bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationships between sea‐level pressure and sea‐level height in the Camargue (French Mediterranean coast) by Vincent Moron and Albin Ullmann, pages 1531–1540, Volume 25, Issue 11, 2005
Authors: Moron Vincent
Published: April 2006

A statistical study of daily maximum sea‐level height at one station (Grau de la Dent) in the Camargue (Rhône delta, French Mediterranean coast) and daily sea‐level pressure (SLP) at 12 h UTC over the eastern North Atlantic is used to identify the meteorological conditions associated with sea‐level variations in the Camargue for the winters 1974–1975 to 2000–2001. Mean SLP composites during and 5 days before major surge events (defined as those with a daily maximum sea‐level height > 80 cm) suggest the dominant influence of storms, moving northwest to southeast across the North Atlantic and strengthening as they approach the Bay of Biscay. During such storms, strong onshore winds may persist for up to 4–5 days. These winds tend to strengthen from 3 days to 1 day before the surge events. The mean October–March correlation between daily maximum sea‐level height in the Camargue and SLP averaged over the Bay of Biscay (10°W–0° , 40° –50°N) is strong (r = − 0.69). A methodology is developed for assessing the low frequency SLP variability impact on sea‐level height in the Camargue. A cross‐validated linear regression is used to hindcast the interannual and intraseasonal variability of the monthly 75th and 90th percentiles of the daily maximum sea‐level height from the monthly mean SLP over the Bay of Biscay. The linear correlation between the cross‐validated hindcast and observed time series is 0.83 (0.77) for the 75th (90th) percentile over the 1974–1975 to 2000–2001 period. The mean bias error, reflecting systematic errors in predicting the monthly percentiles, is close to zero. Copyright © 2006 Royal Meteorological Society.
Validation of the oral mucositis assessment scale in pediatric cancer
Authors: Sung Lillian , Tomlinson George A. , Greenberg Mark L. , Koren Gideon , Judd Peter , Ota Sylvia , Feldman Brian M.
Published: April 2006

Background

Our objective was to examine the construct validity of the Oral Mucositis Assessment Scale (OMAS) in children receiving doxorubicin chemotherapy.

Methods

Children between 6 and 18 years of age with cancer receiving doxorubicin‐containing chemotherapy were included. OMAS was measured on days 7, 10, 14, and 17 after chemotherapy. Other measures of mucositis obtained concurrent with OMAS were the World Health Organization (WHO) mucositis scale and pain visual analogue scale (VAS). We also recorded analgesia administration.

Results

Sixteen children were studied for 45 post‐chemotherapy cycles and 156 OMAS assessments were performed. OMAS was moderately correlated with WHO scores (r = 0.56; P = 0.0006) whereas correlation with the pain VAS was fair (r = 0.37; P = 0.002). OMAS also had fair correlation with the number of doses of topical analgesia (r = 0.43; P = 0.001) and with the cumulative dose of opioid analgesia (r = 0.38; P = 0.003).

Conclusions

The OMAS is valid for use in mucositis clinical trials for children at least 6 years of age. Pediatr Blood Cancer 2007;49:149–153. © 2006 Wiley‐Liss, Inc.
Effect of molecular architecture on quiescent and shear‐induced crystallization of polyethylene
Authors: Bustos Frédéric , Cassagnau Philippe , Fulchiron René
Published: April 2006

The aim of this work is to investigate the effect of the molecular structure of polyethylene on the crystallization kinetics. In static conditions, the increase of the degree of branching leads to the decrease of the crystallization temperature, the melting temperature, and the crystallinity. Indeed, the crystal thickness is controlled by the length of PE segments between branching. The effect of preshear on crystallization kinetics was studied by following the dynamic modulus along the time after a treatment of constant shear rate. Particularly, the effect of the shear rate was investigated. The enhancement of crystallization kinetics appears directly linked to the relaxation time of the melt polymer. Expressed by the Weissenberg number, a “master curve” is obtained independent of the amount and length of branching, leading to the conclusion that the nucleation due to shear is conditioned by the molecular architecture mainly via its effect on the relaxation time. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1597–1607, 2006
On Using a Cancer Center Cancer Registry to Identify Newly Affected Women Eligible for Hereditary Breast Cancer Syndrome Testing: Practical Considerations
Authors: DeMarco Tiffani A. , Loffredo Christopher A. , Sampilo Marilyn L. , Tercyak Kenneth P.
Published: April 2006

