Dipole Flow Research Articles

Performance of the steady-state dipole flow test in layered aquifers

Steady-state numerical simulations of the dipole flow test in layered aquifers demonstrate that the test produces a good estimate of the equivalent hydraulic conductivity anisotropy ratio for the part of the aquifer spanned by the well chambers. The effects of chamber size, different conductivity of layers and layer location on the estimated anisotropy ratios are presented. The steady-state dipole flow test, when performed at different levels in the well, can yield estimates of the down-hole anisotropy ratio distribution. Numerical simulations also illustrate that the skin effect can significantly distort the anisotropy estimates produced by the dipole flow test. © 1997 John Wiley & Sons, Ltd.

Comparison of the SFI peculiar velocities with the IRAS 1.2-Jy gravity field

We present a comparison between the peculiar velocity fields measured from a recently completed l-band Tully–Fisher survey of field spirals (SFI) and that derived from the IRAS 1.2-Jy redshift survey galaxy distribution. The analysis is based on the expansion of these data in redshift space using smooth orthonormal functions, and is performed using low- and high-resolution expansions, with an effective smoothing scale which increases almost linearly with redshift. The effective smoothing scales at 3000 km s−1 are 1500 and 1000 km s−1 for the low- and high-resolution filters. The agreement between the high- and low-resolution SFI velocity maps is excellent. The general features in the filtered SFI and IRAS velocity fields agree remarkably well within 6000 km s−1. This good agreement between the fields allows us to determine the parameter β = Ω0.6 /b, where Ω is the cosmological density parameter, and b is the linear biasing factor. From a likelihood analysis on the SFI and IRAS modes we find that β = 0.6 ± 0.1, independently of the resolution of the modal expansion. For this value of β, the residual fields for the two filters show no systematic variations within 6000 km s−1. Most remarkable is the lack of any coherent, redshift-dependent dipole flow in the residual field.

Particle drift near an oscillating bubble

The drift of fluid particles induced by a bubble oscillating with motions typical of a single sonoluminescent bubble is considered. In the first calculation the bubble is assumed to remain spherical and to oscillate both radially, with large amplitude motion, and laterally, with a smaller amplitude. The paths of marked particles are traced by numerical integration of the velocity field. It is found that the resulting drift motion at large distances from the oscillating sphere is similar to a steady dipole flow. The strength of the dipole, however, is typically seven orders of magnitude less than the streaming motion observed in the laboratory by Lepoint–Mullie et al . A second calculation supposes that the bubble does not remain spherical but collapses asymmetrically, with one side falling inwards towards the other at a greater speed. The resulting impulse again induces a dipole motion in the far field, whose strength may be estimated on certain assumptions. It is found to be quite comparable to that observed.

Average steady nonuniform flow in stratified formations

A mathematical model of average nonuniform flow in heterogeneous stratified media is developed. The averaged Darcy's law is obtained by deriving the analytical expression of the effective conductivity tensor for media with small heterogeneities. The fundamental solution of the average flow equation (mean Green function) corresponding to the flow toward a single point source of deterministic discharge is derived. The mean head distribution is calculated for a fully penetrating well, for a finite length well in an infinite domain, and for a dipole well. The concept of equivalent conductivity is defined for use in identifying the formation conductivity properties. The procedure for identifying the mean conductivity, log conductivity variance, and vertical integral scale is suggested for the case of dipole flow.

The Assessment of Radionuclide Retardation in Fractured Crystalline Rocks

ABSTRACTThe joint Nagra/PNC Radionuclide Migration Programme has been running for over ten years in Nagra‘s Grimsel Test Site in the central Swiss Alps. The programme is specifically aimed at the further development of conceptual models of radionuclide transport in the geosphere, rigorously testing the applicability of current transport codes to quantify radionuclide migration in situ and assessing how successfully laboratory sorption data (specifically, Kd values) may be extrapolated to in situ conditions to predict radionuclide retardation in the geosphere [1]. A large series of field tracer migration experiments was carried out in a hydrologically well characterised water-bearing, complex fracture (or shear zone), increasing in complexity from simple, nonsorbing fluoresceine (a fluorescent dye), 3H, 3,4He, 82Br and 123I through weakly sorbing 22.24Na,85Sr and 86Rb to a final, long-term experiment with moderately sorbing 134,137Cs. The radionuclides were injected into a dipole flow field where the flowpath length, dipole width or shape and groundwater flow velocity were all varied. After a considerable learning period, generally good fits could be obtained between transport code predictions and subsequent field tracer breakthrough curves, suggesting that the transport codes tested were a reasonable representation of in situ conditions.

