bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient flow past a circular cylinder: A benchmark solution
Authors: Engelman Michael S. , Jamnia Mohammad‐Ali 
Published: October 2005

AbstractThe simulation of the von Karman vortex street behind a circular cylinder has long been used as a benchmark problem to test the performance of numerical algorithms for solving the Navier‐Stokes equations. It is particularly suited for comparing different numerical outflow boundary conditions since the computational domain must necessarily be terminated in the vortex street itself. This paper presents detailed numerical results of the flow past a cylinder at a Reynolds number of 100 on a very fine mesh which has been purposely designed to extend past the typically used dimensions. Hopefully, these results can form a basis of a benchmark solution for the comparison of the effects of different outflow boundary conditions.
The thermoconvective instability of plane poiseuille flow heated from below: A proposed benchmark solution for open boundary flows
Authors: Evans G. , Paolucci S. 
Published: October 2005

AbstractThe transient two‐dimensional Navier‐Stokes and energy equations have been solved numerically for flow in a horizontal channel heated from below in the Boussinesq limit. For the set of dimensionless parameters chosen, the flow consists of periodic transverse travelling waves resulting from a convective instability. The solution is proposed as a benchmark for the application of outflow boundary conditions (OBC) in time‐dependent flows with strong buoyancy effects. Richardson extrapolation in both time and space is used in obtaining the solution. Field plots and profiles of velocity, temperature, vorticity and streamfunction at selected axial positions and times are also presented from the finest grid and smallest time step calculation. The calculations have been made on an extended domain so that the effects of OBC used in the present study would be negligible in the test region.
Computer‐aided spillway design using the boundary element method and non‐linear programming
Authors: Henderson H. C. , Kok M. , De Koning W. L. 
Published: October 2005

AbstractThe general context of this paper is to support the design of spillways by a direct mathematical approach instead of trial‐and‐error methods.First, a two‐dimensional model is formulated to determine the free surface and the discharge for a stationary, incompressible, homogeneous, non‐viscous and irrotational flow over a fixed spillway. The flow satisfies the Laplace equation and the Bernoulli equation (potential flow). An important feature of the model is that it can be extended to design the spillway structure when the spillway is not fixed but the pressure on the spillway is described by a cavitation criterion.Next, the continuous model is discretized by the boundary element method (BEM). We use a non‐linear programming algorithm to calculate the pressures and the shape of the spillway. A computer‐aided design package is developed on a PC using the equations describing the free surface, the BEM and standard optimization techniques. The input and output of the model are realized using graphical routines. Finally, we discuss the convergence and the computation time of the algorithms.
Large‐scale computer simulation of fully developed turbulent channel flow with heat transfer
Authors: Lyons Stephen L. , Hanratty Thomas J. , McLaughlin John B. 
Published: October 2005

AbstractRecently, with the advent of supercomputers, there has been considerable interest in the use of direct numerical simulation to obtain information about turbulent shear flow at low Reynolds number. This paper presents a pseudospectral technique to solve the full three‐dimensional time‐dependent Navier‐Stokes and advection‐diffusion equations without the use of subgrid‐scale modelling. The technique has not been previously used for fully developed turbulent channel flow simulation and is based on methods applied in other contexts. The emphasis of this paper is to provide a reasonably detailed account of how the simulation is done rather than to present new calculations of turbulence. The details of an algorithm for turbulent channel flow simulation and the grid and time step sizes needed to integrate through transient behaviour to steady state turbulence have not been published before and are presented here.Results from a Cray‐2 simulation of fully developed turbulent flow in a channel with heat transfer are presented along with a critical comparison between experiment and computation. The first‐ and second‐order moments agree well with experimental measurements; the agreement is poor for higher‐order moments such as the skewness and flatness near the walls of the channel. Detailed information given about the effects of spatial grid resolution on a computed results is important for estimating the size of the computation required to study various aspects of a turbulent flow.
A finite difference analysis of the extrudate swell problem
Authors: Ahn Young‐Cheol , Ryan Michael E. 
Published: October 2005