The goals of this research were to describe the process of identifying and recruiting individuals registered with a cancer center's cancer registry who were eligible to participate in cancer genetic research. This study specifically focused on younger women with personal and family cancer histories strongly suggestive of hereditary breast cancer syndromes, as determined by genetic counselor review. Of special interest was to determine the proportion of women from minority backgrounds who were (a) identifiable in this manner and (b) interested in genetic testing for hereditary breast cancer through a family cancer clinical research program. An initial query of the 292 cases of women newly affected with breast cancer and contained within the registry indicated that 124 met demographic eligibility criteria. The personal and family cancer histories of each of these women were then reviewed by a genetic counselor and the remaining, eligible patients (n = 31) were subsequently contacted by mail and telephone: approximately three‐fifths (18/31) of these patients were White and two‐fifths (13/31) were Black or of another racial background. Of the women who were sent one or more study‐related mailings, 10% (3/31) were unreachable by telephone due to incorrect contact information, 32% (10/31) were reachable by telephone but unresponsive to messages left, 26% (8/31) had already participated in the family cancer program (i.e., were positive controls), 6% (2/31) were interested in participating in the program, 23% (7/31) were uninterested in participating in the program, and 3% (1/31) were later determined to be ineligible. Comparing the racial backgrounds of women who were either positive controls or interested in participating (i.e., “tester” category) to women who were either unreachable, nonresponsive, uninterested, or ineligible (i.e., “nontester” category), there was a nonsignificant trend for more non‐White women to fall into the nontester than tester category, Fisher's Exact Test = .09. This work underscores practical steps in planning and carrying‐out cancer genetic testing research among women newly affected with breast cancer and members of special populations. It also underscores the role that genetic counseling professionals play in this process.
On the collective instability of salt fingers
Authors: Holyer Judith Y.
Published: April 2006

In this paper we consider the stability of salt fingers to long wavelength internal wave perturbations. The Prandtl number of the fluid is assumed to be large, but the ratio of the two diffusivities (KS/KT) is allowed to be any size provided that KS < KT. This problem was first considered by Stern (1969), where several untested assumptions were made about the motion. Here we use a two-scale approach to separate the salt finger motions from the long-scale internal wave perturbations and to obtain the stability criterion. This collective instability of salt fingers succeeds in transferring energy from the small salt finger scales to the long internal wave scales.
Thermal convection in a rotating fluid: effects due to bottom topography
Authors: Leach Harry
Published: April 2006

A study has been made of the effects of non-axisymmetric bottom topography in a differentially heated, rotating fluid annulus. In the absence of free baroclinic waves the disturbance produced by topography of vertical dimensions typically much less than the depth of the fluid and horizontal dimensions comparable to the gap width is steady and confined to the lower part of the fluid. The maximum amplitude of this disturbance depends on the angular speed of rotation of the apparatus and varies with height, being very small above the level where the basic azimuthal flow reverses. The flow pattern shows a closed circulation displaced relative to the topography in the downstream direction. In the presence of free baroclinic waves the topographic wave extends throughout the whole depth of the fluid. Determinations of the amplitude and phase of the various azimuthal Fourier components present show that the topographically forced components exchange energy with the free components as they drift relative to the topography.
Three-dimensional flow in a closed thermosyphon
Authors: Mallinson G. D. , Graham A. D. , Davis G. De Vahl
Published: April 2006

A numerical and experimental study has been made of the three-dimensional flow and heat transfer by natural convection in a closed, rectangular thermosyphon. At low Rayleigh numbers, the flows in the two halves of the cavity remain separate, with heat transfer across the mid-height plane occurring only by conduction. At increasing Rayleigh numbers, an exchange process of increasing complexity occurs. The numerical solutions were used to explore this process and to predict flow patterns which were found to resemble closely those observed during previous investigations of cylindrical thermosyphons. The results were verified by a flow visualization study. Heat-transfer rates are presented and augment previous data for higher values of the governing parameters.
Nonlinear periodic convection in double-diffusive systems
Authors: Knobloch E. , Proctor M. R. E.
Published: April 2006

We study two examples of two-dimensional nonlinear double-diffusive convection (thermohaline convection, and convection in an imposed vertical magnetic field) in the limit where the onset of marginal overstability just precedes the exchange of stabilities. In this limit nonlinear solutions can be found analytically. The branch of oscillatory solutions always terminates on the steady solution branch. If the steady solution branch is subcritical this occurs when the period of the oscillation becomes infinite, while if it is supercritical, it occurs via a Hopf bifurcation. A detailed discussion of the stability of the oscillations is given. The results are in broad agreement with the largeramplitude results obtained previously by numerical techniques.
Nonlinearity of the three-dimensional flow past a flat blunt ship
Authors: Fernandez Gilles
Published: April 2006

The nonlinearity of the gravity sea flow past a three-dimensional flat blunt ship with a length-based Froude number of order unity is studied using the method of matched asymptotic expansions. It is shown that the nonlinearity is important in an inner domain near the ship, whereas the flow in the rest of the fluid domain is the solution of a Neumann-Kelvin problem. Two possible inner solutions – a jet and a wave – are obtained and discussed.
An experimental investigation of convection in a fluid that exhibits phase change
Authors: Fitzjarrald D. E.
Published: April 2006

