bluuebunny/crossref_metadata_2025_split huggingface dataset:
Controlling factors of gullying in the Maracujá Catchment, southeastern Brazil
Authors: de A. P. Bacellar L. , Netto A. L. Coelho , Lacerda W. A. 
Published: October 2005

AbstractHundreds of gullies (‘voçorocas’) of huge dimensions (up to 400–500 m long, 150 m wide and 50 m deep) are very common in the small Maracujá Catchment in southeastern Brazil. These erosional features, which occur with an uneven intensity throughout the area, started due to bad soil management practices at the beginning of European settlement, at the end of the 17th century, and nowadays are still evolving, but at a slower rate. As surface soils are usually very resistant to erosion, the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning. An analysis of well known erosion controlling factors was performed, aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution. Data shows that geology and, mainly, geomorphology are the main controlling factors, since gullies tend to be concentrated in basement rock areas with lower relief (domain 2) of Maracujá Catchment, mainly at the fringes of broad and flat interfluves. At the detailed scale (1:10 000), gullies are more common in amphitheatre‐like headwater hollows that frequently represent upper Quaternary gullies (paleogullies), which demonstrate the recurrence of channel erosion. So, gullies occur in areas of thicker saprolites (domain 2), in places with a natural concentration of surface and underground water (hollows). Saprolites of the preserved, non‐eroded hollows are usually pressurized (confined aquifer) due to a thick seal of Quaternary clay layer, in a similar configuration to the ones found in hollows of mass movement (mudflow) sites in southeastern Brazil. Therefore, the erosion of the resistant soils by human activities, such as road cuts and trenches (‘valos’), or their mobilization by mudflow movements, seem to be likely mechanisms of gullying initiation. Afterwards, gullies evolve by a combination of surface and underground processes, such as wash and tunnel erosion and falls and slumps of gully walls. Copyright © 2005 John Wiley & Sons, Ltd.
The effect of bed mobility on resistance to overland flow
Authors: Hu Shixiong , Abrahams Athol D. 
Published: October 2005

AbstractWhen sediment grains are transported as bed load in overland flow, there is a net transfer of momentum from the flow to the grains. When these grains collide with other grains, whether on the bed or in the flow, streamwise flow velocity decreases and resistance to flow increases. Resistance to flow generated in this manner is termed bed‐load transport resistance. Resistance to flow f over a plane bed may be partitioned into grain resistance fg and bed‐load transport resistance fbt. We use the symbols fbtf and fbtm to denote fbt for flows over fixed beds and over mobile beds, respectively, and we compute the effect of bed mobility on flow resistance fmob by subtracting fbtf from fbtm.The data for this study come from 54 flume experiments with fixed beds and 38 with mobile beds. On average fmob is approximately equal to half of fbtm, which is about one‐quarter of f. Hence, fmob is about one‐tenth of f. Predictive equations are developed for fbtf, fbtm and fmob using dimensional analysis to identify the relevant independent variables and regression analysis to evaluate the coefficients associated with these variables. Values of fmob are always positive which implies that mobile beds offer greater resistance to flow than do fixed beds. Evidently bed‐load grains colliding with mobile beds lose more momentum to the bed than do grains colliding with fixed beds. In other words, grain collisions with mobile beds are less elastic than those with fixed beds. Copyright © 2005 John Wiley & Sons, Ltd.
Symbolic computation of flow in a rotating pipe
Authors: Raszillier H. , Guiasu I. , Durst F. 
Published: October 2005