AbstractThe extrudate swell phenomenon of a purely viscous fluid is analysed by solving simultaneously the Cauchy momentum equations along with the continuity equation by means of a finite difference method. The circular and planar jet flows of Newtonian and power‐law fluids are simulated using a control volume finite difference method suggested by Patankar called SIMPLER (semi‐implicit method for pressure‐linked equations). This method uses the velocity components and pressure as the primitive variables and employs a staggered grid and control volume for each separate variable. The numerical results show good agreement with the analytical solution of the axisymmetric stick‐slip problem and exhibit a Newtonian swelling ratio of 13.2% or 19.2% for a capillary or slit die respectively in accordance with previously reported experimental and numerical results. Shear thinning results in a decrease in swelling ratio, as does the introduction of gravity and surface tension.
Variational parameter estimation for a two‐dimensional numerical tidal model
Authors: Das S. K. , Lardner R. W. 
Published: October 2005

AbstractIt is shown that the parameters in a two‐dimensional (depth‐averaged) numerical tidal model can be estimated accurately by assimilation of data from tide gauges. The tidal model considered is a semi‐linearized one in which kinematical non‐linearities are neglected but non‐linear bottom friction is included. The parameters to be estimated (bottom friction coefficient and water depth) are assumed to be position‐dependent and are approximated by piecewise linear interpolations between certain nodal values. The numerical scheme consists of a two‐level leapfrog method. The adjoint scheme is constructed on the assumption that a certain norm of the difference between computed and observed elevations at the tide gauges should be minimized. It is shown that a satisfactory numerical minimization can be completed using either the Broyden‐Fletcher‐Goldfarb‐Shanno (BFGS) quasi‐Newton algorithm or Nash's truncated Newton algorithm. On the basis of a number of test problems, it is shown that very effective estimation of the nodal values of the parameters can be achieved provided the number of data stations is sufficiently large in relation to the number of nodes.
A finite difference technique for solving the Newtonian jet swell problem
Authors: Han Chin‐Tsu , Tsai Chin‐Chin , Yu Tsai‐An , Liu Ta‐Jo 
Published: October 2005

AbstractA finite difference technique that incorporates a numerical mapping has been successfully applied to analyse both planar and axisymmetric Newtonian jets. A pressure gradient equation and a free‐surface slope equation have been derived for free‐surface iteration. The computation of pressure inside the jet surface using the pressure gradient equation is stable and accurate at high Reynolds numbers. The free‐surface slope equation is needed for updating the free surface and is applicable for jets with strong surface tension effects. The present development can simulate the Newtonian jets for Reynolds numbers as high as 2000 and capillary number as low as 10−5. Numerical predictions by the present technique are close to the results of previous finite element simulations.
A fully implicit direct Newton's method for the steady‐state Navier–Stokes equations
Authors: Knoll Dana A. , McHugh Paul R. 
Published: October 2005

AbstractNewton's method and banded Gaussian elimination can be a CPU efficient method for steady‐state solutions to two‐dimensional Navier–Stokes equations. In this paper we look at techniques that increase the radius of convergence of Newton's method, reduce the number of times the Jacobian must be factored, and simplify evaluation of the Jacobian. The driven cavity and natural convection problems are used as test problems, and finite volume discretization is employed.
Preconditioned finite element algorithms for 3D Stokes flows
Authors: Zhou Richard Q. N. 
Published: October 2005