Convection flows have been systematically observed in a layer of fluid between two isothermal horizontal boundaries. The working fluid was a nematic liquid crystal, which exhibits a liquid–liquid phase change at which latent heat is released and the density changed. In addition to ordinary Rayleigh–Bénard convection when either phase is present alone, there exist two distinct types of convective motions initiated by the unstable density difference. When a thin layer of heavy fluid is present near the top boundary, hexagons with downgoing centres exist with no imposed thermal gradient. When a thin layer of light fluid is brought on near the lower boundary, the hexagons have upshooting centres. In both cases, the motions are kept going once they are initiated by the instability due to release of latent heat. Relation of the results to applicable theories is discussed.
The effect of surface tension on the shape of fingers in a Hele Shaw cell
Authors: McLean J. W. , Saffman P. G.
Published: April 2006

The experimental results of Saffman & Taylor (1958) and Pitts (1980) on fingering in a Hele Shaw cell are modelled by two-dimensional potential flow with surface-tension effects included at the interface. Using free streamline techniques, the shape of the free surface is expressed as the solution of a nonlinear integro-differential equation. The equation is solved numerically and the solutions are compared with experimental results. The shapes of the profiles are very well predicted, but the dependence of finger width on surface tension is not quantitatively accurate, although the qualitative behaviour is correct. A conflict between the numerics and a formal singular perturbation analysis is noted but not resolved. The stability of the steady finger to small disturbances is also examined. Linearized stability analysis indicates that the two-dimensional fingers are not stabilized by the surface-tension effect, which disagrees with the experimental observations. A possible reason for the discrepancy between theory and experiment is suggested.
Coherence between large-scale jet-mixing structure and its pressure field
Authors: Davis M. R.
Published: April 2006

A schlieren system has been arranged to sense the total fluctuation over a cross-section of the flow and thus becomes very sensitive to large-scale azimuthally coherent structures in the flow. For a natural unexcited jet it is found that there is a concentration of the large-scale structure at a characteristic Strouhal number which is not sensitive to the beam thickness and which reduces progressively with distance from the nozzle. This large-scale structure exhibits a coherence of over 70 % with the near-field pressure and convects at between 75 % and 95 % of the jet velocity. The coherence between the potential core-pressure field and the large-scale structure downstream increases rapidly with distance from the nozzle exit plane, rather limited coherence being found at the exit plane for these observations at a jet-exit Mach number Mj = 0·7. Movement of a central microphone from x = 0 to x = 2D introduced a solid centre body over the first 2·5 diameters of flow and gave rise to a set of discrete components in the flow structure in the range 0.6 < S < 1·4.

With harmonic excitation at S = 1·12 a subharmonic at S = 0·55 occurs at x/D = 3 and a second at S = 0.26, x/D = 6. The flow cross-sectional-average sensing thus appears to show up the vortex-pairing mechanism at greater distances from the nozzle than is easily detectable by other means. Under strong impulse excitation a set of discrete components was observed in a transient response extending over times of 400D/Uj. These had a strongest component which decreases more rapidly in Strouhal number with distance than that associated with natural or harmonically excited conditions.
Long-time evolution of an unstable water-wave train
Authors: Stiassnie Michael , Kroszynski Uri I.
Published: April 2006

The long-time evolution of an unstable wave train, consisting of a carrier wave and two 'side-band’ components, is investigated analytically. Mathematical expressions, involving Jacobian elliptic functions, for the wave envelope characteristics are derived. The solution yields the dependence of the long-time evolution on the initial disturbance. Of special interest is the simple formula for the modulation-demodulation recurrence period. The latter is shown to yield results in good agreement with those obtained from numerical solutions of the nonlinear Schrödinger equation.
Simplified theory of the near-wall turbulent layer of Newtonian and drag-reducing fluids
Authors: Goldshtik M. A. , Zametalin V. V. , Shtern V. N.
Published: April 2006

We propose a simplified theory of a viscous layer in near-wall turbulent flow that determines the mean-velocity profile and integral characteristics of velocity fluctuations. The theory is based on the concepts resulting from the experimental data implying a relatively simple almost-ordered structure of fluctuations in close proximity to the wall. On the basis of data on the greatest contribution to transfer processes made by the part of the spectrum associated with the main size of the observed structures, the turbulent fluctuations are simulated by a three-dimensional running wave whose parameters are found from the problem solution. Mathematically the problem reduces to the solution of linearized Navier-Stokes equations. The no-slip condition is satisfied on the wall, whereas on the outer boundary of a viscous layer the conditions of smooth conjunction with the asymptotic shape of velocity and fluctuation-energy profiles resulting from the dimensional analysis are satisfied. The formulation of the problem is completed by the requirement of maximum curvature of the mean-velocity profile on the outer boundary applied from stability considerations.