Theory of Dipole Flow in Uniform Anisotropic Aquifers

A theory of dipole flow is developed to model flow induced by a vertical circulation well consisting of injection and extraction chambers in a single borehole. Included in the theory are an analytical description of the kinematic flow structure around a vertical circulation well and the drawdown in the well chambers. Using Stokes' stream function, simple criteria are derived to determine the region of intensive recirculation. This region extends (from the dipole center) approximately five distances between chamber centers in the radial direction and two distances between chamber centers in both vertical directions. The vertical scale does not depend on anisotropy of hydraulic conductivity, and the radial scale is corrected for anisotropic aquifers. Based on these estimates, criteria are given for the selection of the appropriate aquifer model to employ in five settings, including infinite, semi‐infinite confined, semi‐infinite unconfined, finite confined, and finite unconfined aquifers. Applications of dipole flow theory are given for analytical estimation of the capture zone for recirculation wells and for simultaneous measurement of horizontal and vertical hydraulic conductivity in uniform anisotropic aquifers using steady state measurements of drawdown in the well chambers.

Modeling and measuring lateral line excitation patterns to changing dipole source locations.

In order to determine excitation patterns to the lateral line system from a nearby 50 Hz oscillating sphere, dipole flow field equations were used to model the spatial distribution of pressures along a linear array of lateral line canal pores. Modeled predictions were then compared to pressure distributions measured for the same dipole source with a miniature hydrophone placed in a small test tank used for neurophysiological experiments. Finally, neural responses from posterior lateral line nerve fibers in the goldfish were measured in the test tank to demonstrate that modeled and measured pressure gradient patterns were encoded by the lateral line periphery. Response patterns to a 50 Hz dipole source that slowly changed location along the length of the fish included (1) peaks and valleys in spike-rate responses corresponding to changes in pressure gradient amplitudes, (2) 180 degrees phase-shifts corresponding to reversals in the direction of the pressure gradient and (3) distance-dependent changes in the locations of peaks, valleys and 180 degrees phase-shifts. Modeled pressure gradient patterns also predict that the number of neural amplitude peaks and phase transitions will vary as a function of neuromast orientation and axis of source oscillation. The faithful way in which the lateral line periphery encodes pressure gradient patterns has implications for how source location and distance might be encoded by excitation patterns in the CNS. Phase-shift information may be important for (1) inhibitory/excitatory sculpting of receptive fields and (2) unambiguously encoding source distance so that increases in source distance are not confused with decreases in source amplitude.

