bluuebunny/crossref_metadata_2025_split huggingface dataset:
Controls on englacial sediment deposition during the November 1996 jökulhlaup, Skeiđarárjökull, Iceland
Authors: Roberts Matthew J. , Russell Andrew J. , Tweed Fiona S. , Knudsen Óskar 
Published: January 2005

AbstractThis paper presents sedimentary evidence for rapid englacial debris entrainment during jökulhlaups. Previous studies of jökulhlaup sedimentology have focused predominantly on proglacial impact, rather than depositional processes within glaciers. However, observations of supraglacial floodwater outbursts suggest that englacial sediment emplacement is possible during jökulhlaups. The November 1996 jökulhlaup from Skeiđarárjökull, Iceland presented one of the first opportunities to examine englacial flood deposits in relation to former supraglacial outlets. Using observations from Skeiđarárjökull, this paper identifies and explains controls on the deposition of englacial flood sediments and presents a qualitative model for englacial jökulhlaup deposition. Englacial jökulhlaup deposits were contained within complex networks of upglacier‐dipping fractures. Simultaneous englacial deposition of fines and boulder‐sized sediment demonstrates that englacial fracture discharge had a high transport capacity. Fracture geometry was an important control on the architecture of englacial jökulhlaup deposits. The occurrence of pervasively frozen flood deposits within Skeiđarárjökull is attributed to freeze‐on by glaciohydraulic supercooling. Floodwater, flowing subglacially or through upglacier‐dipping fractures, would have supercooled as it was raised to the surface faster than its pressure‐melting point could increase as glaciostatic pressure decreased. Evidence for floodwater contact with the glacier bed is supported by the ubiquitous occurrence of sheared diamict rip‐ups and intra‐clasts of basal ice within jökulhlaup fractures, deposited englacially some 200–350 m above the bed of Skeiđarárjökull. Evidence for fluidal supercooled sediment accretion is apparent within stratified sands, deposited englacially at exceptionally high angles of rest in the absence of post‐depositional disturbance. Such primary sediment structures cannot be explained unless sediment is progressively accreted to opposing fracture walls. Ice retreat from areas of former supraglacial outbursts revealed distinct ridges characterized by localized upwellings of sediment‐rich floodwater. These deposits are an important addition to current models of englacial sedimentation and demonstrate the potential for post‐jökulhlaup landform development. Copyright © 2001 John Wiley & Sons, Ltd.
Chalk micropalaeontology and the provenancing of middle pleistocene lowestoft formation till in eastern England
Authors: Fish P. R. , Whiteman C. A. 
Published: January 2005

AbstractThe distribution and deposits of British and Scandinavian Middle Pleistocene ice sheets in eastern England remain problematic. A new till provenancing technique based on Chalk micropalaeontology is described, with the object of refining understanding of the ice sheet which deposited the Lowestoft Formation till (Anglian/Elsterian) and its relationship to Scandinavian ice sheets. The technique involves extracting foraminifera from Chalk erratics and till matrix obtained from stratigraphically controlled till sections and comparing their micropalaeontology with that of Upper Cretaceous Chalk bedrock. Application to the Lowestoft Formation till of eastern England suggests that current models of ice‐flow in this region require revision involving reinstatement of some earlier ideas. Chalk provenance data indicate an initial phase of glaciation, with ice streaming southwards across eastern England before fanning across East Anglia from the position of the Fen basin. This was followed by a later phase in which the main southward trajectory of ice‐flow was located further east in the North Sea Basin, but again with ice fanning out across East Anglia. These ice‐flow trajectories imply constraint of the British ice sheet by Scandinavian ice. Copyright © 2001 John Wiley & Sons, Ltd.
Runoff and interrill erosion on sandy soils under cultivation in the western Paris basin: mechanisms and an attempt at measurement
Authors: Larue Jean Pierre 
Published: January 2005

