Showing papers on "Pressure gradient published in 1987"
TL;DR: In this paper, the authors used the sea level data from Davao in the Philippines and from Darwin in Australia to determine the annual signal and the interannual variations of the pressure gradient for the years 1966 to 1985 and concluded that the variability of the through flow can be monitored by sea level measurements.
Abstract: The flow of water from the western Pacific to the eastern Indian Ocean through the Indonesian archipelago is governed by a strong pressure gradient. Dynamic height computations determine the average sea level difference as 16 cm and show that most of the pressure gradient is contained in the upper 200 m. Sea level data from Davao in the Philippines and from Darwin in Australia are used to determine the annual signal and the interannual variations of the pressure gradient for the years 1966 to 1985. The annual signal has a maximum during the southeast monsoon in July and August and a minimum in January and February. Interannual variations are not related to the Southern Oscillation because sea level is low at both stations during El Nino events, and thus there is little influence on the sea level difference. The mechanism of the through flow is discussed, but a determination of its numerical value will have to await direct measurements. A comparison of the sea level difference with results from a numerical model by Kindle shows satisfactory agreement. It is concluded that the variability of the through flow can be monitored by sea level measurements.
282 citations
TL;DR: In this paper, two geomagnetic storms in September 1984 were studied to examine the progressive changes in the radial profiles of particle pressure, plasma beta, and electric currents of the ring current region during the course of geOMagnetic storms and it was shown that enhancements in the particle pressure occur initially in the outer region and reach the inner region in the late phase of the storm.
Abstract: Two geomagnetic storms in September 1984 were studied to examine the progressive changes in the radial profiles of particle pressure, plasma beta, and electric currents of the ring current region during the course of geomagnetic storms. It is shown that enhancements in the particle pressure occur initially in the outer region and reach the inner region in the late phase of the storm. Structures suggestive of multiple particle injections are seen in the pressure profile. The leading and trailing edges of the particle injection structures are respectively associated with the depressions and enhancements of the westward current densities of the ring current. The location of the maximum ring current particle pressure can be several earth radii from where the most intense westward ring current flows.
243 citations
TL;DR: In this article, a generalized three-dimensional model for resin flow during composite processing has been developed, based on a theory of consolidation and flow through a porous medium, which considers that the total force acting on a porosity medium is countered by the sum of the opposing forces, including the force due to the spring-like effect of the fiber network and the hydrostatic force of the liquid within the porous medium.
Abstract: A generalized three-dimensional model for resin flow during composite processing has been developed. The model is based on a theory of consolidation and flow through a porous medium, which considers that the total force acting on a porous medium is countered by the sum of the opposing forces, including the force due to the spring-like effect of the fiber network and the hydrostatic force due to the pressure of the liquid within the porous medium. The flow in the laminate is described in terms of Darcy's Law for flow in a porous medium, which requires a knowledge of the fiber network permeability and the viscosity of the flowing fluid. Unlike previous resin flow models, this model properly considers the flows in different directions to be coupled and provides a unified approach in arriving at the solution. Comparison of numerical solutions with the closed form analytical solution shows good agreement. Resin pressure profiles show that the pressure gradients in the vertical and horizontal directions are not linear, unlike the assumption of linearity made in several previous resin flow models. The effects on the resin pressure of both linear and nonlinear stress-strain behavior of the porous fiber network were considered. The nonlinear behavior simulates a rapidly stiffening spring and the resin pressure decreases much more rapidly after a given initial period compared to the linear stress-strain behavior.
158 citations
TL;DR: In this article, an analytic solution for the pressure response during drawdown and buildup of a horizontal well is presented, which results from solving the three-dimensional diffusion equation with successive integral transforms.
Abstract: An analytic solution is presented for the pressure response during drawdown and buildup of a horizontal well. This method results from solving the three-dimensional diffusion equation with successive integral transforms. Simplified solutions for short, intermediate, and long times that exhibit straight-line sections when pressure is plotted vs. time are presented. The validity of the method is demonstrated by comparing with results generated numerically by a reservoir simulator and with an analogous analytic solution. Methods for analyzing pressure drawdown and buildup data are presented with examples. The method allows reservoir characteristics, including permeability, skin, and distance to boundaries to be determined. The early-time effects, where the well behaves as if it were in an infinite reservoir, are also discussed. Expressions to determine times to critical events, which are important for well test design, are presented.
