U.S. Geological Survey, Department of the Interior — The maximum potential area of eddy bars (MPAEB) represents the cumulative area of the eddy occupied by sand at different times within the photographic record...
Astrophysical ZeV acceleration in the relativistic jet from an accreting supermassive blackhole
Ebisuzaki, Toshikazu; Tajima, Toshiki
2014-04-01
An accreting supermassive blackhole, the central engine of active galactic nucleus (AGN), is capable of exciting extreme amplitude Alfven waves whose wavelength (wave packet) size is characterized by its clumpiness. The pondermotive force and wakefield are driven by these Alfven waves propagating in the AGN (blazar) jet, and accelerate protons/nuclei to extreme energies beyond Zetta-electron volt (ZeV=1021 eV). Such acceleration is prompt, localized, and does not suffer from the multiple scattering/bending enveloped in the Fermi acceleration that causes excessive synchrotron radiation loss beyond 1019 eV. The production rate of ZeV cosmic rays is found to be consistent with the observed gamma-ray luminosity function of blazars and their time variabilities.
Collision avoidance ZEM/ZEV optimal feedback guidance for powered descent phase of landing on Mars
Zhang, Yao; Guo, Yanning; Ma, Guangfu; Zeng, Tianyi
2017-03-01
A novel zero-effort-miss (ZEM)/zero-effort-velocity (ZEV) optimal feedback guidance is proposed in order to rule out the possibility of Martian surface collision caused by the classical ZEM/ZEV optimal feedback guidance. The main approach is to add a collision avoidance term, which has self-adjustment capacity to ensure the near fuel optimality. Its main improvement is that it can not only successfully avoid collisions with the thruster constraint but also guarantee the near fuel optimality, and both of them are pivotal performances in Mars landing missions. Simulations are made to show the effectiveness of the proposed guidance and the parameters effects are simulated as well to analyze the properties of the proposed guidance.
Astrophysical ZeV acceleration in the relativistic jet from an accreting supermassive blackhole
Ebisuzaki, Toshikazu
2013-01-01
An accreting supermassive blackhole, the central engine of active galactic nucleus (AGN), is capable of exciting extreme amplitude Alfven waves whose wavelength (wave packet) size is characterized by its clumpiness. Alfvenic wakefelds excited in the AGN (blazar) jet can accelerate protons/nuclei to extreme energies beyond Zettaelectron volt (ZeV= 10^21 eV). Such acceleration is prompt, localized, and does not suffer from the multiple scattering/bending enveloped in the Fermi acceleration that causes excessive synchrotron radiation loss beyond 10^19 eV. The production rate of ZeV cosmic rays is found to be consistent with the observed gamma-ray luminosity function of blazars and their time variability.
Stationary mesoscale eddies, upgradient eddy fluxes, and the anisotropy of eddy diffusivity
Lu, Jianhua; Wang, Fuchang; Liu, Hailong; Lin, Pengfei
2016-01-01
The mesoscale eddies of which parameterization is needed in coarse-resolution ocean models include not only the transient eddies akin to baroclinic instability but also the stationary eddies associated with topography. By applying a modified Lorenz-type decomposition to the eddy-permitting Southern Ocean State Estimate, we show that the stationary mesoscale eddies contribute a significant part to the total eddy kinetic energy, eddy enstrophy, and the total eddy-induced isopycnal thickness and potential vorticity fluxes. We find that beneath middepth (about 1000 m) the upgradient eddy fluxes, or so-called "negative" eddy diffusivities, are mainly attributed to the stationary mesoscale eddies, whereas the remaining transient eddy diffusivity is positive, for which the Gent and McWilliams (1990) parameterization scheme applies well. A quantitative method of measuring the anisotropy of eddy diffusivity is presented. The effect of stationary mesoscale eddies is one of major sources responsible for the anisotropy of eddy diffusivity. We suggest that an independent parameterization scheme for stationary mesoscale eddies may be needed for coarse-resolution ocean models, although the transient eddies remain the predominant part of mesoscale eddies in the oceans.
Song, Sung Jin; Lee, Hyang Beom; Kim, Young Hwan [Soongsil Univ., Seoul (Korea, Republic of); Shin, Young Kil [Kunsan Univ., Gunsan (Korea, Republic of)
2004-02-15
Eddy current testing has been widely used for non destructive testing of steam generator tubes. In order to retain reliability in ECT, the following subjects were carried out in this study: numerical modeling and analysis of defects by using BC and RPC probes in SG tube, preparation of absolute coil impedance plane diagram by FEM. Signal interpretation of the eddy current signals obtained from nuclear power plants.
Discrete large eddy simulation
L.TAO; K.R.RAJAGOPAL
2001-01-01
Despite the intense effort expended towards obtaining a model for describing the turbulent flows of fluid,there is no model at hand that can do an adequate job.This leads us to look for a non-traditional approach to turbulence modeling.In this work we conjoin the notion of large eddy simulation with those of fuzzy sets and neural networks to describe a class of turbulent flow.in previous works we had discussed several issues concerning large eddy simulation such as filtering and averaging,Here,we discuss the use of fuzzy sets to improve the filtering procedure.
Schaefer, Claire
1989-01-01
Presents a lesson that introduces students in grades K-three to sources of design inspiration in contemporary urban settings. Using Don Eddy's painting of a jewelry store window display, asks students to describe and analyze the interplay of shape, pattern, and color. Suggests studio activities, including an activity in which students build a…
Owen, Hazel
2013-01-01
Eddie Reisch is currently working as a policy advisor for Te Reo Maori Operational Policy within the Student Achievement group with the Ministry of Education in New Zealand, where he has implemented and led a range of e-learning initiatives and developments, particularly the Virtual Learning Network (VLN). He is regarded as one of the leading…
2002-01-01
This true-color satellite image shows a large phytoplankton bloom, several hundred square kilometers in size, in the Indian Ocean off the west coast of Tasmania. In this scene, the rich concentration of microscopic marine plants gives the water a lighter, more turquoise appearance which helps to highlight the current patterns there. Notice the eddies, or vortices in the water, that can be seen in several places. It is possible that these eddies were formed by converging ocean currents flowing around Tasmania, or by fresh river runoff from the island, or both. Often, eddies in the sea serve as a means for stirring the water, thus providing nutrients that help support phytoplankton blooms, which in turn provide nutrition for other organisms. Effectively, these eddies help feed the sea (click to read an article on this topic). This image was acquired November 7, 2000, by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) flying aboard the Orbview-2 satellite. Tasmania is located off Australia's southeastern coast. Image courtesy SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE
Emergent eddy saturation from an energy constrained eddy parameterisation
Mak, J.; Marshall, D. P.; Maddison, J. R.; Bachman, S. D.
2017-04-01
The large-scale features of the global ocean circulation and the sensitivity of these features with respect to forcing changes are critically dependent upon the influence of the mesoscale eddy field. One such feature, observed in numerical simulations whereby the mesoscale eddy field is at least partially resolved, is the phenomenon of eddy saturation, where the time-mean circumpolar transport of the Antarctic Circumpolar Current displays relative insensitivity to wind forcing changes. Coarse-resolution models employing the Gent-McWilliams parameterisation with a constant Gent-McWilliams eddy transfer coefficient seem unable to reproduce this phenomenon. In this article, an idealised model for a wind-forced, zonally symmetric flow in a channel is used to investigate the sensitivity of the circumpolar transport to changes in wind forcing under different eddy closures. It is shown that, when coupled to a simple parameterised eddy energy budget, the Gent-McWilliams eddy transfer coefficient of the form described in Marshall et al. (2012) [A framework for parameterizing eddy potential vorticity fluxes, J. Phys. Oceanogr., vol. 42, 539-557], which includes a linear eddy energy dependence, produces eddy saturation as an emergent property.
2003-01-01
We were saddened to learn that Eddy Powell had passed away on Saturday 26 July after a long illness. Eddy had so many friends at CERN and made such a contribution to the Organisation that it is impossible that his passing goes without comment. Eddy was born in England on 4 August 1939 and, after serving his apprenticeship with the U.K. Ministry of Defence, he joined CERN in September 1965. As an electrical design draftsman with the Synchro-cyclotron Division he played an important role in the upgrades of that machine in the early 1970's, particularly on the RF systems and later on the development of the ISOLDE facility. This brought him into close contact with many of the technical support services in CERN and, unlike many of his compatriots, he acquired a remarkably good fluency in French. Always inquisitive on the physics carried out at CERN, he spent a great deal of time learning from physicists and engineers at all levels. When he felt sufficiently confident he became a CERN Guide for general public visit...
EDDIE RICKENBACKER: RACETRACK ENTREPRENEUR
W. David Lewis
2000-01-01
Full Text Available Edward V. (Eddie Rickenbacker (1890-1973 is best remembered for hisrecord as a combat pilot in World War I, in which he shot down 26 Germa naircraft and won fame as America’s "Ace of Aces." From 1934 until 1963 he was general manager, president, and board chairman of Eastern Air Lines, which was for a time the most profitable air carrier in the United States. This paper shows how Rickenbacker’s fiercely entrepreneurial style of management was born in his early involvement in the automobile industry, and particularly in his career as an automobile racing driver from 1909 through 1916.
Emergent eddy saturation from an energy constrained eddy parameterisation
Mak, Julian; Marshall, David P; Bachman, Scott D
2016-01-01
The large-scale features of the global ocean circulation and the sensitivity of these features with respect to forcing changes are critically dependent upon the influence of the mesoscale eddy field. One such feature, observed in numerical simulations whereby the mesoscale eddy field is at least partially resolved, is the phenomenon of eddy saturation, where the time-mean circumpolar transport of the Antarctic Circumpolar Current displays relative insensitivity to wind forcing changes. Coarse-resolution models employing the Gent--McWilliams parameterisation with a constant Gent--McWilliams coefficient seem unable to reproduce this phenomenon. In this article, an idealised model for a wind-forced, zonally symmetric flow in a channel is used to investigate the sensitivity of the circumpolar transport to changes in wind forcing under different eddy closures. It is shown that, when coupled to a simple parameterised eddy energy budget, the Gent--McWilliams coefficient of the form described in Marshall et al. (2012...
Conditional Eddies in Plasma Turbulence
Johnsen, Helene; Pécseli, Hans; Trulsen, J.
1986-01-01
Conditional structures, or eddies, in turbulent flows are discussed with special attention to electrostatic turbulence in plasmas. The potential variation of these eddies is obtained by sampling the fluctuations only when a certain condition is satisfied in a reference point. The resulting...
Canuto, V. M.; Dubovikov, M. S.
Mesoscale eddies are not resolved in coarse resolution ocean models and must be modeled. They affect both mean momentum and scalars. At present, no generally accepted model exists for the former; in the latter case, mesoscales are modeled with a bolus velocity u∗ to represent a sink of mean potential energy. However, comparison of u∗(model) vs. u∗ (eddy resolving code, [J. Phys. Ocean. 29 (1999) 2442]) has shown that u∗(model) is incomplete and that additional terms, "unrelated to thickness source or sinks", are required. Thus far, no form of the additional terms has been suggested. To describe mesoscale eddies, we employ the Navier-Stokes and scalar equations and a turbulence model to treat the non-linear interactions. We then show that the problem reduces to an eigenvalue problem for the mesoscale Bernoulli potential. The solution, which we derive in analytic form, is used to construct the momentum and thickness fluxes. In the latter case, the bolus velocity u∗ is found to contain two types of terms: the first type entails the gradient of the mean potential vorticity and represents a positive contribution to the production of mesoscale potential energy; the second type of terms, which is new, entails the velocity of the mean flow and represents a negative contribution to the production of mesoscale potential energy, or equivalently, a backscatter process whereby a fraction of the mesoscale potential energy is returned to the original reservoir of mean potential energy. This type of terms satisfies the physical description of the additional terms given by [J. Phys. Ocean. 29 (1999) 2442]. The mesoscale flux that enters the momentum equations is also contributed by two types of terms of the same physical nature as those entering the thickness flux. The potential vorticity flux is also shown to contain two types of terms: the first is of the gradient-type while the other terms entail the velocity of the mean flow. An expression is derived for the mesoscale
Joseph Mathew
2010-10-01
Full Text Available Large eddy simulation (LES is an emerging technique for obtaining an approximation to turbulent flow fields. It is an improvement over the widely prevalent practice of obtaining means of turbulent flows when the flow has large scale, low frequency, unsteadiness. An introduction to the method, its general formulation, and the more common modelling for flows without reaction, is discussed. Some attempts at extension to flows with combustion have been made. Examples from present work for flows with and without combustion are given. The final example of the LES of the combustor of a helicopter engine illustrates the state-of-the-art in application of the technique.Defence Science Journal, 2010, 60(6, pp.598-605, DOI:http://dx.doi.org/10.14429/dsj.60.602
Eddy Correlation Flux Measurement System
Oak Ridge National Laboratory — The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat,...
A simple model of eddy saturation
Marshall, D. P.; Ambaum, M.; Munday, D. R.; Novak, L.; Maddison, J. R.
2016-02-01
A simple model is developed for eddy saturation of the Antarctic Circumpolar Current (ACC): the relative insensitivity of its volume transport to the magnitude of the surface wind stress in ocean models with explicit eddies. The simple model solves prognostic equations for the ACC volume transport and the eddy energy, forming a 2-dimensional nonlinear dynamical system. In equilibrium, the volume transport is independent of the surface wind stress but scales with the bottom drag, whereas the eddy energy scales with the wind stress but is independent of bottom drag. The magnitude of the eddy energy is controlled by the zonal momentum balance between the surface wind stress and eddy form stress, whereas the baroclinic volume transport is controlled by the eddy energy balance between the mean-to-eddy energy conversion and bottom dissipation. The theoretical predictions are confirmed in eddy-resolving numerical calculations for an idealised reentrant channel. The results suggest that the rate of eddy energy dissipation has a strong impact not only the volume transport of the ACC, but also on global ocean stratification and heat content through the thermal wind relation. Moreover, a vital ingredient in this model is a relation between the eddy form stress and eddy energy derived in the eddy parameterisation framework of Marshall et al. (2012, J. Phys. Oceanogr.), offering the prospect of obtaining eddy saturation in ocean models with parameterised eddies.
Applied large eddy simulation.
Tucker, Paul G; Lardeau, Sylvain
2009-07-28
Large eddy simulation (LES) is now seen more and more as a viable alternative to current industrial practice, usually based on problem-specific Reynolds-averaged Navier-Stokes (RANS) methods. Access to detailed flow physics is attractive to industry, especially in an environment in which computer modelling is bound to play an ever increasing role. However, the improvement in accuracy and flow detail has substantial cost. This has so far prevented wider industrial use of LES. The purpose of the applied LES discussion meeting was to address questions regarding what is achievable and what is not, given the current technology and knowledge, for an industrial practitioner who is interested in using LES. The use of LES was explored in an application-centred context between diverse fields. The general flow-governing equation form was explored along with various LES models. The errors occurring in LES were analysed. Also, the hybridization of RANS and LES was considered. The importance of modelling relative to boundary conditions, problem definition and other more mundane aspects were examined. It was to an extent concluded that for LES to make most rapid industrial impact, pragmatic hybrid use of LES, implicit LES and RANS elements will probably be needed. Added to this further, highly industrial sector model parametrizations will be required with clear thought on the key target design parameter(s). The combination of good numerical modelling expertise, a sound understanding of turbulence, along with artistry, pragmatism and the use of recent developments in computer science should dramatically add impetus to the industrial uptake of LES. In the light of the numerous technical challenges that remain it appears that for some time to come LES will have echoes of the high levels of technical knowledge required for safe use of RANS but with much greater fidelity.
Remote field eddy current testing
Cheong, Y. M.; Jung, H. K.; Huh, H.; Lee, Y. S.; Shim, C. M
2001-03-01
The state-of-art technology of the remote field eddy current, which is actively developed as an electromagnetic non-destructive testing tool for ferromagnetic tubes, is described. The historical background and recent R and D activities of remote-field eddy current technology are explained including the theoretical development of remote field eddy current, such as analytical and numerical approach, and the results of finite element analysis. The influencing factors for actual applications, such as the effect of frequency, magnetic permeability, receiving sensitivity, and difficulties of detection and classification of defects are also described. Finally, two examples of actual application, 1) the gap measurement between pressure tubes and calandria tube in CANDU reactor and, 2) the detection of defects in the ferromagnetic heat exchanger tubes, are described. The future research efforts are also included.
Formation and propagation of the Aleutian eddy
Ishiyama, H.; Ueno, H.; Inatsu, M.
2012-12-01
Aleutian eddies are anticyclonic eddies which form south of the Aleutian Islands between 170°E and 175°E and propagate southwestward. In this study we investigated formation and propagation of the Aleutian eddy through analysis of 18-year time series of satellite altimeter data distributed by AVISO. Neighbor enclosed area tracking algorithm was applied to track each eddy identified using Okubo-Weiss parameter. Zero to five Aleutian eddies were formed per year and the number of Aleutian eddy formed per year changed with a period of three to four years. Meanwhile, the propagation route of the Aleutian eddy did not show marked interannual variation. Most of the Aleutian eddies propagate toward the center of western subarctic gyre; the rest propagate toward Kamchatka Peninsula or into the Bering Sea.
Dynamic Model of Mesoscale Eddies
Dubovikov, Mikhail S.
2003-04-01
Oceanic mesoscale eddies which are analogs of well known synoptic eddies (cyclones and anticyclones), are studied on the basis of the turbulence model originated by Dubovikov (Dubovikov, M.S., "Dynamical model of turbulent eddies", Int. J. Mod. Phys.B7, 4631-4645 (1993).) and further developed by Canuto and Dubovikov (Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: I. General formalism", Phys. Fluids8, 571-586 (1996a) (CD96a); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: II. Sheardriven flows", Phys. Fluids8, 587-598 (1996b) (CD96b); Canuto, V.M., Dubovikov, M.S., Cheng, Y. and Dienstfrey, A., "A dynamical model for turbulence: III. Numerical results", Phys. Fluids8, 599-613 (1996c)(CD96c); Canuto, V.M., Dubovikov, M.S. and Dienstfrey, A., "A dynamical model for turbulence: IV. Buoyancy-driven flows", Phys. Fluids9, 2118-2131 (1997a) (CD97a); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: V. The effect of rotation", Phys. Fluids9, 2132-2140 (1997b) (CD97b); Canuto, V.M., Dubovikov, M.S. and Wielaard, D.J., "A dynamical model for turbulence: VI. Two dimensional turbulence", Phys. Fluids9, 2141-2147 (1997c) (CD97c); Canuto, V.M. and Dubovikov, M.S., "Physical regimes and dimensional structure of rotating turbulence", Phys. Rev. Lett. 78, 666-669 (1997d) (CD97d); Canuto, V.M., Dubovikov, M.S. and Dienstfrey, A., "Turbulent convection in a spectral model", Phys. Rev. Lett. 78, 662-665 (1997e) (CD97e); Canuto, V.M. and Dubovikov, M.S., "A new approach to turbulence", Int. J. Mod. Phys.12, 3121-3152 (1997f) (CD97f); Canuto, V.M. and Dubovikov, M.S., "Two scaling regimes for rotating Raleigh-Benard convection", Phys. Rev. Letters78, 281-284, (1998) (CD98); Canuto, V.M. and Dubovikov, M.S., "A dynamical model for turbulence: VII. The five invariants for shear driven flows", Phys. Fluids11, 659-664 (1999a) (CD99a); Canuto, V.M., Dubovikov, M.S. and Yu, G., "A dynamical model for turbulence: VIII. IR and UV
Eddy current thickness measurement apparatus
Rosen, Gary J.; Sinclair, Frank; Soskov, Alexander; Buff, James S.
2015-06-16
A sheet of a material is disposed in a melt of the material. The sheet is formed using a cooling plate in one instance. An exciting coil and sensing coil are positioned downstream of the cooling plate. The exciting coil and sensing coil use eddy currents to determine a thickness of the solid sheet on top of the melt.
Quantifying mesoscale eddies in the Lofoten Basin
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.
Observed eddy dissipation in the Agulhas Current
Braby, Laura; Backeberg, Björn C.; Ansorge, Isabelle; Roberts, Michael J.; Krug, Marjolaine; Reason, Chris J. C.
2016-08-01
Analyzing eddy characteristics from a global data set of automatically tracked eddies for the Agulhas Current in combination with surface drifters as well as geostrophic currents from satellite altimeters, it is shown that eddies from the Mozambique Channel and south of Madagascar dissipate as they approach the Agulhas Current. By tracking the offshore position of the current core and its velocity at 30°S in relation to eddies, it is demonstrated that eddy dissipation occurs through a transfer of momentum, where anticyclones consistently induce positive velocity anomalies, and cyclones reduce the velocities and cause offshore meanders. Composite analyses of the anticyclonic (cyclonic) eddy-current interaction events demonstrate that the positive (negative) velocity anomalies propagate downstream in the Agulhas Current at 44 km/d (23 km/d). Many models are unable to represent these eddy dissipation processes, affecting our understanding of the Agulhas Current.
Transient eddy current flow metering
Forbriger, Jan
2015-01-01
Measuring local velocities or entire flow rates in liquid metals or semiconductor melts is a notorious problem in many industrial applications, including metal casting and silicon crystal growth. We present a new variant of an old technique which relies on the continuous tracking of a flow-advected transient eddy current that is induced by a pulsed external magnetic field. This calibration-free method is validated by applying it to the velocity of a spinning disk made of aluminum. First tests at a rig with a flow of liquid GaInSn are also presented.
Transient eddy current flow metering
Forbriger, J.; Stefani, F.
2015-10-01
Measuring local velocities or entire flow rates in liquid metals or semiconductor melts is a notorious problem in many industrial applications, including metal casting and silicon crystal growth. We present a new variant of an old technique which relies on the continuous tracking of a flow-advected transient eddy current that is induced by a pulsed external magnetic field. This calibration-free method is validated by applying it to the velocity of a spinning disk made of aluminum. First tests at a rig with a flow of liquid GaInSn are also presented.
A. O. Abramovych
2014-06-01
Full Text Available Introduction. At present there are many electrical schematic metal detectors (the most common kind of ground penetrating radar, which are differ in purpose. Each scheme has its own advantages and disadvantages compared to other schemes. Designing metal detector problem of optimal selection of functional units most schemes can only work with a narrow range of special purpose units. Functional units used in circuits can be replaced by better ones, but specialization schemes do not provide such a possibility. Description of problem. Author has created a "complex for research of functional units of metal detectors" that is the universal system that meets the task. With this set of studies conducted on the practical implementation of radar-eddy current method of distinguishing non-ferrous metals (gold, copper, etc. is based. Description of method. Mathematical tools using have to be treated as a signal metal detector to distinguish metals: gold, copper and others. Conclusions. Processing of partial pulses may have information about beforehand signal loss during propagation in heterogeneous media with lossy nonuniform distribution parameters. Using eddy currents To calculate the value of the input voltage depending on the conductivity of the metal in the receiving antenna.Combining two different methods for processing the received signal theoretically it could be proved that with high probability can distinguish non-ferrous metals - gold, copper etc.
Mesoscale Ocean Large Eddy Simulations
Pearson, Brodie; Fox-Kemper, Baylor; Bachman, Scott; Bryan, Frank
2015-11-01
The highest resolution global climate models (GCMs) can now resolve the largest scales of mesoscale dynamics in the ocean. This has the potential to increase the fidelity of GCMs. However, the effects of the smallest, unresolved, scales of mesoscale dynamics must still be parametrized. One such family of parametrizations are mesoscale ocean large eddy simulations (MOLES), but the effects of including MOLES in a GCM are not well understood. In this presentation, several MOLES schemes are implemented in a mesoscale-resolving GCM (CESM), and the resulting flow is compared with that produced by more traditional sub-grid parametrizations. Large eddy simulation (LES) is used to simulate flows where the largest scales of turbulent motion are resolved, but the smallest scales are not resolved. LES has traditionally been used to study 3D turbulence, but recently it has also been applied to idealized 2D and quasi-geostrophic (QG) turbulence. The MOLES presented here are based on 2D and QG LES schemes.
Oceanic eddies in synthetic aperture radar images
Andrei Yu Ivanov; Anna I Ginzburg
2002-09-01
Continuous observations since 1991 by using synthetic aperture radar (SAR) on board the Almaz-1, ERS-1/2, JERS-1, and RADARSAT satellites support the well-known fact that oceanic eddies are distributed worldwide in the ocean. The paper is devoted to an evaluation of the potential of SAR for detection of eddies and vortical motions in the ocean. The classification of typical vortical features in the ocean detected in remote sensing images (visible, infrared, and SAR) is presented as well as available information on their spatial and temporal scales. Examples of the Almaz-1 and ERS-1/2 SAR images showing different eddy types, such as rings, spiral eddies of the open ocean, eddies behind islands and in bays, spin-off eddies and mushroom-like structures (vortex dipoles) are given and discussed. It is shown that a common feature for most of the eddies detected in the SAR images is a broad spectrum of spatial scales, spiral shape and shear nature. It is concluded that the spaceborne SARs give valuable information on ocean eddies, especially in combination with visible and infrared satellite data.
Wind changes above warm Agulhas Current eddies
Rouault, M
2016-01-01
Full Text Available speeds above the eddies at the instantaneous scale; 20 % of cases had incomplete data due to partial global coverage by the scatterometer for one path. For cases where the wind is stronger above warm eddies, there is no relationship between the increase...
Exploring Eddy-Covariance Measurements Using a Spatial Approach: The Eddy Matrix
Engelmann, Christian; Bernhofer, Christian
2016-10-01
Taylor's frozen turbulence hypothesis states that "standard" eddy-covariance measurements of fluxes at a fixed location can replace a spatial ensemble of instantaneous values at multiple locations. For testing this hypothesis, a unique turbulence measurement set-up was used for two measurement campaigns over desert (Namibia) and grassland (Germany) in 2012. This "Eddy Matrix" combined nine ultrasonic anemometer-thermometers and 17 thermocouples in a 10 m × 10 m regular grid with 2.5-m grid distance. The instantaneous buoyancy flux derived from the spatial eddy covariance of the Eddy Matrix was highly variable in time (from -0.3 to 1 m K s^{-1}). However, the 10-min average reflected 83 % of the reference eddy-covariance flux with a good correlation. By introducing a combined eddy-covariance method (the spatial eddy covariance plus the additional flux of the temporal eddy covariance of the spatial mean values), the mean flux increases by 9 % relative to the eddy-covariance reference. Considering the typical underestimation of fluxes by the standard eddy-covariance method, this is seen as an improvement. Within the limits of the Eddy Matrix, Taylor's hypothesis is supported by the results.
Modeling the mesoscale eddy field in the Gulf of Alaska
Xiu, Peng; Chai, Fei; Xue, Huijie; Shi, Lei; Chao, Yi
2012-05-01
Mesoscale anticyclonic eddies are a common feature in the Gulf of Alaska (GOA). A three-dimensional circulation model is used to examine the general characteristics of eddies in the GOA during 1993-2009. Using an eddy detection algorithm, we tracked on average 6.5 eddies formed each year from the modeled results and 6.9 eddies from altimeter data. Modeled eddy characteristics agree with the remote sensing derived eddy statistics in terms of eddy magnitude, propagation speed, and eddy-core diameter. From the model results, strong seasonal and interannual variations were found in both the number and areal coverage of GOA eddies. At the seasonal scale, more eddies are observed to form from March to May, while the eddy-covered area usually peaks around October. At the interannual scale, our results suggest the years with large eddy-covered area do not necessarily have more eddies generated. The long-term variation of eddy-covered area in the GOA is modulated by El Niño/Southern Oscillation (ENSO) events through altering the local wind stress. Model results indicate one typical Haida eddy could transport 37×1018 J of heat and 27 km3 of freshwater from the shelf to the central gulf. The equivalent fluxes caused by Haida eddies are comparable with the annual mean of net heat flux and freshwater flux from the atmosphere into the ocean in the Haida region, implying that mesoscale eddies are important sources contributing to the heat and freshwater budgets.
Intense submesoscale upwelling in anticyclonic eddies
Brannigan, L.
2016-04-01
Observations from around the global ocean show that enhanced biological activity can be found in anticyclonic eddies. This may mean that upwelling of nutrient-rich water occurs within the eddy, but such upwelling is not captured by models that resolve mesoscale processes. High-resolution simulations presented here show intense submesoscale upwelling from the thermocline to the mixed layer in anticyclonic eddies. The properties of the upwelling are consistent with a process known as symmetric instability. A simple limiting nutrient experiment shows that this upwelling can drive much higher biological activity in anticyclonic eddies when there is a high nutrient concentration in the thermocline. An estimate for the magnitude of upwelling associated with symmetric instability in anticyclonic eddies in the Sargasso Sea shows that it may be of comparable magnitude to other processes, though further work is required to understand the full implications for basin-scale nutrient budgets.
Large Eddy Simulations in Astrophysics
Schmidt, Wolfram
2014-01-01
In this review, the methodology of large eddy simulations (LES) is introduced and applications in astrophysics are discussed. As theoretical framework, the scale decomposition of the dynamical equations for neutral fluids by means of spatial filtering is explained. For cosmological applications, the filtered equations in comoving coordinates are also presented. To obtain a closed set of equations that can be evolved in LES, several subgrid scale models for the interactions between numerically resolved and unresolved scales are discussed, in particular the subgrid scale turbulence energy equation model. It is then shown how model coefficients can be calculated, either by dynamical procedures or, a priori, from high-resolution data. For astrophysical applications, adaptive mesh refinement is often indispensable. It is shown that the subgrid scale turbulence energy model allows for a particularly elegant and physically well motivated way of preserving momentum and energy conservation in AMR simulations. Moreover...
Conformable eddy current array delivery
Summan, Rahul; Pierce, Gareth; Macleod, Charles; Mineo, Carmelo; Riise, Jonathan; Morozov, Maxim; Dobie, Gordon; Bolton, Gary; Raude, Angélique; Dalpé, Colombe; Braumann, Johannes
2016-02-01
The external surface of stainless steel containers used for the interim storage of nuclear material may be subject to Atmospherically Induced Stress Corrosion Cracking (AISCC). The inspection of such containers poses a significant challenge due to the large quantities involved; therefore, automating the inspection process is of considerable interest. This paper reports upon a proof-of-concept project concerning the automated NDT of a set of test containers containing artificially generated AISCCs. An Eddy current array probe with a conformable padded surface from Eddyfi was used as the NDT sensor and end effector on a KUKA KR5 arc HW robot. A kinematically valid cylindrical raster scan path was designed using the KUKA|PRC path planning software. Custom software was then written to interface measurement acquisition from the Eddyfi hardware with the motion control of the robot. Preliminary results and analysis are presented from scanning two canisters.
EDDY CURRENT CHARACTERIZATION OF NANOMATERIALS
A YOUNES
2015-06-01
Full Text Available NDT Magnetic measurements as impedance in Eddy currents, corecitif and residual field in hysteresis loop are used to study the different stages of mechanical alloying in the Fe–Co system. In this paper, we changed the electromagnetic properties of Fe-Co, by developing their metallurgical parameters such as grain size. For this we are used a planetary ball mill, we are milled the FeCo alloy for different milling times until to obtain nanostructure, the lamellar structure with some small particles embedded in them was observed during the first stage of mechanical alloying. XRD patterns show after 10 h of milling the formation of a disordered solid solution having a body-centered cubic (bcc structure. After 40h of milling, morphological studies indicated that the average crystallites size is around 15 nm.
A western boundary current eddy characterisation study
Ribbe, Joachim; Brieva, Daniel
2016-12-01
The analysis of an eddy census for the East Australian Current (EAC) region yielded a total of 497 individual short-lived (7-28 days) cyclonic and anticyclonic eddies for the period 1993 to 2015. This was an average of about 23 eddies per year. 41% of the tracked individual cyclonic and anticyclonic eddies were detected off southeast Queensland between about 25 °S and 29 °S. This is the region where the flow of the EAC intensifies forming a swift western boundary current that impinges near Fraser Island on the continental shelf. This zone was also identified as having a maximum in detected short-lived cyclonic eddies. A total of 94 (43%) individual cyclonic eddies or about 4-5 per year were tracked in this region. The census found that these potentially displaced entrained water by about 115 km with an average displacement speed of about 4 km per day. Cyclonic eddies were likely to contribute to establishing an on-shelf longshore northerly flow forming the western branch of the Fraser Island Gyre and possibly presented an important cross-shelf transport process in the life cycle of temperate fish species of the EAC domain. In-situ observations near western boundary currents previously documented the entrainment, off-shelf transport and export of near shore water, nutrients, sediments, fish larvae and the renewal of inner shelf water due to short-lived eddies. This study found that these cyclonic eddies potentially play an important off-shelf transport process off the central east Australian coast.
Anatomy of a subtropical intrathermocline eddy
Barceló-Llull, Bàrbara; Sangrà, Pablo; Pallàs-Sanz, Enric; Barton, Eric D.; Estrada-Allis, Sheila N.; Martínez-Marrero, Antonio; Aguiar-González, Borja; Grisolía, Diana; Gordo, Carmen; Rodríguez-Santana, Ángel; Marrero-Díaz, Ángeles; Arístegui, Javier
2017-06-01
An interdisciplinary survey of a subtropical intrathermocline eddy was conducted within the Canary Eddy Corridor in September 2014. The anatomy of the eddy is investigated using near submesoscale fine resolution two-dimensional data and coarser resolution three-dimensional data. The eddy was four months old, with a vertical extension of 500 m and 46 km radius. It may be viewed as a propagating negative anomaly of potential vorticity (PV), 95% below ambient PV. We observed two cores of low PV, one in the upper layers centered at 85 m, and another broader anomaly located between 175 m and the maximum sampled depth in the three-dimensional dataset (325 m). The upper core was where the maximum absolute values of normalized relative vorticity (or Rossby number), |Ro| =0.6, and azimuthal velocity, U=0.5 m s-1, were reached and was defined as the eddy dynamical core. The typical biconvex isopleth shape for intrathermocline eddies induces a decrease of static stability, which causes the low PV of the upper core. The deeper low PV core was related to the occurrence of a pycnostad layer of subtropical mode water that was embedded within the eddy. The eddy core, of 30 km radius, was in near solid body rotation with period of 4 days. It was encircled by a thin outer ring that was rotating more slowly. The kinetic energy (KE) content exceeded that of available potential energy (APE), KE/APE=1.58; this was associated with a low aspect ratio and a relatively intense rate of spin as indicated by the relatively high value of Ro. Inferred available heat and salt content anomalies were AHA=2.9×1018 J and ASA=14.3×1010 kg, respectively. The eddy AHA and ASA contents per unit volume largely exceed those corresponding to Pacific Ocean intrathermocline eddies. This suggests that intrathermocline eddies may play a significant role in the zonal conduit of heat and salt along the Canary Eddy Corridor.
Modal Wave Number Spectrum for Mesoscale Eddies
KANG Ying; PENG Linhui
2003-01-01
The variations of ocean environmental parameters invariably result in variations of local modal wave numbers of a sound pressure field. The asymptotic Hankel transform with a short sliding window is applied to the complex sound pressure field in the water containing a mesoscale eddy to examine the variation of local modal wave numbers in such a range-dependent environment. The numerical simulation results show that modal wave number spectra obtained by this method can reflect the location and strength of a mesoscale eddy, therefore it can be used to monitor the strength and spatial scale of ocean mesoscale eddies.
Renormalization group formulation of large eddy simulation
Yakhot, V.; Orszag, S. A.