AbstractPreconditioned conjugate gradient algorithms for solving 3D Stokes problems by stable piecewise discontinuous pressure finite elements are presented. The emphasis is on the preconditioning schemes and their numerical implementation for use with Hermitian based discontinuous pressure elements. For the piecewise constant discontinuous pressure elements, a variant implementation of the preconditioner proposed by Cahouet and Chabard for the continuous pressure elements is employed. For the piecewise linear discontinuous pressure elements, a new preconditioner is presented. Numerical examples are presented for the cubic lid‐driven cavity problem with two representative elements, i.e. the Q2‐PO and the Q2‐P1 brick elements. Numerical results show that the preconditioning schemes are very effective in reducing the number of pressure iterations at very reasonable costs. It is also shown that they are insensitive to the mesh Reynolds number except for nearly steady flows (Rem → 0) and are almost independent of mesh sizes. It is demonstrated that the schemes perform reasonably well on non‐uniform meshes.
Semi‐implicit Skew Upwind Method for problems in environmental hydraulics
Authors: Zhou Siping , McCorquodale J. A. , Ji Zhong 
Published: October 2005

AbstractA new computational method is presented for reducing numerical diffusion in environmental fluid problems. This method, which is referred to as the Semi‐Implicit Skew Upwind Method (SISUM), is a robust solution procedure for the conditional convergence of the discretized transport equations. The method retains the advantage of the low numerical diffusion of the conventional skew upwind schemes but does not suffer from over‐ or under‐shooting often found in these methods due to the improved interpolation schemes. The effectiveness of SISUM is demonstrated in several examples. The comparison of the results of a hybrid scheme and SISUM with field observations of convection‐dominated pollutant transport in strongly curvilinear river flow shows that SISUM successfully eliminates the high numerical diffusion produced by the hybrid scheme. The robustness of the method was tested by solving the hydrodynamics of a circular clarifier model with a large density gravity source term in the vertical‐momentum equation.
Implementation and performance of the time integration of a 3D numerical transport model
Authors: Sommeijer B. P. , Kok J. 
Published: October 2005

AbstractThe total solution of a three‐dimensional model for computing the transport of salinity, pollutants, suspended material (such as sediment or mud), etc. in shallow seas involves many aspects, each of which has to be treated in an optimal way in order to cope with the tremendous computational task involved. In this paper we focus on one of these aspects, i.e. on the time integration, and discuss two numerical solution methods. The emphasis in this paper is on the performance of the methods when implemented on a vector/parallel, shared memory computer such as a Cray‐type machine. The first method is an explicit time integrator and can straightforwardly be vectorized and parallelized. Although a stabilizing technique has been applied to this method, it still suffers from a severe time step restriction. The second method is partly implicit, resulting in much beter stability characteristics; however, as a consequence of the implicitness, it requires in each step the solution of a large number of tridiagonal systems. When implemented in a standard way, the recursive nature would prevent vectorization, resulting in a very long solution time. Following a suggestion of Golub and Van Loan, this part of the algorithm has been tuned for use on the Cray C98/4256. On the basis of a large‐scale test problem, performance results will be presented for various implementations.
A vector‐parallel scheme for Navier‐Stokes computations at multi‐gigaflop performance rates
Authors: Lorber A. A. , Carey G. F. 
Published: October 2005

AbstractA class of vector‐parallel schemes for solution of steady compressible or incompressible viscous flow is developed and performance studies carried out. The algorithms employ an artificial transient treatment that permits rapid integration to a steady state. In the present work a four‐stage explicit Runge‐Kutta scheme employing variable local step size is utilized for the ODE system integration. The RK‐4 scheme is restructured to allow vectorization and enhance concurrency in the calculation for a streamfunction‐vorticity formulation of the flow problem. The parameters of the resulting RK scheme can be selected to accelerate convergence of the RK recursion. Four main procedures are considered which permit vector‐parallel solution: a Jacobi update, a hybrid of the Jacobi and Gauss‐Seidel method, red‐black ordering and domain decomposition. Numerical performance studies are conducted with a representative viscous incompressible flow calculation. Results indicate that a scheme involving domain decomposition with a Gauss‐Seidel type of update for the RK four‐stage scheme is most effective and provides performance in excess of 8 Gflops on the Cray C‐90.
Simulations of the unsteady separated flow past a normal flat plate
Authors: Najjar Fady M. , Vanka S. P. 
Published: October 2005

