3D analysis of eddy current loss in the permanent magnet coupling.

PubMed

Zhu, Zina; Meng, Zhuo

2016-07-01

This paper first presents a 3D analytical model for analyzing the radial air-gap magnetic field between the inner and outer magnetic rotors of the permanent magnet couplings by using the Amperian current model. Based on the air-gap field analysis, the eddy current loss in the isolation cover is predicted according to the Maxwell's equations. A 3D finite element analysis model is constructed to analyze the magnetic field spatial distributions and vector eddy currents, and then the simulation results obtained are analyzed and compared with the analytical method. Finally, the current losses of two types of practical magnet couplings are measured in the experiment to compare with the theoretical results. It is concluded that the 3D analytical method of eddy current loss in the magnet coupling is viable and could be used for the eddy current loss prediction of magnet couplings.

Impact of Preferred Eddy Tracks on Transport and Mixing in the Eastern South Pacific

NASA Astrophysics Data System (ADS)

Belmadani, A.; Donoso, D.; Auger, P. A.; Chaigneau, A.

2017-12-01

Mesoscale eddies, which play a fundamental role in the transport of mass, heat, nutrients, and biota across the oceans, have been suggested to propagate preferently along specific tracks. These preferred pathways, also called eddy trains, are near-zonal due to westward drift of individual vortices, and tend to be polarized (ie alternatively dominated by anticyclonic/cyclonic eddies), coinciding with the recently discovered latent striations (quasi-zonal mesoscale jet-like features). While significant effort has been made to understand the dynamics of striations and their interplay with mesoscale eddies, the impact of repeated eddy tracks on physical (temperature, salinity), biogeochemical (oxygen, carbon, nutrients) and other tracers (e.g. chlorophyll, marine debris) has received little attention. Here we report on the results of numerical modeling experiments that simulate the impact of preferred eddy tracks on the transport and mixing of water particles in the Eastern South Pacific off Chile. A 30-year interannual simulation of the oceanic circulation in this region has been performed over 1984-2013 with the ROMS (Regional Oceanic Modeling System) at an eddy-resolving resolution (10 km). Objective tracking of mesoscale coherent vortices is obtained using automated methods, allowing to compute the contribution of eddies to the ocean circulation. Preferred eddy tracks are further isolated from the more random eddies, by comparing the distances between individual tracks and the striated pattern in long-term mean eddy polarity with a least-squares approach. The remaining non-eddying flow may also be decomposed into time-mean and anomalous circulation, and/or small- and large-scale circulation. Neutrally-buoyant Lagrangian floats are then released uniformly into the various flow components as well as the total flow, and tracked forward in time with the ARIANE software. The dispersion patterns of water particles are used to estimate the respective contributions of organized and random eddies, mean flow, large-scale perturbations etc. to mixing properties and transport pathways. Float release into the full flow inside selected vortices is also used to document the impact of eddy trains on the transformation of water masses inferred from changes in temperature/salinity along float trajectories.

PolarWinds I & II

Atmospheric Science Data Center

2018-04-20

... (Organized Large Eddies), and near surface winds over open water, transitional ice zones and the Greenland Ice Cap. Polar Winds I was ... total, twenty-four individual missions with over 80 hours of research flights were flown in the Arctic region near Greenland and Iceland ...

HELLFIRE 6-DOF Simulation Validation for Stockpile Reliability Program with Seeker Test Data

DTIC Science & Technology

1994-09-12

Research, Development and Engineering Centeri U.S. Army Missile Command Willy Albanes and Eddie Hammons COLSA Corporation Lisa Collins AMTEC Corporation I...I 3 AMTEC Corporation ATTN: Lisa Collins 500 Wynn Drive, Suite 314 H

Frontal Eddy Dynamics (FRED) experiment off North Carolina: Volume 1. Executive summary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ebbesmeyer, C.C.

1989-03-01

In preparation for oil and gas lease sales on the outer continental shelf offshore of North Carolina, the Minerals Management Service was requested to investigate the potential transport and impacts of oil spilled offshore. The Gulf Stream and associated eddies are an important aspect of the transport. Although the speed and location of the Gulf Stream are reasonably well known, knowledge of the meanders of the Gulf Stream is limited. How the circulatory structure and movement of associated frontal eddies and filaments affect the North Carolina coastal waters is not clear. This study investigates the interactions of these circulatory elementsmore » and follows the evolution of frontal eddies as they migrate along the North Carolina coast.« less

Magnetic diagnostics for equilibrium reconstructions with eddy currents on the lithium tokamak experimenta)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmitt, J. C.; Bialek, J.; Lazerson, S.

2014-11-01

The Lithium Tokamak eXperiment is a spherical tokamak with a close-fitting low-recycling wall composed of thin lithium layers evaporated onto a stainless steel-lined copper shell. Long-lived non-axisymmetric eddy currents are induced in the shell and vacuum vessel by transient plasma and coil currents and these eddy currents influence both the plasma and the magnetic diagnositc signals that are used as constraints for equilibrium reconstruction. A newly installed set of re-entrant magnetic diagnostics and internal saddle flux loops, compatible with high-temperatures and lithium environments, is discussed. Details of the axisymmetric (2D) and non-axisymmetric (3D) treatments of the eddy currents and themore » equilibrium reconstruction are presented.« less

Modeling uncertainty of evapotranspiration measurements from multiple eddy covariance towers over a crop canopy

USDA-ARS?s Scientific Manuscript database

All measurements have random error associated with them. With fluxes in an eddy covariance system, measurement error can been modelled in several ways, often involving a statistical description of turbulence at its core. Using a field experiment with four towers, we generated four replicates of meas...

From mesoscale eddies to small-scale turbulence in the Antarctic Circumpolar Current

NASA Astrophysics Data System (ADS)

Naveira Garabato, A.; Brearley, J. A.; Sheen, K. L.; Waterman, S. N.

2012-12-01

A foremost question in physical oceanography is that of how the oceanic mesoscale dissipates. The Antarctic Circumpolar Current (ACC), in the Southern Ocean, is forced strongly by the wind and hosts a vigorous mesoscale eddy field. It has been recently suggested that substantial dampening of mesoscale flows in the region may occur through interactions with topography, on the basis of a number of indirect approaches. Here, we present the first direct evidence of a transfer of energy between mesoscale eddies and small-scale turbulence in the ACC, via the radiation, instability and breaking of internal waves generated as mesoscale flows impinge on rough topography. The evidence is provided by analysis of two data sets gathered by the DIMES (Diapycnal and Isopycnal Experiment in the Southern Ocean) experiment: (1) the observations of a mooring cluster, specifically designed to measure dynamical exchanges between the mesoscale eddy and internal wave fields in Drake Passage over a 2-year deployment; and (2) an extensive fine- and microstructure survey of the region. The physical mechanisms implicated in the cascade of energy across scales will be discussed.

Eddy current spectroscopy for near-surface residual stress profiling in surface treated nonmagnetic engine alloys

NASA Astrophysics Data System (ADS)

Abu-Nabah, Bassam A.

Recent research results indicated that eddy current conductivity measurements can be exploited for nondestructive evaluation of near-surface residual stresses in surface-treated nickel-base superalloy components. Most of the previous experimental studies were conducted on highly peened (Almen 10-16A) specimens that exhibit harmful cold work in excess of 30% plastic strain. Such high level of cold work causes thermo-mechanical relaxation at relatively modest operational temperatures; therefore the obtained results were not directly relevant to engine manufacturers and end users. The main reason for choosing peening intensities in excess of recommended normal levels was that in low-conductivity engine alloys the eddy current penetration depth could not be forced below 0.2 mm without expanding the measurements above 10 MHz which is beyond the operational range of most commercial eddy current instruments. As for shot-peened components, it was initially felt that the residual stress effect was more difficult to separate from cold work, texture, and inhomogeneity effects in titanium alloys than in nickel-base superalloys. In addition, titanium alloys have almost 50% lower electric conductivity than nickel-base superalloys; therefore require proportionally higher inspection frequencies, which was not feasible until our recent breakthrough in instrument development. Our work has been focused on six main aspects of this continuing research, namely, (i) the development of an iterative inversion technique to better retrieve the depth-dependent conductivity profile from the measured frequency-dependent apparent eddy current conductivity (AECC), (ii) the extension of the frequency range up to 80 MHz to better capture the peak compressive residual stress in nickel-base superalloys using a new eddy current conductivity measuring system, which offers better reproducibility, accuracy and measurement speed than the previously used conventional systems, (iii) the lift-off effect on high frequency eddy current spectroscopy, (iv) the development of custom-made spiral coils to allow eddy current conductivity characterization over the whole frequency range of interest with reduced coil sensitivity to lift off, (v) the benefits of implementing a semi-quadratic system calibration in reducing the coil sensitivity to lift-off, and (vi) the feasibility of adapting high-frequency eddy current residual stress characterization for shot-peened titanium alloys.

Non-steady wind turbine response to daytime atmospheric turbulence.

PubMed

Nandi, Tarak N; Herrig, Andreas; Brasseur, James G

2017-04-13

Relevant to drivetrain bearing fatigue failures, we analyse non-steady wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and the rotating blades of a GE 1.5 MW wind turbine using a unique dataset from a GE field experiment and computer simulation. Time-resolved local velocity data were collected at the leading and trailing edges of an instrumented blade together with generator power, revolutions per minute, pitch and yaw. Wind velocity and temperature were measured upwind on a meteorological tower. The stability state and other atmospheric conditions during the field experiment were replicated with a large-eddy simulation in which was embedded a GE 1.5 MW wind turbine rotor modelled with an advanced actuator line method. Both datasets identify three important response time scales: advective passage of energy-dominant eddies (≈25-50 s), blade rotation (once per revolution (1P), ≈3 s) and sub-1P scale (<1 s) response to internal eddy structure. Large-amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the aerofoil plane, modulated by eddy passage at longer time scales. Generator power responds strongly to large-eddy wind modulations. We show that internal dynamics of the blade boundary layer near the trailing edge is temporally modulated by the non-steady external flow that was measured at the leading edge, as well as blade-generated turbulence motions.This article is part of the themed issue 'Wind energy in complex terrains'. © 2017 The Author(s).

Non-steady wind turbine response to daytime atmospheric turbulence

PubMed Central

Nandi, Tarak N.; Herrig, Andreas

2017-01-01

Relevant to drivetrain bearing fatigue failures, we analyse non-steady wind turbine responses from interactions between energy-dominant daytime atmospheric turbulence eddies and the rotating blades of a GE 1.5 MW wind turbine using a unique dataset from a GE field experiment and computer simulation. Time-resolved local velocity data were collected at the leading and trailing edges of an instrumented blade together with generator power, revolutions per minute, pitch and yaw. Wind velocity and temperature were measured upwind on a meteorological tower. The stability state and other atmospheric conditions during the field experiment were replicated with a large-eddy simulation in which was embedded a GE 1.5 MW wind turbine rotor modelled with an advanced actuator line method. Both datasets identify three important response time scales: advective passage of energy-dominant eddies (≈25–50 s), blade rotation (once per revolution (1P), ≈3 s) and sub-1P scale (<1 s) response to internal eddy structure. Large-amplitude short-time ramp-like and oscillatory load fluctuations result in response to temporal changes in velocity vector inclination in the aerofoil plane, modulated by eddy passage at longer time scales. Generator power responds strongly to large-eddy wind modulations. We show that internal dynamics of the blade boundary layer near the trailing edge is temporally modulated by the non-steady external flow that was measured at the leading edge, as well as blade-generated turbulence motions. This article is part of the themed issue ‘Wind energy in complex terrains’. PMID:28265026

Atmosphere surface storm track response to resolved ocean mesoscale in two sets of global climate model experiments

NASA Astrophysics Data System (ADS)

Small, R. Justin; Msadek, Rym; Kwon, Young-Oh; Booth, James F.; Zarzycki, Colin

2018-05-01

It has been hypothesized that the ocean mesoscale (particularly ocean fronts) can affect the strength and location of the overlying extratropical atmospheric storm track. In this paper, we examine whether resolving ocean fronts in global climate models indeed leads to significant improvement in the simulated storm track, defined using low level meridional wind. Two main sets of experiments are used: (i) global climate model Community Earth System Model version 1 with non-eddy-resolving standard resolution or with ocean eddy-resolving resolution, and (ii) the same but with the GFDL Climate Model version 2. In case (i), it is found that higher ocean resolution leads to a reduction of a very warm sea surface temperature (SST) bias at the east coasts of the U.S. and Japan seen in standard resolution models. This in turn leads to a reduction of storm track strength near the coastlines, by up to 20%, and a better location of the storm track maxima, over the western boundary currents as observed. In case (ii), the change in absolute SST bias in these regions is less notable, and there are modest (10% or less) increases in surface storm track, and smaller changes in the free troposphere. In contrast, in the southern Indian Ocean, case (ii) shows most sensitivity to ocean resolution, and this coincides with a larger change in mean SST as ocean resolution is changed. Where the ocean resolution does make a difference, it consistently brings the storm track closer in appearance to that seen in ERA-Interim Reanalysis data. Overall, for the range of ocean model resolutions used here (1° versus 0.1°) we find that the differences in SST gradient have a small effect on the storm track strength whilst changes in absolute SST between experiments can have a larger effect. The latter affects the land-sea contrast, air-sea stability, surface latent heat flux, and the boundary layer baroclinicity in such a way as to reduce storm track activity adjacent to the western boundary in the N. Hemisphere storm tracks, but strengthens the storm track over the southern Indian Ocean. A note of caution is that the results are sensitive to the choice of storm track metric. The results are contrasted with those from a high resolution coupled simulation where the SST is smoothed for the purposes of computing air-sea fluxes, an alternative method of testing sensitivity to SST gradients.

The eddy cannon

NASA Astrophysics Data System (ADS)

Pichevin, Thierry; Nof, Doron

1996-09-01

A new nonlinear mechanism for the generation of "Meddies" by a cape is proposed. The essence of the new process is that the flow-force associated with any steady current that curves back on itself around a cape cannot be balanced without generating and shedding eddies. The process is modeled as follows. A westward flowing density current advances along a zonal wall and turns eastward after reaching the edge of the wall (i.e. the Cape of St Vincent). Integration of the steady (and inviscid) momentum equation along the wall gives the long-shore flow-force and shows that, no matter what the details of the turning process are, such a scenario is impossible. It corresponds to an unbalanced flow-force and, therefore, cannot exist. Namely, in an analogy to a rocket, the zonal longshore current forces the entire system to the west. A flow field that can compensate for such a force is westward drifting eddies that push the system to the east. In a similar fashion to the backward push associated with a firing cannon, the westward moving eddies (bullets) balance the integrated momentum of the flow around the cape. Nonlinear solutions are constructed analytically using an approach that enables one to compute the eddies' size and generation frequency without solving for the incredibly complicated details of the generation process itself. The method takes advantage of the fact that, after each eddy is generated, the system returns to its original structure. It is based on the integration of the momentum equation (for periodic flows) over a control volume and a perturbation expansion in ɛ, the ratio between the eddies' westward drift and the parent current speed. It is found that, because of the relatively small size of the Mediterranean eddies, β is not a sufficiently strong mechanism to remove the eddies (from the Cape of St Vincent) at the observed frequency. It is, therefore, concluded that westward advection must also take place. Specifically, it is found that an advection of 2 cm s -1 will remove (and generate) a Meddy once every 50 days or so and an advection of 5 cm s -1 will remove a Meddy every 17 days. "Kitchen-type" laboratory experiments on a rotating table show that, indeed, a flow that curves back on itself produces an eddy next to the tip of the cape. However, since neither significant β nor advection was present in the laboratory, the laboratory eddy was not shed during the limited time that the experiment was in progress. Numerical simulations (using the Bleck and Boudra isopycnic model) demonstrate, however, that eddies are constantly shed as predicted by the model.

Processes influencing formation of low-salinity high-biomass lenses near the edge of the Ross Ice Shelf

NASA Astrophysics Data System (ADS)

Li, Yizhen; McGillicuddy, Dennis J.; Dinniman, Michael S.; Klinck, John M.

2017-02-01

Both remotely sensed and in situ observations in austral summer of early 2012 in the Ross Sea suggest the presence of cold, low-salinity, and high-biomass eddies along the edge of the Ross Ice Shelf (RIS). Satellite measurements include sea surface temperature and ocean color, and shipboard data sets include hydrographic profiles, towed instrumentation, and underway acoustic Doppler current profilers. Idealized model simulations are utilized to examine the processes responsible for ice shelf eddy formation. 3-D model simulations produce similar cold and fresh eddies, although the simulated vertical lenses are quantitatively thinner than observed. Model sensitivity tests show that both basal melting underneath the ice shelf and irregularity of the ice shelf edge facilitate generation of cold and fresh eddies. 2-D model simulations further suggest that both basal melting and downwelling-favorable winds play crucial roles in forming a thick layer of low-salinity water observed along the edge of the RIS. These properties may have been entrained into the observed eddies, whereas that entrainment process was not captured in the specific eddy formation events studied in our 3-D model-which may explain the discrepancy between the simulated and observed eddies, at least in part. Additional sensitivity experiments imply that uncertainties associated with background stratification and wind stress may also explain why the model underestimates the thickness of the low-salinity lens in the eddy interiors. Our study highlights the importance of incorporating accurate wind forcing, basal melting, and ice shelf irregularity for simulating eddy formation near the RIS edge. The processes responsible for generating the high phytoplankton biomass inside these eddies remain to be elucidated. Appendix B. Details for the basal melting and mechanical forcing by the ice shelf edge.

The nonlinear effects of the eddy viscosity and the bottom friction on the Lagrangian residual velocity in a narrow model bay

NASA Astrophysics Data System (ADS)

Deng, Fangjing; Jiang, Wensheng; Feng, Shizuo

2017-09-01

The nonlinear effects of the eddy viscosity and the bottom friction on the Lagrangian residual velocity (LRV) are studied numerically in a narrow model bay. Three groups of the experiments with different eddy viscosity and different forms of the bottom friction are designed and are carried out in the three kinds of the topography. When the eddy viscosity is obtained from a two-equation turbulence closure model, the pattern of the LRV is more complex than that of the time invariant eddy viscosity case and the intensity is from more than 1.3 times to one order smaller than that of the linear eddy viscosity condition. The LRV are also acquired when the eddy viscosity varies from the flood-averaged one to the ebb-averaged one. It is found that when the flood-averaged eddy viscosity is bigger than the ebb-averaged eddy viscosity (flood-dominated asymmetry), the direction of the breadth-averaged LRV and the 3D LRV is nearly opposite to that when the eddy viscosity asymmetry is reverse (ebb-dominated asymmetry). However, the intensity of the LRV for the ebb-dominated case decreases toward the flood-dominated case as the ratio of the maximum depth in the deep channel and the minimum depth on the shoal increases. The different forms of the bottom friction also play a role in the LRV. The structures of the 3D LRV and the depth-integrated LRV are simpler, and the intensity of the LRV is two times smaller when the linear bottom friction is used than those when the quadratic bottom friction is used.

Enhanced Nitrogen Loss by Eddy-Induced Vertical Transport in the Offshore Peruvian Oxygen Minimum Zone

PubMed Central

Callbeck, Cameron M.; Lavik, Gaute; Stramma, Lothar; Kuypers, Marcel M. M.; Bristow, Laura A.

2017-01-01

The eastern tropical South Pacific (ETSP) upwelling region is one of the ocean’s largest sinks of fixed nitrogen, which is lost as N2 via the anaerobic processes of anammox and denitrification. One-third of nitrogen loss occurs in productive shelf waters stimulated by organic matter export as a result of eastern boundary upwelling. Offshore, nitrogen loss rates are lower, but due to its sheer size this area accounts for ~70% of ETSP nitrogen loss. How nitrogen loss and primary production are regulated in the offshore ETSP region where coastal upwelling is less influential remains unclear. Mesoscale eddies, ubiquitous in the ETSP region, have been suggested to enhance vertical nutrient transport and thereby regulate primary productivity and hence organic matter export. Here, we investigated the impact of mesoscale eddies on anammox and denitrification activity using 15N-labelled in situ incubation experiments. Anammox was shown to be the dominant nitrogen loss process, but varied across the eddy, whereas denitrification was below detection at all stations. Anammox rates at the eddy periphery were greater than at the center. Similarly, depth-integrated chlorophyll paralleled anammox activity, increasing at the periphery relative to the eddy center; suggestive of enhanced organic matter export along the periphery supporting nitrogen loss. This can be attributed to enhanced vertical nutrient transport caused by an eddy-driven submesoscale mechanism operating at the eddy periphery. In the ETSP region, the widespread distribution of eddies and the large heterogeneity observed in anammox rates from a compilation of stations suggests that eddy-driven vertical nutrient transport may regulate offshore primary production and thereby nitrogen loss. PMID:28122044

Eddy current compensation for delta relaxation enhanced MR by dynamic reference phase modulation.

PubMed

Hoelscher, Uvo Christoph; Jakob, Peter M

2013-04-01

Eddy current compensation by dynamic reference phase modulation (eDREAM) is a compensation method for eddy current fields induced by B 0 field-cycling which occur in delta relaxation enhanced MR (dreMR) imaging. The presented method is based on a dynamic frequency adjustment and prevents eddy current related artifacts. It is easy to implement and can be completely realized in software for any imaging sequence. In this paper, the theory of eDREAM is derived and two applications are demonstrated. The theory describes how to model the behavior of the eddy currents and how to implement the compensation. Phantom and in vivo measurements are carried out and demonstrate the benefits of eDREAM. A comparison of images acquired with and without eDREAM shows a significant improvement in dreMR image quality. Images without eDREAM suffer from severe artifacts and do not allow proper interpretation while images with eDREAM are artifact free. In vivo experiments demonstrate that dreMR imaging without eDREAM is not feasible as artifacts completely change the image contrast. eDREAM is a flexible eddy current compensation for dreMR. It is capable of completely removing the influence of eddy currents such that the dreMR images do not suffer from artifacts.

Observed and Simulated Eddy Diffusivity Upstream of the Drake Passage

NASA Astrophysics Data System (ADS)

Tulloch, R.; Ferrari, R. M.; Marshall, J.

2012-12-01

Estimates of eddy diffusivity in the Southern Ocean are poorly constrained due to lack of observations. We compare the first direct estimate of isopycnal eddy diffusivity upstream of the Drake Passage (from Ledwell et al. 2011) with a numerical simulation. The estimate is computed from a point tracer release as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). We find that the observational diffusivity estimate of about 500m^2/s at 1500m depth is close to that computed in a data-constrained, 1/20th of a degree simulation of the Drake Passage region. This tracer estimate also agrees with Lagrangian float calculations in the model. The role of mean flow suppression of eddy diffusivity at shallower depths will also be discussed.

Numerical simulation of circular cylinders in free-fall

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romero-Gomez, Pedro; Richmond, Marshall C.

2016-02-01

In this work, we combined the use of (i) overset meshes, (ii) a 6 degree-of-freedom (6- DOF) motion solver, and (iii) an eddy-resolving flow simulation approach to resolve the drag and secondary movement of large-sized cylinders settling in a quiescent fluid at moderate terminal Reynolds numbers (1,500 < Re < 28,000). These three strategies were implemented in a series of computational fluid dynamics (CFD) solutions to describe the fluid-structure interactions and the resulting effects on the cylinder motion. Using the drag coefficient, oscillation period, and maximum angular displacement as baselines, the findings show good agreement between the present CFD resultsmore » and corresponding data of published laboratory experiments. We discussed the computational expense incurred in using the present modeling approach. We also conducted a preceding simulation of flow past a fixed cylinder at Re = 3,900, which tested the influence of the turbulence approach (time-averaging vs eddy-resolving) and the meshing strategy (continuous vs. overset) on the numerical results. The outputs indicated a strong effect of the former and an insignificant influence of the latter. The long-term motivation for the present study is the need to understand the motion of an autonomous sensor of cylindrical shape used to measure the hydraulic conditions occurring in operating hydropower turbines.« less

Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies

NASA Astrophysics Data System (ADS)

Hauss, Helena; Christiansen, Svenja; Schütte, Florian; Kiko, Rainer; Edvam Lima, Miryam; Rodrigues, Elizandro; Karstensen, Johannes; Löscher, Carolin R.; Körtzinger, Arne; Fiedler, Björn

2016-04-01

The eastern tropical North Atlantic (ETNA) features a mesopelagic oxygen minimum zone (OMZ) at approximately 300-600 m depth. Here, oxygen concentrations rarely fall below 40 µmol O2 kg-1, but are expected to decline under future projections of global warming. The recent discovery of mesoscale eddies that harbour a shallow suboxic (< 5 µmol O2 kg-1) OMZ just below the mixed layer could serve to identify zooplankton groups that may be negatively or positively affected by ongoing ocean deoxygenation. In spring 2014, a detailed survey of a suboxic anticyclonic modewater eddy (ACME) was carried out near the Cape Verde Ocean Observatory (CVOO), combining acoustic and optical profiling methods with stratified multinet hauls and hydrography. The multinet data revealed that the eddy was characterized by an approximately 1.5-fold increase in total area-integrated zooplankton abundance. At nighttime, when a large proportion of acoustic scatterers is ascending into the upper 150 m, a drastic reduction in mean volume backscattering (Sv) at 75 kHz (shipboard acoustic Doppler current profiler, ADCP) within the shallow OMZ of the eddy was evident compared to the nighttime distribution outside the eddy. Acoustic scatterers avoided the depth range between approximately 85 to 120 m, where oxygen concentrations were lower than approximately 20 µmol O2 kg-1, indicating habitat compression to the oxygenated surface layer. This observation is confirmed by time series observations of a moored ADCP (upward looking, 300 kHz) during an ACME transit at the CVOO mooring in 2010. Nevertheless, part of the diurnal vertical migration (DVM) from the surface layer to the mesopelagic continued through the shallow OMZ. Based upon vertically stratified multinet hauls, Underwater Vision Profiler (UVP5) and ADCP data, four strategies followed by zooplankton in response to in response to the eddy OMZ have been identified: (i) shallow OMZ avoidance and compression at the surface (e.g. most calanoid copepods, euphausiids); (ii) migration to the shallow OMZ core during daytime, but paying O2 debt at the surface at nighttime (e.g. siphonophores, Oncaea spp., eucalanoid copepods); (iii) residing in the shallow OMZ day and night (e.g. ostracods, polychaetes); and (iv) DVM through the shallow OMZ from deeper oxygenated depths to the surface and back. For strategy (i), (ii) and (iv), compression of the habitable volume in the surface may increase prey-predator encounter rates, rendering zooplankton and micronekton more vulnerable to predation and potentially making the eddy surface a foraging hotspot for higher trophic levels. With respect to long-term effects of ocean deoxygenation, we expect avoidance of the mesopelagic OMZ to set in if oxygen levels decline below approximately 20 µmol O2 kg-1. This may result in a positive feedback on the OMZ oxygen consumption rates, since zooplankton and micronekton respiration within the OMZ as well as active flux of dissolved and particulate organic matter into the OMZ will decline.

Interaction between Meso-scale Eddies and Sub-polar Front in the East (Japan) Sea based on ARGO, AVHRR, and Numerical Model

NASA Astrophysics Data System (ADS)

Ro, Y.; Kim, E.

2008-12-01

The East (Japan) Sea is drawing keen international attentions from broad spectrum of groups such as scientists, diplomats, and defense officers for its geopolitical situation, peculiar scientific assets recognized as miniature ocean. From physical oceanographic aspect, it is very rich with many features such as basin-wide circulation pattern, boundary currents, sub-polar front, meso-scale eddy activities and deep water formation. The circulation pattern in the East (Japan) Sea has been of major interests for its peculiar gyre, a western boundary current and its separation that resembles the currents such as Kuroshio and Gulf Stream. In relation to the gyre system in the East Sea, the formation of the East Korea Warm Current (EKWC) has brought up with many numerical experiments. Numerical experiments suggested a new idea to explain the formation of the EKWC in that the potential energy supply into the Ulleung Basin (UB) from the meso-scale eddy is a key process. This is closely linked with the baroclinic instability and the meandering of offshore component of Tsushima Warm Current. The UB has drawn attentions for its role of the formation of two major boundary currents, EKWC, North Korea Warm Current (NKCC), their interaction with the mesoscale UWE, watermass exchange between the Northern Japan Basin and UB. Numerical experiments along with hydrographic and other satellite datasets such as AVHRR, altimeter and ARGO profiles have been analyzed to understand the formation of the UWE. We found that the influence of the bottom topography and frictional forcing against lateral boundary are all closely associated with the sub-polar front. Meandering of the axis of the sub-polar front is closely linked with the separation point of the EKWC, Ulleung Warm Eddy, and other small and meso-scale eddies on the sub-polar front. These will be demonstrated with results of the numerical modeling experiments and animation movie will be presented.

How does the Red Sea outflow water interact with Gulf of Aden Eddies?

NASA Astrophysics Data System (ADS)

Ilıcak, Mehmet; Özgökmen, Tamay M.; Johns, William E.

As the Red Sea overflow water (RSOW) enters the Gulf of Aden (GOA), it interacts with a sequence of nearly barotropic, mesoscale eddies originating in the Indian Ocean. To investigate how these eddies impact the dispersal and eastward transport of the RSOW toward the Indian Ocean, a high resolution 3D regional model is employed to explore systematically the interaction between the RSOW and mesoscale eddies. Two types of experiments are conducted. In the first set, we simulate the behavior of RSOW in the presence of an idealized cyclone and an idealized anticyclone. The second type of simulation involves nesting of the regional model (ROMS) within a data-assimilating global model (HYCOM), in which a sequence of mesoscale eddies entering the Gulf of Aden is realistically captured. This simulation is integrated for one year, and includes a simple representation of the seasonality of the RSOW. Bower et al. (2002) suggest that the Red Sea overflow might be a western boundary undercurrent. Consistent with these expectations, the idealized simulations show that the preferred pathway of the RSOW in the absence of eddies is along the coast of Somalia (southern continental shelf) as a western boundary undercurrent. Simultaneously, a cyclonic circulation is generated in the far western GOA due to vortex stretching by the descending outflow. The presence of a cyclone in the western GOA increases the peak RSOW transport, but the cyclone itself rapidly loses its coherence after interacting with the rough topography in the western GOA. The presence of an anticyclone tends to block the preferred boundary pathway and inhibits the eastward transport of the RSOW. The eddies also result in substantially increased mixing of the RSOW in the western GOA. On the basis of the more realistic ROMS experiment, it is found that the modeled RSOW leaves the western part of the Gulf of Aden in short episodic bursts with transports that are an order of magnitude greater than that associated with the quasi-steady RSOW inflow into GOA. Such enhancement in RSOW transport is shown to be induced by cyclonic eddies that cause a rapid discharge of RSOW from the western part of the GOA. We conclude that mesoscale eddies play a key role in the transport and mixing of the RSOW within GOA.

Detection and Inspection of Steel Bars in Reinforced Concrete Structures Using Active Infrared Thermography with Microwave Excitation and Eddy Current Sensors

PubMed Central

Szymanik, Barbara; Frankowski, Paweł Karol; Chady, Tomasz; John Chelliah, Cyril Robinson Azariah

2016-01-01

The purpose of this paper is to present a multi-sensor approach to the detection and inspection of steel bars in reinforced concrete structures. In connection with our past experience related to non-destructive testing of different materials, we propose using two potentially effective methods: active infrared thermography with microwave excitation and the eddy current technique. In this article active infrared thermography with microwave excitation is analyzed both by numerical modeling and experiments. This method, based on thermal imaging, due to its characteriatics should be considered as a preliminary method for the assessment of relatively shallowly located steel bar reinforcements. The eddy current technique, on the other hand, allows for more detailed evaluation and detection of deeply located rebars. In this paper a series of measurement results, together with the initial identification of certain features of steel reinforcement bars will be presented. PMID:26891305

Detection and Inspection of Steel Bars in Reinforced Concrete Structures Using Active Infrared Thermography with Microwave Excitation and Eddy Current Sensors.

PubMed

Szymanik, Barbara; Frankowski, Paweł Karol; Chady, Tomasz; John Chelliah, Cyril Robinson Azariah

2016-02-16

The purpose of this paper is to present a multi-sensor approach to the detection and inspection of steel bars in reinforced concrete structures. In connection with our past experience related to non-destructive testing of different materials, we propose using two potentially effective methods: active infrared thermography with microwave excitation and the eddy current technique. In this article active infrared thermography with microwave excitation is analyzed both by numerical modeling and experiments. This method, based on thermal imaging, due to its characteriatics should be considered as a preliminary method for the assessment of relatively shallowly located steel bar reinforcements. The eddy current technique, on the other hand, allows for more detailed evaluation and detection of deeply located rebars. In this paper a series of measurement results, together with the initial identification of certain features of steel reinforcement bars will be presented.

Control of jet noise

NASA Technical Reports Server (NTRS)

Schreck, Stefan

1993-01-01

This reports describes experiments conducted at the High-Speed Jet Facility at the University of Southern California on supersonic jets. The goal of the study was to develop methods for controlling the noise emitted from supersonic jets by passive and/or active means. Work by Seiner et al (1991) indicates that eddy Mach wave radiation is the dominant noise source in a heated high speed jet. Eddy Mach radiation is caused by turbulent eddies traveling at supersonic speed in the shear layer of the jet. The convection velocity of the eddies decays with increasing distance from the nozzle exit due to the mixing of the jet stream with the ambient fluid. Once the convection speed reaches subsonic velocities, eddy Mach wave radiation ceases. To control noise, a rapid decay of the convection velocity is desired. This may be accomplished by enhanced mixing in the jet. In this study, small aspect ratio rectangular jet nozzles were tested. A flapping mode was noticed in the jets. By amplifying screech components of the jets and destabilizing the jet columns with a collar device, the flapping mode was excited. The result was a rapid decay of the jet velocity. A reduction in eddy Mach radiation in rectangular supersonic jets may be achieved with this device.

A High-Sensitivity Flexible Eddy Current Array Sensor for Crack Monitoring of Welded Structures under Varying Environment.

PubMed

Chen, Tao; He, Yuting; Du, Jinqiang

2018-06-01

This paper develops a high-sensitivity flexible eddy current array (HS-FECA) sensor for crack monitoring of welded structures under varying environment. Firstly, effects of stress, temperature and crack on output signals of the traditional flexible eddy current array (FECA) sensor were investigated by experiments that show both stress and temperature have great influences on the crack monitoring performance of the sensor. A 3-D finite element model was established using Comsol AC/DC module to analyze the perturbation effects of crack on eddy currents and output signals of the sensor, which showed perturbation effect of cracks on eddy currents is reduced by the current loop when crack propagates. Then, the HS-FECA sensor was proposed to boost the sensitivity to cracks. Simulation results show that perturbation effect of cracks on eddy currents excited by the HS-FECA sensor gradually grows stronger when the crack propagates, resulting in much higher sensitivity to cracks. Experimental result further shows that the sensitivity of the new sensor is at least 19 times that of the original one. In addition, both stress and temperature variations have little effect on signals of the new sensor.

A Laboratory Activity on the Eddy Current Brake

ERIC Educational Resources Information Center

Molina-Bolivar, J. A.; Abella-Palacios, A. J.