AbstractA perturbation solution of the fully developed flow through a pipe of circular cross‐section, which rotates uniformly around an axis oriented perpendicularly to its own, is considered. The perturbation parameter is given by R = 2Ωa2/ν in terms of the angular velocity Ω, the pipe radius a and the kinematic viscosity ν of the fluid. The two coupled non‐linear equations for the axial velocity ω and the streamfunction ϕ of the transverse (secondary) flow lead to an infinite system of linear equations. This system allows first the computation of a given order ϕn, n ϕ 1, of the perturbation expansion ϕ = ∑ Rnϕn in terms of ωn‐1, the (n‐1)‐th order of the expansion ω = ∑ Rnωn, and of the lower orders ϕ1,…,ϕn − 1. Then it permits the computation of ωn from ω0,…,ωn − 1 and ϕ1,…,ϕ;n. The computation starts from the Hagen–Poiseuille flow ω0, i.e. the perturbation is around this flow.The computations are performed analytically by computer, with the REDUCE and MAPLE systems. The essential elements for this are the appropriate co‐ordinates: in the complex co‐ordinates chosen the two‐dimensional harmonic (Laplace, Δ) and biharmonic (Δ2) operators are ideally suited for (symbolic) quadratures. Symmetry considerations as well as analysis of the equations for ωn, ϕn and of the boundary conditions lead to general (polynomial) formulae for these functions, with coeffcients to be determined. Their determination, order by order, implies, in complex co‐ordinates, only (symbolic) differentiation and quadratures. The coefficients themselves are polynomials in the Reynolds number c of the (unperturbed) Hagen–Poiseuille flow. They are tabulated in the paper for the orders n ⩽ 6 of the perturbation expansion.
Equilibrium and stability of tokamaks
Authors: Kerner Wolfgang 
Published: October 2005

AbstractAxisymmetric, ideal MHD configurations with steady flow are computed by the finite‐element method. Rectangular elements with four to nine nodes are used. The equilibria are obtained in flux co‐ordinates by mesh rearrangement. The properties of the linearized motions around an equilibrium state are studied by a normal‐mode analysis. Dissipation is taken into account. Applying the Galerkin method leads to a large‐scale complex eigenvalue problem 𝒜x = λ ℬ︁x, which is solved by inverse iteration and by the Lanczos algorithm.
Global convergence of inexact Newton methods for transonic flow
Authors: Young David P. , Melvin Robin G. , Bieterman Michael B. , Johnson Forrester T. , Samant Satish S. 
Published: October 2005

AbstractIn computational fluid dynamics, non‐linear differential equations are essential to represent important effects such as shock waves in transonic flow. Discretized versions of these non‐linear equations are solved using iterative methods. In this paper an inexact Newton method using the GMRES algorithm of Saad and Schultz is examined in the context of the full potential equation of aerodynamics. In this setting, reliable and efficient convergence of Newton methods is difficult to achieve. A poor initial solution guess often leads to divergence or very slow convergence. This paper examines several possible solutions to these problems, including a standard local damping strategy for Newton's method and two continuation methods, one of which utilizes interpolation from a coarse grid solution to obtain the initial guess on a finer grid. It is shown that the continuation methods can be used to augment the local damping strategy to achieve convergence for difficult transonic flow problems. These include simple wings with shock waves as well as problems involving engine power effects. These latter cases are modelled using the assumption that each exhaust plume is isentropic but has a different total pressure and/or temperature than the freestream.
Data assimilation for non‐linear tidal models
Authors: Heemink A. W. , Kloosterhuis H. 
Published: October 2005

AbstractA data assimilation procedure to incorporate measurements into a non‐linear tidal model by using Kalman‐filtering techniques is developed. The Kalman filter is based on the two‐dimensional shallow water equations. To account for the inaccuracies, these equations are embedded into a stochastic environment by introducing a coloured system noise process into the momentum equations. The continuity equation is assumed to be perfect. The deterministic part of the equations is discretized using an ADI method, the stochastic part using the Euler scheme. Assuming that the system noise is less spatially variable than the underlying water wave process, this stochastic part can be approximated on a coarser grid than the grid used to approximate the deterministic part. A Chandrasekhar‐type filter algorithm is employed to obtain the constant‐gain extended Kalman filter for weakly non‐linear systems. The capabilities of the filter are illustrated by applying it to the assimilation of water level measurements into a tidal model of the North Sea.
Modelling the initial motion of large cylindrical and spherical bubbles
Authors: Bugg J. D. , Rowe R. D. 
Published: October 2005