AbstractWell‐resolved two‐dimensional numerical simulations of the unsteady separated flow past a normal flat plate at low Reynolds numbers have been performed using a fractional step procedure with high‐order spatial discretization. A fifth‐order upwind‐biased scheme is used for the convective terms and the diffusive terms are represented by a fourth‐order central difference scheme. The pressure Poisson equation is solved using a direct method based on eigenvalue decomposition of the coefficient matrix. A systematic study of the flow has been conducted with high temporal and spatial resolutions for a series of Reynolds numbers. The interactions of the vortices shed form the shear layers in the near‐and far‐wake regions are studied. For Reynolds numbers less than 250 the vortices are observed to convect parallel to the freestream. However, at higher Reynolds numbers (500 and 1000), complex interactions including vortex pairing, tearing and deformations are seen to occur in the far‐wake region. Values of the drag coefficient and the wake closure length are presented and compared with previous experimental and numerical studies.
Microhardness and fracture toughness of dental materials by indentation method
Authors: Şakar‐Deliormanli Aylin , Güden Mustafa 
Published: October 2005

AbstractThe main objective of this study was to measure the fracture toughness of the human teeth enamel using the microindentation technique and to compare the results calculated from the equations developed for Palmqvist and radial‐median cracks. Vickers microhardness measurements of dental ceramic (alumina) and human teeth were performed using indentation fracture method. The fracture toughness of enamel was calculated using different equations reported in the literature. Vickers microhardness of the sintered alumina specimen (98.8% theoretical density) was measured to be 14.92 GPa under 9.8N indentation load. Three equations based on the radial‐median cracks were found to be applicable for the fracture toughness determination of the enamel. Results show that indentation fracture method is adequate to measure microhardness and fracture toughness of dental materials. However the calculation of fracture toughness depended on the nature of the cracks and also on the location of the indentation. Therefore, it is necessary to identify the crack profile and to select the appropriate equation for accurate fracture toughness values. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Structural analysis of dextran‐based hydrogels obtained chemoenzymatically
Authors: Ferreira L. , Figueiredo M. M. , Gil M. H. , Ramos M. A. 
Published: October 2005

AbstractThis work reports the results of structural analysis in novel dextran–acrylate (dexT70‐VA) hydrogels generated chemoenzymatically. Porous structure as well as hydrogel surface and interior morphologies were evaluated by mercury intrusion porosimetry (MIP), nitrogen adsorption (NA), and scanning electron microscopy (SEM) analyses, as a function of the degree of substitution (DS), and initial water content used in the preparation of the hydrogel. MIP analysis showed that the overall networks were clearly macroporous with pore sizes ranging from 0.065 to 10 μm. As expected, the average pore size decreased as DS increased and as initial water content decreased. Moreover, the porosity values ranged from 75 up 90%, which shows that these hydrogels present an interconnected pore structure. Nitrogen adsorption analyses showed that the specific surface area of dexT70‐VA hydrogels increased either by increasing the DS or by decreasing the initial water content of the hydrogel. SEM results revealed that the surface of hydrogels with lower DS presented either a porous structure or a polymeric “skin” covering the pores, whereas hydrogels with higher DS were totally porous. Furthermore, the interior morphology varied according to the DS and the initial water content of the hydrogels. Finally, the average pore size was also determined from the swelling of hydrogel using a theoretical model developed by Flory‐Rehner. The comparison of the SEM and MIP results with the ones obtained by the equilibrium swelling theory of Flory‐Rehner shows that this approach highly underestimates the average pore size. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Frequency effect in fretting wear of Co‐28Cr‐6Mo versus Ti‐6Al‐4V implant alloys
Authors: Schaaff Petra , Dalmiglio Matteo , Holzwarth Uwe 
Published: October 2005