AbstractMeasurements made on different scales, such as rainfall simulations on 1 m2 and 20 m2 experimental plots and water sampling at the outlet of a watershed, enable the analysis of the mechanisms of pluvial erosion and therefore the importance of runoffs and soil losses in the hilly and sandy parts of the western Paris basin. Interrill erosion accounts for slow transfer of materials towards the lower part of plots and slopes. The overland flow caused by restructuring of the surface Tertiary and Cenomanian soils erodes some 150 to 200 kg ha−1 during the month following sowing. Only a part of these deposits reach the river, which carries away less than 50 kg ha−1 each month. Interrill erosion makes slopes still more uneven, fills in valley bottoms, and so paves the way to catastrophic erosion, which scoops out rises in the ground and colluvial deposits in the lower part of slopes and valley bottoms. Copyright © 2001 John Wiley & Sons, Ltd.
Geomorphological conservation and public policy in England: a geomorphological critique of English Nature's ‘Natural Areas’ approach
Authors: Gray J. Murray 
Published: January 2005

AbstractThe traditional top‐down, site‐based approach to nature conservation has been extended in recent years to include the conservation interests of ‘the wider countryside’. English Nature's response to this movement has been to divide the country into Natural Areas which have coherence in terms of geology, landform, soils, plants and wildlife. These represent more meaningful units for setting nature conservation objectives than do administrative boundaries. They are also intended to allow easier integration of Earth science and wildlife conservation objectives and to provide a meaningful framework into which the interests of individual sites can be set, thus leading to a less fragmented approach to nature conservation. This paper reviews the geomorphological content of the 120 Natural Area Profiles, eight regional summaries and the relevant pages of the English Nature web site. It concludes that wildlife conservation, which dominates the profiles, has fully grasped the principles of conservation in the wider countryside, but geomorphological conservation has largely missed the opportunities provided. The site‐based approach still dominates, there is an inconsistency in approach and the few encouraging geomorphological descriptions or objectives that do occur are never fashioned into sustained geomorphological strategies for the wider countryside. What is needed is a strengthening of geomorphological/Quaternary conservation within English Nature and its Local Area Teams, a more detailed approach to geomorphological description of the Natural Areas which recognizes landform evolution, landform character and sensitivity to change, and improved links between geomorphology and the land‐use planning system. Copyright © 2001 John Wiley & Sons, Ltd.
Empirical predictors of annual bed load travel distance, and implications for salmonid habitat restoration and protection
Authors: Beechie Timothy J. 
Published: January 2005

AbstractMeasurements of annual travel distance (Lb) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r2 = 0·86, p < 0·001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce Lb. Longer cumulative duration of bed load transporting flows in a year appears to increase Lb. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with Lb (r2 ranging from 0·27 to 0·51). Stream power per unit bed area, basal shear stress and slope were not significantly related to Lb (r2 < 0·05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short‐term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.
An adaptive Lagrangian boundary element approach for three‐dimensional transient free‐surface Stokes flow as applied to extrusion, thermoforming, and rheometry
Authors: Khayat Roger E. , Genouvrier Delphine 
Published: January 2005

AbstractAn adaptive (Lagrangian) boundary element approach is proposed for the general three‐dimensional simulation of confined free‐surface Stokes flow. The method is stable as it includes remeshing capabilities of the deforming free surface and thus can handle large deformations. A simple algorithm is developed for mesh refinement of the deforming free‐surface mesh. Smooth transition between large and small elements is achieved without significant degradation of the aspect ratio of the elements in the mesh. Several flow problems are presented to illustrate the utility of the approach, particularly as encountered in polymer processing and rheology. These problems illustrate the transient nature of the flow during the processes of extrusion and thermoforming, the elongation of a fluid sample in an extensional rheometer, and the coating of a sphere. Surface tension effects are also explored. Copyright © 2001 John Wiley & Sons, Ltd.
Lung effect on the hemodynamics in pulmonary artery
Authors: Tsai S. F. , Sheu Tony W. H. , Chang T. M. 
Published: January 2005