1985-01-01
Renormalization group (RNG) methods are applied to eliminate small scales and construct a subgrid scale (SSM) transport eddy model for transition phenomena. The RNG and SSM procedures are shown to provide a more accurate description of viscosity near the wall than does the Smagorinski approach and also generate farfield turbulence viscosity values which agree well with those of previous researchers. The elimination of small scales causes the simultaneous appearance of a random force and eddy viscosity. The RNG method permits taking these into account, along with other phenomena (such as rotation) for large-eddy simulations.
Eddy Current Testing, RQA/M1-5330.17.
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,…
Large Eddy Simulations in Astrophysics
Schmidt, Wolfram
2015-12-01
In this review, the methodology of large eddy simulations (LES) is introduced and applications in astrophysics are discussed. As theoretical framework, the scale decomposition of the dynamical equations for neutral fluids by means of spatial filtering is explained. For cosmological applications, the filtered equations in comoving coordinates are also presented. To obtain a closed set of equations that can be evolved in LES, several subgrid-scale models for the interactions between numerically resolved and unresolved scales are discussed, in particular the subgrid-scale turbulence energy equation model. It is then shown how model coefficients can be calculated, either by dynamic procedures or, a priori, from high-resolution data. For astrophysical applications, adaptive mesh refinement is often indispensable. It is shown that the subgrid-scale turbulence energy model allows for a particularly elegant and physically well-motivated way of preserving momentum and energy conservation in adaptive mesh refinement (AMR) simulations. Moreover, the notion of shear-improved models for in-homogeneous and non-stationary turbulence is introduced. Finally, applications of LES to turbulent combustion in thermonuclear supernovae, star formation and feedback in galaxies, and cosmological structure formation are reviewed.
Work done by atmospheric winds on mesoscale ocean eddies
Xu, Chi; Zhai, Xiaoming; Shang, Xiao-Dong
2016-12-01
Mesoscale eddies are ubiquitous in the ocean and dominate the ocean's kinetic energy. However, physical processes influencing ocean eddy energy remain poorly understood. Mesoscale ocean eddy-wind interaction potentially provides an energy flux into or out of the eddy field, but its effect on ocean eddies has not yet been determined. Here we examine work done by atmospheric winds on more than 1,200,000 mesoscale eddies identified from satellite altimetry data and show that atmospheric winds significantly damp mesoscale ocean eddies, particularly in the energetic western boundary current regions and the Southern Ocean. Furthermore, the large-scale wind stress curl is found to on average systematically inject kinetic energy into anticyclonic (cyclonic) eddies in the subtropical (subpolar) gyres while mechanically damps anticyclonic (cyclonic) eddies in the subpolar (subtropical) gyres.
Eddies in the Red Sea: A statistical and dynamical study
Zhan, Peng
2014-06-01
Sea level anomaly (SLA) data spanning 1992–2012 were analyzed to study the statistical properties of eddies in the Red Sea. An algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks. Statistics suggest that eddies are generated across the entire Red Sea but that they are prevalent in certain regions. A high number of eddies is found in the central basin between 18°N and 24°N. More than 87% of the detected eddies have a radius ranging from 50 to 135 km. Both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase. The averaged eddy lifespan is approximately 6 weeks. AEs and cyclonic eddies (CEs) have different deformation features, and those with stronger intensities are less deformed and more circular. Analysis of long-lived eddies suggests that they are likely to appear in the central basin with AEs tending to move northward. In addition, their eddy kinetic energy (EKE) increases gradually throughout their lifespans. The annual cycles of CEs and AEs differ, although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in February and August, respectively. The seasonal cycle of EKE is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate, suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the Red Sea.
Temporal Large-Eddy Simulation
Pruett, C. D.; Thomas, B. C.
2004-01-01
In 1999, Stolz and Adams unveiled a subgrid-scale model for LES based upon approximately inverting (defiltering) the spatial grid-filter operator and termed .the approximate deconvolution model (ADM). Subsequently, the utility and accuracy of the ADM were demonstrated in a posteriori analyses of flows as diverse as incompressible plane-channel flow and supersonic compression-ramp flow. In a prelude to the current paper, a parameterized temporal ADM (TADM) was developed and demonstrated in both a priori and a posteriori analyses for forced, viscous Burger's flow. The development of a time-filtered variant of the ADM was motivated-primarily by the desire for a unifying theoretical and computational context to encompass direct numerical simulation (DNS), large-eddy simulation (LES), and Reynolds averaged Navier-Stokes simulation (RANS). The resultant methodology was termed temporal LES (TLES). To permit exploration of the parameter space, however, previous analyses of the TADM were restricted to Burger's flow, and it has remained to demonstrate the TADM and TLES methodology for three-dimensional flow. For several reasons, plane-channel flow presents an ideal test case for the TADM. Among these reasons, channel flow is anisotropic, yet it lends itself to highly efficient and accurate spectral numerical methods. Moreover, channel-flow has been investigated extensively by DNS, and a highly accurate data base of Moser et.al. exists. In the present paper, we develop a fully anisotropic TADM model and demonstrate its utility in simulating incompressible plane-channel flow at nominal values of Re(sub tau) = 180 and Re(sub tau) = 590 by the TLES method. The TADM model is shown to perform nearly as well as the ADM at equivalent resolution, thereby establishing TLES as a viable alternative to LES. Moreover, as the current model is suboptimal is some respects, there is considerable room to improve TLES.
Transformed eddy-PV flux and positive synoptic eddy feedback onto low-frequency flow
Ren, Hong-Li [University of Hawaii, School of Ocean and Earth Sciences and Technology, Honolulu, HI (United States); China Meteorological Administration, Laboratory for Climate Studies, National Climate Center, Beijing (China); Jin, Fei-Fei [University of Hawaii, School of Ocean and Earth Sciences and Technology, Honolulu, HI (United States); Kug, Jong-Seong [Korea Ocean Research and Development Institute, Ansan (Korea, Republic of); Gao, Li [University of Hawaii, School of Ocean and Earth Sciences and Technology, Honolulu, HI (United States); China Meteorological Administration, Numerical Prediction Center, National Meteorological Center, Beijing (China)
2011-06-15
Interaction between synoptic eddy and low-frequency flow (SELF) has been the subject of many studies. In this study, we further examine the interaction by introducing a transformed eddy-potential-vorticity (TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticity inversion. The main advantage of using the TEPV flux is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-frequency flow in such a way that the TEPV flux tends to be analogous to the eddy-vorticity fluxes in the barotropic framework. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climate modes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is a convenient three-dimensional indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. By projecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimate the eddy-induced growth rates for the low frequency flow anomalies. This positive eddy-induced growth rate is larger (smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may play an important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow by balancing some of the strong damping effect of surface friction. (orig.)
Transformed eddy-PV flux and positive synoptic eddy feedback onto low-frequency flow
Ren, Hong-Li; Jin, Fei-Fei; Kug, Jong-Seong; Gao, Li
2011-06-01
Interaction between synoptic eddy and low-frequency flow (SELF) has been the subject of many studies. In this study, we further examine the interaction by introducing a transformed eddy-potential-vorticity (TEPV) flux that is obtained from eddy-potential-vorticity flux through a quasi-geostrophic potential-vorticity inversion. The main advantage of using the TEPV flux is that it combines the effects of the eddy-vorticity and heat fluxes into the net acceleration of the low-frequency flow in such a way that the TEPV flux tends to be analogous to the eddy-vorticity fluxes in the barotropic framework. We show that the anomalous TEPV fluxes are preferentially directed to the left-hand side of the low-frequency flow in all vertical levels throughout the troposphere for monthly flow anomalies and for climate modes such as the Arctic Oscillation (AO). Furthermore, this left-hand preference of the TEPV flux direction is a convenient three-dimensional indicator of the positive reinforcement of the low-frequency flow by net eddy-induced acceleration. By projecting the eddy-induced net accelerations onto the low-frequency flow anomalies, we estimate the eddy-induced growth rates for the low frequency flow anomalies. This positive eddy-induced growth rate is larger (smaller) in the lower (upper) troposphere. The stronger positive eddy feedback in the lower troposphere may play an important role in maintaining an equivalent barotropic structure of the low-frequency atmospheric flow by balancing some of the strong damping effect of surface friction.
An eddy tracking algorithm based on dynamical systems theory
Conti, Daniel; Orfila, Alejandro; Mason, Evan; Sayol, Juan Manuel; Simarro, Gonzalo; Balle, Salvador
2016-11-01
This work introduces a new method for ocean eddy detection that applies concepts from stationary dynamical systems theory. The method is composed of three steps: first, the centers of eddies are obtained from fixed points and their linear stability analysis; second, the size of the eddies is estimated from the vorticity between the eddy center and its neighboring fixed points, and, third, a tracking algorithm connects the different time frames. The tracking algorithm has been designed to avoid mismatching connections between eddies at different frames. Eddies are detected for the period between 1992 and 2012 using geostrophic velocities derived from AVISO altimetry and a new database is provided for the global ocean.
Vertical eddy heat fluxes from model simulations
Stone, Peter H.; Yao, Mao-Sung
1991-01-01
Vertical eddy fluxes of heat are calculated from simulations with a variety of climate models, ranging from three-dimensional GCMs to a one-dimensional radiative-convective model. The models' total eddy flux in the lower troposphere is found to agree well with Hantel's analysis from observations, but in the mid and upper troposphere the models' values are systematically 30 percent to 50 percent smaller than Hantel's. The models nevertheless give very good results for the global temperature profile, and the reason for the discrepancy is unclear. The model results show that the manner in which the vertical eddy flux is carried is very sensitive to the parameterization of moist convection. When a moist adiabatic adjustment scheme with a critical value for the relative humidity of 100 percent is used, the vertical transports by large-scale eddies and small-scale convection on a global basis are equal: but when a penetrative convection scheme is used, the large-scale flux on a global basis is only about one-fifth to one-fourth the small-scale flux. Comparison of the model results with observations indicates that the results with the latter scheme are more realistic. However, even in this case, in mid and high latitudes the large and small-scale vertical eddy fluxes of heat are comparable in magnitude above the planetary boundary layer.
Modelling of the North Atlantic eddy characteristics
Ushakov, Konstantin; Ibrayev, Rashit
2017-04-01
We investigate eddy characteristics of the Atlantic basin circulation and their impact on the ocean heat transport. A 15-year-long numerical experiment is performed with the global 3-dimensional z-coordinate INMIO ocean general circulation model of 0.1 deg., 49 levels resolution in conditions of the CORE-II protocol. The model is tuned to maximal intensity of eddies production by using only biharmonic filters instead of lateral viscous and diffusive terms in the model equations. Comparison with viscous and coarse-resolution simulations shows the increase of explicitly resolved heat transfer fraction and absolute values. Vertical turbulent mixing is parameterized by the Munk-Anderson scheme including convective adjustment. The sea ice is described by a simple thermodynamic submodel. The eddying velocity and temperature field components are defined as anomalies relative to the 3-month sliding mean. The regional distributions of hydrological parameters, eddy kinetic energy, heat convergence, meridional heat transport (MHT) and Atlantic meridional overturning circulation (AMOC) streamfunction, and their temporal variability are analyzed. In some parts of the basin the simulated eddy heat transport is opposite to the mean flow transport and may change direction with depth. The MHT intensity is slightly below observationally based assessments with notable influence of the East Greenland current simulation bias. The work is supported by the Russian Science Foundation (project N 14-27-00126) and performed in the Institute of Numerical Mathematics, Russian Academy of Sciences.
Turbulent fluxes by "Conditional Eddy Sampling"
Siebicke, Lukas
2015-04-01
Turbulent flux measurements are key to understanding ecosystem scale energy and matter exchange, including atmospheric trace gases. While the eddy covariance approach has evolved as an invaluable tool to quantify fluxes of e.g. CO2 and H2O continuously, it is limited to very few atmospheric constituents for which sufficiently fast analyzers exist. High instrument cost, lack of field-readiness or high power consumption (e.g. many recent laser-based systems requiring strong vacuum) further impair application to other tracers. Alternative micrometeorological approaches such as conditional sampling might overcome major limitations. Although the idea of eddy accumulation has already been proposed by Desjardin in 1972 (Desjardin, 1977), at the time it could not be realized for trace gases. Major simplifications by Businger and Oncley (1990) lead to it's widespread application as 'Relaxed Eddy Accumulation' (REA). However, those simplifications (flux gradient similarity with constant flow rate sampling irrespective of vertical wind velocity and introduction of a deadband around zero vertical wind velocity) have degraded eddy accumulation to an indirect method, introducing issues of scalar similarity and often lack of suitable scalar flux proxies. Here we present a real implementation of a true eddy accumulation system according to the original concept. Key to our approach, which we call 'Conditional Eddy Sampling' (CES), is the mathematical formulation of conditional sampling in it's true form of a direct eddy flux measurement paired with a performant real implementation. Dedicated hardware controlled by near-real-time software allows full signal recovery at 10 or 20 Hz, very fast valve switching, instant vertical wind velocity proportional flow rate control, virtually no deadband and adaptive power management. Demonstrated system performance often exceeds requirements for flux measurements by orders of magnitude. The system's exceptionally low power consumption is ideal
HUANG Rui Xin
2014-01-01
Two important nonlinear properties of seawater thermodynamics linked to changes of water density, cab-beling and elasticity (compressibility), are discussed. Eddy diffusion and advection lead to changes in den-sity;as a result, gravitational potential energy of the system is changed. Therefore, cabbeling and elasticity play key roles in the energetics of lateral eddy diffusion and advection. Vertical eddy diffusion is one of the key elements in the mechanical energy balance of the global oceans. Vertical eddy diffusion can be con-ceptually separated into two steps:stirring and subscale diffusion. Vertical eddy stirring pushes cold/dense water upward and warm/light water downward;thus, gravitational potential energy is increased. During the second steps, water masses from different places mix through subscale diffusion, and water density is increased due to cabbeling. Using WOA01 climatology and assuming the vertical eddy diffusivity is equal to a constant value of 2×103 Pa2/s, the total amount of gravitational potential energy increase due to vertical stirring in the world oceans is estimated at 263 GW. Cabbeling associated with vertical subscale diffusion is a sink of gravitational potential energy, and the total value of energy lost is estimated at 73 GW. Therefore, the net source of gravitational potential energy due to vertical eddy diffusion for the world oceans is estimated at 189 GW.
Eddy parameterization challenge suite I: Eady spindown
Bachman, S.; Fox-Kemper, B.
2013-04-01
The first set of results in a suite of eddy-resolving Boussinesq, hydrostatic simulations is presented. Each set member consists of an initially linear stratification and shear as in the Eady problem, but this profile occupies only a limited region of a channel and is allowed to spin-down via baroclinic instability. The diagnostic focus is on the spatial structure and scaling of the eddy transport tensor, which is the array of coefficients in a linear flux-gradient relationship. The advective (antisymmetric) and diffusive (symmetric) components of the tensor are diagnosed using passive tracers, and the resulting diagnosed tensor reproduces the horizontal transport of the active tracer (buoyancy) to within ± 7% and the vertical transport to within ± 12%. The derived scalings are shown to be close in form to the standard Gent-McWilliams (antisymmetric) and Redi diffusivity (symmetric) tensors with a magnitude that varies in space (concentrated in the horizontal and vertical near the center of the frontal shear) and time as the eddies energize. The Gent-McWilliams eddy coefficient is equal to the Redi isopycnal diffusivity to within ± 6%, even as these coefficients vary with depth. The scaling for the magnitude of simulation parameters is determined empirically to within ± 28%. To achieve this accuracy, the eddy velocities are diagnosed directly and used in the tensor scalings, rather than assuming a correlation between eddy velocity and the mean flow velocity where ± 97% is the best accuracy achievable. Plans for the next set of models in the challenge suite are described.
Eddy Correlation Flux Measurement System (ECOR) Handbook
Cook, DR
2011-01-31
The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration.
About Eddy Currents in Induction Melting Processes
Gafiţa Nicolae-Bogdan
2008-05-01
Full Text Available In this paper we present a method forcomputing the eddy currents in induction meltingprocesses for non-ferrous alloys. We take intoconsideration the situation when only the crucible ismoving, inside the coils. This fact makes differentialcomputation methods to be hard to apply, because isnecessary to generate a new mesh and a new systemmatrix for every for every new position of the cruciblerelated to the coils. Integral methods cancel thisdrawback because the mesh is generated only for thedomains with eddy currents. For integral methods, themesh and the inductance matrix remain unchangedduring the movement of the crucible; only the free termsof the equation system will change.
Visualization and analysis of eddies in a global ocean simulation
Williams, Sean J [Los Alamos National Laboratory; Hecht, Matthew W [Los Alamos National Laboratory; Petersen, Mark [Los Alamos National Laboratory; Strelitz, Richard [Los Alamos National Laboratory; Maltrud, Mathew E [Los Alamos National Laboratory; Ahrens, James P [Los Alamos National Laboratory; Hlawitschka, Mario [UC DAVIS; Hamann, Bernd [UC DAVIS
2010-10-15
Eddies at a scale of approximately one hundred kilometers have been shown to be surprisingly important to understanding large-scale transport of heat and nutrients in the ocean. Due to difficulties in observing the ocean directly, the behavior of eddies below the surface is not very well understood. To fill this gap, we employ a high-resolution simulation of the ocean developed at Los Alamos National Laboratory. Using large-scale parallel visualization and analysis tools, we produce three-dimensional images of ocean eddies, and also generate a census of eddy distribution and shape averaged over multiple simulation time steps, resulting in a world map of eddy characteristics. As expected from observational studies, our census reveals a higher concentration of eddies at the mid-latitudes than the equator. Our analysis further shows that mid-latitude eddies are thicker, within a range of 1000-2000m, while equatorial eddies are less than 100m thick.
Evolution of oceanic circulation theory：From gyres to eddies*
HUANG Rui-xin
2013-01-01
Physical oceanography is now entering the eddy-resolving era. Eddies are commonly referred to the so-called mesoscale or submesoscale eddies;by definition, they have horizontal scales from 1 to 500 km and vertical scales from meters to hundreds of meters. In one word, the ocean is a turbulent environment; thus, eddy motions are one of the fundamental aspects of oceanic circulation. Studies of these eddies, including observations, theory, laboratory experiments, and parameterization in numerical models, will be the most productive research frontiers for the next 10 to 20 years. Although we have made great efforts to collect data about eddies in the ocean; thus far, we know very little about the three-dimensional structure of these eddies and their contributions to the oceanic general circulation and climate. Therefore, the most important breakthrough may come from observations and physical reasoning about the fundament aspects of eddy structure and their contributions to ocean circulation and climate.
2013-09-30
layer the eddy flux is significantly diabatic with a shallow eddy-induced (Lagrangian) circulation cell and down-gradient lateral diapycnal flux. These...3D Schematic representation of the eddy effects on the mean buoyancy field decomposed between adiabatic eddy-induced advection and diabatic ...plane). The diabatic component acts to smooth out surface buoyancy extrema and is shown as sinuous arrows in the top plane. Interior diabatic fluxes
Cycloidal meandering of a mesoscale anticyclonic eddy
Kizner, Ziv; Shteinbuch-Fridman, Biana; Makarov, Viacheslav; Rabinovich, Michael
2017-08-01
By applying a theoretical approach, we propose a hypothetical scenario that might explain some features of the movement of a long-lived mesoscale anticyclone observed during 1990 in the Bay of Biscay [R. D. Pingree and B. Le Cann, "Three anticyclonic slope water oceanic eddies (SWODDIES) in the southern Bay of Biscay in 1990," Deep-Sea Res., Part A 39, 1147 (1992)]. In the remote-sensing infrared images, at the initial stage of observations, the anticyclone was accompanied by two cyclonic eddies, so the entire structure appeared as a tripole. However, at later stages, only the anticyclone was seen in the images, traveling generally west. Unusual for an individual eddy were the high speed of its motion (relative to the expected planetary beta-drift) and the presence of almost cycloidal meanders in its trajectory. Although surface satellites seem to have quickly disappeared, we hypothesize that subsurface satellites continued to exist, and the coherence of the three vortices persisted for a long time. A significant perturbation of the central symmetry in the mutual arrangement of three eddies constituting a tripole can make reasonably fast cycloidal drift possible. This hypothesis is tested with two-layer contour-dynamics f-plane simulations and with finite-difference beta-plane simulations. In the latter case, the interplay of the planetary beta-effect and that due to the sloping bottom is considered.
Intrathermocline eddies in the Southern Indian Ocean
Nauw, J.J.; van Aken, H.M.; Lutjeharms, J.R.E.; de Ruijter, W.P.M.
2006-01-01
In 2001, two relatively saline intrathermocline eddies (ITEs) were observed southeast of Madagascar at 200 m depth. They are characterized by a subsurface salinity maximum of over 35.8 at potential temperatures between 18 and 22 C. The oxygen concentrations within the high salinity cores are slightl
Inverse modeling for Large-Eddy simulation
Geurts, Bernardus J.
1998-01-01
Approximate higher order polynomial inversion of the top-hat filter is developed with which the turbulent stress tensor in Large-Eddy Simulation can be consistently represented using the filtered field. Generalized (mixed) similarity models are proposed which improved the agreement with the kinetic
Wind changes above warm Agulhas Current eddies
Roualt, M
2016-10-01
Full Text Available )C to the surrounding ocean. The analysis of 960 twice daily instantaneous charts of equivalent stability neutral wind speed estimates from the SeaWinds scatterometer onboard the QuikScat satellite collocated with SST during the lifespan of six warm eddies show stronger...
Methane fluxes above the Hainich forest by True Eddy Accumulation and Eddy Covariance
Siebicke, Lukas; Gentsch, Lydia; Knohl, Alexander
2016-04-01
Understanding the role of forests for the global methane cycle requires quantifying vegetation-atmosphere exchange of methane, however observations of turbulent methane fluxes remain scarce. Here we measured turbulent fluxes of methane (CH4) above a beech-dominated old-growth forest in the Hainich National Park, Germany, and validated three different measurement approaches: True Eddy Accumulation (TEA, closed-path laser spectroscopy), and eddy covariance (EC, open-path and closed-path laser spectroscopy, respectively). The Hainich flux tower is a long-term Fluxnet and ICOS site with turbulent fluxes and ecosystem observations spanning more than 15 years. The current study is likely the first application of True Eddy Accumulation (TEA) for the measurement of turbulent exchange of methane and one of the very few studies comparing open-path and closed-path eddy covariance (EC) setups side-by-side. We observed uptake of methane by the forest during the day (a methane sink with a maximum rate of 0.03 μmol m-2 s-1 at noon) and no or small fluxes of methane from the forest to the atmosphere at night (a methane source of typically less than 0.01 μmol m-2 s-1) based on continuous True Eddy Accumulation measurements in September 2015. First results comparing TEA to EC CO2 fluxes suggest that True Eddy Accumulation is a valid option for turbulent flux quantifications using slow response gas analysers (here CRDS laser spectroscopy, other potential techniques include mass spectroscopy). The TEA system was one order of magnitude more energy efficient compared to closed-path eddy covariance. The open-path eddy covariance setup required the least amount of user interaction but is often constrained by low signal-to-noise ratios obtained when measuring methane fluxes over forests. Closed-path eddy covariance showed good signal-to-noise ratios in the lab, however in the field it required significant amounts of user intervention in addition to a high power consumption. We conclude
A modified method to estimate eddy diffusivity in the North Pacific using altimeter eddy statistics
ZHANG Zhiwei; LI Yaru; TIAN Jiwei
2013-01-01
The method proposed by Stammer (1998) is modified using eddy statistics from altimeter observation to obtain more realistic eddy diffusivity (K) for the North Pacific.Compared with original estimates,the modified K has remarkably reduced values in the Kuroshio Extension (KE) and North Equatorial Counter Current (NECC) regions,but slightly enhanced values in the Subtropical Counter Current (STCC) region.In strong eastward flow areas like the KE and NECC,owing to a large difference between mean flow velocity and propagation velocity of mesoscale eddies,tracers inside the mesoscale eddies are transported outside rapidly by advection,and mixing length L is hence strongly suppressed.The low eddy probability (P) is also responsible for the reduced K in the NECC area.In the STCC region,however,L is mildly suppressed and P is very high,so K there is enhanced.The zonally-averaged K has two peaks with comparable magnitudes,in the latitude bands of the STCC and KE.In the core of KE,because of the reduced values of P and L,the zonally-averaged K is a minimum.Zonally-integrated eddy heat transport in the KE band,calculated based on the modified K,is much closer to the results of previous independent research,indicating the robustness of our modified K.The map of modified K provides useful information for modeling studies in the North Pacific.
Obituary: John Allen Eddy (1931-2009)
Gingerich, Owen
2011-12-01
Jack Eddy, who was born 25 March 1931 in Pawnee City in southeastern Nebraska, died after a long battle with cancer in Tucson, Arizona, on 10 June 2009. Best known for his work on the long-term instability of the sun, described in a landmark paper in Science titled "The Maunder Minimum," he also deserves recognition as one of the triumvirate who founded the Historical Astronomy Division of the AAS. His father ran a cooperative farm store where Jack worked as a teenager; his parents were of modest means and there were concerns whether he could afford college, but one of the state senators, also from Pawnee City, nominated him for the U.S. Naval Academy. A course in celestial navigation gave him a love of the sky. After graduation in 1953, he served four years on aircraft carriers in the Pacific during the Korean War and then as a navigator and operations officer on a destroyer in the Persian Gulf. In 1957, he left the Navy and entered graduate school at the University of Colorado in Boulder, where in 1962 he received a Ph.D. in astro-geophysics. His thesis, supervised by Gordon Newkirk, dealt with light scattering in the upper atmosphere, based on data from stratospheric balloon flights. He then worked as teacher and researcher at the High Altitude Observatory in Boulder. Always adventuresome and willing to explore new frontiers, on his own time Eddy examined an Amerindian stone circle in the Big Horn mountains of Wyoming, a so-called medicine wheel, concluding that there were alignments with both the solstitial sun and Aldebaran. His conjectures became a cover story on Science magazine in June of 1974. In 1971 Jack privately reproduced for his friends a small collection of his own hilarious cartoons titled "Job Opportunities for Out-of-work Astronomers," with an abstract beginning, "Contrary to popular belief, a PhD in Astronomy/Astrophysics need not be a drawback in locating work in this decade." For example, under merchandising, a used car salesman advertises
A new gauge-invariant method for diagnosing eddy diffusivities
Mak, Julian; Marshall, David P
2015-01-01
Coarse resolution numerical ocean models must typically include a parameterisation for mesoscale turbulence. A common recipe for such parameterisations is to invoke down-gradient mixing, or diffusion, of some tracer quantity, such as potential vorticity or buoyancy. However, it is well known that eddy fluxes include large rotational components which necessarily do not lead to any mixing; eddy diffusivities diagnosed from unfiltered fluxes are thus contaminated by the presence of these rotational components. Here a new methodology is applied whereby eddy diffusivities are diagnosed directly from the eddy force function. The eddy force function depends only upon flux divergences, is independent of any rotational flux components, and is inherently non-local and smooth. A one-shot inversion procedure is applied, minimising the mis-match between parameterised force functions and force functions derived from eddy resolving calculations. This enables diffusivities associated with the eddy potential vorticity and buo...
Biogeochemical properties of eddies in the California Current System
Chenillat, Fanny; Franks, Peter J. S.; Combes, Vincent
2016-06-01
The California Current System (CCS) has intense mesoscale activity that modulates and exports biological production from the coastal upwelling system. To characterize and quantify the ability of mesoscale eddies to affect the local and regional planktonic ecosystem of the CCS, we analyzed a 10 year-long physical-biological model simulation, using eddy detection and tracking to isolate the dynamics of cyclonic and anticyclonic eddies. As they propagate westward across the shelf, cyclonic eddies efficiently transport coastal planktonic organisms and maintain locally elevated production for up to 1 year (800 km offshore). Anticyclonic eddies, on the other hand, have a limited impact on local production over their ~6 month lifetime as they propagate 400 km offshore. At any given time ~8% of the model domain was covered by eddy cores. Though the eddies cover a small area, they explain ~50 and 20% of the transport of nitrate and plankton, respectively.
Oceanic mass transport by mesoscale eddies.
Zhang, Zhengguang; Wang, Wei; Qiu, Bo
2014-07-18
Oceanic transports of heat, salt, fresh water, dissolved CO2, and other tracers regulate global climate change and the distribution of natural marine resources. The time-mean ocean circulation transports fluid as a conveyor belt, but fluid parcels can also be trapped and transported discretely by migrating mesoscale eddies. By combining available satellite altimetry and Argo profiling float data, we showed that the eddy-induced zonal mass transport can reach a total meridionally integrated value of up to 30 to 40 sverdrups (Sv) (1 Sv = 10(6) cubic meters per second), and it occurs mainly in subtropical regions, where the background flows are weak. This transport is comparable in magnitude to that of the large-scale wind- and thermohaline-driven circulation.
Eddy diffusivities of inertial particles under gravity
Afonso, Marco Martins; Muratore-Ginanneschi, Paolo
2011-01-01
The large-scale/long-time transport of inertial particles of arbitrary mass density under gravity is investigated by means of a formal multiple-scale perturbative expansion in the scale-separation parametre between the carrier flow and the particle concentration field. The resulting large-scale equation for the particle concentration is determined, and is found to be diffusive with a positive-definite eddy diffusivity. The calculation of the latter tensor is reduced to the resolution of an auxiliary differential problem, consisting of a coupled set of two differential equations in a (6+1)-dimensional coordinate system (3 space coordinates plus 3 velocity coordinates plus time). Although expensive, numerical methods can be exploited to obtain the eddy diffusivity, for any desirable non-perturbative limit (e.g. arbitrary Stokes and Froude numbers). The aforementioned large-scale equation is then specialized to deal with two different relevant perturbative limits: i) vanishing of both Stokes time and sedimenting...
Large Eddy Simulation of Turbulent Combustion
2006-03-15
Application to an HCCI Engine . Proceedings of the 4th Joint Meeting of the U.S. Sections of the Combustion Institute, 2005. [34] K. Fieweger...LARGE EDDY SIMULATION OF TURBULENT COMBUSTION Principle Investigator: Heinz Pitsch Flow Physics and Computation Department of Mechanical Engineering ...burners and engines found in modern, industrially relevant equipment. In the course of this transition of LES from a scientifically interesting method
HYCOM High-resolution Eddying Simulations
2014-07-01
number of vertical profiles of temperature and salinity in place of XBT temperature profiles. The reanalysis was completed in February 2014. As noted...10.1016/j.ocemod.2011.02.011. Metzger, E. J., and Coauthors, 2014a: US Navy operational global ocean and Arctic ice prediction systems. Oceanography...has collaborated on developing and demonstrating the performance and application of eddy-resolving, real-time global and basin-scale ocean prediction
Anisotropic Mesoscale Eddy Transport in Ocean General Circulation Models
Reckinger, S. J.; Fox-Kemper, B.; Bachman, S.; Bryan, F.; Dennis, J.; Danabasoglu, G.
2014-12-01
Modern climate models are limited to coarse-resolution representations of large-scale ocean circulation that rely on parameterizations for mesoscale eddies. The effects of eddies are typically introduced by relating subgrid eddy fluxes to the resolved gradients of buoyancy or other tracers, where the proportionality is, in general, governed by an eddy transport tensor. The symmetric part of the tensor, which represents the diffusive effects of mesoscale eddies, is universally treated isotropically in general circulation models. Thus, only a single parameter, namely the eddy diffusivity, is used at each spatial and temporal location to impart the influence of mesoscale eddies on the resolved flow. However, the diffusive processes that the parameterization approximates, such as shear dispersion, potential vorticity barriers, oceanic turbulence, and instabilities, typically have strongly anisotropic characteristics. Generalizing the eddy diffusivity tensor for anisotropy extends the number of parameters to three: a major diffusivity, a minor diffusivity, and the principal axis of alignment. The Community Earth System Model (CESM) with the anisotropic eddy parameterization is used to test various choices for the newly introduced parameters, which are motivated by observations and the eddy transport tensor diagnosed from high resolution simulations. Simply setting the ratio of major to minor diffusivities to a value of five globally, while aligning the major axis along the flow direction, improves biogeochemical tracer ventilation and reduces global temperature and salinity biases. These effects can be improved even further by parameterizing the anisotropic transport mechanisms in the ocean.
Large Eddy Simulation of Transitional Boundary Layer
Sayadi, Taraneh; Moin, Parviz
2009-11-01
A sixth order compact finite difference code is employed to investigate compressible Large Eddy Simulation (LES) of subharmonic transition of a spatially developing zero pressure gradient boundary layer, at Ma = 0.2. The computational domain extends from Rex= 10^5, where laminar blowing and suction excites the most unstable fundamental and sub-harmonic modes, to fully turbulent stage at Rex= 10.1x10^5. Numerical sponges are used in the neighborhood of external boundaries to provide non-reflective conditions. Our interest lies in the performance of the dynamic subgrid scale (SGS) model [1] in the transition process. It is observed that in early stages of transition the eddy viscosity is much smaller than the physical viscosity. As a result the amplitudes of selected harmonics are in very good agreement with the experimental data [2]. The model's contribution gradually increases during the last stages of transition process and the dynamic eddy viscosity becomes fully active and dominant in the turbulent region. Consistent with this trend the skin friction coefficient versus Rex diverges from its laminar profile and converges to the turbulent profile after an overshoot. 1. Moin P. et. al. Phys Fluids A, 3(11), 2746-2757, 1991. 2. Kachanov Yu. S. et. al. JFM, 138, 209-247, 1983.
LARGE EDDY SIMULATION FOR PLUNGING BREAKER WAVE
Bai Yu-chuan; Wang Zhao-yin
2003-01-01
As wave propagates into shallow water, the shoaling effect leads to increase of wave height, and at a certain position, the wave will be breaking. The breaking wave is powerful agents for generating turbulence, which plays an important role in most of the fluid dynamical processes in the surf zone, so a proper numerical model for describing the turbulent effect is needed urgently. A numerical model is set up to simulate the wave breaking process, which consists of a free surface model using the surface marker method and the vertical two-dimensional model that solves the flow equations. The turbulence is described by Large Eddy Simulation (LES) method where the larger turbulent features are simulated by solving the flow equations, and the small-scale turbulence that is represented by a sub-grid model. A dynamic eddy viscosity sub-grid scale stress model has been used for the present simulation. The large eddy simulation model, which we presented in this paper, can be used to study the propagation of a solitary wave in constant water depth and the shoaling of a non-breaking solitary wave on a beach. To track free-surface movements, The TUMMAC method is employed. By applying the model to wave breaking problem in the surf zone, we found that these model results compared very well with experimental data. In addition, this model is able to reproduce the complicated flow phenomena, especially the plunging breaker.
Why Eddy Momentum Fluxes are Concentrated in the Upper Troposphere
Ait-Chaalal, Farid
2015-01-01
The extratropical eddy momentum flux (EMF) is controlled by generation, propagation, and dissipation of large-scale eddies and is concentrated in Earth's upper troposphere. An idealized GCM is used to investigate how this EMF structure arises. In simulations in which the poles are heated more strongly than the equator, EMF is concentrated near the surface, demonstrating that surface drag generally is not responsible for the upper-tropospheric EMF concentration. Although Earth's upper troposphere favors linear wave propagation, quasi-linear simulations in which nonlinear eddy-eddy interactions are suppressed demonstrate that this is likewise not primarily responsible for the upper-tropospheric EMF concentration. The quasi-linear simulations reveal the essential role of nonlinear eddy-eddy interactions in the surf zone in the upper troposphere, where wave activity absorption away from the baroclinic generation regions occurs through the nonlinear generation of small scales. In Earth-like atmospheres, wave activ...