2012-01-01

The aim of this paper is to introduce a simple and low-cost experimental setup that can be used to study the eddy current brake, which considers the motion of a sliding magnet on an inclined conducting plane in terms of basic physical principles. We present a set of quantitative experiments performed to study the influence of the geometrical and…

Circulation in the South China Sea during summer 2000 as obtained from observations and a generalized topography-following ocean model

NASA Astrophysics Data System (ADS)

Wang, Huiqun; Yuan, Yaochu; Guan, Weibing; Lou, Ruyun; Wang, Kangshan

2004-07-01

On the basis of the recently obtained hydrographic data in the South China Sea, the improved Princeton Ocean Model with a generalized topography-following coordinate system is used to study the circulation in the region during summer 2000. Several sensitivity experiments are carried out to achieve reasonable model parameters for the South China Sea (SCS). It is shown from the resting stratification experiments that the generalized topography-following coordinate scheme is better than the standard sigma grid scheme for reducing the pressure gradient errors. The combination of sea surface height anomaly derived from TOPEX/Poseidon and numerical results with both diagnostic and semidiagnostic simulations provides a consistent circulation pattern for the SCS in August, and the main circulation features can be summarized as follows: (1) There is a notable anticyclonic warm eddy southeast of Vietnam with a horizontal scale of ˜300 km, and there is a cyclonic cold eddy. The simultaneous existence of these cold and warm eddies is one of the important circulation characteristics in the SCS during summer 2000. (2) A secondary cold eddy is found east of Vietnam. (3) The northwestern part of the SCS is dominated by an anticyclonic circulation system. (4) There is also a secondary warm eddy southwest off the Luzon Island. (5) A cyclonic eddy is found west off the Borneo Island. (6) A western intensification phenomenon obviously occurs in the SCS. The dynamical mechanisms of the above-mentioned circulation pattern in the SCS are the interaction between the wind stress and bottom topography and the joint effect of baroclinicity and relief.

The Role of Ocean Eddies in the Southern Ocean Response to Observed Greenhouse Gas Forcing

NASA Astrophysics Data System (ADS)

Bilgen, S. I.; Kirtman, B. P.

2017-12-01

The Southern Ocean (SO) is crucial to understanding the possible future response to a changing climate. This is a principal region where energy is conveyed to the ocean by the westerly winds and it is here that mesoscale ocean eddies field dominate meridional heat and momentum transport. Compared to the Arctic, the Antarctic and the surrounding SO have a "delayed warming" anthropogenic greenhouse gas (GHG) response. Understanding the role of the ocean dynamics in modulating the mesoscale atmosphere-ocean interactions in the SO in a fully coupled regime is crucial to efforts aimed at predicting the consequences of the warming and variability to the climate system. The response of model run at multiple resolutions (eddy permitting, eddy resolving) to both GHG forcing and historical forcing are examined in NCAR CCSM4 with four experiments. The first simulation, 0.5° atmosphere coupled to ocean and sea ice components with 1° resolution (LR). The second simulation uses the identical atmospheric model but coupled to 0.1° ocean and sea ice component models (HR). For the third and fourth experiments, the global ocean is simulated for LR an HR models, and a climate change scenario are produced by applying a fixed (present-day) CO2 concentration. The analysis focuses on the last 55 years of two individual 155 year simulations. We discuss results from a set of state-of-art model experiments in comparison with observational estimates and explore mechanisms by examining sea surface temperature, westerly winds, surface heat flux, ocean heat transport. In LR simulations, the patterns and mechanisms of SO changes under GHG forcing are similar to those over the historical period: warming is damped southward of the ACC and enhanced to the north, however major changes between the HR simulations are explored. We find that in recent decades the Southern Annual Mode has shown a distinct upward trend, the result of an anthropogenic global warming. Also, HR simulations show that strengthening of the SAM and associated surface wind stress have been invoked to posit enhancement in the strength of the upwelling of the MOC, and increases eddy activity of the ACC. The results also indicate that eddy-permitting models are not able to capture the eddy-driven SST response since ocean dynamics is playing crucial role in the HR simulation but not in the LR models.

Continuous assimilation of simulated Geosat altimetric sea level into an eddy-resolving numerical ocean model. I - Sea level differences. II - Referenced sea level differences

NASA Technical Reports Server (NTRS)

White, Warren B.; Tai, Chang-Kou; Holland, William R.

1990-01-01

The optimal interpolation method of Lorenc (1981) was used to conduct continuous assimilation of altimetric sea level differences from the simulated Geosat exact repeat mission (ERM) into a three-layer quasi-geostrophic eddy-resolving numerical ocean box model that simulates the statistics of mesoscale eddy activity in the western North Pacific. Assimilation was conducted continuously as the Geosat tracks appeared in simulated real time/space, with each track repeating every 17 days, but occurring at different times and locations within the 17-day period, as would have occurred in a realistic nowcast situation. This interpolation method was also used to conduct the assimilation of referenced altimetric sea level differences into the same model, performing the referencing of altimetric sea sevel differences by using the simulated sea level. The results of this dynamical interpolation procedure are compared with those of a statistical (i.e., optimum) interpolation procedure.

Multiple sensor multifrequency eddy current monitor for solidification and growth

NASA Technical Reports Server (NTRS)

Wallace, John

1990-01-01

A compact cylindrical multisensor eddy current measuring system with integral furnace was develop to monitor II-VI crystal growth to provide interfacial information, solutal segregation, and conductivities of the growth materials. The use of an array of sensors surrounding the furnace element allows one to monitor the volume of interest. Coupling these data with inverse multifrequency analysis allows radial conductivity profiles to be generated at each sensor position. These outputs were incorporated to control the processes within the melt volume. The standard eddy current system functions with materials whose electric conductivities are as low as 2E2 Mhos/m. A need was seen to extend the measurement range to poorly conducting media so the unit was modified to allow measurement of materials conductivities 4 order of magnitude lower and bulk dielectric properties. Typically these included submicron thick films and semiinsulating GaAs. This system was used to monitor complex heat transfer in grey bodies as well as semiconductor and metallic solidification.

Eddy Current Minimizing Flow Plug for Use in Flow Conditioning and Flow Metering

NASA Technical Reports Server (NTRS)

England, John Dwight (Inventor); Kelley, Anthony R. (Inventor)

2015-01-01

An eddy-current-minimizing flow plug has open flow channels formed between the plug's inlet and outlet. Each open flow channel includes (i) a first portion that originates at the inlet face and converges to a location within the plug that is downstream of the inlet, and (ii) a second portion that originates within the plug and diverges to the outlet. The diverging second portion is approximately twice the length of the converging first portion. The plug is devoid of planar surface regions at its inlet and outlet, and in fluid flow planes of the plug that are perpendicular to the given direction of a fluid flowing therethrough.

Evaluating CMEMS products in the Western Mediterranean using multiplatform in situ data and an eddy tracker

NASA Astrophysics Data System (ADS)

Mason, Evan; Burgoa, Nadia; Pascual, Ananda; Sánchez-Román, Antonio; Tintoré, Joaquín; Ruiz, Simón

2017-04-01

Assessment of three CMEMS forecast modelling products (MEDSEA, IBI and GLOBAL) available for the Western Mediterranean has been done for the period 2013-2016. The final objective is to contribute to the improvement of these products by providing feedback to the Monitoring and Forecasting Centers (MFCs). To achieve this objective, a multiplatform approach, combining in-situ and satellite data in synergy with numerical simulations is followed. We present new results on the mesoscale content of three operational models operating in the Western Mediterranean, based on standard statistical analysis and an automated eddy tracker (py-eddy-tracker, v2.1.0; Mason et al., 2014). Properties such as eddy radius, amplitude, polarity, eddy center and tracks have been produced for the three products. For each product the eddy tracker is run over the same period, at a sampling frequency of 1 day. The parameters used for the tracking are the same for each product. Eddy tracks reveal clear areas of dominance of either cyclones or anticyclones. These patterns are visible in all three products. In addition, CMEMS products have been evaluated for specific dates, using high-resolution multiplatform observations from different field experiments carried out in the Western Mediterranean. This study is a contribution to the MedSUB project, funded by Copernicus Marine Service within the Service Evolution 21-SE-CALL1.

Eddy current-nulled convex optimized diffusion encoding (EN-CODE) for distortion-free diffusion tensor imaging with short echo times.

PubMed

Aliotta, Eric; Moulin, Kévin; Ennis, Daniel B

2018-02-01

To design and evaluate eddy current-nulled convex optimized diffusion encoding (EN-CODE) gradient waveforms for efficient diffusion tensor imaging (DTI) that is free of eddy current-induced image distortions. The EN-CODE framework was used to generate diffusion-encoding waveforms that are eddy current-compensated. The EN-CODE DTI waveform was compared with the existing eddy current-nulled twice refocused spin echo (TRSE) sequence as well as monopolar (MONO) and non-eddy current-compensated CODE in terms of echo time (TE) and image distortions. Comparisons were made in simulations, phantom experiments, and neuro imaging in 10 healthy volunteers. The EN-CODE sequence achieved eddy current compensation with a significantly shorter TE than TRSE (78 versus 96 ms) and a slightly shorter TE than MONO (78 versus 80 ms). Intravoxel signal variance was lower in phantoms with EN-CODE than with MONO (13.6 ± 11.6 versus 37.4 ± 25.8) and not different from TRSE (15.1 ± 11.6), indicating good robustness to eddy current-induced image distortions. Mean fractional anisotropy values in brain edges were also significantly lower with EN-CODE than with MONO (0.16 ± 0.01 versus 0.24 ± 0.02, P < 1 x 10 -5 ) and not different from TRSE (0.16 ± 0.01 versus 0.16 ± 0.01, P = nonsignificant). The EN-CODE sequence eliminated eddy current-induced image distortions in DTI with a TE comparable to MONO and substantially shorter than TRSE. Magn Reson Med 79:663-672, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Subminiature eddy-current transducers designed to study welded joints of titanium alloys

NASA Astrophysics Data System (ADS)

Malikov, V. N.; Dmitriev, S. F.; Katasonov, A. O.; Sagalakov, A. M.; Ishkov, A. V.

2017-12-01

Eddy current transducers (ECT) are used to construct a sensor for investigating titanium sheets connected by a welded joint. The paper provides key technical information about the eddy current transducer used and describes the procedure of measurements that makes it possible to control defects in welded joints of titanium alloys. It is capable of automatically changing the filtering cutoff frequency and operating frequency of the device. Experiments were conducted on welded VT1-0 titanium plates. The paper contains the results of these measurements. The dependence data facilitates the assessment of the quality of the welded joints and helps make an educated conclusion about welding quality.

Transport induced by mean-eddy interaction: II. Analysis of transport processes

NASA Astrophysics Data System (ADS)

Ide, Kayo; Wiggins, Stephen

2015-03-01

We present a framework for the analysis of transport processes resulting from the mean-eddy interaction in a flow. The framework is based on the Transport Induced by the Mean-Eddy Interaction (TIME) method presented in a companion paper (Ide and Wiggins, 2014) [1]. The TIME method estimates the (Lagrangian) transport across stationary (Eulerian) boundaries defined by chosen streamlines of the mean flow. Our framework proceeds after first carrying out a sequence of preparatory steps that link the flow dynamics to the transport processes. This includes the construction of the so-called "instantaneous flux" as the Hovmöller diagram. Transport processes are studied by linking the signals of the instantaneous flux field to the dynamical variability of the flow. This linkage also reveals how the variability of the flow contributes to the transport. The spatio-temporal analysis of the flux diagram can be used to assess the efficiency of the variability in transport processes. We apply the method to the double-gyre ocean circulation model in the situation where the Rossby-wave mode dominates the dynamic variability. The spatio-temporal analysis shows that the inter-gyre transport is controlled by the circulating eddy vortices in the fast eastward jet region, whereas the basin-scale Rossby waves have very little impact.

Stationary Waves of the Ice Age Climate.

NASA Astrophysics Data System (ADS)

Cook, Kerry H.; Held, Isaac M.

1988-08-01

A linearized, steady state, primitive equation model is used to simulate the climatological zonal asymmetries (stationary eddies) in the wind and temperature fields of the 18 000 YBP climate during winter. We compare these results with the eddies simulated in the ice age experiments of Broccoli and Manabe, who used CLIMAP boundary conditions and reduced atmospheric CO2 in an atmospheric general circulation model (GCM) coupled with a static mixed layer ocean model. The agreement between the models is good, indicating that the linear model can be used to evaluate the relative influences of orography, diabatic heating, and transient eddy heat and momentum transports in generating stationary waves. We find that orographic forcing dominates in the ice age climate. The mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies. This concept of the ice age climate is complicated by the sensitivity of the stationary eddies to the large increase in the magnitude of the zonal mean meridional temperature gradient simulated in the ice age GCM.

An optimized velocity selective arterial spin labeling module with reduced eddy current sensitivity for improved perfusion quantification.

PubMed

Meakin, James A; Jezzard, Peter

2013-03-01

Velocity-selective (VS) arterial spin labeling is a promising method for measuring perfusion in areas of slow or collateral flow by eliminating the bolus arrival delay associated with other spin labeling techniques. However, B(0) and B(1) inhomogeneities and eddy currents during the VS preparation hinder accurate quantification of perfusion with VS arterial spin labeling. In this study, it is demonstrated through simulations and experiments in healthy volunteers that eddy currents cause erroneous tagging of static tissue. Consequently, mean gray matter perfusion is overestimated by up to a factor of 2, depending on the VS preparation used. A novel eight-segment B(1) insensitive rotation VS preparation is proposed to reduce eddy current effects while maintaining the B(0) and B(1) insensitivity of previous preparations. Compared to two previous VS preparations, the eight-segment B(1) insensitive rotation is the most robust to eddy currents and should improve the quality and reliability of VS arterial spin labeling measurements in future studies. Copyright © 2012 Wiley Periodicals, Inc.

The dependence of the oceans MOC on mesoscale eddy diffusivities: A model study

NASA Technical Reports Server (NTRS)

Marshall, John; Scott, Jeffery R.; Romanou, Anastasia; Kelley, Maxwell; Leboissetier, Anthony

2017-01-01

The dependence of the depth and strength of the ocean's global meridional overturning cells (MOC) on the specification of mesoscale eddy diffusivity (K) is explored in two ocean models. The GISS and MIT ocean models are driven by the same prescribed forcing fields, configured in similar ways, spun up to equilibrium for a range of K 's and the resulting MOCs mapped and documented. Scaling laws implicit in modern theories of the MOC are used to rationalize the results. In all calculations the K used in the computation of eddy-induced circulation and that used in the representation of eddy stirring along neutral surfaces, is set to the same value but is changed across experiments. We are able to connect changes in the strength and depth of the Atlantic MOC, the southern ocean upwelling MOC, and the deep cell emanating from Antarctica, to changes in K.

Eddy Current Testing for Detecting Small Defects in Thin Films

NASA Astrophysics Data System (ADS)

Obeid, Simon; Tranjan, Farid M.; Dogaru, Teodor

2007-03-01

Presented here is a technique of using Eddy Current based Giant Magneto-Resistance sensor (GMR) to detect surface and sub-layered minute defects in thin films. For surface crack detection, a measurement was performed on a copper metallization of 5-10 microns thick. It was done by scanning the GMR sensor on the surface of the wafer that had two scratches of 0.2 mm, and 2.5 mm in length respectively. In another experiment, metal coatings were deposited over the layers containing five defects with known lengths such that the defects were invisible from the surface. The limit of detection (resolution), in terms of defect size, of the GMR high-resolution Eddy Current probe was studied using this sample. Applications of Eddy Current testing include detecting defects in thin film metallic layers, and quality control of metallization layers on silicon wafers for integrated circuits manufacturing.

Experimental study and large eddy simulation of effect of terrain slope on marginal burning in shrub fuel beds

Treesearch

Xiangyang Zhou; Shankar Mahalingam; David Weise

2007-01-01

This paper presents a combined study of laboratory scale fire spread experiments and a three-dimensional large eddy simulation (LES) to analyze the effect of terrain slope on marginal burning behavior in live chaparral shrub fuel beds. Line fire was initiated in single species fuel beds of four common chaparral plants under various fuel bed configurations and ambient...

Coupling of electromagnetics and structural/fluid dynamics - application to the dual coolant blanket subjected to plasma disruptions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jordan, T.

Some aspects concerning the coupling of quasi-stationary electromagnetics and the dynamics of structure and fluid are investigated. The necessary equations are given in a dimensionless form. The dimensionless parameters in these equations are used to evaluate the importance of the different coupling effects. A finite element formulation of the eddy-current damping in solid structures is developed. With this formulation, an existing finite element method (FEM) structural dynamics code is extended and coupled to an FEM eddy-current code. With this program system, the influence of the eddy-current damping on the dynamic loading of the dual coolant blanket during a centered plasmamore » disruption is determined. The analysis proves that only in loosely fixed or soft structures will eddy-current damping considerably reduce the resulting stresses. Additionally, the dynamic behavior of the liquid metal in the blankets` poloidal channels is described with a simple two-dimensional magnetohydrodynamic approach. The analysis of the dimensionless parameters shows that for small-scale experiments, which are designed to model the coupled electromagnetic and structural/fluid dynamic effects in such a blanket, the same magnetic fields must be applied as in the real fusion device. This will be the easiest way to design experiments that produce transferable results. 10 refs., 7 figs.« less

Note: Void effects on eddy current distortion in two-phase liquid metal.

PubMed

Kumar, M; Tordjeman, Ph; Bergez, W; Cavaro, M

2015-10-01

A model based on the first order perturbation expansion of magnetic flux in a two-phase liquid metal flow has been developed for low magnetic Reynolds number Rem. This model takes into account the distortion of the induced eddy currents due to the presence of void in the conducting medium. Specific experiments with an eddy current flow meter have been realized for two periodic void distributions. The results have shown, in agreement with the model, that the effects of velocity and void on the emf modulation are decoupled. The magnitude of the void fraction and the void spatial frequency can be determined from the spectral density of the demodulated emf.

Seasonal Ozone Variations in the Isentropic Layer between 330 and 380 K as Observed by SAGE 2: Implications of Extratropical Cross-Tropopause Transport

NASA Technical Reports Server (NTRS)

Wang, Pi-Huan; Cunnold, Derek M.; Zawodny, Joseph M.; Pierce, R. Bradley; Olson, Jennifer R.; Kent, Geoffrey S.; Skeens, Kristi, M.

1998-01-01

To provide observational evidence on the extratropical cross-tropopause transport between the stratosphere and the troposphere via quasi-isentropic processes in the middleworld (the part of the atmosphere in which the isentropic surfaces intersect the tropopause), this report presents an analysis of the seasonal variations of the ozone latitudinal distribution in the isentropic layer between 330 K and 380 K based on the measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) II. The results from SAGE II data analysis are consistent with (1) the buildup of ozone-rich air in the extratropical middleworld through the large-scale descending mass circulation during winter, (2) the spread of ozone-rich air in the isentropic layer from midlatitudes to subtropics via quasi-isentropic transport during spring, (3) significant photochemical ozone removal and the absence of an ozone-rich supply of air to the layer during summer, and (4) air mass exchange between the subtropics and the extratropics during the summer monsoon period. Thus the SAGE II observed ozone seasonal variations in the middleworld are consistent with the existing model calculated annual cycle of the diabatic circulation as well as the conceptual role of the eddy quasi-adiabatic transport in the stratosphere-troposphere exchange reported in the literature.

A two-dimensional model study of the QBO signal in SAGE II NO2 and O3

NASA Technical Reports Server (NTRS)

Chipperfield, M. P.; Gray, L. J.; Kinnersley, J. S.; Zawodny, J.

1994-01-01

Calculations of the quasi biennial oscillation (QBO) signal in Stratospheric Aerosol and Gas Experiment (SAGE) II O3 and NO2 data between 1984 and 1991 are presented and have been investigated by using a two-dimensional model. The isentropic 2D model is a fully interactive radiative-dynamical-chemical model in which the eddy fluxes of chemical species are calculated in a consistent manner. The QBO in the model has been forced by relaxing the equatorial zonal wind toward the observations at Singapore allowing the comparison of the model with observations from specific years. The model reproduces the observed vertical structure of the equatorial ozone anomaly with the well-known transition from dynamical to photochemical control at around 28km. The model also reproduces the observed vertical structure of the SAGE II observed NO2 anomaly. The model studies have shown that it is the QBO modulation of NO2 which the main cause of QBO signal in O3 above 30 km. The model also reproduces the observed latitudinal structure of the QBO signals in O3 and NO2. Due to the differing horizontal distribution of O3 and NO(y) the ozone signal shows a distinct phase change in the subtropics whereas the NO2 anomaly gives a broader signal.

Horizontal mixing in the Southern Ocean from Argo float trajectories

NASA Astrophysics Data System (ADS)

Roach, Christopher J.; Balwada, Dhruv; Speer, Kevin

2016-08-01

We provide the first observational estimate of the circumpolar distribution of cross-stream eddy diffusivity at 1000 m in the Southern Ocean using Argo float trajectories. We show that Argo float trajectories, from the float surfacing positions, can be used to estimate lateral eddy diffusivities in the ocean and that these estimates are comparable to those obtained from RAFOS floats, where they overlap. Using the Southern Ocean State Estimate (SOSE) velocity fields to advect synthetic particles with imposed behavior that is "Argo-like" and "RAFOS-like" diffusivity estimates from both sets of synthetic particles agreed closely at the three dynamically very different test sites, the Kerguelen Island region, the Southeast Pacific Ocean, and the Scotia Sea, and support our approach. Observed cross-stream diffusivities at 1000 m, calculated from Argo float trajectories, ranged between 300 and 2500 m2 s-1, with peaks corresponding to topographic features associated with the Scotia Sea, the Kerguelen Plateau, the Campbell Plateau, and the Southeast Pacific Ridge. These observational estimates agree with previous regional estimates from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) near the Drake Passage, and other estimates from natural tracers (helium), inverse modeling studies, and current meter measurements. These estimates are also compared to the suppressed eddy diffusivity in the presence of mean flows. The comparison suggests that away from regions of strong topographic steering suppression explains both the structure and magnitude of eddy diffusivity but that eddy diffusivities in the regions of topographic steering are greater than what would be theoretically expected and the ACC experiences localized enhanced cross-stream mixing in these regions.

Tidal Residual Eddies and their Effect on Water Exchange in Puget Sound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhaoqing; Wang, Taiping

Tidal residual eddies are one of the important hydrodynamic features in tidally dominant estuaries and coastal bays, and they could have significant effects on water exchange in a tidal system. This paper presents a modeling study of tides and tidal residual eddies in Puget Sound, a tidally dominant fjord-like estuary in the Pacific Northwest coast, using a three-dimensional finite-volume coastal ocean model. Mechanisms of vorticity generation and asymmetric distribution patterns around an island/headland were analyzed using the dynamic vorticity transfer approach and numerical experiments. Model results of Puget Sound show that a number of large twin tidal residual eddies existmore » in the Admiralty Inlet because of the presence of major headlands in the inlet. Simulated residual vorticities near the major headlands indicate that the clockwise tidal residual eddy (negative vorticity) is generally stronger than the anticlockwise eddy (positive vorticity) because of the effect of Coriolis force. The effect of tidal residual eddies on water exchange in Puget Sound and its sub-basins were evaluated by simulations of dye transport. It was found that the strong transverse variability of residual currents in the Admiralty Inlet results in a dominant seaward transport along the eastern shore and a dominant landward transport along the western shore of the Inlet. A similar transport pattern in Hood Canal is caused by the presence of tidal residual eddies near the entrance of the canal. Model results show that tidal residual currents in Whidbey Basin are small in comparison to other sub-basins. A large clockwise residual circulation is formed around Vashon Island near entrance of South Sound, which can potentially constrain the water exchange between the Central Basin and South Sound.« less

Characterization and optimization of spiral eddy current coils for in-situ crack detection

NASA Astrophysics Data System (ADS)

Mandache, Catalin

2018-03-01

In-situ condition-based maintenance is making strides in the aerospace industry and it is seen as an alternative to scheduled, time-based maintenance. With fatigue cracks originating from fastener holes as the main reason for structural failures, embedded eddy current coils are a viable non-invasive solution for their timely detection. The development and potential broad use of these coils are motivated by a few consistent arguments: (i) inspection of structures of complicated geometries and hard to access areas, that often require disassembly, (ii) alternative to regular inspection actions that could introduce inadvertent damage, (iii) for structures that have short inspection intervals, and (iv) for repaired structures where fastener holes contain bushings and prevent further bolt-hole inspections. Since the spiral coils are aiming at detecting radial cracks emanating from the fastener holes, their design parameters should allow for high inductance, low ohmic losses and power requirements, as well as optimal size and high sensitivity to discontinuities. In this study, flexible, surface conformable, spiral eddy current coils are empirically investigated on mock-up specimens, while numerical analysis is performed for their optimization and design improvement.

Effects of Mesoscale Eddies in the Active Mixed Layer: Test of the Parametrisation in Eddy Resolving Simulations

NASA Technical Reports Server (NTRS)

Luneva, M. V.; Clayson, C. A.; Dubovikov, Mikhail

2015-01-01

In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200-207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1-2 degrees and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher (0.5-0.74) correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.

Tracer transport in the tropical lower stratosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trepte, C.R.

1993-12-31

Distributions of aerosol extinction ratio ({beta}{sub r}) and ozone, derived from the Stratospheric Aerosol and Gas Experiment (SAGE I/II) satellite experiments (1979-1981 and 1984-1992), are used in conjunction with conventional meteorological analyses to deduce patterns of stratospheric tracer transport. Following volcanic eruptions at low latitudes, the aerosol observations suggest that two transport regimes exist in the tropical lower stratosphere. Aerosols disperse rapidly poleward and downward within a layer several kilometers above the tropopause. More pronounced transport is biased toward the winter hemisphere. At higher altitudes, however, volcanic aerosols tend to remain over the equator in a reservoir bounded by strongmore » meridional gradients near 20{degrees}N and S. Over the equator, enhanced lofting of aerosols occurs during QBO easterly shear, while subsidence relative to the mean meridional flow takes place during QBO westerly shear. While particle growth and evaporation effects are important, many interesting features of the aerosol distribution can only be explained by air motions. It is also shown that QBO induced ozone anomalies over the equator are also consistent with QBO aerosol variations. In the upper transport regime, the subtropical gradients of {beta}{sub r} coincide with the location of a meridional gradient in potential vorticity. Since isentropic transport is inhibited across potential vorticity gradients, the tropics are temporarily isolated from eddy mixing taking place in the winter extratropics. Zonal mean distributions of ozone; however, do not have similar meridional gradients in the subtropics. Detrainment of aerosol from the equatorial reservoir depends upon the phase of the QBO and the strength of winter eddy disturbances in the subtropics. Anticyclonic circulation systems form occasionally in the subtropics and can shear-off enhanced {beta}{sub r} air from the periphery of the aerosol reservoir.« less

Large Eddy Simulation of stratified flows over structures

NASA Astrophysics Data System (ADS)

Fuka, V.; Brechler, J.

2013-04-01

We tested the ability of the LES model CLMM (Charles University Large-Eddy Microscale Model) to model the stratified flow around three dimensional hills. We compared the quantities, as the height of the dividing streamline, recirculation zone length or length of the lee waves with experiments by Hunt and Snyder[3] and numerical computations by Ding, Calhoun and Street[5]. The results mostly agreed with the references, but some important differences are present.

Very-high-Reynolds-number vortex dynamics via Coherent-vorticity-Preserving (CvP) Large-eddy simulations

NASA Astrophysics Data System (ADS)

Chapelier, Jean-Baptiste; Wasistho, Bono; Scalo, Carlo

2017-11-01

A new approach to Large-Eddy Simulation (LES) is introduced, where subgrid-scale (SGS) dissipation is applied proportionally to the degree of local spectral broadening, hence mitigated in regions dominated by large-scale vortical motion. The proposed CvP-LES methodology is based on the evaluation of the ratio of the test-filtered to resolved (or grid-filtered) enstrophy: σ = ξ ∧ / ξ . Values of σ = 1 indicate low sub-test-filter turbulent activity, justifying local deactivation of any subgrid-scale model. Values of σ < 1 span conditions ranging from incipient spectral broadening σ <= 1 , to equilibrium turbulence σ =σeq < 1 , where σeq is solely as a function of the test-to-grid filter-width ratio Δ ∧ / Δ , derived assuming a Kolmogorov's spectrum. Eddy viscosity is fully restored for σ <=σeq . The proposed approach removes unnecessary SGS dissipation, can be applied to any eddy-viscosity model, is algorithmically simple and computationally inexpensive. A CvP-LES of a pair of unstable helical vortices, representative of rotor-blade wake dynamics, show the ability of the method to sort the coherent motion from the small-scale dynamics. This work is funded by subcontract KSC-17-001 between Purdue University and Kord Technologies, Inc (Huntsville), under the US Navy Contract N68335-17-C-0159 STTR-Phase II, Purdue Proposal No. 00065007, Topic N15A-T002.

Determining confounding sensitivities in eddy current thin film measurements

NASA Astrophysics Data System (ADS)

Gros, Ethan; Udpa, Lalita; Smith, James A.; Wachs, Katelyn

2017-02-01

Eddy current (EC) techniques are widely used in industry to measure the thickness of non-conductive films on a metal substrate. This is done by using a system whereby a coil carrying a high-frequency alternating current is used to create an alternating magnetic field at the surface of the instrument's probe. When the probe is brought near a conductive surface, the alternating magnetic field will induce ECs in the conductor. The substrate characteristics and the distance of the probe from the substrate (the coating thickness) affect the magnitude of the ECs. The induced currents load the probe coil affecting the terminal impedance of the coil. The measured probe impedance is related to the lift off between coil and conductor as well as conductivity of the test sample. For a known conductivity sample, the probe impedance can be converted into an equivalent film thickness value. The EC measurement can be confounded by a number of measurement parameters. It was the goal of this research to determine which physical properties of the measurement set-up and sample can adversely affect the thickness measurement. The eddy-current testing was performed using a commercially available, hand-held eddy-current probe (ETA3.3H spring-loaded eddy probe running at 8 MHz) that comes with a stand to hold the probe. The stand holds the probe and adjusts the probe on the z-axis to help position the probe in the correct area as well as make precise measurements. The signal from the probe was sent to a hand-held readout, where the results are recorded directly in terms of liftoff or film thickness. Understanding the effect of certain factors on the measurements of film thickness, will help to evaluate how accurate the ETA3.3H spring-loaded eddy probe was at measuring film thickness under varying experimental conditions. This research studied the effects of a number of factors such as i) conductivity, ii) edge effect, iii) surface finish of base material and iv) cable condition.

The North Pacific Acoustic Laboratory deep-water acoustic propagation experiments in the Philippine Sea.

PubMed

Worcester, Peter F; Dzieciuch, Matthew A; Mercer, James A; Andrew, Rex K; Dushaw, Brian D; Baggeroer, Arthur B; Heaney, Kevin D; D'Spain, Gerald L; Colosi, John A; Stephen, Ralph A; Kemp, John N; Howe, Bruce M; Van Uffelen, Lora J; Wage, Kathleen E

2013-10-01

A series of experiments conducted in the Philippine Sea during 2009-2011 investigated deep-water acoustic propagation and ambient noise in this oceanographically and geologically complex region: (i) the 2009 North Pacific Acoustic Laboratory (NPAL) Pilot Study/Engineering Test, (ii) the 2010-2011 NPAL Philippine Sea Experiment, and (iii) the Ocean Bottom Seismometer Augmentation of the 2010-2011 NPAL Philippine Sea Experiment. The experimental goals included (a) understanding the impacts of fronts, eddies, and internal tides on acoustic propagation, (b) determining whether acoustic methods, together with other measurements and ocean modeling, can yield estimates of the time-evolving ocean state useful for making improved acoustic predictions, (c) improving our understanding of the physics of scattering by internal waves and spice, (d) characterizing the depth dependence and temporal variability of ambient noise, and (e) understanding the relationship between the acoustic field in the water column and the seismic field in the seafloor. In these experiments, moored and ship-suspended low-frequency acoustic sources transmitted to a newly developed distributed vertical line array receiver capable of spanning the water column in the deep ocean. The acoustic transmissions and ambient noise were also recorded by a towed hydrophone array, by acoustic Seagliders, and by ocean bottom seismometers.

Eddy current compensated double diffusion encoded (DDE) MRI.

PubMed

Mueller, Lars; Wetscherek, Andreas; Kuder, Tristan Anselm; Laun, Frederik Bernd

2017-01-01

Eddy currents might lead to image distortions in diffusion-weighted echo planar imaging. A method is proposed to reduce their effects on double diffusion encoding (DDE) MRI experiments and the thereby derived microscopic fractional anisotropy (μFA). The twice-refocused spin echo scheme was adapted for DDE measurements. To assess the effect of individual diffusion encodings on the image distortions, measurements of a grid of plastic rods in water were performed. The effect of eddy current compensation on μFA measurements was evaluated in the brains of six healthy volunteers. The use of an eddy current compensation reduced the signal variation. As expected, the distortions caused by the second encoding were larger than those of the first encoding, entailing a stronger need to compensate for them. For an optimal result, however, both encodings had to be compensated. The artifact reduction strongly improved the measurement of the μFA in ventricles and gray matter by reducing the overestimation. An effect of the compensation on absolute μFA values in white matter was not observed. It is advisable to compensate both encodings in DDE measurements for eddy currents. Magn Reson Med 77:328-335, 2017. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies

NASA Astrophysics Data System (ADS)

Hauss, H.; Christiansen, S.; Schütte, F.; Kiko, R.; Edvam Lima, M.; Rodrigues, E.; Karstensen, J.; Löscher, C. R.; Körtzinger, A.; Fiedler, B.

2015-11-01

The eastern tropical North Atlantic (ETNA) features a mesopelagic oxygen minimum zone (OMZ) at approximately 300-600 m depth. Here, oxygen concentrations rarely fall below 40 μmol O2 kg-1, but are thought to decline in the course of climate change. The recent discovery of mesoscale eddies that harbour a shallow suboxic (< 5 μmol O2 kg-1) OMZ just below the mixed layer could serve to identify zooplankton groups that may be negatively or positively affected by on-going ocean deoxygenation. In spring 2014, a detailed survey of a suboxic anticyclonic modewater eddy (ACME) was carried out near the Cape Verde Ocean Observatory (CVOO), combining acoustic and optical profiling methods with stratified multinet hauls and hydrography. The multinet data revealed that the eddy was characterized by an approximately 1.5-fold increase in total area-integrated zooplankton abundance. A marked reduction in acoustic target strength (derived from shipboard ADCP, 75kHz) within the shallow OMZ at nighttime was evident. Acoustic scatterers were avoiding the depth range between about 85 to 120 m, where oxygen concentrations were lower than approximately 20 μmol O2 kg-1, indicating habitat compression to the oxygenated surface layer. This observation is confirmed by time-series observations of a moored ADCP (upward looking, 300 kHz) during an ACME transit at the CVOO mooring in 2010. Nevertheless, part of the diurnal vertical migration (DVM) from the surface layer to the mesopelagic continued through the shallow OMZ. Based upon vertically stratified multinet hauls, Underwater Vision Profiler (UVP5) and ADCP data, four strategies have been identified followed by zooplankton in response to the eddy OMZ: (i) shallow OMZ avoidance and compression at the surface (e.g. most calanoid copepods, euphausiids), (ii) migration to the shallow OMZ core during daytime, but paying O2 debt at the surface at nighttime (e.g. siphonophores, Oncaea spp., eucalanoid copepods), (iii) residing in the shallow OMZ day and night (e.g. ostracods, polychaetes), and iv) DVM through the shallow OMZ from deeper oxygenated depths to the surface and back. For strategy (i), (ii) and (iv), compression of the habitable volume in the surface may increase prey-predator encounter rates, rendering zooplankton more vulnerable to predation and potentially making the eddy surface a foraging hotspot for higher trophic levels. With respect to long-term effects of ocean deoxygenation, we expect zooplankton avoidance of the mesopelagic OMZ to set in if oxygen levels decline below approximately 20 μmol O2 kg-1. This may result in a positive feedback on the OMZ oxygen consumption rates, since zooplankton respiration within the OMZ as well as active flux of dissolved and particulate organic matter into the OMZ will decline.