136 citations
TL;DR: Saturated resistive pressuregradient driven turbulence is studied analytically and with numerical calculations in this article, which guarantees the existence of a stable, high-m dissipation range, which serves as an energy sink.
Abstract: Saturated resistive pressure‐gradient‐driven turbulence is studied analytically and with numerical calculations Fluid viscosity and thermal diffusivity are retained in the analysis and calculations Such dissipation guarantees the existence of a stable, high‐m dissipation range, which serves as an energy sink An accurate saturation criterion is proposed The resulting predicted pressure diffusivity scales similarly to the mixing length estimate but is significantly larger in magnitude The predictions of the analytic theory are in good quantitative agreement with the numerical results for fluctuation levels
135 citations
TL;DR: In this paper, a model of continuous breakdown of laminar instability waves, together with an estimate of the dominant disturbance frequency, is introduced to model the minimum possible length of transitional flow in terms of local boundarylayer parameters.
Abstract: Correlations of data from constant-pressure flows are shown to seriously overestimate the transition length on axial turbomachine blades in regions of positive pressure gradient. The differences largely can be ascribed to the influence of the pressure gradient on the mechanism of laminar-turbu lent transition. A hypothesis of continuous breakdown of laminar instability waves, together with an estimate of the dominant disturbance frequency, is introduced to model the minimum possible length of transitional flow in terms of local boundarylayer parameters. This model should be preferable to a point transition assumption for predicting turbomachine blade flows. In practice, the transition length most probably will lie between the predictions of the minimum length model and those of constant-pres sure flow correlations.
128 citations
TL;DR: In this article, the ideal magnetohydrodynamic stability of cylindrical equilibria with mass flows is investigated analytically and numerically, and the authors modify the local Suydam criterion for instability at the resonant surfaces where the shear of the flow exactly balances the propagation of the slow wave along the sheared magnetic field.
Abstract: The ideal magnetohydrodynamic stability of cylindrical equilibria with mass flows is investigated analytically and numerically The flows modify the local (Suydam) criterion for instability at the resonant surfaces where k⋅B=0 Sheared flows below the propagation speed for the slow wave are found to be destabilizing for the Suydam modes At a critical velocity, where the shear of the flow exactly balances the propagation of the slow wave along the sheared magnetic field, and the k⋅B=0 surface is at the edge of a slow wave continuum, there is instability regardless of the pressure gradient Above the critical velocity, the k⋅B=0 surface is stable, but an infinite sequence of unstable modes still exists with frequencies accumulating toward the edge of the slow wave continuum at nonzero Doppler shifted frequency The stability of the infinite sequences becomes a nonlocal problem whenever the accumulation frequency overlaps with a continuum at some other radial location
123 citations
TL;DR: In this paper, hot-wire anemometry was used to study traveling waves in an unstable three-dimensional boundary layer with the use of hot-wired anemometers, and it was shown that in a more strongly amplified state, the travelling waves propagate in a direction different from that of the mean flow.
Abstract: Travelling waves in an unstable three-dimensional boundary layer are studied experimentally with the use of hot-wire anemometry. For the sake of realistic comparisons with stability theory, the tests were performed on a swept flat plate where infinite swept-wing conditions were approximated by means of contoured end plates. The required pressure gradient was imposed by a displacement body. The Reynolds number for the first appearance of travelling waves is roughly the same as that of stationary vortices. The frequencies of the most amplified waves depend on the Reynolds number. It is shown with the aid of a twin probe that in a more strongly amplified state, the travelling waves propagate in a direction different from that of the mean flow. Further upstream, where stationary waves first become visible in the oil-flow pattern, a uniform direction could not be identified. Under certain conditions, travelling waves of two frequency ranges are amplified that propagate in different directions. The present work is part of the transition experiment started at the DFVLR. It is closely connected to the theoretical work by Dallmann and Bieler.
123 citations
TL;DR: In this paper, two experiments were performed to study the response of turbulent boundary layers to sudden changes in surface curvature and pressure gradient, and the results showed that an internal layer formed in the flow over the curved hill, and that this internal layer displays many similarities to the boundary layer observed on the free wing.