On the relationship between Southern Ocean eddies and phytoplankton
Frenger, Ivy; Münnich, Matthias; Gruber, Nicolas
2017-04-01
Effects on phytoplankton in the Southern Ocean are crucial for the global ocean nutrient and carbon cycles. Such effects potentially arise from mesoscale eddies which are omnipresent in the region. Eddies are known to affect phytoplankton through either advection and mixing, or the stimulation/suppression of growth. Yet, the climatological relationship between Southern Ocean eddies and phytoplankton has not been quantified in detail. To provide an estimate of this relationship, we identified more than100,000 eddies in the Southern Ocean and determined associated phytoplankton anomalies using satellite-based chlorophyll-a (chl) measurements. The eddies have a very substantial impact on the chl levels, with eddy associated chl differing by more than 10% from the background over wide areas. The structure of these anomalies is largely zonal, with positive anomalies north of the Antarctic Circumpolar Current (ACC) and negative anomalies within the circumpolar belt of the ACC for cyclonic eddies. The pattern is similar but of opposite sign for anticyclonic eddies. The seasonality of this signal is weak north to the ACC, but pronounced in the vicinity of the ACC. The spatial structure and seasonality of the signal can be explained largely by advection, i.e., the eddy-circulation driven lateral transport of anomalies across large-scale gradients. We conclude this based on the shape of local chl anomalies of eddies and ambient chl gradients. In contrast, ACC winter anomalies are consistent with an effect of eddies on the light exposure of phytoplankton. The clear impact of eddies on chl implies a downstream effect on Southern Ocean biogeochemical properties.
Tidal generation of large sub-mesoscale eddy dipoles
W. Callendar
2011-08-01
Full Text Available Numerical simulations of tidal flow past Cape St. James on the south tip of Haida Gwaii (Queen Charlotte Islands are presented that indicate mesoscale dipoles are formed from coalescing tidal eddies. Observations in this region demonstrate robust eddy generation at the Cape, with the primary process being flow separation of buoyant or wind driven outflows forming large anti-cyclonic, negative potential vorticity, Haida Eddies. However, there are other times where dipoles are observed in satellites, indicating a source of positive potential vorticity must also be present. The simulations here build on previous work that implicates oscillating tidal flow past the cape in creating the positive vorticity. Small headland eddies of alternating vorticity are created each tide. During certain tidal cycles, the headland eddies coalesce and self organize in such a way as to create large >20-km diameter eddies that then self-advect into deep water. The self advection speed is faster than the beta drift of anti-cyclones, and the propagation direction appears to be more southerly than typical Haida Eddies, though the model contains no mean wind-driven flows. These eddies are smaller than Haida Eddies, but given their tidal origin, may represent a more consistent source of coastal water that is injected into the interior of the subpolar gyre.
Tidal generation of large sub-mesoscale eddy dipoles
Callendar, W.; Klymak, J. M.; Foreman, M. G. G.
2011-08-01
Numerical simulations of tidal flow past Cape St. James on the south tip of Haida Gwaii (Queen Charlotte Islands) are presented that indicate mesoscale dipoles are formed from coalescing tidal eddies. Observations in this region demonstrate robust eddy generation at the Cape, with the primary process being flow separation of buoyant or wind driven outflows forming large anti-cyclonic, negative potential vorticity, Haida Eddies. However, there are other times where dipoles are observed in satellites, indicating a source of positive potential vorticity must also be present. The simulations here build on previous work that implicates oscillating tidal flow past the cape in creating the positive vorticity. Small headland eddies of alternating vorticity are created each tide. During certain tidal cycles, the headland eddies coalesce and self organize in such a way as to create large >20-km diameter eddies that then self-advect into deep water. The self advection speed is faster than the beta drift of anti-cyclones, and the propagation direction appears to be more southerly than typical Haida Eddies, though the model contains no mean wind-driven flows. These eddies are smaller than Haida Eddies, but given their tidal origin, may represent a more consistent source of coastal water that is injected into the interior of the subpolar gyre.
Tidal generation of large sub-mesoscale eddy dipoles
W. Callendar
2011-04-01
Full Text Available Numerical simulations of tidal flow past Cape St. James on the south tip of Haida Gwai (Queen Charlotte Islands are presented that indicate mesoscale dipoles are formed from coalescing tidal eddies. Observations in this region demonstrate robust eddy generation at the Cape, with the primary process being flow separation of buoyant or wind driven outflows forming large anti-cyclonic, negative potential vorticity, Haida Eddies. However, there are other times where dipoles are observed in satellites, indicating a source of positive potential vorticity must also be present. The simulations here build on previous work that implicates oscillating tidal flow past the cape in creating the positive vorticity. Small headland eddies of alternating vorticity are created each tide. During certain tidal cycles, the headland eddies coalesce and self organize in such a way as to create large >20-km diameter eddies that then self-advect into deep water. The self advection speed is faster than the beta drift of anti-cyclones, and the propagation direction appears to be more southerly than typical Haida Eddies, though the model contains no mean wind-driven flows. These eddies are smaller than Haida Eddies, but given their tidal origin, may represent a more consistent source of coastal water that is injected into to the interior of the subpolar gyre.
IVA Ultrasonic and Eddy Current NDE for ISS Project
National Aeronautics and Space Administration — Phased array ultrasonic testing (PAUT) instruments and array eddy current testing instruments were tested on hypervelocity impact damaged aluminum plates simulating...
Large eddy simulation of stably stratified turbulence
无
2010-01-01
Stable stratification turbulence, as a common phenomenon in atmospheric and oceanic flows, is an important mechanism for numerical prediction of such flows. In this paper the large eddy simulation is utilized for investigating stable stratification turbulence numerically. The paper is expected to provide correct statistical results in agreement with those measured in the atmosphere or ocean. The fully developed turbulence is obtained in the stable stratification fluid by large eddy simulation with different initial velocity field and characteristic parameters, i.e. Reynolds number Re and Froude number Fr. The evolution of turbulent kinetic energy, characteristic length scales and parameters is analyzed for investigating the development of turbulence in stable stratification fluid. The three-dimensional energy spectra, horizontal and vertical energy spectrum, are compared between numerical simulation and real observation in the atmosphere and ocean in order to test the reliability of the numerical simulation. The results of numerical cases show that the large eddy simulation is capable of predicting the properties of stable stratification turbulence in consistence with real measurements at less computational cost. It has been found in this paper that the turbulence can be developed under different initial velocity conditions and the internal wave energy is dominant in the developed stable stratification turbulence. It is also found that the characteristic parameters must satisfy certain conditions in order to have correct statistical property of stable stratification turbulence in the atmosphere and ocean. The Reynolds number and Froude number are unnecessarily equal to those in atmosphere or ocean, but the Reynolds number must be large enough, say, greater than 10 2 , and Froude number must be less than 0.1. The most important parameter is ReFr 2 which must be greater than 10.
Essential parameters in eddy current inspection
Stepinski, T. [Uppsala Univ. (Sweden). Signals and Systems
2000-05-01
Our aim was to qualitatively analyze a number of variables that may affect the result of eddy current (EC) inspection but because of various reasons are not considered as essential in common practice. In the report we concentrate on such variables that can vary during or between inspections but their influence is not determined during routine calibrations. We present a qualitative analysis of the influence of the above-mentioned variables on the ability to detect and size flaws using mechanized eddy current testing (ET). ET employs some type of coil or probe, sensing magnetic flux generated by eddy currents induced in the tested specimen. An amplitude-phase modulated signal (with test frequency f0 ) from the probe is sensed by the EC instrument. The amplitude-phase modulated signal is amplified and demodulated in phase-sensitive detectors removing carrier frequency f0 from the signal. The detectors produce an in-phase and a quadrature component of the signal defining it as a point in the impedance plane. Modern instruments are provided with a screen presenting the demodulated and filtered signal in complex plane. We focus on such issues, related to the EC equipment as, probe matching, distortion introduced by phase discriminators and signal filters, and the influence of probe resolution and lift-off on sizing. The influence of different variables is investigated by means of physical reasoning employing theoretical models and demonstrated using simulated and real EC signals. In conclusion, we discuss the way in which the investigated variables may affect the result of ET. We also present a number of practical recommendations for the users of ET and indicate the areas that are to be further analyzed.
An Angular Momentum Eddy Detection Algorithm (AMEDA) applied to coastal eddies
Le Vu, Briac; Stegner, Alexandre; Arsouze, Thomas
2016-04-01
We present a new automated eddy detection and tracking algorithm based on the computation of the LNAM (Local and Normalized Angular Momentum). This method is an improvement of the previous method by Mkhinini et al. (2014) with the aim to be applied to multiple datasets (satellite data, numerical models, laboratory experiments) using as few objective criteria as possible. First, we show the performance of the algorithm for three different source of data: a Mediterranean 1/8° AVISO geostrophic velocities fields based on the Absolute Dynamical Topography (ADT), a ROMS idealized simulation and a high resolution velocity field derived from PIV measurements in a rotating tank experiment. All the velocity fields describe the dynamical evolution of mesoscale eddies generated by the instability of coastal currents. Then, we compare the results of the AMEDA algorithm applied to regional 1/8° AVISO Mediterranean data set with in situ measurements (drifter, ARGO, ADCP…). This quantitative comparisons with few specific test cases enables us to estimate the accuracy of the method to quantify the eddies features: trajectory, size and intensity. We also use the AMEDA algorithm to identify the main formation areas of long-lived eddies in the Mediterranean Sea during the last 15 years.
Large-eddy simulation in hydraulics
Rodi, Wolfgang
2013-01-01
Complex turbulence phenomena are of great practical importance in hydraulics, including environmental flows, and require advanced methods for their successful computation. The Large Eddy Simulation (LES), in which the larger-scale turbulent motion is directly resolved and only the small-scale motion is modelled, is particularly suited for complex situations with dominant large-scale structures and unsteadiness. Due to the increasing computer power, LES is generally used more and more in Computational Fluid Dynamics. Also in hydraulics, it offers great potential, especially for near-field probl
Large eddy simulation in the ocean
Scotti, Alberto
2010-12-01
Large eddy simulation (LES) is a relative newcomer to oceanography. In this review, both applications of traditional LES to oceanic flows and new oceanic LES still in an early stage of development are discussed. The survey covers LES applied to boundary layer flows, traditionally an area where LES has provided considerable insight into the physics of the flow, as well as more innovative applications, where new SGS closure schemes need to be developed. The merging of LES with large-scale models is also briefly reviewed.
Towards technical application of large eddy simulation
Breuer, M. [Erlangen-Nuernberg Univ., Erlangen (DE). Inst. of Fluid Mechanics (LSTM)
2001-07-01
The paper is concerned with the computation of high Reynolds number circular cylinder flow (Re = 3900/140,000) based on the large eddy simulation (LES) technique. Because this flow involves a variety of complex flow features encountered in technical applications, successful simulations for this test case, especially at high Reynolds numbers, can be considered as the first step to real world applications of LES. Based on an efficient finite-volume LES code, a detailed study on different aspects influencing the quality of LES results was carried out. In the present paper, some of the results are presented and compared with experimental measurements available. (orig.)
Decay of eddies at the South-West Indian Ridge
Andrew C. Coward
2011-11-01
Full Text Available The South-West Indian Ridge in the Indian sector of the Southern Ocean is a region recognised for the creation of particularly intense eddy disturbances in the mean flow of the Antarctic Circumpolar Current. Eddies formed at this ridge have been extensively studied over the past decade using hydrographic, satellite, drifter and float data and it is hypothesised that they could provide a vehicle for localised meridional heat and salt exchange. The effectiveness of this process is dependent on the rate of decay of the eddies. However, in order to investigate eddy decay, logistically difficult hydrographic monitoring is required. This study presents the decay of cold eddies at the South-West Indian Ridge, using outputs from a high-resolution ocean model. The model’s representation of the dynamic nature of this region is fully characteristic of observations. On average, 3–4 intense and well-defined cold eddies are generated per year; these eddies have mean longevities of 5.0±2.2 months with average advection speeds of 5±2 km/day. Most simulated eddies reach their peak intensity within 1.5–2.5 months after genesis and have depths of 2000 m – 3000 m. Thereafter they dissipate within approximately 3 months. The decay of eddies is generally characterised by a decrease in their sea surface height signature, a weakening in their rotation rates and a modification in their temperature–salinity characteristics. Subantarctic top predators are suspected to forage preferentially along the edges of eddies. The process of eddy dissipation may thus influence their feeding behaviour.
Developing large eddy simulation for turbomachinery applications.
Eastwood, Simon J; Tucker, Paul G; Xia, Hao; Klostermeier, Christian
2009-07-28
For jets, large eddy resolving simulations are compared for a range of numerical schemes with no subgrid scale (SGS) model and for a range of SGS models with the same scheme. There is little variation in results for the different SGS models, and it is shown that, for schemes which tend towards having dissipative elements, the SGS model can be abandoned, giving what can be termed numerical large eddy simulation (NLES). More complex geometries are investigated, including coaxial and chevron nozzle jets. A near-wall Reynolds-averaged Navier-Stokes (RANS) model is used to cover over streak-like structures that cannot be resolved. Compressor and turbine flows are also successfully computed using a similar NLES-RANS strategy. Upstream of the compressor leading edge, the RANS layer is helpful in preventing premature separation. Capturing the correct flow over the turbine is particularly challenging, but nonetheless the RANS layer is helpful. In relation to the SGS model, for the flows considered, evidence suggests issues such as inflow conditions, problem definition and transition are more influential.
Magnetoresistive flux focusing eddy current flaw detection
Wincheski, Russell A. (Inventor); Namkung, Min (Inventor); Simpson, John W. (Inventor)
2005-01-01
A giant magnetoresistive flux focusing eddy current device effectively detects deep flaws in thick multilayer conductive materials. The probe uses an excitation coil to induce eddy currents in conducting material perpendicularly oriented to the coil's longitudinal axis. A giant magnetoresistive (GMR) sensor, surrounded by the excitation coil, is used to detect generated fields. Between the excitation coil and GMR sensor is a highly permeable flux focusing lens which magnetically separates the GMR sensor and excitation coil and produces high flux density at the outer edge of the GMR sensor. The use of feedback inside the flux focusing lens enables complete cancellation of the leakage fields at the GMR sensor location and biasing of the GMR sensor to a location of high magnetic field sensitivity. In an alternate embodiment, a permanent magnet is positioned adjacent to the GMR sensor to accomplish the biasing. Experimental results have demonstrated identification of flaws up to 1 cm deep in aluminum alloy structures. To detect deep flaws about circular fasteners or inhomogeneities in thick multilayer conductive materials, the device is mounted in a hand-held rotating probe assembly that is connected to a computer for system control, data acquisition, processing and storage.
Eddy generation in the Mediterranean undercurrent
Serra, Nuno; Ambar, Isabel
In the framework of the European Union MAST III project Canary Islands Gibraltar Azores Observations, 24 RAFOS floats were deployed in the Mediterranean Water (MW) undercurrent off south Portugal between September 1997 and September 1998. A preliminary analysis of this Lagrangian approach, complemented with XBT and current-meter data, show some of the major aspects of the flow associated with the undercurrent as well as associated eddy activity. Floats that stayed in the undercurrent featured a downstream deceleration and a steering by bottom topography. Three meddy formations at Cape St. Vincent could be isolated from the float data. The dynamical coupling of meddies and cyclones was observed for a considerable period of time. The generation of two dipolar structures in the Portimão Canyon region also was observed with the float data. A major bathymetric relief—Gorringe Bank—was not only an important constraint to the eddy trajectories and of the flow at the MW levels but also a site for meddy formation.
Eddy correlation measurements of submarine groundwater discharge
Crusius, J.; Berg, P.; Koopmans, D.J.; Erban, L.
2008-01-01
This paper presents a new, non-invasive means of quantifying groundwater discharge into marine waters using an eddy correlation approach. The method takes advantage of the fact that, in virtually all aquatic environments, the dominant mode of vertical transport near the sediment-water interface is turbulent mixing. The technique thus relies on measuring simultaneously the fluctuating vertical velocity using an acoustic Doppler velocimeter and the fluctuating salinity and/or temperature using rapid-response conductivity and/or temperature sensors. The measurements are typically done at a height of 5-15??cm above the sediment surface, at a frequency of 16 to 64??Hz, and for a period of 15 to 60??min. If the groundwater salinity and/or temperature differ from that of the water column, the groundwater specific discharge (cm d- 1) can be quantified from either a heat or salt balance. Groundwater discharge was estimated with this new approach in Salt Pond, a small estuary on Cape Cod (MA, USA). Estimates agreed well with previous estimates of discharge measured using seepage meters and 222Rn as a tracer. The eddy correlation technique has several desirable characteristics: 1) discharge is quantified under in-situ hydrodynamic conditions; 2) salinity and temperature can serve as two semi-independent tracers of discharge; 3) discharge can be quantified at high temporal resolution, and 4) long-term records of discharge may be possible, due to the low power requirements of the instrumentation. ?? 2007 Elsevier B.V. All rights reserved.
Mesoscale eddies are oases for higher trophic marine life
Godø, Olav R.
2012-01-17
Mesoscale eddies stimulate biological production in the ocean, but knowledge of energy transfers to higher trophic levels within eddies remains fragmented and not quantified. Increasing the knowledge base is constrained by the inability of traditional sampling methods to adequately sample biological processes at the spatio-temporal scales at which they occur. By combining satellite and acoustic observations over spatial scales of 10 s of km horizontally and 100 s of m vertically, supported by hydrographical and biological sampling we show that anticyclonic eddies shape distribution and density of marine life from the surface to bathyal depths. Fish feed along density structures of eddies, demonstrating that eddies catalyze energy transfer across trophic levels. Eddies create attractive pelagic habitats, analogous to oases in the desert, for higher trophic level aquatic organisms through enhanced 3-D motion that accumulates and redistributes biomass, contributing to overall bioproduction in the ocean. Integrating multidisciplinary observation methodologies promoted a new understanding of biophysical interaction in mesoscale eddies. Our findings emphasize the impact of eddies on the patchiness of biomass in the sea and demonstrate that they provide rich feeding habitat for higher trophic marine life. 2012 God et al.
A subsurface cyclonic eddy in the Bay of Bengal
Babu, M.T.; PrasannaKumar, S.; Rao, D.P.
CTD data collected from the Northwestern Bay of Bengal during late July 1984 reveal the existence of a cold core subsurface eddy centred at 17 degrees 40'N and 85 degrees 19'E. The thermal structure observed across the eddy indicate...
Anisotropy of eddy variability in the global ocean
Stewart, K. D.; Spence, P.; Waterman, S.; Sommer, J. Le; Molines, J.-M.; Lilly, J. M.; England, M. H.
2015-11-01
The anisotropy of eddy variability in the global ocean is examined in geostrophic surface velocities derived from satellite observations and in the horizontal velocities of a 1/12° global ocean model. Eddy anisotropy is of oceanographic interest as it is through anisotropic velocity fluctuations that the eddy and mean-flow fields interact dynamically. This study is timely because improved observational estimates of eddy anisotropy will soon be available with Surface Water and Ocean Topography (SWOT) altimetry data. We find there to be good agreement between the characteristics and distributions of eddy anisotropy from the present satellite observations and model ocean surface. In the model, eddy anisotropy is found to have significant vertical structure and is largest close to the ocean bottom, where the anisotropy aligns with the underlying isobaths. The highly anisotropic bottom signal is almost entirely contained in the barotropic variability. Upper-ocean variability is predominantly baroclinic and the alignment is less sensitive to the underlying bathymetry. These findings offer guidance for introducing a parameterization of eddy feedbacks, based on the eddy kinetic energy and underlying bathymetry, to operate on the barotropic flow and better account for the effects of barotropic Reynolds stresses unresolved in coarse-resolution ocean models.
Significant sink of ocean-eddy energy near western boundaries
Zhai, Xiaoming; Johnson, Helen L.; Marshall, David P.
2010-09-01
Ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean. In equilibrium, the sources and sinks of eddy energy have to be balanced. However, where and how eddy energy is removed remains uncertain. Ocean eddies are observed to propagate westwards at speeds similar to the phase speeds of classical Rossby waves, but what happens to the eddies when they encounter the western boundary is unclear. Here we use a simple reduced-gravity model along with satellite altimetry data to show that the western boundary acts as a `graveyard' for the westward-propagating ocean eddies. We estimate a convergence of eddy energy near the western boundary of approximately 0.1-0.3TW, poleward of 10° in latitude. This energy is most probably scattered into high-wavenumber vertical modes, resulting in energy dissipation and diapycnal mixing. If confirmed, this eddy-energy sink will have important implications for the ocean circulation.
Eddy Currents: Levitation, Metal Detectors, and Induction Heating
Wouch, G.; Lord, A. E., Jr.
1978-01-01
A simple and accessible calculation is given of the effects of eddy currents for a sphere in the field of a single circular loop of alternating current. These calculations should help toward the inclusion of eddy current effects in upper undergraduate physics courses. (BB)
Calculation of Eddy currents in the ETE spherical torus
Ludwig, Gerson Otto
2002-07-01
A circuit model based on a Green's function method was developed to evaluate the currents induced during startup in the vessel of ETE (Spherical Tokamak Experiment). The eddy currents distribution is calculated using a thin shell approximation for the vacuum vessel and local curvilinear coordinates. The results are compared with values of the eddy currents measured in ETE. (author)
A synthesis of similarity and eddy-viscosity models
Verstappen, R.; Friedrich, R; Geurts, BJ; Metais, O
2004-01-01
In large-eddy simulation, a low-pass spatial filter is usually applied to the Navier-Stokes equations. The resulting commutator of the filter and the nonlinear term is usually modelled by an eddy-viscosity model, by a similarity model or by a mix thereof. Similarity models possess the proper mathema
Nonlinear Eddy Viscosity Models applied to Wind Turbine Wakes
Laan, van der, Paul Maarten; Sørensen, Niels N.; Réthoré, Pierre-Elouan;
2013-01-01
The linear k−ε eddy viscosity model and modified versions of two existing nonlinear eddy viscosity models are applied to single wind turbine wake simulations using a Reynolds Averaged Navier-Stokes code. Results are compared with field wake measurements. The nonlinear models give better results...
ON THE EDDY VISCOSITY MODEL OF PERIODIC TURBULENT SHEAR FLOWS
王新军; 罗纪生; 周恒
2003-01-01
Physical argument shows that eddy viscosity is essentially different from molecular viscosity. By direct numerical simulation, it was shown that for periodic turbulent flows, there is phase difference between Reynolds stress and rate of strain. This finding posed great challenge to turbulence modeling, because most turbulence modeling, which use the idea of eddy viscosity, do not take this effect into account.
Conditional eddies, or clumps, in ion-beam-generated turbulence
Johnsen, Helene; Pecseli, H. L.; Trulsen, J.
1985-01-01
with a relatively long lifetime in terms of the average bounce period is observed. Particles bouncing in the potential well associated with these `eddies' will necessarily remain correlated for times determined by the eddy lifetime. The results thus provide evidence for clump formation in plasmas...
Nonlinear inertial oscillations of a multilayer eddy: An analytical solution
Dotsenko, S. F.; Rubino, A.
2008-06-01
Nonlinear axisymmetric oscillations of a warm baroclinic eddy are considered within the framework of an reduced-gravity model of the dynamics of a multilayer ocean. A class of exact analytical solutions describing pure inertial oscillations of an eddy formation is found. The thicknesses of layers in the eddy vary according to a quadratic law, and the horizontal projections of the velocity in the layers depend linearly on the radial coordinate. Owing to a complicated structure of the eddy, weak limitations on the vertical distribution of density, and an explicit form of the solution, the latter can be treated as a generalization of the exact analytical solutions of this form that were previously obtained for homogeneous and baroclinic eddies in the ocean.
Effects of Drake Passage on a strongly eddying global ocean
Viebahn, Jan P; Bars, Dewi Le; Dijkstra, Henk A
2015-01-01
The climate impact of ocean gateway openings during the Eocene-Oligocene transition is still under debate. Previous model studies employed grid resolutions at which the impact of mesoscale eddies has to be parameterized. We present results of a state-of-the-art eddy-resolving global ocean model with a closed Drake Passage, and compare with results of the same model at non-eddying resolution. An analysis of the pathways of heat by decomposing the meridional heat transport into eddy, horizontal, and overturning circulation components indicates that the model behavior on the large scale is qualitatively similar at both resolutions. Closing Drake Passage induces (i) sea surface warming around Antarctica due to changes in the horizontal circulation of the Southern Ocean, (ii) the collapse of the overturning circulation related to North Atlantic Deep Water formation leading to surface cooling in the North Atlantic, (iii) significant equatorward eddy heat transport near Antarctica. However, quantitative details sign...
On the interactions between planetary geostrophy and mesoscale eddies
Grooms, Ian; Julien, Keith; Fox-Kemper, Baylor
2011-04-01
Multiscale asymptotics are used to derive three systems of equations connecting the planetary geostrophic (PG) equations for gyre-scale flow to a quasigeostrophic (QG) equation set for mesoscale eddies. Pedlosky (1984), following similar analysis, found eddy buoyancy fluxes to have only a small effect on the large-scale flow; however, numerical simulations disagree. While the impact of eddies is relatively small in most regions, in keeping with Pedlosky's result, eddies have a significant effect on the mean flow in the vicinity of strong, narrow currents. First, the multiple-scales analysis of Pedlosky is reviewed and amplified. Novel results of this analysis include new multiple-scales models connecting large-scale PG equations to sets of QG eddy equations. However, only introducing anisotropic scaling of the large-scale coordinates allows us to derive a model with strong two-way coupling between the QG eddies and the PG mean flow. This finding reconciles the analysis with simulations, viz. that strong two-way coupling is observed in the vicinity of anisotropic features of the mean flow like boundary currents and jets. The relevant coupling terms are shown to be eddy buoyancy fluxes. Using the Gent-McWilliams parameterization to approximate these fluxes allows solution of the PG equations with closed tracer fluxes in a closed domain, which is not possible without mesoscale eddy (or other small-scale) effects. The boundary layer width is comparable to an eddy mixing length when the typical eddy velocity is taken to be the long Rossby wave phase speed, which is the same result found by Fox-Kemper and Ferrari (2009) in a reduced gravity layer.
Larsson, Johan; Wang, Qiqi
2014-08-13
In this paper, we try to look into the future to envision how large eddy and detached eddy simulations will be used in the engineering design process about 20-30 years from now. Some key challenges specific to the engineering design process are identified, and some of the critical outstanding problems and promising research directions are discussed.
Chen, Juhui; Yin, Weijie; Wang, Shuai; Meng, Cheng; Li, Jiuru; Qin, Bai; Yu, Guangbin
2016-07-01
Large-eddy simulation (LES) approach is used for gas turbulence, and eddy dissipation concept (EDC)-sub-grid scale (SGS) reaction model is employed for reactions in small eddies. The simulated gas molar fractions are in better agreement with experimental data with EDC-SGS reaction model. The effect of reactions in small eddies on biomass gasification is emphatically analyzed with EDC-SGS reaction model. The distributions of the SGS reaction rates which represent the reactions in small eddies with particles concentration and temperature are analyzed. The distributions of SGS reaction rates have the similar trend with those of total reactions rates and the values account for about 15% of the total reactions rates. The heterogeneous reaction rates with EDC-SGS reaction model are also improved during the biomass gasification process in bubbling fluidized bed.
Large eddy simulations in 2030 and beyond.
Piomelli, U
2014-08-13
Since its introduction, in the early 1970s, large eddy simulations (LES) have advanced considerably, and their application is transitioning from the academic environment to industry. Several landmark developments can be identified over the past 40 years, such as the wall-resolved simulations of wall-bounded flows, the development of advanced models for the unresolved scales that adapt to the local flow conditions and the hybridization of LES with the solution of the Reynolds-averaged Navier-Stokes equations. Thanks to these advancements, LES is now in widespread use in the academic community and is an option available in most commercial flow-solvers. This paper will try to predict what algorithmic and modelling advancements are needed to make it even more robust and inexpensive, and which areas show the most promise.
Large eddy simulation of breaking waves
Christensen, Erik Damgaard; Deigaard, Rolf
2001-01-01
is described by large eddy simulation where the larger turbulent features are simulated by solving the flow equations, and the small scale turbulence that is not resolved by the flow model is represented by a sub-grid model. A simple Smagorinsky sub-grid model has been used for the present simulations......A numerical model is used to simulate wave breaking, the large scale water motions and turbulence induced by the breaking process. The model consists of a free surface model using the surface markers method combined with a three-dimensional model that solves the flow equations. The turbulence....... The incoming waves are specified by a flux boundary condition. The waves are approaching in the shore-normal direction and are breaking on a plane, constant slope beach. The first few wave periods are simulated by a two-dimensional model in the vertical plane normal to the beach line. The model describes...
Large eddy simulation applications in gas turbines.
Menzies, Kevin
2009-07-28
The gas turbine presents significant challenges to any computational fluid dynamics techniques. The combination of a wide range of flow phenomena with complex geometry is difficult to model in the context of Reynolds-averaged Navier-Stokes (RANS) solvers. We review the potential for large eddy simulation (LES) in modelling the flow in the different components of the gas turbine during a practical engineering design cycle. We show that while LES has demonstrated considerable promise for reliable prediction of many flows in the engine that are difficult for RANS it is not a panacea and considerable application challenges remain. However, for many flows, especially those dominated by shear layer mixing such as in combustion chambers and exhausts, LES has demonstrated a clear superiority over RANS for moderately complex geometries although at significantly higher cost which will remain an issue in making the calculations relevant within the design cycle.
Large-eddy simulation of contrails
Chlond, A. [Max-Planck-Inst. fuer Meteorologie, Hamburg (Germany)
1997-12-31
A large eddy simulation (LES) model has been used to investigate the role of various external parameters and physical processes in the life-cycle of contrails. The model is applied to conditions that are typical for those under which contrails could be observed, i.e. in an atmosphere which is supersaturated with respect to ice and at a temperature of approximately 230 K or colder. The sensitivity runs indicate that the contrail evolution is controlled primarily by humidity, temperature and static stability of the ambient air and secondarily by the baroclinicity of the atmosphere. Moreover, it turns out that the initial ice particle concentration and radiative processes are of minor importance in the evolution of contrails at least during the 30 minutes simulation period. (author) 9 refs.
Eddy-current-damped microelectromechanical switch
Christenson, Todd R. (Albuquerque, NM); Polosky, Marc A. (Tijeras, NM)
2007-10-30
A microelectromechanical (MEM) device is disclosed that includes a shuttle suspended for movement above a substrate. A plurality of permanent magnets in the shuttle of the MEM device interact with a metal plate which forms the substrate or a metal portion thereof to provide an eddy-current damping of the shuttle, thereby making the shuttle responsive to changes in acceleration or velocity of the MEM device. Alternately, the permanent magnets can be located in the substrate, and the metal portion can form the shuttle. An electrical switch closure in the MEM device can occur in response to a predetermined acceleration-time event. The MEM device, which can be fabricated either by micromachining or LIGA, can be used for sensing an acceleration or deceleration event (e.g. in automotive applications such as airbag deployment or seat belt retraction).
Eddy-current-damped microelectromechanical switch
Christenson, Todd R. (Albuquerque, NM); Polosky, Marc A. (Tijeras, NM)
2009-12-15
A microelectromechanical (MEM) device is disclosed that includes a shuttle suspended for movement above a substrate. A plurality of permanent magnets in the shuttle of the MEM device interact with a metal plate which forms the substrate or a metal portion thereof to provide an eddy-current damping of the shuttle, thereby making the shuttle responsive to changes in acceleration or velocity of the MEM device. Alternately, the permanent magnets can be located in the substrate, and the metal portion can form the shuttle. An electrical switch closure in the MEM device can occur in response to a predetermined acceleration-time event. The MEM device, which can be fabricated either by micromachining or LIGA, can be used for sensing an acceleration or deceleration event (e.g. in automotive applications such as airbag deployment or seat belt retraction).
Large-eddy simulation of propeller noise
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.
Direct and large-eddy simulation IX
Kuerten, Hans; Geurts, Bernard; Armenio, Vincenzo
2015-01-01
This volume reflects the state of the art of numerical simulation of transitional and turbulent flows and provides an active forum for discussion of recent developments in simulation techniques and understanding of flow physics. Following the tradition of earlier DLES workshops, these papers address numerous theoretical and physical aspects of transitional and turbulent flows. At an applied level it contributes to the solution of problems related to energy production, transportation, magneto-hydrodynamics and the environment. A special session is devoted to quality issues of LES. The ninth Workshop on 'Direct and Large-Eddy Simulation' (DLES-9) was held in Dresden, April 3-5, 2013, organized by the Institute of Fluid Mechanics at Technische Universität Dresden. This book is of interest to scientists and engineers, both at an early level in their career and at more senior levels.
Evaluation of scale-aware subgrid mesoscale eddy models in a global eddy-rich model
Pearson, Brodie; Fox-Kemper, Baylor; Bachman, Scott; Bryan, Frank
2017-07-01
Two parameterizations for horizontal mixing of momentum and tracers by subgrid mesoscale eddies are implemented in a high-resolution global ocean model. These parameterizations follow on the techniques of large eddy simulation (LES). The theory underlying one parameterization (2D Leith due to Leith, 1996) is that of enstrophy cascades in two-dimensional turbulence, while the other (QG Leith) is designed for potential enstrophy cascades in quasi-geostrophic turbulence. Simulations using each of these parameterizations are compared with a control simulation using standard biharmonic horizontal mixing.Simulations using the 2D Leith and QG Leith parameterizations are more realistic than those using biharmonic mixing. In particular, the 2D Leith and QG Leith simulations have more energy in resolved mesoscale eddies, have a spectral slope more consistent with turbulence theory (an inertial enstrophy or potential enstrophy cascade), have bottom drag and vertical viscosity as the primary sinks of energy instead of lateral friction, and have isoneutral parameterized mesoscale tracer transport. The parameterization choice also affects mass transports, but the impact varies regionally in magnitude and sign.
Turbulence Spectra and Eddy Diffusivity over Forests.
Lee, Xuhui
1996-08-01
The main objectives of this observational study are to examine the stability dependence of velocity and air temperature spectra and to employ the spectral quantities to establish relations for eddy diffusivity over forests. The datasets chosen for the analysis were collected above the Browns River forest and the Camp Borden forest over a wide range of stability conditions.Under neutral and unstable conditions the nondimensional dissipation rate of turbulent kinetic energy (TKE) over the forests is lower than that from its Monin-Obukhov similarity (MOS) function for the smooth-wall surface layer. The agreement is somewhat better under stable conditions but a large scatter is evident. When the frequency is made nondimensional by the height of the stand (h) and the longitudinal velocity at this height (uh, the Kaimal spectral model for neutral air describes the observations very well. The eddy diffusivity formulation K = c 4w/ provides a promising alternative to the MOS approach, where w is the standard deviation of the vertical velocity and TKE dissipation rate. Current datasets yield a constant of 0.43 for c for sensible heat in neutral and stable air, a value very close to that for the smooth-wall surface layer. It is postulated that c is a conservative parameter for sensible heat in the unstable air, its value probably falling between 0.41 and 0.54. In the absence of data, it is possible to estimate K from measurements of the local mean wind u and air stability. As a special case, it is shown that K = 0.27(uh/uh)w under neutral stability. This relation is then used to establish a profile model for wind speed and scalar concentration in the roughness sublayer. The analysis points out that uh and h are important scaling parameters in attempts to formulate quantitative relations for turbulence over tall vegetation.