A Multi-wavenumber Theory for Eddy Diffusivities: Applications to the DIMES Region

NASA Astrophysics Data System (ADS)

Chen, R.; Gille, S. T.; McClean, J.; Flierl, G.; Griesel, A.

2014-12-01

Climate models are sensitive to the representation of ocean mixing processes. This has motivated recent efforts to collect observations aimed at improving mixing estimates and parameterizations. The US/UK field program Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES), begun in 2009, is providing such estimates upstream of and within the Drake Passage. This region is characterized by topography, and strong zonal jets. In previous studies, mixing length theories, based on the assumption that eddies are dominated by a single wavenumber and phase speed, were formulated to represent the estimated mixing patterns in jets. However, in spite of the success of the single wavenumber theory in some other scenarios, it does not effectively predict the vertical structures of observed eddy diffusivities in the DIMES area. Considering that eddy motions encompass a wide range of wavenumbers, which all contribute to mixing, in this study we formulated a multi-wavenumber theory to predict eddy mixing rates. We test our theory for a domain encompassing the entire Southern Ocean. We estimated eddy diffusivities and mixing lengths from one million numerical floats in a global eddying model. These float-based mixing estimates were compared with the predictions from both the single-wavenumber and the multi-wavenumber theories. Our preliminary results in the DIMES area indicate that, compared to the single-wavenumber theory, the multi-wavenumber theory better predicts the vertical mixing structures in the vast areas where the mean flow is weak; however in the intense jet region, both theories have similar predictive skill.

A quantitative comparison of two methods to correct eddy current-induced distortions in DT-MRI.

PubMed

Muñoz Maniega, Susana; Bastin, Mark E; Armitage, Paul A

2007-04-01

Eddy current-induced geometric distortions of single-shot, diffusion-weighted, echo-planar (DW-EP) images are a major confounding factor to the accurate determination of water diffusion parameters in diffusion tensor MRI (DT-MRI). Previously, it has been suggested that these geometric distortions can be removed from brain DW-EP images using affine transformations determined from phantom calibration experiments using iterative cross-correlation (ICC). Since this approach was first described, a number of image-based registration methods have become available that can also correct eddy current-induced distortions in DW-EP images. However, as yet no study has investigated whether separate eddy current calibration or image-based registration provides the most accurate way of removing these artefacts from DT-MRI data. Here we compare how ICC phantom calibration and affine FLIRT (http://www.fmrib.ox.ac.uk), a popular image-based multi-modal registration method that can correct both eddy current-induced distortions and bulk subject motion, perform when registering DW-EP images acquired with different slice thicknesses (2.8 and 5 mm) and b-values (1000 and 3000 s/mm(2)). With the use of consistency testing, it was found that ICC was a more robust algorithm for correcting eddy current-induced distortions than affine FLIRT, especially at high b-value and small slice thickness. In addition, principal component analysis demonstrated that the combination of ICC phantom calibration (to remove eddy current-induced distortions) with rigid body FLIRT (to remove bulk subject motion) provided a more accurate registration of DT-MRI data than that achieved by affine FLIRT.

Large-Eddy Simulation (LES) of a Compressible Mixing Layer and the Significance of Inflow Turbulence

NASA Technical Reports Server (NTRS)

Mankbadi, Mina Reda; Georgiadis, Nicholas J.; Debonis, James R.

2017-01-01

In the context of Large Eddy Simulations (LES), the effects of inflow turbulence are investigated through the Synthetic Eddy Method (SEM). The growth rate of a turbulent compressible mixing layer corresponding to operating conditions of GeobelDutton Case 2 is investigated herein. The effects of spanwise width on the growth rate of the mixing layer is investigated such that spanwise width independence is reached. The error in neglecting inflow turbulence effects is quantified by comparing two methodologies: (1) Hybrid-RANS-LES methodology and (2) SEM-LES methodology. Best practices learned from Case 2 are developed herein and then applied to a higher convective mach number corresponding to Case 4 experiments of GeobelDutton.

Estimation of Eddy Dissipation Rates from Mesoscale Model Simulations

NASA Technical Reports Server (NTRS)

Ahmad, Nashat N.; Proctor, Fred H.

2012-01-01

The Eddy Dissipation Rate is an important metric for representing the intensity of atmospheric turbulence and is used as an input parameter for predicting the decay of aircraft wake vortices. In this study, the forecasts of eddy dissipation rates obtained from the current state-of-the-art mesoscale model are evaluated for terminal area applications. The Weather Research and Forecast mesoscale model is used to simulate the planetary boundary layer at high horizontal and vertical mesh resolutions. The Bougeault-Lacarrer and the Mellor-Yamada-Janji schemes implemented in the Weather Research and Forecast model are evaluated against data collected during the National Aeronautics and Space Administration s Memphis Wake Vortex Field Experiment. Comparisons with other observations are included as well.

Correction of eddy current distortions in high angular resolution diffusion imaging.

PubMed

Zhuang, Jiancheng; Lu, Zhong-Lin; Vidal, Christine Bouteiller; Damasio, Hanna

2013-06-01

To correct distortions caused by eddy currents induced by large diffusion gradients during high angular resolution diffusion imaging without any auxiliary reference scans. Image distortion parameters were obtained by image coregistration, performed only between diffusion-weighted images with close diffusion gradient orientations. A linear model that describes distortion parameters (translation, scale, and shear) as a function of diffusion gradient directions was numerically computed to allow individualized distortion correction for every diffusion-weighted image. The assumptions of the algorithm were successfully verified in a series of experiments on phantom and human scans. Application of the proposed algorithm in high angular resolution diffusion images markedly reduced eddy current distortions when compared to results obtained with previously published methods. The method can correct eddy current artifacts in the high angular resolution diffusion images, and it avoids the problematic procedure of cross-correlating images with significantly different contrasts resulting from very different gradient orientations or strengths. Copyright © 2012 Wiley Periodicals, Inc.

Model Validation for Propulsion - On the TFNS and LES Subgrid Models for a Bluff Body Stabilized Flame

NASA Technical Reports Server (NTRS)

Wey, Thomas

2017-01-01

This paper summarizes the reacting results of simulating a bluff body stabilized flame experiment of Volvo Validation Rig using a releasable edition of the National Combustion Code (NCC). The turbulence models selected to investigate the configuration are the sub-grid scaled kinetic energy coupled large eddy simulation (K-LES) and the time-filtered Navier-Stokes (TFNS) simulation. The turbulence chemistry interaction used is linear eddy mixing (LEM).

Eddy covariance measurements of carbon dioxide, latent and sensible energy fluxes above a meadow on a mountain slope

PubMed Central

Hammerle, Albin; Haslwanter, Alois; Schmitt, Michael; Bahn, Michael; Tappeiner, Ulrike; Cernusca, Alexander; Wohlfahrt, Georg

2014-01-01

Carbon dioxide, latent and sensible energy fluxes were measured by means of the eddy covariance method above a mountain meadow situated on a steep slope in the Stubai Valley/Austria, based on the hypothesis that, due to the low canopy height, measurements can be made in the shallow equilibrium layer where the wind field exhibits characteristics akin to level terrain. In order to test the validity of this hypothesis and to identify effects of complex terrain in the turbulence measurements, data were subjected to a rigorous testing procedure using a series of quality control measures established for surface layer flows. The resulting high-quality data set comprised 36 % of the original observations, the substantial reduction being mainly due to a change in surface roughness and associated fetch limitations in the wind sector dominating during nighttime and transition periods. The validity of the high-quality data set was further assessed by two independent tests: i) a comparison with the net ecosystem carbon dioxide exchange measured by means of ecosystem chambers and ii) the ability of the eddy covariance measurements to close the energy balance. The net ecosystem CO2 exchange measured by the eddy covariance method agreed reasonably with ecosystem chamber measurements. The assessment of the energy balance closure showed that there was no significant difference in the correspondence between the meadow on the slope and another one situated on flat ground at the bottom of the Stubai Valley, available energy being underestimated by 28 and 29 %, respectively. We thus conclude that, appropriate quality control provided, the eddy covariance measurements made above a mountain meadow on a steep slope are of similar quality as compared to flat terrain. PMID:24465032

Can we reconstruct mean and eddy fluxes from Argo floats?

NASA Astrophysics Data System (ADS)

Chapman, Christopher; Sallée, Jean-Baptiste

2017-12-01

The capacity of deep velocity estimates provided by the Argo float array to reconstruct both mean and eddying quantities, such as the heat flux, is addressed using an idealized eddy resolving numerical model, designed to be representative of the Southern Ocean. The model is seeded with 450 "virtual" Argo floats, which are then advected by the model fields for 10 years. The role of temporal sampling, array density and length of the float experiment are then systematically investigated by comparing the reconstructed velocity, eddy kinetic energy and heat-flux from the virtual Argo floats with the "true" values from the model output. We find that although errors in all three quantities decrease with increasing temporal sampling rate, number of floats and experiment duration, the error approaches an asymptotic limit. Thus, as these parameters exceed this limit, only marginal reductions in the error are observed. The parameters of the real Argo array, when scaled to match those of the virtual Argo array, generally fall near to, or within, the asymptotic region. Using the numerical model, a method for the calculation of cross-stream heat-fluxes is demonstrated. This methodology is then applied to 5 years of Argo derived velocities using the ANDRO dataset of Ollitrault & Rannou (2013) in order to estimate the eddy heat flux at 1000m depth across the Polar Front in the Southern Ocean. The heat-flux is concentrated in regions downstream of large bathymetric features, consistent with the results of previous studies. 2 ± 0.5 TW of heat transport across the Polar Front at this depth is found, with more than 90% of that total concentrated in less than 20% of the total longitudes spanned by the front. Finally, the implications of this work for monitoring the ocean climate are discussed.

Role of mesoscale eddies on exchanges between coastal regions

NASA Astrophysics Data System (ADS)

Kersalé, M.; Petrenko, A. A.; Doglioli, A. M.; Nencioli, F.; Bouffard, J.; Dekeyser, I.

2012-04-01

The general circulation in the northwestern Mediterranean Sea is characterized by a cyclonic circulation. The northern part of this gyre is formed by the Northern Current (NC), which flows along the continental slope from the Ligurian Sea towards the Catalan Shelf. The NC has an important influence on the Gulf of Lion (GoL), a large continental margin in the northern part of the basin. The NC constitutes an effective dynamical barrier which blocks coastal waters on the continental shelf. The western part of the GoL is a key region for regulating the outflow from the continental shelf to the Catalan Basin. These exchanges are mainly induced by partially ageostrophic processes originating from the interaction between the NC and mesoscale activity like meanders, filaments and eddies. Both GoL and Catalan shelf are characterized by an intense mesoscale activity. Eddies in the GoL are baroclinic structures extending throughout the mixed layer (30 to 50m), often elliptic in shape and about 20-30km in diameter. Catalan eddies are characterized by a vertical extension between 70 and 100m and a diameter of about 45km. The LAgrangian Transport EXperiment (LATEX, 2008-2011) was designed to study the mechanisms of formation of anticyclones in the western part of the GoL and their influence on cross-shelf exchanges. Mesoscale anticyclones have been observed in the western part of the GoL and over the Catalan shelf by the combined use of data from satellite observations, in situ measurements and numerical modeling. Recent numerical experiments show an anticyclonic circulation extending over a large part of the coastal area (latitudinal range : 41°50' to 43°N ; longitudinal range : 3°10' to 4°10'E). Interaction with a meander of the NC induces the separation of this circulation in two different eddies, one in the GoL and the other in the Catalan shelf. These eddies exhibit strong interaction between them, resulting in important exchanges between the two coastal regions. On one hand the Catalan eddy causes a heat transfer to the GoL; and, on the other hand, the interaction between the GoL eddy and a topographic barrier (Cap Creus) leads to a transfer of energy to the Catalan eddy. In order to quantify this exchange, a balance of kinetic energy has been analyzed from the model results. Numerical results are also discussed in comparison with in situ observations collected during the Latex09 campaign (August 24-28, 2009). The analysis of Sea Surface Temperature (SST) satellite images, Acoustic Doppler Current Profiler (ADCP) and Lagrangian drifter trajectories, confirmed the above interpretation derived from numerical model.

Computer studies of baroclinic flow. [Atmospheric General Circulation Experiment

NASA Technical Reports Server (NTRS)

Gall, R.

1985-01-01

Programs necessary for computing the transition curve on the regime diagram for the atmospheric general circulation experiment (AGOE) were completed and used to determine the regime diagram for the rotating annulus and some axisymmetric flows for one possible AGOE configuration. The effect of geometrical constraints on the size of eddies developing from a basic state is being examined. In AGOE, the geometric constraint should be the width of the shear zone or the baroclinic zone. Linear and nonlinear models are to be used to examine both barotropic and baroclinic flows. The results should help explain the scale selection mechanism of baroclinic eddies in the atmosphere experimental models such as AGOE, and the multiple vortex phenomenon in tornadoes.

Prospects and Techniques for Eddy-Resolving Acoustic Tomography in the Eastern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Caruthers, J. W.; Nechaev, D.; Roman, D. A.; Sidorovskaia, N. A.; Ioup, G. E.; Ioup, J.; Yaremchuk, M.

2007-05-01

For several decades monitoring and modeling the dynamics and physical structure of the Gulf of Mexico have been major efforts undertaken by oceanographers of the United States and other American countries. There are very interesting physical oceanographic features in the Gulf, not the least of which are the Gulf Loop Current and the eddies it spawns. Satellite sensing of IR and altimeter imagery has been a major input to modeling those features. Such efforts are very important to the economy and well being of much of the United States and Mexico, including fisheries, mineral economies, hurricane strengths and paths in the summer, and severe snow storms in the eastern US in the winter. A major shortcoming of the present monitoring of the Gulf is the lack of subsurface input to the dynamic models of the Gulf. Acoustic tomography is a viable means of providing that missing input. Several universities have come together to investigate the prospects for establishing a Gulf Eddy Monitoring System (GEMS) for the deep eastern half of the Gulf using acoustic tomography. The group has conducted several acoustics experiments and propagation studies to determine the feasibility of long-range propagation in the eastern Gulf and the mitigation of adverse effects on marine mammal populations in that region under the Office of Naval Research project entitled the Littoral Acoustic Demonstration Center (LADC). The group has also convened an invited session for the 9th World Multiconference on Systemics, Cybernetics and Informatics (WMSCI 2005) Orlando, FL, July 2005. This paper discusses prospects for establishing the GEMS tomographic system, its technical characteristics, and its contributions to advancing the knowledge of the dynamics of the Gulf. This presentation will concentrate on the characteristics of a single-slice tomographic system, called GEMS Phase I, across the approaches to the DeSoto Canyon in the northeastern Gulf and its prospect for monitoring the movements of eddies into the canyon. It will also touch on the prospects for expanding the network to include the entire eastern Gulf with a moored system on the Campeche Bank and several along the US Gulf shelf. This projected tomographic system is called GEMS Phase II. The paper will invite the participation of Mexican organizations to help plan and develop this proposed extensive project.

A True Eddy Accumulation - Eddy Covariance hybrid for measurements of turbulent trace gas fluxes

NASA Astrophysics Data System (ADS)

Siebicke, Lukas

2016-04-01

Eddy covariance (EC) is state-of-the-art in directly and continuously measuring turbulent fluxes of carbon dioxide and water vapor. However, low signal-to-noise ratios, high flow rates and missing or complex gas analyzers limit it's application to few scalars. True eddy accumulation, based on conditional sampling ideas by Desjardins in 1972, requires no fast response analyzers and is therefore potentially applicable to a wider range of scalars. Recently we showed possibly the first successful implementation of True Eddy Accumulation (TEA) measuring net ecosystem exchange of carbon dioxide of a grassland. However, most accumulation systems share the complexity of having to store discrete air samples in physical containers representing entire flux averaging intervals. The current study investigates merging principles of eddy accumulation and eddy covariance, which we here refer to as "true eddy accumulation in transient mode" (TEA-TM). This direct flux method TEA-TM combines true eddy accumulation with continuous sampling. The TEA-TM setup is simpler than discrete accumulation methods while avoiding the need for fast response gas analyzers and high flow rates required for EC. We implemented the proposed TEA-TM method and measured fluxes of carbon dioxide (CO2), methane (CH4) and water vapor (H2O) above a mixed beech forest at the Hainich Fluxnet and ICOS site, Germany, using a G2301 laser spectrometer (Picarro Inc., USA). We further simulated a TEA-TM sampling system using measured high frequency CO2 time series from an open-path gas analyzer. We operated TEA-TM side-by-side with open-, enclosed- and closed-path EC flux systems for CO2, H2O and CH4 (LI-7500, LI-7200, LI-6262, LI-7700, Licor, USA, and FGGA LGR, USA). First results show that TEA-TM CO2 fluxes were similar to EC fluxes. Remaining differences were similar to those between the three eddy covariance setups (open-, enclosed- and closed-path gas analyzers). Measured TEA-TM CO2 fluxes from our physical sampling system closely reproduced dynamics of simulated TEA-TM fluxes. In conclusion this study introduces a new approach to trace gas flux measurements using transient-mode true eddy accumulation. First TEA-TM CO2 fluxes compared favorably with side-by-side EC fluxes, in agreement with our previous experiments comparing discrete TEA to EC. True eddy accumulation has thus potential for measuring turbulent fluxes of a range of atmospheric tracers using slow response analyzers.

A new method for electric impedance imaging using an eddy current with a tetrapolar circuit.

PubMed

Ahsan-Ul-Ambia; Toda, Shogo; Takemae, Tadashi; Kosugi, Yukio; Hongo, Minoru

2009-02-01

A new contactless technique for electrical impedance imaging, using an eddy current managed along with the tetrapolar circuit method, is proposed. The eddy current produced by a magnetic field is superimposed on a constant current that is normally used in the tetrapolar circuit method, and thus is used to control the current distribution in the body. By changing the current distribution, a set of voltage differences is measured with a pair of electrodes. This set of voltage differences is used in the image reconstruction of the resistivity distribution. The least square error minimization method is used in the reconstruction algorithm. The principle of this method is explained theoretically. A backprojection algorithm was used to get 2-D images. Based on this principle, a measurement system was developed and model experiments were conducted with a saline-filled phantom. The estimated shape of each model in the reconstructed image was similar to that of the corresponding model. From the results of these experiments, it is confirmed that the proposed method is applicable to the realization of electrical conductivity imaging.

Kicker field simulation and measurement for the muon g-2 experiment at FNAL

NASA Astrophysics Data System (ADS)

Chang, Seung Pyo; Kim, Young Im; Choi, Jihoon; Semertzidis, Yannis; muon g-2 experiment Collaboration

2017-01-01

In the Muon g-2 experiment, muon beam is injected to the storage ring in a slightly tilted orbit whose center is 77 mm away from the center of the ring. The kicker is needed to send the muon beam to the central orbit. The magnetic kicker is designed for the experiment and about 0.1 Tm field integral is needed. The peak current pulse is 4200 A to make this field integral. This strong kicker pulse could make unwanted eddy current occur. This eddy current could spoil the main magnetic field of the storage ring. This could be a critical threat to the precision of experiment. The kicker field simulation has done using OPERA to estimate the effects. Also the kicker field should be measured based on Faraday effect. The measurement has tested in the lab before install the experiment area. In this presentation, the simulation and measurement results will be discussed. This work was supported by IBS-R017-D1-2016-a00.

Eddy interaction model for turbulent suspension in Reynolds-averaged Euler-Lagrange simulations of steady sheet flow

NASA Astrophysics Data System (ADS)

Cheng, Zhen; Chauchat, Julien; Hsu, Tian-Jian; Calantoni, Joseph

2018-01-01

A Reynolds-averaged Euler-Lagrange sediment transport model (CFDEM-EIM) was developed for steady sheet flow, where the inter-granular interactions were resolved and the flow turbulence was modeled with a low Reynolds number corrected k - ω turbulence closure modified for two-phase flows. To model the effect of turbulence on the sediment suspension, the interaction between the turbulent eddies and particles was simulated with an eddy interaction model (EIM). The EIM was first calibrated with measurements from dilute suspension experiments. We demonstrated that the eddy-interaction model was able to reproduce the well-known Rouse profile for suspended sediment concentration. The model results were found to be sensitive to the choice of the coefficient, C0, associated with the turbulence-sediment interaction time. A value C0 = 3 was suggested to match the measured concentration in the dilute suspension. The calibrated CFDEM-EIM was used to model a steady sheet flow experiment of lightweight coarse particles and yielded reasonable agreements with measured velocity, concentration and turbulence kinetic energy profiles. Further numerical experiments for sheet flow suggested that when C0 was decreased to C0 < 3, the simulation under-predicted the amount of suspended sediment in the dilute region and the Schmidt number is over-predicted (Sc > 1.0). Additional simulations for a range of Shields parameters between 0.3 and 1.2 confirmed that CFDEM-EIM was capable of predicting sediment transport rates similar to empirical formulations. Based on the analysis of sediment transport rate and transport layer thickness, the EIM and the resulting suspended load were shown to be important when the fall parameter is less than 1.25.

A Carbon Flux Super Site. New Insights and Innovative Atmosphere-Terrestrial Carbon Exchange Measurements and Modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leclerc, Monique Y.

2014-11-17

This final report presents the main activities and results of the project “A Carbon Flux Super Site: New Insights and Innovative Atmosphere-Terrestrial Carbon Exchange Measurements and Modeling” from 10/1/2006 to 9/30/2014. It describes the new AmeriFlux tower site (Aiken) at Savanna River Site (SC) and instrumentation, long term eddy-covariance, sodar, microbarograph, soil and other measurements at the site, and intensive field campaigns of tracer experiment at the Carbon Flux Super Site, SC, in 2009 and at ARM-CF site, Lamont, OK, and experiments in Plains, GA. The main results on tracer experiment and modeling, on low-level jet characteristics and their impactmore » on fluxes, on gravity waves and their influence on eddy fluxes, and other results are briefly described in the report.« less

Improved Climate Simulations through a Stochastic Parameterization of Ocean Eddies

NASA Astrophysics Data System (ADS)

Williams, Paul; Howe, Nicola; Gregory, Jonathan; Smith, Robin; Joshi, Manoj

2016-04-01

In climate simulations, the impacts of the sub-grid scales on the resolved scales are conventionally represented using deterministic closure schemes, which assume that the impacts are uniquely determined by the resolved scales. Stochastic parameterization relaxes this assumption, by sampling the sub-grid variability in a computationally inexpensive manner. This presentation shows that the simulated climatological state of the ocean is improved in many respects by implementing a simple stochastic parameterization of ocean eddies into a coupled atmosphere-ocean general circulation model. Simulations from a high-resolution, eddy-permitting ocean model are used to calculate the eddy statistics needed to inject realistic stochastic noise into a low-resolution, non-eddy-permitting version of the same model. A suite of four stochastic experiments is then run to test the sensitivity of the simulated climate to the noise definition, by varying the noise amplitude and decorrelation time within reasonable limits. The addition of zero-mean noise to the ocean temperature tendency is found to have a non-zero effect on the mean climate. Specifically, in terms of the ocean temperature and salinity fields both at the surface and at depth, the noise reduces many of the biases in the low-resolution model and causes it to more closely resemble the high-resolution model. The variability of the strength of the global ocean thermohaline circulation is also improved. It is concluded that stochastic ocean perturbations can yield reductions in climate model error that are comparable to those obtained by refining the resolution, but without the increased computational cost. Therefore, stochastic parameterizations of ocean eddies have the potential to significantly improve climate simulations. Reference PD Williams, NJ Howe, JM Gregory, RS Smith, and MM Joshi (2016) Improved Climate Simulations through a Stochastic Parameterization of Ocean Eddies. Journal of Climate, under revision.

Frontal Eddy Dynamics (FRED) experiment off North Carolina: Volume 2. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ebbesmeyer, C.C.

1988-03-01

In preparation for oil and gas lease sales on the outer continental shelf offshore of North Carolina, the Minerals Management Service was requested to investigate the potential transport and impacts of oil spilled offshore. Of particular concern is estimating the movement of spilled oil, especially the probability of shoreward transport and/or beaching of the floatable fraction. Although the speed and location of the Gulf Stream are well known, knowledge of the meanders of the Gulf Stream is limited. How the circulatory structure and movement of associated frontal eddies and filaments affect the North Carolina coastal waters is not clear. Thismore » present study investigates the interactions of these circulatory elements and follows the evolution of frontal eddies as they migrate along the North Carolina coast.« less

Effect of turbulent eddy viscosity on the unstable surface mode above an acoustic liner

NASA Astrophysics Data System (ADS)

Marx, David; Aurégan, Yves

2013-07-01

Lined ducts are used to reduce noise radiation from ducts in turbofan engines. In certain conditions they may sustain hydrodynamic instabilities. A local linear stability analysis of the flow in a 2D lined channel is performed using a numerical integration of the governing equations. Several model equations are used, one of them taking into account turbulent eddy viscosity, and a realistic turbulent mean flow profile is used that vanishes at the wall. The stability analysis results are compared to published experimental results. Both the model and the experiments show the existence of an unstable mode, and the importance of taking into account eddy viscosity in the model is shown. When this is done, quantities such as the growth rate and the velocity eigenfunctions are shown to agree correctly.

Hybrid Reynolds-Averaged/Large-Eddy Simulations of a Coaxial Supersonic Free-Jet Experiment

NASA Technical Reports Server (NTRS)

Baurle, Robert A.; Edwards, Jack R.

2010-01-01

Reynolds-averaged and hybrid Reynolds-averaged/large-eddy simulations have been applied to a supersonic coaxial jet flow experiment. The experiment was designed to study compressible mixing flow phenomenon under conditions that are representative of those encountered in scramjet combustors. The experiment utilized either helium or argon as the inner jet nozzle fluid, and the outer jet nozzle fluid consisted of laboratory air. The inner and outer nozzles were designed and operated to produce nearly pressure-matched Mach 1.8 flow conditions at the jet exit. The purpose of the computational effort was to assess the state-of-the-art for each modeling approach, and to use the hybrid Reynolds-averaged/large-eddy simulations to gather insight into the deficiencies of the Reynolds-averaged closure models. The Reynolds-averaged simulations displayed a strong sensitivity to choice of turbulent Schmidt number. The initial value chosen for this parameter resulted in an over-prediction of the mixing layer spreading rate for the helium case, but the opposite trend was observed when argon was used as the injectant. A larger turbulent Schmidt number greatly improved the comparison of the results with measurements for the helium simulations, but variations in the Schmidt number did not improve the argon comparisons. The hybrid Reynolds-averaged/large-eddy simulations also over-predicted the mixing layer spreading rate for the helium case, while under-predicting the rate of mixing when argon was used as the injectant. The primary reason conjectured for the discrepancy between the hybrid simulation results and the measurements centered around issues related to the transition from a Reynolds-averaged state to one with resolved turbulent content. Improvements to the inflow conditions were suggested as a remedy to this dilemma. Second-order turbulence statistics were also compared to their modeled Reynolds-averaged counterparts to evaluate the effectiveness of common turbulence closure assumptions.

Flow Around Steep Topography

DTIC Science & Technology

2015-09-30

interest in these activities. These tours are being coordinated with the Coral Reef Research Foundation (CRRF), a research organization in Palau...form drag, lee waves , eddy generation) over small-scale topographic features and (ii) fundamentally nonlinear processes (turbulent island wakes...detail in another annual report. From 9 October to 12 November 2015, another SeaSoar cruise on Revelle will focus on wakes and arrested lee waves near

On the cyclonic eddy generation in Panay Strait, Philippines

NASA Astrophysics Data System (ADS)

Flament, P. J.; Repollo, C. L. A.; Flores-vidal, X.; Villanoy, C.

2016-12-01

High Frequency Doppler Radar (HFDR), shallow pressure gauges and Acoustic Doppler Current Profiler (ADCP) time-series observations during the Philippine Straits Dynamics Experiment (PhilEx) were analyzed to describe the mesoscale currents in Panay Strait, Philippines. Low frequency surface currents inferred from three HFDR (July 2008 { July 2009), revealed a clear seasonal signal in concurrent with the reversal of the Asian monsoon. The mesoscale cyclonic eddy west of Panay Island is generated during the winter northeast (NE) monsoon. This causes changes in the strength, depth and width of the intra-seasonal Panay coastal jet as its eastern limb. Winds from QuikSCAT satellite and from a nearby airport indicate that these flow structures correlate with the strength and direction of the prevailing local wind. An intensive survey of the cyclonic eddy in February 8-9, 2009, obtaining a 24-hour successive cross-shore Conductivity-Temperature- Depth (CTD) sections in conjunction with shipboard ADCP measurements showed a well- developed cyclonic eddy characterized by near-surface velocities reaching 50 cm/s. This observation coincides with the intensification of the wind in between Mindoro and Panay islands generating a positive wind stress curl in the lee of Panay, which in turn induces divergent surface currents. Water column response from the mean transects showed a pronounced signal of upwelling, indicated by the doming of isotherms and isopycnals. A pressure gradient then was sets up, resulting in the spin-up of a cyclonic eddy in geostrophic balance. Evaluation of the surface vorticity balance equation suggests that the wind stress curl via Ekman pumping mechanism provides the necessary input in the formation and evolution of the cyclonic eddy. In particular, the cumulative effect of the wind stress curl plays a key role on the generation of the eddy. The Beta-effect on the other hand may led to propagation of the eddy westward.

Structure measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.

Extensive hot-wire measurements were made to determine the structure of the large eddy in a synthetic turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five delta long in the steamwise direction and about one delta apart in the spanwise direction, where delta is the mean boundary-layer thickness. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal velocity in the outer flow.

Eddy Covariance Method: Overview of General Guidelines and Conventional Workflow

NASA Astrophysics Data System (ADS)

Burba, G. G.; Anderson, D. J.; Amen, J. L.

2007-12-01

Atmospheric flux measurements are widely used to estimate water, heat, carbon dioxide and trace gas exchange between the ecosystem and the atmosphere. The Eddy Covariance method is one of the most direct, defensible ways to measure and calculate turbulent fluxes within the atmospheric boundary layer. However, the method is mathematically complex, and requires significant care to set up and process data. These reasons may be why the method is currently used predominantly by micrometeorologists. Modern instruments and software can potentially expand the use of this method beyond micrometeorology and prove valuable for plant physiology, hydrology, biology, ecology, entomology, and other non-micrometeorological areas of research. The main challenge of the method for a non-expert is the complexity of system design, implementation, and processing of the large volume of data. In the past several years, efforts of the flux networks (e.g., FluxNet, Ameriflux, CarboEurope, Fluxnet-Canada, Asiaflux, etc.) have led to noticeable progress in unification of the terminology and general standardization of processing steps. The methodology itself, however, is difficult to unify, because various experimental sites and different purposes of studies dictate different treatments, and site-, measurement- and purpose-specific approaches. Here we present an overview of theory and typical workflow of the Eddy Covariance method in a format specifically designed to (i) familiarize a non-expert with general principles, requirements, applications, and processing steps of the conventional Eddy Covariance technique, (ii) to assist in further understanding the method through more advanced references such as textbooks, network guidelines and journal papers, (iii) to help technicians, students and new researchers in the field deployment of the Eddy Covariance method, and (iv) to assist in its use beyond micrometeorology. The overview is based, to a large degree, on the frequently asked questions received from new users of the Eddy Covariance method and relevant instrumentation, and employs non-technical language to be of practical use to those new to this field. Information is provided on theory of the method (including state of methodology, basic derivations, practical formulations, major assumptions and sources of errors, error treatment, and use in non- traditional terrains), practical workflow (e.g., experimental design, implementation, data processing, and quality control), alternative methods and applications, and the most frequently overlooked details of the measurements. References and access to an extended 141-page Eddy Covariance Guideline in three electronic formats are also provided.

A regime perspective on the North Atlantic eddy-driven jet stream response to sudden stratospheric warmings

NASA Astrophysics Data System (ADS)

Maycock, A.; Masukwedza, G.; Hitchcock, P.

2017-12-01

The winter North Atlantic eddy-driven jet (NAJ) has been shown to exhibit three preferred latitudinal positions. Here we examine, for the first time, the influence of major Sudden Stratospheric Warmings (SSWs) on the regime behaviour of the NAJ using an ensemble of climate model experiments with stratospheric conditions nudged towards a major SSW, but with each ensemble member having freely evolving tropospheric conditions. The SSW experiment is compared to a control ensemble in which stratospheric variability is absent. The experiments show that the SSW leads to an increased occupancy of the southerly NAJ state and reduced occupancy of the northerly state. This effect is distinct from the mean southward shift of the NAJ identified in many previous studies, and instead suggests changes to the characteristics of NAJ variability as a result of SSWs. These results may aid in understanding the mechanisms by which SSWs impact on Euro-Atlantic climate.

Renormalization group estimates of transport coefficients in the advection of a passive scalar by incompressible turbulence

NASA Technical Reports Server (NTRS)

Zhou, YE; Vahala, George

1993-01-01

The advection of a passive scalar by incompressible turbulence is considered using recursive renormalization group procedures in the differential sub grid shell thickness limit. It is shown explicitly that the higher order nonlinearities induced by the recursive renormalization group procedure preserve Galilean invariance. Differential equations, valid for the entire resolvable wave number k range, are determined for the eddy viscosity and eddy diffusivity coefficients, and it is shown that higher order nonlinearities do not contribute as k goes to 0, but have an essential role as k goes to k(sub c) the cutoff wave number separating the resolvable scales from the sub grid scales. The recursive renormalization transport coefficients and the associated eddy Prandtl number are in good agreement with the k-dependent transport coefficients derived from closure theories and experiments.