Abstract: Two experiments were performed to study the response of turbulent boundary layers to sudden changes in surface curvature and pressure gradient. In the first experiment, the behaviour of a boundary layer negotiating a two-dimensional curved hill was examined. Prior to separating on the leeward side of the hill, the layer experienced a short region of concave surface curvature, followed by a prolonged region of convex surface curvature. The corresponding pressure gradient changed from adverse to favourable, and back to adverse. In the second experiment, the flow over a symmetrical wing was studied. This wing had the same profile as the hill with a very similar pressure distribution. The obvious difference between the two experiments was the use of leading and trailing edge plates in the hill flow. The results show that an internal layer forms in the flow over the curved hill, and that this internal layer displays many similarities to the boundary layer observed on the free wing. The internal layer grows as an independent boundary layer beneath a turbulent free-shear layer, and as it develops it establishes its own wall (inner) and wake (outer) regions. The perturbation responsible for initiating the growth of the internal boundary layer seems to be an abrupt change in surface curvature. Once formed, the internal boundary layer dictates the skin-friction distribution and the process of separation over the hill. The effect of the perturbation in wall curvature appears to be different from that due to prolonged convex curvature in that the former affects the flow in the vicinity of the wall instantly, while the latter affects the flow far away from the wall only after the flow turns through some angle. Physical explanations are offered for the qualitative difference between the effects of mild and strong convex curvature, and for the saturated behaviour observed in strongly curved flows. Finally, the results are compared with the behaviour of wind flow over terrestrial hills. In both cases, the internal layer dominates the flow behaviour, even though the scaling laws for the flows over actual hills are not obeyed in the present case. A qualitative comparison reveals that the present internal layer is thicker than that reported in meteorological flows. This appears to be due to the effect of curvature, which perturbs the wake region of the internal layer in the present hill flow, while in meteorological studies the effect of curvature is generally small enough to be neglected.
99 citations
TL;DR: In this article, the forces exerted by the gas jet on the molten layer in laser cutting are investigated theoretically by solving the equations of motion of the gas flow, while frictional forces are obtained from boundary layer theory.
Abstract: The forces exerted by the gas jet on the molten layer in laser cutting are investigated theoretically by solving the equations of motion of the gas flow. The pressure distribution along the cutting front is found by the method of conformal mapping, while frictional forces are obtained from boundary layer theory. Both the pressure gradient and the frictional force are of the same importance for the melt ejection. For both contributions, simple scaling laws are presented. The cooling rate of the melt due to the gas stream is shown to be negligible.
96 citations
TL;DR: When inertial effects are augmented, as in exercise and other hyperdynamic states, the intrinsic component of the total left ventricular systolic load can be substantial, even with no outflow tract or valve abnormalities.
Abstract: Simultaneous intraventricular pressure gradients and ejection flow patterns were measured by a multisensor catheter in 6 patients with normal left ventricular function and no valve abnormalities, at rest and in exercise. Peak measured intraventricular pressure gradients were attained very early in ejection, amounted to 6.7 +/- 1.9 (SD) mm Hg at rest, and were intensified to 13.0 +/- 2.3 mm Hg during submaximal supine bicycle exercise. The augmentation of the gradients during exercise was associated with a pronounced accentuation of the flow acceleration and flow at the instant of peak gradient. A peak flow, the intraventricular gradients amounted to 5.4 +/- 1.7 mm Hg at rest and 10.0 +/- 1.8 mm Hg during submaximal exercise. The exercise-induced enhancement of the measured intraventricular pressure difference at the time of peak flow was underlain by an accentuation of the peak flow itself. A semiempirical fluid dynamic model for ejection was applied to the pressure gradient and simultaneous outflow rate and acceleration data to identify the contributions by local and convective acceleration effects to the instantaneous intraventricular gradient values. The peak intraventricular pressure gradient, which is attained very early in ejection, is mostly accounted for by local acceleration effects (85 +/- 5% of the total). Conversely, at peak flow only convective acceleration effects are responsible for the measured pressure gradient. Thus, when inertial effects are augmented, as in exercise and other hyperdynamic states, the intrinsic component of the total left ventricular systolic load can be substantial, even with no outflow tract or valve abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this article, a dynamic model of melt ejection by a gas jet in laser cutting is presented, where the molten material is removed due to friction forces and the pressure gradient of the gas flow.