Eddy Correlation Flux Measurement System Handbook
Cook, D. R. [Argonne National Lab. (ANL), Argonne, IL (United States)
2016-01-01
The eddy correlation (ECOR) flux measurement system provides in situ, half-hour measurements of the surface turbulent fluxes of momentum, sensible heat, latent heat, and carbon dioxide (CO2) (and methane at one Southern Great Plains extended facility (SGP EF) and the North Slope of Alaska Central Facility (NSA CF). The fluxes are obtained with the eddy covariance technique, which involves correlation of the vertical wind component with the horizontal wind component, the air temperature, the water vapor density, and the CO2 concentration. The instruments used are: • a fast-response, three-dimensional (3D) wind sensor (sonic anemometer) to obtain the orthogonal wind components and the speed of sound (SOS) (used to derive the air temperature) • an open-path infrared gas analyzer (IRGA) to obtain the water vapor density and the CO2 concentration, and • an open-path infrared gas analyzer (IRGA) to obtain methane density and methane flux at one SGP EF and at the NSA CF. The ECOR systems are deployed at the locations where other methods for surface flux measurements (e.g., energy balance Bowen ratio [EBBR] systems) are difficult to employ, primarily at the north edge of a field of crops. A Surface Energy Balance System (SEBS) has been installed collocated with each deployed ECOR system in SGP, NSA, Tropical Western Pacific (TWP), ARM Mobile Facility 1 (AMF1), and ARM Mobile Facility 2 (AMF2). The surface energy balance system consists of upwelling and downwelling solar and infrared radiometers within one net radiometer, a wetness sensor, and soil measurements. The SEBS measurements allow the comparison of ECOR sensible and latent heat fluxes with the energy balance determined from the SEBS and provide information on wetting of the sensors for data quality purposes. The SEBS at one SGP and one NSA site also support upwelling and downwelling PAR measurements to qualify those two locations as Ameriflux sites.
An eddy closure for potential vorticity
Ringler, Todd D [Los Alamos National Laboratory
2009-01-01
The Gent-McWilliams (GM) parameterization is extended to include a direct influence in the momentum equation. The extension is carried out in two stages; an analysis of the inviscid system is followed by an analysis of the viscous system. In the inviscid analysis the momentum equation is modified such that potential vorticity is conserved along particle trajectories following a transport velocity that includes the Bolus velocity in a manner exactly analogous to the continuity and tracer equations. In addition (and in contrast to traditional GM closures), the new formulation of the inviscid momentum equation results in a conservative exchange between potential and kinetic forms of energy. The inviscid form of the eddy closure conserves total energy to within an error proportional to the time derivative of the Bolus velocity. The hypothesis that the viscous term in the momentum equation should give rise to potential vorticity being diffused along isopycnals in a manner analogous to other tracers is examined in detail. While the form of the momentum closure that follows from a strict adherence to this hypothesis is not immediately interpretable within the constructs of traditional momentum closures, three approximations to this hypothesis results in a form of dissipation that is consistent with traditional Laplacian diffusion. The first two approximations are that relative vorticity, not potential vorticity, is diffused along isopyncals and that the flow is in approximate geostrophic balance. An additional approximation to the Jacobian term is required when the dissipation coefficient varies in space. More importantly, the critique of this hypothesis results in the conclusion that the viscosity parameter in the momentum equation should be identical to the tradition GM closure parameter {Kappa}. Overall, we deem the viscous form of the eddy closure for potential vorticity as a viable closure for use in ocean circulation models.
Modelling cyclonic eddies in the Delagoa Bight region
Cossa, O.; Pous, S.; Penven, P.; Capet, X.; Reason, C. J. C.
2016-05-01
The objective of this study is to document and shed light on the circulation around the Delagoa Bight region in the southern Mozambique Channel using a realistic modelling approach. A simulation including mesoscale forcings at the boundaries of our regional configuration succeeds in reproducing the general circulation in the region as well as the existence of a semi-permanent cyclonic eddy, whose existence is attested by in situ measurements in the Bight. Characterised by a persistent local minimum in SSH located around 26°S-34°E, this cyclonic eddy termed herein the Delagoa Bight lee eddy occurs about 25% of the time with no clear seasonal preference. Poleward moving cyclones, mostly generated further north, occur another 25% of the time in the Bight area. A tracking method applied to eddies generated in Delagoa Bight using model outputs as well as AVISO data confirms the model realism and provides additional statistics. The diameter of the eddy core varies between 61 and 147 km and the average life time exceeds 20 days. Additional model analyses reveal the systematic presence of negative vorticity in the Bight that can organise and form a Delagoa Bight lee eddy depending on the intensity of an intermittent southward flow along the shore and the spatial distribution of surrounding mesoscale features. In addition, the model solution shows other cyclonic eddies generated near Inhambane and eventually travelling through the Bight. Their generation and pathways appears to be linked with large Mozambique Channel rings.
Eddies spatial variability at Makassar Strait – Flores Sea
Nuzula, F.; Syamsudin, M. L.; Yuliadi, L. P. S.; Purba, N. P.; Martono
2017-01-01
This study was aimed to get the distribution of eddies spatially and temporally from Makassar Waters (MW) to Flores Sea (FS), as well as its relations with the upwelling, the downwelling, and chlorophyll-a concentration. The study area extends from 115º–125º E to 2.5º–8º S. The datasets were consisted of monthly geostrophic currents, sea surface heights, sea surface temperatures, and chlorophyll-a from 2008 – 2012. The results showed that eddies which found at Makassar Strait (MS) has the highest diameter and speed of 255.3 km and 21.4 cm/s respectively, while at the southern MW has 266.4 km and 15.6 cm/s, and at FS has 182.04 km and 11.4 cm/s. From a total of 51 eddies found, the majority of eddies type was anticyclonic. At MS and FS, eddies formed along the year, whereas at southern MW were found missing in West Season. Moreover, the chlorophyll-a concentration was consistently higher at the eddies area. Even though, the correlation among eddies and the upwelling downwelling phenomena was not significantly as shown by sea surface temperatures value.
Dynamics of Eddies in the Southeastern Tropical Indian Ocean
Hanifah, F.; Ningsih, N. S.; Sofian, I.
2016-08-01
A holistic study was done on eddies in the Southeastern Tropical Indian Ocean (SETIO) using the HYbrid Coordinate Ocean Model (HYCOM) for 64 years (from 1950 to 2013). The results from the model were verified against the current and the Sea Surface Height Anomaly (SSHA) from Ocean Surface Current Analyses - Real time (OSCAR) and Archiving, Validation and Interpretation of Satellite Oceanographic Data (AVISO) respectively. The verification showed that the model simulates the condition in the area of study relatively well. We discovered that the local wind was not the only factor that contributed to the formation of eddies in the area. The difference in South Java Current (SJC) flow compared to the Indonesian Throughflow (ITF) and South Equatorial Current (SEC) flow as well as the difference in the relative velocity between the currents in the area led us to suspect that shear velocity may be responsible for the formation of eddies. The results from our model corroborated our prediction about shear velocity. Therefore, we attempted to explain the appearance of eddies in the SETIO based on the concept of shear velocity. By observing and documenting the occurrences of eddies in the area, we found that there are 8 cyclonic and 7 anticyclonic eddies in the SETIO. The distribution and frequency of the appearance of eddies varies, depending on the season.
Study on the mesoscale eddies around the Ryukyu Islands
HAN Shuzong; XU Changsan; WU Huiming; WANG Gang; PEI Junfeng; FAN Yongbin; WANG Xingchi
2016-01-01
Results of the Ocean General Circulation Model for the Earth Simulator (OFES) from January 1977 to December 2006 are used to investigate mesoscale eddies near the Ryukyu Islands. The results show that: (1) Larger eddies are mainly east of Taiwan, above the Ryukyu Trench and south of the Shikoku Island. These three sea areas are all in the vicinity of the Ryukyu Current. (2) Eddies in the area of the Ryukyu Current are mainly anticyclonic, and conducive to that current. The transport of water east of the Ryukyu Islands is mainly toward the northeast. (3) The Ryukyu Current is significantly affected by the eddies. The lower the latitude, the greater these effects. However, the Kuroshio is relatively stable, and the effect of mesoscale eddies is not significant. (4) A warm eddy south of the Shikoku Island break away from the Kuroshio and move southwest, and is clearly affected by the Ryukyu Current and Kuroshio. Relationships between the mesoscale eddies, Kuroshio meanders, and Ryukyu Current are discussed.
Conjugate spectrum filters for eddy current signal processing
Stepinski, T.; Maszi, N. (Univ. of Uppsala (Sweden). Dept. of Technology.)
1993-07-01
The paper addresses the problem of detection and classification of material defects during eddy current inspection. Digital signal processing algorithms for detection and characterization of flaws are considered and a new type of filter for classification of eddy current data is proposed. In the first part of the paper the signal processing blocks used in modern eddy current instruments are presented and analyzed in terms of information transmission. The processing usually consists of two steps: detection by means of amplitude-phase detectors and filtering of the detector output signals by means of analog signal filters. Distortion introduced by the signal filters is considered and illustrated using real eddy current responses. The nature of the distortion is explained and the way to avoid it is indicated. A novel method for processing the eddy current responses is presented in the second part of the paper. The method employs two-dimensional conjugate spectrum filters (CSFs) that are sensitive both to the phase angle and the shape of the eddy current responses. First the theoretical background of the CSF is presented and then two different ways of application, matched filters and orthogonal conjugate spectrum filters, are considered. The matched CSFs can be used for attenuation of all signals with the phase angle different from the selected prototype. The orthogonal filters are able to suppress completely a specific interference, e.g. the response of supporting plate when testing heat exchanger tubes. The performance of the CSFs is illustrated by means of real and simulated eddy current signals.
Eddy energy sources and flux in the Red Sea
Zhan, Peng
2015-04-01
In the Red Sea, eddies are reported to be one of the key features of hydrodynamics in the basin. They play a significant role in converting the energy among the large-scale circulation, the available potential energy (APE) and the eddy kinetic energy (EKE). Not only do eddies affect the horizontal circulation, deep-water formation and overturning circulation in the basin, but they also have a strong impact on the marine ecosystem by efficiently transporting heat, nutrients and carbon across the basin and by pumping the nutrient-enriched subsurface water to sustain the primary production. Previous observations and modeling work suggest that the Red Sea is rich of eddy activities. In this study, the eddy energy sources and sinks have been studied based on a high-resolution MITgcm. We have also investigated the possible mechanisms of eddy generation in the Red Sea. Eddies with high EKE are found more likely to appear in the central and northern Red Sea, with a significant seasonal variability. They are more inclined to occur during winter when they acquire their energy mainly from the conversion of APE. In winter, the central and especially the northern Red Sea are subject to important heat loss and extensive evaporation. The resultant densified upper-layer water tends to sink and release the APE through baroclinic instability, which is about one order larger than the barotropic instability contribution and is the largest source term for the EKE in the Red Sea. As a consequence, the eddy energy is confined to the upper layer but with a slope deepening from south to north. In summer, the positive surface heat flux helps maintain the stratification and impedes the gain of APE. The EKE is, therefore, much lower than that in winter despite a higher wind power input. Unlike many other seas, the wind energy is not the main source of energy to the eddies in the Red Sea.
A novel eddy current damper: theory and experiment
Ebrahimi, Babak; Khamesee, Mir Behrad [Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, N2L 3G1 (Canada); Golnaraghi, Farid, E-mail: khamesee@mecheng1.uwaterloo.c [Mechatronic Systems Engineering, Simon Fraser University, Surrey, British Columbia, V3T 0A3 (Canada)
2009-04-07
A novel eddy current damper is developed and its damping characteristics are studied analytically and experimentally. The proposed eddy current damper consists of a conductor as an outer tube, and an array of axially magnetized ring-shaped permanent magnets separated by iron pole pieces as a mover. The relative movement of the magnets and the conductor causes the conductor to undergo motional eddy currents. Since the eddy currents produce a repulsive force that is proportional to the velocity of the conductor, the moving magnet and the conductor behave as a viscous damper. The eddy current generation causes the vibration to dissipate through the Joule heating generated in the conductor part. An accurate, analytical model of the system is obtained by applying electromagnetic theory to estimate the damping properties of the proposed eddy current damper. A prototype eddy current damper is fabricated, and experiments are carried out to verify the accuracy of the theoretical model. The experimental test bed consists of a one-degree-of-freedom vibration isolation system and is used for the frequency and transient time response analysis of the system. The eddy current damper model has a 0.1 m s{sup -2} (4.8%) RMS error in the estimation of the mass acceleration. A damping coefficient as high as 53 Ns m{sup -1} is achievable with the fabricated prototype. This novel eddy current damper is an oil-free, inexpensive damper that is applicable in various vibration isolation systems such as precision machinery, micro-mechanical suspension systems and structure vibration isolation.
Eddy-Current Inspection Of Tab Seals On Beverage Cans
Bar-Cohen, Yoseph
1994-01-01
Eddy-current inspection system monitors tab seals on beverage cans. Device inspects all cans at usual production rate of 1,500 to 2,000 cans per minute. Automated inspection of all units replaces visual inspection by microscope aided by mass spectrometry. System detects defects in real time. Sealed cans on conveyor pass near one of two coils in differential eddy-current probe. Other coil in differential eddy-current probe positioned near stationary reference can on which tab seal is known to be of acceptable quality. Signal of certain magnitude at output of probe indicates defective can, automatically ejected from conveyor.
Oceanic eddy detection and lifetime forecast using machine learning methods
Ashkezari, Mohammad D.; Hill, Christopher N.; Follett, Christopher N.; Forget, Gaël.; Follows, Michael J.
2016-12-01
We report a novel altimetry-based machine learning approach for eddy identification and characterization. The machine learning models use daily maps of geostrophic velocity anomalies and are trained according to the phase angle between the zonal and meridional components at each grid point. The trained models are then used to identify the corresponding eddy phase patterns and to predict the lifetime of a detected eddy structure. The performance of the proposed method is examined at two dynamically different regions to demonstrate its robust behavior and region independency.
Eddy Surface properties and propagation at Southern Hemisphere western boundary current systems
G. S. Pilo
2015-02-01
Full Text Available Oceanic eddies occur in all world oceans, but are more energetic when associated to western boundary currents (WBC systems. In these regions, eddies play an important role on mixing and energy exchange. Therefore, it is important to quantify and qualify eddies occurring within these systems. Previous studies performed eddy censuses in Southern Hemisphere WBC systems. However, important aspects of local eddy population are still unknown. Main questions to be answered relate to eddies' spatial distribution, propagation and lifetime within each system. Here, we use a global eddy dataset to qualify eddies based on their surface characteristics at the Agulhas Current (AC, the Brazil Current (BC and the East Australian Current (EAC Systems. We show that eddy propagation within each system is highly forced by the local mean flow and bathymetry. In the AC System, eddy polarity dictates its propagation distance. BC system eddies do not propagate beyond the Argentine Basin, and are advected by the local ocean circulation. EAC System eddies from both polarities cross south of Tasmania, but only anticyclonics reach the Great Australian Bight. Eddies in all systems and from both polarities presented a geographical segregation according to size. Large eddies occur along the Agulhas Retroflection, the Agulhas Return Current, the Brazil-Malvinas Confluence and the Coral Sea. Small eddies occur in the systems southernmost domains. Understanding eddies' propagation helps to establish monitoring programs, and to better understand how these features would affect local mixing.
Ergodicity test of the eddy correlation method
Chen, J.; Hu, Y.; Yu, Y.; Lü, S.
2014-07-01
The turbulent flux observation in the near-surface layer is a scientific issue which researchers in the fields of atmospheric science, ecology, geography science, etc. are commonly interested in. For eddy correlation measurement in the atmospheric surface layer, the ergodicity of turbulence is a basic assumption of the Monin-Obukhov (M-O) similarity theory, which is confined to steady turbulent flow and homogenous surface; this conflicts with turbulent flow under the conditions of complex terrain and unsteady, long observational period, which the study of modern turbulent flux tends to focus on. In this paper, two sets of data from the Nagqu Station of Plateau Climate and Environment (NaPlaCE) and the cooperative atmosphere-surface exchange study 1999 (CASE99) were used to analyze and verify the ergodicity of turbulence measured by the eddy covariance system. Through verification by observational data, the vortex of atmospheric turbulence, which is smaller than the scale of the atmospheric boundary layer (i.e., its spatial scale is less than 1000 m and temporal scale is shorter than 10 min) can effectively meet the conditions of the average ergodic theorem, and belong to a wide sense stationary random processes. Meanwhile, the vortex, of which the spatial scale is larger than the scale of the boundary layer, cannot meet the conditions of the average ergodic theorem, and thus it involves non-ergodic stationary random processes. Therefore, if the finite time average is used to substitute for the ensemble average to calculate the average random variable of the atmospheric turbulence, then the stationary random process of the vortex, of which spatial scale was less than 1000 m and thus below the scale of the boundary layer, was possibly captured. However, the non-ergodic random process of the vortex, of which the spatial scale was larger than that of the boundary layer, could not be completely captured. Consequently, when the finite time average was used to substitute
Eddy sensors for small diameter stainless steel tubes.
Skinner, Jack L.; Morales, Alfredo Martin; Grant, J. Brian; Korellis, Henry James; LaFord, Marianne Elizabeth; Van Blarigan, Benjamin; Andersen, Lisa E.
2011-08-01
The goal of this project was to develop non-destructive, minimally disruptive eddy sensors to inspect small diameter stainless steel metal tubes. Modifications to Sandia's Emphasis/EIGER code allowed for the modeling of eddy current bobbin sensors near or around 1/8-inch outer diameter stainless steel tubing. Modeling results indicated that an eddy sensor based on a single axial coil could effectively detect changes in the inner diameter of a stainless steel tubing. Based on the modeling results, sensor coils capable of detecting small changes in the inner diameter of a stainless steel tube were designed, built and tested. The observed sensor response agreed with the results of the modeling and with eddy sensor theory. A separate limited distribution SAND report is being issued demonstrating the application of this sensor.
Does the wind systematically energize or damp ocean eddies?
Wilson, Chris
2016-12-01
Globally, mesoscale ocean eddies are a key component of the climate system, involved in transport and mixing of heat, carbon, and momentum. However, they represent one of the major challenges of climate modeling, as the details of their nonlinear dynamics affect all scales. Recent progress analyzing satellite observations of the surface ocean and atmosphere has uncovered energetic interactions between the atmospheric wind stress and ocean eddies that may change our understanding of key processes affecting even large-scale climate. Wind stress acts systematically on ocean eddies and may explain observed asymmetry in the distribution of eddies and details of their lifecycle of growth and decay. These findings provide powerful guidance for climate model development.
Kurczyn, J. A.; Beier, Emilio; Lavín, Miguel,; Chaigneau, Alexis
2012-01-01
Mesoscale eddies in the northeastern Pacific tropical-subtropical transition zone (16 degrees N-30 degrees N; 130 degrees W-102 degrees W) are analyzed using nearly 18 years of satellite altimetry and an automated eddy-identification algorithm. Eddies that lasted more than 10 weeks are described based on the analysis of 465 anticyclonic and 529 cyclonic eddy trajectories. We found three near-coastal eddy-prolific areas: (1) Punta Eugenia, (2) Cabo San Lucas, and (3) Cabo Corrientes. These thr...
Eddy heat flux in the Southern Ocean: response to variable wind forcing
Hogg, Andrew Mcc.; Meredith, Michael P.; Blundell, Jeffrey R.; Wilson, Christopher
2008-01-01
We assess the role of time-dependent eddy variability in the Antarctic Circumpolar Current (ACC) in influencing warming of the Southern Ocean. For this, we use an eddy-resolving quasigeostrophic model of the wind-driven circulation, and quantify the response of circumpolar transport, eddy kinetic energy and eddy heat transport to changes in winds. On interannual timescales, the model exhibits the behaviour of an "eddy saturated" ocean state, where increases in wind stress do not signicantly ...
Coastal GPS Altimetry for Eddy Monitoring
Cardellach, E.; Treuhaft, R. N.; Chao, Y.; Lowe, S. T.; Young, L. E.; Zuffada, C.
2003-04-01
Coastal zones (within approximately 20-30 km of the coast) are dominated by fast-changing (on the order of days) and small-scale (on the order of km or less) processes. The dynamics and thermodynamics associated with these coastal processes influence the physics, biogeochemistry and the associated carbon cycling in the coastal zones. To monitor these important processes at the highest possible resolution (both spatial and temporal) is therefore an integrated component of the Earth's observing system. Coastal processes are currently not adequately monitored from existing spaceborne observations. The infrared instruments can measure the sea surface temperature in coastal zones with a resolution of approximately 1km daily, but are heavily contaminated by clouds usually found in the land-sea boundaries. The conventional radar altimetry, even with the wide-swath (e.g., OSTM) configuration, can only provide measurements every 10 days, too long to resolve the fast-changing coastal processes, not mentioning the land contamination within the first few footprints (on the order of 20 km) away from the coast. Coastal GPS altimetry from cliffs or structures near the coastline provides a complementary way to measure these coastal processes. The precision of such ground-based grazing angle GPS measurements has been proven to be 2-cm over the smooth surface at Crater Lake [Treuhaft et al., 2001]. Nevertheless, the accuracy of the GPS altimetry over the open sea, significantly affected by roughness, has yet to be assessed. This poster aims to present a set of experiments and analyses to prove the coastal GPS altimetry concept with a few-cm accuracy goal. It includes the analysis of data gathered over the ocean from an oil platform, Platform Harvest, as well as simulations of the GPS reflected signal to identify and correct the effects of the sea roughness. The results of this research are planned to feed the design, execution and processing of an eddy monitoring experiment. It will
Nearby boundaries create eddies near microscopic filter feeders
Pepper, Rachel E.; Roper, Marcus; Ryu, Sangjin; Matsudaira, Paul; Stone, Howard A.
2009-01-01
We show through calculations, simulations and experiments that the eddies often observed near sessile filter feeders are frequently due to the presence of nearby boundaries. We model the common filter feeder Vorticella, which is approximately 50 µm across and which feeds by removing bacteria from ocean or pond water that it draws towards itself. We use both an analytical stokeslet model and a Brinkman flow approximation that exploits the narrow-gap geometry to predict the size of the eddy cau...
Eddy current pulsed phase thermography and feature extraction
He, Yunze; Tian, GuiYun; Pan, Mengchun; Chen, Dixiang
2013-08-01
This letter proposed an eddy current pulsed phase thermography technique combing eddy current excitation, infrared imaging, and phase analysis. One steel sample is selected as the material under test to avoid the influence of skin depth, which provides subsurface defects with different depths. The experimental results show that this proposed method can eliminate non-uniform heating and improve defect detectability. Several features are extracted from differential phase spectra and the preliminary linear relationships are built to measure these subsurface defects' depth.
Application of altimetry data assimilation on mesoscale eddies simulation
2008-01-01
Mesoscale eddy plays an important role in the ocean circulation. In order to improve the simulation accuracy of the mesoscale eddies, a three-dimensional variation (3DVAR) data assimilation system called Ocean Variational Analysis System (OVALS) is coupled with a POM model to simulate the mesoscale eddies in the Northwest Pacific Ocean. In this system, the sea surface height anomaly (SSHA) data by satellite altimeters are assimilated and translated into pseudo temperature and salinity (T-S) profile data. Then, these profile data are taken as observation data to be assimilated again and produce the three-dimensional analysis T-S field. According to the characteristics of mesoscale eddy, the most appropriate assimilation parameters are set up and testified in this system. A ten years mesoscale eddies simulation and comparison experiment is made, which includes two schemes: assimilation and non-assimilation. The results of comparison between two schemes and the observation show that the simulation accuracy of the assimilation scheme is much better than that of non-assimilation, which verified that the altimetry data assimilation method can improve the simulation accuracy of the mesoscale dramatically and indicates that it is possible to use this system on the forecast of mesoscale eddies in the future.
Sonic eddy model of the turbulent boundary layer
Breidenthal, Robert; Dintilhac, Paul; Williams, Owen
2016-11-01
A model of the compressible turbulent boundary layer is proposed. It is based on the notion that turbulent transport by an eddy requires that information of nonsteady events propagates across the diameter of that eddy during one rotation period. The finite acoustic signaling speed then controls the turbulent fluxes. As a consequence, the fluxes are limited by the largest eddies that satisfies this requirement. Therefore "sonic eddies" with a rotational Mach number of about unity would determine the skin friction, which is predicted to vary inversely with Mach number. This sonic eddy model contrasts with conventional models that are based on the energy equation and variations in the density. The effect of density variations is known to be weak in free shear flows, and the sonic eddy model assumes the same for the boundary layer. In general, Mach number plays two simultaneous roles in compressible flow, one related to signaling and the other related to the energy equation. The predictions of the model are compared with experimental data and DNS results from the literature.
Ladislav Janousek
2006-01-01
Full Text Available The paper deals with variation of eddy current density distribution along material depth and investigates an effect of the variation on a crack signal in eddy current non-destructive testing. Four coaxial rectangular tangential coils are used to induce eddy currents in a tested conductive object. The exciting coils are driven independently by phase-shifted AC currents; a ratio of amplitudes of the exciting currents is continuously changed to vary the distribution of eddy current density along material depth under a circular pick-up coil positioned in centre between the exciting coils. Dependences of a crack signal amplitude and its phase on the ratio are evaluated and special features are extracted. It is revealed that the dependences are strongly influenced by depth of a crack, and thus the extracted features can enhance evaluation of a detected crack.
Eddy Current Flexible Probes for Complex Geometries
Gilles-Pascaud, C.; Decitre, J. M.; Vacher, F.; Fermon, C.; Pannetier, M.; Cattiaux, G.
2006-03-01
The inspection of materials used in aerospace, nuclear or transport industry is a critical issue for the safety of components exposed to stress or/and corrosion. The industry claims for faster, more sensitive, and more flexible techniques. Technologies based on Eddy Current (EC) flexible array probe and magnetic sensor with high sensitivity such as giant magneto-resistance (GMR) could be a good solution to detect surface-breaking flaws in complex shaped surfaces. The CEA has recently developed, with support from the French Institute for Radiological Protection and Nuclear Safety (IRSN), a flexible array probe based on micro-coils etched on Kapton. The probe's performances have been assessed for the inspection of reactor residual heat removal pipes, and for aeronautical applications within the framework of the European project VERDICT. The experimental results confirm the very good detection of narrow cracks on plane and curve shaped surfaces. This paper also describes the recent progresses concerning the application of GMR sensors to EC testing, and the results obtained for the detection of small surface breaking flaws.
Advanced Eddy current NDE steam generator tubing.
Bakhtiari, S.
1999-03-29
As part of a multifaceted project on steam generator integrity funded by the U.S. Nuclear Regulatory Commission, Argonne National Laboratory is carrying out research on the reliability of nondestructive evaluation (NDE). A particular area of interest is the impact of advanced eddy current (EC) NDE technology. This paper presents an overview of work that supports this effort in the areas of numerical electromagnetic (EM) modeling, data analysis, signal processing, and visualization of EC inspection results. Finite-element modeling has been utilized to study conventional and emerging EC probe designs. This research is aimed at determining probe responses to flaw morphologies of current interest. Application of signal processing and automated data analysis algorithms has also been addressed. Efforts have focused on assessment of frequency and spatial domain filters and implementation of more effective data analysis and display methods. Data analysis studies have dealt with implementation of linear and nonlinear multivariate models to relate EC inspection parameters to steam generator tubing defect size and structural integrity. Various signal enhancement and visualization schemes are also being evaluated and will serve as integral parts of computer-aided data analysis algorithms. Results from this research will ultimately be substantiated through testing on laboratory-grown and in-service-degraded tubes.
LARGE-EDDY AND DETACHED-EDDY SIMULATIONS OF THE SEPARATED FLOW AROUND A CIRCULAR CYLINDER
无
2007-01-01
The separated turbulent flow around a circular cylinder is investigated using Large-Eddy Simulation (LES), Detached-Eddy Simulation (DES, or hybrid RANS/LES methods), and Unsteady Reynolds-Averaged Navier-Stokes (URANS). The purpose of this study is to examine some typical simulation approaches for the prediction of complex separated turbulent flow and to clarify the capability of applying these approaches to a typical case of the separated turbulent flow around a circular cylinder. Several turbulence models, I.e. Dynamic Sub-grid Scale (SGS) model in LES, the DES-based Spalart-Allmaras (S-A) and Shear-Stress- Transport (SST) models in DES, and the S-A and SST models in URANS, are used in the calculations. Some typical results, e.g., the mean pressure and drag coefficients, velocity profiles, Strouhal number, and Reynolds stresses, are obtained and compared with previous computational and experimental data. Based on our extensive calculations, we assess the capability and performance of these simulation approaches coupled with the relevant turbulence models to predict the separated turbulent flow.
Scalar excursions in large-eddy simulations
Matheou, Georgios; Dimotakis, Paul E.
2016-12-01
The range of values of scalar fields in turbulent flows is bounded by their boundary values, for passive scalars, and by a combination of boundary values, reaction rates, phase changes, etc., for active scalars. The current investigation focuses on the local conservation of passive scalar concentration fields and the ability of the large-eddy simulation (LES) method to observe the boundedness of passive scalar concentrations. In practice, as a result of numerical artifacts, this fundamental constraint is often violated with scalars exhibiting unphysical excursions. The present study characterizes passive-scalar excursions in LES of a shear flow and examines methods for diagnosis and assesment of the problem. The analysis of scalar-excursion statistics provides support of the main hypothesis of the current study that unphysical scalar excursions in LES result from dispersive errors of the convection-term discretization where the subgrid-scale model (SGS) provides insufficient dissipation to produce a sufficiently smooth scalar field. In the LES runs three parameters are varied: the discretization of the convection terms, the SGS model, and grid resolution. Unphysical scalar excursions decrease as the order of accuracy of non-dissipative schemes is increased, but the improvement rate decreases with increasing order of accuracy. Two SGS models are examined, the stretched-vortex and a constant-coefficient Smagorinsky. Scalar excursions strongly depend on the SGS model. The excursions are significantly reduced when the characteristic SGS scale is set to double the grid spacing in runs with the stretched-vortex model. The maximum excursion and volume fraction of excursions outside boundary values show opposite trends with respect to resolution. The maximum unphysical excursions increase as resolution increases, whereas the volume fraction decreases. The reason for the increase in the maximum excursion is statistical and traceable to the number of grid points (sample size
Large eddy simulation of powered Fontan hemodynamics.
Delorme, Y; Anupindi, K; Kerlo, A E; Shetty, D; Rodefeld, M; Chen, J; Frankel, S
2013-01-18
Children born with univentricular heart disease typically must undergo three open heart surgeries within the first 2-3 years of life to eventually establish the Fontan circulation. In that case the single working ventricle pumps oxygenated blood to the body and blood returns to the lungs flowing passively through the Total Cavopulmonary Connection (TCPC) rather than being actively pumped by a subpulmonary ventricle. The TCPC is a direct surgical connection between the superior and inferior vena cava and the left and right pulmonary arteries. We have postulated that a mechanical pump inserted into this circulation providing a 3-5 mmHg pressure augmentation will reestablish bi-ventricular physiology serving as a bridge-to-recovery, bridge-to-transplant or destination therapy as a "biventricular Fontan" circulation. The Viscous Impeller Pump (VIP) has been proposed by our group as such an assist device. It is situated in the center of the 4-way TCPC intersection and spins pulling blood from the vena cavae and pushing it into the pulmonary arteries. We hypothesized that Large Eddy Simulation (LES) using high-order numerical methods are needed to capture unsteady powered and unpowered Fontan hemodynamics. Inclusion of a mechanical pump into the CFD further complicates matters due to the need to account for rotating machinery. In this study, we focus on predictions from an in-house high-order LES code (WenoHemo(TM)) for unpowered and VIP-powered idealized TCPC hemodynamics with quantitative comparisons to Stereoscopic Particle Imaging Velocimetry (SPIV) measurements. Results are presented for both instantaneous flow structures and statistical data. Simulations show good qualitative and quantitative agreement with measured data.
Recurrence Analysis of Eddy Covariance Fluxes
Lange, Holger; Flach, Milan; Foken, Thomas; Hauhs, Michael
2015-04-01
The eddy covariance (EC) method is one key method to quantify fluxes in biogeochemical cycles in general, and carbon and energy transport across the vegetation-atmosphere boundary layer in particular. EC data from the worldwide net of flux towers (Fluxnet) have also been used to validate biogeochemical models. The high resolution data are usually obtained at 20 Hz sampling rate but are affected by missing values and other restrictions. In this contribution, we investigate the nonlinear dynamics of EC fluxes using Recurrence Analysis (RA). High resolution data from the site DE-Bay (Waldstein-Weidenbrunnen) and fluxes calculated at half-hourly resolution from eight locations (part of the La Thuile dataset) provide a set of very long time series to analyze. After careful quality assessment and Fluxnet standard gapfilling pretreatment, we calculate properties and indicators of the recurrent structure based both on Recurrence Plots as well as Recurrence Networks. Time series of RA measures obtained from windows moving along the time axis are presented. Their interpretation is guided by three different questions: (1) Is RA able to discern periods where the (atmospheric) conditions are particularly suitable to obtain reliable EC fluxes? (2) Is RA capable to detect dynamical transitions (different behavior) beyond those obvious from visual inspection? (3) Does RA contribute to an understanding of the nonlinear synchronization between EC fluxes and atmospheric parameters, which is crucial for both improving carbon flux models as well for reliable interpolation of gaps? (4) Is RA able to recommend an optimal time resolution for measuring EC data and for analyzing EC fluxes? (5) Is it possible to detect non-trivial periodicities with a global RA? We will demonstrate that the answers to all five questions is affirmative, and that RA provides insights into EC dynamics not easily obtained otherwise.
The eddy kinetic energy budget in the Red Sea
Zhan, Peng
2016-06-09
The budget of eddy kinetic energy (EKE) in the Red Sea, including the sources, redistributions and sink, is examined using a high-resolution eddy-resolving ocean circulation model. A pronounced seasonally varying EKE is identified, with its maximum intensity occurring in winter, and the strongest EKE is captured mainly in the central and northern basins within the upper 200 m. Eddies acquire kinetic energy from conversion of eddy available potential energy (EPE), from transfer of mean kinetic energy (MKE), and from direct generation due to time-varying (turbulent) wind stress, the first of which contributes predominantly to the majority of the EKE. The EPE-to-EKE conversion occurs almost in the entire basin, while the MKE-to-EKE transfer appears mainly along the shelf boundary of the basin (200 miso-bath) where high horizontal shear interacts with topography. The EKE generated by the turbulent wind stress is relatively small and limited to the southern basin. All these processes are intensified during winter, when the rate of energy conversion is about four to five times larger than that in summer. The EKE is redistributed by the vertical and horizontal divergence of energy flux and the advection of the mean flow. As a main sink of EKE, dissipation processes is ubiquitously found in the basin. The seasonal variability of these energy conversion terms can explain the significant seasonality of eddy activities in the Red Sea. This article is protected by copyright. All rights reserved.
Investigation of long-lived eddies on Jupiter
Lewis, S. R.; Calcutt, S. B.; Taylor, F. W.; Read, P. L.
1986-01-01
Quasi-geostrophic, two layer models of the Jovian atmosphere are under development; these may be used to simulate eddy phemonena in the atmosphere and include tracer dynamics explicitly. The models permit the investigation of the dynamics of quasi-geostrophic eddies under more controlled conditions than are possible in the laboratory. They can also be used to predict the distribution and behavior of tracer species, and hence to discriminate between different models of the mechanisms forcing the eddies, provided suitable observations can be obtained. At the same time, observational strategies are being developed for the Near Infrared Mapping Spectrometer on the Galileo Orbiter, with the objective of obtaining composition measurements for comparison with the models. Maps of features at thermal infrared wavelengths near 5 micron and reflected sunlight maps as a function of wavelength and phase angle will be obtained. These should provide further useful information on the morphology, composition and microstructure of clouds within eddy features. Equilibrium chemistry models which incorporate advection may then be used to relate these results of the dynamical models and provide addtional means of classifying different types of eddies.