AbstractA piezo‐electrically driven fretting testing device has been constructed and fretting release and release rates have been determined with highest accuracy, using a radiotracer technique. First results on the fretting release and release rate of titanium alloy fretting pads against cobalt‐chrome alloy fatigue specimens are reported. The frequency dependency of fretting release has been determined between 1 and 8 Hz and shows higher release rates for low frequencies, thus indicating that accelerated testing of materials and components of artificial joints must be analyzed extremely carefully. The present experiments under simple conditions present a base‐line study for step‐wise applying more complex and realistic testing conditions and for using radiotracer methods to quantify fretting release in simulated testing of artificial hip‐ and knee‐prostheses. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006
Integrated Modeling Program, Applied Chemical Theory (IMPACT)
Authors: Banks Jay L. , Beard Hege S. , Cao Yixiang , Cho Art E. , Damm Wolfgang , Farid Ramy , Felts Anthony K. , Halgren Thomas A. , Mainz Daniel T. , Maple Jon R. , Murphy Robert , Philipp Dean M. , Repasky Matthew P. , Zhang Linda Y. , Berne Bruce J. , Friesner Richard A. , Gallicchio Emilio , Levy Ronald M. 
Published: October 2005

AbstractWe provide an overview of the IMPACT molecular mechanics program with an emphasis on recent developments and a description of its current functionality. With respect to core molecular mechanics technologies we include a status report for the fixed charge and polarizable force fields that can be used with the program and illustrate how the force fields, when used together with new atom typing and parameter assignment modules, have greatly expanded the coverage of organic compounds and medicinally relevant ligands. As we discuss in this review, explicit solvent simulations have been used to guide our design of implicit solvent models based on the generalized Born framework and a novel nonpolar estimator that have recently been incorporated into the program. With IMPACT it is possible to use several different advanced conformational sampling algorithms based on combining features of molecular dynamics and Monte Carlo simulations. The program includes two specialized molecular mechanics modules: Glide, a high‐throughput docking program, and QSite, a mixed quantum mechanics/molecular mechanics module. These modules employ the IMPACT infrastructure as a starting point for the construction of the protein model and assignment of molecular mechanics parameters, but have then been developed to meet specialized objectives with respect to sampling and the energy function. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1752–1780, 2005
Preparation and Characterisation of Thermoresponsive Poly[(N‐isopropylacrylamide‐co‐acrylamide‐co‐(hydroxyethyl acrylate)] Microspheres as a Matrix for the Pulsed Release of Drugs
Authors: Fundueanu Gheorghe , Constantin Marieta , Bortolotti Fabrizio , Ascenzi Paolo , Cortesi Rita , Menegatti Enea 
Published: October 2005

AbstractSummary: Despite the large number of publications and patents concerning pH/thermoresponsive polymers, few data are available concerning the preparation of thermoresponsive cross‐linked microspheres from preformed polymers. Therefore, N‐isopropylacrylamide‐co‐acrylamide‐co‐(2‐hydroxyethyl acrylate) copolymers were obtained as a new thermoresponsive material with a lower critical solution temperature (LCST) around 36 °C, in phosphate buffer at pH 7.4, and with a cross‐linkable OH group in their structure. The LCST value was determined both by UV spectroscopy and microcalorimetric analysis. These copolymers were solubilised in acidified aqueous solution below their LCST, dispersed in mineral oil, and transformed into stable microspheres by cross‐linking with glutaraldehyde. The thermoresponsive microspheres were characterised by optical and scanning electron microscopy, degree of swelling, and water retention. The pore dimensions of the microspheres and the retention volumes of some drugs and typical compounds were evaluated at different temperatures by liquid chromatography. Indomethacin, as a model drug, was included in the microspheres by the solvent evaporation method. Finally, the influence of temperature and of temperature cycling on drug release was investigated.Effect of temperature and temperature cycling on indomethacin release from poly(NIPAAm‐co‐AAm‐co‐HEA) microspheres.magnified imageEffect of temperature and temperature cycling on indomethacin release from poly(NIPAAm‐co‐AAm‐co‐HEA) microspheres.