Abstract: A dynamic model of melt ejection by a gas jet in laser cutting is presented. The molten material is removed due to friction forces and the pressure gradient of the gas flow. The solution of the stationary equations yields the thickness of the molten layer and its velocity of flow, dependent on cutting speed, gas jet formation and the viscosities and densities of the melt and the gas. A stability analysis of the stationary flow shows instabilities for a pressure gradient controlled melt removal. It is argued that these instabilities correlate with ripple formation on the cutting surface.
TL;DR: In this paper, a five-day integration of a nonlinear numerical model of the sea breeze at the equator, 20°N, 30°N and 45°N is presented.
Abstract: Long-term (five-day) integrations of a nonlinear numerical model of the sea breeze at the equator, 20°N, 30°N and 45°N indicate the importance of latitude on the sea breeze circulation. During the hours of strong heating when friction is largest and the static stability is smallest, a local sea-breeze frontal circulation develops in a similar way at all four latitudes. Evaluation of the terms in the circulation theorem indicates the dominance of the solenoid term (horizontal pressure gradient force) associated with the strong temperature contrast during this period. During the rest of the period, however, the pressure gradient and frictional forces weaken, the static stability increases, and the Coriolis force is dominant (except at the equator). Therefore, quite different circulations evolve at the different latitudes. At the equator, the absence of the Coriolis force results in a sea breeze at all times. At the other latitudes, the Coriolis force is responsible for producing the large-scale lan...
TL;DR: In this article, the authors apply the model of quasistatic equilibrium sequences to describe the time development of magnetic field structures in the plasma of the solar corona, and to determine onset points of a dynamical evolution.
Abstract: We apply the model of quasistatic equilibrium sequences to describe the time development of magnetic field structures in the plasma of the solar corona, and to determine onset points of a dynamical evolution. The representation of the magnetic field by Euler potentials provides a realistic modeling of the photospheric boundary conditions. We present a numerical method suited for the computation of magnetohydrodynamic equilibrium states and for analysing their stability against perturbations within ideal MHD. Pressure and magnetic footpoint displacement can be prescribed separately as boundary conditions. We consider magnetic arcade structures typical for large two-ribbon flares. Our results indicate that a finite pressure gradient seems to be essential for the existence of onset points. Furthermore, it is shown that magnetic shear destabilizes for intermediate values, but can have a stabilizing effect for a large amount of shear.
TL;DR: The magnitude, timing and contour of these high velocity flow signals support the hypothesis that true obstruction is present in patients with hypertrophic cardiomyopathy who have a significant gradient.
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11 Sep 1987TL;DR: In this article, a core sample from a subterranean reservoir is placed in a pressure cell holder and the core pressure is measured at a plurality of pressure points along the core before and during fluid flooding.
Abstract: A core sample from a subterranean reservoir is placed in a pressure cell holder and the core pressure is measured at a plurality of pressure points along the core before and during fluid flooding. A computed tomography (CT) scanning system provides images of the density distribution within the core sample during such waterflooding. Fluid saturation, determined from these CT images, and pressure gradients, determined from the pressure measurements are used to determine the relative permeability of the subterranean reservoir.
TL;DR: In this paper, the seasonal variations of the zonal pressure gradient along the equator and the height of the dynamic ridge along 3°N relative to the Equator and 9°N are described.
Abstract: From February 1983 through September 1984, 18 inverted echo sounder deployments yielded time series from 10 locations as part of the Seasonal Response of the Equatorial Atlantic (SEQUAL) program. Using historical and in situ data, the sounders' travel time data are interpreted as dynamic height (0 relative to 500 dbar) and then related to representations of the synoptic wind field. The seasonal variations of the zonal pressure gradient along the equator and the height of the dynamic ridge along 3°N relative to the equator and 9°N are described. The pressure gradient between 10°W and 34°W has a minimum each April and a maximum each July. Its value ranges between 1.4 (not significantly different from zero) and 8.3 × 10−5 dyn g−1 during the observational period. The zonal pressure gradient is correlated with zonal wind stress from an in situ wind sensor at midfetch, and a 10-day lag time is indicated. The North Equatorial Countercurrent trough attains a maximum in the late boreal summer and fall and a minimum in the spring. It ranges from +39 to −8 dyn cm deep at 38.5°W and from 18 to −1 dyn cm at 28°W. A two-layer model calculation, using monthly mean winds derived by Servain et al. (1986) for the appropriate time period, generally reproduces the observed seasonal variation along the two meridians and the large zonal variation between them. Tracking the individual terms, month by month, illustrates the rate of the Sverdrup adjustment to the local wind stress with surface elevation rising as fast as 10 cm per month.