Mesoscale eddies in the Subantarctic Front-Southwest Atlantic
Pablo D. Glorioso
2005-12-01
Full Text Available Satellite and ship observations in the southern southwest Atlantic (SSWA reveal an intense eddy field and highlight the potential for using continuous real-time satellite altimetry to detect and monitor mesoscale phenomena with a view to understanding the regional circulation. The examples presented suggest that mesoscale eddies are a dominant feature of the circulation and play a fundamental role in the transport of properties along and across the Antarctic Circumpolar Current (ACC. The main ocean current in the SSWA, the Falkland-Malvinas Current (FMC, exhibits numerous embedded eddies south of 50°S which may contribute to the patchiness, transport and mixing of passive scalars by this strong, turbulent current. Large eddies associated with meanders are observed in the ACC fronts, some of them remaining stationary for long periods. Two particular cases are examined using a satellite altimeter in combination with in situ observations, suggesting that cross-frontal eddy transport and strong meandering occur where the ACC flow intensifies along the sub-Antarctic Front (SAF and the Southern ACC Front (SACCF.
Eddy Current Sensing of Torque in Rotating Shafts
Varonis, Orestes J.; Ida, Nathan
2013-12-01
The noncontact torque sensing in machine shafts is addressed based on the stress induced in a press-fitted magnetoelastic sleeve on the shaft and eddy current sensing of the changes of electrical conductivity and magnetic permeability due to the presence of stress. The eddy current probe uses dual drive, dual sensing coils whose purpose is increased sensitivity to torque and decreased sensitivity to variations in distance between probe and shaft (liftoff). A mechanism of keeping the distance constant is also employed. Both the probe and the magnetoelastic sleeve are evaluated for performance using a standard eddy current instrument. An eddy current instrument is also used to drive the coils and analyze the torque data. The method and sensor described are general and adaptable to a variety of applications. The sensor is suitable for static and rotating shafts, is independent of shaft diameter and operational over a large range of torques. The torque sensor uses a differential eddy current measurement resulting in cancellation of common mode effects including temperature and vibrations.
Coastal Kelvin waves and dynamics of Gulf of Aden eddies
Valsala, Vinu K.; Rao, Rokkam R.
2016-10-01
The Gulf of Aden (GA) is a small semi-enclosed oceanic region between the Red Sea and the western Arabian Sea. The GA is characterised with westward propagating cyclonic and anti-cyclonic eddies throughout the year. The genesis and propagation of these eddies into the GA have been the focus of several studies which concluded that oceanic instabilities (both barotropic and baroclinic) as well as the Rossby waves from the Arabian Sea are the responsible mechanisms for the presence and maintenance of these eddies. Using a high-resolution (~11 km) reduced gravity hydrodynamic layered model with controlled lateral boundary conditions at the three sides of the GA here we show yet another factor, the coastally propagating Kelvin waves along the coastal Arabia (coasts of Oman and Yemen), is also critically important in setting up a favourable condition for the oceanic instabilities and sustenance of meso-scale eddies in the GA. These Kelvin waves at both seasonal and intra-seasonal time scales are found play an important role in the timing and amplitudes of eddies observed in the GA.
The eddy kinetic energy budget in the Red Sea
Zhan, Peng; Subramanian, Aneesh C.; Yao, Fengchao; Kartadikaria, Aditya R.; Guo, Daquan; Hoteit, Ibrahim
2016-07-01
The budget of eddy kinetic energy (EKE) in the Red Sea, including the sources, redistributions, and sink, is examined using a high'resolution eddy-resolving ocean circulation model. A pronounced seasonally varying EKE is identified, with its maximum intensity occurring in winter, and the strongest EKE is captured mainly in the central and northern basins within the upper 200 m. Eddies acquire kinetic energy from conversion of eddy available potential energy (EPE), from transfer of mean kinetic energy (MKE), and from direct generation due to time-varying (turbulent) wind stress, the first of which contributes predominantly to the majority of the EKE. The EPE-to-EKE conversion occurs almost in the entire basin, while the MKE-to-EKE transfer appears mainly along the shelf boundary of the basin (200 m isobath) where high horizontal shear interacts with topography. The EKE generated by the turbulent wind stress is relatively small and limited to the southern basin. All these processes are intensified during winter, when the rate of energy conversion is about 4-5 times larger than that in summer. The EKE is redistributed by the vertical and horizontal divergence of energy flux and the advection of the mean flow. As a main sink of EKE, dissipation processes is ubiquitously found in the basin. The seasonal variability of these energy conversion terms can explain the significant seasonality of eddy activities in the Red Sea.
Event Detection and Visualization of Ocean Eddies based on SSH and Velocity Field
Matsuoka, Daisuke; Araki, Fumiaki; Inoue, Yumi; Sasaki, Hideharu
2016-04-01
Numerical studies of ocean eddies have been progressed using high-resolution ocean general circulation models. In order to understand ocean eddies from simulation results with large amount of information volume, it is necessary to visualize not only distribution of eddies of each time step, but also events or phenomena of eddies. However, previous methods cannot precisely detect eddies, especially, during the events such as eddies' amalgamation, bifurcation. In the present study, we propose a new approach of eddy's detection, tracking and event visualization based on sea surface height (SSH) and velocity field. The proposed method detects eddies region as well as streams and currents region, and classifies detected eddies into several types. By tracking the time-varying change of classified eddies, it is possible to detect not only eddies event such as amalgamation and bifurcation but also the interaction between eddy and ocean current. As a result of visualizing detected eddies and events, we succeeded in creating the movie which enables us to intuitively understand the region of interest.
Yu-Hsin Cheng
2014-06-01
Full Text Available The sea level anomaly data derived from satellite altimetry are analyzed to investigate statistical characteristics of mesoscale eddies in the North Pacific. Eddies are detected by a free-threshold eddy identification algorithm. The results show that the distributions of size, amplitude, propagation speed, and eddy kinetic energy of eddy follow the Rayleigh distribution. The most active regions of eddies are the Kuroshio Extension region, the Subtropical Counter Current zone, and the Northeastern Tropical Pacific region. By contrast, eddies are seldom observed around the center of the eastern part of the North Pacific Subarctic Gyre. The propagation speed and kinetic energy of cyclonic and anticyclonic eddies are almost the same, but anticyclonic eddies possess greater lifespans, sizes, and amplitudes than those of cyclonic eddies. Most eddies in the North Pacific propagate westward except in the Oyashio region. Around the northeastern tropical Pacific and the California currents, cyclonic and anticyclonic eddies propagate westward with slightly equatorward (197° average azimuth relative to east and poleward (165° deflection, respectively. This implies that the background current may play an important role in formation of the eddy pathway patterns.
Investigation on a new inducer of pulsed eddy current thermography
He, Min; Zhang, Laibin; Zheng, Wenpei; Feng, Yijing
2016-09-01
In this paper, a new inducer of pulsed eddy current thermography (PECT) is presented. The use of the inducer can help avoid the problem of blocking the infrared (IR) camera's view in eddy current thermography technique. The inducer can also provide even heating of the test specimen. This paper is concerned with the temperature distribution law around the crack on a specimen when utilizing the new inducer. Firstly, relative mathematical models are provided. In the following section, eddy current distribution and temperature distribution around the crack are studied using the numerical simulation method. The best separation distance between the inducer and the specimen is also determined. Then, results of temperature distribution around the crack stimulated by the inducer are gained by experiments. Effect of current value on temperature rise is studied as well in the experiments. Based on temperature data, temperature features of the crack are discussed.
Non-Destructive Techniques Based on Eddy Current Testing
García-Martín, Javier; Gómez-Gil, Jaime; Vázquez-Sánchez, Ernesto
2011-01-01
Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future. PMID:22163754
Large eddy simulation of water flow over series of dunes
Jun LU
2011-12-01
Full Text Available Large eddy simulation was used to investigate the spatial development of open channel flow over a series of dunes. The three-dimensional filtered Navier-Stokes (N-S equations were numerically solved with the fractional-step method in sigma coordinates. The subgrid-scale turbulent stress was modeled with a dynamic coherent eddy viscosity model proposed by the authors. The computed velocity profiles are in good agreement with the available experimental results. The mean velocity and the turbulent Reynolds stress affected by a series of dune-shaped structures were compared and analyzed. The variation of turbulence statistics along the flow direction affected by the wavy bottom roughness has been studied. The turbulent boundary layer in a complex geographic environment can be simulated well with the proposed large eddy simulation (LES model.
Investigation on a new inducer of pulsed eddy current thermography
Min He
2016-09-01
Full Text Available In this paper, a new inducer of pulsed eddy current thermography (PECT is presented. The use of the inducer can help avoid the problem of blocking the infrared (IR camera’s view in eddy current thermography technique. The inducer can also provide even heating of the test specimen. This paper is concerned with the temperature distribution law around the crack on a specimen when utilizing the new inducer. Firstly, relative mathematical models are provided. In the following section, eddy current distribution and temperature distribution around the crack are studied using the numerical simulation method. The best separation distance between the inducer and the specimen is also determined. Then, results of temperature distribution around the crack stimulated by the inducer are gained by experiments. Effect of current value on temperature rise is studied as well in the experiments. Based on temperature data, temperature features of the crack are discussed.
A Synoptic Snapshot of the East Cape Eddy (ECE)
LIU Wei; LIU Qinyu
2005-01-01
A synoptic snapshot in this study is made for the East Cape Eddy (ECE) based on the World Ocean Circulation Experiment (WOCE) P14C Hydrographic Section and Shipboard ADCP velocity vector data collected in September 1992.The ECE is an anticyclonic eddy, barotropically structured and centered at 33.64°S and 176.21°E, with warm and salinouscored subsurface water. The radius of the eddy is of the order O (110 km) and the maximum circumferential velocity is O(40cms-1); as a result, the relative vorticity is estimated to be O (7 × 10-6s-1). Due to the existence of the ECE, the mixed layer north of New Zealand becomes deeper, reaching a depth of 300 m in the austral winter. The ECE plays an important role in the formation and distribution of the Subtropical Mode Water (STMW) over a considerable area in the South Pacific.
Strong eddy compensation for the Gulf Stream heat transport
Saenko, Oleg A.
2015-12-01
Using a high-resolution ocean model forced with high-resolution atmospheric fields, a 5 year mean heat budget of the upper ocean in the Gulf Stream (GS) region is analyzed. The heat brought to the region with the mean flows along the GS path is 2-3 times larger than the heat loss to the atmosphere, with the difference being balanced by a strong cooling effect due to lateral eddy heat fluxes. However, over a broad area off the Grand Banks, the eddies warm the uppermost ocean layers, partly compensating for the loss of heat to the atmosphere. The upward eddy heat flux, which brings heat from the deeper ocean to the upper layers, is 30-80% of the surface heat loss.
Non-Destructive Techniques Based on Eddy Current Testing
Ernesto Vázquez-Sánchez
2011-02-01
Full Text Available Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.
Exact temporal eddy current compensation in magnetic resonance imaging systems.
Morich, M A; Lampman, D A; Dannels, W R; Goldie, F D
1988-01-01
A step-response method has been developed to extract the properties (amplitudes and decay time constants) of intrinsic-eddy-current-sourced magnetic fields generated in whole-body magnetic resonance imaging systems when pulsed field gradients are applied. Exact compensation for the eddy-current effect is achieved through a polynomial rooting procedure and matrix inversion once the 2 N properties of the N-term decay process are known. The output of the inversion procedure yields the required characteristics of the filter for spectrum magnitude and phase equalization. The method is described for the general case along with experimental results for one-, two-, and three-term inversions. The method's usefulness is demonstrated for the usually difficult case of long-term (200-1000-ms) eddy-current compensation. Field-gradient spectral flatness measurements over 30 mHz-100 Hz are given to validate the method.
Eddy current pulsed thermography for fatigue evaluation of gear
Tian, Gui Yun; Yin, Aijun; Gao, Bin; Zhang, Jishan; Shaw, Brian
2014-02-01
The pulsed eddy current (PEC) technique generates responses over a wide range of frequencies, containing more spectral coverage than traditional eddy current inspection. Eddy current pulsed thermography (ECPT), a newly developed non-destructive testing (NDT) technique, has advantages such as rapid inspection of a large area within a short time, high spatial resolution, high sensitivity and stand-off measurement distance. This paper investigates ECPT for the evaluation of gear fatigue tests. The paper proposes a statistical method based on single channel blind source separation to extract details of gear fatigue. The discussion of transient thermal distribution and patterns of fatigue contact surfaces as well as the non-contact surfaces have been reported. In addition, the measurement for gears with different cycles of fatigue tests by ECPTand the comparison results between ECPT with magnetic Barkhausen noise (MBN) have been evaluated. The comparison shows the competitive capability of ECPT in fatigue evaluation.
Non-destructive techniques based on eddy current testing.
García-Martín, Javier; Gómez-Gil, Jaime; Vázquez-Sánchez, Ernesto
2011-01-01
Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.
Stray Capacitances of an Air-Cored Eddy Current Sensor
Yi Jia
2009-12-01
Full Text Available Stray capacitance of an air-cored eddy current sensor is one of the most crucial issues for successful development of an eddy current based residual stress assessment technology at frequency above 50 MHz. A two dimensional finite element model and an equivalent lumped capacitance network have been developed to accurately quantify overall stray capacitances of an air-cored eddy current sensor with specimen being tested. A baseline model was used to evaluate sensor design parameters, including the effects of pitch distance, trace width, trace thickness, number of turns, inner diameter, substrate thickness, lift-off distance, and dielectric constant of shim on the stray capacitances of the sensor. The results clearly indicate that an appropriate sensor design parameters could reduce the stray capacitance and improve the sensor performance. This research opens up a new design space to minimize stray capacitance effect and improve the sensor sensitivity and its lift-off uncertainty at elevated high frequencies.
Eddies reduce denitrification and compress habitats in the Arabian Sea
Lachkar, Zouhair; Smith, Shafer; Lévy, Marina; Pauluis, Olivier
2016-09-01
The combination of high biological production and weak oceanic ventilation in regions, such as the northern Indian Ocean and the eastern Pacific and Atlantic, cause large-scale oxygen minimum zones (OMZs) that profoundly affect marine habitats and alter key biogeochemical cycles. Here we investigate the effects of eddies on the Arabian Sea OMZ—the world's thickest—using a suite of regional model simulations with increasing horizontal resolution. We find that isopycnal eddy transport of oxygen to the OMZ region limits the extent of suboxia so reducing denitrification, increasing the supply of nitrate to the surface, and thereby enhancing biological production. That same enhanced production generates more organic matter in the water column, amplifying oxygen consumption below the euphotic zone, thus increasing the extent of hypoxia. Eddy-driven ventilation likely plays a similar role in other low-oxygen regions and thus may be crucial in shaping marine habitats and modulating the large-scale marine nitrogen cycle.
Large-Eddy Simulation of Wind-Plant Aerodynamics: Preprint
Churchfield, M. J.; Lee, S.; Moriarty, P. J.; Martinez, L. A.; Leonardi, S.; Vijayakumar, G.; Brasseur, J. G.
2012-01-01
In this work, we present results of a large-eddy simulation of the 48 multi-megawatt turbines composing the Lillgrund wind plant. Turbulent inflow wind is created by performing an atmospheric boundary layer precursor simulation and turbines are modeled using a rotating, variable-speed actuator line representation. The motivation for this work is that few others have done wind plant large-eddy simulations with a substantial number of turbines, and the methods for carrying out the simulations are varied. We wish to draw upon the strengths of the existing simulations and our growing atmospheric large-eddy simulation capability to create a sound methodology for performing this type of simulation. We have used the OpenFOAM CFD toolbox to create our solver.
Eddy turbulence parameters inferred from radar observations at Jicamarca
M. N. Vlasov
2007-03-01
Full Text Available Significant electron density striations, neutral temperatures 27 K above nominal, and intense wind shear were observed in the E-region ionosphere over the Jicamarca Radio Observatory during an unusual event on 26 July 2005 (Hysell et al., 2007. In this paper, these results are used to estimate eddy turbulence parameters and their effects. Models for the thermal balance in the mesosphere/lower thermosphere and the charged particle density in the E region are developed here. The thermal balance model includes eddy conduction and viscous dissipation of turbulent energy as well as cooling by infrared radiation. The production and recombination of ions and electrons in the E region, together with the production and transport of nitric oxide, are included in the plasma density model. Good agreement between the model results and the experimental data is obtained for an eddy diffusion coefficient of about 1×10^{3} m^{2}/s at its peak, which occurs at an altitude of 107 km. This eddy turbulence results in a local maximum of the temperature in the upper mesosphere/lower thermosphere and could correspond either to an unusually high mesopause or to a double mesosphere. Although complicated by plasma dynamic effects and ongoing controversy, our interpretation of Farley-Buneman wave phase velocity (Hysell et al., 2007 is consistent with a low Brunt-Väisälä frequency in the region of interest. Nitric oxide transport due to eddy diffusion from the lower thermosphere to the mesosphere causes electron density changes in the E region whereas NO density modulation due to irregularities in the eddy diffusion coefficient creates variability in the electron density.
Observation of baroclinic eddies southeast of Okinawa Island
PARK; Jae-Hun
2008-01-01
In the region southeast of Okinawa, during May to July 2001, a cyclonic and an anticyclonic eddy were observed from combined measurements of hydrocasts, an upward-looking moored acoustic Doppler current profiler (MADCP), pressure-recording inverted echo sounders (PIESs), satellite altimetry, and a coastal tide gauge. The hydrographic data showed that the lowest/highest temperature (T) and salinity (S) anomalies from a 13-year mean for the same season were respectively -3.0/+2.5℃ and -0.20/+0.15 psu at 380/500 dbar for the cyclonic/anticyclonic eddies. From the PIES data, using a gravest empirical mode method, we estimated time-varying surface dynamic height (D) anomaly referred to 2000 dbar changing from -20 to 30 cm, and time-varying T and S anomalies at 500 dbar ranging through about ±2 ℃ and ±0.2 psu, respectively. The passage of the eddies caused variations of both satellite-measured sea surface height anomaly (SSHA) and tide-gauge-measured sea level anomaly to change from about –20 to 30 cm, consistent with the D anomaly from the PIESs. Bottom pressure sensors measured no variation related to these eddy activities, which indicated that the two eddies were dominated by baro-clinicity. Time series of SSHA map confirmed that the two eddies, originating from the North Pacific Subtropical Countercurrent region near 20°―30°N and 150°―160°E, traveled about 3000 km for about 18 months with mean westward propagation speed of about 6 cm/s, before arriving at the region southeast of Okinawa Island.
An eddy viscosity calculation method for a turbulent duct flow
Antonia, R. A.; Bisset, D. K.; Kim, J.
1991-01-01
The mean velocity profile across a fully developed turbulent duct flow is obtained from an eddy viscosity relation combined with an empirical outer region wake function. Results are in good agreement with experiments and with direct numerical simulations in the same flow at two Reynolds numbers. In particular, the near-wall trend of the Reynolds shear stress and its variation with Reynolds number are similar to those of the simulations. The eddy viscosity method is more accurate than previous mixing length or implicit function methods.
Eddy current NDE performance demonstrations using simulation tools
Maurice, L. [EDF - CEIDRE, 2 rue Ampere, 93206 Saint-Denis Cedex 1 (France); Costan, V.; Guillot, E.; Thomas, P. [EDF - R and D, THEMIS, 1, avenue du General de Gaulle, 92141 Clamart (France)
2013-01-25
To carry out performance demonstrations of the Eddy-Current NDE processes applied on French nuclear power plants, EDF studies the possibility of using simulation tools as an alternative to measurements on steam generator tube mocks-up. This paper focuses on the strategy led by EDF to assess and use code{sub C}armel3D and Civa, on the case of Eddy-Current NDE on wears problem which may appear in the U-shape region of steam generator tubes due to the rubbing of anti-vibration bars.
Large—eddy Simulation of Bubble—Liquid Confined Jets
YANGMin; ZHOULixing
2002-01-01
The Large-eddy simulation (LES) with two-way coupling is used to study bubble-liquid two-phase confined multiple jets discharged into a 2D channel.The LES results reveal the large-eddy vortex structures of both liquid flow and bubble motion,the shear-generated and bubble-induced liquid turbulence,and indicate much stronger bubble fluctuation than that of the liquid,the enhancement of liquid turbulence by bubbles.Both shear and bubble-liquid interaction are important for the liquid turbulence generation in the case studied.
PHREATOPHYTE WATER USE ESTIMATED BY EDDY-CORRELATION METHODS.
Weaver, H.L.; Weeks, E.P.; Campbell, G.S.; Stannard, D.I.; Tanner, B.D.
1986-01-01
Water-use was estimated for three phreatophyte communities: a saltcedar community and an alkali-Sacaton grass community in New Mexico, and a greasewood rabbit-brush-saltgrass community in Colorado. These water-use estimates were calculated from eddy-correlation measurements using three different analyses, since the direct eddy-correlation measurements did not satisfy a surface energy balance. The analysis that seems to be most accurate indicated the saltcedar community used from 58 to 87 cm (23 to 34 in. ) of water each year. The other two communities used about two-thirds this quantity.
Parameter identification of internal wave and mesoscale eddy
无
2003-01-01
A simplified parameter identification algorithm for the inverse refractive indexes of the mesoscale eddy and the internal wave in the ocean is proposed by researching into the incident field and the scattered field that comprise the total field of a wave in the ocean, considering that the total field and the incident field satisfy the Helmholtz equations and the scattered field conforms to the Sommerfield radiation condition. Two examples for the calculation of refractive index and inverse refractive index respectively of the mesoscale eddy and the internal wave demonstrate the applicability of the algorithm.
Large Eddy Simulation of the ventilated wave boundary layer
Lohmann, Iris P.; Fredsøe, Jørgen; Sumer, B. Mutlu
2006-01-01
A Large Eddy Simulation (LES) of (1) a fully developed turbulent wave boundary layer and (2) case 1 subject to ventilation (i.e., suction and injection varying alternately in phase) has been performed, using the Smagorinsky subgrid-scale model to express the subgrid viscosity. The model was found...... size. The results indicate that the large eddies develop in the resolved scale, corresponding to fluid with an effective viscosity decided by the sum of the kinematic and subgrid viscosity. Regarding case 2, the results are qualitatively in accordance with experimental findings. Injection generally...... significantly. Ventilation therefore results in a net current, even in symmetric waves....
Defect detection in conducting materials using eddy current testing techniques
Brauer Hartmut
2014-01-01
Full Text Available Lorentz force eddy current testing (LET is a novel nondestructive testing technique which can be applied preferably to the identification of internal defects in nonmagnetic moving conductors. The LET is compared (similar testing conditions with the classical eddy current testing (ECT. Numerical FEM simulations have been performed to analyze the measurements as well as the identification of internal defects in nonmagnetic conductors. The results are compared with measurements to test the feasibility of defect identification. Finally, the use of LET measurements to estimate of the electrical conductors under test are described as well.
Estimating surface fluxes using eddy covariance and numerical ogive optimization
Sievers, J.; Papakyriakou, T.; Larsen, Søren Ejling;
2015-01-01
Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low-frequency con......Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low...
RECENT PROGRESS IN NONLINEAR EDDY-VISCOSITY TURBULENCE MODELING
符松; 郭阳; 钱炜祺; 王辰
2003-01-01
This article presents recent progresses in turbulence modeling in the Unit for Turbulence Simulation in the Department of Engineering Mechanics at Tsinghua University. The main contents include: compact Non-Linear Eddy-Viscosity Model (NLEVM) based on the second-moment closure, near-wall low-Re non-linear eddy-viscosity model and curvature sensitive turbulence model.The models have been validated in a wide range of complex flow test cases and the calculated results show that the present models exhibited overall good performance.
Cinlar Subgrid Scale Model for Large Eddy Simulation
Kara, Rukiye
2016-01-01
We construct a new subgrid scale (SGS) stress model for representing the small scale effects in large eddy simulation (LES) of incompressible flows. We use the covariance tensor for representing the Reynolds stress and include Clark's model for the cross stress. The Reynolds stress is obtained analytically from Cinlar random velocity field, which is based on vortex structures observed in the ocean at the subgrid scale. The validity of the model is tested with turbulent channel flow computed in OpenFOAM. It is compared with the most frequently used Smagorinsky and one-equation eddy SGS models through DNS data.
Large-Eddy Simulations of Tropical Convective Systems, the Boundary Layer, and Upper Ocean Coupling
2014-09-30
1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Large - Eddy Simulations of Tropical Convective Systems... large eddy simulation (LES) of organized convective systems, which resolve boundary layer eddy scales to mesoscale Report Documentation Page Form...COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE Large - Eddy Simulations of Tropical Convective Systems, the Boundary Layer, and Upper Ocean
Observed and modeled surface eddy heat fluxes in the eastern Nordic Seas
Isachsen, P.E. .; Koszalka, Inga Monika; LaCasce, J. H.
2012-01-01
Large-scale budget calculations and numerical model process studies suggest that lateral eddy heat fluxes have an important cooling effect on the Norwegian Atlantic Current (NwAC) as it flows through the Nordic Seas. But observational estimates of such fluxes have been lacking. Here, wintertime surface eddy heat fluxes in the eastern Nordic Seas are estimated from surface drifter data, satellite data and an eddy-permitting numerical model. Maps of the eddy heat flux divergence suggest advecti...
Nondestructive Testing Eddy Current Basic Principles RQA/M1-5330.12 (V-I).
National Aeronautics and Space Administration, Huntsville, AL. George C. Marshall Space Flight Center.
As one in the series of programmed instruction handbooks, prepared by the U.S. space program, home study material is presented in this volume concerning familiarization and orientation on basic eddy current principles. The subject is presented under the following headings: Basic Eddy Current Concepts, Eddy Current Generation and Distribution,…
Magnetic Flux Fluctuations Due to Eddy Currents and Thermal Noise in Metallic Disks
Uzunbajakau, S.; Rijpma, A.P.; Dolfsma, J.; Krooshoop, H.J.G.; Brake, ter H.J.M.; Peters, M.J.; Rogalla, H.
2003-01-01
We derive expressions for the magnetic flux in a circular loop due to eddy currents and thermal noise in coaxial metallic disks. The eddy currents are induced by an applied field that changes sinusoidally in time. We give expressions for the eddy current noise when the frequency of the applied field
Magnetic Flux Fluctuations Due to Eddy Currents and Thermal Noise in Metallic Disks
Uzunbajakau, S.; Rijpma, A.P.; Dolfsma, J.; Krooshoop, Hendrikus J.G.; ter Brake, Hermanus J.M.; Peters, M.J.; Rogalla, Horst
2003-01-01
We derive expressions for the magnetic flux in a circular loop due to eddy currents and thermal noise in coaxial metallic disks. The eddy currents are induced by an applied field that changes sinusoidally in time. We give expressions for the eddy current noise when the frequency of the applied field
Detection of Bay of Bengal eddies from TOPEX and insitu observations
Ali, M.M.; Sharma, R.; Gopalakrishna, V.V.
anticyclonic eddy is located around 13 degrees N and 83 degrees E from the TOPEX observations averaged over 10-19 August 1993. The thermal sections pass through the southern periphery of the eddy with a prominent trough over the eddy region. The crest noticed...
PrasannaKumar, S.; Navelkar, G.S.; Murty, T.V.R.; Murty, C.S.
by about 100-200 ms under the influence of eddy. The intensity computations show that when the ray passes through the eddy, it suffers an additional loss of 20-25 dB. From the simulated travel time delays, the eddy profile is reconstructed through...
SIMULATION OF EDDIES AFFECTED BY TOPOGRAPHY IN A BAROTROPICAL QUASI-GEOSTROPHIC FLUID
无
2001-01-01
Based upon the quasi-geostrophic barotropic equation, taking into account the effect of seabed topography, analytical solutions and simulated eddies associated with different topographies are obtained. Through exhibiting the shape of various eddies we have found some interesting phenomena and had a better understanding of the importance of seabed topography to the eddy shape.
Eddy correlation measurements of oxygen uptake in deep ocean sediments
Berg, P.; Glud, Ronnie Nøhr; Hume, A.
2010-01-01
Abstract: We present and compare small sediment-water fluxes of O-2 determined with the eddy correlation technique, with in situ chambers, and from vertical sediment microprofiles at a 1450 m deep-ocean site in Sagami Bay, Japan. The average O-2 uptake for the three approaches, respectively, was ...
76 FR 59394 - Big Eddy-Knight Transmission Project
2011-09-26
... and ancillary facilities between BPA's existing Big Eddy Substation in The Dalles, Oregon, to a proposed new Knight Substation that would be connected to an existing BPA line about 4 miles northwest of... Oregon side of the Columbia River, as described in the final EIS. For the proposed new Knight Substation...
When Does Eddy Viscosity Damp Subfilter Scales Sufficiently?
Verstappen, Roel
2011-01-01
Large eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. The very essence is that the LES-solution contains only scales of size >=Delta, where Delta denotes some user-chosen length scale. This property enables us to perform a LES when it is not feasible to com
Large Eddy Simulations of an Airfoil in Turbulent Inflow
Gilling, Lasse; Sørensen, Niels
2008-01-01
Wind turbines operate in the turbulent boundary layer of the atmosphere and due to the rotational sampling effect the blades experience a high level of turbulence [1]. In this project the effect of turbulence is investigated by large eddy simulations of the turbulent flow past a NACA 0015 airfoil...
When Does Eddy Viscosity Damp Subfilter Scales Sufficiently?
Verstappen, Roel
2011-01-01
Large eddy simulation (LES) seeks to predict the dynamics of spatially filtered turbulent flows. The very essence is that the LES-solution contains only scales of size ≥Δ, where Δ denotes some user-chosen length scale. This property enables us to perform a LES when it is not feasible to compute the
NASA's Large-Eddy Simulation Research for Jet Noise Applications
DeBonis, James R.
2009-01-01
Research into large-eddy simulation (LES) for application to jet noise is described. The LES efforts include in-house code development and application at NASA Glenn along with NASA Research Announcement sponsored work at Stanford University and Florida State University. Details of the computational methods used and sample results for jet flows are provided.
Aero-acoustic modeling using large eddy simulation
Shen, Wen Zhong; Sørensen, Jens Nørkær
2007-01-01
The splitting technique for aero-acoustic computations is extended to simulate three-dimensional flow and acoustic waves from airfoils. The aero-acoustic model is coupled to a sub-grid-scale turbulence model for Large-Eddy Simulations. In the first test case, the model is applied to compute laminar...
Mind the gap: a guideline for large eddy simulation.
George, William K; Tutkun, Murat
2009-07-28
This paper briefly reviews some of the fundamental ideas of turbulence as they relate to large eddy simulation (LES). Of special interest is how our thinking about the so-called 'spectral gap' has evolved over the past decade, and what this evolution implies for LES applications.
Analysis of inadvertent microprocessor lag time on eddy covariance results
Karl Zeller; Gary Zimmerman; Ted Hehn; Evgeny Donev; Diane Denny; Jeff Welker
2001-01-01
Researchers using the eddy covariance approach to measuring trace gas fluxes are often hoping to measure carbon dioxide and energy fluxes for ecosystem intercomparisons. This paper demonstrates a systematic microprocessor- caused lag of 20.1 to 20.2 s in a commercial sonic anemometer-analog-to-digital datapacker system operated at 10 Hz. The result of the inadvertent...
Detached Eddy Simulations of an Airfoil in Turbulent Inflow
Gilling, Lasse; Sørensen, Niels; Davidson, Lars
2009-01-01
The effect of resolving inflow turbulence in detached eddy simulations of airfoil flows is studied. Synthetic turbulence is used for inflow boundary condition. The generated turbulence fields are shown to decay according to experimental data as they are convected through the domain with the free ...
Eddie Murphy grimmile kulus üheksa kuud / Triin Tael
Tael, Triin
2007-01-01
Uues USA komöödiafilmis "Norbit" (režissöör Brian Robbins, stsenarist näitleja vend Charles Murphy) mängib Eddie Murphy kolme täiesti erinevat rolli. Seejuures aitas teda grimmikunstnik Rick Baker
Eddie Murphy grimmile kulus üheksa kuud / Triin Tael
Tael, Triin
2007-01-01
Uues USA komöödiafilmis "Norbit" (režissöör Brian Robbins, stsenarist näitleja vend Charles Murphy) mängib Eddie Murphy kolme täiesti erinevat rolli. Seejuures aitas teda grimmikunstnik Rick Baker
Physical interpretation and separation of eddy current pulsed thermography
Yin, Aijun; Gao, Bin; Yun Tian, Gui; Woo, W. L.; Li, Kongjing
2013-02-01
Eddy current pulsed thermography (ECPT) applies induction heating and a thermal camera for non-destructive testing and evaluation (NDT&E). Because of the variation in resultant surface heat distribution, the physical mechanism that corresponds to the general behavior of ECPT can be divided into an accumulation of Joule heating via eddy current and heat diffusion. However, throughout the literature, the heating mechanisms of ECPT are not given in detail in the above two thermal phenomena and they are difficult to be separated. Nevertheless, once these two physical parameters are separated, they can be directly used to detect anomalies and predict the variation in material properties such as electrical conductivity, magnetic permeability and microstructure. This paper reports physical interpretation of these two physical phenomena that can be found in different time responses given the ECPT image sequences. Based on the phenomenon and their behaviors, the paper proposes a statistical method based on single channel blind source separation to decompose the two physical phenomena using different stages of eddy current and thermal propagation from the ECPT images. Links between mathematical models and physical models have been discussed and verified. This fundamental understanding of transient eddy current distribution and heating propagation can be applied to the development of feature extraction and pattern recognition for the quantitative analysis of ECPT measurement images and defect characterization.
Distant Influence of Kuroshio Eddies on North Pacific Weather Patterns?
Ma, Xiaohui; Chang, Ping; Saravanan, R.; Montuoro, Raffaele; Hsieh, Jen-Shan; Wu, Dexing; Lin, Xiaopei; Wu, Lixin; Jing, Zhao
2015-12-01
High-resolution satellite measurements of surface winds and sea-surface temperature (SST) reveal strong coupling between meso-scale ocean eddies and near-surface atmospheric flow over eddy-rich oceanic regions, such as the Kuroshio and Gulf Stream, highlighting the importance of meso-scale oceanic features in forcing the atmospheric planetary boundary layer (PBL). Here, we present high-resolution regional climate modeling results, supported by observational analyses, demonstrating that meso-scale SST variability, largely confined in the Kuroshio-Oyashio confluence region (KOCR), can further exert a significant distant influence on winter rainfall variability along the U.S. Northern Pacific coast. The presence of meso-scale SST anomalies enhances the diabatic conversion of latent heat energy to transient eddy energy, intensifying winter cyclogenesis via moist baroclinic instability, which in turn leads to an equivalent barotropic downstream anticyclone anomaly with reduced rainfall. The finding points to the potential of improving forecasts of extratropical winter cyclones and storm systems and projections of their response to future climate change, which are known to have major social and economic impacts, by improving the representation of ocean eddy-atmosphere interaction in forecast and climate models.
Large Eddy Simulation of Sydney Swirl Non-Reaction Jets
Yang, Yang; Kær, Søren Knudsen; Yin, Chungen
The Sydney swirl burner non-reaction case was studied using large eddy simulation. The two-point correlation method was introduced and used to estimate grid resolution. Energy spectra and instantaneous pressure and velocity plots were used to identify features in flow field. By using these method...