AbstractA two‐dimensional, transient, finite difference technique based on a volume fraction specification of the free surface position and accounting for the effects of surface tension is shown to accurately predict the initial motion of large cylindrical and spherical bubbles. The predictions compare very favourably with the experimental data of Walters and Davidson. The initial acceleration of cylindrical and spherical bubbles is properly predicted as g and 2g respectively. The penetration of a tongue of liquid from below is the dominant process by which large deformations from the original shape take place and is well predicted by the model in both cases. For the spherical case the eventual transition into a toroidal bubble is demonstrated and the circulation associated with a rising toroidal bubble as a function of its volume upon release is shown to agree very well with experiments. Iterative linear equation‐solving techniques applicable to the special nature of the linear system resulting from such a free surface specification are surveyed and a simple Jacobi iteration based on red‐black ordering is found to perform well. The impact of the free surface on the relaxation of the linear system and the convergence criteria is also explored.
A coupled multigrid‐domain‐splitting technique for simulating incompressible flows in geometrically complex domains
Authors: Perng C. Y. , Street R. L. 
Published: October 2005

AbstractThis paper describes a domain decomposition numerical procedure for solving the Navier‐Stokes equations in regions with complex geometries. The numerical method includes a modified version of QUICK (quadratic upstream interpolation convective kinematics) for the formulation of convective terms and a central difference scheme for the diffusion terms. A second‐order‐accurate predictor‐corrector scheme is employed for the explicit time stepping. Although the momentum equations are solved independently on each subdomain, the pressure field is computed simultaneously on the entire flow field. A multigrid technique coupled with a Schwarz‐like iteration method is devised to solve the pressure equation over the composite domains. The success of this strategy depends crucially on appropriate methods for specifying intergrid pressure boundary conditions on subdomains. A proper method for exchanging information among subdomains during the Schwarz sweep is equally important to the success of the multigrid solution for the overall pressure field. These methods are described and subsequently applied to two forced convection flow problems involving complex geometries to demonstrate the power and versatility of the technique. The resulting pressure and velocity fields exhibit excellent global consistency. The ability to simulate complex flow fields with this method provides a powerful tool for analysis and prediction of mixing and transport phenomenon.
Investigation of use of reach‐back characteristics method for 2D dispersion equation
Authors: Yang Jinn‐Chuang , Chen Kun‐Nan , Lee Hong‐Yuan 
Published: October 2005

AbstractThe use of the Holly‐Preissmann two‐point scheme has been very popular for the calculation of the dispersion equation. The key to this scheme is to use the characteristics method incorporating the Hermite cubic interpolation technique to approximate the trajectory foot of the characteristics. This method can avoid the excessive numerical damping and oscillation associated with most finite difference schemes for advection computation. On the basis of the fundamental idea of the Holly‐Preissmann two‐point scheme, a new technique is introduced herein for the computation of the two‐dimensional dispersion equation. This new scheme allows the characteristics projecting back several time steps to fall on the spatial or temporal axis, while the characteristics foot is still solved by the Holly‐Preissmann two‐point method. The diffusion portion of the dispersion equation is solved by the commonly used Crank‐Nicholson method. The calculation for these two processes consisting of advection and diffusion is carried out separately but consecutively in one time step, a method known as the split operator algorithm. A hypothetical model was constructed to demonstrate the applicability of this new technique for the calculation of the pure advection and dispersion equation in two dimensions.
The two‐dimensional transmission and reflection of a solitary wave
Authors: Lu Q. Q. 
Published: October 2005

AbstractIn the present paper, limited to the discussion of weak non‐linear shallow water waves, the transmission and reflection of a planar soliton on a two‐dimensional structure are considered. The whole flow field is divided mainly into two subfields. One is in the vicinity of the structure, called the inner field; the other is far from the structure, called the outer field. In the outer field, according to its definition, the influence of the structure on the flow is negligible; to the order O(α, β) the governing equation for the flow is replaced by the Boussinesq equation. In the inner field the effect of the structure on the flow is significant, so the full Laplace equation is adopted as the governing equation for the flow field. Then the matched asymptotic expansion method is employed to connect smoothly the inner and outer solutions. Owing to the irregularity of the bottom of the structure, the boundary element method is incorporated. As an example, the case in which the incoming wave is a solitary wave is calculated and the time histories of transmitted and reflected waves are plotted.
Implementation of the Lagrange‐Galerkin method for the incompressible Navier‐Stokes equations
Authors: Buscaglia Gustavo C. , Dari Enzo A. 
Published: October 2005