TL;DR: In this article, a particle dynamics approach relying on particle dynamics is exploited to provide an independent estimate of the total cross-shock potential of slow mode shocks which form the plasma sheet boundary in the deep geomagnetic tail as observed by ISEE 3.
Abstract: In the de Hoffmann-Teller reference frame, the cross-shock electric field is simply the thermoelectric field responsible for preserving charge neutrality. As such, it gives information regarding the heating and dissipation occurring within the shock. The total cross-shock potential can be determined by integrating a weighted electron pressure gradient through the shock, but this requires knowledge of the density and temperature profiles. Here, a recently proposed alternative approach relying on particle dynamics is exploited to provide an independent estimate of this potential. Both determinations are applied to slow mode shocks which form the plasma sheet boundary in the deep geomagnetic tail as observed by ISEE 3. The two methods correlate well. There is no indication of the expected transition from resistive to viscous shocks, although the highest Mach number shocks show the highest potentials. The implications of these results for the electron dissipation mechanisms and turbulence at the shock are discussed.
01 Jan 1987
TL;DR: In this article, the effect of a moderate adverse pressure gradient on the interaction between a single streamwise vortex and a turbulent boundary layer is investigated experimentally, based on measurements of the mean cross-flow velocity components.
Abstract: The effect of a moderate adverse pressure gradient on the interaction between a single streamwise vortex and a turbulent boundary layer is investigated experimentally. Quantitative characterization of vortex properties based on measurements of the mean cross-flow velocity components is attained. Growth of the vortex core is observed, followed by a flattening of the core shape which occurs when the core radius becomes comparable to the distance of the vortex center from the surface. The adverse pressure gradient causes an increase in the rate of core growth and, therefore, a stronger distortion of the core shape. Turbulence properties are even more strongly disturbed by an adverse pressure gradient than by constant pressure.
TL;DR: In this paper, the mean flow structure of supersonic, turbulent, adiabatic-wall flow in a square duct is investigated experimentally over a development length x/D = 0-50 for a uniform flow, Mach 3.9 condition at the duct inlet.
Abstract: The mean-flow structure of supersonic, turbulent, adiabatic-wall flow in a square duct is investigated experimentally over a development length x/D = 0-50 for a uniform flow, Mach 3.9 condition at the duct inlet. The results show that a secondary flow cell structure develops which is similar to that for the incompressible case. Development of the primary flow is influenced by the combined effects of the secondary flow and the streamwise adverse pressure gradient. Total pressure, axial mean velocity, and Mach number profiles are presented which show that the outer flow is sensitive primarily to the streamwise pressure gradient, while flow in the near-wall region is dominated by the secondary flow. Axial mean-velocity profiles plotted in terms of van Driest-scaled variables show that a well-defined log-law region exists in the near-wall layer. This region exists in the presence of a secondary flow which continuously modifies spanwise wall shear stress behavior along the length of the duct.
TL;DR: In this article, a detailed study was carried out to understand the dynamics of pressure variations at different points in the injection-molding system, including hydraulic, nozzle, and cavity pressures.
Abstract: A detailed study was carried out to understand the dynamics of pressure variations at different points in the injection-molding system. Thus, hydraulic, nozzle, and cavity pressures were evaluated, in addition to the pressure gradient in the cavity. Both steps and pseudorandom binary sequences (PRBS) were employed to obtain and compare dynamic models describing these variables. Subsequently, these models were employed to evaluate and select optimal controllers for the different variables.
TL;DR: In this article, the authors quantify the relative magnitudes of terms involving the mean pressure gradient and Reynolds stresses in the balance of turbulent kinetic energy and heat flux in a strongly sheared, high-Reynolds-number, reacting flow.