The solution of the problem does not require any quantitative empirical data, although the conditions of conjunction were formulated according to the well-known concepts obtained experimentally. As a result, the near-wall law for the averaged velocity has been calculated theoretically and is in good agreement with experiment, and the characteristic scales for fluctuations have also been determined. The developed theory is applied to turbulent-flow calculations in Maxwell and Oldroyd media. The elastic properties of fluids are shown to lead to near-wall region reconstruction and its associated drag reduction, as is the case in turbulent flows of dilute polymer solutions. This theory accounts for several features typical of the Toms effect, such as the threshold character of the effect and the decrease in the normal fluctuating velocity. The analysis of the near-wall Oldroyd fluid flow permits us to elucidate several new aspects of the drag-reduction effect. It has been established that the Toms effect does not always result in thickening of the viscous sublayer; on the contrary, the most intense drag reduction takes place without thickening in the viscous sublayer.
Statistical properties of water waves. Part 1. Steady-state distribution of wind-driven gravity-capillary waves
Authors: West Bruce J.
Published: April 2006

The Miles–Phillips model of the linear coupling between waves on the ocean surface and a fluctuating wind field is generalized to include the average effect of the nonlinear water-wave interactions in the dynamic equations for gravity–capillary waves. A statistical-linearization procedure is applied to the general problem and yields the optimum linear description of the nonlinear terms by linear terms. The linearized dynamic equations are stochastic with solutions that have stable moments, i.e. the average nonlinear interactions quench the linear instability generated by the coupling to the mean wind field. In particular, an asymptotic steady-state power-spectral density for the water-wave field is calculated exactly in the context of the model for various wind speeds.
Nonlinear-wave effects on fixed and floating bodies
Authors: Isaacson Michael De St Q.
Published: April 2006

A numerical method for calculating the interaction of steep (nonlinear) ocean waves with large fixed or floating structures of arbitrary shape is described. The interaction is treated as a transient problem with known initial conditions corresponding to still water in the vicinity of the structure and a prescribed incident waveform approaching it. The development of the flow, together with the associated fluid forces and structural motions, are obtained by a time-stepping procedure in which the flow at each time step is calculated by an integral-equation method based on Green's theorem. A few results are presented for two reference situations and these serve to illustrate the effects of nonlinearities in the incident waves.
On the spectra of high-frequency wind waves
Authors: Liu Hsien-Ta , Lin Jung-Tai
Published: April 2006

Displacements of wind waves in the laboratory were measured with a laser displacement gauge, a recent,ly developed, optical, non-intrusive sensor, which avoids the meniscus effect's that severely limit the frequency response of conventional thin- wire gauges. The new gauge is a digital device, which has a maximum frequency response of 2.5 kHz. Its spatial resolution, which depends on the field of view, is t,ypically 0.016 cm for a 4 cm field of view. The wind-wave displacements were measured at several fetches for three wind speeds. Wave-variance spectra derived from these measurements indicate the presence of a quasi-equilibrium spectrum in the capillary-wave regime. The quasi-equilibrium spectrum follows an $f^{-\frac{7}{3}}$ power law that has been predicted on dimensional grounds. The spect'ral density increases with increasing wind speed from 4 to 10 m/s but is independent of the fetch from 3 to 5 m. In addition, the capillary-wave spectrum is practically unchanged when a, relatively long but. low-amplitude mechanical wave is superposed onto the wind- generat'cd waves.
Patterns of convection in spherical shells. Part 2
Authors: Busse F. H. , Riahi N.
Published: April 2006

The analysis by Busse (1975) of preferred patterns of convection in spherical shells is extended to include the case of odd degreeslof spherical harmonics. In the general part of the paper only the property of spherical symmetry of the basic state is used. The results are thus applicable to all bifurcation problems with spherical symmetry. Except in the case1= 1 a pattern degeneracy of the linear problem exists, which is partly removed by the solvability conditions that are generated when nonlinear terms are taken into account as perturbations. In each of the cases1considered so far, at least1physically different solutions have been found. The preferred solution among I existing ones is determined for1≥2 by a stability analysis. In the casel= 3 emphasized in this paper the axisymmetric solution is found to be always unstable, and the solution of tetrahedronal symmetry appears to be generally preferred. The latter result is rigorously established in the special case of a thin layer with nearly insulating boundaries treated in the second part of the paper.
Free convection from a disk rotating in a vertical plane
Authors: Chawla S. S. , Verma A. R.
Published: April 2006

An exact solution of the free convective flow of a viscous incompressible fluid from a heated disk, rotating in a vertical plane, is obtained. The non-axisymmetric fluid motion consists of two parts; the primary von Kármán axisymmetric flow and the secondary buoyancy-induced cross-flow. A highly accurate solution of the energy equation is also derived for its subsequent use in the analysis of the cross-flow.
A new type of boundary layer in a rapidly rotating gas
Authors: Matsuda Takuya , Nakagawa Keizo
Published: April 2006

Gaseous flow in a pie-shaped cylinder of infinite length rotating about the apex is considered. The horizontal flow is induced either by the temperature distribution or by the source/sink distribution on the walls θ = constant. It is found that along the vertical walls θ = constant the E½ boundary layer is formed, where E is the Ekman number. Although the equation governing the above boundary layer is very similar to that of the Ekman layer, it is a new type of boundary layer which may be called the buoyancy layer. Along the wall on which r is constant thermal boundary layers very similar to the Stewartson layers are found to be formed. The role of these layers is to mediate the temperature jump. These layers disappear in the incompressible limit.
Instabilities in the slit-jet flow field
Authors: Foss J. F. , Korschelt D.
Published: April 2006