Toward finding a universally applicable parameterization of the β factor for Relaxed Eddy Accumulation applications

NASA Astrophysics Data System (ADS)

Vogl, Teresa; Hrdina, Amy; Thomas, Christoph

2016-04-01

The traditional eddy covariance (EC) technique requires the use of fast responding sensors (≥ 10 Hz) that do not exist for many chemical species found in the atmosphere. In this case, the Relaxed Eddy Accumulation (REA) method offers a means to calculate fluxes of trace gases and other scalar quantities (Businger and Oncley, 1990) and was originally derived from the eddy accumulation method (EA) first proposed by Desjardins (1972). While REA lessens the requirements for sensors and sampling and thus offers practical appeal, it introduces a dependence of the computed flux from a proportionality factor β. The accuracy of the REA fluxes hinges upon the correct determination of β, which was found to vary between 0.40 and 0.63 (Milne et al., 1999, Ammann and Meixner, 2002, Ruppert et al., 2006). However, formulating a universally valid parameterization for β instead of empirical evaluation has remained a conundrum and has been a main limitation for REA. In this study we take a fresh look at the dependencies and mathematical models of β by analyzing eddy covariance (EC) data and REA simulations for two field experiments in drastically contrasting environments: an exclusively physically driven environment in the Dry Valleys of Antarctica, and a biologically active system in a grassland in Germany. The main objective is to work toward a model parameterization for β that can be applied over wide range of surface conditions and forcings without the need for empirical evaluation, which is not possible for most REA applications. Our study discusses two different models to define β: (i) based upon scalar-scalar similarity, in which a different scalar is measured with fast-response sensors as a proxy for the scalar of interest, here referred to as β0; and (ii) computed solely from the vertical wind statistics, assuming a linear relationship between the scalar of interest and the vertical wind speed, referred to as βw. Results are presented for the carbon-dioxide, latent and sensible heat fluxes across the contrasting environments. First, the choice of an appropriate scalar to calculate β0 is discussed considering the sources and sinks of each scalar with an emphasis on the carbon dioxide flux, which shows strongly dissimilar dynamics between the Antarctic ecosystem and the grassland. Secondly, the impact of atmospheric stability on both β models is investigated. In a next step, we attempt to find a physically meaningful explanation for the overestimation of the REA scalar fluxes compared to those from EC for using βw. We do so by analyzing the probability density function (pdf) and its statistical moments for the vertical wind speed. We found its pdf to be non-Gaussian for the majority of cases, and detected a close to linear relationship of its kurtosis with βw. Finally, in an attempt to provide practical guidance for field measurements, we integrate our findings and propose an enhanced model parameterization, and evaluate the differences between our new model and a constant β. Ammann, C. and Meixner, F.X. (2002) Stability dependence of the relaxed eddy accumulation coefficient for various scalar quantities. J. Geophys. Res. 107. ACL7.1-ACL7.9 doi:10.1029/2001JD000649 Businger, J.A., Oncley, S.P. (1990) Flux measurement with conditional sampling. J. Atmos. Ocean. Tech. 7:349-352. Desjardins, R. L. (1972) A study of carbon-dioxide and sensible heat fluxes using the eddy correlation technique, Ph.D. dissertation, Cornell University, 189 pp. Desjardins, R.L. (1977) Description and evaluation of sensible heat flux detector. Boundary-Layer Meteorol. 11:147-154. Katul, G., Finkelstein, P. L., Clarke, J. F., and Ellestad, T. G. (1996) An Investigation of the Conditional Sampling Methods Used to Estimate Fluxes of Active, Reactive and Passive Scalars. J. Appl. Meteorol. 35: 1835-1845. Milne, R., Beverland, I. J., Hargreaves, K., and Moncrieff, J. B. (1999) Variation of the beta coefficient in the relaxed eddy accumulation method. Boundary-Layer Meteorol. 93: 211-225. Ruppert, J. ATEM software for atmospheric turbulent exchange measurements using eddy covariance and relaxed eddy accumulation systems: Bayreuth whole-air REA system setup, Universität Bayreuth, Abt. Mikrometeorologie, Print, ISSN 1614-8916, Arbeitsergebnisse 28, 29 S, 2005 Ruppert, J., Thomas, C., and Foken, T. (2006) scalar similarity for relaxed eddy accumulation methods. Boundary-Layer Meteorol. 120: 39-63.

Mesoscale eddies in the Gulf of Aden and their impact on the spreading of Red Sea Outflow Water

NASA Astrophysics Data System (ADS)

Bower, Amy S.; Furey, Heather H.

2012-04-01

The Gulf of Aden (GOA) in the northwestern Indian Ocean is the receiving basin for Red Sea Outflow Water (RSOW), one of the World’s few high-salinity dense overflows, but relatively little is known about spreading pathways and transformation of RSOW through the gulf. Here we combine historical data, satellite altimetry, new synoptic hydrographic surveys and the first in situ direct observations of subsurface currents in the GOA to identify the most important processes in the spreading of RSOW. The new in situ data sets were collected in 2001-2003 as part of the Red Sea Outflow Experiment (REDSOX) and consist of two CTD/LADCP Surveys and 49 one-year trajectories from acoustically tracked floats released at the depth of RSOW. The results indicate that the prominent positive and negative sea level anomalies frequently observed in the GOA with satellite altimetry are associated with anticyclonic and cyclonic eddies that often reach to at least 1000 m depth, i.e., through the depth range of equilibrated RSOW. The eddies dominate RSOW spreading pathways and help to rapidly mix the outflow water with the background. Eddies in the central and eastern gulf are basin-scale (∼250-km diameter) and have maximum azimuthal speeds of about 30 cm/s at the RSOW level. In the western gulf, smaller eddies not detectable with satellite altimetry appear to form as the larger westward-propagating eddies impale themselves on the high ridges flanking the Tadjura Rift. Both the hydrographic and Lagrangian observations show that eddies originating outside the gulf often transport a core of much cooler, fresher water from the Arabian Sea all the way to the western end of the GOA, where the highest-salinity outflow water is found. This generates large vertical and horizontal gradients of temperature and salinity, setting up favorable conditions for salt fingering and diffusive convection. Both of these mixing processes were observed to be active in the gulf. Two new annually appearing anticyclonic eddies are added to the previously identified Gulf of Aden Eddy (GAE; Prasad and Ikeda, 2001) and Somali Current Ring (SCR; Fratantoni et al., 2006). These are the Summer Eddy (SE) and the Lee Eddy (LE), both of which form at the beginning of the summer monsoon when strong southwest winds blowing through Socotra Passage effectively split the GAE into two smaller eddies. The SE strengthens as it propagates westward deeper in the GOA, while the Lee Eddy remains stationary in the lee of Socotra Island. Both eddies are strengthened or sustained by Ekman convergence associated with negative wind stress curl patches caused by wind jets through or around high orography. The annual cycle in the appearance, propagation and demise of these new eddies and those described in earlier work is documented to provide a comprehensive view of the most energetic circulation features in the GOA. The observations contain little evidence of features that have been shown previously to be important in the spreading of Mediterranean Outflow Water (MOW) in the North Atlantic, namely a wall-bounded subsurface jet (the Mediterranean Undercurrent) and submesoscale coherent lenses containing a core of MOW (‘meddies’). This is attributed to the fact that the RSOW enters the open ocean on a western boundary. High background eddy kinetic energy typical of western boundary regimes will tend to shear apart submesoscale eddies and boundary undercurrents. Even if a submesoscale lens of RSOW did form in the GOA, westward self-propagation would transport the eddy and its cargo of outflow water back toward, rather than away from, its source.

Eddy Current Rail Inspection Using AC Bridge Techniques.

PubMed

Liu, Ze; Koffman, Andrew D; Waltrip, Bryan C; Wang, Yicheng

2013-01-01

AC bridge techniques commonly used for precision impedance measurements have been adapted to develop an eddy current sensor for rail defect detection. By using two detection coils instead of just one as in a conventional sensor, we can balance out the large baseline signals corresponding to a normal rail. We have significantly enhanced the detection sensitivity of the eddy current method by detecting and demodulating the differential signal of the two coils induced by rail defects, using a digital lock-in amplifier algorithm. We have also explored compensating for the lift-off effect of the eddy current sensor due to vibrations by using the summing signal of the detection coils to measure the lift-off distance. The dominant component of the summing signal is a constant resulting from direct coupling from the excitation coil, which can be experimentally determined. The remainder of the summing signal, which decreases as the lift-off distance increases, is induced by the secondary eddy current. This dependence on the lift-off distance is used to calibrate the differential signal, allowing for a more accurate characterization of the defects. Simulated experiments on a sample rail have been performed using a computer controlled X-Y moving table with the X-axis mimicking the train's motion and the Y-axis mimicking the train's vibrational bumping. Experimental results demonstrate the effectiveness of the new detection method.

Combined chamber-tower approach: Using eddy covariance measurements to cross-validate carbon fluxes modeled from manual chamber campaigns

NASA Astrophysics Data System (ADS)

Brümmer, C.; Moffat, A. M.; Huth, V.; Augustin, J.; Herbst, M.; Kutsch, W. L.

2016-12-01

Manual carbon dioxide flux measurements with closed chambers at scheduled campaigns are a versatile method to study management effects at small scales in multiple-plot experiments. The eddy covariance technique has the advantage of quasi-continuous measurements but requires large homogeneous areas of a few hectares. To evaluate the uncertainties associated with interpolating from individual campaigns to the whole vegetation period, we installed both techniques at an agricultural site in Northern Germany. The presented comparison covers two cropping seasons, winter oilseed rape in 2012/13 and winter wheat in 2013/14. Modeling half-hourly carbon fluxes from campaigns is commonly performed based on non-linear regressions for the light response and respiration. The daily averages of net CO2 modeled from chamber data deviated from eddy covariance measurements in the range of ± 5 g C m-2 day-1. To understand the observed differences and to disentangle the effects, we performed four additional setups (expert versus default settings of the non-linear regressions based algorithm, purely empirical modeling with artificial neural networks versus non-linear regressions, cross-validating using eddy covariance measurements as campaign fluxes, weekly versus monthly scheduling of campaigns) to model the half-hourly carbon fluxes for the whole vegetation period. The good agreement of the seasonal course of net CO2 at plot and field scale for our agricultural site demonstrates that both techniques are robust and yield consistent results at seasonal time scale even for a managed ecosystem with high temporal dynamics in the fluxes. This allows combining the respective advantages of factorial experiments at plot scale with dense time series data at field scale. Furthermore, the information from the quasi-continuous eddy covariance measurements can be used to derive vegetation proxies to support the interpolation of carbon fluxes in-between the manual chamber campaigns.

The metallic sphere in a uniform ac magnetic field: A simple and precise experiment for exploring eddy currents and non-destructive testing

NASA Astrophysics Data System (ADS)

Honke, Michael L.; Bidinosti, Christopher P.

2018-06-01

We describe a very simple experiment that utilizes standard laboratory equipment to measure the electromagnetic response of a metallic sphere exposed to a uniform ac magnetic field. Measurements were made for a variety of non-magnetic and magnetic metals, and in all cases the results fit very well with theory over the four orders of frequency (25 Hz to 102 kHz) explored here. Precise values of magnetic permeability and electrical conductivity can be extracted from fits to the data given the sphere radius only. The same apparatus is also used to explore the effects of geometry on eddy current generation as well as to demonstrate non-destructive testing through measurements on coins of different composition.

Detached Eddy Simulation of the UH-60 Rotor Wake Using Adaptive Mesh Refinement

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.; Ahmad, Jasim U.

2012-01-01

Time-dependent Navier-Stokes flow simulations have been carried out for a UH-60 rotor with simplified hub in forward flight and hover flight conditions. Flexible rotor blades and flight trim conditions are modeled and established by loosely coupling the OVERFLOW Computational Fluid Dynamics (CFD) code with the CAMRAD II helicopter comprehensive code. High order spatial differences, Adaptive Mesh Refinement (AMR), and Detached Eddy Simulation (DES) are used to obtain highly resolved vortex wakes, where the largest turbulent structures are captured. Special attention is directed towards ensuring the dual time accuracy is within the asymptotic range, and verifying the loose coupling convergence process using AMR. The AMR/DES simulation produced vortical worms for forward flight and hover conditions, similar to previous results obtained for the TRAM rotor in hover. AMR proved to be an efficient means to capture a rotor wake without a priori knowledge of the wake shape.

Eddy Current Minimizing Flow Plug for Use in Flow Conditioning and Flow Metering

NASA Technical Reports Server (NTRS)

England, John Dwight (Inventor); Kelley, Anthony R. (Inventor)

2015-01-01

An eddy-current-minimizing flow plug has an outer radial wall with open flow channels formed between the plug's inlet and outlet. The plug has a central region coupled to the inner surface of the outer radial wall. Each open flow channel includes (i) a first portion originating at the inlet and converging to a location in the plug where convergence is contributed to by changes in thickness of the outer radial wall and divergence of the central region, and (ii) a second portion originating in the plug and diverging to the outlet where divergence is contributed to by changes in thickness of the outer radial wall and convergence of the central region. For at least a portion of the open flow channels, a central axis passing through the first and second portions is non-parallel with respect to the given direction of the flow.

Summer circulation in the Mexican tropical Pacific

NASA Astrophysics Data System (ADS)

Trasviña, A.; Barton, E. D.

2008-05-01

The main components of large-scale circulation of the eastern tropical Pacific were identified in the mid 20th century, but the details of the circulation at length scales of 10 2 km or less, the mesoscale field, are less well known particularly during summer. The winter circulation is characterized by large mesoscale eddies generated by intense cross-shore wind pulses. These eddies propagate offshore to provide an important source of mesoscale variability for the eastern tropical Pacific. The summer circulation has not commanded similar attention, the main reason being that the frequent generation of hurricanes in the area renders in situ observations difficult. Before the experiment presented here, the large-scale summer circulation of the Gulf of Tehuantepec was thought to be dominated by a poleward flow along the coast. A drifter-deployment experiment carried out in June 2000, supported by satellite altimetry and wind data, was designed to characterize this hypothesized Costa Rica Coastal Current. We present a detailed comparison between altimetry-estimated geostrophic and in situ currents estimated from drifters. Contrary to expectation, no evidence of a coherent poleward coastal flow across the gulf was found. During the 10-week period of observations, we documented a recurrent pattern of circulation within 500 km of shore, forced by a combination of local winds and the regional-scale flow. Instead of the Costa Rica Coastal Current, we found a summer eddy field capable of influencing large areas of the eastern tropical Pacific. Even in summer, the cross-isthmus wind jet is capable of inducing eddy formation.

Coherent structures in turbulence and Prandtl's mixing length theory (27th Ludwig Prandtl Memorial Lecture)

NASA Astrophysics Data System (ADS)

Landahl, M. T.

1984-08-01

The fundamental ideas behind Prandtl's famous mixing length theory are discussed in the light of newer findings from experimental and theoretical research on coherent turbulence structures in the region near solid walls. A simple theoretical model for 'flat' structures is used to examine the fundamental assumptions behind Prandtl's theory. The model is validated by comparisons with conditionally sampled velocity data obtained in recent channel flow experiments. Particular attention is given to the role of pressure fluctuations on the evolution of flat eddies. The validity of Prandtl's assumption that an element of fluid retains its streamwise momentum as it is moved around by turbulence is confirmed for flat eddies. It is demonstrated that spanwise pressure gradients give rise to a contribution to the vertical displacement of a fluid element which is proportional to the distance from the wall. This contribution is particularly important for eddies that are highly elongated in the streamwise direction.

Large-eddy simulation of a boundary layer with concave streamwise curvature

NASA Technical Reports Server (NTRS)

Lund, Thomas S.

1994-01-01

Turbulence modeling continues to be one of the most difficult problems in fluid mechanics. Existing prediction methods are well developed for certain classes of simple equilibrium flows, but are still not entirely satisfactory for a large category of complex non-equilibrium flows found in engineering practice. Direct and large-eddy simulation (LES) approaches have long been believed to have great potential for the accurate prediction of difficult turbulent flows, but the associated computational cost has been prohibitive for practical problems. This remains true for direct simulation but is no longer clear for large-eddy simulation. Advances in computer hardware, numerical methods, and subgrid-scale modeling have made it possible to conduct LES for flows or practical interest at Reynolds numbers in the range of laboratory experiments. The objective of this work is to apply ES and the dynamic subgrid-scale model to the flow of a boundary layer over a concave surface.

Eddy Current Pulsed Thermography with Different Excitation Configurations for Metallic Material and Defect Characterization.

PubMed

Tian, Gui Yun; Gao, Yunlai; Li, Kongjing; Wang, Yizhe; Gao, Bin; He, Yunze

2016-06-08

This paper reviews recent developments of eddy current pulsed thermography (ECPT) for material characterization and nondestructive evaluation (NDE). Due to the fact that line-coil-based ECPT, with the limitation of non-uniform heating and a restricted view, is not suitable for complex geometry structures evaluation, Helmholtz coils and ferrite-yoke-based excitation configurations of ECPT are proposed and compared. Simulations and experiments of new ECPT configurations considering the multi-physical-phenomenon of hysteresis losses, stray losses, and eddy current heating in conjunction with uniform induction magnetic field have been conducted and implemented for ferromagnetic and non-ferromagnetic materials. These configurations of ECPT for metallic material and defect characterization are discussed and compared with conventional line-coil configuration. The results indicate that the proposed ECPT excitation configurations can be applied for different shapes of samples such as turbine blade edges and rail tracks.

Design of Diaphragm and Coil for Stable Performance of an Eddy Current Type Pressure Sensor.

PubMed

Lee, Hyo Ryeol; Lee, Gil Seung; Kim, Hwa Young; Ahn, Jung Hwan

2016-07-01

The aim of this work was to develop an eddy current type pressure sensor and investigate its fundamental characteristics affected by the mechanical and electrical design parameters of sensor. The sensor has two key components, i.e., diaphragm and coil. On the condition that the outer diameter of sensor is 10 mm, two key parts should be designed so as to keep a good linearity and sensitivity. Experiments showed that aluminum is the best target material for eddy current detection. A round-grooved diaphragm is suggested in order to measure more precisely its deflection caused by applied pressures. The design parameters of a round-grooved diaphragm can be selected depending on the measuring requirements. A developed pressure sensor with diaphragm of t = 0.2 mm and w = 1.05 mm was verified to measure pressure up to 10 MPa with very good linearity and errors of less than 0.16%.

Fast valve based on double-layer eddy-current repulsion for disruption mitigation in Experimental Advanced Superconducting Tokamak.

PubMed

Zhuang, H D; Zhang, X D

2015-05-01

A fast valve based on the double-layer eddy-current repulsion mechanism has been developed on Experimental Advanced Superconducting Tokamak (EAST). In addition to a double-layer eddy-current coil, a preload system was added to improve the security of the valve, whereby the valve opens more quickly and the open-valve time becomes shorter, making it much safer than before. In this contribution, testing platforms, open-valve characteristics, and throughput of the fast valve are discussed. Tests revealed that by choosing appropriate parameters the valve opened within 0.15 ms, and open-valve times were no longer than 2 ms. By adjusting working parameter values, the maximum number of particles injected during this open-valve time was estimated at 7 × 10(22). The fast valve will become a useful tool to further explore disruption mitigation experiments on EAST in 2015.

A two-equation model for heat transport in wall turbulent shear flows

NASA Astrophysics Data System (ADS)

Nagano, Y.; Kim, C.

1988-08-01

A new proposal for closing the energy equation is presented at the two-equation level of turbulence modeling. The eddy diffusivity concept is used in modeling. However, just as the eddy viscosity is determined from solutions of the k and epsilon equations, so the eddy diffusivity for heat is given as functions of temperature variance, and the dissipation rate of temperature fluctuations, together with k and epsilon. Thus, the proposed model does not require any questionable assumptions for the 'turbulent Prandtl number'. Modeled forms of the equations are developed to account for the physical effects of molecular Prandtl number and near-wall turbulence. The model is tested by application to a flat-plate boundary layer, the thermal entrance region of a pipe, and the turbulent heat transfer in fluids over a wide range of the Prandtl number. Agreement with the experiment is generally very satisfactory.

Improved Climate Simulations through a Stochastic Parameterization of Ocean Eddies

NASA Astrophysics Data System (ADS)

Williams, Paul; Howe, Nicola; Gregory, Jonathan; Smith, Robin; Joshi, Manoj

2017-04-01

In climate simulations, the impacts of the subgrid scales on the resolved scales are conventionally represented using deterministic closure schemes, which assume that the impacts are uniquely determined by the resolved scales. Stochastic parameterization relaxes this assumption, by sampling the subgrid variability in a computationally inexpensive manner. This study shows that the simulated climatological state of the ocean is improved in many respects by implementing a simple stochastic parameterization of ocean eddies into a coupled atmosphere-ocean general circulation model. Simulations from a high-resolution, eddy-permitting ocean model are used to calculate the eddy statistics needed to inject realistic stochastic noise into a low-resolution, non-eddy-permitting version of the same model. A suite of four stochastic experiments is then run to test the sensitivity of the simulated climate to the noise definition by varying the noise amplitude and decorrelation time within reasonable limits. The addition of zero-mean noise to the ocean temperature tendency is found to have a nonzero effect on the mean climate. Specifically, in terms of the ocean temperature and salinity fields both at the surface and at depth, the noise reduces many of the biases in the low-resolution model and causes it to more closely resemble the high-resolution model. The variability of the strength of the global ocean thermohaline circulation is also improved. It is concluded that stochastic ocean perturbations can yield reductions in climate model error that are comparable to those obtained by refining the resolution, but without the increased computational cost. Therefore, stochastic parameterizations of ocean eddies have the potential to significantly improve climate simulations. Reference Williams PD, Howe NJ, Gregory JM, Smith RS, and Joshi MM (2016) Improved Climate Simulations through a Stochastic Parameterization of Ocean Eddies. Journal of Climate, 29, 8763-8781. http://dx.doi.org/10.1175/JCLI-D-15-0746.1

Coupled circuit numerical analysis of eddy currents in an open MRI system.

PubMed

Akram, Md Shahadat Hossain; Terada, Yasuhiko; Keiichiro, Ishi; Kose, Katsumi

2014-08-01

We performed a new coupled circuit numerical simulation of eddy currents in an open compact magnetic resonance imaging (MRI) system. Following the coupled circuit approach, the conducting structures were divided into subdomains along the length (or width) and the thickness, and by implementing coupled circuit concepts we have simulated transient responses of eddy currents for subdomains in different locations. We implemented the Eigen matrix technique to solve the network of coupled differential equations to speed up our simulation program. On the other hand, to compute the coupling relations between the biplanar gradient coil and any other conducting structure, we implemented the solid angle form of Ampere's law. We have also calculated the solid angle for three dimensions to compute inductive couplings in any subdomain of the conducting structures. Details of the temporal and spatial distribution of the eddy currents were then implemented in the secondary magnetic field calculation by the Biot-Savart law. In a desktop computer (Programming platform: Wolfram Mathematica 8.0®, Processor: Intel(R) Core(TM)2 Duo E7500 @ 2.93GHz; OS: Windows 7 Professional; Memory (RAM): 4.00GB), it took less than 3min to simulate the entire calculation of eddy currents and fields, and approximately 6min for X-gradient coil. The results are given in the time-space domain for both the direct and the cross-terms of the eddy current magnetic fields generated by the Z-gradient coil. We have also conducted free induction decay (FID) experiments of eddy fields using a nuclear magnetic resonance (NMR) probe to verify our simulation results. The simulation results were found to be in good agreement with the experimental results. In this study we have also conducted simulations for transient and spatial responses of secondary magnetic field induced by X-gradient coil. Our approach is fast and has much less computational complexity than the conventional electromagnetic numerical simulation methods. Copyright © 2014 Elsevier Inc. All rights reserved.

Toward variational assimilation of SARAL/Altika altimeter data in a North Atlantic circulation model at eddy-permitting resolution: assessment of a NEMO-based 4D-VAR system

NASA Astrophysics Data System (ADS)

Bouttier, Pierre-Antoine; Brankart, Jean-Michel; Candille, Guillem; Vidard, Arthur; Blayo, Eric; Verron, Jacques; Brasseur, Pierre

2015-04-01

In this project, the response of a variational data assimilation system based on NEMO and its linear tangent and adjoint model is investigated using a 4DVAR algorithm into a North-Atlantic model at eddy-permitting resolution. The assimilated data consist of Jason-2 and SARAL/AltiKA dataset collected during the 2013-2014 period. The main objective is to explore the robustness of the 4DVAR algorithm in the context of a realistic turbulent oceanic circulation at mid-latitude constrained by multi-satellite altimetry missions. This work relies on two previous studies. First, a study with similar objectives was performed based on academic double-gyre turbulent model and synthetic SARAL/AltiKA data, using the same DA experimental framework. Its main goal was to investigate the impact of turbulence on variational DA methods performance. The comparison with this previous work will bring to light the methodological and physical issues encountered by variational DA algorithms in a realistic context at similar, eddy-permitting spatial resolution. We also have demonstrated how a dataset mimicking future SWOT observations improves 4DVAR incremental performances at eddy-permitting resolution. Then, in the context of the OSTST and FP7 SANGOMA projects, an ensemble DA experiment based on the same model and observational datasets has been realized (see poster by Brasseur et al.). This work offers the opportunity to compare efficiency, pros and cons of both DA methods in the context of KA-band altimetric data, at spatial resolution commonly used today for research and operational applications. In this poster we will present the validation plan proposed to evaluate the skill of variational experiment vs. ensemble assimilation experiments covering the same period using independent observations (e.g. from Cryosat-2 mission).

Estimation of stress distribution in ferromagnetic tensile specimens using low cost eddy current stress measurement system and BP neural network.

PubMed

Li, Jianwei; Zhang, Weimin; Zeng, Weiqin; Chen, Guolong; Qiu, Zhongchao; Cao, Xinyuan; Gao, Xuanyi

2017-01-01

Estimation of the stress distribution in ferromagnetic components is very important for evaluating the working status of mechanical equipment and implementing preventive maintenance. Eddy current testing technology is a promising method in this field because of its advantages of safety, no need of coupling agent, etc. In order to reduce the cost of eddy current stress measurement system, and obtain the stress distribution in ferromagnetic materials without scanning, a low cost eddy current stress measurement system based on Archimedes spiral planar coil was established, and a method based on BP neural network to obtain the stress distribution using the stress of several discrete test points was proposed. To verify the performance of the developed test system and the validity of the proposed method, experiment was implemented using structural steel (Q235) specimens. Standard curves of sensors at each test point were achieved, the calibrated data were used to establish the BP neural network model for approximating the stress variation on the specimen surface, and the stress distribution curve of the specimen was obtained by interpolating with the established model. The results show that there is a good linear relationship between the change of signal modulus and the stress in most elastic range of the specimen, and the established system can detect the change in stress with a theoretical average sensitivity of -0.4228 mV/MPa. The obtained stress distribution curve is well consonant with the theoretical analysis result. At last, possible causes and improving methods of problems appeared in the results were discussed. This research has important significance for reducing the cost of eddy current stress measurement system, and advancing the engineering application of eddy current stress testing.

Estimation of stress distribution in ferromagnetic tensile specimens using low cost eddy current stress measurement system and BP neural network

PubMed Central

Li, Jianwei; Zeng, Weiqin; Chen, Guolong; Qiu, Zhongchao; Cao, Xinyuan; Gao, Xuanyi

2017-01-01

Estimation of the stress distribution in ferromagnetic components is very important for evaluating the working status of mechanical equipment and implementing preventive maintenance. Eddy current testing technology is a promising method in this field because of its advantages of safety, no need of coupling agent, etc. In order to reduce the cost of eddy current stress measurement system, and obtain the stress distribution in ferromagnetic materials without scanning, a low cost eddy current stress measurement system based on Archimedes spiral planar coil was established, and a method based on BP neural network to obtain the stress distribution using the stress of several discrete test points was proposed. To verify the performance of the developed test system and the validity of the proposed method, experiment was implemented using structural steel (Q235) specimens. Standard curves of sensors at each test point were achieved, the calibrated data were used to establish the BP neural network model for approximating the stress variation on the specimen surface, and the stress distribution curve of the specimen was obtained by interpolating with the established model. The results show that there is a good linear relationship between the change of signal modulus and the stress in most elastic range of the specimen, and the established system can detect the change in stress with a theoretical average sensitivity of -0.4228 mV/MPa. The obtained stress distribution curve is well consonant with the theoretical analysis result. At last, possible causes and improving methods of problems appeared in the results were discussed. This research has important significance for reducing the cost of eddy current stress measurement system, and advancing the engineering application of eddy current stress testing. PMID:29145500

A theoretically based determination of bowen-ratio fetch requirements

USGS Publications Warehouse

Stannard, D.I.

1997-01-01

Determination of fetch requirements for accurate Bowen-ratio measurements of latent- and sensible-heat fluxes is more involved than for eddy-correlation measurements because Bowen-ratio sensors are located at two heights, rather than just one. A simple solution to the diffusion equation is used to derive an expression for Bowen-ratio fetch requirements, downwind of a step change in surface fluxes. These requirements are then compared to eddy-correlation fetch requirements based on the same diffusion equation solution. When the eddy-correlation and upper Bowen-ratio sensor heights are equal, and the available energy upwind and downwind of the step change is constant, the Bowen-ratio method requires less fetch than does eddy correlation. Differences in fetch requirements between the two methods are greatest over relatively smooth surfaces. Bowen-ratio fetch can be reduced significantly by lowering the lower sensor, as well as the upper sensor. The Bowen-ratio fetch model was tested using data from a field experiment where multiple Bowen-ratio systems were deployed simultaneously at various fetches and heights above a field of bermudagrass. Initial comparisons were poor, but improved greatly when the model was modified (and operated numerically) to account for the large roughness of the upwind cotton field.

Extension to the dynamic modeling of the large angle magnetic suspension test fixture. M.S. Thesis - Old Dominion Univ., May 1995 Progress Report, 1 Nov. 1994 - 30 Apr. 1995

NASA Technical Reports Server (NTRS)

Foster, Lucas E.; Britcher, Colin P.

1995-01-01

The Large Angle Magnetic Suspension Test Fixture (LAMSTF) is a laboratory scale proof-of-concept system. The configuration is unique in that the electromagnets are mounted in a circular planar array. A mathematical model of the system had previously been developed, but was shown to have inaccuracies. These inaccuracies showed up in the step responses. Eddy currents were found to be the major cause of the modeling errors. In the original system, eddy currents existed in the aluminum baseplate, iron cores, and the sensor support frame. An attempt to include the eddy current dynamics in the system model is presented. The dynamics of a dummy sensor ring were added to the system. Adding the eddy current dynamics to the simulation improves the way it compares to the actual experiment. Also presented is a new method of determining the yaw angle of the suspended element. From the coil currents the yaw angle can be determined and the controller can be updated to suspend at the new current. This method has been used to demonstrate a 360 degree yaw angle rotation.

On the use of water phantom images to calibrate and correct eddy current induced artefacts in MR diffusion tensor imaging.

PubMed

Bastin, M E; Armitage, P A

2000-07-01

The accurate determination of absolute measures of diffusion anisotropy in vivo using single-shot, echo-planar imaging techniques requires the acquisition of a set of high signal-to-noise ratio, diffusion-weighted images that are free from eddy current induced image distortions. Such geometric distortions can be characterized and corrected in brain imaging data using magnification (M), translation (T), and shear (S) distortion parameters derived from separate water phantom calibration experiments. Here we examine the practicalities of using separate phantom calibration data to correct high b-value diffusion tensor imaging data by investigating the stability of these distortion parameters, and hence the eddy currents, with time. It is found that M, T, and S vary only slowly with time (i.e., on the order of weeks), so that calibration scans need not be performed after every patient examination. This not only minimises the scan time required to collect the calibration data, but also the computational time needed to characterize these eddy current induced distortions. Examples of how measurements of diffusion anisotropy are improved using this post-processing scheme are also presented.

On the nonlinear forced response of the North Atlantic atmosphere to meridional shifts of the Gulf Stream path

NASA Astrophysics Data System (ADS)

Seo, H.; Kwon, Y. O.; Joyce, T. M.; Ummenhofer, C.

2016-12-01

This study examines the North Atlantic atmospheric circulation response to the meridional shift of Gulf Stream path using a large-ensemble, high-resolution, and hemispheric-scale WRF simulations. The model is forced with wintertime SST anomalies derived from a wide range of Gulf Stream shift scenarios. The key result of the model experiments, supported in part by an independent analysis of a reanalysis data set, is that the large-scale, quasi-steady North Atlantic circulation response is unambiguously nonlinear about the sign and amplitude of chosen SST anomalies. This nonlinear response prevails over the weak linear response and resembles the negative North Atlantic Oscillation, the leading intrinsic mode of variability in the model and the observations. Further analysis of the associated dynamics reveals that the nonlinear responses are accompanied by the anomalous southward shift of the North Atlantic eddy-driven jet stream, which is reinforced nearly equally by the high-frequency transient eddy feedback and the low-frequency high-latitude wave breaking events. The result highlights the importance of the intrinsically nonlinear transient eddy dynamics and eddy-mean flow interactions in generating the nonlinear forced response to the meridional shift in the Gulf Stream.

Large Eddy Simulations of the Tilted Rig Experiment: A Two-dimensional Rayleigh-Taylor Instability Case

NASA Astrophysics Data System (ADS)

Rollin, Bertrand; Denissen, Nicholas A.; Reisner, Jon M.; Andrews, Malcolm J.

2012-11-01

The tilted rig experiment is a derivative of the rocket rig experiment designed to investigate turbulent mixing induced by the Rayleigh-Taylor (RT) instability. A tank containing two fluids of different densities is accelerated downwards between two parallel guiding rods by rocket motors. The acceleration is such that the pressure and density gradients face opposite directions at the fluids interface, creating a Rayleigh-Taylor unstable configuration. The rig is tilted such that the tank is initially at an angle and the acceleration is not perpendicular to the fluids interface when the rockets fire. This results in a two dimensional Rayleigh-Taylor instability case where the fluids experience RT mixing and a bulk overturning motion. The tilted rig is therefore a valuable experiment to help calibrating two-dimensional mixing models. Large Eddy Simulations of the tilted rig experiments will be compared to available experimental results. A study of the behavior of turbulence variables relevant to turbulence modeling will be presented. LA-UR 12-23829. This work was performed for the U.S. Department of Energy by Los Alamos National Laboratory under Contract No.DEAC52- 06NA2-5396.

An avenue of eddies: Quantifying the biophysical properties of mesoscale eddies in the Tasman Sea

NASA Astrophysics Data System (ADS)

Everett, J. D.; Baird, M. E.; Oke, P. R.; Suthers, I. M.

2012-08-01

The Tasman Sea is unique - characterised by a strong seasonal western boundary current that breaks down into a complicated field of mesoscale eddies almost immediately after separating from the coast. Through a 16-year analysis of Tasman Sea eddies, we identify a region along the southeast Australian coast which we name ‘Eddy Avenue’ where eddies have higher sea level anomalies, faster rotation and greater sea surface temperature and chlorophyll a anomalies. The density of cyclonic and anticyclonic eddies within Eddy Avenue is 23% and 16% higher respectively than the broader Tasman Sea. We find that Eddy Avenue cyclonic and anticyclonic eddies have more strongly differentiated biological properties than those of the broader Tasman Sea, as a result of larger anticyclonic eddies formed from Coral Sea water depressing chl. a concentrations, and for coastal cyclonic eddies due to the entrainment of nutrient-rich shelf waters. Cyclonic eddies within Eddy Avenue have almost double the chlorophyll a (0.35 mg m-3) of anticyclonic eddies (0.18 mg m-3). The average chlorophyll a concentration for cyclonic eddies is 16% higher in Eddy Avenue and 28% lower for anticyclonic eddies when compared to the Tasman Sea. With a strengthening East Australian Current, the propagation of these eddies will have significant implications for heat transport and the entrainment and connectivity of plankton and larval fish populations.

Existence of k⁻¹ power-law scaling in the equilibrium regions of wall-bounded turbulence explained by Heisenberg's eddy viscosity.