Abstract: Simultaneous measurements of time-resolved velocity and temperature have been obtained by laser-Doppler anemometry and numerically compensated fine-wire thermocouples in the near wake of a premixed flame stabilized on a disk baffle located on the axis, and at the exit, of a confining pipe. The diameter of the disk was 0.056 m, the diameter of the pipe was 0.080 m, the volumetric equivalence ratio with natural gas as the fuel was 0.79 and the Reynolds number, based on pipe diameter and upstream pipe bulk velocity of 9 m/s, was 46 800. The purpose of the measurements is to quantify the relative magnitudes of terms involving the mean pressure gradient and Reynolds stresses in the balance of turbulent kinetic energy and heat flux in a strongly sheared, high-Reynolds-number, reacting flow. The latter term has been associated with non-gradient diffusion in other flows. Source terms involving the mean pressure gradient are large in the conservation of turbulent heat flux but not in the conservation of Reynolds stress. The ‘thin-flame’ model of burning suggests that the sign and magnitude of the heat flux is closely related to the conditioned mean velocities. The mean axial velocity of the reactants is larger (by up to 0.27 of the reference velocity) than that of the products on the low-velocity side of the shear layer that surrounds the recirculation bubble but the reverse is true on the high-velocity side. These observations are related to the sign of the axial pressure gradient, which is associated with the streamline curvature, and the consequent preferential acceleration of the low-density products. Generally, the Reynolds stresses of the products are higher than those of the reactants and, in contrast to previously reported measurements, the contribution to the unconditioned stresses by the difference in the mean velocity between products and reactants, the so-called ‘intermittent’ contribution, is small. This is a consequence of the high Reynolds number of our flow.
TL;DR: In this paper, the relative motion of gas and liquid in a two-phase region at the surface is considered, with influences of pressure gradients and of surface-tension gradients taken into account for the drops and bubbles.
TL;DR: In this paper, a two-dimensional turbulent wake was deflected by an airfoil-like thin plate placed at small angles in the external flow, and the response of the mean-flow and turbulence properties of the wake to the "mild" pressure gradient and the'mild' streamline curvature caused by the deflection was studied.
Abstract: A fully developed two-dimensional turbulent wake was deflected by an airfoil-like thin plate placed at small angles in the external flow. The response of the mean-flow and turbulence properties of the wake to the ‘mild’ pressure gradient and the ‘mild’ streamline curvature caused by the deflection is studied. Owing to the small defect velocity, the extra strain rates are large compared with the main shear strain and the Reynolds stresses are strongly influenced by both the pressure gradient and the streamline curvature. The defect velocity relative to an appropriately chosen ‘potential-flow velocity’, and the mean vorticity, however, are not as strongly influenced by the curvature. Changes in the magnitudes of the Reynolds-stress components are much larger than would be caused by the simple rotation of coordinates aligned with the wake path. Most turbulence-model parameters are influenced significantly, while some pure turbulence parameters, such as the Taylor microscale, are relatively uninfluenced. The rapid and lagged responses are apparent and the terms in the transport equation for turbulent kinetic energy indicate that the response of the production terms is almost instantaneous, while the diffusion and dissipation terms are delayed.
TL;DR: In this article, normalized pseudovariables or transforms are introduced to linearize the governing diffusivity equation so that proper test interpretation can be made, and two methods for estimating the rate-dependent skin, together with permeability, mechanical skin, and well deliverability.
Abstract: Pressure data from gas wells are normally analyzed by use of pseudopressure, which is a transformation of measured pressure. When tests are associated with large pressure changes accompanied by a severe wellbore storage effect, such as in tight reservoirs, use is made of pseudopressure and pseudotime transforms. The purpose of the pseudovariables is to linearize ''effectively'' the governing diffusivity equation so that proper test interpretation can be made. In this study, normalized pseudovariables or transforms are introduced. Use of these new pseudovariables produces results identical to those obtained with the conventional pseudovariables. However, the proposed pseudovariables offer some distinct practical advantages. For example, units of pressure and time are retained, thus giving a physical ''feel'' for the pseudovariable definitions. Other features include use of liquid equations for solving the gas flow problems - i.e., constants of the working equations remain unchanged. This study also proposes two methods for estimating the rate-dependent skin, together with permeability, mechanical skin, and well deliverability. The first method involves logarithmic convolution of pressure with flow rate, both measured downhole, by use of a radial model. A trial-and-error approach is used to obtain the rate-dependent skin on a convolution plot. The second method requires a transientmore » flow-after-flow test of short duration; a standard graphic technique allows the estimation of the desired reservoir parameters. Once the reservoir parameters are estimated with either method, the absolute open-flow potential (AOFP) of a well can be established by assuming a reservoir radius because the AOFP is relatively insensitive to this assumption.« less
TL;DR: In this article, Tsyganenko and Usmanov (TU) models were used to determine the self-consistent plasma pressure gradients and anisotropies along the midnight meridian in the near-Earth magnetosphere.