Three modes of instabilities in the slit-jet flow field are recognized. Additional evidence for the universality of the Strouhal number for the second mode ST = fw/U0 ≈ 0.43 and additional information on the wavelength (λ) between, and convection speed uc of the symmetrically placed, large-scale motions that result from this instability are presented. Specifically λ/w ≈ 1.2 and uc/U0 ≈ 0.51. The third instability mode is initiated at a Reynolds number U0w/v of approximately 1600; this instability results in a loss of the regular pattern associated with the large-scale motions.
Peristaltic pumping in water waves
Authors: Longuet-Higgins M. S.
Published: April 2006

In this paper we calculate the streaming induced by gravity waves passing over a thin fluid layer, one side of which is rigid while the other is a flexible, inextensible membrane. The problem is relevant to some recent laboratory experiments by Allison (1983) on the pumping action of water waves.

On the assumption that the flow is laminar and that the lateral displacement b of the membrane is small compared with the thickness Δ of the fluid layer, we calculate the velocity profile of the streaming U within the layer. This depends on the ratio Δ/δ, where δ is the thickness of the Stokes layers at the upper and lower boundaries. When 0 < Δ/δ > 6 the boundary layers interact strongly and the velocity profile is unimodal. At large values of Δ/δ the profile of U exhibits thin ‘jets’ near the boundaries.

The calculated drift velocities agree as regards order of magnitude with those observed. However, the pressure gradients observed were larger than those calculated, due possibly to turbulence, but probably also to finite-amplitude and end-effects.

The theory given here can be considered as an extension of the theory of peristaltic pumping to flows at higher Reynolds number.
Effects of imperfect spatial resolution on measurements of wall-bounded turbulentbx shear flows
Authors: Johansson Arne V. , Alfredsson P. Henrik
Published: April 2006

The effects of imperfect spatial resolution on hot-film and hot-wire measurements of wall-bounded turbulent shear flows were studied. Two hot-film probes of different length were used for measurements of fully developed turbulent channel flow in a water tunnel. In the near-wall region significant effects of spanwise spatial averaging due to finite probe size were found for a probe 32 viscous units long. The maximum turbulence intensity attained a 10% lower value than that for a probe about half as long, and the zero-crossing of the skewness factor was shifted away from the wall. This could be attributed to spatial averaging of narrow low-speed regions. Results for different Reynolds numbers, but with the same sensor length in viscous units, showed that Reynolds-number effects are small, and that much of the reported discrepancies for turbulence measurements in the near-wall region can be ascribed to effects of imperfect spatial resolution. Also the number of events detected with the variable-interval time-averaging (VITA) technique was found to depend strongly on the sensor length, especially for events with short duration.
Measurements near a laminar separation point
Authors: Varty R. L. , Currie I. G.
Published: April 2006

Measurements in the neighbourhood of a laminar separation point at a high subcritical Reynolds number are reported. These results are used to test the validity of various theories relating to laminar separation. It is concluded that the boundary-layer equations are valid in the neighbourhood of the separation point without the existence of a singularity.

The velocity field was measured using a dual-beam laser-Doppler anemometer with optical frequency shifting. The wall-shear-stress distribution was measured with a flush-mounted hot-film sensor and the wall-pressure distribution was measured using a strain-gauge pressure sensor. The various terms in the Navier–Stokes equations were evaluated directly from the measurements, permitting the validity of the boundary-layer equations to be established. Proposed solutions for the flow field are compared with the measured flow field.
Sound generated by instability waves of supersonic flows. Part 2. Axisymmetric jets
Authors: Tam Christopher K. W. , Burton Dale E.
Published: April 2006

A solution describing the spatial evolution of small-amplitude instability waves and their associated sound field of axisymmetric supersonic jets is found using the method of matched asymptotic expansions (see Part 1, Tam & Burton 1984). The inherent axisymmetry of the problem allows the instability waves to be decomposed into azimuthal wave modes. In addition, it is found that because of the cylindrical geometry of the problem the gauge functions of the inner expansion, unlike the case of two-dimensional mixing layers, are no longer just powers of ε. Instead they contain logarithmic terms. To test the validity of the theory, numerical results of the solution are compared with the experimental measurements of Troutt (1978) and Troutt & McLaughlin (1982). Two series of comparisons at Strouhal numbers 0.2 and 0.4 for a Mach-number 2.1 cold supersonic jet are made. The data compared include hot-wire measurements of the axial distribution of root-mean-squared jet centreline mass-velocity fluctuations and radial and axial distributions of near-field pressure-level contours measured by microphones. The former is used to test the accuracy of the inner (or instability-wave) solution. The latter is used to verify the correctness of the outer solution. Very favourable overall agreements between the calculated results and the experimental measurements are found. These very favourable agreements strongly suggest that the method of solution developed in Part 1 paper is indeed valid. Furthermore, they also offer concrete support to the proposition made previously by a number of investigators that instability waves are important noise sources in supersonic jets.
Two-phase displacement in Hele Shaw cells: theory
Authors: Park C.-W. , Homsy G. M.
Published: April 2006

