dimensional finite element model for interconnected aquifer systems. Steady and unsteady equations, with the E.N.S. method for fluid mass balance evaluation
Authors: Sartori L. , Peverieri G.
Published: August 2005

The quasi‐three‐dimensional equations controlling the groundwater flow in heterogeneous and interconnected aquifer systems are discretized by finite elements, considering also the aquifer branching. A new method for fluid mass balance evaluation based on the equivalent nodal source (E.N.S.) concept allows one to express the balance in conservative terms, and interpret finite element equations as nodal balance equations. The solution of the system is based on the frontal method. Use of substructures limits the frontal increase in correspondence to the aquifer branching. In the steady state, the frontal method is integrated with an iterative solution technique to eliminate the frontal increase caused by the presence of aquitards. It converges very rapidly, using a forcing technique with an automatic parameter definition. In the unsteady case the same scope is achieved using a predictor‐corrector procedure which employs the Crank‐Nicolson method in the corrector phase.

This very stable procedure permits use of fairly long time‐steps and concerns the case of source terms depending on piezometry (problem of interaction between water table and river). This method has been tested with several fairly complex cases.
Lifting aerofoil calculation using the boundary element method
Authors: Carey G. F. , Kim S. W.
Published: August 2005

The bbundary integral formulation and boundary element method are extended to include lifting flow problems. This involves inclusion of a branch cut in the flow field and imposition of a Kutta condition to determine the circulation, Γ Additional boundary integral contributions arise from the cut surface. Techniques for calculating Γ are developed and we treat, in particular, a superposition procedure which permits very efficient computation. Numerical results are presented for an NACA0012 aerofoil at several angles of attack.
Wave envelope and infinite elements for acoustical radiation
Authors: Astley R. J.
Published: August 2005

Finite element models are presented for the calculation of near and far field acoustical radiation. These models are applied to the specific problem of fan noise radiation from axisymmetric turbofan inlets. In all cases conventional acoustic finite elements are used within an inner region close to the inlet. The far field is represented by infinite elements or wave envelope elements. Theory and results are presented for the case with zero mean flow. Comparisons of computed data with analytic solutions and measured values establish the utility of both the infinite element and wave envelope element schemes in determining the near field values of acoustical pressure. The wave envelope scheme is shown to be effective also in the far field. Both schemes use meshes an order of magnitude more sparse that would be required in conventional numerical discretizations, and may consequently be applied at modest computational cost.
Incompressible flow in a rapidly rotating cylinder with a source/sink distribution in the lateral wall and a free inner boundary
Authors: Ribando Robert J.
Published: August 2005

The flow of an incompressible fluid in a rapidly rotating right circular cylinder is considered. A source/sink mass distribution at the lateral wall, which is azimuthally uniform and symmetric across the midplane, causes a deviation from wheel flow. The container is only partially full and the inner free surface is allowed to deviate slightly from the vertical. A finite‐difference solution of the full axisymmetric, non‐linear governing equations was used to obtain the flow field. A special implicit technique for the Coriolis terms which maintains geostrophy was developed and is described. The results obtained for a low Rossby number flow compare quite favourably with the linearized solution. Results are also presented for a case wherein the non‐linear terms are important.
Numerically induced oscillations in finite element approximations to the shallow water equations
Authors: Walters Roy A.
Published: August 2005

Numerical noise has been a problem with finite element solutions to the shallow water equations. Two methods used to reduce the noise level are evaluated, and these results are compared with published results for equal‐order interpolations. The two methods are mixed‐interpolation (quadratic interpolation for velocity and linear interpolation for sea level) and a spectral form of the wave equation. Whereas mixed interpolation removes the troublesome sea level mode, it can still have considerable noise in velocity. The spectral wave equation is efficient and does not contain the spurious eigenmodes which contribute to high noise levels.