AbstractThe present study investigates blood flow in a pulmonary artery. The aim is to gain a better understanding of offset value in vascular circulation through a two‐dimensional analysis of the Navier–Stokes equations. In this study, the hemodynamics in a blood vessel with truncated outlets at which constant pressure is specified is examined. To simplify the analysis, the vessel walls are regarded as being rigid. In quadratic elements, the streamline upwind Petrov–Galerkin finite element model is employed to simulate the incompressible Newtonian blood flow. The adopted finite element model introduces artificial damping terms solely in the streamline direction. With these terms added to the formulation, the discrete system is enhanced while solution accuracy is maintained without deterioration due to numerical diffusion errors. Copyright © 2001 John Wiley & Sons, Ltd.
Finite element simulation of fully non‐linear interaction between vertical cylinders and steep waves. Part 1: methodology and numerical procedure
Authors: Ma Q. W. , Wu G. X. , Eatock Taylor R. 
Published: January 2005

AbstractA methodology for computing three‐dimensional interaction between waves and fixed bodies is developed based on a fully non‐linear potential flow theory. The associated boundary value problem is solved using a finite element method (FEM). A recovery technique has been implemented to improve the FEM solution. The velocity is calculated by a numerical differentiation technique. The corresponding algebraic equations are solved by the conjugate gradient method with a symmetric successive overrelaxation (SSOR) preconditioner. The radiation condition at a truncated boundary is imposed based on the combination of a damping zone and the Sommerfeld condition. This paper (Part 1) focuses on the technical procedure, while Part 2 [Finite element simulation of fully non‐linear interaction between vertical cylinders and steep waves. Part 2. Numerical results and validation. International Journal for Numerical Methods in Fluids 2001] gives detailed numerical results, including validation, for the cases of steep waves interacting with one or two vertical cylinders. Copyright © 2001 John Wiley & Sons, Ltd.
Large‐scale eigenvalue calculations for stability analysis of steady flows on massively parallel computers
Authors: Lehoucq Richard B. , Salinger Andrew G. 
Published: January 2005

AbstractThis paper presents an approach for determining the linear stability of steady states of partial differential equations (PDEs) on massively parallel computers. Linearizing the transient behavior around a steady state solution leads to an eigenvalue problem. The eigenvalues with the largest real part are calculated using Arnoldi's iteration driven by a novel implementation of the Cayley transformation. The Cayley transformation requires the solution of a linear system at each Arnoldi iteration. This is done iteratively so that the algorithm scales with problem size. A representative model problem of three‐dimensional incompressible flow and heat transfer in a rotating disk reactor is used to analyze the effect of algorithmic parameters on the performance of the eigenvalue algorithm. Successful calculations of leading eigenvalues for matrix systems of order up to 4 million were performed, identifying the critical Grashof number for a Hopf bifurcation. Copyright © 2001 John Wiley & Sons, Ltd.
Advection upwinding splitting method to solve a compressible two‐fluid model
Authors: Niu Yang‐Yao 
Published: January 2005

AbstractIn this study, the advection upwinding splitting method (AUSM) is modified for the resolution of two‐phase mixtures with interfaces. The compressible two‐fluid model proposed by Saurel and Abgrall is chosen as the model equations. Dense and dilute phases are described in terms of the volume fraction and equations of state to represent multi‐phase mixtures. Test cases involving an air–water shock tube, water faucet, and dilute particulate turbulent flows through a 90° bend are used to verify the current work. It is shown that the AUSM based on flux differences (AUSMD) contains the mechanism to correctly capture the contact discontinuity and interfaces between phases. In addition, a successful application to dilute particulate turbulence flows by the AUSMD is demonstrated. Copyright © 2001 John Wiley & Sons, Ltd.
Viscoelastic simulations of stick‐slip and die‐swell flows
Authors: Ngamaramvaranggul V. , Webster M. F. 
Published: January 2005