AbstractThis paper is concerned with the implementation of Lagrange‐Galerkin finite element methods for the Navier‐Stokes equations. A scheme is developed to efficiently handle unstructed meshes with local refinement, using a quad‐tree‐based algorithm for the geometric search. Several difficulties that arise in the construction of the right‐hand side are discussed in detail and some useful tricks are proposed.The resulting method is tested on the lid‐driven square cavity and the vortex shedding behind a rectangular cylinder and is found to give satisfactory agreement with previous works. A detailed analysis of the effect of time discretization is included.
Non‐Newtonian flow over a wedge with suction
Authors: Garg Vijay K. 
Published: October 2005

AbstractA pseudo‐similarity solution is obtained for the flow of an incompressible fluid of second grade past a wedge with suction at the surface. The non‐linear differential equation is solved using quasi‐linearization and orthonormalization. The numerical method developed for this purpose enables computation of the flow characteristics for any values of the parameters K, a and b, where K is the dimensionless normal stress modulus of the fluid, a is related to the wedge angle and b is the suction parameter. A significant effect of suction on the wall shear stress is observed. The present results match exactly those from an earlier perturbation analysis for Kx2a ⩽ 0·01 but differ significantly as Kx2a increases.
An efficient pressure‐velocity procedure for gas‐droplet two‐phase flow calculations
Authors: Chen C. P. , Shang H. M. , Jiang Y. 
Published: October 2005

AbstractThis paper presents a non‐iterative numerical technique for computing time‐dependent gas‐droplet flows. The method is a fully interacting combination of Eulerian fluid and Lagrangian particle calculations. The interaction calculations between the two phases are formulated on a pressure‐velocity‐coupling procedure based on the operator‐splitting technique. This procedure eliminates the global iterations required in the conventional particle‐source‐in‐cell (PSIC) procedure. Turbulent dispersion calculations are treated by a stochastic procedure. Numerical calculations and comparisons with available experimental data as well as efficiency assessments are given for some sprays typical of spray combustion applications.
An ILU preconditioner with coupled node fill‐in for iterative solution of the mixed finite element formulation of the 2D and 3D Navier‐Stokes equations
Authors: Dahl O. , Wille S. Ø 
Published: October 2005

AbstractIn the present paper, preconditioning of iterative equation solvers for the Navier‐Stokes equations is investigated. The Navier‐Stokes equations are solved for the mixed finite element formulation. The linear equation solvers used are the orthomin and the Bi‐CGSTAB algorithms. The storage structure of the equation matrix is given special attention in order to avoid swapping and thereby increase the speed of the preconditioner. The preconditioners considered are Jacobian, SSOR and incomplete LU preconditioning of the matrix associated with the velocities. A new incomplete LU preconditioning with fill‐in for the pressure matrix at locations in the matrix where the corner nodes are coupled is designed. For all preconditioners, inner iterations are investigated for possible improvement of the preconditioning. Numerical experiments are executed both in two and three dimensions.
Drift forces on a pair of vertical cylinders
Authors: Rahman M. , Satish M. G. , Perrie W. , Zhu J. 
Published: October 2005

AbstractAn approximate method is presented here for estimating the hydrodynamic second‐order drift forces on a pair of bottom‐mounted, surface‐piercing circular cylinders in water of arbitrary uniform depth. The theoretical results are based upon the large‐spacing approximation. Results are presented to illustrate the influence of the various wave and structural parameters on the hydrodynamic forces on each of the cylinders.
Applications of boundary integral equation methods for two‐dimensional non‐linear water wave problems
Authors: Liu Philip L.‐F. , Hsu H.‐W. , Lean Meng H. 
Published: October 2005