A STIMULUS PARADIGM FOR ANALYSIS OF NEAR-FIELD HYDRODYNAMIC SENSITIVITY IN CRUSTACEANS

We present several relatively simple procedures for studying the physiology of near-field mechanoreceptors in crustaceans which extend previous measures of sensitivity. The advantages include the quantitative analysis of range fractionation and directionality of receptors and interneurons in the sensory hierarchy of the central nervous system (CNS), based on a stimulus paradigm that is reproducible and easy to use. The technical considerations for quantitative fluid-coupled stimulation addressed by this paper are the complexity of dipole flow fields, reflected interference from traveling waves, and the underlying stimulus wave form. The techniques described here offer corresponding advantages for physiological experiments using other aquatic organisms. In electrophysiological experiments, crustacean preparations are typically placed in an experimental chamber filled with water or saline solution. For studies on near-field sensory receptors, i.e. those responding to flow fields in the aquatic medium, a dipole or vibrating sphere is frequently used to generate stimulus waves (Tautz et al. 1981; Wiese and Wollnik, 1983; Ebina and Wiese, 1984; Hatt, 1986; Heinisch and Wiese, 1987; Tautz, 1987; Wiese and Marschall, 1990; Killian and Page, 1992b). A dipole stimulator is easily constructed by attaching a spherical probe to an electromechanical device such as a loudspeaker, pen motor or piezo crystal. A periodic signal fed to the transducer generates the oscillating dipole movements. With the sphere immersed in the bathing medium, dipole flow fields are generated (see Kalmijn, 1988, for further discussion of dipole sources), whereas dipole oscillations introduced at the air­saline interface generate traveling surface waves. Numerous additional devices and techniques have been used to stimulate crustacean receptors. Several involve wave motion introduced from one end of the chamber by diaphragms or paddles (Laverack, 1962b, 1963; Flood and Wilkens, 1978), by cylindrical dippers (Wilkens and Larimer, 1972; Wiese et al. 1976; Wiese and Schultz, 1982; Reichert et al. 1983) or by water drops (Laverack, 1962b; Strandburg and Krasne, 1985). Another form of fluid-coupled stimulation involves small jets of saline (Laverack, 1963; Tautz, 1990; Schmitz, 1992). In other studies, receptor hairs have been stimulated directly by using a stylus in place of the dipole, e.g. a needle or glass capillary in contact with the hair (Laverack, 1962a; Killian and Page, 1992a; Yen et al. 1992; Nagayama and Sato, 1993) or a miniature wire loop or capillary tube placed over the hair shaft (Mellon, 1963; Wiese, 1976; Tautz et al. 1981; Killian and Page, 1992b).

Anomalous dispersion in a dipole flow geometry

The dispersion of a passive tracer in fluid flowing between a source and a sink in a Hele–Shaw geometry, characteristic of field scale flows in a layer or fracture, is considered. A combination of analytic and numerical techniques and complementary experimental measurements are employed, leading to a consistent picture. This dispersion process is found to be characterized by a power-law decay in time of the tracer concentration, with an exponential cutoff at very long times, in strong contrast to the Gaussian behavior associated with the widely used quasi-one-dimensional (1-D) models.

Dipole flow test: a new single-borehole test for aquifer characterization : Kabala, Z J Water Resour ResV29, N1, Jan 1993, P99–107

Dipole flow test: a new single-borehole test for aquifer characterization : Kabala, Z J Water Resour ResV29, N1, Jan 1993, P99–107

The dipole flow test: A new single‐borehole test for aquifer characterization

A new single‐borehole measurement technique for confined aquifers, the dipole flow test, yields the vertical distributions of the horizontal hydraulic conductivity, the vertical hydraulic conductivity, and the specific storativity when applied to different borehole intervals. The test utilizes straddle packers to isolate two chambers in the borehole, pressure transducers to monitor drawdown in them, and a small pump to create a dipole flow pattern in the aquifer by pumping water at a constant rate from the aquifer into one chamber, transferring it within the well to the next chamber, and finally injecting it back to the aquifer. A mathematical model describing the drawdown in each chamber is derived for the transient as well as the steady state cases. The aquifer parameters may be estimated from data produced by the dipole flow test alone or in conjunction with conventional pumping tests. The dipole flow regime reaches a steady state relatively quickly, especially in well permeable aquifers. A robust computational methodology for estimating the aquifer parameters, suitable for automatization, is based on the Newton‐Raphson algorithm applied to a system of up to three nonlinear equations, each describing the well drawdown at a different judiciously chosen time. Due to the relatively small drawdown it invokes, the dipole flow test may be applicable to unconfined aquifers as well.