AbstractNumerical solutions of viscoelastic flows are demonstrated for a time marching, semi‐implicit Taylor–Galerkin/pressure‐correction algorithm. Steady solutions are sought for free boundary problems involving combinations of die‐swell and stick‐slip conditions. Flows with and without drag flow are investigated comparatively, so that the influence of the additional component of the drag flow may be analysed effectively. The influence of die‐swell is considered that has application to various industrial processes, such as wire coating. Solutions for two‐dimensional axisymmetric flows with an Oldroyd‐B model are presented that compare favourably with the literature. The study advances our prior fixed domain formulation with this algorithm, into the realm of free‐surface viscoelastic flows. The work involves streamline‐upwind/Petrov–Galerkin weighting and velocity gradient recovery techniques that are applied upon the constitutive equation. Free surface solution reprojection and a new pressure‐drop/mass balance scheme are proposed. Copyright © 2001 John Wiley & Sons, Ltd.
Finite volume multigrid method of the planar contraction flow of a viscoelastic fluid
Authors: Al Moatssime H. , Esselaoui D. , Hakim A. , Raghay S. 
Published: January 2005

AbstractThis paper reports on a numerical algorithm for the steady flow of viscoelastic fluid. The conservative and constitutive equations are solved using the finite volume method (FVM) with a hybrid scheme for the velocities and first‐order upwind approximation for the viscoelastic stress. A non‐uniform staggered grid system is used. The iterative SIMPLE algorithm is employed to relax the coupled momentum and continuity equations. The non‐linear algebraic equations over the flow domain are solved iteratively by the symmetrical coupled Gauss–Seidel (SCGS) method. In both, the full approximation storage (FAS) multigrid algorithm is used. An Oldroyd‐B fluid model was selected for the calculation. Results are reported for planar 4:1 abrupt contraction at various Weissenberg numbers. The solutions are found to be stable and smooth. The solutions show that at high Weissenberg number the domain must be long enough. The convergence of the method has been verified with grid refinement. All the calculations have been performed on a PC equipped with a Pentium III processor at 550 MHz. Copyright © 2001 John Wiley & Sons, Ltd.
The design of improved smoothing operators for finite volume flow solvers on unstructured meshes
Authors: de Foy Benjamin , Dawes William 
Published: January 2005

AbstractSpatial operators used in unstructured finite volume flow solvers are analysed for accuracy using Taylor series expansion and Fourier analysis. While approaching second‐order accuracy on very regular grids, operators in common use are shown to have errors resulting in accuracy of only first‐, zeroth‐ or even negative‐order on three‐dimensional tetrahedral meshes. A technique using least‐squares optimization is developed to design improved operators on arbitrary meshes. This is applied to the fourth‐order edge sum smoothing operator. The improved numerical dissipation leads to a much more accurate prediction of the Strouhal number for two‐dimensional flow around a cylinder and a reduction of a factor of three in the loss coefficient for inviscid flow over a three‐dimensional hump. Copyright © 2001 John Wiley & Sons, Ltd.
An implicit time‐marching algorithm for shallow water models based on the generalized wave continuity equation
Authors: Dresback Kendra M. , Kolar Randall L. 
Published: January 2005

AbstractWave equation models currently discretize the generalized wave continuity equation with a three‐time‐level scheme centered at k and the momentum equation with a two‐time‐level scheme centered at k+1/2; non‐linear terms are evaluated explicitly. However in highly non‐linear applications, the algorithm becomes unstable at even moderate Courant numbers. This paper examines an implicit treatment of the non‐linear terms using an iterative time‐marching algorithm. Depending on the domain, results from one‐dimensional experiments show up to a tenfold increase in stability and temporal accuracy. The sensitivity of stability to variations in the G‐parameter (a numerical weighting parameter in the generalized wave continuity equation) was examined; results show that the greatest increase in stability occurs with G/τ=2–50. In the one‐dimensional experiments, three different types of node spacing techniques—constant, variable, and LTEA (Localized Truncation Error Analysis)—were examined; stability is positively correlated to the uniformity of the node spacing. Lastly, a scaling analysis demonstrates that the magnitudes of the non‐linear terms are positively correlated to those that most influence stability, particularly the term containing the G‐parameter. It is evident that the new algorithm improves stability and temporal accuracy in a cost‐effective manner. Copyright © 2001 John Wiley & Sons, Ltd.
Towards a transparent boundary condition for compressible Navier–Stokes equations
Authors: Bruneau C. H. , Creusé E. 
Published: January 2005