Ekman Spiral in Horizontally Inhomogeneous Ocean with Varying Eddy Viscosity
2015-01-01
1 Ekman Spiral in Horizontally Inhomogeneous Ocean with Varying Eddy Viscosity...Oceanography Naval Postgraduate School, Monterey, California, USA Manuscript Click here to download Manuscript: Ekman -chu-pageoph-rev.docx 1...currently valid OMB control number. 1. REPORT DATE 2015 2. REPORT TYPE 3. DATES COVERED 00-00-2015 to 00-00-2015 4. TITLE AND SUBTITLE Ekman Spiral
Subminiature eddy current transducers for studying boride coatings
Dmitriev, S. F.; Ishkov, A. V.; Malikov, V. N.; Sagalakov, A. M.
2016-07-01
Strengthening of parts and units of machines, increased reliability and longer service life is an important task of modern mechanical engineering. The main objects of study in the work were selected steel 65G and 50HGA, wear-resistant boride coatings ternary system Fe-B-Fe n B which were investigated by scanning electron microscopy and eddy-current nondestructive methods.
The influence of mesoscale eddies on shallow water acoustic propagation
Deferrari, Harry; Olson, Donald
2003-10-01
Acoustic propagation measurements in 150 m depth on the Florida escarpment observe the effects of the passage of a cyclonic eddy. As the stream core of the Florida Current meanders, the eddy is formed and propagates along the shelf edge. The sequence over a roughly a fortnight is as follows: ahead of the eddy, warm surface water and cold bottom water are swept onto the terrace forming a steep thermocline and corresponding strong downward refracting C(z). The gradient produce intense, focused RBR arrivals and the thermocline becomes a duct for internal waves to propagate shoreward. At first, the internal wave energy is minimal and propagation is stable and coherent. As the internal tides attempt to propagate on shelf, the sound speed field and the acoustic signals become increasingly variable. The variability reaches a crescendo as the 200 m long internal tide is blocked from propagating on to the narrower shelf and begins to break and overturn producing small-scale variability. As the eddy passes, nearly iso-thermal conditions are restored along with quiescent internal wave fields and reduced signal variability. Here, the effects are quantized with data from fixed-system acoustic and oceanographic measurements demonstrating that the mesoscale determines acoustic propagation conditions days in advance.
A Laboratory Activity on the Eddy Current Brake
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…
Grade and Recovery Prediction for Eddy Current Separation Processes
Rem, P.C.; Beunder, E.M.; Kuilman, W.
1998-01-01
Grade and recovery of eddy current separation can be estimated on the basis of trajectory simulations for particles of simple shapes. In order to do so, the feed is characterized in terms of a small set of test-particles, each test-particle representing a fraction of the feed of a given size, shape
A Novel Interface for Eddy Current Displacement Sensors
Nabavi, M.R.; Nihtianov, S.
2009-01-01
In this paper, we propose a novel interface concept for eddy current displacement sensors. A measurement method and a new front-end circuit are also proposed. The front-end circuit demonstrates excellent thermal stability, high resolution, and low-power consumption. The proposed idea is analytically
Eddy covariance based methane flux in Sundarbans mangroves, India
Chandra Shekhar Jha; Suraj Reddy Rodda; Kiran Chand Thumaty; A K Raha; V K Dadhwal
2014-07-01
We report the initial results of the methane flux measured using eddy covariance method during summer months from the world’s largest mangrove ecosystem, Sundarbans of India. Mangrove ecosystems are known sources for methane (CH4) having very high global warming potential. In order to quantify the methane flux in mangroves, an eddy covariance flux tower was recently erected in the largest unpolluted and undisturbed mangrove ecosystem in Sundarbans (India). The tower is equipped with eddy covariance flux tower instruments to continuously measure methane fluxes besides the mass and energy fluxes. This paper presents the preliminary results of methane flux variations during summer months (i.e., April and May 2012) in Sundarbans mangrove ecosystem. The mean concentrations of CH4 emission over the study period was 1682 ± 956 ppb. The measured CH4 fluxes computed from eddy covariance technique showed that the study area acts as a net source for CH4 with daily mean flux of 150.22 ± 248.87 mg m−2 day−1. The methane emission as well as its flux showed very high variability diurnally. Though the environmental conditions controlling methane emission is not yet fully understood, an attempt has been made in the present study to analyse the relationships of methane efflux with tidal activity. This present study is part of Indian Space Research Organisation–Geosphere Biosphere Program (ISRO–GBP) initiative under ‘National Carbon Project’.
A study of eddy current measurement (1986-1987)
Ramachandran, R.S.; Armstrong, K.P.
1989-06-22
A study was conducted in 1986 to evaluate a modified eddy current system for measuring copper thickness on Kapton. Results showed a measurement error of 0.42 {mu}in. for a thickness range of 165 to 170 {mu}in. and a measurement variability of 3.2 {mu}in.
Probability of detection models for eddy current NDE methods
Rajesh, S.N.
1993-04-30
The development of probability of detection (POD) models for a variety of nondestructive evaluation (NDE) methods is motivated by a desire to quantify the variability introduced during the process of testing. Sources of variability involved in eddy current methods of NDE include those caused by variations in liftoff, material properties, probe canting angle, scan format, surface roughness and measurement noise. This thesis presents a comprehensive POD model for eddy current NDE. Eddy current methods of nondestructive testing are used widely in industry to inspect a variety of nonferromagnetic and ferromagnetic materials. The development of a comprehensive POD model is therefore of significant importance. The model incorporates several sources of variability characterized by a multivariate Gaussian distribution and employs finite element analysis to predict the signal distribution. The method of mixtures is then used for estimating optimal threshold values. The research demonstrates the use of a finite element model within a probabilistic framework to the spread in the measured signal for eddy current nondestructive methods. Using the signal distributions for various flaw sizes the POD curves for varying defect parameters have been computed. In contrast to experimental POD models, the cost of generating such curves is very low and complex defect shapes can be handled very easily. The results are also operator independent.
Video Analysis of Eddy Structures from Explosive Volcanic Eruptions
Fisher, M. A.; Kobs-Nawotniak, S. E.
2013-12-01
We present a method of analyzing turbulent eddy structures in explosive volcanic eruptions using high definition video. Film from the eruption of Sakurajima on 25 September 2011 was analyzed using a modified version of FlowJ, a Java-based toolbox released by National Institute of Health. Using the Lucas and Kanade algorithm with a Gaussian derivative gradient, it tracks the change in pixel position over a 23 image buffer to determine the optical flow. This technique assumes that the optical flow, which is the apparent motion of the pixels, is equivalent to the actual flow field. We calculated three flow fields per second for the duration of the video. FlowJ outputs flow fields in pixels per frame that were then converted to meters per second in Matlab using a known distance and video rate. We constructed a low pass filter using proper orthogonal decomposition (POD) and critical point analysis to identify the underlying eddy structure with boundaries determined by tracing the flow lines. We calculated the area of each eddy and noted its position over a series of velocity fields. The changes in shape and position were tracked to determine the eddy growth rate and overall eddy rising velocity. The eddies grow in size 1.5 times quicker than they rise vertically. Presently, this method is most successful in high contrast videos when there is little to no effect of wind on the plumes. Additionally, the pixel movement from the video images represents a 2D flow with no depth, while the actual flow is three dimensional; we are continuing to develop an algorithm that will allow 3D reprojection of the 2D data. Flow in the y-direction lessens the overall velocity magnitude as the true flow motion has larger y-direction component. POD, which only uses the pattern of the flow, and analysis of the critical points (points where flow is zero) is used to determine the shape of the eddies. The method allows for video recorded at remote distances to be used to study eruption dynamics
GEM: a dynamic tracking model for mesoscale eddies in the ocean
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.
Instantaneous Wavelet Energetic Transfers between Atmospheric Blocking and Local Eddies.
Fournier, Aimé
2005-07-01
A new wavelet energetics technique, based on best-shift orthonormal wavelet analysis (OWA) of an instantaneous synoptic map, is constructed for diagnosing nonlinear kinetic energy (KE) transfers in five observed blocking cases. At least 90% of the longitudinal variance of time and latitude band mean 50-kPa geopotential is reconstructed by only two wavelets using best shift. This superior efficiency to the standard OWAs persists for time-evolving structures. The cases comprise two categories, respectively dominated by zonal-wavenumber sets {1} and {1, 2}. Further OWA of instantaneous residual nonblocking structures, combined with new “nearness” criteria, yields three more orthogonal components, representing smaller-scale eddies near the block (upstream and downstream) and distant structures. This decomposition fulfills a vision expressed to the author by Saltzman. Such a decomposition is not obtainable by simple Fourier analysis.Eddy patterns apparent in the components' contours suggest inferring geostrophic energetic interactions, but the component Rossby numbers may be too large to support the inference. However, a new result enabled by this method is the instantaneous attribution of blocking strain-field effects to particular energetically interactive eddies, consistent with Shutts' hypothesis. Such attribution was only possible before in simplified models or in a time-average sense. In four of five blocks, the upstream eddies feed KE to the block, which in turn, in three of four cases, transmits KE to the downstream eddies. The small case size precludes statistically significant conclusions. The appendixes link low-order blocking structure and dynamics to some wavelet design principles and propose a new interaction diagnosis, similar to E-vector analysis, but instantaneous.
Sea Surface Height Variability and Eddy Statistical Properties in the Red Sea
Zhan, Peng
2013-05-01
Satellite sea surface height (SSH) data over 1992-2012 are analyzed to study the spatial and temporal variability of sea level in the Red Sea. Empirical orthogonal functions (EOF) analysis suggests the remarkable seasonality of SSH in the Red Sea, and a significant correlation is found between SSH variation and seasonal wind cycle. A winding-angle based eddy identification algorithm is employed to derive the mesoscale eddy information from SSH data. Totally more than 5500 eddies are detected, belonging to 2583 eddy tracks. Statistics suggest that eddies generate over the entire Red Sea, with two regions in the central basin of high eddy frequency. 76% of the detected eddies have a radius ranging from 40km to 100km, of which both intensity and absolute vorticity decrease with eddy radius. The average eddy lifespan is about 5 weeks, and eddies with longer lifespan tend to have larger radius but less intensity. Different deformation rate exists between anticyclonic eddies (AEs) and cyclonic eddies (CEs), those eddies with higher intensity appear to be less deformed and more circular. Inspection of the 84 long-lived eddies suggests the AEs tend to move a little more northward than CEs. AE generation during summer is obviously lower than that during other seasons, while CE generation is higher during spring and summer. Other features of AEs and CEs are similar with both vorticity and intensity reaching the summer peaks in August and winter peaks in January. Inter-annual variability reveals that the eddies in the Red Sea are isolated from the global event. The eddy property tendencies are different from the south and north basin, both of which exhibit a two-year cycle. Showing a correlation coefficient of -0.91, Brunt–Väisälä frequency is negatively correlated with eddy kinetic energy (EKE), which results from AE activities in the high eddy frequency region. Climatological vertical velocity shear variation is identical with EKE except in the autumn, suggesting the
McGloin, Ryan; McGowan, Hamish; McJannet, David
2014-01-01
Accurate quantification of evaporation from small water storages is essential for water management and planning, particularly in water-scarce regions. In order to ascertain suitable methods for direct measurement of evaporation from small water bodies, this study presents a comparison of eddy......% greater than eddy covariance measurements. We suggest possible reasons for this difference and provide recommendations for further research for improving measurements of surface energy fluxes over small water bodies using eddy covariance and scintillometry. Key Points Source areas for Eddy covariance...... and scintillometry were on the water surface Reasonable agreement was shown between the sensible heat flux measurements Scintillometer estimates of latent heat flux were greater than eddy covariance...
Permanent Magnet Eddy Current Loss Analysis of a Novel Motor Integrated Permanent Magnet Gear
Zhang, Yuqiu; Lu, Kaiyuan; Ye, Yunyue
2012-01-01
In this paper, a new motor integrated permanent magnet gear (MIPMG) is discussed. The focus is on eddy current loss analysis associated to permanent magnets (PMs). A convenient model of MIPMG is provided based on 2-D field-motion coupled time-stepping finite element method for transient eddy...... current analysis. The model takes the eddy current effect of PMs into account in determination of the magnetic field in the air-gap and in the magnet regions. The eddy current losses generated in the magnets are properly interpreted. Design improvements for reducing the eddy current losses are suggested...
Eddy current heating of irregularly shaped plates by slow ramped fields
Dresner, L.
1979-09-01
Eddy current heating of thin conducting plates of various shapes by a perpendicular field is studied, assuming that the magnetic field created by the eddy currents is negligible in comparison with the external field. The method is to introduce the stream function of the eddy currents, which is shown to satisfy Poisson's equation, and then employ a pair of complementary variational principles (i.e., a minimum principle and a maximum principle), the extrema of which equal the eddy current heating. Two such complementary principles give not only an estimate of the eddy current heating, but a bound on the error of the estimate as well.
Rem, P.C.; Bakker, M.C.M.; Berkhout, S.P.M.; Rahman, M.A.
2012-01-01
Eddy current separation apparatus (1) for separating particles (20) from a particle stream (w), wherein the apparatus (1) comprises a separator drum (4) adapted to create a first particle fraction (21) and a second particle fraction (23), a feeding device (2) upstream of the separator drum (4) for s
Response of the Kuroshio Current to Eddies in the Luzon Strait
ZHAO Jie; LUO De-Hai
2010-01-01
The impact of eddies on the Kuroshio Current in the Luzon Strait(LS)area is investigated by using the sea surface height anomaly(SSHA)satellite observation data and the sea surface height(SSH)assimilation data.The influence of the eddies on the mean current depends upon the type of eddies and their relative position.The mean current is enhanced(weakened)as the cyclonic(anticyclonic)eddy becomes slightly far from it,whereas it is weakened(enhanced)as the cyclonic(anticyclonic)eddy moves near or within the position of the mean current;this is explained as the eddy-induced meridional velocity and geostrophic flow relationship.The anticyclonic(cyclonic)eddy can increase(decrease)the mean meridional flow due to superimposition of the eddy-induced meridional flow when the eddy is within the region of the mean current.However,when the eddy is slightly far from the mean current region,the anticyclonic(cyclonic)eddy tends to decrease(increase)the zonal gradient of the SSH,which thus results in weakening(strengthening)of the mean current in the LS region.
Coupling between SST and wind speed over mesoscale eddies in the South China Sea
Sun, Shuangwen; Fang, Yue; Liu, Baochao; ᅟ, Tana
2016-11-01
The coupling between sea surface temperature (SST) and sea surface wind speed over mesoscale eddies in the South China Sea (SCS) was studied using satellite measurements. Positive correlations between SST anomalies (SSTA) and wind speed anomalies were found over both cyclonic and anticyclonic eddies. In contrast to the open oceans, the spatial patterns of the coupling over mesoscale eddies in the SCS depend largely on the seasonal variations of the background SST gradient, wind speed, and wind directional steadiness. In summer, the maximum SSTA location coincides with the center of eddy-induced sea surface height anomalies. In winter, the eddy-induced SSTA show a clear dipole pattern. The spatial patterns of wind speed anomalies over eddies are similar to those of the SSTA in both seasons. Wind speed anomalies are linearly correlated with SSTA over anticyclonic and cyclonic eddies. The coupling coefficients between SSTA and wind speed anomalies in the SCS are comparable to those in the open oceans.
Finite element analysis of gradient z-coil induced eddy currents in a permanent MRI magnet.
Li, Xia; Xia, Ling; Chen, Wufan; Liu, Feng; Crozier, Stuart; Xie, Dexin
2011-01-01
In permanent magnetic resonance imaging (MRI) systems, pulsed gradient fields induce strong eddy currents in the conducting structures of the magnet body. The gradient field for image encoding is perturbed by these eddy currents leading to MR image distortions. This paper presents a comprehensive finite element (FE) analysis of the eddy current generation in the magnet conductors. In the proposed FE model, the hysteretic characteristics of ferromagnetic materials are considered and a scalar Preisach hysteresis model is employed. The developed FE model was applied to study gradient z-coil induced eddy currents in a 0.5 T permanent MRI device. The simulation results demonstrate that the approach could be effectively used to investigate eddy current problems involving ferromagnetic materials. With the knowledge gained from this eddy current model, our next step is to design a passive magnet structure and active gradient coils to reduce the eddy current effects.
Spatial information recognizing of ocean eddies based on virtual force field and its application
LI Ce; DU Yunyan; SU Fenzhen; YANG Xiaomei; XU Jun
2007-01-01
A new approach to detecting ocean eddies automatically from remote sensing imageries based on the ocean eddy's eigen-pattern in remote sensing imagery and "force field-based shape extracting method" is proposed. First, the analysis on extracting eddies' edges from remote sensing imagery using conventional edge detection arithmetic operators is performed and returns digitized vector edge data as a result. Second, attraction forces and fusion forces between edge curves were analyzed and calculated based on the vector eddy edges. Thirdly, the virtual significant spatial patterns of eddy were detected automatically using iterative repetition followed by optimized rule. Finally, the spatial form auto-detection of different types of ocean eddies was done using satellite images.The study verified that this is an effective way to identify and detect the ocean eddy with a complex form.
Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean
Schütte, Florian; Brandt, Peter; Karstensen, Johannes
2016-05-01
Coherent mesoscale features (referred to here as eddies) in the tropical northeastern Atlantic Ocean (between 12-22° N and 15-26° W) are examined and characterized. The eddies' surface signatures are investigated using 19 years of satellite-derived sea level anomaly (SLA) data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo-Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST) and sea surface salinity (SSS) anomalies are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are identified by an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, about 20 % of all anticyclonically rotating eddies show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs). About 146 ± 4 eddies per year with a minimum lifetime of 7 days are identified (52 % cyclones, 39 % anticyclones, 9 % ACMEs) with rather similar mean radii of about 56 ± 12 km. Based on concurrent in situ temperature and salinity profiles (from Argo float, shipboard, and mooring data) taken inside of eddies, distinct mean vertical structures of the three eddy types are determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland regions and carry South Atlantic Central Water supplied by the northward flow within the Mauretanian coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d-1) is confined to distinct zonal corridors with a small meridional deflection dependent on the eddy type (anticyclones - equatorward, cyclones - poleward, ACMEs - no deflection). Heat and salt fluxes out of the coastal region and across the Cape Verde Frontal Zone, which separates the shadow zone from
Mesoscale eddies over the Laptev Sea continental slope in the Arctic Ocean
Pnyushkov, A.; Polyakov, I.; Nguyen, A. T.
2015-12-01
Mesoscale eddies are an important component in Arctic Ocean dynamics and can play a role in vertical redistribution of ocean heat from the intermediate layer of warm Atlantic Water (AW). We analyze mooring data collected along the continental slope of the Laptev Sea in 2007-11 to improve the characterization of Arctic mesoscale eddies in this region of the Eurasian Basin (EB).Wavelet analyses suggest that ~20% of the mooring record is occupied by mesoscale eddies, whose vertical scales can be large, often >600 m. Based on similarity between temperature/salinity profiles measured inside eddies and modern climatology for the 2000s, we found two distinct sources of eddy formation in the EB; one in the vicinity of Fram Strait and the other at the continental slope of the Severnaya Zemlya Archipelago. Both sources of eddies are on the route of AW propagation along the EB margins, so that the Arctic Circumpolar Boundary Current (ACBC) can carry these eddies along the continental slope.The lateral advection of waters isolated inside the eddy cores by ACBC affect the heat and salt balance of the eastern EB. The average temperature anomaly inside Fram Strait eddies in the layer above the AW temperature core (i.e., above 350 m depth level) was ~0.1º C with the strongest temperature anomaly in this layer exceeding 0.5ºC. In contrast to Fram Strait eddies, Severnaya Zemlya eddies carry anomalously cold and fresh water, and likely contribute to ventilation of the AW core. In addition, we found increased vertical shears of the horizontal velocities inside eddies that result in enhanced mixing. Our estimates made using the Pacanowski and Philander (1981) relationship suggest that, on average, vertical diffusivity coefficients inside eddies are four times larger than those in the surrounding waters. We will use the high resolution ECCO model to investigate the relative contributions of along and across slope transports induced by eddies along the ACBC path.
N2 fixation in eddies of the eastern tropical South Pacific Ocean
Loscher, Carolin R.; Bourbonnais, Annie; Dekaezemacker, Julien; Charoenpong, Chawalit N.; Altabet, Mark A.; Bange, Hermann W.; Czeschel, Rena; Hoffmann, Chris; Schmitz, Ruth
2016-05-01
Mesoscale eddies play a major role in controlling ocean biogeochemistry. By impacting nutrient availability and water column ventilation, they are of critical importance for oceanic primary production. In the eastern tropical South Pacific Ocean off Peru, where a large and persistent oxygen-deficient zone is present, mesoscale processes have been reported to occur frequently. However, investigations into their biological activity are mostly based on model simulations, and direct measurements of carbon and dinitrogen (N2) fixation are scarce.We examined an open-ocean cyclonic eddy and two anticyclonic mode water eddies: a coastal one and an open-ocean one in the waters off Peru along a section at 16° S in austral summer 2012. Molecular data and bioassay incubations point towards a difference between the active diazotrophic communities present in the cyclonic eddy and the anticyclonic mode water eddies.In the cyclonic eddy, highest rates of N2 fixation were measured in surface waters but no N2 fixation signal was detected at intermediate water depths. In contrast, both anticyclonic mode water eddies showed pronounced maxima in N2 fixation below the euphotic zone as evidenced by rate measurements and geochemical data. N2 fixation and carbon (C) fixation were higher in the young coastal mode water eddy compared to the older offshore mode water eddy. A co-occurrence between N2 fixation and biogenic N2, an indicator for N loss, indicated a link between N loss and N2 fixation in the mode water eddies, which was not observed for the cyclonic eddy. The comparison of two consecutive surveys of the coastal mode water eddy in November 2012 and December 2012 also revealed a reduction in N2 and C fixation at intermediate depths along with a reduction in chlorophyll by half, mirroring an aging effect in this eddy. Our data indicate an important role for anticyclonic mode water eddies in stimulating N2 fixation and thus supplying N offshore.
Determining Confounding Sensitivities In Eddy Current Thin Film Measurements
Gros, Ethan; Udpa, Lalita; Smith, James A.; Wachs, Katelyn
2016-07-01
Determining Confounding Sensitivities In Eddy Current Thin Film Measurements Ethan Gros, Lalita Udpa, Electrical Engineering, Michigan State University, East Lansing MI 48824 James A. Smith, Experiment Analysis, Idaho National Laboratory, Idaho Falls ID 83415 Eddy current (EC) techniques are widely used in industry to measure the thickness of non-conductive films on a metal substrate. This is done 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 is 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 is 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 is 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
Large Eddy Simulation for Wave Breaking in the Surf Zone
白玉川; 蒋昌波; 沈焕庭
2001-01-01
In this paper, the large eddy simulation method is used combined with the marker and cell method to study the wave propagation or shoaling and breaking process. As wave propagates into shallow water, the shoaling leads to the increase of wave height, and then at a certain position, the wave will be breaking. The breaking wave is a powerful agent for generating turbulence, which plays an important role in most of the fluid dynamic processes throughout the sarf zone, such as transformation of wave energy, generation of near-shore current and diffusion of materials. So a proper numerical model for describing the turbulence effect is needed. In this paper, a revised Smagorinsky subgrid-scale model is used to describe the turbulence effect. The present study reveals that the coefficient of the Smagorinsky model for wave propagation or breaking simulation may be taken as a varying function of the water depth and distance away from the wave breaking point. The large eddy simulation model presented in this paper has been used to study the propagation of the solitary wave in constant water depth and the shoaling of the non-breaking solitary wave on a beach. The model is based on large eddy simulation, and to track free-surface movements, the Tokyo University Modified Marker and Cell (TUMMAC) method is employed. In order to ensure the accuracy of each component of this wave mathematical model,several steps have been taken to verify calculated solutions with either analytical solutions or experimental data. For non-breaking waves, very accurate results are obtained for a solitary wave propagating over a constant depth and on a beach. Application of the model to cnoidal wave breaking in the surf zone shows that the model results are in good agreement with analytical solution and experimental data. From the present model results, it can be seen that the turbulent eddy viscosity increases from the bottom to the water surface in surf zone. In the eddy viscosity curve, there is a
Eddy Flow during Magma Emplacement: The Basemelt Sill, Antarctica
Petford, N.; Mirhadizadeh, S.
2014-12-01
The McMurdo Dry Valleys magmatic system, Antarctica, forms part of the Ferrar dolerite Large Igneous Province. Comprising a vertical stack of interconnected sills, the complex provides a world-class example of pervasive lateral magma flow on a continental scale. The lowermost intrusion (Basement Sill) offers detailed sections through the now frozen particle macrostructure of a congested magma slurry1. Image-based numerical modelling where the intrusion geometry defines its own unique finite element mesh allows simulations of the flow regime to be made that incorporate realistic magma particle size and flow geometries obtained directly from field measurements. One testable outcome relates to the origin of rhythmic layering where analytical results imply the sheared suspension intersects the phase space for particle Reynolds and Peclet number flow characteristic of macroscopic structures formation2. Another relates to potentially novel crystal-liquid segregation due to the formation of eddies locally at undulating contacts at the floor and roof of the intrusion. The eddies are transient and mechanical in origin, unrelated to well-known fluid dynamical effects around obstacles where flow is turbulent. Numerical particle tracing reveals that these low Re number eddies can both trap (remove) and eject particles back into the magma at a later time according to their mass density. This trapping mechanism has potential to develop local variations in structure (layering) and magma chemistry that may otherwise not occur where the contact between magma and country rock is linear. Simulations indicate that eddy formation is best developed where magma viscosity is in the range 1-102 Pa s. Higher viscosities (> 103 Pa s) tend to dampen the effect implying eddy development is most likely a transient feature. However, it is nice to think that something as simple as a bumpy contact could impart physical and by implication chemical diversity in igneous rocks. 1Marsh, D.B. (2004), A
An atmospheric electrical method to determine the eddy diffusion coefficient
M N Kulkarni; A K Kamra
2010-02-01
The ion–aerosol balance equations are solved to get the profiles of atmospheric electric parameters over the ground surface in an aerosol-rich environment under the conditions of surface radioactivity. Combining the earlier results for low aerosol concentrations and the present results for high aerosol concentrations, a relation is obtained between the average value of atmospheric electric space charge in the lowest ∼2m, the surface electric field and eddy diffusivity/aerosol concentration. The values of eddy diffusivity estimated from this method using some earlier measurements of space charge and surface electric field are in reasonably good agreement with those calculated from other standard methods using meteorological or electrical variables.
Comparative performance of image fusion methodologies in eddy current testing
S. Thirunavukkarasu
2012-12-01
Full Text Available Image fusion methodologies have been studied for improving the detectability of eddy current Nondestructive Testing (NDT. Pixel level image fusion has been performed on C-scan eddy current images of a sub-surface defect at two different frequencies. Multi-resolution analysis based Laplacian pyramid and wavelet fusion methodologies, statistical inference based Bayesian fusion and Principal Component Analysis (PCA based fusion methodologies have been studied towards improving the detectability of defects. The performance of the fusion methodologies has been compared using image metrics such as SNR and entropy. Bayesian based fusion methodology has shown better performance as compared to other methodologies with 33.75 dB improvement in the SNR and an improvement of 3.22 in the entropy.
Synthetic-Eddy Method for Urban Atmospheric Flow Modelling
Pavlidis, D.; Gorman, G. J.; Gomes, J. L. M. A.; Pain, C. C.; Apsimon, H.
2010-08-01
The computational fluid dynamics code Fluidity, with anisotropic mesh adaptivity, is used as a multi-scale obstacle-accommodating meteorological model. A novel method for generating realistic inlet boundary conditions based on the view of turbulence as a superposition of synthetic eddies is adopted. It is able to reproduce prescribed first-order and second-order one-point statistics and turbulence length scales. The aim is to simulate an urban boundary layer. The model is validated against two standard benchmark tests: a plane channel flow numerical simulation and a flow past a cube physical simulation. The performed large-eddy simulations are in good agreement with both reference models giving confidence that the model can be used to successfully simulate urban atmospheric flows.
Quality and Reliability of Large-Eddy Simulations
Meyers, Johan; Sagaut, Pierre
2008-01-01
Computational resources have developed to the level that, for the first time, it is becoming possible to apply large-eddy simulation (LES) to turbulent flow problems of realistic complexity. Many examples can be found in technology and in a variety of natural flows. This puts issues related to assessing, assuring, and predicting the quality of LES into the spotlight. Several LES studies have been published in the past, demonstrating a high level of accuracy with which turbulent flow predictions can be attained, without having to resort to the excessive requirements on computational resources imposed by direct numerical simulations. However, the setup and use of turbulent flow simulations requires a profound knowledge of fluid mechanics, numerical techniques, and the application under consideration. The susceptibility of large-eddy simulations to errors in modelling, in numerics, and in the treatment of boundary conditions, can be quite large due to nonlinear accumulation of different contributions over time, ...
Eddy current analysis of thin film recording heads
Shenton, D.; Cendes, Z. J.
1984-03-01
Due to inherently thin pole tips which enhance the sharpness of read/write pulses, thin-film magnetic recording heads provide a unique potential for increasing disk file capacity. However, the very feature of these heads which makes them attractive in the recording process, namely, their small size, also makes thin-film heads difficult to study experimentally. For this reason, a finite element simulation of the thin-film head has been developed to provide the magnetic field distribution and the resistance/inductance characteristics of these heads under a variety of conditions. A study based on a one-step multipath eddy current procedure is reported. This procedure may be used in thin film heads to compute the variation of magnetic field with respect to frequency. Computations with the IBM 3370 head show that a large phase shift occurs due to eddy currents in the frequency range 1-10 MHz.
Numeral eddy current sensor modelling based on genetic neural network
Yu A-Long
2008-01-01
This paper presents a method used to the numeral eddy current sensor modelling based on the genetic neural network to settle its nonlinear problem. The principle and algorithms of genetic neural network are introduced. In this method, the nonlinear model parameters of the numeral eddy current sensor are optimized by genetic neural network (GNN) according to measurement data. So the method remains both the global searching ability of genetic algorithm and the good local searching ability of neural network. The nonlinear model has the advantages of strong robustness,on-line modelling and high precision.The maximum nonlinearity error can be reduced to 0.037% by using GNN.However, the maximum nonlinearity error is 0.075% using the least square method.
Low oxygen eddies in the eastern tropical North Atlantic
Grundle, D. S.; Löscher, C. R.; Krahmann, G.
2017-01-01
Nitrous oxide (N2O) is a climate relevant trace gas, and its production in the ocean generally increases under suboxic conditions. The Atlantic Ocean is well ventilated, and unlike the major oxygen minimum zones (OMZ) of the Pacific and Indian Oceans, dissolved oxygen and N2O concentrations...... in the Atlantic OMZ are relatively high and low, respectively. This study, however, demonstrates that recently discovered low oxygen eddies in the eastern tropical North Atlantic (ETNA) can produce N2O concentrations much higher (up to 115 nmol L-1) than those previously reported for the Atlantic Ocean, and which...... are within the range of the highest concentrations found in the open-ocean OMZs of the Pacific and Indian Oceans. N2O isotope and isotopomer signatures, as well as molecular genetic results, also point towards a major shift in the N2O cycling pathway in the core of the low oxygen eddy discussed here, and we...
Eddy current characterization of magnetic treatment of materials
Chern, E. James
1992-01-01
Eddy current impedance measuring methods have been applied to study the effect that magnetically treated materials have on service life extension. Eddy current impedance measurements have been performed on Nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in a material's electromagnetic properties and does exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic-field processing effect on machine tool service life.
Large Eddy Simulation of Coherent Structure of Impinging Jet
Mingzhou YU; Lihua CHEN; Hanhui JIN; Jianren FAN
2005-01-01
@@ The flow field of a rectangular exit, semi-confined and submerged turbulent jet impinging orthogonally on a flat plate with Reynolds number 8500 was studied by large eddy simulation (LES). A dynamic sub-grid stress model has been used for the small scales of turbulence. The evolvements such as the forming, developing, moving,pairing and merging of the coherent structures of vortex in the whole regions were obtained. The results revealed that the primary vortex structures were generated periodically, which was the key factor to make the secondary vortices generate in the wall jet region. In addition, the eddy intensity of the primary vortices and the secondary vortices induced by the primary vortices along with the time were also analyzed.
Practical Application of Eddy Currents Generated by Wind
Dirba, I; Kleperis, J, E-mail: imants.dirba@gmail.com [Institute of Solid State Physics of University of Latvia, 8 Kengaraga Street, Riga, LV-1063 (Latvia)
2011-06-23
When a conductive material is subjected to time-varying magnetic fluxes, eddy (Foucault) currents are generated in it and magnetic field of opposite polarity as the applied one arises. Due to the internal resistance of the conductive material, the eddy currents will be dissipated into heat (Joule heating). Conventional domestic water heaters utilize gas burners or electric resistance heating elements to heat the water in the tank and substantial part of the energy to use for it is wasted. In this paper the origin of electromagnetic induction heat generated by wind turbine in special heat exchange camera connected to water boiler is discussed and material evaluation performed using mathematical modelling (comparing the 2D finite element model with analytical and numerical calculation results).
Modeling and strain gauging of eddy current repulsion deicing systems
Smith, Samuel O.
1993-01-01
Work described in this paper confirms and extends work done by Zumwalt, et al., on a variety of in-flight deicing systems that use eddy current repulsion for repelling ice. Two such systems are known as electro-impulse deicing (EIDI) and the eddy current repulsion deicing strip (EDS). Mathematical models for these systems are discussed for their capabilities and limitations. The author duplicates a particular model of the EDS. Theoretical voltage, current, and force results are compared directly to experimental results. Dynamic strain measurements results are presented for the EDS system. Dynamic strain measurements near EDS or EIDI coils are complicated by the high magnetic fields in the vicinity of the coils. High magnetic fields induce false voltage signals out of the gages.
Estimating surface fluxes using eddy covariance and numerical ogive optimization
Sievers, J.; Papakyriakou, T.; Larsen, Søren Ejling
2015-01-01
Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low-frequency con......Estimating representative surface fluxes using eddy covariance leads invariably to questions concerning inclusion or exclusion of low-frequency flux contributions. For studies where fluxes are linked to local physical parameters and up-scaled through numerical modelling efforts, low......-frequency contributions interfere with our ability to isolate local biogeochemical processes of interest, as represented by turbulent fluxes. No method currently exists to disentangle low-frequency contributions on flux estimates. Here, we present a novel comprehensive numerical scheme to identify and separate out low...
Limitations of eddy current testing in a fast reactor environment
Wu, Tao; Bowler, John R.
2016-02-01
The feasibility of using eddy current probes for detecting flaws in fast nuclear reactor structures has been investigated with the aim of detecting defects immersed in electrically conductive coolant including under liquid sodium during standby. For the inspections to be viable, there is a need to use an encapsulated sensor system that can be move into position with the aid of visualization tools. The initial objective being to locate the surface to be investigated using, for example, a combination of electromagnetic sensors and sonar. Here we focus on one feature of the task in which eddy current probe impedance variations due to interaction with the external surface of a tube are evaluated in order to monitor the probe location and orientation during inspection.
Practical Application of Eddy Currents Generated by Wind
Dirba, I.; Kleperis, J.
2011-06-01
When a conductive material is subjected to time-varying magnetic fluxes, eddy (Foucault) currents are generated in it and magnetic field of opposite polarity as the applied one arises. Due to the internal resistance of the conductive material, the eddy currents will be dissipated into heat (Joule heating). Conventional domestic water heaters utilize gas burners or electric resistance heating elements to heat the water in the tank and substantial part of the energy to use for it is wasted. In this paper the origin of electromagnetic induction heat generated by wind turbine in special heat exchange camera connected to water boiler is discussed and material evaluation performed using mathematical modelling (comparing the 2D finite element model with analytical and numerical calculation results).