PubMed

Katul, Gabriel G; Porporato, Amilcare; Nikora, Vladimir

2012-12-01

The existence of a "-1" power-law scaling at low wavenumbers in the longitudinal velocity spectrum of wall-bounded turbulence was explained by multiple mechanisms; however, experimental support has not been uniform across laboratory studies. This letter shows that Heisenberg's eddy viscosity approach can provide a theoretical framework that bridges these multiple mechanisms and explains the elusiveness of the "-1" power law in some experiments. Novel theoretical outcomes are conjectured about the role of intermittency and very-large scale motions in modifying the k⁻¹ scaling.

Subgrid or Reynolds stress-modeling for three-dimensional turbulence computations

NASA Technical Reports Server (NTRS)

Rubesin, M. W.

1975-01-01

A review is given of recent advances in two distinct computational methods for evaluating turbulence fields, namely, statistical Reynolds stress modeling and turbulence simulation, where large eddies are followed in time. It is shown that evaluation of the mean Reynolds stresses, rather than use of a scalar eddy viscosity, permits an explanation of streamline curvature effects found in several experiments. Turbulence simulation, with a new volume averaging technique and third-order accurate finite-difference computing is shown to predict the decay of isotropic turbulence in incompressible flow with rather modest computer storage requirements, even at Reynolds numbers of aerodynamic interest.

Discovery and Utilization of Nanoscale and Mesoscale Enabling Materials and Processes for Optoelectronics and Electronic Interconnects

DTIC Science & Technology

2003-12-01

Heating and Cooling Device 42 5.2.3 Multiple Tip STM ~ 43 5.2.3.1 Novel Nanomanipulator MM3 43 5.2.3.2 Four Tip STM Assembly 44 5.2.3.3 Vibration ...Analysis of Eddy Current Damping System of Multiple TIP STM " 44 5.2.3.4 Active Vibration Damping System 46 5.3 First Results 47 5.3.1 UHV-SEM...side: Actual device side and top view. 44 46. Setup for the vibration analysis experiment. 45 47. Relaxation of the STM unit, (a) without the eddy

Simulation of hydrodynamics using large eddy simulation-second-order moment model in circulating fluidized beds

NASA Astrophysics Data System (ADS)

Juhui, Chen; Yanjia, Tang; Dan, Li; Pengfei, Xu; Huilin, Lu

2013-07-01

Flow behavior of gas and particles is predicted by the large eddy simulation of gas-second order moment of solid model (LES-SOM model) in the simulation of flow behavior in CFB. This study shows that the simulated solid volume fractions along height using a two-dimensional model are in agreement with experiments. The velocity, volume fraction and second-order moments of particles are computed. The second-order moments of clusters are calculated. The solid volume fraction, velocity and second order moments are compared at the three different model constants.

Flowpath evaluation and reconnaissance by remote field Eddy current testing (FERRET)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smoak, A.E.; Zollinger, W.T.

1993-12-31

This document describes the design and development of FERRET (Flowpath Evaluation and Reconnaisance by Remote-field Eddy current Testing). FERRET is a system for inspecting the steel pipes which carry cooling water to underground nuclear waste storage tanks. The FERRET system has been tested in a small scale cooling pipe mock-up, an improved full scale mock-up, and in flaw detection experiments. Early prototype designs of FERRET and the FERRET launcher (a device which inserts, moves, and retrieves probes from a piping system) as well as the field-ready design are discussed.

Note: Eddy current displacement sensors independent of target conductivity.

PubMed

Wang, Hongbo; Li, Wei; Feng, Zhihua

2015-01-01

Eddy current sensors (ECSs) are widely used for non-contact displacement measurement. In this note, the quantitative error of an ECS caused by target conductivity was analyzed using a complex image method. The response curves (L-x) of the ECS with different targets were similar and could be overlapped by shifting the curves on x direction with √2δ/2. Both finite element analysis and experiments match well with the theoretical analysis, which indicates that the measured error of high precision ECSs caused by target conductivity can be completely eliminated, and the ECSs can measure different materials precisely without calibration.

Prospects for Problems Associated with Integrative and Inter-comparative Analysis of Eddy Flux Data Sets

NASA Astrophysics Data System (ADS)

Kobayashi, Y.; Miyata, A.; Nagai, H.; Mano, M.; Yamamoto, S.

2005-12-01

In last decade, numerous long-term eddy flux measurements have been conducted worldwide to assess annual/seasonal energy, water and carbon exchanges between terrestrial ecosystem and the atmosphere. And FLUXNET communities now seem to come into a next phase with the objectives: integration of flux data observed at various ecosystems and/or inter-sites comparative studies. For example, a big research project "S-1" is ongoing in Japan and other eastern Asian region to set up terrestrial carbon management of Asia in the 21st century. One of the highlights of S-1 project is to provide a carbon budget map of all over Asia based on integrated and inter-compared eddy flux data collected at 15 sites of S-1 membership. FLUXNET communities including S-1 project have recognized that integration and inter-comparison of eddy flux data are the key issues to understand aspects of energy, water and carbon budgets at regional scale. However, the issues have difficulties to be settled because each flux site applies own data processing methods and gap-filling methods with site-specified classification and threshold values. In order to conduct appropriate integrative and inter-comparative analysis for eddy flux data effectively, we made it clear that how the differences in the data processing method affect the obtained flux values and searched for suitable and common gap-filling methodology. The differences in the data processing methods affect the obtained flux data in the present study was discussed based on a comparative experiment in S-1 project. We prepared one-month common test data sets, which consisted of 10 Hz eddy covariance raw data and related half-hourly meteorological data obtained at a larch forest site and a paddy site, in the comparative experiment. The 15 sites of S-1 memberships processed the test data by using their own processing methods. The results indicated that combined influences of coordinate rotation, detrending and frequency response correction brought about up to 10% of flux discrepancy, and that the forest sites were more sensitive to differences in the data processing methods than the non-forest sites. Multiple imputation method (MI), one of the statistical operations for analyzing incomplete multivariate data set, is likely to be an easy-to-use and objective gap-filling method to account for missing eddy flux data. We also discussed validity of application of MI to fill missing flux data by comparing a gap-filled complete eddy flux data set obtained by MI with that by nonlinear regression method and look-up table method. It was revealed that, with suitable separation of the periods to be filled and proper selection of reference variables, MI has potential to be applied commonly to gap-filling missing flux data, and that MI can be a useful tool for FLUXNET communities to make inter-site comparison of long-term flux data.

Numerics and subgrid-scale modeling in large eddy simulations of stratocumulus clouds.

PubMed

Pressel, Kyle G; Mishra, Siddhartha; Schneider, Tapio; Kaul, Colleen M; Tan, Zhihong

2017-06-01

Stratocumulus clouds are the most common type of boundary layer cloud; their radiative effects strongly modulate climate. Large eddy simulations (LES) of stratocumulus clouds often struggle to maintain fidelity to observations because of the sharp gradients occurring at the entrainment interfacial layer at the cloud top. The challenge posed to LES by stratocumulus clouds is evident in the wide range of solutions found in the LES intercomparison based on the DYCOMS-II field campaign, where simulated liquid water paths for identical initial and boundary conditions varied by a factor of nearly 12. Here we revisit the DYCOMS-II RF01 case and show that the wide range of previous LES results can be realized in a single LES code by varying only the numerical treatment of the equations of motion and the nature of subgrid-scale (SGS) closures. The simulations that maintain the greatest fidelity to DYCOMS-II observations are identified. The results show that using weighted essentially non-oscillatory (WENO) numerics for all resolved advective terms and no explicit SGS closure consistently produces the highest-fidelity simulations. This suggests that the numerical dissipation inherent in WENO schemes functions as a high-quality, implicit SGS closure for this stratocumulus case. Conversely, using oscillatory centered difference numerical schemes for momentum advection, WENO numerics for scalars, and explicitly modeled SGS fluxes consistently produces the lowest-fidelity simulations. We attribute this to the production of anomalously large SGS fluxes near the cloud tops through the interaction of numerical error in the momentum field with the scalar SGS model.

Numerics and subgrid‐scale modeling in large eddy simulations of stratocumulus clouds

PubMed Central

Mishra, Siddhartha; Schneider, Tapio; Kaul, Colleen M.; Tan, Zhihong

2017-01-01

Abstract Stratocumulus clouds are the most common type of boundary layer cloud; their radiative effects strongly modulate climate. Large eddy simulations (LES) of stratocumulus clouds often struggle to maintain fidelity to observations because of the sharp gradients occurring at the entrainment interfacial layer at the cloud top. The challenge posed to LES by stratocumulus clouds is evident in the wide range of solutions found in the LES intercomparison based on the DYCOMS‐II field campaign, where simulated liquid water paths for identical initial and boundary conditions varied by a factor of nearly 12. Here we revisit the DYCOMS‐II RF01 case and show that the wide range of previous LES results can be realized in a single LES code by varying only the numerical treatment of the equations of motion and the nature of subgrid‐scale (SGS) closures. The simulations that maintain the greatest fidelity to DYCOMS‐II observations are identified. The results show that using weighted essentially non‐oscillatory (WENO) numerics for all resolved advective terms and no explicit SGS closure consistently produces the highest‐fidelity simulations. This suggests that the numerical dissipation inherent in WENO schemes functions as a high‐quality, implicit SGS closure for this stratocumulus case. Conversely, using oscillatory centered difference numerical schemes for momentum advection, WENO numerics for scalars, and explicitly modeled SGS fluxes consistently produces the lowest‐fidelity simulations. We attribute this to the production of anomalously large SGS fluxes near the cloud tops through the interaction of numerical error in the momentum field with the scalar SGS model. PMID:28943997

Helicopter- and ship-based measurements of mesoscale ocean color and thermal features in the marginal ice zone

NASA Astrophysics Data System (ADS)

Tanis, Fred J.; Manley, Thomas O.; Mitchell, Brian G.

1990-09-01

Eddies along the Polar Front/Marginal Ice Zone (MIZ) in Fram Strait are thought to make important contributions to nutrient flux and stimulation of primary productivity. During the Coordinated Eastern Arctic Regional Experiment (CEAREX) helicopter-based measurements of upwelling radiance were made in four visible spectral bands and in the thermal IR across mesoscale features associated with the MIZ. These structures were mapped by flying a grid pattern over the ocean surface to define eddy boundaries. Subsequently, the area was also sampled vertically with CTD and spectral radiometer profilers. Data obtained from a single structure were integrated to construct a three dimensional picture of physical and optical properties. Volume modeling of temperature, salinity, and density fields obtained from CTD survey define the subsurface eddy structure and are in good agreement with infrared derived characteristics. Maximum temperature in the core was found to be four degrees higher than the surrounding water. Volume modeling further indicates that a subsurface layer of Arctic Intermediate Water is intrinsically associated with the surface expression of the eddy. The ratio of upwelling radiances, L(44l)/L(565), was found to be correlated to surface chlorophyll, particulate absorption coefficient, and in water determinations of L using the optical profiling system. The remote sensing reflectance ratio along with the IR sea surface temperature were found to be useful to detect the surface expression of the eddy and to indicate near surface biological and physical processes.

Comprehensive characterization of measurement data gathered by the pressure tube to calandria tube gap probe

NASA Astrophysics Data System (ADS)

Shokralla, Shaddy Samir Zaki

Multi-frequency eddy current measurements are employed in estimating pressure tube (PT) to calandria tube (CT) gap in CANDU fuel channels, a critical inspection activity required to ensure fitness for service of fuel channels. In this thesis, a comprehensive characterization of eddy current gap data is laid out, in order to extract further information on fuel channel condition, and to identify generalized applications for multi-frequency eddy current data. A surface profiling technique, generalizable to multiple probe and conductive material configurations has been developed. This technique has allowed for identification of various pressure tube artefacts, has been independently validated (using ultrasonic measurements), and has been deployed and commissioned at Ontario Power Generation. Dodd and Deeds solutions to the electromagnetic boundary value problem associated with the PT to CT gap probe configuration were experimentally validated for amplitude response to changes in gap. Using the validated Dodd and Deeds solutions, principal components analysis (PCA) has been employed to identify independence and redundancies in multi-frequency eddy current data. This has allowed for an enhanced visualization of factors affecting gap measurement. Results of the PCA of simulation data are consistent with the skin depth equation, and are validated against PCA of physical experiments. Finally, compressed data acquisition has been realized, allowing faster data acquisition for multi-frequency eddy current systems with hardware limitations, and is generalizable to other applications where real time acquisition of large data sets is prohibitive.

Initial Ferritic Wall Mode studies on HBT-EP

NASA Astrophysics Data System (ADS)

Hughes, Paul; Bialek, J.; Boozer, A.; Mauel, M. E.; Levesque, J. P.; Navratil, G. A.

2013-10-01

Low-activation ferritic steels are leading material candidates for use in next-generation fusion development experiments such as a prospective US component test facility and DEMO. Understanding the interaction of plasmas with a ferromagnetic wall will provide crucial physics for these experiments. Although the ferritic wall mode (FWM) was seen in a linear machine, the FWM was not observed in JFT-2M, probably due to eddy current stabilization. Using its high-resolution magnetic diagnostics and positionable walls, HBT-EP has begun exploring the dynamics and stability of plasma interacting with high-permeability ferritic materials tiled to reduce eddy currents. We summarize a simple model for plasma-wall interaction in the presence of ferromagnetic material, describe the design of a recently-installed set of ferritic shell segments, and report initial results. Supported by U.S. DOE Grant DE-FG02-86ER53222.

Using high-fidelity computational fluid dynamics to help design a wind turbine wake measurement experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Churchfield, M.; Wang, Q.; Scholbrock, A.

Here, we describe the process of using large-eddy simulations of wind turbine wake flow to help design a wake measurement campaign. The main goal of the experiment is to measure wakes and wake deflection that result from intentional yaw misalignment under a variety of atmospheric conditions at the Scaled Wind Farm Technology facility operated by Sandia National Laboratories in Lubbock, Texas. Prior simulation studies have shown that wake deflection may be used for wind-plant control that maximizes plant power output. In this study, simulations are performed to characterize wake deflection and general behavior before the experiment is performed to ensuremore » better upfront planning. Beyond characterizing the expected wake behavior, we also use the large-eddy simulation to test a virtual version of the lidar we plan to use to measure the wake and better understand our lidar scan strategy options. This work is an excellent example of a 'simulation-in-the-loop' measurement campaign.« less

Using High-Fidelity Computational Fluid Dynamics to Help Design a Wind Turbine Wake Measurement Experiment

NASA Astrophysics Data System (ADS)

Churchfield, M.; Wang, Q.; Scholbrock, A.; Herges, T.; Mikkelsen, T.; Sjöholm, M.

2016-09-01

We describe the process of using large-eddy simulations of wind turbine wake flow to help design a wake measurement campaign. The main goal of the experiment is to measure wakes and wake deflection that result from intentional yaw misalignment under a variety of atmospheric conditions at the Scaled Wind Farm Technology facility operated by Sandia National Laboratories in Lubbock, Texas. Prior simulation studies have shown that wake deflection may be used for wind-plant control that maximizes plant power output. In this study, simulations are performed to characterize wake deflection and general behavior before the experiment is performed to ensure better upfront planning. Beyond characterizing the expected wake behavior, we also use the large-eddy simulation to test a virtual version of the lidar we plan to use to measure the wake and better understand our lidar scan strategy options. This work is an excellent example of a “simulation-in-the-loop” measurement campaign.

Using high-fidelity computational fluid dynamics to help design a wind turbine wake measurement experiment

DOE PAGES

Churchfield, M.; Wang, Q.; Scholbrock, A.; ...

2016-10-03

Here, we describe the process of using large-eddy simulations of wind turbine wake flow to help design a wake measurement campaign. The main goal of the experiment is to measure wakes and wake deflection that result from intentional yaw misalignment under a variety of atmospheric conditions at the Scaled Wind Farm Technology facility operated by Sandia National Laboratories in Lubbock, Texas. Prior simulation studies have shown that wake deflection may be used for wind-plant control that maximizes plant power output. In this study, simulations are performed to characterize wake deflection and general behavior before the experiment is performed to ensuremore » better upfront planning. Beyond characterizing the expected wake behavior, we also use the large-eddy simulation to test a virtual version of the lidar we plan to use to measure the wake and better understand our lidar scan strategy options. This work is an excellent example of a 'simulation-in-the-loop' measurement campaign.« less

Photocopy of photograph. Photographer unknown. Typical suggestion award photograph from ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Photocopy of photograph. Photographer unknown. Typical suggestion award photograph from the World War II period. Useful suggestions were awarded a $ 50 bond and usually a photo in the shipyard newspaper, the beacon. This photo shows an improved bilge block template layout table left to right: Stuart S. Sanders, Rosalie Moschella, Eddie Ormond, Lt. CDR. J.M. Ballinger, and A.A. Goldman. - Naval Base Philadelphia-Philadelphia Naval Shipyard, League Island, Philadelphia, Philadelphia County, PA

Large-Eddy/Lattice Boltzmann Simulations of Micro-blowing Strategies for Subsonic and Supersonic Drag Control

NASA Technical Reports Server (NTRS)

Menon, Suresh

2003-01-01

This report summarizes the progress made in the first 8 to 9 months of this research. The Lattice Boltzmann Equation (LBE) methodology for Large-eddy Simulations (LES) of microblowing has been validated using a jet-in-crossflow test configuration. In this study, the flow intake is also simulated to allow the interaction to occur naturally. The Lattice Boltzmann Equation Large-eddy Simulations (LBELES) approach is capable of capturing not only the flow features associated with the flow, such as hairpin vortices and recirculation behind the jet, but also is able to show better agreement with experiments when compared to previous RANS predictions. The LBELES is shown to be computationally very efficient and therefore, a viable method for simulating the injection process. Two strategies have been developed to simulate multi-hole injection process as in the experiment. In order to allow natural interaction between the injected fluid and the primary stream, the flow intakes for all the holes have to be simulated. The LBE method is computationally efficient but is still 3D in nature and therefore, there may be some computational penalty. In order to study a large number or holes, a new 1D subgrid model has been developed that will simulate a reduced form of the Navier-Stokes equation in these holes.

Tools and Methods for Visualization of Mesoscale Ocean Eddies

NASA Astrophysics Data System (ADS)

Bemis, K. G.; Liu, L.; Silver, D.; Kang, D.; Curchitser, E.

2017-12-01

Mesoscale ocean eddies form in the Gulf Stream and transport heat and nutrients across the ocean basin. The internal structure of these three-dimensional eddies and the kinematics with which they move are critical to a full understanding of their transport capacity. A series of visualization tools have been developed to extract, characterize, and track ocean eddies from 3D modeling results, to visually show the ocean eddy story by applying various illustrative visualization techniques, and to interactively view results stored on a server from a conventional browser. In this work, we apply a feature-based method to track instances of ocean eddies through the time steps of a high-resolution multidecadal regional ocean model and generate a series of eddy paths which reflect the life cycle of individual eddy instances. The basic method uses the Okubu-Weiss parameter to define eddy cores but could be adapted to alternative specifications of an eddy. Stored results include pixel-lists for each eddy instance, tracking metadata for eddy paths, and physical and geometric properties. In the simplest view, isosurfaces are used to display eddies along an eddy path. Individual eddies can then be selected and viewed independently or an eddy path can be viewed in the context of all eddy paths (longer than a specified duration) and the ocean basin. To tell the story of mesoscale ocean eddies, we combined illustrative visualization techniques, including visual effectiveness enhancement, focus+context, and smart visibility, with the extracted volume features to explore eddy characteristics at multiple scales from ocean basin to individual eddy. An evaluation by domain experts indicates that combining our feature-based techniques with illustrative visualization techniques provides an insight into the role eddies play in ocean circulation. A web-based GUI is under development to facilitate easy viewing of stored results. The GUI provides the user control to choose amongst available datasets, to specify the variables (such as temperature or salinity) to display on the isosurfaces, and to choose the scale and orientation of the view. These techniques allow an oceanographer to browse the data based on eddy paths and individual eddies rather than slices or volumes of data.

Influence of deep vortices on the ocean surface

NASA Astrophysics Data System (ADS)

Ciani, Daniele; Carton, Xavier; Bashmachnikov, Igor; Chapron, Bertrand

2015-04-01

The oceanic motion at mesoscale (20-200 km) and submesoscale (0.5-20 km) is highly populated by vortices. These recirculating structures are more energetic than the mean flow, they trap water masses from their origination areas and advect them across the ocean, with consequent impact on the 3D distribution of heat and tracers. Mesoscale and submesoscale structures characterize the ocean dynamics both at the sea-surface and at intrathermocline depths (0-1500 m), and are presently investigated by means of model outputs and satellite (surface) data, the latest being the only way to get high resolution and synoptic observations at planetary scale (e.g., thermal-band observations, future altimetric observations given by the SWOT mission). The scientific question arising from this context is related to the role of the ocean surface for inferring informations on mesoscale and submesoscale vortices at depth. This study has also been motivated by the recent detection of subsurface eddies east of the Arabian Peninsula (PHYSINDIEN experiment - 2011). Using analytical models in the frame of the quasi-geostrophic (QG) theory, we could describe the theoretical altimetric signature of non-drifting and of drifting subsurface eddies. Numerical experiments, using both QG and primitive equations models, allowed us to investigate the surface expression of intrathermocline eddies interacting with baroclinic currents or evolving under planetary beta-effect. The eddies' characteristics (radius, depth, thickness, velocity) were varied in order to represent various oceanic examples (Meddies, Swoddies, Reddies, Peddies, Leddies). Idealized simulations with the ROMS model, confirming theoretical estimates, showed that drifting subsurface-intensified vortices can induce dipolar sea level anomalies, up to 3 cm. This result, compatibly with future SWOT measurement accuracies (about 2 cm), represents a contribution for systematic and synoptic detection of subsurface vortices.

Modification of ocean-estuary salt fluxes by density-driven advection of a headland eddy

NASA Astrophysics Data System (ADS)

Fram, J. P.; Stacey, M. T.

2005-05-01

Scalar exchange between San Francisco Bay and the coastal ocean is examined using shipboard observations made across the Golden Gate Channel. Ocean-estuary exchange is often described as a combination of two independent types of mechanisms: density-driven exchange such as gravitational circulation and tidal asymmetries such as tidal trapping. In this study we found that exchange is also governed by an interaction between these mechanisms. Tidally trapped eddies created in shallow shoals are mixed into the main channel earlier in the tidal cycle during the rainy season because the eddies are pushed seaward by gravitational circulation. This interaction increases the tidally averaged dispersive salt flux into the bay. The study consists of experiments during each of three 'seasons': winter/spring runoff (March 2002), summer upwelling (July 2003), and fall relaxation (October 2002). Within each experiment, transects across the channel were repeated approximately every 12 minutes for 25 hours during both spring tide and the following neap tide. Velocity was measured from a boat-mounted ADCP. Scalar concentrations were measured from a tow-yoed SeaSciences Acrobat. Salinity exchange over each spring-neap cycle is quantified with harmonic analysis. Harmonic results are decomposed into flux mechanisms using temporal and spatial correlations. The temporal correlation of cross-sectional averaged salinity and velocity (tidal pumping flux) is the largest part of the dispersive flux of salinity into the bay. From the tidal pumping portion of the dispersive flux, it is shown that there is less exchange than was found in earlier studies. Furthermore, tidal pumping flux scales strongly with flow due to density-driven movement of tidally trapped eddies and density-driven increases in ebb-flood frictional phasing. Complex bathymetry makes salinity exchange scale differently with flow than would be expected from simple tidal pumping and gravitational circulation models.

Sensitivity of idealised baroclinic waves to mean atmospheric temperature and meridional temperature gradient changes

NASA Astrophysics Data System (ADS)

Rantanen, Mika; Räisänen, Jouni; Sinclair, Victoria A.; Järvinen, Heikki

2018-06-01

The sensitivity of idealised baroclinic waves to different atmospheric temperature changes is studied. The temperature changes are based on those which are expected to occur in the Northern Hemisphere with climate change: (1) uniform temperature increase, (2) decrease of the lower level meridional temperature gradient, and (3) increase of the upper level temperature gradient. Three sets of experiments are performed, first without atmospheric moisture, thus seeking to identify the underlying adiabatic mechanisms which drive the response of extra-tropical storms to changes in the environmental temperature. Then, similar experiments are performed in a more realistic, moist environment, using fixed initial relative humidity distribution. Warming the atmosphere uniformly tends to decrease the kinetic energy of the cyclone, which is linked both to a weaker capability of the storm to exploit the available potential energy of the zonal mean flow, and less efficient production of eddy kinetic energy in the wave. Unsurprisingly, the decrease of the lower level temperature gradient weakens the resulting cyclone regardless of the presence of moisture. The increase of the temperature gradient in the upper troposphere has a more complicated influence on the storm dynamics: in the dry atmosphere the maximum eddy kinetic energy decreases, whereas in the moist case it increases. Our analysis suggests that the slightly unexpected decrease of eddy kinetic energy in the dry case with an increased upper tropospheric temperature gradient originates from the weakening of the meridional heat flux by the eddy. However, in the more realistic moist case, the diabatic heating enhances the interaction between upper- and low-level potential vorticity anomalies and hence helps the surface cyclone to exploit the increased upper level baroclinicity.

Temporal evolution of near-surface chlorophyll over cyclonic eddy lifecycles in the southeastern Pacific

NASA Astrophysics Data System (ADS)

Huang, Jie; Xu, Fanghua; Zhou, Kuanbo; Xiu, Peng; Lin, Yanluan

2017-08-01

Temporal evolution of near-surface chlorophyll (CHL) associated with mesoscale eddies over entire eddy lifespan is complicated. Based on satellite measurements and a reanalysis data set, we identify and quantify major temporal and spatial CHL responses in cyclonic eddies in the southeastern Pacific, and explore the associated mechanisms. Only few temporal CHL variations can be directly linked to the four primary mechanisms: "eddy pumping," "eddy trapping," "eddy stirring," and "eddy-induced Ekman pumping." About 80% of the temporal CHL variations are too complex to be explained by a single mechanism. Five characteristic CHL responses, including classic dipoles (CD), positive-dominant dipoles (PD), negative-dominant dipoles (ND), positive monopoles (PM), and negative monopoles (NM) are identified using the self-organizing map (SOM). CD, a dominant response induced primarily by "eddy stirring," has a continued increasing of frequency of occurrence with time, although its contribution to the total CHL variability remains low. As the secondary prominent response, NM has two peaks of frequency of occurrence at eddy formation and maturation stages, mainly accounted by "eddy trapping" after eddy breakup and "eddy-induced Ekman pumping," respectively. The sum of frequency of occurrence of PD and PM are comparable to that of NM. The initial positive CHL at eddy formation stage is associated with "eddy trapping." The significant positive CHL increase from the eddy intensification to early decay stage is mainly attributed to "eddy pumping." Although the frequency of occurrence of ND is the smallest, its contribution to negative CHL anomalies is unnegligible.

A comparison of the structure, properties, and water mass composition of quasi-isotropic eddies in western boundary currents in an eddy-resolving ocean model

NASA Astrophysics Data System (ADS)

Rykova, Tatiana; Oke, Peter R.; Griffin, David A.

2017-06-01

Using output from a near-global eddy-resolving ocean model, we analyse the properties and characteristics of quasi-isotropic eddies in five Western Boundary Current (WBC) regions, including the extensions of the Agulhas, East Australian Current (EAC), Brazil-Malvinas Confluence (BMC), Kuroshio and Gulf Stream regions. We assess the model eddies by comparing to satellite and in situ observations, and show that most aspects of the model's representation of eddies are realistic. We find that the mean eddies differ dramatically between these WBC regions - all with some unique and noteworthy characteristics. We find that the vertical displacement of isopycnals of Agulhas eddies is the greatest, averaging 350-450 m at depths of over 800-900 m. EAC (BMC) eddies are the least (most) barotropic, with only 50% (85-90%) of the velocity associated with the barotropic mode. Kuroshio eddies are the most stratified, resulting in small isopycnal displacement, even for strong eddies; and Gulf Stream eddies carry the most heat. Despite their differences, we explicitly show that the source waters for anticyclonic eddies are a mix of the WBC water (from the boundary current itself) and water that originates equatorward of the WBC eddy-field; and cyclonic eddies are a mix of WBC water and water that originates poleward of the WBC eddy-field.

Long-term Trends and Variability of Eddy Activities in the South China Sea

NASA Astrophysics Data System (ADS)

Zhang, M.; von Storch, H.

2017-12-01

For constructing empirical downscaling models and projecting possible future states of eddy activities in the South China Sea (SCS), long-term statistical characteristics of the SCS eddy are needed. We use a daily global eddy-resolving model product named STORM covering the period of 1950-2010. This simulation has employed the MPI-OM model with a mean horizontal resolution of 10km and been driven by the NCEP reanalysis-1 data set. An eddy detection and tracking algorithm operating on the gridded sea surface height anomaly (SSHA) fields was developed. A set of parameters for the criteria in the SCS are determined through sensitivity tests. Our method detected more than 6000 eddy tracks in the South China Sea. For all of them, eddy diameters, track length, eddy intensity, eddy lifetime and eddy frequency were determined. The long-term trends and variability of those properties also has been derived. Most of the eddies propagate westward. Nearly 100 eddies travel longer than 1000km, and over 800 eddies have a lifespan of more than 2 months. Furthermore, for building the statistical empirical model, the relationship between the SCS eddy statistics and the large-scale atmospheric and oceanic phenomena has been investigated.

The Stability of Outcropping Ocean Eddies

NASA Astrophysics Data System (ADS)

Paldor, N.; Cohen, Y.; Dvorkin, Y.

2017-12-01

In the end of the last century numerous ship-borne observations and linear instability studies have addressed the long life span of meso-scale ocean eddies. These eddies are observed to persist in the ocean for periods of 2-3 years with little deformation. As eddy instabilities occur because Rossby waves in the surrounding (assumed motionless) ocean interact with various waves in the eddy itself, the stability was attributed to some eddy structure that hinders such wave-wave interactions. However, instabilities with growthrates of the order of the inertial period were found in various multilayer models including hypothesized structures and several observed eddy structures. A solution to the difference between instability theory and observed stability was ultimately suggested by relaxing the assumption of a motionless ocean that surrounds the eddy and prescribing the mean flow in the ocean such that it counterbalances the depth changes imposed by the eddy while maintaining a constant PV-ocean. This hypothesis was successfully applied to Gaussian eddies for mathematical simplicity. Yet, the Gaussian eddy has no surface front - thus avoiding instabilities that involve frontal waves - and it disagrees with observation that clearly show that most eddies have surface fronts. Here the constant PV ocean hypothesis is applied to two frontal eddies: constant PV-eddies and solidly rotating eddy. A complete account of the mean flow of the coupled eddy-ocean system is analyzed using a canonical formulation of the gradient balance. The phase speeds of waves in the eddy-ocean system are computed by a shooting method. Both eddies are found to be unstable in motionless ocean, yet in a constant PV-ocean no instabilities are found using the exact same numerical search. While many eddy structures can be hypothesized there are only a handful of physical mechanisms for instability and in these eddies the assumed constant PV-ocean negates many of these physical mechanisms for instability. This implies that meso-scale eddies should be stable in a constant PV ocean, regardless to their structure, which is not precisely one of the above mentioned. This theory stimulates observations of the ocean under the eddies. To maintain the uniform PV value, relative vorticity must develop in the ocean under the eddy as it moves in the ocean.

Characterization of potential EC flux underestimation of "sticky" trace gas species

NASA Astrophysics Data System (ADS)

Neftel, Albrecht; Hensen, Arjan; Ibrom, Andreas; Ammann, Christof; Voglmeier, Karl; Brümmer, Christian

2017-04-01

Eddy covariance (EC) flux measurements of "sticky" trace gas species are affected of damping of high frequency variations of the gas concentration. Several approaches have been developed to correct for this effect (see e.g. Ibrom et al., 2007, Ammann et al., 2006). These approaches have in common that the spectral properties of the scalar are compared with the sonic temperature deduced from the Sonic anemometer data that is only marginally damped. A main difference between the two method is that one uses power spectra, while the other is based on co-spectra of the gas concentration with the vertical wind speed. NH3 fluxes used in the analysis stem from two field experiments: a) Posieux intercomparison October 2015: NH3 emissions of a grazed pasture measured with Eddy Covariance using an Aerodyne quantum cascade laser and with a horizontal gradient measurement using MiniDOAS systems (Sintermann et al., 2016) in conjunction with a dispersion model. b) Dronten experiment June 2016 in the Netherlands: NH3 emissions from two manured circles within 40m diameters have been determined with four different approaches (Eddy Covariance, Integrated Horizontal Flux approach, horizontal gradients and plume measurements). Despite correction with standard methods, turbulent NH3 flux measurements with the eddy covariance method seem still be underestimated when, e.g., compared to flux estimated using gradient methods. We discuss possible correction algorithms and how such underestimations can be recognized in the usual case, where no alternative flux estimation methods are available. References: Ammann, C., Brunner, A., Spirig, C., and Neftel, A. 2006: Technical note: Water vapour concentration and flux measurements with PTR-MS, Atmos. Chem. Phys., 6, 4643-4651 Ibrom, A., Dellwik, E., Jensen, N.O., Flyvbjerg, H. and Pilegaard, K., 2007. Strong low-pass filtering effects on water vapour flux measurements with closed-path eddy correlation systems. Agricultural and Forest Meteorology, 147: 140 -156. Sintermann, J., Dietrich, K., Hani, C., Bell, M., Jocher, M., and Neftel, A. 2016 A miniDOAS instrument optimised for ammonia field measurements, Atmos Meas Tech, 9, 2721-2734

Magnetic diagnostics for equilibrium reconstructions in the presence of nonaxisymmetric eddy current distributions in tokamaks (invited).

PubMed

Berzak, L; Jones, A D; Kaita, R; Kozub, T; Logan, N; Majeski, R; Menard, J; Zakharov, L

2010-10-01

The lithium tokamak experiment (LTX) is a modest-sized spherical tokamak (R(0)=0.4 m and a=0.26 m) designed to investigate the low-recycling lithium wall operating regime for magnetically confined plasmas. LTX will reach this regime through a lithium-coated shell internal to the vacuum vessel, conformal to the plasma last-closed-flux surface, and heated to 300-400 °C. This structure is highly conductive and not axisymmetric. The three-dimensional nature of the shell causes the eddy currents and magnetic fields to be three-dimensional as well. In order to analyze the plasma equilibrium in the presence of three-dimensional eddy currents, an extensive array of unique magnetic diagnostics has been implemented. Sensors are designed to survive high temperatures and incidental contact with lithium and provide data on toroidal asymmetries as well as full coverage of the poloidal cross-section. The magnetic array has been utilized to determine the effects of nonaxisymmetric eddy currents and to model the start-up phase of LTX. Measurements from the magnetic array, coupled with two-dimensional field component modeling, have allowed a suitable field null and initial plasma current to be produced. For full magnetic reconstructions, a three-dimensional electromagnetic model of the vacuum vessel and shell is under development.

Large-Eddy Simulation of Propeller Crashback

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Mahesh, Krishnan

2013-11-01

Crashback is an operating condition to quickly stop a propelled vehicle, where the propeller is rotated in the reverse direction to yield negative thrust. The crashback condition is dominated by the interaction of free stream flow with strong reverse flow. Crashback causes highly unsteady loads and flow separation on blade surface. This study uses Large-Eddy Simulation to predict the highly unsteady flow field in propeller crashback. Results are shown for a stand-alone open propeller, hull-attached open propeller and a ducted propeller. The simulations are compared to experiment, and used to discuss the essential physics behind the unsteady loads. This work is supported by the Office of Naval Research.