AbstractA new artificial boundary condition for two‐dimensional subsonic flows governed by the compressible Navier–Stokes equations is derived. It is based on the hyperbolic part of the equations, according to the way of propagation of the characteristic waves. A reference flow, as well as a convection velocity, is used to properly discretize the terms corresponding to the entering waves. Numerical tests on various classical model problems, whose solutions are known, and comparisons with other boundary conditions (BCs), show the efficiency of the BC. Direct numerical simulations of more complex flows over a dihedral plate are simulated, without creation of acoustic waves going back in the flow. Copyright © 2001 John Wiley & Sons, Ltd.
Numerical simulation of the flow field in the vicinity of an axial flow fan
Authors: Meyer C.J. , Kröger D.G. 
Published: January 2005

AbstractThe main purpose of the current investigation is the development and evaluation of a numerical model used to simulate the effect of an axial flow fan on the velocity field in the vicinity of the fan blades. The axial flow fan is modeled as an actuator disc, where the actuator disc forces are calculated using blade element theory. The calculated disc forces are expressed as sources/sinks of momentum in the Navier–Stokes equations solved by a commercially available computational fluid dynamic (CFD) code, Flo++. The model is used to determine the fan performance characteristics of an axial flow fan as well as the velocity fields directly up‐ and downstream of the fan blades. The results are compared with experimental data. In general, good agreement is obtained between the numerical results and experimental data, although the fan power consumption, as well as radial velocity downstream of the fan blades, is underpredicted by the fan model. Copyright © 2001 John Wiley & Sons, Ltd.
On estimation of entrance boundary parameters from downstream measurements using adjoint approach
Authors: Alekseev A.K. 
Published: January 2005

AbstractAn estimation of entrance boundary conditions from the downstream measurements is considered in variational statement form for two‐dimensional supersonic laminar flow. The adjoint problem is used for the calculation of the discrepancy gradient in space of control parameters. The numerical tests presented demonstrate the successful estimation of boundary parameters of spatial distribution by using gradient methods. Copyright © 2001 John Wiley & Sons, Ltd.
Boundary element analysis of driven cavity flow for low and moderate Reynolds numbers
Authors: Aydin M. , Fenner R. T. 
Published: January 2005

AbstractA boundary element method for steady two‐dimensional low‐to‐moderate‐Reynolds number flows of incompressible fluids, using primitive variables, is presented. The velocity gradients in the Navier–Stokes equations are evaluated using the alternatives of upwind and central finite difference approximations, and derivatives of finite element shape functions. A direct iterative scheme is used to cope with the non‐linear character of the integral equations. In order to achieve convergence, an underrelaxation technique is employed at relatively high Reynolds numbers. Driven cavity flow in a square domain is considered to validate the proposed method by comparison with other published data. Copyright © 2001 John Wiley & Sons, Ltd.
Vortex surface method: some numerical problems of the potential calculation
Authors: Belamri T. , Bakir F. , Kouidri S. , Rey R. 
Published: January 2005

AbstractThe singularities method is used to analyze the flow around an isolated profile or through a plane cascade. In this paper, a numerical study has been developed in order to discuss the accuracy of solutions. The aims of this study are summarized as follows: (1) to expose the elements that influence the method—precision in the geometrical profile definition, trailing‐edge geometry, smoothing problems, number of discretization points, precision of calculation, etc.; (2) to provide an accurate solution for these different problems. For example, some profiles, obtained by the Joukowski transformation, present, in spite of an analytical definition, a crossing of the suction and pressure sides at the trailing edge. This crossing causes a serious error in the velocity field computation. A new procedure to solve this problem is presented. Copyright © 2001 John Wiley & Sons, Ltd.