Abstract: Using the empirical magnetospheric magnetic field models of Tsyganenko and Usmanov (TU), we have determined the self-consistent plasma pressure gradients and anisotropies along the midnight meridian in the near-Earth magnetosphere. By “inverting” the magnetic field, we determine what distributions of an anisotropic plasma, confined within the specified magnetic field configuration, are consistent with the magnetohydrostatic equilibrium condition, J × B = ∇ · P. The TU model, parameterized for different levels of geomagnetic activity by the Kp index, provided the magnetic field values from which J × B was numerically evaluated. A best fit solution was found that minimized the average difference between J × B and ∇ · P along an entire flux tube. Unlike previous semi-empirical models, the TU models contain magnetic stresses that can be balanced by a nearly isotropic plasma pressure with a reasonable radial gradient at the equator.
TL;DR: In this article, it was shown that the Rayleigh-Taylor instability of an accelerating incompressible, inviscid fluid layer is the result of pressure gradients, not gravitational acceleration.
Abstract: It is shown that the Rayleigh-Taylor instability of an accelerating incompressible, inviscid fluid layer is the result of pressure gradients, not gravitational acceleration. As in the classical Rayleigh-Taylor instability of a semi-infinite layer, finite fluid layers form long thin spikes whose structure is essentially independent of the initial thickness of the layer. A pressure maximum develops above the spike that effectively uncouples the flow in the spike from the rest of the fluid. Interspersed between the spikes are rising bubbles. The bubble motion is seriously affected by the thickness of the layer. For thin layers, the bubbles accelerate upwards exponentially in time and the layer thins so rapidly that it may disrupt at finite times.
TL;DR: In this paper, the depths and potential thicknesses of such hydrate formations as a function of the geothermal gradient, gas composition, and where appropriate, permafrost thickness, pressure gradient, and ocean-bottom temperature are given.
Abstract: When natural gas and water contact at low temperature and high pressure, gas hydrates can form. In colder climates (such as Alaska, Northern Canada, and Siberia) and beneath the oceans, conditions are appropriate for gas-hydrate formation. This paper gives the depths and potential thicknesses of such hydrate formations as a function of the geothermal gradient, gas composition, and where appropriate, permafrost thickness, pressure gradient, and ocean-bottom temperature.
01 Mar 1987
TL;DR: In this paper, surface pressure fluctuation spectra, coherence and convective wave speeds from zero and favorable pressure gradient turbulent boundary layers are reported for momentum Reynolds numbers from 3000 to 18,800.
Abstract: Measurements of surface pressure fluctuation spectra, coherence and convective wave speeds from zero and favorable pressure gradient turbulent boundary layers are reported for momentum Reynolds numbers from 3000 to 18,800. The acceleration parameter K is near 2 x 10 to the -7 power for the favorable pressure gradient flow. The outer variables, U sub e, tau sub w and delta sub 1 non-dimensionalize and collapse the spectra for the low to middle range of frequencies for most test cases. The grouping using the inner variable, U sub tau and gamma, collapse the spectra for the middle to high range of frequencies for all test cases. The value of p'/tau sub w was near 3.8 and 2.8 for the smallest values of d+ in the zero and favorable pressure gradient flows, respectively. The coherence exhibits a decay that is not exponential in some cases, but the Corcos similarity parameters omega Delta x/U sub c and omega Delta z/U sub c collapse the data for all test cases. The ratio of U sub c/U sub e increases with omega delta sub 1/U sub e up to omega delta sub 1/U sub e on the order of unity, where U sub c/U sub e becomes nearly constant. This was observed in the present results for both streamwise pressure gradient flows. The experimental results presented show good agreement with previous research.
TL;DR: In this article, the velocity of this flow is found as a function of the material constants, and the volume flow rate calculated, from which it is possible to construct an estimate of the elevation or depression of the surface of the weld.
Abstract: In penetration welding with a laser, the pressure in the keyhole is in excess at atmospheric pressure. A pressure gradient related to this is produced in the liquid region surrounding it, with the result that there is a flow parallel to the axis of the laser. The velocity of this flow is found as a function of the material constants, and the volume flow rate calculated. From this it is possible to construct an estimate of the elevation or depression of the surface of the weld. the shape of the surface cross section is discussed, and some deductions made about the pressure distribution in the liquid metal.