Quantifying mesoscale eddies in the Lofoten Basin

NASA Astrophysics Data System (ADS)

Raj, R. P.; Johannessen, J. A.; Eldevik, T.; Nilsen, J. E. Ø.; Halo, I.

2016-07-01

The Lofoten Basin is the most eddy rich region in the Norwegian Sea. In this paper, the characteristics of these eddies are investigated from a comprehensive database of nearly two decades of satellite altimeter data (1995-2013) together with Argo profiling floats and surface drifter data. An automated method identified 1695/1666 individual anticyclonic/cyclonic eddies in the Lofoten Basin from more than 10,000 altimeter-based eddy observations. The eddies are found to be predominantly generated and residing locally. The spatial distributions of lifetime, occurrence, generation sites, size, intensity, and drift of the eddies are studied in detail. The anticyclonic eddies in the Lofoten Basin are the most long-lived eddies (>60 days), especially in the western part of the basin. We reveal two hotspots of eddy occurrence on either side of the Lofoten Basin. Furthermore, we infer a cyclonic drift of eddies in the western Lofoten Basin. Barotropic energy conversion rates reveals energy transfer from the slope current to the eddies during winter. An automated colocation of surface drifters trapped inside the altimeter-based eddies are used to corroborate the orbital speed of the anticyclonic and cyclonic eddies. Moreover, the vertical structure of the altimeter-based eddies is examined using colocated Argo profiling float profiles. Combination of altimetry, Argo floats, and surface drifter data is therefore considered to be a promising observation-based approach for further studies of the role of eddies in transport of heat and biomass from the slope current to the Lofoten Basin.

Flow and thermal characteristics of high Reynolds number (2800-17,000) dye cell: simulation and experiment.

PubMed

Mishra, G K; Kumar, Abhay; Prakash, O; Biswal, R; Dixit, S K; Nakhe, S V

2015-04-10

This paper presents computational and experimental studies on wavelength/frequency fluctuation characteristics of a high pulse repetition rate (18 kHz) dye laser pumped by a frequency-doubled Nd:YAG laser (532 nm). The temperature gradient in the dye solution is found to be responsible for wavelength fluctuations of the dye laser at low flow rates (2800

Tests of Parameterized Langmuir Circulation Mixing in the Oceans Surface Mixed Layer II

DTIC Science & Technology

2017-08-11

inertial oscillations in the ocean are governed by three-dimensional processes that are not accounted for in a one-dimensional simulation , and it was...Unlimited 52 Paul Martin (228) 688-5447 Recent large-eddy simulations (LES) of Langmuir circulation (LC) within the surface mixed layer (SML) of...used in the Navy Coastal Ocean Model (NCOM) and tested for (a) a simple wind-mixing case, (b) simulations of the upper ocean thermal structure at Ocean

Nonperiodic eddy pulsations

USGS Publications Warehouse

Rubin, David M.; McDonald, Richard R.

1995-01-01

Recirculating flow in lateral separation eddies is typically weaker than main stem flow and provides an effective environment for trapping sediment. Observations of recirculating flow and sedimentary structures demonstrate that eddies pulsate in size and in flow velocity even when main stem flow is steady. Time series measurements of flow velocity and location of the reattachment point indicate that these pulsations are nonperiodic. Nonperiodic flow in the lee of a channel margin constriction is grossly different from the periodic flow in the lee of a cylinder that is isolated in a flow. Our experiments demonstrate that placing a flow-parallel plate adjacent to a cylinder is sufficient to cause the leeside flow to change from a periodic sequence of vortices to a nonperiodically pulsating lateral separation eddy, even if flow conditions are otherwise unchanged. Two processes cause the leeside flow to become nonperiodic when the plate is added. First, vortices that are shed from the cylinder deform and become irregular as they impact the plate or interfere with remnants of other vortices near the reattachment point. Second, these deformed vortices and other flow structures are recirculated in the lateral separation eddy, thereby influencing the future state (pressure and momentum distribution) of the recirculating flow. The vortex deformation process was confirmed experimentally by documenting spatial differences in leeside flow; vortex shedding that is evident near the separation point is undetectable near the reattachment point. Nonlinear forecasting techniques were used in an attempt to distinguish among several possible kinds of nonperiodic flows. The computational techniques were unable to demonstrate that any of the nonperiodic flows result from low-dimensional nonlinear processes.

Toward large eddy simulation of turbulent flow over an airfoil

NASA Technical Reports Server (NTRS)

Choi, Haecheon

1993-01-01

The flow field over an airfoil contains several distinct flow characteristics, e.g. laminar, transitional, turbulent boundary layer flow, flow separation, unstable free shear layers, and a wake. This diversity of flow regimes taxes the presently available Reynolds averaged turbulence models. Such models are generally tuned to predict a particular flow regime, and adjustments are necessary for the prediction of a different flow regime. Similar difficulties are likely to emerge when the large eddy simulation technique is applied with the widely used Smagorinsky model. This model has not been successful in correctly representing different turbulent flow fields with a single universal constant and has an incorrect near-wall behavior. Germano et al. (1991) and Ghosal, Lund & Moin have developed a new subgrid-scale model, the dynamic model, which is very promising in alleviating many of the persistent inadequacies of the Smagorinsky model: the model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model has been remarkably successful in prediction of several turbulent and transitional flows. We plan to simulate turbulent flow over a '2D' airfoil using the large eddy simulation technique. Our primary objective is to assess the performance of the newly developed dynamic subgrid-scale model for computation of complex flows about aircraft components and to compare the results with those obtained using the Reynolds average approach and experiments. The present computation represents the first application of large eddy simulation to a flow of aeronautical interest and a key demonstration of the capabilities of the large eddy simulation technique.

Parameterized and resolved Southern Ocean eddy compensation

NASA Astrophysics Data System (ADS)

Poulsen, Mads B.; Jochum, Markus; Nuterman, Roman

2018-04-01

The ability to parameterize Southern Ocean eddy effects in a forced coarse resolution ocean general circulation model is assessed. The transient model response to a suite of different Southern Ocean wind stress forcing perturbations is presented and compared to identical experiments performed with the same model in 0.1° eddy-resolving resolution. With forcing of present-day wind stress magnitude and a thickness diffusivity formulated in terms of the local stratification, it is shown that the Southern Ocean residual meridional overturning circulation in the two models is different in structure and magnitude. It is found that the difference in the upper overturning cell is primarily explained by an overly strong subsurface flow in the parameterized eddy-induced circulation while the difference in the lower cell is mainly ascribed to the mean-flow overturning. With a zonally constant decrease of the zonal wind stress by 50% we show that the absolute decrease in the overturning circulation is insensitive to model resolution, and that the meridional isopycnal slope is relaxed in both models. The agreement between the models is not reproduced by a 50% wind stress increase, where the high resolution overturning decreases by 20%, but increases by 100% in the coarse resolution model. It is demonstrated that this difference is explained by changes in surface buoyancy forcing due to a reduced Antarctic sea ice cover, which strongly modulate the overturning response and ocean stratification. We conclude that the parameterized eddies are able to mimic the transient response to altered wind stress in the high resolution model, but partly misrepresent the unperturbed Southern Ocean meridional overturning circulation and associated heat transports.

Ingredients of the Eddy Soup: A Geometric Decomposition of Eddy-Mean Flow Interactions

NASA Astrophysics Data System (ADS)

Waterman, S.; Lilly, J. M.

2014-12-01

Understanding eddy-mean flow interactions is a long-standing problem in geophysical fluid dynamics with modern relevance to the task of representing eddy effects in coarse resolution models while preserving their dependence on the underlying dynamics of the flow field. Exploiting the recognition that the velocity covariance matrix/eddy stress tensor that describes eddy fluxes, also encodes information about eddy size, shape and orientation through its geometric representation in the form of the so-called variance ellipse, suggests a potentially fruitful way forward. Here we present a new framework that describes eddy-mean flow interactions in terms of a geometric description of the eddy motion, and illustrate it with an application to an unstable jet. Specifically we show that the eddy vorticity flux divergence F, a key dynamical quantity describing the average effect of fluctuations on the time-mean flow, may be decomposed into two components with distinct geometric interpretations: 1. variations in variance ellipse orientation; and 2. variations in the anisotropic part of the eddy kinetic energy, a function of the variance ellipse size and shape. Application of the divergence theorem shows that F integrated over a region is explained entirely by variations in these two quantities around the region's periphery. This framework has the potential to offer new insights into eddy-mean flow interactions in a number of ways. It identifies the ingredients of the eddy motion that have a mean flow forcing effect, it links eddy effects to spatial patterns of variance ellipse geometry that can suggest the mechanisms underpinning these effects, and finally it illustrates the importance of resolving eddy shape and orientation, and not just eddy size/energy, to accurately represent eddy feedback effects. These concepts will be both discussed and illustrated.

Dynamically consistent parameterization of mesoscale eddies. Part III: Deterministic approach

NASA Astrophysics Data System (ADS)

Berloff, Pavel

2018-07-01

This work continues development of dynamically consistent parameterizations for representing mesoscale eddy effects in non-eddy-resolving and eddy-permitting ocean circulation models and focuses on the classical double-gyre problem, in which the main dynamic eddy effects maintain eastward jet extension of the western boundary currents and its adjacent recirculation zones via eddy backscatter mechanism. Despite its fundamental importance, this mechanism remains poorly understood, and in this paper we, first, study it and, then, propose and test its novel parameterization. We start by decomposing the reference eddy-resolving flow solution into the large-scale and eddy components defined by spatial filtering, rather than by the Reynolds decomposition. Next, we find that the eastward jet and its recirculations are robustly present not only in the large-scale flow itself, but also in the rectified time-mean eddies, and in the transient rectified eddy component, which consists of highly anisotropic ribbons of the opposite-sign potential vorticity anomalies straddling the instantaneous eastward jet core and being responsible for its continuous amplification. The transient rectified component is separated from the flow by a novel remapping method. We hypothesize that the above three components of the eastward jet are ultimately driven by the small-scale transient eddy forcing via the eddy backscatter mechanism, rather than by the mean eddy forcing and large-scale nonlinearities. We verify this hypothesis by progressively turning down the backscatter and observing the induced flow anomalies. The backscatter analysis leads us to formulating the key eddy parameterization hypothesis: in an eddy-permitting model at least partially resolved eddy backscatter can be significantly amplified to improve the flow solution. Such amplification is a simple and novel eddy parameterization framework implemented here in terms of local, deterministic flow roughening controlled by single parameter. We test the parameterization skills in an hierarchy of non-eddy-resolving and eddy-permitting modifications of the original model and demonstrate, that indeed it can be highly efficient for restoring the eastward jet extension and its adjacent recirculation zones. The new deterministic parameterization framework not only combines remarkable simplicity with good performance but also is dynamically transparent, therefore, it provides a powerful alternative to the common eddy diffusion and emerging stochastic parameterizations.

Hybrid Reynolds-Averaged/Large-Eddy Simulations of a Co-Axial Supersonic Free-Jet Experiment

NASA Technical Reports Server (NTRS)

Baurle, R. A.; Edwards, J. R.

2009-01-01

Reynolds-averaged and hybrid Reynolds-averaged/large-eddy simulations have been applied to a supersonic coaxial jet flow experiment. The experiment utilized either helium or argon as the inner jet nozzle fluid, and the outer jet nozzle fluid consisted of laboratory air. The inner and outer nozzles were designed and operated to produce nearly pressure-matched Mach 1.8 flow conditions at the jet exit. The purpose of the computational effort was to assess the state-of-the-art for each modeling approach, and to use the hybrid Reynolds-averaged/large-eddy simulations to gather insight into the deficiencies of the Reynolds-averaged closure models. The Reynolds-averaged simulations displayed a strong sensitivity to choice of turbulent Schmidt number. The baseline value chosen for this parameter resulted in an over-prediction of the mixing layer spreading rate for the helium case, but the opposite trend was noted when argon was used as the injectant. A larger turbulent Schmidt number greatly improved the comparison of the results with measurements for the helium simulations, but variations in the Schmidt number did not improve the argon comparisons. The hybrid simulation results showed the same trends as the baseline Reynolds-averaged predictions. The primary reason conjectured for the discrepancy between the hybrid simulation results and the measurements centered around issues related to the transition from a Reynolds-averaged state to one with resolved turbulent content. Improvements to the inflow conditions are suggested as a remedy to this dilemma. Comparisons between resolved second-order turbulence statistics and their modeled Reynolds-averaged counterparts were also performed.

The 360 Degree Fulldome Production "Clockwork Ocean"

NASA Astrophysics Data System (ADS)

Baschek, B.; Heinsohn, R.; Opitz, D.; Fischer, T.; Baschek, T.

2016-02-01

The investigation of submesoscale eddies and fronts is one of the leading oceanographic topics at the Ocean Sciences Meeting 2016. In order to observe these small and short-lived phenomena, planes equipped with high-resolution cameras and fast vessels were deployed during the Submesoscale Experiments (SubEx) leading to some of the first high-resolution observations of these eddies. In a future experiment, a zeppelin will be used the first time in marine sciences. The relevance of submesoscale processes for the oceans and the work of the eddy hunters is described in the fascinating 9-minute long 360 degree fulldome production Clockwork Ocean. The fully animated movie is introduced in this presentation taking the observer from the bioluminescence in the deep ocean to a view of our blue planet from space. The immersive media is used to combine fascination for a yet unknown environment with scientific education of a broad audience. Detailed background information is available at the parallax website www.clockwork-ocean.com. The Film is also available for Virtual Reality glasses and smartphones to reach a broader distribution. A unique Mobile Dome with an area of 70 m² and seats for 40 people is used for science education at events, festivals, for politicians and school classes. The spectators are also invited to participate in the experiments by presenting 360 degree footage of the measurements. The premiere of Clockwork Ocean was in July 2015 in Hamburg, Germany and will be worldwide available in English and German as of fall 2015. Clockwork Ocean is a film of the Helmholtz-Zentrum Geesthacht produced by Daniel Opitz and Ralph Heinsohn.

Cyclonic eddies identified in the Cape Basin of the South Atlantic Ocean

NASA Astrophysics Data System (ADS)

Hall, C.; Lutjeharms, J. R. E.

2011-03-01

Inter-ocean exchange south of Africa takes place largely through the movement of Agulhas Rings into the Cape Basin. Recent observations have shown that the highly energetic flow field in this basin consists of anti-cyclonic rings as well as cyclonic eddies. Very little is known of the characteristics of the cyclonic eddies. Using altimetric data, this study determines the location, frequency and seasonality of these cyclonic eddies their size, trajectories, life spans and their association with Agulhas Rings. Cyclonic eddies were seen to split, merge and link with other cyclonic eddies, where splitting events created child cyclonic eddies. The 105 parent and 157 child cyclonic eddies identified over a decade show that on average 11 parent and 17 child cyclonic eddies appear annually in AVISO merged absolute dynamic topography data along the continental slope. Thirty-two percent follow an overall west south-westward direction, with 27% going west north-westward. Average translocation speeds are 2.2 ± 0.1 km/day for parent and 3.0 ± 0.2 km/day for child cyclonic eddies. Parent cyclonic eddy lifespan averaged 250 ± 18 days; whereas child cyclonic eddies survived for only 118 ± 11 days. A significant difference in lifespan for parent and child cyclonic eddies identified in the north and south region of the study area was detected. Seventy-seven percent of the northern and 93% of the southern cyclonic eddies were first detected directly adjacent to passing Agulhas Rings, suggesting a vital interaction between these mesoscale eddies within the region. Topographical features appeared to affect the behaviour and lifespan of these deep cyclonic eddies.

Assessment of subgrid-scale models with a large-eddy simulation-dedicated experimental database: The pulsatile impinging jet in turbulent cross-flow

NASA Astrophysics Data System (ADS)

Baya Toda, Hubert; Cabrit, Olivier; Truffin, Karine; Bruneaux, Gilles; Nicoud, Franck

2014-07-01

Large-Eddy Simulation (LES) in complex geometries and industrial applications like piston engines, gas turbines, or aircraft engines requires the use of advanced subgrid-scale (SGS) models able to take into account the main flow features and the turbulence anisotropy. Keeping this goal in mind, this paper reports a LES-dedicated experiment of a pulsatile hot-jet impinging a flat-plate in the presence of a cold turbulent cross-flow. Unlike commonly used academic test cases, this configuration involves different flow features encountered in complex configurations: shear/rotating regions, stagnation point, wall-turbulence, and the propagation of a vortex ring along the wall. This experiment was also designed with the aim to use quantitative and nonintrusive optical diagnostics such as Particle Image Velocimetry, and to easily perform a LES involving a relatively simple geometry and well-controlled boundary conditions. Hence, two eddy-viscosity-based SGS models are investigated: the dynamic Smagorinsky model [M. Germano, U. Piomelli, P. Moin, and W. Cabot, "A dynamic subgrid-scale eddy viscosity model," Phys. Fluids A 3(7), 1760-1765 (1991)] and the σ-model [F. Nicoud, H. B. Toda, O. Cabrit, S. Bose, and J. Lee, "Using singular values to build a subgrid-scale model for large eddy simulations," Phys. Fluids 23(8), 085106 (2011)]. Both models give similar results during the first phase of the experiment. However, it was found that the dynamic Smagorinsky model could not accurately predict the vortex-ring propagation, while the σ-model provides a better agreement with the experimental measurements. Setting aside the implementation of the dynamic procedure (implemented here in its simplest form, i.e., without averaging over homogeneous directions and with clipping of negative values to ensure numerical stability), it is suggested that the mitigated predictions of the dynamic Smagorinsky model are due to the dynamic constant, which strongly depends on the mesh resolution. Indeed, the shear-stress near the wall increases during the vortex-ring impingement leading to a less refined mesh in terms of wall units, y+. This loss of resolution induces a poor damping of the dynamic constant, which is no longer able to adjust itself to ensure the expected y3-behavior near the wall. It is shown that the dynamic constant is never small enough to properly balance the large values of the squared magnitude of the strain-rate tensor, 2SijSij. The experimental database is made available to the community upon request to the authors.

Climate change and the middle atmosphere. II - The impact of volcanic aerosols

NASA Technical Reports Server (NTRS)

Rind, D.; Balachandran, N. K.; Suozzo, R.

1992-01-01

The response of the middle atmosphere to an increase in stratospheric aerosols, normally associated with increased volcanic activity, is investigated. The aerosols are found to induce a direct stratospheric response, with warming in the tropical lower stratosphere, and cooling at higher latitudes. On the shorter time scales, this radiative effect increases tropospheric static stability at low- to midlatitudes, which reduces the intensity of the Hadley cell and Ferrel cell. There is an associated increase in tropospheric standing wave energy and a decrease in midlatitude west winds, which result in additional wave energy propagation into the stratosphere at lower midlatitudes in both hemispheres. On the longer time scale, a strong hemispheric asymmetry arises. In the Northern Hemisphere eddy energy decreases, as does the middle-atmosphere residual circulation, and widespread stratospheric cooling results. In the Southern Hemisphere, the large increase in sea ice increases the tropospheric latitudinal temperature gradient, leading to increased eddy energy, an increased middle-atmosphere residual circulation, and some high-latitude stratospheric warming.

Can CO2 Turbulent Flux Be Measured by Lidar? A Preliminary Study

NASA Technical Reports Server (NTRS)

Gilbert, Fabien; Koch, Grady; Beyon, Jeffrey Y.; Hilton, Timothy W.; Davis, Kenneth J.; Andrews, Arlyn; Flamant, Pierre H.; Singh, Upendra N.

2011-01-01

The vertical profiling ofCO2 turbulent fluxes in the atmospheric boundary layer (ABL) is investigated using a coherent differential absorption lidar (CDIAL) operated nearby a tall tower in Wisconsin during June 2007. A CDIAL can perform simultaneous range-resolved CO2 DIAL and velocity measurements. The lidar eddy covariance technique is presented. The aims of the study are (i) an assessment of performance and current limitation of available CDIAL for CO2 turbulent fluxes and (ii) the derivation of instrument specifications to build a future CDIAL to perform accurate range-resolved CO2 fluxes. Experimental lidar CO2 mixing ratio and vertical velocity profiles are successfully compared with in situ sensors measurements. Time and space integral scales of turbulence in the ABL are addressed that result in limitation for time averaging and range accumulation. A first attempt to infer CO2 fluxes using an eddy covariance technique with currently available 2-mm CDIAL dataset is reported.

Entrainment, Drizzle, and Stratocumulus Cloud Albedo

NASA Technical Reports Server (NTRS)

Ackerman, A. S.; Kirkpatrick, M. P.; Stevens, D. E.; Toon, O. B.

2004-01-01

Globally averaged cloud changes from GCMs on average show a doubling of the Twomey effect, which is the change in cloud albedo with respect to changes in droplet concentrations for fixed cloud water and droplet dispersion. In contrast, ship-track measurements show a much more modest amplification of the Twomey effect, suggesting that the GCMs are exaggerating the indirect aerosol effect. We have run large-eddy simulations with bin microphysics of marine stratocumulus from multiple field campaigns, and find that the large-eddy simulations are in much better agreement with the ship-track measurements. The inversion strength over N. Pacific stratocumulus (as measured during DYCOMS-II) is generally much stronger than over N. Atlantic stratocumulus (as measured during ASTEX), and we have found that the response of cloud water to increasing droplet concentration changes sign as the inversion strengthens. For the different environmental conditions, we will show the overall response of cloud albedo to droplet concentrations, and decompose the response into its contributing factors of changes in cloud water, droplet dispersion, and horizontal inhomogeneity.

A numerical study of circulation in the Gulf of Riga, Baltic Sea. Part II: Mesoscale features and freshwater transport pathways

NASA Astrophysics Data System (ADS)

Lips, Urmas; Zhurbas, Victor; Skudra, Maris; Väli, Germo

2016-03-01

A regional eddy-resolving model is developed to study mesoscale processes in the Gulf of Riga in relation to river runoff, saltwater inflow, and atmospheric forcing. A number of mesoscale phenomena are simulated and discussed, such as meandering of coastal buoyant plume/current of riverine waters and formation and splitting of cyclonic eddies related to the saltwater inflow. It is shown that the Daugava River discharge forms a surface-advected plume (Yankovsky and Chapman, 1997) consisting of an anticyclonic bulge and coastal buoyant jet. In case of no saltwater inflow and no atmospheric forcing, the river runoff is distributed between the growing anticyclonic bulge and the coastal current in proportion of about 7:6. In the summer season, a substantial fraction of freshwater from the anticyclonic bulge can be transported to the north by the anticyclonic whole-basin circulation gyre leading to the bimodal transport pathways of the Daugava River plume.

Decomposing the permeability spectra of nanocrystalline finemet core

NASA Astrophysics Data System (ADS)

Varga, Lajos K.; Kovac, Jozef

2018-04-01

In this paper we present a theoretical and experimental investigation on the magnetization contributions to permeability spectra of normal annealed Finemet core with round type hysteresis curve. Real and imaginary parts of the permeability were determined as a function of exciting magnetic field (HAC) between 40 Hz -110 MHz using an Agilent 4294A type Precision Impedance Analyzer. The amplitude of the exciting field was below and around the coercive field of the sample. The spectra were decomposed using the Levenberg-Marquardt algorithm running under Origin 9 software in four contributions: i) eddy current; ii) Debye relaxation of magnetization rotation, iii) Debye relaxation of damped domain wall motion and iv) resonant type DW motion. For small exciting amplitudes the first two components dominate. The last two contributions connected to the DW appear for relative large HAC only, around the coercive force. All the contributions will be discussed in detail accentuating the role of eddy current that is not negligible even for the smallest applied exciting field.

Analysis of a general circulation model. II - Distribution of kinetic energy in the South Atlantic and Kuroshio/Oyashio systems

NASA Technical Reports Server (NTRS)

Garraffo, Zulema; Garzoli, Silvia L.; Haxby, William; Olson, Donald

1992-01-01

It was found (Garzoli et al., 1992) that the general circulation model of Semtner and Chervin (1992) provides accurate descriptions of the Brazil-Malvinas and the Kuroshio/Oyashio confluence systems, except for the fact that the model prediction shows less variability than that present in observations. This paper investigates the problem of model variability by analyzing the mean and the eddy kinetic energy from the model and comparing the values with the Geosat altimeter observations for the South Atlantic Ocean and for the Kuroshio system. It is found that, while the model shows transient eddy activity in the areas that overlap the Geosat observations, the energy level of the model transient motions is considerably smaller following an arch along the bottom topography. The same was found from the comparisons made with values obtained from FGGE and surface drifters. It is suggested that the model is poorly resolving instabilities in the confluence front, and is not resolving other transients appearing in regions of marked topography.

Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon

NASA Astrophysics Data System (ADS)

Muraleedharan, K. R.; Jasmine, P.; Achuthankutty, C. T.; Revichandran, C.; Dinesh Kumar, P. K.; Anand, P.; Rejomon, G.

2007-03-01

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July-August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m -3), low surface primary production (2.55 mg C m -3 day -1) and low zooplankton biovolume (0.14 ml m -3). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO 3-N > 8.2 μM, PO 4-P > 0.8 μM, SiO 4-Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a - 0.25 mg m -3, PP - 9.23 mg C m -3 day -1), and mesozooplankton biovolume (1.12 ml m -3) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.

Further Studies on Oceanic Biogeochemistry and Carbon Cycling

NASA Technical Reports Server (NTRS)

Signorini, S. R.; McClain, C. R.

2003-01-01

This TM consists of two chapters. Chapter I describes the development of a coupled, one-dimensional biogeochemical model using turbulence closure mixed layer (TCMLM) dynamics. The model is applied to the Sargasso Sea at the BATS (Bermuda Atlantic Time Series) site and the results are compared with a previous model study in the same region described in NASNTP-2001-209991. The use of the TCMLM contributed to some improvements in the model simulation of chlorophyll, PAR, nitrate, phosphate, and oxygen, but most importantly, the current model achieved good agreement with the data with much more realistic background eddy diffusivity. However, off-line calculations of horizontal transport of biogeochemical properties revealed that one-dimensional dynamics can only provide a limited assessment of the nutrient and carbon balances at BATS. Future studies in the BATS region will require comprehensive three-dimensional field studies, combined with three-dimensional eddy resolving numerical experiments, to adequately quantify the impact of the local and remote forcing on ecosystem dynamics and carbon cycling. Chapter II addresses the sensitivity of global sea-air CO, flux estimates to wind speed, temperature, and salinity. Sensitivity analyses of sea-air CO, flux to wind speed climatologies, gas transfer algorithms, SSS and SST were conducted for the global oceans and regional domains. Large uncertainties in the global sea-air flux are identified, primarily due to the different gas transfer algorithms used. The sensitivity of the sea-air flux to SST and SSS is similar in magnitude to the effect of using different wind climatologies. Globally, the mean ocean uptake of CO, changes by 5 to 16%, depending upon the combination of SST and SSS used.

Evidence for production and lateral transport of dissolved organic phosphorus in the eastern subtropical North Atlantic

NASA Astrophysics Data System (ADS)

Reynolds, Sarah; Mahaffey, Claire; Roussenov, Vassil; Williams, Richard G.

2014-08-01

The concentration of phosphate and dissolved organic phosphorus (DOP) is chronically low and limits phytoplankton growth in the subtropical North Atlantic relative to other ocean basins. Transport of phosphate and DOP from the productive flanks of the gyre to its interior has been hypothesized as an important phosphorus supply pathway. During a cruise in the eastern Atlantic in spring 2011, the rates of phosphate uptake, alkaline phosphatase activity (APA), and DOP production were measured in the northwest African shelf region, subtropics, and tropics. Rates of DOP production were sixfold higher in the shelf region (43 ± 41 nM d-1) relative to the subtropics (6.9 ± 4.4 nM d-1). In contrast, APA was threefold higher in the subtropics (8.0 ± 7.3 nM d-1), indicative of enhanced DOP utilization, relative to the shelf region (2.6 ± 2.1 nM d-1). Hence, observations suggest net production of DOP in the shelf region and either net consumption of DOP or a near balance in DOP production and consumption in the gyre interior. Eddy-permitting model experiments demonstrate that (i) DOP accounts for over half the total phosphorus in surface waters, (ii) DOP is transported westward from the shelf region by a combination of gyre and eddy circulations, and (iii) advected DOP supports up to 70% of the particle export over much of the subtropical gyre. Our combined observational and modeling study supports the view that the horizontal transport of DOP from the shelf region is an important mechanism supplying phosphorus to the surface subtropical North Atlantic.

Eddy-resolving 1/10° model of the World Ocean

NASA Astrophysics Data System (ADS)

Ibrayev, R. A.; Khabeev, R. N.; Ushakov, K. V.

2012-02-01

The first results on simulating the intra-annual variability of the World Ocean circulation by use of the eddy-resolving model are considered. For this purpose, a model of the World Ocean with a 1/10° horizontal resolution and 49 vertical levels was developed (a 1/10 × 1/10 × 49 model of the World Ocean). This model is based on the traditional system of three-dimensional equations of the large-scale dynamics of the ocean and boundary conditions with an explicit allowance for water fluxes on the free surface of the ocean. The equations are written in the tripolar coordinate system. The numerical method is based on the separation of the barotropic and baroclinic components of the solution. Discretization in time is implemented using explicit schemes allowing effective parallelization for a large number of processors. The model uses the sub-models of the boundary layer of the atmosphere and the submodel of sea-ice thermodynamics. The model of the World Ocean was developed at the Institute of Numerical Mathematics of the Russian Academy of Sciences (INM RAS) and the P.P. Shirshov Institute of Oceanogy (IO RAS). The formulation of the problem of simulating the intra-annual variability of thermohydrodynamic processes of the World Ocean and the parameterizations that were used are considered. In the numerical experiment, the temporal evolution of the atmospheric effect is determined by the normal annual cycle according to the conditions of the international Coordinated Ocean-Ice Reference Experiment (CORE-I). The calculation was carried out on a multiprocessor computer with distributed memory; 1601 computational cores were used. The presented analysis demonstrates that the obtained results are quite satisfactory when compared to the results that were obtained by other eddy-resolving models of the global ocean. The analysis of the model solution is, to a larger extent, of a descriptive character. A detailed analysis of the results is to be presented in following works. This experiment is a significant first step in developing the eddy-resolving model of the World Ocean.

Automatic tracking of dynamical evolutions of oceanic mesoscale eddies with satellite observation data

NASA Astrophysics Data System (ADS)

Sun, Liang; Li, Qiu-Yang

2017-04-01

The oceanic mesoscale eddies play a major role in ocean climate system. To analyse spatiotemporal dynamics of oceanic mesoscale eddies, the Genealogical Evolution Model (GEM) based on satellite data is developed, which is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean. It can distinguish different dynamic processes (e.g., merging and splitting) within a dynamic evolution pattern, which is difficult to accomplish using other tracking methods. To this end, a mononuclear eddy detection method was firstly developed with simple segmentation strategies, e.g. watershed algorithm. The algorithm is very fast by searching the steepest descent path. Second, the GEM uses a two-dimensional similarity vector (i.e. a pair of ratios of overlap area between two eddies to the area of each eddy) rather than a scalar to measure the similarity between eddies, which effectively solves the ''missing eddy" problem (temporarily lost eddy in tracking). Third, for tracking when an eddy splits, GEM uses both "parent" (the original eddy) and "child" (eddy split from parent) and the dynamic processes are described as birth and death of different generations. Additionally, a new look-ahead approach with selection rules effectively simplifies computation and recording. All of the computational steps are linear and do not include iteration. Given the pixel number of the target region L, the maximum number of eddies M, the number N of look-ahead time steps, and the total number of time steps T, the total computer time is O (LM(N+1)T). The tracking of each eddy is very smooth because we require that the snapshots of each eddy on adjacent days overlap one another. Although eddy splitting or merging is ubiquitous in the ocean, they have different geographic distribution in the Northern Pacific Ocean. Both the merging and splitting rates of the eddies are high, especially at the western boundary, in currents and in "eddy deserts". GEM is useful not only for satellite-based observational data but also for numerical simulation outputs. It is potentially useful for studying dynamic processes in other related fields, e.g., the dynamics of cyclones in meteorology.

Dynamically Consistent Parameterization of Mesoscale Eddies This work aims at parameterization of eddy effects for use in non-eddy-resolving ocean models and focuses on the effect of the stochastic part of the eddy forcing that backscatters and induces eastward jet extension of the western boundary currents and its adjacent recirculation zones.

NASA Astrophysics Data System (ADS)

Berloff, P. S.

2016-12-01

This work aims at developing a framework for dynamically consistent parameterization of mesoscale eddy effects for use in non-eddy-resolving ocean circulation models. The proposed eddy parameterization framework is successfully tested on the classical, wind-driven double-gyre model, which is solved both with explicitly resolved vigorous eddy field and in the non-eddy-resolving configuration with the eddy parameterization replacing the eddy effects. The parameterization focuses on the effect of the stochastic part of the eddy forcing that backscatters and induces eastward jet extension of the western boundary currents and its adjacent recirculation zones. The parameterization locally approximates transient eddy flux divergence by spatially localized and temporally periodic forcing, referred to as the plunger, and focuses on the linear-dynamics flow solution induced by it. The nonlinear self-interaction of this solution, referred to as the footprint, characterizes and quantifies the induced eddy forcing exerted on the large-scale flow. We find that spatial pattern and amplitude of each footprint strongly depend on the underlying large-scale flow, and the corresponding relationships provide the basis for the eddy parameterization and its closure on the large-scale flow properties. Dependencies of the footprints on other important parameters of the problem are also systematically analyzed. The parameterization utilizes the local large-scale flow information, constructs and scales the corresponding footprints, and then sums them up over the gyres to produce the resulting eddy forcing field, which is interactively added to the model as an extra forcing. Thus, the assumed ensemble of plunger solutions can be viewed as a simple model for the cumulative effect of the stochastic eddy forcing. The parameterization framework is implemented in the simplest way, but it provides a systematic strategy for improving the implementation algorithm.

Calculation of transonic aileron buzz

NASA Technical Reports Server (NTRS)

Steger, J. L.; Bailey, H. E.

1979-01-01

An implicit finite-difference computer code that uses a two-layer algebraic eddy viscosity model and exact geometric specification of the airfoil has been used to simulate transonic aileron buzz. The calculated results, which were performed on both the Illiac IV parallel computer processor and the Control Data 7600 computer, are in essential agreement with the original expository wind-tunnel data taken in the Ames 16-Foot Wind Tunnel just after World War II. These results and a description of the pertinent numerical techniques are included.

Mesoscale Eddies in the Northwestern Pacific Ocean: Three-Dimensional Eddy Structures and Heat/Salt Transports

NASA Astrophysics Data System (ADS)

Dong, Di; Brandt, Peter; Chang, Ping; Schütte, Florian; Yang, Xiaofeng; Yan, Jinhui; Zeng, Jisheng

2017-12-01

The region encompassing the Kuroshio Extension (KE) in the Northwestern Pacific Ocean (25°N-45°N and 130°E-180°E) is one of the most eddy-energetic regions of the global ocean. The three-dimensional structures and transports of mesoscale eddies in this region are comprehensively investigated by combined use of satellite data and Argo profiles. With the allocation of Argo profiles inside detected eddies, the spatial variations of structures of eddy temperature and salinity anomalies are analyzed. The results show that eddies predominantly have subsurface (near-surface) intensified temperature and salinity anomalies south (north) of the KE jet, which is related to different background stratifications between these regions. A new method based on eddy trajectories and the inferred three-dimensional eddy structures is proposed to estimate heat and salt transports by eddy movements in a Lagrangian framework. Spatial distributions of eddy transports are presented over the vicinity of the KE for the first time. The magnitude of eddy-induced meridional heat (freshwater volume) transport is on the order of 0.01 PW (103 m3/s). The eddy heat transport divergence results in an oceanic heat loss south and heat gain north of the KE, thereby reinforcing and counteracting the oceanic heat loss from air-sea fluxes south and north of the KE jet, respectively. It also suggests a poleward heat transport across the KE jet due to eddy propagation.