A theory describing two-phase displacement in the gap between closely spaced planes is developed. The main assumptions of the theory are that the displaced fluid wets the walls, and that the capillary number Ca and the ratio of gap width to transverse characteristic length ε are both small. Relatively mild restrictions apply to the ratio M of viscosities of displacing to displaced fluids; in particular the theory holds for M = o(Ca−1/3). We formulate the theory as a double asymptotic expansion in the small parameters ε and Ca1/3. The expansion in ε is uniform while that in Ca1/3 is not, necessitating the use of matched asymptotic expansions. The previous work of Bretherton (1961) is clarified and extended, and both the form and the constants in the effective boundary condition of Chouke, van Meurs & van der Poel (1959) and of Saffman & Taylor (1958) are determined.
Gravity current upstream of a buoyant influx in an open-channel flow: a numerical study
Authors: Valentine Daniel T. , Kao Timothy W.
Published: April 2006

The establishment of an upstream intrusion of a buoyant fluid discharged into an open-channel flow of uniform density and finite depth is studied numerically using the full Navier-Stokes and diffusion equations. The problem is posed as an initial-boundary-value problem for the laminar motions of a Boussinesq fluid. The equations are integrated numerically by finite-difference methods. The flow patterns produced are controlled by the influx of buoyancy; therefore they are characterized by an inflow densimetric Froude number. A comparison with available experimental data provides favourable support to the theoretical predictions. The critical value of densimetric Froude number of the source of a vertically downward inflow at the free surface of a channel is determined. For densimetric Froude number less than critical, an intrusion is established on the upstream side of the source. Because dissipative mechanisms associated with viscosity take a finite time to intervene, the intrusion starts as an inviscid gravity current with a propagation speed greater than the surface velocity of the stream. The front speed is proportional to the phase velocity of long internal waves. Subsequently, the front decelerates as the interfacial friction, and, if applicable, the boundary frictional forces increase simultaneously with mass entrainment across the interface. The current slows down towards a two-zone equilibrium: (1) the zone encompassing the current behind the frontal zone, where a steady state is approached with respect to the inertial frame of reference; (2) the frontal zone, where the upstream speed approaches a steady speed of frontal advance, albeit small. The upstream intrusion alters the flow pattern of the ambient stream dramatically. A significant feature of both the upstream and downstream currents is the presence of surface convergence with concomitant downwelling near the fronts. As the upstream front decelerates, wavelike disturbances are excited just behind the front at frequencies characteristic of internal waves. As the front approaches steady state, these disturbances appear to be damped. This problem has practical implications in the design of once-through cooling-water systems for power plants taking their cooling water from rivers.
Third sound: the propagation of waves on the surface of superfluid helium with healing and relaxation
Authors: Johnson R. S.
Published: April 2006

The propagation of surface waves – that is ‘third’ sound – on superfluid helium is considered. The fluid is treated as a continuum, using the two-fluid model of Landau, and incorporating the effects of healing, relaxation, thermal conductivity and Newtonian viscosity. Under the assumptions only of a small amplitude and long wavelength, a linear theory is developed which includes some discussion of the matching to the outer regions of the vapour. This results in a comprehensive propagation speed for linear waves, although a few properties of the flow are left undetermined at this order. A nonlinear theory is then outlined (without dwelling on the details) which leads to the Burgers equation in an appropriate far field, and enables the leading-order theory to be concluded.

Some numerical results, for two temperatures, are presented by first recording the Helmholtz free energy as a polynomial in densities. Owing to the inaccuracies inherent in this procedure, only the equilibrium state can be satisfactorily reproduced, but this is sufficient to predict the onset phenomenon. The propagation speed, as a function of film thickness, is roughly estimated by using the earlier results of Johnson (without healing) suitably doctored to incorporate the new computed superfluid density distributions. The looked-for reduction in the predicted speeds is evident, but the magnitude of this reduction is too large for very thin films. However, it is hoped that the analytical results presented here will prove more effective when a complete and accurate description of the Helmholtz free energy is available.
Shock structure near a wall in pure inert gas and in binary inert-gas mixtures
Authors: Schmidt B. , Seiler F. , Wörner M.
Published: April 2006

The shock-wave structure close to a wall in pure argon and binary mixtures of noble gases (argon–helium, xenon–helium) is investigated experimentally and numerically in the shock-wave Mach-number range 2·24 ≤ Ms ≤ 9.21. Measured and calculated density profiles are compared, and some conclusions are drawn about the accommodation at the wall and the intermolecular force potential.