On the approach to criticality of a vibrating, macroscopic object in superfluid 3HeB

Abstract An intuitive picture of pair breaking by a vibrating wire is developed, which makes dear how quasi-particles can escape from the wire at critical velocities below the Landau critical velocity νL. Assuming strong gap suppression at the wire surface, a critical velocity of ν ∗ = ν L 5 is obtained, for ideal dipole flow around a wire of circular cross-section. In addition, a further transition to enhanced quasi-particle emission is predicted to occur at a velocity ν 1 ∗ = ν L 3 More generally, for non-dipole flow, ν ∗ = ν L (1 + 2α 1 ) and ν 1 ∗ = solν L (1 + α l where at αl characterizes the local superflow near the surface of the wire.

Searching for the great attractor

view Abstract Citations (60) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Searching for the Great Attractor Bertschinger, Edmund ; Juszkiewicz, Roman Abstract We test several scenarios for the growth of cosmic structure against recent observations of large-scale peculiar velocities, the velocity field being represented as (1) a dipole flow; (2) a spherical flow toward a great attractor; and (3) a minimal cylindrical model proposed by Faber and Burstein. We show that if the observationally derived flow models are correct, then all the theoretical scenarios we consider have difficulties. For the standard {OMEGA} = 1 biased cold dark matter (CDM) scenario, we confirm earlier conclusions based on the dipole flow model that the CDM predictions fail by a large margin. A drastic revision of the existing fits to the observational data would be required to save this scenario. The isocurvature baryon models (with {OMEGA} = 0.4) fare much better: they naturally lead to large-scale flows. However, these models have difficulty reproducing the observed velocity gradients. The cylindrical flow model constrains theories less than the spherical Great Attractor model does, illustrating the importance of extending present surveys to greater redshift. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/185312 Bibcode: 1988ApJ...334L..59B Keywords: Astronomical Models; Big Bang Cosmology; Dark Matter; Galactic Clusters; Probability Density Functions; Baryons; Normal Density Functions; Statistical Tests; Velocity Distribution; Astrophysics; COSMOLOGY; GALAXIES: CLUSTERING full text sources ADS |

Calculations pertaining to the dipole nature of the edgetone

Calculations are performed to verify the dipole nature of the edgetone in which the flow consists of an incompressible two-dimensional jet issuing from a nozzle and impinging on a fixed rigid wedge-shaped body. The wedge body is abruptly removed from a previously computed, laboratory-verified, multifrequency edgetone flow at a Reynolds number of 450 and replaced by an oscillating dipole. The dipole strength is treated as unknown and part of the solution process but is such that the combination of the dipole flow and jet flow yields a transverse jet velocity time trace near the the dipole identical to that from the previously computed edgetone flow. The resultant flow field is numerically computed for a Reynolds number of 450 and, after initial start-up effects, the flow field for the latest cycle computed strongly resembles that of the previously computed edgetone flow. Results for the jet–dipole flow are given in the form of stream function and equivorticity contour plots and jet spectra. In addition, sound-pressure radiation due to a fluctuating pressure distribution at the surface of the wedge-shaped body is computed using data from the previously calculated edgetone flow. The moduli of the computed sound-pressure components corresponding to various time frequencies reveal on polar plots a figure eight pattern in the farfield with the largest component or tone associated with the frequency of jet impingement. According to theory, this is the farfield sound pattern due to a fluctuating dipole centered at the wedge tip with axis transverse to the wedge tip.

A new model of wall pressure fluctuations

Recent work has led to a new spectral model for pressure fluctuations at a rigid plane wall bounding a turbulent boundary layer, based on an explicit representation of structures in the boundary layer near the wall—bursts and sweeps—that exchange momentum within the layer and support the shear stress there [J. M. Witting, Noise Control. Eng. J. 26, 28—43 (1986)]. The fluctuating wall pressure results from the contributions of a collection of independent bursts and sweeps. Each burst and sweep is modeled as a dipole flow that moves with the local mean flow, has a finite duration, and has the correct strength to mix the fluid through a Prandtl mixing length above and below its center. This paper describes some of the salient features and extensions of the model, emphasizing (1) the physical interpretation of the model structure and its three adjustable parameters, which are sufficient to yield predictions for all frequencies and wavelengths, (2) the ranges of frequencies and wavenumbers over which the model...