Nonlinear Eddy-Eddy Interactions in Dry Atmospheres Macroturbulence

NASA Astrophysics Data System (ADS)

Ait Chaalal, F.; Schneider, T.

2012-12-01

The statistical moment equations derived from the atmospheric equation of motions are not closed. However neglecting the large-scale eddy-eddy nonlinear interactions in an idealized dry general circulation model (GCM), which is equivalent to truncating the moment equations at the second order, can reproduce some of the features of the general circulation ([1]), highlighting the significance of eddy-mean flow interactions and the weakness of eddy-eddy interactions in atmospheric macroturbulence ([2]). The goal of the present study is to provide new insight into the rôle of these eddy-eddy interactions and discuss the relevance of a simple stochastic parametrization to represent them. We investigate in detail the general circulation in an idealized dry GCM, comparing full simulations with simulations where the eddy-eddy interactions are removed. The radiative processes are parametrized through Newtonian relaxation toward a radiative-equilibrium state with a prescribed equator to pole temperature contrast. A convection scheme relaxing toward a prescribed convective vertical lapse rate mimics some aspects of moist convection. The study is performed over a wide range of parameters covering the planetary rotation rate, the equator to pole temperature contrast and the vertical lapse rate. Particular attention is given to the wave-mean flow interactions and to the spectral budget. It is found that the no eddy-eddy simulations perform well when the baroclinic activity is weaker, for example for lower equator to pole temperature contrasts or higher rotation rates: the mean meridional circulation is well reproduced, with realistic eddy-driven jets and energy-containing eddy length scales of the order of the Rossby deformation radius. For a stronger baroclinic activity the no eddy-eddy model does not achieve a realistic isotropization of the eddies, the meridional circulation is compressed in the meridional direction and secondary eddy-driven jets emerge. In addition, the baroclinic wave activity does not reach the upper troposphere in association with a very weak or absent Rossby wave absorption in the upper subtropical troposphere. Understanding these deficiencies and the rôle of the eddy-eddy nonlinear interactions in determining the mean meridional circulation paves the way to the development of stochastic third order moments parametrizations, to eventually build GCMs that directly solve for the flow statistics and that could provide a deeper understanding of anthropogenic and natural climate changes. [1] O'Gorman, P. A., & Schneider, T. 2007, Geophysical Research Letters, 34, 22801 [2] Schneider, T., and C. C. Walker, 2006, Journal of the Atmospheric Sciences, 63, 1569-1586.

Increasing of eddy activity in the northeastern Pacific during 1993-2011

NASA Astrophysics Data System (ADS)

Ding, M.; Lin, P.; Liu, H.; Chai, F.

2017-12-01

We study the long-term behaviors of eddy activity in the northeastern Pacific (NEP) and the dynamic mechanism behind them based on the 3rd version of the mesoscale eddy trajectories dataset released by Chelton et al. (2013) combined with other observation and reanalysis datasets. Both the eddy kinetic energy (EKE) and eddy occurrence number (EON) present prominent increasing trends, with inter-annual and decadal variabilities northeast of the Hawaii-Emperor seamounts. The increasing trend of the EON is mainly due to prolongation of the eddy lifetime associated with the eddy intensification, particularly for anticyclonic eddies (AEs). Weakened surface winds tend to prolong the eddy lifetimes, as the eddy attenuation time scale is inversely proportional to the wind speed. The enhanced anticyclonic wind stress curl (WSC) anomalies inject more energy into the AE over the study region and provide a more suitable environment for AEs growth. The decadal climate modes, such as the Pacific decadal oscillation (PDO) and the North Pacific gyre oscillation (NPGO), may also modulate eddy activities in the NEP by exerting fluctuations in the surface wind system.

On the role of mesoscale eddies for the biological productivity and biogeochemistry in the eastern tropical Pacific Ocean off Peru

NASA Astrophysics Data System (ADS)

Stramma, L.; Bange, H. W.; Czeschel, R.; Lorenzo, A.; Frank, M.

2013-06-01

Mesoscale eddies seem to play an important role for both the hydrography and biogeochemistry of the eastern tropical Pacific Ocean (ETSP) off Peru. However, detailed surveys of these eddies are not available, which has so far hampered an in depth understanding of their implications for nutrient distribution and biological productivity. In this study three eddies along a section at 16°45' S have been surveyed intensively during R/V Meteor cruise M90 in November 2012. A coastal mode water eddy, an open ocean mode water eddy and an open ocean cyclonic eddy have been identified and sampled in order to determine both their hydrographic properties and their influence on the biogeochemical setting of the ETSP. In the thermocline the temperature of the coastal anticyclonic eddy was up to 2 °C warmer, 0.2 more saline and the swirl velocity was up to 35 cm s-1. The observed temperature and salinity anomalies, as well as swirl velocities of both types of eddies were about twice as large as had been described for the mean eddies in the ETSP and the observed heat and salt anomalies (AHA, ASA) show a much larger variability than the mean AHA and ASA. We found that the eddies contributed significantly to productivity by maintaining pronounced subsurface maxima of chlorophyll. Based on a comparison of the coastal (young) mode water eddy and the open ocean (old) mode water eddy we conclude that the aging of eddies when they detach from the coast and move westward to the open ocean considerably influences the eddies' properties: chlorophyll maxima are weaker and nutrients are subducted. The coastal mode water eddy was found to be a hotspot of nitrogen loss in the OMZ, whereas, the open ocean cyclonic eddy was of negligible importance for nitrogen loss. Our results show that the important role the eddies play in the ETSP can only be fully deciphered and understood through dedicated high spatial and temporal resolution oceanographic/biogeochemical surveys.

Eddy properties in the Southern California Current System

NASA Astrophysics Data System (ADS)

Chenillat, Fanny; Franks, Peter J. S.; Capet, Xavier; Rivière, Pascal; Grima, Nicolas; Blanke, Bruno; Combes, Vincent

2018-05-01

The California Current System (CCS) is an eastern boundary upwelling system characterized by strong eddies that are often generated at the coast. These eddies contribute to intense, long-distance cross-shelf transport of upwelled water with enhanced biological activity. However, the mechanisms of formation of such coastal eddies, and more importantly their capacity to trap and transport tracers, are poorly understood. Their unpredictability and strong dynamics leave us with an incomplete picture of the physical and biological processes at work, their effects on coastal export, lateral water exchange among eddies and their surrounding waters, and how long and how far these eddies remain coherent structures. Focusing our analysis on the southern part of the CCS, we find a predominance of cyclonic eddies, with a 25-km radius and a SSH amplitude of 6 cm. They are formed near shore and travel slightly northwest offshore for 190 days at 2 km day-1. We then study one particular, representative cyclonic eddy using a combined Lagrangian and Eulerian numerical approach to characterize its kinematics. Formed near shore, this eddy trapped a core made up of 67% California Current waters and 33% California Undercurrent waters. This core was surrounded by other waters while the eddy detached from the coast, leaving the oldest waters at the eddy's core and the younger waters toward the edge. The eddy traveled several months as a coherent structure, with only limited lateral exchange within the eddy.

Mesoscale Eddy Activity and Transport in the Atlantic Water Inflow Region North of Svalbard

NASA Astrophysics Data System (ADS)

Crews, L.; Sundfjord, A.; Albretsen, J.; Hattermann, T.

2018-01-01

Mesoscale eddies are known to transport heat and biogeochemical properties from Arctic Ocean boundary currents to basin interiors. Previous hydrographic surveys and model results suggest that eddy formation may be common in the Atlantic Water (AW) inflow area north of Svalbard, but no quantitative eddy survey has yet been done for the region. Here vorticity and water property signatures are used to identify and track AW eddies in an eddy-resolving sea ice-ocean model. The boundary current sheds AW eddies along most of the length of the continental slope considered, from the western Yermak Plateau to 40°E, though eddies forming east of 20°E are likely more important for slope-to-basin transport. Eddy formation seasonality reflects seasonal stability properties of the boundary current in the eastern portion of the study domain, but on and immediately east of the Yermak Plateau enhanced eddy formation during summer merits further investigation. AW eddies tend to be anticyclonic, have radii close to the local deformation radius, and be centered in the halocline. They transport roughly 0.16 Sv of AW and, due to their warm cores, 1.0 TW away from the boundary current. These findings suggest eddies may be important for halocline ventilation in the Eurasian Basin, as has been shown for Pacific Water eddies in the Canadian Basin.

Large-eddy simulation of propeller noise

NASA Astrophysics Data System (ADS)

Keller, Jacob; Mahesh, Krishnan

2016-11-01

We will discuss our ongoing work towards developing the capability to predict far field sound from the large-eddy simulation of propellers. A porous surface Ffowcs-Williams and Hawkings (FW-H) acoustic analogy, with a dynamic endcapping method (Nitzkorski and Mahesh, 2014) is developed for unstructured grids in a rotating frame of reference. The FW-H surface is generated automatically using Delaunay triangulation and is representative of the underlying volume mesh. The approach is validated for tonal trailing edge sound from a NACA 0012 airfoil. LES of flow around a propeller at design advance ratio is compared to experiment and good agreement is obtained. Results for the emitted far field sound will be discussed. This work is supported by ONR.

Eddy current probe response to open and closed surface flaws

NASA Technical Reports Server (NTRS)

Auld, B. A.; Muennemann, F.; Winslow, D. K.

1981-01-01

A general analysis of eddy current response to certain types of open and closed surface flaws is presented for both standard low-frequency and ferromagnetic-resonance (FMR) probes. It is shown analytically that for two-dimensional and three-dimensional surface flaws interrogated by a uniform probe field, the crack opening sensitivity increases with the operating frequency of the probe, this behavior being due to the Faraday induction effect. Experiments with low-frequency probes operating at or below 1 MHz and with the FMR probe operating at approximately 1000 MHz confirm this increase of the crack mouth opening displacement for practical situations where the probe field is not uniform in the vicinity of the flaw.

A daily global mesoscale ocean eddy dataset from satellite altimetry.

PubMed

Faghmous, James H; Frenger, Ivy; Yao, Yuanshun; Warmka, Robert; Lindell, Aron; Kumar, Vipin

2015-01-01

Mesoscale ocean eddies are ubiquitous coherent rotating structures of water with radial scales on the order of 100 kilometers. Eddies play a key role in the transport and mixing of momentum and tracers across the World Ocean. We present a global daily mesoscale ocean eddy dataset that contains ~45 million mesoscale features and 3.3 million eddy trajectories that persist at least two days as identified in the AVISO dataset over a period of 1993-2014. This dataset, along with the open-source eddy identification software, extract eddies with any parameters (minimum size, lifetime, etc.), to study global eddy properties and dynamics, and to empirically estimate the impact eddies have on mass or heat transport. Furthermore, our open-source software may be used to identify mesoscale features in model simulations and compare them to observed features. Finally, this dataset can be used to study the interaction between mesoscale ocean eddies and other components of the Earth System.

Anticyclonic eddies are more productive than cyclonic eddies in subtropical gyres because of winter mixing.

PubMed

Dufois, François; Hardman-Mountford, Nick J; Greenwood, Jim; Richardson, Anthony J; Feng, Ming; Matear, Richard J

2016-05-01

Mesoscale eddies are ubiquitous features of ocean circulation that modulate the supply of nutrients to the upper sunlit ocean, influencing the rates of carbon fixation and export. The popular eddy-pumping paradigm implies that nutrient fluxes are enhanced in cyclonic eddies because of upwelling inside the eddy, leading to higher phytoplankton production. We show that this view does not hold for a substantial portion of eddies within oceanic subtropical gyres, the largest ecosystems in the ocean. Using space-based measurements and a global biogeochemical model, we demonstrate that during winter when subtropical eddies are most productive, there is increased chlorophyll in anticyclones compared with cyclones in all subtropical gyres (by 3.6 to 16.7% for the five basins). The model suggests that this is a consequence of the modulation of winter mixing by eddies. These results establish a new paradigm for anticyclonic eddies in subtropical gyres and could have important implications for the biological carbon pump and the global carbon cycle.

A daily global mesoscale ocean eddy dataset from satellite altimetry

PubMed Central

Faghmous, James H.; Frenger, Ivy; Yao, Yuanshun; Warmka, Robert; Lindell, Aron; Kumar, Vipin

2015-01-01

Mesoscale ocean eddies are ubiquitous coherent rotating structures of water with radial scales on the order of 100 kilometers. Eddies play a key role in the transport and mixing of momentum and tracers across the World Ocean. We present a global daily mesoscale ocean eddy dataset that contains ~45 million mesoscale features and 3.3 million eddy trajectories that persist at least two days as identified in the AVISO dataset over a period of 1993–2014. This dataset, along with the open-source eddy identification software, extract eddies with any parameters (minimum size, lifetime, etc.), to study global eddy properties and dynamics, and to empirically estimate the impact eddies have on mass or heat transport. Furthermore, our open-source software may be used to identify mesoscale features in model simulations and compare them to observed features. Finally, this dataset can be used to study the interaction between mesoscale ocean eddies and other components of the Earth System. PMID:26097744

A technique for estimating dry deposition velocities based on similarity with latent heat flux

NASA Astrophysics Data System (ADS)

Pleim, Jonathan E.; Finkelstein, Peter L.; Clarke, John F.; Ellestad, Thomas G.

Field measurements of chemical dry deposition are needed to assess impacts and trends of airborne contaminants on the exposure of crops and unmanaged ecosystems as well as for the development and evaluation of air quality models. However, accurate measurements of dry deposition velocities require expensive eddy correlation measurements and can only be practically made for a few chemical species such as O 3 and CO 2. On the other hand, operational dry deposition measurements such as those used in large area networks involve relatively inexpensive standard meteorological and chemical measurements but rely on less accurate deposition velocity models. This paper describes an intermediate technique which can give accurate estimates of dry deposition velocity for chemical species which are dominated by stomatal uptake such as O 3 and SO 2. This method can give results that are nearly the quality of eddy correlation measurements of trace gas fluxes at much lower cost. The concept is that bulk stomatal conductance can be accurately estimated from measurements of latent heat flux combined with standard meteorological measurements of humidity, temperature, and wind speed. The technique is tested using data from a field experiment where high quality eddy correlation measurements were made over soybeans. Over a four month period, which covered the entire growth cycle, this technique showed very good agreement with eddy correlation measurements for O 3 deposition velocity.

Temperature sensitivity study of eddy current and digital gauge probes for nuclear fuel rod oxide measurement

NASA Astrophysics Data System (ADS)

Beck, Faith R.; Lind, R. Paul; Smith, James A.

2018-04-01

Novel fuels are part of the nationwide effort to reduce the enrichment of Uranium for energy production. Performance of such fuels is determined by irradiating their surfaces. To test irradiated samples, the instrumentation must operate remotely. The plate checker used in this experiment at Idaho National Lab (INL) performs non-destructive testing on fuel rod and plate geometries with two different types of sensors: eddy current and digital thickness gauges. The sensors measure oxide growth and total sample thickness on research fuels, respectively. Sensor measurement accuracy is crucial because even 10 microns of error is significant when determining the viability of an experimental fuel. One parameter known to affect the eddy current and thickness gauge sensors is temperature. Since both sensor accuracies depend on the ambient temperature of the system, the plate checker has been characterized for these sensitivities. The manufacturer of the digital gauge probes has noted a rather large coefficient of thermal expansion for their linear scale. It should also be noted that the accuracy of the digital gauge probes are specified at 20°C, which is approximately 7°C cooler than the average hot-cell temperature. In this work, the effect of temperature on the eddy current and digital gauge probes is studied, and thickness measurements are given as empirical functions of temperature.

Eddy-driven sediment transport in the Argentine Basin: Is the height of the Zapiola Rise hydrodynamically controlled?

DOE PAGES

Weijer, Wilbert; Maltrud, Mathew E.; Homoky, William B.; ...

2015-03-27

In this study, we address the question whether eddy-driven transports in the Argentine Basin can be held responsible for enhanced sediment accumulation over the Zapiola Rise, hence accounting for the existence and growth of this sediment drift. To address this question, we perform a 6 year simulation with a strongly eddying ocean model. We release two passive tracers, with settling velocities that are consistent with silt and clay size particles. Our experiments show contrasting behavior between the silt fraction and the lighter clay. Due to its larger settling velocity, the silt fraction reaches a quasisteady state within a few years,more » with abyssal sedimentation rates that match net input. In contrast, clay settles only slowly, and its distribution is heavily stratified, being transported mainly along isopycnals. Yet, both size classes display a significant and persistent concentration minimum over the Zapiola Rise. We show that the Zapiola Anticyclone, a strong eddy-driven vortex that circulates around the Zapiola Rise, is a barrier to sediment transport, and hence prevents significant accumulation of sediments on the Rise. We conclude that sediment transport by the turbulent circulation in the Argentine Basin alone cannot account for the preferred sediment accumulation over the Rise. We speculate that resuspension is a critical process in the formation and maintenance of the Zapiola Rise.« less

Observed and modeled mesoscale variability near the Gulf Stream and Kuroshio Extension

NASA Astrophysics Data System (ADS)

Schmitz, William J.; Holland, William R.

1986-08-01

Our earliest intercomparisons between western North Atlantic data and eddy-resolving two-layer quasi-geostrophic symmetric-double-gyre steady wind-forced numerical model results focused on the amplitudes and largest horizontal scales in patterns of eddy kinetic energy, primarily abyssal. Here, intercomparisons are extended to recent eight-layer model runs and new data which allow expansion of the investigation to the Kuroshio Extension and throughout much of the water column. Two numerical experiments are shown to have realistic zonal, vertical, and temporal eddy scales in the vicinity of the Kuroshio Extension in one case and the Gulf Stream in the other. Model zonal mean speeds are larger than observed, but vertical shears are in general agreement with the data. A longitudinal displacement between the maximum intensity in surface and abyssal eddy fields as observed for the North Atlantic is not found in the model results. The numerical simulations examined are highly idealized, notably with respect to basin shape, topography, wind-forcing, and of course dissipation. Therefore the zero-order agreement between modeled and observed basic characteristics of mid-latitude jets and their associated eddy fields suggests that such properties are predominantly determined by the physical mechanisms which dominate the models, where the fluctuations are the result of instability processes. The comparatively high vertical resolution of the model is needed to compare with new higher-resolution data as well as for dynamical reasons, although the precise number of layers required either kinematically or dynamically (or numerically) has not been determined; we estimate four to six when no attempt is made to account for bottom- or near-surface-intensified phenomena.

Mapping B(1)-induced eddy current effects near metallic structures in MR images: a comparison of simulation and experiment.

PubMed

Vashaee, S; Goora, F; Britton, M M; Newling, B; Balcom, B J

2015-01-01

Magnetic resonance imaging (MRI) in the presence of metallic structures is very common in medical and non-medical fields. Metallic structures cause MRI image distortions by three mechanisms: (1) static field distortion through magnetic susceptibility mismatch, (2) eddy currents induced by switched magnetic field gradients and (3) radio frequency (RF) induced eddy currents. Single point ramped imaging with T1 enhancement (SPRITE) MRI measurements are largely immune to susceptibility and gradient induced eddy current artifacts. As a result, one can isolate the effects of metal objects on the RF field. The RF field affects both the excitation and detection of the magnetic resonance (MR) signal. This is challenging with conventional MRI methods, which cannot readily separate the three effects. RF induced MRI artifacts were investigated experimentally at 2.4 T by analyzing image distortions surrounding two geometrically identical metallic strips of aluminum and lead. The strips were immersed in agar gel doped with contrast agent and imaged employing the conical SPRITE sequence. B1 mapping with pure phase encode SPRITE was employed to measure the B1 field around the strips of metal. The strip geometry was chosen to mimic metal electrodes employed in electrochemistry studies. Simulations are employed to investigate the RF field induced eddy currents in the two metallic strips. The RF simulation results are in good agreement with experimental results. Experimental and simulation results show that the metal has a pronounced effect on the B1 distribution and B1 amplitude in the surrounding space. The electrical conductivity of the metal has a minimal effect. Copyright © 2014 Elsevier Inc. All rights reserved.

The formation processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean

NASA Astrophysics Data System (ADS)

Chang, Yu-Lin; Miyazawa, Yasumasa; Oey, Lie-Yauw; Kodaira, Tsubasa; Huang, Shihming

2017-05-01

In this study, we investigate the processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean based on the in situ chlorophyll data obtained from 52 cruises conducted by the Japan Meteorological Agency together with idealized numerical simulations. Both the observation and model results suggest that chlorophyll/phytoplankton concentrations are higher in cold than in warm eddies in near-surface water (z > -70 m). In the idealized simulation, the isopycnal movements associated with upwelling/downwelling transport phytoplankton and nutrients to different vertical depths during eddy formation (stage A). Phytoplankton and nutrients in cold eddies is transported toward shallower waters while those in warm eddies move toward deeper waters. In the period after the eddy has formed (stage B), sunlight and initially upwelled nutrients together promote the growth of phytoplankton in cold eddies. Phytoplankton in warm eddies decays due to insufficient sunlight in deeper waters. In stage B, upwelling and downwelling coexist in both warm and cold eddies, contributing nearly equally to vertical displacement. The upwelling/downwelling-induced nitrate flux accounts for a small percentage (˜3%) of the total nitrate flux in stage B. The vertical velocity caused by propagating eddies, therefore, is not the primary factor causing differences in phytoplankton concentrations between stage-B warm and cold eddies.

Coherent mesoscale eddies in the North Atlantic subtropical gyre: 3-D structure and transport with application to the salinity maximum

NASA Astrophysics Data System (ADS)

Amores, Angel; Melnichenko, Oleg; Maximenko, Nikolai

2017-01-01

The mean vertical structure and transport properties of mesoscale eddies are investigated in the North Atlantic subtropical gyre by combining historical records of Argo temperature/salinity profiles and satellite sea level anomaly data in the framework of the eddy tracking technique. The study area is characterized by a low eddy kinetic energy and sea surface salinity maximum. Although eddies have a relatively weak signal at surface (amplitudes around 3-7 cm), the eddy composites reveal a clear deep signal that penetrates down to at least 1200 m depth. The analysis also reveals that the vertical structure of the eddy composites is strongly affected by the background stratification. The horizontal patterns of temperature/salinity anomalies can be reconstructed by a linear combination of a monopole, related to the elevation/depression of the isopycnals in the eddy core, and a dipole, associated with the horizontal advection of the background gradient by the eddy rotation. A common feature of all the eddy composites reconstructed is the phase coherence between the eddy temperature/salinity and velocity anomalies in the upper ˜300 m layer, resulting in the transient eddy transports of heat and salt. As an application, a box model of the near-surface layer is used to estimate the role of mesoscale eddies in maintaining a quasi-steady state distribution of salinity in the North Atlantic subtropical salinity maximum. The results show that mesoscale eddies are able to provide between 4 and 21% of the salt flux out of the area required to compensate for the local excess of evaporation over precipitation.

GEM: a dynamic tracking model for mesoscale eddies in the ocean

NASA Astrophysics Data System (ADS)

Li, Qiu-Yang; Sun, Liang; Lin, Sheng-Fu

2016-12-01

The Genealogical Evolution Model (GEM) presented here is an efficient logical model used to track dynamic evolution of mesoscale eddies in the ocean. It can distinguish between different dynamic processes (e.g., merging and splitting) within a dynamic evolution pattern, which is difficult to accomplish using other tracking methods. To this end, the GEM first uses a two-dimensional (2-D) similarity vector (i.e., a pair of ratios of overlap area between two eddies to the area of each eddy) rather than a scalar to measure the similarity between eddies, which effectively solves the "missing eddy" problem (temporarily lost eddy in tracking). Second, for tracking when an eddy splits, the GEM uses both "parent" (the original eddy) and "child" (eddy split from parent) and the dynamic processes are described as the birth and death of different generations. Additionally, a new look-ahead approach with selection rules effectively simplifies computation and recording. All of the computational steps are linear and do not include iteration. Given the pixel number of the target region L, the maximum number of eddies M, the number N of look-ahead time steps, and the total number of time steps T, the total computer time is O(LM(N + 1)T). The tracking of each eddy is very smooth because we require that the snapshots of each eddy on adjacent days overlap one another. Although eddy splitting or merging is ubiquitous in the ocean, they have different geographic distributions in the North Pacific Ocean. Both the merging and splitting rates of the eddies are high, especially at the western boundary, in currents and in "eddy deserts". The GEM is useful not only for satellite-based observational data, but also for numerical simulation outputs. It is potentially useful for studying dynamic processes in other related fields, e.g., the dynamics of cyclones in meteorology.

49 CFR 180.209 - Requirements for requalification of specification cylinders.

Code of Federal Regulations, 2012 CFR

2012-10-01

... Requalification period (years) Eddy current examination combined with visual inspection Eddy current—In accordance... performing eddy current must be familiar with the eddy current equipment and must standardize (calibrate) the system in accordance with the requirements provided in Appendix C to this part. 2 The eddy current must...

49 CFR 180.209 - Requirements for requalification of specification cylinders.

Code of Federal Regulations, 2013 CFR

2013-10-01

... Requalification period (years) Eddy current examination combined with visual inspection Eddy current—In accordance... performing eddy current must be familiar with the eddy current equipment and must standardize (calibrate) the system in accordance with the requirements provided in Appendix C to this part. 2 The eddy current must...

Eddy Current Testing, RQA/M1-5330.17.

ERIC Educational Resources Information Center

National Aeronautics and Space Administration, Huntsville, AL. George C. Marshall Space Flight Center.

As one in the series of classroom training handbooks, prepared by the U.S. space program, instructional material is presented in this volume concerning familiarization and orientation on eddy current testing. The subject is presented under the following headings: Introduction, Eddy Current Principles, Eddy Current Equipment, Eddy Current Methods,…

49 CFR 180.209 - Requirements for requalification of specification cylinders.

Code of Federal Regulations, 2014 CFR

2014-10-01

... Requalification period (years) Eddy current examination combined with visual inspection Eddy current—In accordance... performing eddy current must be familiar with the eddy current equipment and must standardize (calibrate) the system in accordance with the requirements provided in Appendix C to this part. 2 The eddy current must...

Impacts of mesoscale eddies on biogeochemical cycles in the South China Sea

NASA Astrophysics Data System (ADS)

Xiu, P.; Chai, F.; Guo, M.

2016-02-01

Biogeochemical cycles associated with mesoscale eddies in the South China Sea (SCS) are investigated by using satellite surface chlorophyll concentration, altimeter data, satellite sea surface temperature, and a coupled physical-biogeochemical Pacific Ocean model (ROMS-CoSiNE) simulation for the period from 1991 to 2007. Considering the annual mean, composite analysis reveals that cyclonic eddies are associated with higher concentrations of nutrients, phytoplankton and zooplankton while the anticyclonic eddies are with lower concentrations compared with surrounding waters, which is generally controlled by the eddy pumping mechanism. Dipole structures of vertical fluxes with net upward motion in cyclonic eddies and net downward motion in anticyclonic eddies are also revealed. During the lifetime of an eddy, the evolutions of physical, biological, and chemical structures are not linearly coupled at the eddy core where plankton grow and composition of the community depend not only on the physical and chemical processes but also on the adjustments by the predator-prey relationship. Considering the seasonal variability, we find eddy pumping mechanisms are generally dominant in winter and eddy advection effects are dominant in summer. Over the space, variability of chlorophyll to the west of Luzon Strait and off northwest of Luzon Island are mainly controlled by eddy pumping mechanism. In regions off the Vietnam coast, chlorophyll distributions are generally associated with horizontal eddy advection. This research highlights different mesoscale mechanisms affecting biological structures that can potentially disturb ocean biogeochemical cycling processes in the South China Sea.

PSF mapping-based correction of eddy-current-induced distortions in diffusion-weighted echo-planar imaging.

PubMed

In, Myung-Ho; Posnansky, Oleg; Speck, Oliver

2016-05-01

To accurately correct diffusion-encoding direction-dependent eddy-current-induced geometric distortions in diffusion-weighted echo-planar imaging (DW-EPI) and to minimize the calibration time at 7 Tesla (T). A point spread function (PSF) mapping based eddy-current calibration method is newly presented to determine eddy-current-induced geometric distortions even including nonlinear eddy-current effects within the readout acquisition window. To evaluate the temporal stability of eddy-current maps, calibration was performed four times within 3 months. Furthermore, spatial variations of measured eddy-current maps versus their linear superposition were investigated to enable correction in DW-EPIs with arbitrary diffusion directions without direct calibration. For comparison, an image-based eddy-current correction method was additionally applied. Finally, this method was combined with a PSF-based susceptibility-induced distortion correction approach proposed previously to correct both susceptibility and eddy-current-induced distortions in DW-EPIs. Very fast eddy-current calibration in a three-dimensional volume is possible with the proposed method. The measured eddy-current maps are very stable over time and very similar maps can be obtained by linear superposition of principal-axes eddy-current maps. High resolution in vivo brain results demonstrate that the proposed method allows more efficient eddy-current correction than the image-based method. The combination of both PSF-based approaches allows distortion-free images, which permit reliable analysis in diffusion tensor imaging applications at 7T. © 2015 Wiley Periodicals, Inc.

Modeling possible spreadings of a buoyant surface plume with lagrangian and eulerian approaches at different resolutions using flow syntheses from 1992-2007 - a Gulf of Mexico study

NASA Astrophysics Data System (ADS)

Tulloch, R.; Hill, C. N.; Jahn, O.

2010-12-01

We present results from an ensemble of BP oil spill simulations. The oil spill slick is modeled as a buoyant surface plume that is transported by ocean currents modulated, in some experiments, by surface winds. Ocean currents are taken from ECCO2 project (see http://ecco2.org ) observationally constrained state estimates spanning 1992-2007. In this work we (i) explore the role of increased resolution of ocean eddies, (ii) compare inferences from particle based, lagrangian, approaches with eulerian, field based, approaches and (ii) examine the impact of differential response of oil particles and water to normal and extreme, hurricane derived, wind stress. We focus on three main questions. Is the simulated response to an oil spill markedly different for different years, depending on ocean circulation and wind forcing? Does the simulated response depend heavily on resolution and are lagrangian and eulerian estimates comparable? We start from two regional configurations of the MIT General Circulation Model (MITgcm - see http://mitgcm.org ) at 16km and 4km resolutions respectively, both covering the Gulf of Mexico and western North Atlantic regions. The simulations are driven at open boundaries with momentum and hydrographic fields from ECCO2 observationally constrained global circulation estimates. The time dependent surface flow fields from these simulations are used to transport a dye that can optionally decay over time (approximating biological breakdown) and to transport lagrangian particles. Using these experiments we examine the robustness of conclusions regarding the fate of a buoyant slick, injected at a single point. In conclusion we discuss how future drilling operations could use similar approaches to better anticipate outcomes of accidents both in this region and elsewhere.

Annual Research Briefs: 1995

NASA Technical Reports Server (NTRS)

1995-01-01

This report contains the 1995 annual progress reports of the Research Fellows and students of the Center for Turbulence Research (CTR). In 1995 CTR continued its concentration on the development and application of large-eddy simulation to complex flows, development of novel modeling concepts for engineering computations in the Reynolds averaged framework, and turbulent combustion. In large-eddy simulation, a number of numerical and experimental issues have surfaced which are being addressed. The first group of reports in this volume are on large-eddy simulation. A key finding in this area was the revelation of possibly significant numerical errors that may overwhelm the effects of the subgrid-scale model. We also commissioned a new experiment to support the LES validation studies. The remaining articles in this report are concerned with Reynolds averaged modeling, studies of turbulence physics and flow generated sound, combustion, and simulation techniques. Fundamental studies of turbulent combustion using direct numerical simulations which started at CTR will continue to be emphasized. These studies and their counterparts carried out during the summer programs have had a noticeable impact on combustion research world wide.

Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling

NASA Technical Reports Server (NTRS)

El-Hady, Nabil M.

1993-01-01

The laminar-turbulent breakdown of a boundary-layer flow along a hollow cylinder at Mach 4.5 is investigated with large-eddy simulation. The subgrid scales are modeled dynamically, where the model coefficients are determined from the local resolved field. The behavior of the dynamic-model coefficients is investigated through both an a priori test with direct numerical simulation data for the same case and a complete large-eddy simulation. Both formulations proposed by Germano et al. and Lilly are used for the determination of unique coefficients for the dynamic model and their results are compared and assessed. The behavior and the energy cascade of the subgrid-scale field structure are investigated at various stages of the transition process. The investigations are able to duplicate a high-speed transition phenomenon observed in experiments and explained only recently by the direct numerical simulations of Pruett and Zang, which is the appearance of 'rope-like' waves. The nonlinear evolution and breakdown of the laminar boundary layer and the structure of the flow field during the transition process were also investigated.

Modeling and analysis of a novel planar eddy current damper

NASA Astrophysics Data System (ADS)

Zhang, He; Kou, Baoquan; Jin, Yinxi; Zhang, Lu; Zhang, Hailin; Li, Liyi

2014-05-01

In this paper, a novel 2-DOF permanent magnet planar eddy current damper is proposed, of which the stator is made of a copper plate and the mover is composed of two orthogonal 1-D permanent magnet arrays with a double sided structure. The main objective of the planar eddy current damper is to provide two orthogonal damping forces for dynamic systems like the 2-DOF high precision positioning system. Firstly, the basic structure and the operating principle of the planar damper are introduced. Secondly, the analytical model of the planar damper is established where the magnetic flux density distribution of the permanent magnet arrays is obtained by using the equivalent magnetic charge method and the image method. Then, the analytical expressions of the damping force and damping coefficient are derived. Lastly, to verify the analytical model, the finite element method (FEM) is adopted for calculating the flux density and a planar damper prototype is manufactured and thoroughly tested. The results from FEM and experiments are in good agreement with the ones from the analytical expressions indicating that the analytical model is reasonable and correct.

Structure measurements in a synthetic turbulent boundary layer

NASA Astrophysics Data System (ADS)

Arakeri, Jaywant H.