Analytical Modeling for the Grating Eddy Current Displacement Sensors
Lv Chunfeng
2015-02-01
Full Text Available As a new type of displacement sensor, grating eddy current displacement sensor (GECDS combines traditional eddy current sensors and grating structure in one. The GECDS performs a wide range displacement measurement without precision reduction. This paper proposes an analytical modeling approach for the GECDS. The solution model is established in the Cartesian coordinate system, and the solving domain is limited to finite extents by using the truncated region eigenfunction expansion method. Based on the second order vector potential, expressions for the electromagnetic field as well as coil impedance related to the displacement can be expressed in closed-form. Theoretical results are then confirmed by experiments, which prove the suitability and effectiveness of the analytical modeling approach.
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
Schalkwijk, J.; Jonker, H.J.J.; Siebesma, A.P.
2016-01-01
The low-frequency contribution to the systematic and random sampling errors in single-tower eddy-covariance flux measurements is investigated using large-eddy simulation (LES). We use a continuous LES integration that covers a full year of realistic weather conditions over Cabauw, the Netherlands, a
Hughes, T.J.R.; Wells, G.N.; Wray, A.A.
2004-01-01
Energy transfers within large-eddy simulation (LES) and direct numerical simulation (DNS) grids are studied. The spectral eddy viscosity for conventional dynamic Smagorinsky and variational multiscale LES methods are compared with DNS results. Both models underestimate the DNS results for a very coa
4. Large-Eddy Simulation of Turbulent Channel Flow
Yasuaki, DOI; Tsukasa, KIMURA; Hiroshima University; Mitsubishi Precision
1989-01-01
Turbulent channel flow is studied numerically by using Large-Eddy Simulation (LES). Finite difference method is employed in the LES. The simulation is stably executed by using the 3rd order upwind difference scheme which dissipate numerical errors. Several pilot tests are performed in order to investigate the effect of numerical dissipation and the wall damping function on the calculated results. Time dependent feature and turbulent flow structures in a turbulent channel flow are numerically ...
Large Eddy Simulation for Dispersed Bubbly Flows: A Review
M. T. Dhotre
2013-01-01
Full Text Available Large eddy simulations (LES of dispersed gas-liquid flows for the prediction of flow patterns and its applications have been reviewed. The published literature in the last ten years has been analysed on a coherent basis, and the present status has been brought out for the LES Euler-Euler and Euler-Lagrange approaches. Finally, recommendations for the use of LES in dispersed gas liquid flows have been made.
Large-Eddy Simulations of Dust Devils and Convective Vortices
Spiga, Aymeric; Barth, Erika; Gu, Zhaolin; Hoffmann, Fabian; Ito, Junshi; Jemmett-Smith, Bradley; Klose, Martina; Nishizawa, Seiya; Raasch, Siegfried; Rafkin, Scot; Takemi, Tetsuya; Tyler, Daniel; Wei, Wei
2016-11-01
In this review, we address the use of numerical computations called Large-Eddy Simulations (LES) to study dust devils, and the more general class of atmospheric phenomena they belong to (convective vortices). We describe the main elements of the LES methodology. We review the properties, statistics, and variability of dust devils and convective vortices resolved by LES in both terrestrial and Martian environments. The current challenges faced by modelers using LES for dust devils are also discussed in detail.
Eddy current testing probe optimization using a parallel genetic algorithm
Dolapchiev Ivaylo
2008-01-01
Full Text Available This paper uses the developed parallel version of Michalewicz's Genocop III Genetic Algorithm (GA searching technique to optimize the coil geometry of an eddy current non-destructive testing probe (ECTP. The electromagnetic field is computed using FEMM 2D finite element code. The aim of this optimization was to determine coil dimensions and positions that improve ECTP sensitivity to physical properties of the tested devices.
Cold HI in Turbulent Eddies and Galactic Spiral Shocks
Steven J Gibson; Taylor, A. Russell; Stil, Jeroen M.; Brunt, Christopher M.; Kavars, Dain W.; Dickey, John M.
2007-01-01
HI 21cm-line self-absorption (HISA) reveals the shape and distribution of cold atomic clouds in the Galactic disk. Many of these clouds lack corresponding CO emission, despite being colder than purely atomic gas in equilibrium models. HISA requires background line emission at the same velocity, hence mechanisms that can produce such backgrounds. Weak, small-scale, and widespread absorption is likely to arise from turbulent eddies, while strong, large-scale absorption appears organized in clou...
Eddy-Mean Flow Interactions in Western Boundary Current Jets
2009-02-01
relevance to the atmosphere, the enstrophy variance budget (assuming eddy en- strophy advection, a triple correlation term, is small) reduces to a two-term...producing an increase in the barotropic component of the zonal jet. The other term however, v′2 − u′2, the term producing the quadrupole pattern that...shooting technique ” that varies the complex phase speed until the numerical solutions in the interior match the exterior analytic solutions at the edge of
Recent Improvements in High-Frequency Eddy Current Conductivity Spectroscopy
Abu-Nabah, Bassam A.; Nagy, Peter B.
2008-02-01
Due to its frequency-dependent penetration depth, eddy current measurements are capable of mapping near-surface residual stress profiles based on the so-called piezoresistivity effect, i.e., the stress-dependence of electric conductivity. To capture the peak compressive residual stress in moderately shot-peened (Almen 4-8A) nickel-base superalloys, the eddy current inspection frequency has to go as high as 50-80 MHz. Recently, we have reported the development of a new high-frequency eddy current conductivity measuring system that offers an extended inspection frequency range up to 80 MHz. Unfortunately, spurious self- and stray-capacitance effects render the complex coil impedance variation with lift-off more nonlinear as the frequency increases, which makes it difficult to achieve accurate apparent eddy current conductivity (AECC) measurements with the standard four-point linear interpolation method beyond 25 MHz. In this paper, we will demonstrate that reducing the coil size reduces its sensitivity to capacitive lift-off variations, which is just the opposite of the better known inductive lift-off effect. Although reducing the coil size also reduces its absolute electric impedance and relative sensitivity to conductivity variations, a smaller coil still yields better overall performance for residual stress assessment. In addition, we will demonstrate the benefits of a semi-quadratic interpolation scheme that, together with the reduced lift-off sensitivity of the smaller probe coil, minimizes and in some cases completely eliminates the sensitivity of AECC measurements to lift-off uncertainties. These modifications allow us to do much more robust measurements up to as high as 80-100 MHz with the required high relative accuracy of +/-0.1%.
Mesolayer of attached eddies in turbulent channel flow
Hwang, Yongyun
2016-10-01
Recent experimental measurements have reported that the outer peak of the streamwise wave-number spectra of the streamwise velocity depends on the Reynolds number. Starting from this puzzling observation, here it is proposed that the wall-parallel velocity components of each of the energy-containing motions in the form of Towsnend's attached eddies exhibit an inner-scaling nature in the region close to the wall. Some compelling evidence on this proposition has been presented with a careful inspection of scaling of velocity spectra from direct numerical simulations, a linear analysis with an eddy viscosity, and the recently computed statistical structure of the self-similar energy-containing motions in the logarithmic region. This observation suggests that the viscous wall effect would not be negligible at least below the peak wall-normal location of each of the energy-containing motions in the logarithmic and outer regions, reminiscent of the concept of the mesolayer previously observed in the mean momentum balance. It is shown that this behavior emerges due to a minimal form of scale interaction, modeled by the eddy viscosity in the linear theory, and enables one to explain the Reynolds-number-dependent behavior of the outer peak as well as the near-wall penetration of the large-scale outer structures in a consistent manner. Incorporation of this viscous wall effect to Townsend's attached eddies, which were originally built with an inviscid approximation at the wall, also reveals that the self-similarity of the wall-parallel velocity components of the energy-containing motions would be theoretically broken in the region close to the wall.
ARRAY PULSED EDDY CURRENT IMAGING SYSTEM USED TO DETECT CORROSION
Yang Binfeng; Luo Feilu; Cao Xiongheng; Xu Xiaojie
2005-01-01
A theory model is established to describe the voltage-current response function. The peak amplitude and the zero-crossing time of the transient signal is extracted as the imaging features, array pulsed eddy current (PEC) imaging is proposed to detect corrosion. The test results show that this system has the advantage of fast scanning speed, different imaging mode and quantitative detection, it has a broad application in the aviation nondestructive testing.
Nondestructive examination of PHWR pressure tube using eddy current technique
Lee, Hee Jong; Choi, Sung Nam; Cho, Chan Hee; Yoo, Hyun Joo; Moon, Gyoon Young [KHNP Central Research Institute, Daejeon (Korea, Republic of)
2014-06-15
A pressurized heavy water reactor (PHWR) core has 380 fuel channels contained and supported by a horizontal cylindrical vessel known as the calandria, whereas a pressurized water reactor (PWR) has only a single reactor vessel. The pressure tube, which is a pressure-retaining component, has a 103.4 mm inside diameter x 4.19 mm wall thickness, and is 6.36 m long, made of a zirconium alloy (Zr-2.5 wt% Nb). This provides support for the fuel while transporting the D2O heat-transfer fluid. The simple tubular geometry invites highly automated inspection, and good approach for all inspection. Similar to all nuclear heat-transfer pressure boundaries, the PHWR pressure tube requires a rigorous, periodic inspection to assess the reactor integrity in accordance with the Korea Nuclear Safety Committee law. Volumetric-based nondestructive evaluation (NDE) techniques utilizing ultrasonic and eddy current testing have been adopted for use in the periodic inspection of the fuel channel. The eddy current testing, as a supplemental NDE method to ultrasonic testing, is used to confirm the flaws primarily detected through ultrasonic testing, however, eddy current testing offers a significant advantage in that its ability to detect surface flaws is superior to that of ultrasonic testing. In this paper, effectiveness of flaw detection and the depth sizing capability by eddy current testing for the inside surface of a pressure tube, will be introduced. As a result of this examination, the ET technique is found to be useful only as a detection technique for defects because it can detect fine defects on the surface with high resolution. However, the ET technique is not recommended for use as a depth sizing method because it has a large degree of error for depth sizing.
Potential and limitations of eddy current lockin-thermography
Riegert, G.; Gleiter, A.; Busse, G.
2006-04-01
Eddy current thermography uses an induction coil to induce eddy currents in conductive materials. The involved resistive losses heat the sample. By modulation of the eddy current amplitude, thermal waves are generated which interact with boundaries thereby revealing defects. Conventional eddy current testing has only a limited depth range due to the skin effect of metal samples. In Induction-Lockin-Thermography (ILT) the depth range is extended by the thermal penetration depth. An infrared camera monitors the modulation of the temperature field on the surface as a response to the coded excitation thereby allowing for fast imaging of defects in larger areas without the need of slow point-by-point mapping. This response is decoded by a Fourier analysis at the modulation frequency. So the extracted information is displayed by just two images where one displays local amplitude and the other local phase. ILT has significant advantages as compared to inductive heating with visual inspection of the thermographic sequence: Phase angle images are independent of most artifacts like reflections, variation in emission coefficient, or inhomogeneous heating. Due to the performed Fourier analysis of the temperature image sequence, the signal-to-noise ratio in the amplitude and phase images is significantly better than in single temperature images of the sequence. Induction heating is confined to conductive materials. However, it is applicable not only to metals but also to carbon fiber reinforced laminates (CFRP) or carbon fiber reinforced ceramics (C/C-SiC). The presented examples for applications of ILT illustrate the potential and limitations of this new non-destructive inspection method.
An examination of double-diffusive processes in a mesoscale eddy in the Arctic Ocean
Bebieva, Yana; Timmermans, Mary-Louise
2016-01-01
Temperature and salinity measurements of an Atlantic Water mesoscale eddy in the Arctic Ocean's Canada Basin are analyzed to understand the effects of velocity shear on a range of double-diffusive processes. Double-diffusive structures in and around the eddy are examined through the transition from low shear (outside the eddy and within its solid body core) to high geostrophic shear zones at the eddy flanks. The geostrophic Richardson number takes large values where a double-diffusive staircase is observed and lowest values at the eddy flanks where geostrophic velocity is largest and a well-formed staircase is not present. A Thorpe scale analysis is used to estimate turbulent diffusivities in the flank regions. Double-diffusive and turbulent heat, salt, and buoyancy fluxes from the eddy are computed, and used to infer that the eddy decays on time scales of around 4-9 years. Fluxes highlight that Atlantic Water heat within the eddy can be fluxed downward into deeper water layers by means of both double-diffusive and turbulent mixing. Estimated lateral variations in vertical fluxes across the eddy allow for speculation that double diffusion speeds up the eddy decay, having important implications for the transfer of Atlantic Water heat in the Arctic Ocean.
Large eddy simulation of the atmosphere on various scales.
Cullen, M J P; Brown, A R
2009-07-28
Numerical simulations of the atmosphere are routinely carried out on various scales for purposes ranging from weather forecasts for local areas a few hours ahead to forecasts of climate change over periods of hundreds of years. Almost without exception, these forecasts are made with space/time-averaged versions of the governing Navier-Stokes equations and laws of thermodynamics, together with additional terms representing internal and boundary forcing. The calculations are a form of large eddy modelling, because the subgrid-scale processes have to be modelled. In the global atmospheric models used for long-term predictions, the primary method is implicit large eddy modelling, using discretization to perform the averaging, supplemented by specialized subgrid models, where there is organized small-scale activity, such as in the lower boundary layer and near active convection. Smaller scale models used for local or short-range forecasts can use a much smaller averaging scale. This allows some of the specialized subgrid models to be dropped in favour of direct simulations. In research mode, the same models can be run as a conventional large eddy simulation only a few orders of magnitude away from a direct simulation. These simulations can then be used in the development of the subgrid models for coarser resolution models.
Turbulent eddy-time-correlation in the solar convective zone
Belkacem, K; Goupil, M J; Baudin, F; Salabert, D; Appourchaux, T
2010-01-01
Theoretical modeling of the driving processes of solar-like oscillations is a powerful way of understanding the properties of the convective zones of solar-type stars. In this framework, the description of the temporal correlation between turbulent eddies is an essential ingredient to model mode amplitudes. However, there is a debate between a Gaussian or Lorentzian description of the eddy-time correlation function (Samadi et al. 2003, Chaplin et al. 2005). Indeed, a Gaussian description reproduces the low-frequency shape of the mode amplitude for the Sun, but is unsatisfactory from a theoretical point of view (Houdek, 2009) and leads to other disagreements with observations (Samadi et al., 2007). These are solved by using a Lorentzian description, but there the low-frequency shape of the solar observations is not correctly reproduced. We reconcile the two descriptions by adopting the sweeping approximation, which consists in assuming that the eddy-time-correlation function is dominated by the advection of ed...
Comparison of analytical eddy current models using principal components analysis
Contant, S.; Luloff, M.; Morelli, J.; Krause, T. W.
2017-02-01
Monitoring the gap between the pressure tube (PT) and the calandria tube (CT) in CANDU® fuel channels is essential, as contact between the two tubes can lead to delayed hydride cracking of the pressure tube. Multifrequency transmit-receive eddy current non-destructive evaluation is used to determine this gap, as this method has different depths of penetration and variable sensitivity to noise, unlike single frequency eddy current non-destructive evaluation. An Analytical model based on the Dodd and Deeds solutions, and a second model that accounts for normal and lossy self-inductances, and a non-coaxial pickup coil, are examined for representing the response of an eddy current transmit-receive probe when considering factors that affect the gap response, such as pressure tube wall thickness and pressure tube resistivity. The multifrequency model data was analyzed using principal components analysis (PCA), a statistical method used to reduce the data set into a data set of fewer variables. The results of the PCA of the analytical models were then compared to PCA performed on a previously obtained experimental data set. The models gave similar results under variable PT wall thickness conditions, but the non-coaxial coil model, which accounts for self-inductive losses, performed significantly better than the Dodd and Deeds model under variable resistivity conditions.
Nearby boundaries create eddies near microscopic filter feeders.
Pepper, Rachel E; Roper, Marcus; Ryu, Sangjin; Matsudaira, Paul; Stone, Howard A
2010-05-06
We show through calculations, simulations and experiments that the eddies often observed near sessile filter feeders are frequently due to the presence of nearby boundaries. We model the common filter feeder Vorticella, which is approximately 50 microm across and which feeds by removing bacteria from ocean or pond water that it draws towards itself. We use both an analytical stokeslet model and a Brinkman flow approximation that exploits the narrow-gap geometry to predict the size of the eddy caused by two parallel no-slip boundaries that represent the slides between which experimental observations are often made. We also use three-dimensional finite-element simulations to fully solve for the flow around a model Vorticella and analyse the influence of multiple nearby boundaries. Additionally, we track particles around live feeding Vorticella in order to determine the experimental flow field. Our models are in good agreement both with each other and with experiments. We also provide approximate equations to predict the experimental eddy sizes owing to boundaries both for the case of a filter feeder between two slides and for the case of a filter feeder attached to a perpendicular surface between two slides.
Application of relaxed eddy accumulation (REA on managed grassland
M. Riederer
2014-05-01
Full Text Available Relaxed eddy accumulation is applied for measuring fluxes of trace gases for which there is a lack of sensors fast enough in their resolution for eddy-covariance. On managed grasslands, the length of time between management events and the application of relaxed eddy accumulation has an essential influence on the determination of the proportionality factor b and thereby on the resulting flux. In this study this effect is discussed for the first time. Also, scalar similarity between proxy scalars and scalars of interest is affected until the ecosystem has completely recovered. Against this background, CO2 fluxes were continuously measured and 13CO2 isofluxes were determined with a high measurement precision on two representative days in summer 2010. This enabled the evaluation of the 13CO2 flux portion of the entire CO2 flux, in order to estimate potential influences on tracer experiments in ecosystem sciences and to compare a common method for the partitioning of the net ecosystem exchange into assimilation and respiration based on temperature and light response with an isotopic approach directly based on the isotope discrimination of the biosphere.
A Study of Eddy Viscosity Coefficient in Numerical Tidal Simulation
陈永平; 雷智益
2001-01-01
Based on the fluid motion equations, the physical meaning of eddy viscosity coefficient and the rationality of theBoussinesq hypothesis are discussed in this paper. The effect of the coefficient on numerical stability is analyzed briefly.A semi-enclosed rectangular sea area, with an orthogonal spur dike, is applied in a 2-D numerical model to study the effect of horizontal eddy viscosity coefficient (AH). The computed result shows that AH has little influence on the tidal level and averaged flow velocity, but has obvious influence on the intensity and the range of return flow around near thespur dike. Correspondingly, a wind-driven current pool and an annular current are applied in a 3-D numerical modelrespectively to study the effect of vertical eddy viscosity coefficient (AV). The computed result shows that the absolute value of AV is inversely proportional to that of horizontal velocity, and the vertical gradient value of AV determines the ver-tical distribution of horizontal velocity. The distribution form of AV is theoretically recommended as a parabolic type, ofwhich the maximum value appears at 0.5 H.
Modeling of the eddy viscosity by breaking waves
无
2007-01-01
Breaking wave induced nearsurface turbulence has important consequences for many physical and biochemical processes including water column and nutrients mixing, heat and gases exchange across air-sea interface. The energy loss from wave breaking and the bubble plume penetration depth are estimated. As a consequence, the vertical distribution of the turbulent kinetic energy (TKE), the TKE dissipation rate and the eddy viscosity induced by wave breaking are also provided. It is indicated that model results are found to be consistent with the observational evidence that most TKE generated by wave breaking is lost within a depth of a few meters near the sea surface. High turbulence level with intensities of eddy viscosity induced by breaking is nearly four orders larger than υwl(=κu *wz), the value predicted for the wall layer scaling close to the surface, where u *w is the friction velocity in water, κ with 0.4 is the von Kármán constant, and z is the water depth, and the strength of the eddy viscosity depends both on wind speed and sea state, and decays rapidly through the depth. This leads to the conclusion that the breaking wave induced vertical mixing is mainly limited to the near surface layer, well above the classical values expected from the similarity theory. Deeper down, however, the effects of wave breaking on the vertical mixing become less important.
Simulation of Cracks Detection in Tubes by Eddy Current Testing
S Bennoud
2016-12-01
Full Text Available The eddy current testing can be used such as a perfect tool to characterize defects in conducting materials. However, in the latest years, an important progress was made in the development of software for the eddy current testing simulations. Evaluation of the NDT modeling tools is the principal goal of this study. Main concerns of the aeronautic industry and the potential contribution of modeling are discussed and illustrated. Simulation by finite element method is realized with the aim to calculate the electromagnetic energy of interaction between coil and tested part that enables to deduce the impedance response. The objective of this work is the development of a code for efficient resolution of an electromagnetic problem modeling, especially, for the analysis of probe response due to the eddy current process. The validation of developed code was made. The obtained results converge quickly towards the solution given by the (FEMM code with an average error of 0.018 for real parts of impedance and 0.004 for imaginary parts. The presented results in this work serve to illustrate that the proposed method is practical and they are also of some intrinsic interest especially in the control of aluminum tubes used in aeronautics.
Tew Kai, Emilie; Marsac, Francis
2010-07-01
Mesoscale physical features as fronts and eddies appear to play a key role in the dynamics of marine communities. In the Indian Ocean, the Mozambique Channel (MC) is a natural laboratory to investigate mesoscale eddies (100-300 km in diameter); indeed, four to seven eddies per year are know to transit through the Channel, from North to South. We studied the structuring role of the mesoscale eddies on spatial dynamics and foraging strategy of top predators using seabirds and tuna as examples. Emphasis was on the central part of the MC (16-24°S) where eddy activity is most developed. We integrated three main categories of information: (i) satellite altimetry for sea-level anomaly (SLA) and geostrophic current, remotely-sensed surface temperature (SST) and SeaWiFS data for chlorophyll concentration (CC); (ii) individual tracking of Great Frigatebirds ( Fregata minor) to characterize foraging areas; and (iii) detailed catch statistics from purse-seine fisheries to describe distribution of tuna schools. Generalized Additive Models were applied to quantify the relative influence of mesoscale descriptors, SST and CC on foraging behaviour of Great Frigatebirds and location of purse-seine sets. Our results show that seabirds are more closely tied to mesoscale eddies compared to tuna. We underline the role of eddy boundaries on the response of frigatebirds and tuna. Good foraging conditions are promoted along the edge of eddies as a result of the interplay of the maturation process from cyclonic eddies and the concentration process by eddy interactions. A decrease in the number or intensity of eddies in the MC, as observed during strong El Niño events, could potentially affect the eddy-related ecosystem with putative negative repercussions on central-place foragers such as Great Frigatebirds. We discuss the importance of a better understanding of the “eddy system”, in marine conservation and tuna fisheries management in the Mozambique Channel.
Mackas, D. L.; Tsurumi, M.; Galbraith, M. D.; Yelland, D. R.
2005-04-01
Mesoscale anticyclonic eddies form annually in late winter along the eastern margin of the subarctic North Pacific. Eddies that originate off the southern tip of the Queen Charlotte Islands (near 52°N 132°W) are called 'Haida Eddies'. During the subsequent 1-3 years, they propagate westward into the Alaska Gyre. Enroute, the eddies are colonized by zooplankton originating from the central British Columbia continental shelf, the continental slope and along-slope boundary current, and the oceanic Alaska Gyre. Eddies also gradually lose kinetic energy, water properties, and biota to the surrounding ocean. In this paper, we analyze zooplankton samples from Haida eddies obtained in late winter, early summer and autumn of 2000, and in early summer and autumn of 2001, and compare the within-eddy zooplankton distributions, abundances, and community composition of the oceanic-origin species to observations from the continental margin and Alaska Gyre source regions. Most between-region comparisons were consistent with a hypothesis that the eddy zooplankton are a mixture intermediate in abundance and community composition between the BC continental margin and offshore Alaska Gyre source regions (although usually closer to the Alaska Gyre). However, about 30% of the comparisons showed within-eddy abundances higher than in either source region. This outcome cannot arise from mixing alone. Aggregation and retention appear to be linked to vertical distribution behavior: most of the successful taxa spend much of their time below the surface mixed layer. This minimizes their exposure to wash-out by three physical processes: Slow upwelling and surface divergence that accompanies weakening of the anticyclonic geostrophic currents. Rapid but intermittent flushing of the surface layer by Ekman transport during strong wind events. Exchange across the eddy margin/geostrophic streamlines caused by temporary displacement by wind-driven inertial currents.
Determining confounding sensitivities in eddy current thin film measurements
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.
Eddy-Induced Ekman Pumping from Sea-Surface Temperature and Surface Current Effects
Gaube, P.; Chelton, D. B.; O'Neill, L. W.
2011-12-01
Numerous past studies have discussed the biological importance of upwelling of nutrients into the interiors of nonlinear eddies. Such upwelling can occur during the transient stages of formation of cyclones from shoaling of the thermocline. In their mature stages, upwelling can occur from Ekman pumping driven by eddy-induced wind stress curl. Previous investigations of ocean-atmosphere interaction in regions of persistent sea-surface temperature (SST) frontal features have shown that the wind field is locally stronger over warm water and weaker over cold water. Spatial variability of the SST field thus results in a wind stress curl and an associated Ekman pumping in regions of crosswind temperature gradients. It can therefore be anticipated that any SST anomalies associated with eddies can generate Ekman pumping in the eddy interiors. Another mechanism for eddy-induced Ekman pumping is the curl of the stress on the sea surface that arises from the difference between the surface wind velocity and the surface ocean velocity. While SST-induced Ekman upwelling can occur over eddies of either polarity surface current effects on Ekman upwelling occur only over anticyclonic eddies The objective of this study is to determine the spatial structures and relative magnitudes of the two mechanisms for eddy-induced Ekman pumping within the interiors of mesoscale eddies. This is achieved by collocating satellite-based measurements of SST, surface winds and wind stress curl to the interiors of eddies identified and tracked with an automated procedure applied to the sea-surface height (SSH) fields in the Reference Series constructed by AVISO from the combined measurements by two simultaneously operating altimeters. It is shown that, on average, the wind stress curl from eddy-induced surface currents is largest at the eddy center, resulting in Ekman pumping velocities of order 10 cm day-1. While this surface current-induced Ekman pumping depends only weakly on the wind direction
Observing mesoscale eddy effects on mode-water subduction and transport in the North Pacific.
Xu, Lixiao; Li, Peiliang; Xie, Shang-Ping; Liu, Qinyu; Liu, Cong; Gao, Wendian
2016-02-01
While modelling studies suggest that mesoscale eddies strengthen the subduction of mode waters, this eddy effect has never been observed in the field. Here we report results from a field campaign from March 2014 that captured the eddy effects on mode-water subduction south of the Kuroshio Extension east of Japan. The experiment deployed 17 Argo floats in an anticyclonic eddy (AC) with enhanced daily sampling. Analysis of over 3,000 hydrographic profiles following the AC reveals that potential vorticity and apparent oxygen utilization distributions are asymmetric outside the AC core, with enhanced subduction near the southeastern rim of the AC. There, the southward eddy flow advects newly ventilated mode water from the north into the main thermocline. Our results show that subduction by eddy lateral advection is comparable in magnitude to that by the mean flow--an effect that needs to be better represented in climate models.
Swiderski, Waldemar
2016-10-01
Eddy current thermography is a new NDT-technique for the detection of cracks in electro conductive materials. It combines the well-established inspection techniques of eddy current testing and thermography. The technique uses induced eddy currents to heat the sample being tested and defect detection is based on the changes of induced eddy currents flows revealed by thermal visualization captured by an infrared camera. The advantage of this method is to use the high performance of eddy current testing that eliminates the known problem of the edge effect. Especially for components of complex geometry this is an important factor which may overcome the increased expense for inspection set-up. The paper presents the possibility of applying eddy current thermography method for detecting defects in ballistic covers made of carbon fiber reinforced composites used in the construction of military vehicles.
Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma
Arakawa, H.; Inagaki, S.; Sasaki, M.; Kosuga, Y.; Kobayashi, T.; Kasuya, N.; Nagashima, Y.; Yamada, T.; Lesur, M.; Fujisawa, A.; Itoh, K.; Itoh, S.-I.
2016-09-01
Turbulence and its structure formation are universal in neutral fluids and in plasmas. Turbulence annihilates global structures but can organize flows and eddies. The mutual-interactions between flow and the eddy give basic insights into the understanding of non-equilibrium and nonlinear interaction by turbulence. In fusion plasma, clarifying structure formation by Drift-wave turbulence, driven by density gradients in magnetized plasma, is an important issue. Here, a new mutual-interaction among eddy, drift wave and flow in magnetized plasma is discovered. A two-dimensional solitary eddy, which is a perturbation with circumnavigating motion localized radially and azimuthally, is transiently organized in a drift wave - zonal flow (azimuthally symmetric band-like shear flows) system. The excitation of the eddy is synchronized with zonal perturbation. The organization of the eddy has substantial impact on the acceleration of zonal flow.
Evolution of the eddy field in the Arctic Ocean's Canada Basin, 2005-2015
Zhao, Mengnan; Timmermans, Mary-Louise; Cole, Sylvia; Krishfield, Richard; Toole, John
2016-08-01
The eddy field across the Arctic Ocean's Canada Basin is analyzed using Ice-Tethered Profiler (ITP) and moored measurements of temperature, salinity, and velocity spanning 2005 to 2015. ITPs encountered 243 eddies, 98% of which were anticyclones, with approximately 70% of these having anomalously cold cores. The spatially and temporally varying eddy field is analyzed accounting for sampling biases in the unevenly distributed ITP data and caveats in detection methods. The highest concentration of eddies was found in the western and southern portions of the basin, close to topographic margins and boundaries of the Beaufort Gyre. The number of lower halocline eddies approximately doubled from 2005-2012 to 2013-2014. The increased eddy density suggests more active baroclinic instability of the Beaufort Gyre that releases available potential energy to balance the wind energy input; this may stabilize the Gyre spin-up and associated freshwater increase.
Escudier, Romain; Mourre, Baptiste; Juza, Mélanie; Tintoré, Joaquín.
2016-08-01
Algerian eddies are the strongest and largest propagating mesoscale structures in the Western Mediterranean Sea. They have a large influence on the mean circulation, water masses and biological processes. Over 20 years of satellite altimeter data have been analyzed to characterize the propagation of these eddies using automatic detection methods and cross-correlation analysis. We found that, on average, Algerian eddy trajectories form two subbasin scale anticlockwise gyres that coincide with the two Algerian gyres which were described in the literature as the barotropic circulation in the area. This result suggests that altimetry sea surface observations can provide information on subsurface currents and their variability through the study of the propagation of deep mesoscale eddies in semienclosed seas. The analysis of eddy sea level anomalies along the mean pathways reveals three preferred areas of formation. Eddies are usually formed at a specific time of the year in these areas, with a strong interannual variability over the last 20 years.
PROPAGATION OF LONG-LIVED ANTICYCLONIC ROSSBY EDDIES OVER AN ISOLATED TOPOGRAPHY AND THEIR MERGING
无
2001-01-01
In this paper, in a barotropic model the propagation of long-lived anticylonic Gaussian eddies larger than the radius of deformation over a Gaussian-shaped topography and the merging of the two anticyclonic eddies are investigated by solving the generalized Flierl-Yamagata equation. It is shown that whether or not the basic flow is present, the isoated topography seems to encourage the amplification of an anticyclonic eddy and its southwest movement around the hill. In the absence of both the westward flow and the topography, two anticyclonic eddies of indentical sizes and amplitudes can merge. However, either the including of the topography or the westward basic flow can make them not merge. In the presence of both, the eddies can merge, but this merging depends on whether the parameter condition is appropriate or not. Therefore, it can be concluded that the topographic forcing might be a possible mechanism for the merging of two anticyclonic eddies.
Luo, Dehai; Cha, Jing; Zhong, Linhao; Dai, Aiguo
2014-05-01
In this paper, a nonlinear multi-scale interaction (NMI) model is used to propose an eddy-blocking matching (EBM) mechanism to account for how synoptic eddies reinforce or suppress a blocking flow. It is shown that the spatial structure of the eddy vorticity forcing (EVF) arising from upstream synoptic eddies determines whether an incipient block can grow into a meandering blocking flow through its interaction with the transient synoptic eddies from the west. Under certain conditions, the EVF exhibits a low-frequency oscillation on timescales of 2-3 weeks. During the EVF phase with a negative-over- positive dipole structure, a blocking event can be resonantly excited through the transport of eddy energy into the incipient block by the EVF. As the EVF changes into an opposite phase, the blocking decays. The NMI model produces life cycles of blocking events that resemble observations. Moreover, it is shown that the eddy north-south straining is a response of the eddies to a dipole- or Ω-type block. In our model, as in observations, two synoptic anticyclones (cyclones) can attract and merge with one another as the blocking intensifies, but only when the feedback of the blocking on the eddies is included. Thus, we attribute the eddy straining and associated vortex interaction to the feedback of the intensified blocking on synoptic eddies. The results illustrate the concomitant nature of the eddy deformation, whose role as a PV source for the blocking flow becomes important only during the mature stage of a block. Our EBM mechanism suggests that an incipient block flow is amplified (or suppressed) under certain conditions by the EVF coming from the upstream of the blocking region.
Eddy heat and salt transports in the South China Sea and their seasonal modulations
Chen, Gengxin; Gan, Jianping; Xie, Qiang; Chu, Xiaoqing; Wang, Dongxiao; Hou, Yijun
2012-05-01
This study describes characteristics of eddy (turbulent) heat and salt transports, in the basin-scale circulation as well as in the embedded mesoscale eddy found in the South China Sea (SCS). We first showed the features of turbulent heat and salt transports in mesoscale eddies using sea level anomaly (SLA) data, in situ hydrographic data, and 375 Argo profiles. We found that the transports were horizontally variable due to asymmetric distributions of temperature and salinity anomalies and that they were vertically correlated with the thermocline and halocline depths in the eddies. An existing barrier layer caused the halocline and eddy salt transport to be relatively shallow. We then analyzed the transports in the basin-scale circulation using an eddy diffusivity method and the sea surface height data, the Argo profiles, and the climatological hydrographic data. We found that relatively large poleward eddy heat transports occurred to the east of Vietnam (EOV) in summer and to the west of the Luzon Islands (WOL) in winter, while a large equatorward heat transport was located to the west of the Luzon Strait (WLS) in winter. The eddy salt transports were mostly similar to the heat transports but in the equatorward direction due to the fact that the mean salinity in the upper layer in the SCS tended to decrease toward the equator. Using a 21/2-layer reduced-gravity model, we conducted a baroclinic instability study and showed that the baroclinic instability was critical to the seasonal variation of eddy kinetic energy (EKE) and thus the eddy transports. EOV, WLS, and WOL were regions with strong baroclinic instability, and, thus, with intensified eddy transports in the SCS. The combined effects of vertical velocity shear, latitude, and stratification determined the intensity of the baroclinic instability, which intensified the eddy transports EOV during summer and WLS and WOL during winter.
