Core Of Maximum Velocity Research Articles

Bottom water flows in the tropical fractures of the Northern Mid-Atlantic Ridge

The goal of this paper is to study the flows of Antarctic Bottom Water through the fracture zones in the northern part of the Mid-Atlantic Ridge based on the Conductivity-Temperature-Depth and Lowered Acoustic Doppler Current Profiler observations in 2014, 2015, and 2016. We measured the thermohaline properties and velocities and analyzed the flows of bottom water in the Strakhov, Bogdanov, nameless (07°28′N), Vernadsky, Doldrums, Arkhangelsky, Ten Degree, Vema, Marathon, Fifteen Twenty, and Kane fracture zones. These abyssal channels connect the deep basins of the East and West Atlantic. In addition to the known fact that the main portion of water propagates through the Vema Fracture Zone (11°N), we estimated that additionally a half of this volume propagates through the other fractures. Nevertheless, the pathway for the coldest water is located in the Vema Fracture Zone. Velocities of bottom currents in this fracture reach 45 cm/s. We found strong difference in the structure and transport through the Vema Fracture Zone based on four sections across the fracture occupied in 3 years from 2014 to 2016. The transport varies from 0.7 to 1.2 Sv. The core of maximum velocity in the main channel of this fracture changes its depth between 4000 m and the bottom at 4650 m. The total transport through the other fracture zones is as high as 0.48 ± 0.05 Sv.

Experimental analysis of cross‐sectional flow motion in a large amplitude meandering bend

AbstractFlow in meandering bends is characterized by the formation of a large cross‐sectional central‐region circulation cell. The width‐to‐depth ratio is one of the most important parameters affecting the entity of the cross‐circulation motion. In steep outside bends, beside the central‐region cell, a counter‐rotating circulation cell often forms in the upper part of the outer‐bank. In spite of its practical importance, the evolving mechanisms of both the circulation cells and their role on boundary shear stress distribution in bends are not yet fully understood. The aim of the present paper is to gain some insight into how cross‐sectional flow motion evolves along meandering bends. Experiments have been carried out in a laboratory meandering channel of large amplitude, over a deformed‐rigid bed, for two values of the width‐to‐depth ratio. The three‐dimensional flow velocity field has been measured in detail at five cross‐sections, almost equally spaced along the channel reach between two consecutive apex sections. The measurements have been carried out on a fine grid by an acoustic Doppler velocity profiler. The distributions of the cross‐sectional flow (e.g. cross‐sectional flow velocity, net transversal flux) and turbulent kinetic energy are analyzed in each investigated section. Measurements show that the counter‐rotating circulation cell is evident only in the case of ‘small’ width‐to‐depth ratio. Such circulation cell begins at the bend entrance and it is fully developed at the bend apex; then it decays. At the bend apex, the core of maximum velocity is found near the bed at about the separation between the central and the outer‐bank circulation cells. Moreover, the presence of the counter‐rotating circulation cell allows the bank shear stress to maintain low values in the outer‐side of the bend. Copyright © 2010 John Wiley & Sons, Ltd.

Electro-osmotic flow in a sector microchannel

The study presents analytical solutions of electro-osmotic flow in a sector microchannel with particular emphasis on the corner effects. The analytical solutions are obtained by the method of eigenfunction expansions in sequel for steady state, starting transient flow and oscillatory flow. It is shown that the smaller the opening angle is, the faster the flow approaches to steady state. For large nondimensional electrokinetic lengths, especially near an obtuse corner, a core of maximum velocity is soon established after the flow is started. The oscillatory flow exhibits phase lags between different modes that depend on their eigenvalues as well as the frequency of the externally applied voltage, hence distinguishing itself significantly from the steady state solution. This fact has an important physical implication about fast mixing of electrolytes in microchannels.

Experiments in a high‐amplitude Kinoshita meandering channel: 1. Implications of bend orientation on mean and turbulent flow structure

Meandering rivers exhibit complex planform patterns with both upstream and downstream valley oriented meander bends. In order to describe the effects of bend orientation on long‐term river evolution, it is of great importance to be able to describe bend orientation (curvature) effects on the hydrodynamics of the flow as a first approximation. Mean flow and turbulence characteristics were investigated experimentally in a periodic, asymmetric, meandering channel herein called “the Kinoshita channel”. The channel planform configuration retains high‐order harmonic modes. Upstream and downstream valley oriented meander bends can be studied by reversing the flow. A flat, smooth bed (without sediment) condition has been considered to avoid further complexity. Spatial distributions of mean flow (e.g., velocities) and turbulence parameters (Reynolds stresses, turbulent kinetic energy) were observed at several cross sections along the meander wavelength. Measurements show that at the bend apex, the core of maximum velocity is found near the inner bank for both planform orientations. At the same cross section, observations show that when bends are oriented upstream valley, the secondary flow is not as well developed as in the case where bends are oriented downstream valley. Furthermore, for the upstream condition the energy gradient is smaller than that for the downstream condition, suggesting that the friction (i.e., flow resistance) due to curvature is higher for the downstream‐skewed condition. Implications about having upstream and downstream bends in the meandering river migration framework are also discussed herein.

Variability of subtidal current structure in a fjord estuary: Puget Sound, Washington

Simultaneous observations of currents and water properties were made in a section across East Passage in Puget Sound over a 31‐day period between March and April 1983. These observations, supplemented with CTD profiles, shore‐based wind data, and far‐field current measurements, were used to describe the cross‐channel variability of subtidal currents. The mean circulation consisted of seaward flow in the near surface and landward flow below 7 m, with a core of maximum velocity at mid‐depth. Volume transport was 22,000 m3/s. Topographic effects force most of the seaward compensating flow through an adjacent channel, creating a clockwise circulation around an intervening island. Empirical orthogonal function analysis was used to describe the spatial structure of current fluctuations. At subtidal time scales, three circulation modes are evident: (1) a near‐surface (upper 20 m), wind‐driven shear; (2) a near‐bottom layer (150–200 m) dominated by density currents that propagate up estuary after generation during neap tidal mixing at the entrance sill to Puget Sound; and (3) an intermediate layer (25–75 m) influenced by partial refluxing of Colvos Passage water and modulated at fortnightly periods by nonlinear mixed tides. These current observations are the first to show recirculation of seaward flowing water from Colvos Passage to landward flow in East Passage.

PROPAGATION OF SYSTEMATIC ERRORS IN A ONE LAYER PRIMITIVE-EQUATION MODEL FOR SYNOPTIC SCALE MOTION

Abstract A one-layer, mid-latitude, beta-plane channel model of an incompressible homogeneous fluid is constructed to study the propagation of systematic errors on a nearly stationary synoptic scale wave. A time- and space-centered difference scheme is used to evaluate the governing primitive equations. Data fields resulting from height field perturbations injected at various locations in the synoptic wave are compared to the unperturbed synoptic wave at 3-hr intervals for 5 model days. Results show that the low-frequency or quasi-geostrophic component of the error tends to move toward the core of maximum velocity in the basic state and that, after 5 days, these maximum height errors are in the core regardless of the location of the initial perturbation.