1987-09-01

Extensive hot-wire measurements have been made to determine the structure of the large eddy in a synthejc turbulent boundary layer on a flat-plate model. The experiments were carried out in a wind tunnel at a nominal free-stream velocity of 12 m/s. The synthetic turbulent boundary layer had a hexagonal pattern of eddies and a ratio of streamwise scale to spanwise scale of 3.2:1. The measured celerity of the large eddy was 84.2 percent of the free-stream velocity. There was some loss of coherence, but very little distortion, as the eddies moved downstream. Several mean properties of the synthetic boundary layer were found to agree quite well with the mean properties of a natural turbulent boundary layer at the same Reynolds number. The large eddy is composed of a pair of primary counter-rotating vortices about five [...] long in the streamwise direction and about one [...] apart in the spanwise direction, where [...] is the mean boundary-layer thickness. The sense of the primary pair is such as to pump fluid away from the wall in the region between the vortices. A secondary pair of counter-rotating streamwise vortices, having a sense opposite to that of the primary pair, is observed outside of and slightly downstream from the primary vortices. Both pairs of vortices extend across the full thickness of the boundary layer and are inclined at a shallow angle to the surface of the flat plate. The data show that the mean vorticity vectors are not tangential to the large-eddy vortices. In fact, the streamwise and normal vorticity components that signal the presence of the eddy are of the same order of magnitude. Definite signatures are obtained in terms of the mean skin-friction coefficient and the mean wake parameter averaged at constant phase. Velocities induced by the vortices are partly responsible for entrainment of irrotational fluid, for transport of momentum, for generation of Reynolds stresses, and for maintenance of streamwise and normal vorticity in the outer flow. A stretching mechanism is important in matching spanwise vorticity close to the wall to variations in turbulent shearing stress. Regions where the stretching term is large coincide with regions of large wall shearing stress and large turbulence production.

An ensemble of eddy-permitting global ocean reanalyses from the MyOcean project

NASA Astrophysics Data System (ADS)

Masina, Simona; Storto, Andrea; Ferry, Nicolas; Valdivieso, Maria; Haines, Keith; Balmaseda, Magdalena; Zuo, Hao; Drevillon, Marie; Parent, Laurent

2017-08-01

A set of four eddy-permitting global ocean reanalyses produced in the framework of the MyOcean project have been compared over the altimetry period 1993-2011. The main differences among the reanalyses used here come from the data assimilation scheme implemented to control the ocean state by inserting reprocessed observations of sea surface temperature (SST), in situ temperature and salinity profiles, sea level anomaly and sea-ice concentration. A first objective of this work includes assessing the interannual variability and trends for a series of parameters, usually considered in the community as essential ocean variables: SST, sea surface salinity, temperature and salinity averaged over meaningful layers of the water column, sea level, transports across pre-defined sections, and sea ice parameters. The eddy-permitting nature of the global reanalyses allows also to estimate eddy kinetic energy. The results show that in general there is a good consistency between the different reanalyses. An intercomparison against experiments without data assimilation was done during the MyOcean project and we conclude that data assimilation is crucial for correctly simulating some quantities such as regional trends of sea level as well as the eddy kinetic energy. A second objective is to show that the ensemble mean of reanalyses can be evaluated as one single system regarding its reliability in reproducing the climate signals, where both variability and uncertainties are assessed through the ensemble spread and signal-to-noise ratio. The main advantage of having access to several reanalyses differing in the way data assimilation is performed is that it becomes possible to assess part of the total uncertainty. Given the fact that we use very similar ocean models and atmospheric forcing, we can conclude that the spread of the ensemble of reanalyses is mainly representative of our ability to gauge uncertainty in the assimilation methods. This uncertainty changes a lot from one ocean parameter to another, especially in global indices. However, despite several caveats in the design of the multi-system ensemble, the main conclusion from this study is that an eddy-permitting multi-system ensemble approach has become mature and our results provide a first step towards a systematic comparison of eddy-permitting global ocean reanalyses aimed at providing robust conclusions on the recent evolution of the oceanic state.

New challenges and opportunities in the eddy-covariance methodology for long-term monitoring networks

NASA Astrophysics Data System (ADS)

Papale, Dario; Fratini, Gerardo

2013-04-01

Eddy-covariance is the most direct and most commonly applied methodology for measuring exchange fluxes of mass and energy between ecosystems and the atmosphere. In recent years, the number of environmental monitoring stations deploying eddy-covariance systems increased dramatically at the global level, exceeding 500 sites worldwide and covering most climatic and ecological regions. Several long-term environmental research infrastructures such as ICOS, NEON and AmeriFlux selected the eddy-covariance as a method to monitor GHG fluxes and are currently collaboratively working towards defining common measurements standards, data processing approaches, QA/QC procedures and uncertainty estimation strategies, to the aim of increasing defensibility of resulting fluxes and intra and inter-comparability of flux databases. In the meanwhile, the eddy-covariance research community keeps identifying technical and methodological flaws that, in some cases, can introduce - and can have introduced to date - significant biases in measured fluxes or increase their uncertainty. Among those, we identify three issues of presumably greater concern, namely: (1) strong underestimation of water vapour fluxes in closed-path systems, and its dependency on relative humidity; (2) flux biases induced by erroneous measurement of absolute gas concentrations; (3) and systematic errors due to underestimation of vertical wind variance in non-orthogonal anemometers. If not properly addressed, these issues can reduce the quality and reliability of the method, especially as a standard methodology in long-term monitoring networks. In this work, we review the status of the art regarding such problems, and propose new evidences based on field experiments as well as numerical simulations. Our analyses confirm the potential relevance of these issues but also hint at possible coping approaches, to minimize problems during setup design, data collection and post-field flux correction. Corrections are under implementation in eddy-covariance processing software and will be readily applicable by individual investigators as well as by centralized processing facilities of long-term research infrastructures. This new understandings suggest that a reanalysis of eddy-covariance data collected in the last 20 years may be appropriate in order to obtain more accurate and consistent flux time series. The availability of dedicated powerful computing facilities at the research infrastructures today makes this goal achievable at an affordable cost.

Understanding Wave-mean Flow Feedbacks and Tropospheric Annular Variability

NASA Astrophysics Data System (ADS)

Lorenz, D. J.

2016-12-01

The structure of internal tropospheric variability is important for determining the impact of the stratosphere on the troposphere. This study aims to better understand the fundamental dynamical mechanisms that control the feedbacks between the eddies and the mean flow, which in turn select the tropospheric annular mode. Recent work using Rossby Wave Chromatography suggests that "barotropic processes", which directly impact the meridional propagation of wave activity (specifically the reflectivity of the poleward flank of the mid-latitude jet), are more important for the positive feedback between the annular mode and the eddies than "baroclinic processes", which involve changes in the generation of wave activity by baroclinic instability. In this study, experiments with a fully nonlinear quasi-geostrophic model are discussed which provide independent confirmation of the importance of barotropic versus baroclinic processes. The experiments take advantage of the steady-state balance at upper-levels between the meridional gradient in diabatic heating and the second derivative of the upper-level EP flux divergence. Simulations with standard Newtonian heating are compared to simulations with constant-in-time heating taken from the climatology of the standard run and it is found that the forced annular mode response to changes in surface friction is very similar. Moreover, as expected from the annular mode response, the eddy momentum fluxes are also very similar. This is despite the fact that the upper-level EP flux divergence is very different between the two simulations (upper-level EP flux divergence must remain constant in the constant heating simulation while in the standard simulation there is no such constraint). The upper-level balances are maintained by a large change in the baroclinic wave source (i.e. vertical EP flux), which is accompanied by little momentum flux change. Therefore the eddy momentum fluxes appear to be relatively insensitive to the wave activity source. A more detailed comparison suggests a helpful rule-of-thumb relating the amplitude of the baroclinic wave source to the upper-level vorticity flux forced by this wave source.

Impacts of mesoscale eddies in the South China Sea on biogeochemical cycles

NASA Astrophysics Data System (ADS)

Guo, Mingxian; Chai, Fei; Xiu, Peng; Li, Shiyu; Rao, Shivanesh

2015-09-01

Biogeochemical cycles associated with mesoscale eddies in the South China Sea (SCS) were investigated. The study was based on a coupled physical-biogeochemical Pacific Ocean model (Regional Ocean Model System-Carbon, Silicate, and Nitrogen Ecosystem, ROMS-CoSiNE) simulation for the period from 1991 to 2008. A total of 568 mesoscale eddies with lifetime longer than 30 days were used in the analysis. Composite analysis revealed that the cyclonic eddies were associated with abundance of nutrients, phytoplankton, and zooplankton while the anticyclonic eddies depressed biogeochemical cycles, which are generally controlled by the eddy pumping mechanism. In addition, diatoms were dominant in phytoplankton species due to the abundance of silicate. Dipole structures of vertical fluxes with net upward motion in cyclonic eddies and net downward motion in anticyclonic eddies were revealed. During the lifetime of an eddy, the evolutions of physical, biological, and chemical structures were not linearly coupled at the eddy core where plankton grew, and composition of the community depended not only on the physical and chemical processes but also on the adjustments by the predator-prey relationship.

On the unified estimation of turbulence eddy dissipation rate using Doppler cloud radars and lidars: Radar and Lidar Turbulence Estimation

DOE PAGES

Borque, Paloma; Luke, Edward; Kollias, Pavlos

2016-05-27

Coincident profiling observations from Doppler lidars and radars are used to estimate the turbulence energy dissipation rate (ε) using three different data sources: (i) Doppler radar velocity (DRV), (ii) Doppler lidar velocity (DLV), and (iii) Doppler radar spectrum width (DRW) measurements. Likewise, the agreement between the derived ε estimates is examined at the cloud base height of stratiform warm clouds. Collocated ε estimates based on power spectra analysis of DRV and DLV measurements show good agreement (correlation coefficient of 0.86 and 0.78 for both cases analyzed here) during both drizzling and nondrizzling conditions. This suggests that unified (below and abovemore » cloud base) time-height estimates of ε in cloud-topped boundary layer conditions can be produced. This also suggests that eddy dissipation rate can be estimated throughout the cloud layer without the constraint that clouds need to be nonprecipitating. Eddy dissipation rate estimates based on DRW measurements compare well with the estimates based on Doppler velocity but their performance deteriorates as precipitation size particles are introduced in the radar volume and broaden the DRW values. And, based on this finding, a methodology to estimate the Doppler spectra broadening due to the spread of the drop size distribution is presented. Furthermore, the uncertainties in ε introduced by signal-to-noise conditions, the estimation of the horizontal wind, the selection of the averaging time window, and the presence of precipitation are discussed in detail.« less

Coherent structure dynamics and identification during the multistage transitions of polymeric turbulent channel flow

NASA Astrophysics Data System (ADS)

Zhu, Lu; Xi, Li

2018-04-01

Drag reduction induced by polymer additives in wall-bounded turbulence has been studied for decades. A small dosage of polymer additives can drastically reduce the energy dissipation in turbulent flows and alter the flow structures at the same time. As the polymer-induced fluid elasticity increases, drag reduction goes through several stages of transition with drastically different flow statistics. While much attention in the area of polymer-turbulence interactions has been focused on the onset and the asymptotic stage of maximum drag reduction, the transition between the two intermediate stages – low-extent drag reduction (LDR) and high-extent drag reduction (HDR) – likely reflects a qualitative change in the underlying vortex dynamics according to our recent study [1]. In particular, we proposed that polymers start to suppress the lift-up and bursting of vortices at HDR, leading to the localization of turbulent structures. To test our hypothesis, a statistically robust conditional sampling algorithm, based on Jenong and Hussain [2]’s work, was adopted in this study. The comparison of conditional eddies between the Newtonian and the highly elastic turbulence shows that (i) the lifting “strength” of vortices is suppressed by polymers as reflected by the decreasing lifting angle of the conditional eddy and (ii) the curvature of vortices is also eliminated as the orientation of the head of the conditional eddy changes. In summary, the results of conditional sampling support our hypothesis of polymer-turbulence interactions during the LDR-HDR transition.

On the unified estimation of turbulence eddy dissipation rate using Doppler cloud radars and lidars: Radar and Lidar Turbulence Estimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borque, Paloma; Luke, Edward; Kollias, Pavlos

Coincident profiling observations from Doppler lidars and radars are used to estimate the turbulence energy dissipation rate (ε) using three different data sources: (i) Doppler radar velocity (DRV), (ii) Doppler lidar velocity (DLV), and (iii) Doppler radar spectrum width (DRW) measurements. Likewise, the agreement between the derived ε estimates is examined at the cloud base height of stratiform warm clouds. Collocated ε estimates based on power spectra analysis of DRV and DLV measurements show good agreement (correlation coefficient of 0.86 and 0.78 for both cases analyzed here) during both drizzling and nondrizzling conditions. This suggests that unified (below and abovemore » cloud base) time-height estimates of ε in cloud-topped boundary layer conditions can be produced. This also suggests that eddy dissipation rate can be estimated throughout the cloud layer without the constraint that clouds need to be nonprecipitating. Eddy dissipation rate estimates based on DRW measurements compare well with the estimates based on Doppler velocity but their performance deteriorates as precipitation size particles are introduced in the radar volume and broaden the DRW values. And, based on this finding, a methodology to estimate the Doppler spectra broadening due to the spread of the drop size distribution is presented. Furthermore, the uncertainties in ε introduced by signal-to-noise conditions, the estimation of the horizontal wind, the selection of the averaging time window, and the presence of precipitation are discussed in detail.« less

Modeling Sediment Transport Using a Lagrangian Particle Tracking Algorithm Coupled with High-Resolution Large Eddy Simulations: a Critical Analysis of Model Limits and Sensitivity

NASA Astrophysics Data System (ADS)

Garcia, M. H.

2016-12-01

Modeling Sediment Transport Using a Lagrangian Particle Tracking Algorithm Coupled with High-Resolution Large Eddy Simulations: a Critical Analysis of Model Limits and Sensitivity Som Dutta1, Paul Fischer2, Marcelo H. Garcia11Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Il, 61801 2Department of Computer Science and Department of MechSE, University of Illinois at Urbana-Champaign, Urbana, Il, 61801 Since the seminal work of Niño and Garcia [1994], one-way coupled Lagrangian particle tracking has been used extensively for modeling sediment transport. Over time, the Lagrangian particle tracking method has been coupled with Eulerian flow simulations, ranging from Reynolds Averaged Navier-Stokes (RANS) based models to Detached Eddy Simulations (DES) [Escauriaza and Sotiropoulos, 2011]. Advent of high performance computing (HPC) platforms and faster algorithms have resulted in the work of Dutta et al. [2016], where Lagrangian particle tracking was coupled with high-resolution Large Eddy Simulations (LES) to model the complex and highly non-linear phenomenon of Bulle-Effect at diversions. Despite all the advancements in using Lagrangian particle tracking, there has not been a study that looks in detail at the limits of the model in the context of sediment transport, and also analyzes the sensitivity of the various force formulation in the force balance equation of the particles. Niño and Garcia [1994] did a similar analysis, but the vertical flow velocity distribution was modeled as the log-law. The current study extends the analysis by modeling the flow using high-resolution LES at a Reynolds number comparable to experiments of Niño et al. [1994]. Dutta et al., (2016), Large Eddy Simulation (LES) of flow and bedload transport at an idealized 90-degree diversion: insight into Bulle-Effect, River Flow 2016 - Constantinescu, Garcia & Hanes (Eds), Taylor & Francis Group, London, 101-109. Escauriaza and Sotiropoulos, (2011), Lagrangian model of bed-load transport in turbulent junction flows, Journal of Fluid Mechanics, 666,36-76. Niño and García, (1994), Gravel saltation: 2. Modeling, Water Resources Research, 30(6),1915-1924. Niño et al., (1994), Gravel saltation: 1. Experiments, Water Resources Research, 30(6), 1907-1914.

1988 Year End Report for Road Following at Carnegie Mellon

DTIC Science & Technology

1989-05-01

Christophe Robert, David Simon , Hans Thomas, Eddie Wyatt Visiting scientists: Yoshi Goto, Taka Fujimori, Keith Gremban, Hide Kuga, Masatoshi Okutomi Graduate...Acknowledgements Mike Blackwell, James Frazier, and David Simon made the NAVLAB experiments possible. Chuck Thorpe provided the path planner used in

Inference of physical/biological dynamics from synthetic ocean colour images

NASA Technical Reports Server (NTRS)

Eert, J.; Holloway, G.; Gower, J. F. R.; Denman, K.; Abbott, M.

1987-01-01

High resolution numerical experiments with well resolved eddies are performed including advection of a biologically active plankton field. Shelf wave propagation and bottom topographic features are included. The resulting synthetic ocean color fields are examined for sensitivity to the (known) underlying physical dynamics.

On the role of mesoscale eddies for the biological productivity and biogeochemistry in the eastern tropical Pacific Ocean off Peru

NASA Astrophysics Data System (ADS)

Stramma, L.; Bange, H. W.; Czeschel, R.; Lorenzo, A.; Frank, M.

2013-11-01

Mesoscale eddies seem to play an important role for both the hydrography and biogeochemistry of the eastern tropical Pacific Ocean (ETSP) off Peru. However, detailed surveys of these eddies are not available, which has so far hampered an in depth understanding of their implications for nutrient distribution and biological productivity. In this study, three eddies along a section at 16°45´ S have been surveyed intensively during R/V Meteor cruise M90 in November 2012. A coastal mode water eddy, an open ocean mode water eddy and an open ocean cyclonic eddy have been identified and sampled in order to determine both their hydrographic properties and their influence on the biogeochemical setting of the ETSP. In the thermocline the temperature of the coastal anticyclonic eddy was up to 2 °C warmer, 0.2 more saline and the swirl velocity was up to 35 cm s-1. The observed temperature and salinity anomalies, as well as swirl velocities of both types of eddies were about twice as large as had been described for the mean eddies in the ETSP. The observed heat and salt anomalies (AHA, ASA) of the anticyclonic eddy near the shelf-break of 17.7 × 1018 J and 36.6 × 1010 kg are more than twice as large as the mean AHA and ASA for the ETSP. We found that the eddies contributed to the productivity by maintaining pronounced subsurface maxima of chlorophyll of up to 6 μg L-1. Based on a comparison of the coastal (young) mode water eddy and the open ocean (old) mode water eddy we suggest that the ageing of eddies when they detach from the shelf-break and move westward to the open ocean influences the eddies' properties: chlorophyll maxima are reduced to about half (2.5-3 μg L-1) and nutrients are subducted. However, different settings at the time of formation may also contribute to the observed differences between the young and old mode water eddies. The coastal mode water eddy was found to be a site of nitrogen (N) loss in the OMZ with a maximum ΔNO3- anomaly (i.e. N loss) of about -25 μmol L-1 in 250 m water depth, whereas, the open ocean mode water and cyclonic eddies were of minor and negligible importance for the N loss, respectively. Our results show that the important role of eddies for the distribution of nutrients, as well as biogeochemical processes in the ETSP (and other OMZ/upwelling regions) can only be fully deciphered and understood through dedicated high spatial and temporal resolution oceanographic/biogeochemical surveys.

Mesoscale eddies: hotspots of prokaryotic activity and differential community structure in the ocean.

PubMed

Baltar, Federico; Arístegui, Javier; Gasol, Josep M; Lekunberri, Itziar; Herndl, Gerhard J

2010-08-01

To investigate the effects of mesoscale eddies on prokaryotic assemblage structure and activity, we sampled two cyclonic eddies (CEs) and two anticyclonic eddies (AEs) in the permanent eddy-field downstream the Canary Islands. The eddy stations were compared with two far-field (FF) stations located also in the Canary Current, but outside the influence of the eddy field. The distribution of prokaryotic abundance (PA), bulk prokaryotic heterotrophic activity (PHA), various indicators of single-cell activity (such as nucleic acid content, proportion of live cells, and fraction of cells actively incorporating leucine), as well as bacterial and archaeal community structure were determined from the surface to 2000 m depth. In the upper epipelagic layer (0-200 m), the effect of eddies on the prokaryotic community was more apparent, as indicated by the higher PA, PHA, fraction of living cells, and percentage of active cells incorporating leucine within eddies than at FF stations. Prokaryotic community composition differed also between eddy and FF stations in the epipelagic layer. In the mesopelagic layer (200-1000 m), there were also significant differences in PA and PHA between eddy and FF stations, although in general, there were no clear differences in community composition or single-cell activity. The effects on prokaryotic activity and community structure were stronger in AE than CE, decreasing with depth in both types of eddies. Overall, both types of eddies show distinct community compositions (as compared with FF in the epipelagic), and represent oceanic 'hotspots' of prokaryotic activity (in the epi- and mesopelagic realms).

Open ocean dead zones in the tropical North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Karstensen, J.; Fiedler, B.; Schütte, F.; Brandt, P.; Körtzinger, A.; Fischer, G.; Zantopp, R.; Hahn, J.; Visbeck, M.; Wallace, D.

2015-04-01

Here we present first observations, from instrumentation installed on moorings and a float, of unexpectedly low (<2 μmol kg-1) oxygen environments in the open waters of the tropical North Atlantic, a region where oxygen concentration does normally not fall much below 40 μmol kg-1. The low-oxygen zones are created at shallow depth, just below the mixed layer, in the euphotic zone of cyclonic eddies and anticyclonic-modewater eddies. Both types of eddies are prone to high surface productivity. Net respiration rates for the eddies are found to be 3 to 5 times higher when compared with surrounding waters. Oxygen is lowest in the centre of the eddies, in a depth range where the swirl velocity, defining the transition between eddy and surroundings, has its maximum. It is assumed that the strong velocity at the outer rim of the eddies hampers the transport of properties across the eddies boundary and as such isolates their cores. This is supported by a remarkably stable hydrographic structure of the eddies core over periods of several months. The eddies propagate westward, at about 4 to 5 km day-1, from their generation region off the West African coast into the open ocean. High productivity and accompanying respiration, paired with sluggish exchange across the eddy boundary, create the "dead zone" inside the eddies, so far only reported for coastal areas or lakes. We observe a direct impact of the open ocean dead zones on the marine ecosystem as such that the diurnal vertical migration of zooplankton is suppressed inside the eddies.

The EOLE experiment: Early results and current objectives

NASA Technical Reports Server (NTRS)

Morel, P.; Bandeen, W. R.

1972-01-01

The EOLE experiment with 480 constant level balloons released in the Southern Hemisphere is described. Each balloon floating freely at approximately the 200 mb level, is a precise tracer of the horizontal motion of air masses, the accuracy of which is limited only by the laminated structure of the stratospheric flow, within an RMS uncertainty of 1.5 m/sec. The balloons were found after 2 months to distribute at random over the whole hemisphere outside the tropics, irrespective of their original launching site. Early results of Eulerian and Lagrangian averages of the EOLE wind data are given for describing the mean 200 mb zonal and meridional circulations. The effect of the small scale eddies of two-dimensional turbulence has been studied with respect to the relative eddy diffusion of pairs of balloons and the relative dispersion of triangular clusters. New estimates of the RMS divergence of the 200 mb flow are given, together with their scale dependence which was found to be a logarithmic law.

Implicit Large Eddy Simulation of a wingtip vortex at Rec =1.2x106

NASA Astrophysics Data System (ADS)

Lombard, Jean-Eloi; Moxey, Dave; Sherwin, Spencer; SherwinLab Team

2015-11-01

We present recent developments in numerical methods for performing a Large Eddy Simulation (LES) of the formation and evolution of a wingtip vortex. The development of these vortices in the near wake, in combination with the large Reynolds numbers present in these cases, make these types of test cases particularly challenging to investigate numerically. To demonstrate the method's viability, we present results from numerical simulations of flow over a NACA 0012 profile wingtip at Rec = 1.2 x106 and compare them against experimental data, which is to date the highest Reynolds number achieved for a LES that has been correlated with experiments for this test case. Our model correlates favorably with experiment, both for the characteristic jetting in the primary vortex and pressure distribution on the wing surface. The proposed method is of general interest for the modeling of transitioning vortex dominated flows over complex geometries. McLaren Racing/Royal Academy of Engineering Research Chair.

Detecting defects in marine structures by using eddy current infrared thermography.

PubMed

Swiderski, W

2016-12-01

Eddy current infrared (IR) thermography is a new nondestructive testing (NDT) technique used for the detection of cracks in electroconductive materials. By combining the well-established inspection methods of eddy current NDT and IR thermography, this technique uses induced eddy currents to heat test samples. In this way, IR thermography allows the visualization of eddy current distribution that is distorted in defect sites. This paper discusses the results of numerical modeling of eddy current IR thermography procedures in application to marine structures.

Automated detection of Lagrangian eddies and coherent transport of heat and salinity in the Agulhas leakage

NASA Astrophysics Data System (ADS)

Huhn, Florian; Haller, George

2014-05-01

Haller and Beron-Vera(2013) have recently introduced a new objective method to detect coherent Lagrangian eddies in turbulence. They find that closed null-geodesics of a generalized Green-Lagrange strain tensor act as coherent Lagrangian eddy boundaries, showing near-zero and uniform material stretching. We make use of this method to develop an automated detection procedure for coherent Lagrangian eddies in large-scale ocean data. We apply our results to a recent 3D general circulation model, the Southern Ocean State Estimate (SOSE), with focus on the South Atlantic Ocean and the inter-ocean exchange between the Indian and Atlantic ocean. We detect a large number of coherent Lagrangian eddies and present statistics of their properties. The largest and most circular eddy boundaries represent Lagrangian Agulhas rings. Circular regions inside these rings with higher temperature and salinity than the surrounding waters can be explained by the coherent eddy boundaries that enclose and isolate the eddy interiors. We compare eddy boundaries at different depths with eddy boundaries obtained from geostrophic velocities derived from the model's sea surface height (SSH). The transport of mass, heat and salinity enclosed by coherent eddies through a section in the Cape basin is quantified and compared to the non-coherent transport by the background flow.

Seismic Imaging of Circumpolar Deep Water Exchange across the Shelf Break of the Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Gunn, K.; White, N.; Larter, R. D.; Falder, M.; Caulfield, C. C. P.

2016-02-01

The western Antarctic Peninsula is an area of recent extreme atmospheric warming. In the adjacent ocean, there is particular interest in on-shelf movement of Circumpolar Deep Water as a possible link to changing climate by affecting ice shelf processes. Here, we investigate on-shelf intrusions using two-dimensional seismic imaging of the water column which has vertical and horizontal resolutions of 10 m. 8 seismic profiles were acquired in February 2015 using the RRS James Clark Ross. These profiles traverse the shelf break and cross two bathymetric features, the Marguerite and Biscoe troughs, which may play a role in water exchange processes. Seismic data were acquired using two Generator-Injector air guns fired every 10 s with a pressure of 2000 psi. Reflections were recorded on a 2.4 km streamer of 192 receivers spaced every 12.5 m. Observed reflections in the processed records are caused by rapid changes of temperature ( 80%) and salinity ( 20%), delineating water masses of different properties. 13 XCTDs and XBTs plus a 38 kHz echo-sounder profile were simultaneously acquired along seismic profiles and used for calibration. Preliminary results show the top of the Winter Water layer as a bright reflection at 50-120 m depth across the entire survey, corresponding to temperatures ≤ -1°C. Curved, discontinuous, eddy-like reflections, also seen on echo-sounder profiles, are attributed to modified Upper Circumpolar Deep Water with temperatures ≥ 1.34°C. A warm core eddy, 11 km long and 220 m high, is visible 2 km inland of the shelf break. Pure Upper Circumpolar Deep Water of temperatures ≥ 1.80°C is aligned with weak but discernible, lens-shaped reflections. Eddy-like structures and the overall reflective morphology yield useful insights into shelf exchange processes, suggestive of three potential mechanisms: (i) topography controlled flow; (ii) an 'ice-pump' mechanism; and (iii) mesoscale eddies.

Intense mesoscale variability in the Sardinia Sea

NASA Astrophysics Data System (ADS)

Russo, Aniello; Borrione, Ines; Falchetti, Silvia; Knoll, Michaela; Fiekas, Heinz-Volker; Heywood, Karen; Oddo, Paolo; Onken, Reiner

2015-04-01

From the 6 to 25 June 2014, the REP14-MED sea trial was conducted by CMRE, supported by 20 partners from six different nations. The at-sea activities were carried out onboard the research vessels Alliance (NATO) and Planet (German Ministry of Defense), comprising a marine area of about 110 x 110 km2 to the west of the Sardinian coast. More than 300 CTD casts typically spaced at 10 km were collected; both ships continuously recorded vertical profiles of currents by means of their ADCPs, and a ScanFish® and a CTD chain were towed for almost three days by Alliance and Planet, respectively, following parallel routes. Twelve gliders from different manufacturers (Slocum, SeaGliderTM and SeaExplorer) were continuously sampling the study area following zonal tracks spaced at 10 km. In addition, six moorings, 17 surface drifters and one ARVOR float were deployed. From a first analysis of the observations, several mesoscale features were identified in the survey area, in particular: (i) a warm-core anticyclonic eddy in the southern part of the domain, about 50 km in diameter and with the strongest signal at about 50-m depth (ii) another warm-core anticyclonic eddy of comparable dimensions in the central part of the domain, but extending to greater depth than the former one, and (iii) a small (less than 15 km in diameter) cold-core cyclonic eddy of Winter Intermediate Water in the depth range between 170 m and 370 m. All three eddies showed intensified currents, up to 50 cm s-1. The huge high-resolution observational data set and the variety of observation techniques enabled the mesoscale features and their variability to be tracked for almost three weeks. In order to obtain a deeper understanding of the mesoscale dynamic behaviour and their interactions, assimilation studies with an ocean circulation model are underway.

Eddy Properties and their Spatiotemporal Variability in the North Indian Ocean from Satellite Altimetry

NASA Astrophysics Data System (ADS)

Dandapat, S.; Chakraborty, A.

2016-12-01

A comprehensive study on the statistics and variability of mesoscale eddies in the North Indian Ocean (NIO) are investigated using satellite altimetry data for the period of 1993-2014. A hybrid algorithm based on the physical and geometrical properties of mesoscale eddies is applied to detect the eddies and track their propagation. The potential eddies with radius larger than 50 km and lifespan longer than 30 days are considered for the analysis. The NIO consists of two unique tropical basins with the high number of eddy generations and activity: the Arabian Sea (AS) and the Bay of Bengal (BOB). It is noticed that the occurrence of cyclonic eddies (CEs) are found to be significant in AS, while the anticyclonic eddies (ACEs) dominate the BOB. In both the oceans eddies mostly propagate westward. The AS eddies showed the higher mean values, propagation speed, mean radius, mean lifetime than BOB eddies. In the AS, it is found that eddies formed on the western side of the basin persist longer and move towards north where as the number of eddies in the eastern coast of the basin is fewer and short lived. In the BOB, two highly eddy productive zones are identified: offshore of Visakhapatnam and the northern part of western BOB. The occurrence of ACEs dominate the offshore of Visakhapatnam, whereas the CEs in the northern part of western BOB. The ACEs are larger but the CEs have longer lifetime and are more energetic in the BOB. Along with the statistical properties, we also examined the eddy temporal variability in seasonal scale and their structural properties from ARGO data in the NIO. The seasonal variations are found to be significant in AS and BOB and in both the oceans significant correlation has been found between the eddy genesis and local wind stress curl. The strong positive wind stress curl during summer favors the formation of more CEs. In general, both ACEs and CEs in the NIO have single-core vertical structure with the core at a depth of about 100-200 dbar.

The pines of the Eddy Arboretum

Treesearch

John Duffield

1949-01-01

The Eddy Arboretum at Placerville, California, contains more than 90 species, varieties, and hybrids of pines, and is therefore of great interest to horticulturists. The Arboretum was established in 1925 as a source of breeding stock for the Eddy Tree Breeding Station, founded in the same year by Mr. James G. Eddy of Seattle. In 1934 Mr. Eddy presented the Arboretum...

Technical and Scientific Evaluation of EM-APEX in Hurricane Frances

DTIC Science & Technology

2006-09-30

as part of the 2004 CBLAST experiment (Figure 1). Four of these initial floats were deployed again in the 2005 EDDIES experiment (NSF) near Bermuda . In... triangles indicate ascending and descending profiles, respectively. Circles indicate 500 mn deep profiles, while the rest are 200 mn deep. The figure shows...times marked with triangles can be used to reconstruct surface wave properties using more sophisticated methods. RESULTS Technical Results. a

Recent and Future Enhancements in NDI for Aircraft Structures

DTIC Science & Technology

2015-11-30

accomplish NDI of aircraft structure. This includes improved eddy current probes, improved eddy current instrumentation, as well as other...Aircraft Structures,” which is currently in Revision C [8]. The document divides various inspection methods, such as eddy current and fluorescent...efforts at AFRL to address technology shortfalls include improved eddy current probes, improved eddy current instrumentation, as well as other

Recent and Future Enhancements in NDI for Aircraft Structures (Postprint)

DTIC Science & Technology

2015-11-30

accomplish NDI of aircraft structure. This includes improved eddy current probes, improved eddy current instrumentation, as well as other...Aircraft Structures,” which is currently in Revision C [8]. The document divides various inspection methods, such as eddy current and fluorescent...efforts at AFRL to address technology shortfalls include improved eddy current probes, improved eddy current instrumentation, as well as other

Recent and Future Enhancements in NDI for Aircraft Structures (Postprint)

DTIC Science & Technology

2015-11-01

accomplish NDI of aircraft structure. This includes improved eddy current probes, improved eddy current instrumentation, as well as other...Aircraft Structures,” which is currently in Revision C [8]. The document divides various inspection methods, such as eddy current and fluorescent...efforts at AFRL to address technology shortfalls include improved eddy current probes, improved eddy current instrumentation, as well as other

Recent and Future Enhancements in NDI for Aircraft Structures (POSTPRINT)

DTIC Science & Technology

2015-11-16

accomplish NDI of aircraft structure. This includes improved eddy current probes, improved eddy current instrumentation, as well as other...Aircraft Structures,” which is currently in Revision C [8]. The document divides various inspection methods, such as eddy current and fluorescent...efforts at AFRL to address technology shortfalls include improved eddy current probes, improved eddy current instrumentation, as well as other

A submesoscale coherent vortex in the Ligurian Sea: From dynamical barriers to biological implications

NASA Astrophysics Data System (ADS)

Bosse, Anthony; Testor, Pierre; Mayot, Nicolas; Prieur, Louis; D'Ortenzio, Fabrizio; Mortier, Laurent; Le Goff, Hervé; Gourcuff, Claire; Coppola, Laurent; Lavigne, Héloïse; Raimbault, Patrick

2017-08-01

In June 2013, a glider equipped with oxygen and fluorescence sensors has been used to extensively sample an anticyclonic Submesoscale Coherent Vortex (SCV) in the Ligurian Sea (NW Mediterranean Sea). Those measurements are complemented by full-depth CTD casts (T, S, and oxygen) and water samples documenting nutrients and phytoplankton pigments within the SCV and outside. The SCV has a very homogeneous core of oxygenated waters between 300 and 1200 m formed 4.5 months earlier during the winter deep convection event. It has a strong dynamical signature with peak velocities at 700 m depth of 13.9 cm s-1 in cyclogeostrophic balance. The eddy has a small radius of 6.2 km corresponding to high Rossby number of -0.45. The vorticity at the eddy center reaches -0.8f. Cross-stream isopycnic diffusion of tracers between the eddy core and the surroundings is found to be very limited due to dynamical barriers set by the SCV associated with a diffusivity coefficient of about 0.2 m2 s-1. The deep core is nutrients-depleted with concentrations of nitrate, phosphate, and silicate, 13-18% lower than the rich surrounding waters. However, the nutriclines are shifted of about 20-50 m toward the surface thus increasing the nutrients availability for phytoplankton. Chlorophyll-a concentrations at the deep chlorophyll maximum are subsequently about twice bigger as compared to outside. Pigments further reveal the predominance of nanophytoplankton inside the eddy and an enhancement of the primary productivity. This study demonstrates the important impact of postconvective SCVs on nutrients distribution and phytoplankton community, as well as on the subsequent primary production and carbon sequestration.