AbstractOn the basis of the integral equation approach, numerical algorithms for solving non‐linear water wave problem are presented. The free surface flow is assumed to be irrotational. Two different Green functions are used in the integral equations. The non‐linear free‐surface boundary conditions are treated by a time‐stepping Lagrangian technique. Several numerical examples are given, including permanent periodic waves, overturning progressive waves, breaking standing waves and sloshing problems.
An improved approximation technique to obtain numerical solution of a class of two‐point boundary value similarity problems in fluid mechanics
Authors: Kafoussias N. G. , Williams E. W. 
Published: October 2005

AbstractA simple and efficient approximate numerical technique is presented to obtain solutions to a wide class of two‐point boundary value similarity problems in fluid mechanics. This technique is based on the common finite difference method with central differencing, a tridiagonal matrix manipulation and an iterative procedure. The technique described in this paper has been successfully applied to three different representative similarity problems of fluid mechanics. Each one of these problems is described by a coupled, non‐linear system of three ordinary differential equations and has already been solved elsewhere using a different numerical method. So, the obtained numerical results, by our efficient numerical technique, permit a comparative study and show the accuracy and the effectiveness of this technique.
A frontal approach for internal node generation in Delaunay triangulations
Authors: Müller J.‐D. , Roe P. L. , Deconinck H. 
Published: October 2005

AbstractThe past decade has known an increasing interest in the solution of the Euler equations on unstructured grids due to the simplicity with which an unstructured grid can be tailored around very complex geometries and be adapted to the solution. It is desirable that the mesh can be generated with minimum input from the user, ideally, just specifying the boundary geometry and, perhaps, a function to prescribe some desired mesh size. The internal nodes should then be found automatically by the grid generation code. The approach we propose here combines the Delaunay triangulation with ideas from the advancing front method of Peraire et al. and Löhner et al. Both methods are briefly reviewed in Section 1. Our method uses a background grid to interpolate local mesh size parameters that is taken from the triangulation of the given boundary nodes. Geometric criteria are used to find a set of nodes in a frontal manner. This set is subsequently introduced into the existing mesh, thus providing an update Delaunay triangulation. The procedure is repeated until no more improvement of the grid can be achieved by inserting new nodes.
A least‐squares finite element method for time‐dependent incompressible flows with thermal convection
Authors: Tang Li Q. , Tsang Tate T. H. 
Published: October 2005

AbstractThe time‐dependent Navier–Stokes equations and the energy balance equation for an incompressible, constant property fluid in the Boussinesq approximation are solved by a least‐squares finite element method based on a velocity–pressure–vorticity–temperature–heat‐flux (u–P–ω–T–q) formulation discretized by backward finite differencing in time. The discretization scheme leads to the minimization of the residual in the l2‐norm for each time step. Isoparametric bilinear quadrilateral elements and reduced integration are employed. Three examples, thermally driven cavity flow at Rayleigh numbers up to 106, lid‐driven cavity flow at Reynolds numbers up to 104 and flow over a square obstacle at Reynolds number 200, are presented to validate the method.
A height–flux method for simulating free surface flows and interfaces
Authors: Mashayek F. , Ashgriz N. 
Published: October 2005

AbstractA new technique for the numerical simulation of the free surface flows is developed. This technique is based on the finite element method with penalty formulation, and a flux method for surface advection. The advection part which is completely independent of the momentum solver is based on subdividing the fluid domain into small subvolumes along one of the co‐ordinate axis. The subvolumes are then used to find the height function which will later describe the free surface. The free surface of the fluid in each subvolume is approximated by a line segment and its slope is calculated using the volume of the fluid in the two neighbouring subvolumes. Later, the unidirectional volume flux from one subvolume to its neighbouring one is calculated using the conservation laws, and the new surface line segments are reconstructed. This technique, referred to as the Height–Flux Method (HFM) is implemented to simulate the temporal instability of a capillary jet. The results of the numerical simulation well predict the experimental data. It is also shown that the HFM is computationally more efficient than the techniques which use a kinematic boundary condition for the surface advection.