For binary gas mixtures only a few results are presented. Weak argon signals of the electron-beam-luminescence method on the experimental side and the computer time needed for the numerical simulation allowed the treatment of a few parameter combinations only.
Reflection of a shallow-water soliton. Part 1. Edge layer for shallow-water waves
Authors: Sugimoto N. , Kakutani T.
Published: April 2006

To investigate reflection of a shallow-water soliton at a sloping beach, the edge-layer theory is developed to obtain a ‘reduced’ boundary condition relevant to the simplified shallow-water equation describing the weakly dispersive waves of small but finite amplitude. An edge layer is introduced to take account of the essentially two-dimensional motion that appears in the narrow region adjacent to the beach. By using the matched-asymptotic-expansion method, the edge-layer theory is formulated to cope with the shallow-water theory in the offshore region and the boundary condition at the beach. The ‘reduced’ boundary condition is derived as a result of the matching condition between the two regions. An explicit edge-layer solution is obtained on assuming a plane beach.
Numerical solution of free-boundary problems in fluid mechanics. Part 2. Buoyancy-driven motion of a gas bubble through a quiescent liquid
Authors: Ryskin G. , Leal L. G.
Published: April 2006

In this paper numerical results are presented for the buoyancy-driven rise of a deformable bubble through an unbounded quiescent fluid. Complete solutions, including the bubble shape, are obtained for Reynolds numbers in the range 1 ≤ R ≤ 200 and for Weber numbers up to 20. For Reynolds numbers R ≤ 20 the shape of the bubble changes from nearly spherical to oblate-ellipsoidal to spherical-cap depending on Weber number; at higher Reynolds numbers ‘disk-like’ and ‘saucer-like’ shapes appear at W = O(10). The present results show clearly that flow separation may occur at a smooth free surface at intermediate Reynolds numbers; this fact suggests a qualitative explanation of the often-observed irregular (zigzag or helical) paths of rising bubbles.
The plane turbulent shear layer with periodic excitation
Authors: Fiedler H. E. , Mensing P.
Published: April 2006

The influence of periodic excitation on a plane turbulent one-stream shear layer with turbulent separation was investigated. For the qualitative study flow visualization was employed. Quantitative data were obtained with hot-wire anemometry and spectrum analysis. It was found that sinusoidal perturbations with frequencies of order f0 [lsim ] u0/100θ0 (depending on excitation strength), introduced at the trailing edge are always amplified. Maximum amplification factors are observed for the lowest perturbation levels. The frequency and amplitude of excitation determine the downstream location of the amplification maximum in the flow. At sufficient amplitude two-dimensional vortices are formed which subsequently decay without pairing. The development of the periodic r.m.s. values along x follows a universal curve for all frequencies and amplitudes when properly normalized.

At high excitation amplitudes the flow development depends strongly on the geometrical conditions of the excitation arrangement at the trailing edge. Thus regular vortex pairing as well as suppression of pairing can be achieved.

The excited shear layer has considerably stronger, yet nonlinear, spread than the neutral. The region of vortex formation, irrespective of whether it includes pairing or not, is associated with a step-like increase in width, while after the position of maximum vortex energy, i.e. in the region of decay, the spread is reduced to values below the neutral. There the overall lateral fluctuation energy is increased, while the longitudinal may be decreased as compared with the neutral flow.
Stability of convection rolls in a layer with stress-free boundaries
Authors: Bolton E. W. , Busse F. H.
Published: April 2006

Steady finite-amplitude solutions for two-dimensional convection in a layer heated from below with stress-free boundaries are obtained numerically by a Galerkin method. The stability of the steady convection rolls with respect to arbitrary three-dimensional infinitesimal disturbances is investigated. Stability is found only in a small fraction of the Rayleigh-number-wavenumber space where steady solutions exist. The cross-roll instability and the oscillatory and monotonic skewed varicose instabilities are most important in limiting the stability of steady convection rolls. The Prandtlnumbers P = 0.71, 7, 104 areemphasized, but the stability boundaries are sufficiently smoothly dependent on the parameters of the problem to permit qualitative extrapolations to other Prandtl numbers.
Nonlinear progressive edge waves: their instability and evolution
Authors: Yeh Harry H.
Published: April 2006

The fundamental properties of nonlinear progressive edge waves are investigated experimentally in a physical model with a uniformly and mildly sloping beach with a straight shoreline. An evolution equation for the envelope of progressive edge waves is the nonlinear Schrödinger (NLS) equation. It is found that the timescale of viscous-dissipation effects in the experiments is comparable with the timescale of the theoretical evolution process for inviscid progressive edge waves. This lack of timescale separation indicates a major shortcoming of the NLS equation as a model of the laboratory experiments. Even with this limitation, a uniform train of edge waves is found to be unstable to a modulational perturbation as predicted by the NLS equation. However, behaviour of the evolution is both qualitatively and quantitatively different from the theoretical predictions. The evolution of the periodogram for the unstable wavetrain shows an asymmetric development of the sidebands about the fundamental frequency; instability growth is limited to the lower sideband. This behaviour leads to a sequential shift of wave energy to lower frequencies as the waves propagate. It is found that a locally soliton-shaped wave packet is unstable in the laboratory environment. It is estimated that a much-larger-scale experimental facility is required to achieve inviscid experiments for the NLS equation.
The effect of a shear flow on convection in a layer heated non-uniformly from below
Authors: Walton I. C.
Published: April 2006

In an earlier paper (Walton 1982) we showed that, when a fluid layer is heated non-uniformly from below in such a way that the vertical temperature difference maintained across the layer is a slowly varying monotonic function of a horizontal coordinate x, then convection occurs for x > xc, where xc is the point where the local Rayleigh number is equal to the critical value for a uniformly heated layer. Furthermore, the amplitude of the convection increases smoothly from exponentially small values for x [Lt ] xc and asymptotes to a value given by Stuart–Watson theory for x [Gt ] xc.

At the present time no solutions of this kind are available for a class of problems in which the onset of instability is heavily influenced by a shear flow (e.g. Görtler vortices in a boundary layer on a curved wall, convection in a heated Blasius boundary layer). In a first step to bridge the gap between these problems and in order to elucidate the difficulties associated with the presence of a shear flow, we investigate the effect of a (weak) shear flow on our earlier convection problem. We show that the onset of convection is delayed and that it appears more suddenly, but still smoothly. The role of horizontal diffusion is shown to be of paramount importance in enabling a solution of this kind to be found, and the implications of these results for instabilities in higher-speed shear flows are discussed.
Pressure pulses generated by the interaction of a discrete vortex with an edge
Authors: Panaras Argyris G.
Published: April 2006

A central role in the mechanism of the self-sustained oscillations of the flow about cavity-type bodies is played by the reattachment edge. Experimentally it has been found that periodic pressure pulses generated on this edge are fed back to the origin of the shear layer and cause the production of discrete vortices. The oscillations have been found to be suppressed or attenuated when the edge has the shape of a ramp of small angle, or when it is properly rounded. To clarify the role of the shape of the reattachment edge in the mechanism of the oscillations, a mathematical model is developed for the vortex–edge interaction. In this model the interaction of one discrete vortex, imbedded within a constant-speed parallel flow, with the reattachment edge is studied. Two typical shapes of the reattachment edge are examined; a ramp of variable angle and an ellipse. The main conclusion of the present analysis is the strong dependence of the pressure pulses, that are induced on the surface of the edge, on the specific shape of the edge. The pressure pulses on reattachment edges with shapes that give rise to steady flows have been found to be of insignificant amplitude. On the other hand, when the reattachment edge has a shape that is known to result in oscillating flow, the induced pressure pulses are of very large amplitude. Intermediate values of the pressure are found for configurations known to stabilize partially the flow. The present results indicate that, for the establishment of the oscillation, the feedback force generated by the vortex–edge interaction must have an appropriate value. The feedback force may be eliminated if the shape of the lip of the edge is properly designed.
A linear analysis of rotating stratified flow past a circular cylinder on an f-plane
Authors: Merkine Lee-Or
Published: April 2006

A linear analysis of rotating stratified flow past a circular cylinder on an f-plane is made for moderate and strong stratification, i.e. for σS = O(E½) and σS = O(1) respectively. E is the Ekman number and σS is the product of the Prandtl number and the inverse rotational Froude number. The most striking result is that, for oncoming flows that are of one sign and possess vertical shear, reversed-flow regions can exist next to the cylinder. Depending on the degree of stratification, these backflow regions can occupy the inner part of the vertical boundary layer or can extend horizontally across distances comparable to the horizontal scale of the cylinder.
Simulation of blast waves with tailored explosive charges
Authors: Sanai M. , Lindberg H. E. , Colton J. D.
Published: April 2006

We have developed a compact and cost-effective shock tube to simulate the static and dynamic pressures of blast waves. The shock tube is open at both ends and is driven by high explosives distributed over a finite length of the tube near one end. The overall charge length is determined by the simulation time of interest, and the charge-density distribution is tailored to produce the pressure-waveform shape desired. For the shock tube to simulate a typical blast wave, the charge density must be highest at the charge front (closest to the test section) and gradually reduced towards the back. The resulting shock tube is an order of magnitude shorter than a conventional dynamic airblast simulator (DABS) in which concentrated explosives are used to drive the shock.

Tailored charges designed using this method were built and tested in a simulation development programme sponsored by the U.S. Defense Nuclear Agency (DNA). The pressures measured for several charge distributions agreed very well with SRI's PUFF hydrocode computations and demonstrated the feasibility of the compact simulator under realistic test conditions.
Numerical investigation of the steady viscous flow past a stationary deformable bubble
Authors: Christov C. I. , Volkov P. K.
Published: April 2006

A method for solving the Navier–Stokes equations in domains with moving boundaries is proposed. By means of a coordinate transformation, the region under consideration is converted to a region with known boundaries which are coordinate surfaces. An appropriate difference scheme with an algorithm for its implementation is constructed. The method is applied to the case of steady incompressible viscous flow past a resting deformable bubble. Results are obtained for wide ranges for Reynolds and Weber numbers and compared with other theoretical or experimental works in the common regions for the governing parameters. A separation of the flow and the occurrence of a toroidal vortex in the rear of the bubble is observed and verified through a number of computations. Typical flow patterns as well as a variety of practically important relations between the parameters of the flow are shown graphically.