Occurrence and characteristics of mesoscale eddies in the tropical northeast Atlantic Ocean
F. Schütte
2015-12-01
Full Text Available Coherent mesoscale features (referred to here as eddies in the tropical northeast Atlantic (between 12–22° N and 15–26° W are examined and characterised. The eddies' surface signatures are investigated using 19 years of satellite derived sea level anomaly (SLA data. Two automated detection methods are applied, the geometrical method based on closed streamlines around eddy cores, and the Okubo–Weiß method based on the relation between vorticity and strain. Both methods give similar results. Mean eddy surface signatures of SLA, sea surface temperature (SST and salinity (SSS are obtained from composites of all snapshots around identified eddy cores. Anticyclones/cyclones are associated with elevation/depression of SLA and enhanced/reduced SST and SSS patterns. However, about 20 % of all detected anticyclones show reduced SST and reduced SSS instead. These kind of eddies are classified as anticyclonic mode-water eddies (ACMEs. About 146 ± 4 eddies per year are identified (52 % cyclones, 39 % anticylones, 9 % ACMEs with rather similar mean radii of about 56 ± 12 km. Based on concurrent in-situ temperature and salinity profile data (from Argo float, shipboard and mooring data inside of the three eddy types, their distinct differences in vertical structure is determined. Most eddies are generated preferentially in boreal summer and along the West African coast at three distinct coastal headland region and carry South Atlantic Central Water that originates from the northward transport within the Mauretania coastal current system. Westward eddy propagation (on average about 3.00 ± 2.15 km d−1 is confined to distinct corridors with a small meridional deflection dependent on the eddy type (anticyclones – equatorward, cyclones – poleward, ACMEs – no deflection. Heat and salt flux out of the coastal region and across the Cap Verde Frontal Zone, which separates the shadow zone from the ventilated gyre, are calculated.
Mesoscale eddies in the South China Sea and their impact on temperature profiles
WANG Guihua; SU Jilan; LI Rongfeng
2005-01-01
Some life history statistics of the mesoscale eddies ofthe South China Sea (SCS) derived from altimetry data will be further discussed according their different formation periods.A total of three ATLAS (autonomous temperature line acquisition system)mooring buoys data will be analyzed to discuss eddies' impact on temperature profiles.They identify that the intraseasonal variation of SCSthermocline is partly controlled by mesoscale eddies.
On the energetics of the mean and eddy circulations in the lower stratosphere
Oort, Abraham H.
2011-01-01
A hemispheric network of radiosonde stations is used in order to study the energetics of the lower stratosphere during the IGY period July 1957 through June 1958. For a hemispheric polar cap with 30 and 100 mb as top and bottom boundaries the balance equations of zonal and eddy kinetic energy, and zonal and eddy available potential energy are considered in detail. The eddies appear to build up the kinetic energy of the zonal flow at the expense of the eddy kinetic energy during all seasons. T...
Multifractal filtering method for extraction of ocean eddies from remotely sensed imagery
GE Yong; DU Yunyan; CHENG Qiuming; LI Ce
2006-01-01
Traditional methods of extracting the ocean wave eddy information from remotely sensed imagery mainly use the edge detection technology such as Canny and Hough operators. However, due to the complexities of ocean eddies and image itself, it is sometimes difficult to successfully detect ocean eddies using these methods. A multifractal filtering technology is proposed for extraction of ocean eddies and demonstrated using NASA MODIS,SeaWiFS and NOAA satellite data set in the typical area, such as ocean west boundary current. Results showed that the new method has a superior performance over the traditional methods.
Study of eddy current power loss in an RCS vacuum chamber
XU Shou-Yan; WANG Sheng
2012-01-01
In a Rapid Cycling Synchrotron (RCS),power loss due to an eddy current on the metal vacuum chamber would cause heating of the vacuum chamber.It is important to study the effect for estimating eddy current induced power loss and temperature growth.Analytical formulas for eddy current power loss for various types of vacuum chambers are derived for dipole and quadrupole repectively.By using the prototype of dipole of CSNS/RCS,an experiment was done to test the analytical formula.The derived formulas were applied to calculating the eddy current power loss on some special structures of an RCS vacuum chamber.
A sub-surface eddy at inertial current layer in the Canada Basin, Arctic Ocean
无
2007-01-01
An Arctic Ocean eddy in sub-surface layer is analyzed in this paper by use of temperature, salinity and current profiles data obtained at an ice camp in the Canada Basin during the second Chinese Arctic Expedition in summer of 2003.In the vertical temperature section, the eddy shows itself as an isolated cold water block at depth of 60 m with a minimum temperature of-1.5℃, about 0.5℃ colder than the ambient water.Isopycnals in the eddy form a pattern of convex, which indicates the eddy is anticyclonic.Although maximum velocity near O.4 m s-1 occurs in the current records observed synchronously, the current pattern is far away from a typical eddy.By further analysis, inertial frequency oscillations with amplitudes comparable with the eddy velocity are found in the sub-surface layer currents.After filter the inertial current and mean current, an axisymmetric current pattern of an eddy with maximum velocity radius of 5 km is obtained.The analysis of the T-S characteristics of the eddy core water and its ambient waters supports the conclusion that the eddy was formed on the Chukchi Shelf and migrated northeastward into the northern Canada Basin.
An initial note on quasistationary, cold-core Lanyu eddies southeast off Taiwan Island
JING Chunsheng; LI Li
2003-01-01
Drifting buoys, satellite altimetry and satellite-derived sea surface thermal images are used to identify the existence of a large cold-core, cyclonic Kuroshio frontal eddy between Hengchun Peninsula and Lanyu, southeast off Taiwan Island around March 1996. The cold eddy accompahies an offshore meander of the Kuroshio near Lanyu, about 70 km and 100 km in horizontal zonal and meridional scales,respectively. The cold eddy is different from normal Kuroshio frontal eddies for its persisting of about 2 months near Lanyu. Supporting evidence suggests that the Kuroshio intruded into the South China Sea (SCS, hereafter) forming a loop-like structure during the persisting period of the cold eddy and that similar eddies occur occasionally in the same location. Compared with the corresponding studies in the Gulf of Mexico, it is suggested that Lanyu cold eddies are SCS analogues of Tortugas eddies found in the southern Straits of Florida. Overshooting of the meandering Kuroshio when it leaves the SCS and effects from conservation of potential vorticity are the possible mechanism of eddy genesis.
Analysis of eddy currents in the two-half isolated vacuum vessel of an iron core tokamak
Liu, L.J., E-mail: liulongjian001@yeah.net [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Rao, B.; Zhang, M.; Yu, K.X.; Zhuang, G. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074 (China); School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)
2015-12-15
Eddy currents in the vacuum vessel can cause many problems in plasma diagnostics and control, the fast analysis of eddy current is very important. In this paper, the characteristic of eddy currents in the thin shell of a two-half isolated vacuum vessel and the iron core's effect on eddy currents are analyzed, then an analytical method is used to calculate toroidal eddy currents in the vacuum vessel. Using this method, the eddy currents can be calculated rapidly which will benefit more accurate plasma reconstruction and real-time control. The calculated results by this method agree well with finite element method simulations based on J-TEXT configuration.
Large Eddy Simulation for Plunge Breaker and Sediment Suspension
BAI Yuchuan(白玉川); C.O.NG
2002-01-01
Breaking waves are a powerful agent for generating turbulence that plays an important role in many fluid dynamicalprocesses, particularly in the mixing of materials. Breaking waves can dislodge sediment and throw it into suspension,which will then be carried by wave-induced steady current and tidal flow. In order to investigate sediment suspension bybreaking waves, a numerical model based on large-eddy-simulation (LES) is developed. This numerical model can beused to simulate wave breaking and sediment suspension. The model consists of a free-surface model using the surfacemarker method combined with a two-dimensional model that solves the flow equations. The turbulence and the turbulentdiffusion are described by a large-eddy-simulation (LES) method where the large turbulence features are simulated bysolving the flow equations, and a subgrid model represents the small-scale turbulence that is not resolved by the flowmodel. A dynamic eddy viscosity subgrid scale stress model has been used for the present simulation. By applying thismodel to Stokes' wave breaking problem in the surf zone, we find that the model results agree very well with experimentaldata. By use of this model to simulation of the breaking process of a periodic wave, it can be found that the model canreproduce the complicated flow phenomena, especially the plunging breaker. It reflects the dynamic structures of roller orvortex in the plunging breaker, and when the wave breaks, many strong vortex structures will be produced in the innersurf zone where the concentration of suspended sediment can thereby become relatively high.
On integrating large eddy simulation and laboratory turbulent flow experiments.
Grinstein, Fernando F
2009-07-28
Critical issues involved in large eddy simulation (LES) experiments relate to the treatment of unresolved subgrid scale flow features and required initial and boundary condition supergrid scale modelling. The inherently intrusive nature of both LES and laboratory experiments is noted in this context. Flow characterization issues becomes very challenging ones in validation and computational laboratory studies, where potential sources of discrepancies between predictions and measurements need to be clearly evaluated and controlled. A special focus of the discussion is devoted to turbulent initial condition issues.
Efficient Large Eddy Simulation for the Discontinuous Galerkin Method
Creech, Angus; Maddison, James; Percival, James; Bruce, Tom
2016-01-01
In this paper we present a new technique for efficiently implementing Large Eddy Simulation with the Discontin- uous Galerkin method on unstructured meshes. In particular, we will focus upon the approach to overcome the computational complexity that the additional degrees of freedom in Discontinuous Galerkin methods entail. The turbulence algorithms have been implemented within Fluidity, an open-source computational fluid dynamics solver. The model is tested with the well known backward-facing step problem, and is shown to concur with published results.
Eddy diffusivities of inertial particles in random Gaussian flows
Boi, Simone; Muratore-Ginanneschi, Paolo
2016-01-01
We investigate the large-scale transport of inertial particles. We derive explicit analytic expressions for the eddy diffusivities for generic Stokes times. These latter expressions are exact for any shear flow while they correspond to the leading contribution either in the deviation from the shear flow geometry or in the P\\'eclet number of general random Gaussian velocity fields. Our explicit expressions allow us to investigate the role of inertia for such a class of flows and to make exact links with the analogous transport problem for tracer particles.
The Role of Eddy-Tansport in the Thermohaline Circulation
Dr. Paola Cessi
2011-11-17
Several research themes were developed during the course of this project. (1) Low-frequency oceanic varibility; (2) The role of eddies in the Antarctic Circumpolar Current (ACC) region; (3) Deep stratification and the overturning circulation. The key findings were as follows: (1) The stratification below the main thermocline (at about 500m) is determined in the circumpolar region and then communicated to the enclosed portions of the oceans through the overturning circulation. (2) An Atlantic pole-to-pole overturning circulation can be maintained with very small interior mixing as long as surface buoyancy values are shared between the northern North Atlantic and the ACC region.
Large-eddy simulation of trans- and supercritical injection
Müller, H.; Niedermeier, C. A.; Jarczyk, M.; Pfitzner, M.; Hickel, S.; Adams, N. A.
2016-07-01
In a joint effort to develop a robust numerical tool for the simulation of injection, mixing, and combustion in liquid rocket engines at high pressure, a real-gas thermodynamics model has been implemented into two computational fluid dynamics (CFD) codes, the density-based INCA and a pressure-based version of OpenFOAM. As a part of the validation process, both codes have been used to perform large-eddy simulations (LES) of trans- and supercritical nitrogen injection. Despite the different code architecture and the different subgrid scale turbulence modeling strategy, both codes yield similar results. The agreement with the available experimental data is good.
Eddy current pulsed phase thermography for subsurface defect quantitatively evaluation
He, Yunze; Pan, Mengchun; Tian, GuiYun; Chen, Dixiang; Tang, Ying; Zhang, Hong
2013-09-01
This Letter verified eddy current pulse phase thermography through numerical and experimental studies. During the numerical studies, two characteristic features, blind frequency and min phase, were extracted from differential phase spectra, and their monotonic relationships with defects' depth under different heating time were compared. According to the numerical studies, 100 ms was employed as heating time during the improved experimental studies. The experimental results agreed with the numerical results. Based on their linear relationship with defects' depths, both features can be used to measure the defect's depth.
Thickness Evaluation of Aluminium Plate Using Pulsed Eddy Current Technique
Singh, Gurpartap; Bapat, Harsh Madhukar; Singh, Bhanu Pratap; Bandyopadhyay, Manojit; Puri, Rakesh Kumar; Badodkar, Deepak Narayanrao
2013-10-01
This paper describes a pulsed eddy current (PEC) based non-destructive testing system used for detection of thickness variation in aluminium plate. A giant magneto-resistive sensor has been used instead of pick up coil for detecting resultant magnetic field. The PEC response signals obtained from 1 to 5 mm thickness change in aluminium plate were investigated. Two time domain features, namely peak value and time to peak, of PEC response were used for extracting information about thickness variation in aluminium plate. The variation of peak value and time to peak with thickness was compared. A program was developed to display the thickness variation of the tested sample.
Eddy current system for inspection of train hollow axles
Chady, Tomasz; Psuj, Grzegorz; Sikora, Ryszard; Kowalczyk, Jacek; Spychalski, Ireneusz [Department of Electrical and Computer Engineering, Faculty of Electrical Engineering, West Pomeranian University of Technology, Szczecin (Poland)
2014-02-18
The structural integrity of wheelsets used in rolling stock is of great importance to the safety. In this paper, electromagnetic system with an eddy current transducer suitable for the inspection of hollow axles have been presented. The transducer was developed to detect surface braking defects having depth not smaller than 0.5 mm. Ultrasound technique can be utilized to inspect the whole axle, but it is not sufficiently sensitive to shallow defects located close to the surface. Therefore, the electromagnetic technique is proposed to detect surface breaking cracks that cannot be detected by ultrasonic technique.
Spectral large-eddy simulations and vortex dynamics in turbulence
Lesieur, M
1999-01-01
We present a point of view of large-eddy simulations (LES) in Fourier space, where the eddy coefficients are expressed thanks to a two- point spectral closure of isotropic turbulence, the EDQNM theory. Returning to real space, this leads to models of the structure- function family (plain, selective or filtered). These models are applied with success to predict the statistical distributions and coherent-vortex dynamics for a wide variety of turbulent flows. In three-dimensional decaying isotropic turbulence, we confirm the existence of a k/sup 4/ infrared backscatter in the kinetic-energy spectrum, and predict a new k/sup 2/ law for the pressure spectrum in this range. In the mixing layer (temporal or spatial), we show how to manipulate the topology of Kelvin-Helmholtz vortices, from quasi two- dimensionality to helical pairing. The latter vortex organization is found in a backward-facing step just behind the step, and yields big staggered Lambda -vortices which are carried away downstream. In a developed turb...
A family of dynamic models for large-eddy simulation
Carati, D.; Jansen, K.; Lund, T.
1995-01-01
Since its first application, the dynamic procedure has been recognized as an effective means to compute rather than prescribe the unknown coefficients that appear in a subgrid-scale model for Large-Eddy Simulation (LES). The dynamic procedure is usually used to determine the nondimensional coefficient in the Smagorinsky (1963) model. In reality the procedure is quite general and it is not limited to the Smagorinsky model by any theoretical or practical constraints. The purpose of this note is to consider a generalized family of dynamic eddy viscosity models that do not necessarily rely on the local equilibrium assumption built into the Smagorinsky model. By invoking an inertial range assumption, it will be shown that the coefficients in the new models need not be nondimensional. This additional degree of freedom allows the use of models that are scaled on traditionally unknown quantities such as the dissipation rate. In certain cases, the dynamic models with dimensional coefficients are simpler to implement, and allow for a 30% reduction in the number of required filtering operations.
Large eddy simulation of mechanical mixing in anaerobic digesters.
Wu, Binxin
2012-03-01
A comprehensive study of anaerobic digestion requires an advanced turbulence model technique to accurately predict mixing flow patterns because the digestion process that involves mass transfer between anaerobes and their substrates is primarily dependent on detailed information about the fine structure of turbulence in the digesters. This study presents a large eddy simulation (LES) of mechanical agitation of non-Newtonian fluids in anaerobic digesters, in which the sliding mesh method is used to characterize the impeller rotation. The three subgrid scale (SGS) models investigated are: (i) Smagorinsky-Lilly model, (ii) wall-adapting local eddy-viscosity model, and (iii) kinetic energy transport (KET) model. The simulation results show that the three SGS models produce very similar flow fields. A comparison of the simulated and measured axial velocities indicates that the LES profile shapes are in general agreement with the experimental data but they differ markedly in velocity magnitudes. A check of impeller power and flow numbers demonstrates that all the SGS models give excellent predictions, with the KET model performing the best. Moreover, the performance of six Reynolds-averaged Navier-Stokes turbulence models are assessed and compared with the LES results.
Large eddy simulation of vertical turbulent jets under JONSWAP waves
Jun Lu; Ling-Ling Wang; Hong-Wu Tang; Hui-Chao Dai
2011-01-01
The effect of random waves on vertical plane turbulent jets is studied numerically and the mechanism behind the interaction of the jet and waves is analyzed. The large eddy simulation method is used and the σ-coordinate system is adopted. Turbulence is modeled by a dynamic coherent eddy model. The σ-coordinate transformation is introduced to map the irregular physical domain with a wavy free surface and an uneven bottom onto a regular computational domain. The fractional step method is used to solve the filtered Navier-Stokes equations. Results presented include the distribution of velocity, the decay law of the mean velocity along the jet axis, self-similar characteristics and volume flux per unit width. In particular, the role of coherent structures on the momentum transfer along the jet centerline and the jet instantaneous characteristics in JONSWAP waves are a special focus of this research. The numerical results obtained are of great theoretical importance in understanding the behavior of turbulent jets in random wave environments.
Generation of deep eddies by a turning baroclinic jet
Sutyrin, Georgi
2015-07-01
The North Atlantic Current (NAC) travels northward east of the Grand Banks until approximately 50°N where it makes a sharp turn to the east. Previous analysis of sea level variability in this region, known as the Northwest Corner, showed large-amplitude meandering and a quasi-regular production of anticyclonic eddies playing an important role in the air-sea heat exchange. Here we investigate key physical mechanisms of meandering of an idealized upper ocean turning jet using a two-layer model. The existing reduced-gravity thin jet theory is modified to take into account the crossjet velocity in the lower layer induced by the jet meanders. Such coupled system is capable to describe realistically baroclinic instability and to reduce the two-dimensional initial value problem to a rather simple one-dimensional formulation. Its linearized version is solved here to describe the fluid motion in both layers in terms of jet curvature. It is found that transient meander growth is enhanced in the vicinity of turning point owing to vertical coupling with deep eddies generated due to stretching in water column beneath growing meanders. Scaling for initial growth of deep cyclone-anticyclone pair is suggested based on a generalized thin jet theory. Patterns of further nonlinear evolution resembling observational data are described.
The Fidelity of Ocean Models With Explicit Eddies (Chapter 17)
McClean, J; Jayne, S; Maltrud, M; Ivanova, D
2007-08-01
Current practices within the oceanographic community have been reviewed with regard to the use of metrics to assess the realism of the upper-ocean circulation, ventilation processes diagnosed by time-evolving mixed layer depth and mode water formation, and eddy heat fluxes in large-scale fine resolution ocean model simulations. We have striven to understand the fidelity of these simulations in the context of their potential use in future fine-resolution coupled climate system studies. A variety of methodologies are used to assess the veracity of the numerical simulations. Sea surface height variability and the location of western boundary current paths from altimetry have been used routinely as basic indicators of fine-resolution model performance. Drifters and floats have also been used to provide pseudo-Eulerian measures of the mean and variability of surface and sub-surface flows, while statistical comparisons of observed and simulated means have been carried out using James tests. Probability density functions have been used to assess the Gaussian nature of the observed and simulated flows. Length and time scales have been calculated in both Eulerian and Lagrangian frameworks from altimetry and drifters, respectively. Concise measures of multiple model performance have been obtained from Taylor diagrams. The time-evolution of the mixed layer depth at monitoring stations has been compared with simulated time series. Finally, eddy heat fluxes are compared to climatological inferences.
Bayesian flaw characterization from eddy current measurements with grain noise
McMahan, Jerry A.; Aldrin, John C.; Shell, Eric; Oneida, Erin
2017-02-01
The Bayesian approach to inference from measurement data has the potential to provide highly reliable characterizations of flaw geometry by quantifying the confidence in the estimate results. The accuracy of these confidence estimates depends on the accuracy of the model for the measurement error. Eddy current measurements of electrically anisotropic metals, such as titanium, exhibit a phenomenon called grain noise in which the measurement error is spatially correlated even with no flaw present. We show that the most commonly used statistical model for the measurement error, which fails to account for this correlation, results in overconfidence in the flaw geometry estimates from eddy current data, thereby reducing the effectiveness of the Bayesian approach. We then describe a method of modeling the grain noise as a Gaussian process (GP) using spectral mixture kernels, a type of non-parametric model for the covariance kernel of a GP This provides a broadly applicable, data-driven way of modeling correlation in measurement error. Our results show that incorporation of this noise model results in a more reliable estimate of the flaw and better agreement with the available validation data.
Design and optimization of a flexible arrayed eddy current sensor
Sun, Zhenguo; Cai, Dong; Zou, Cheng; Zhang, Wenzeng; Chen, Qiang
2017-04-01
The inspection of the hollow axle inner surfaces is a key process to guarantee the safety of high-speed trains. A novel flexible arrayed eddy current sensor was developed to improve the reliability of the non-destructive testing of the hollow axle inner surfaces, whose main innovative aspect was the new design of excitation/sensing traces to achieve a differential and arrayed configuration. Only two independent excitation traces were used in the sensor to induce eddy currents, which can be detected by 16 differential sensing elements. The lift-off effects and the influence of the excitation frequency and geometrical parameters of the proposed sensor was investigated and presented in this paper. Finite element models were built to analyze the effects of each parameter on the sensor response amplitude. Experimental validations were conducted using a representative set of sensors. Results from experiments and simulations were consistent with each other, which showed that the sensor design can substantially suppress the lift-off effects and modifications of the studied parameters can substantially improve the sensor performance.
Finecasting for renewable energy with large-eddy simulation
Jonker, Harmen; Verzijlbergh, Remco
2016-04-01
We present results of a single, continuous Large-Eddy Simulation of actual weather conditions during the timespan of a full year, made possible through recent computational developments (Schalkwijk et al, MWR, 2015). The simulation is coupled to a regional weather model in order to provide an LES dataset that is representative of the daily weather of the year 2012 around Cabauw, the Netherlands. This location is chosen such that LES results can be compared with both the regional weather model and observations from the Cabauw observational supersite. The run was made possible by porting our Large-Eddy Simulation program to run completely on the GPU (Schalkwijk et al, BAMS, 2012). GPU adaptation allows us to reach much improved time-to-solution ratios (i.e. simulation speedup versus real time). As a result, one can perform runs with a much longer timespan than previously feasible. The dataset resulting from the LES run provides many avenues for further study. First, it can provide a more statistical approach to boundary-layer turbulence than the more common case-studies by simulating a diverse but representative set of situations, as well as the transition between situations. This has advantages in designing and evaluating parameterizations. In addition, we discuss the opportunities of high-resolution forecasts for the renewable energy sector, e.g. wind and solar energy production.
Three-dimensional parabolic equation modeling of mesoscale eddy deflection.
Heaney, Kevin D; Campbell, Richard L
2016-02-01
The impact of mesoscale oceanography, including ocean fronts and eddies, on global scale low-frequency acoustics is examined using a fully three-dimensional parabolic equation model. The narrowband acoustic signal, for frequencies from 2 to 16 Hz, is simulated from a seismic event on the Kerguellen Plateau in the South Indian Ocean to an array of receivers south of Ascension Island in the South Atlantic, a distance of 9100 km. The path was chosen for its relevance to seismic detections from the HA10 Ascension Island station of the International Monitoring System, for its lack of bathymetric interaction, and for the dynamic oceanography encountered as the sound passes the Cape of Good Hope. The acoustic field was propagated through two years (1992 and 1993) of the eddy-permitting ocean state estimation ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) system. The range of deflection of the back-azimuth was 1.8° with a root-mean-square of 0.34°. The refraction due to mesoscale oceanography could therefore have significant impacts upon localization of distant low-frequency sources, such as seismic or nuclear test events.
THE EDDY LOSSES OF A MAGNETIC THRUST BEARING
徐华; 王艳
2004-01-01
Accurate calculations of losses associated with the operation of magnetic bearings are particularly important for high speed applications where the rotor losses are expected to be large and for some particular applications where even low power losses will be critical. Power losses in the magnetic thrust bearing is often neglected, but if there is misaligned in the rotor and bearing, the magnetic field in the thrust bearing is no longer axisymmetric one, or the dynamic control current in the winding is time dependent one, eddy currents are caused to flow inside the conducting material, then the power losses are very important for magnetic bearing design. This paper presents an analytical model of a thrust magnetic bearing, and the magnetic fields, forces and losses of thrust magnetic bearing are calculated. In the calculations the frequency of dynamic control current is up to 1000Hz, rotating speed is from 60rpm to 1200rpm, and the non-linearity of material is also taken into consideration. The results shows that if the magnetic field is not saturation, the eddy losses is proportional to dynamic control current frequency and a square function of dynamic control current, and also 5/2 power function of shaft's speed.
Comparison of numerical schemes in large-eddy simulation of the temporal mixing layer
Vreman, A.W.; Geurts, Bernardus J.; Kuerten, Johannes G.M.
1996-01-01
A posteriori tests of large-eddy simulations for the temporal mixing layer are performed using a variety of numerical methods in conjunction with the dynamic mixed subgrid model for the turbulent stress tensor. The results of the large-eddy simulations are compared with filtered direct numerical
Direct and Large-Eddy Simulation of the Compressible Turbulent Mixing Layer
Vreman, A.W.
1995-01-01
The Large-Eddy Simulation technique of compressible flows and the effect of compressibility on mixing layers are the main subjects of this thesis. Direct Numerical Simulations (DNS) and Large-Eddy Simulations (LES) of the temporal compressible mixing layer at various Mach and Reynolds numbers have
Geurts, Bernard J.; Meyers, Johan
2006-01-01
We propose the successive inverse polynomial interpolation method to optimize model parameters in subgrid parameterization for large-eddy simulation. This approach is illustrated for the Smagorinsky eddy-viscosity model used in homogeneous decaying turbulence. The optimal Smagorinsky parameter is re
Large-eddy simulations of the non-reactive flow in the Sydney swirl burner
Yang, Yang; Kær, Søren Knudsen
2012-01-01
This paper presents a numerical investigation using large-eddy simulation. Two isothermal cases from the Sydney swirling flame database with different swirl numbers were tested. Rational grid system and mesh details were presented firstly. Validations showed overall good agreement in time averaged...... package in predicting complex flow field and presented the potential of large eddy simulation in understanding dynamics....
Cost Reduction of Large Eddy Simulation of Airfoils in Turbulent Inflow
Gilling, Lasse; Sørensen, Niels; Rethore, Pierre-Elouan
2009-01-01
This paper discusses simulations of airfoil flows by use of computational fluid dynamics. In recent work large eddy simulations (LES) of airfoil flows have proved superior to detached eddy simulations (DES); by resolving the inflow turbulence the agreement with experiments is improved. The scope...
Permanent Magnet Eddy Current Loss Analysis of a Novel Motor Integrated Permanent Magnet Gear
Zhang, Yuqiu; Lu, Kaiyuan; Ye, Yunyue
2012-01-01
In this paper, a new motor integrated permanent magnet gear (MIPMG) is discussed. The focus is on eddy current loss analysis associated to permanent magnets (PMs). A convenient model of MIPMG is provided based on 2-D field-motion coupled time-stepping finite element method for transient eddy...
Eddy-mediated biological productivity in the Bay of Bengal during fall and spring intermonsoons
PrasannaKumar, S.; Nuncio, M.; Ramaiah, N.; Sardesai, S.; Narvekar, J.; Fernandes, V.; Paul, J.T.
the temperature, which varied from 3oC to 7oC at 120 m depth. Maximum depression of temperature was associated with spring-time eddies in the northern Bay, where subsurface stability was low. The reduced water column stability in spring leads to greater eddy-pumping...
Heat balance and eddies in the Peru-Chile current system
Colas, Francois; McWilliams, James C.; Kurian, Jaison [University of California, Institute of Geophysics and Planetary Physics, Los Angeles, CA (United States); Capet, Xavier [Laboratoire de Physique des Oceans, Ifremer, Plouzane (France)
2012-07-15
The Peru-Chile current System (PCS) is a region of persistent biases in global climate models. It has strong coastal upwelling, alongshore boundary currents, and mesoscale eddies. These oceanic phenomena provide essential heat transport to maintain a cool oceanic surface underneath the prevalent atmospheric stratus cloud deck, through a combination of mean circulation and eddy flux. We demonstrate these behaviors in a regional, quasi-equilibrium oceanic model that adequately resolves the mesoscale eddies with climatological forcing. The key result is that the atmospheric heating is large (>50 W m{sup -2}) over a substantial strip >500 km wide off the coast of Peru, and the balancing lateral oceanic flux is much larger than provided by the offshore Ekman flux alone. The atmospheric heating is weaker and the coastally influenced strip is narrower off Chile, but again the Ekman flux is not sufficient for heat balance. The eddy contribution to the oceanic flux is substantial. Analysis of eddy properties shows strong surface temperature fronts and associated large vorticity, especially off Peru. Cyclonic eddies moderately dominate the surface layer, and anticyclonic eddies, originating from the nearshore poleward Peru-Chile Undercurrent (PCUC), dominate the subsurface, especially off Chile. The sensitivity of the PCS heat balance to equatorial intra-seasonal oscillations is found to be small. We demonstrate that forcing the regional model with a representative, coarse-resolution global reanalysis wind product has dramatic and deleterious consequences for the oceanic circulation and climate heat balance, the eddy heat flux in particular. (orig.)
Geurts, Bernardus J.; Meyers, Johan
We propose the successive inverse polynomial interpolation method to optimize model parameters in subgrid parameterization for large-eddy simulation. This approach is illustrated for the Smagorinsky eddy-viscosity model used in homogeneous decaying turbulence. The optimal Smagorinsky parameter is
Evidence of a southward eddy corridor in the South-West Indian ocean
Ansorge, IJ
2015-09-01
Full Text Available of this eddy corridor appears to be restricted to the deep channel separating the Conrad Rise from the Del Cano and Crozet Plateau. However, while the fate of eddies formed at the SWIR has been widely investigated and the frontal character of this eastward...
Rifai, Damhuji; Abdalla, Ahmed N; Ali, Kharudin; Razali, Ramdan
2016-02-26
Non-destructive eddy current testing (ECT) is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR) sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper.
Tropical Wave-Induced Oceanic Eddies at Cabo Corrientes and the Maria Islands, Mexico
2007-05-30
Hurlburt (1996), Coupled dynamics of the South (2002), Formation of the Haida -1998 oceanic eddy, J. Geophys. Res., China Sea, the Sulu Sea, and the...generation of Haida eddies, Deep Sea Res.. Part 11, 52(7-8), 853-874. Metzger, E. J., H. E. Hurlburt, J. C. Kindle, Z. Sirkes, and J. M. Pringle Enfield, D
Comparison between tower and aircraft-based eddy covariance fluxes in five European regions
Gioli, B.; Miglietta, F.; Martino, De B.; Hutjes, R.W.A.; Dolman, A.J.; Lindroth, A.; Schumacher, M.; Sanz, M.J.; Manca, G.; Peressotti, A.; Dumas, E.J.
2004-01-01
Airborne eddy covariance measurements provide a unique opportunity to directly measure surface energy, mass and momentum fluxes at the regional scale. This offers the possibility to complement the data that are obtained by the ground-based eddy covariance networks and to validate estimates of the su
Damhuji Rifai
2016-02-01
Full Text Available Non-destructive eddy current testing (ECT is widely used to examine structural defects in ferromagnetic pipe in the oil and gas industry. Implementation of giant magnetoresistance (GMR sensors as magnetic field sensors to detect the changes of magnetic field continuity have increased the sensitivity of eddy current techniques in detecting the material defect profile. However, not many researchers have described in detail the structure and issues of GMR sensors and their application in eddy current techniques for nondestructive testing. This paper will describe the implementation of GMR sensors in non-destructive testing eddy current testing. The first part of this paper will describe the structure and principles of GMR sensors. The second part outlines the principles and types of eddy current testing probe that have been studied and developed by previous researchers. The influence of various parameters on the GMR measurement and a factor affecting in eddy current testing will be described in detail in the third part of this paper. Finally, this paper will discuss the limitations of coil probe and compensation techniques that researchers have applied in eddy current testing probes. A comprehensive review of previous studies on the application of GMR sensors in non-destructive eddy current testing also be given at the end of this paper.
Numerical Simulation of Wintertime Mesoscale Eddies in the East China Sea
陈敏; 侯一筠; 方国洪
2003-01-01
A POM based three-dimension baroclinic prognostic model in σ-coordinate was established to simulate the eddies in the East China Seas wintertime circulation, considering the topography, inflow and outflow on the open boundary, Changjiang runoff, heat, flux, and wind stress on the sea surface. The model results showed that three branches separate from the Kuroshio flow toward the interior of the Yellow Sea, and form three eddies respectively. The middle eddy is centered at 124°37′E,37°00′N,the southern eddy is centered at 124°00′E,35°30′N. The large cyclonic eddy centered at 125°06′E,30°30′N and located southwest of Cheju Island is a closed structure formed by the northeastward flowing Taiwan Warm Current, northwestward flowing Yellow Sea Warm Current and southward flowing coastal current. The Kuroshio intrusion engenders an eddy west of Kyushu Island of Japan. The branching of the Kuroshio is the direct dynamic cause of the formation of this large eddy. Moreover, both the topographic influence and the northward wind prevailing in winter affect the eddy's formation obviously.
Study on Eddy-current of Disc Permanent-magnet Eddy-current Couplings%盘式永磁涡流耦合器涡流研究
上官璇峰; 杨帅
2015-01-01
本文旨在研究盘式涡流耦合器涡流分布特点。采用解析法得到了涡流密度的函数表达式；利用三维有限元法分别计算正常工作状态和起动状态下涡流径向分量和周向分量沿径向和周向分布的三维图形并总结涡流沿周向、径向、轴向的分布特点。根据涡流密度的函数表达式着重分析了导体盘材料、气隙长度和转差率三个重要因素对涡流的影响。通过对盘式永磁涡流耦合器涡流特点的把握，合理的解释了轴向磁力随转差率变化的规律。%The purpose of this paper is to study the changing discipline of eddy-current of disc permanent-magnet eddy-current coupling.Analytical method was adopted to get expression of the eddy-current density. 3D FEMwas adopted to obtain the 3D distribution graph along with radial and circumferential direction of eddy-current on radial and circumferential components.And the characteristics of distribution of eddy-current along with radial,circumferential and axial directions were summarized.Three important factors of the influence of eddy-current,conductor plate material,air-gap length and slip were analyzed according to the expression of eddy-current density.Through the grasp of the characteristics of eddy-current,the law of the axial magnetic force changing with slip was explained reasonably.
Haruyasu Yamada
Full Text Available Diffusion imaging is a unique noninvasive tool to detect brain white matter trajectory and integrity in vivo. However, this technique suffers from spatial distortion and signal pileup or dropout originating from local susceptibility gradients and eddy currents. Although there are several methods to mitigate these problems, most techniques can be applicable either to susceptibility or eddy-current induced distortion alone with a few exceptions. The present study compared the correction efficiency of FSL tools, "eddy_correct" and the combination of "eddy" and "topup" in terms of diffusion-derived fractional anisotropy (FA. The brain diffusion images were acquired from 10 healthy subjects using 30 and 60 directions encoding schemes based on the electrostatic repulsive forces. For the 30 directions encoding, 2 sets of diffusion images were acquired with the same parameters, except for the phase-encode blips which had opposing polarities along the anteroposterior direction. For the 60 directions encoding, non-diffusion-weighted and diffusion-weighted images were obtained with forward phase-encoding blips and non-diffusion-weighted images with the same parameter, except for the phase-encode blips, which had opposing polarities. FA images without and with distortion correction were compared in a voxel-wise manner with tract-based spatial statistics. We showed that images corrected with eddy and topup possessed higher FA values than images uncorrected and corrected with eddy_correct with trilinear (FSL default setting or spline interpolation in most white matter skeletons, using both encoding schemes. Furthermore, the 60 directions encoding scheme was superior as measured by increased FA values to the 30 directions encoding scheme, despite comparable acquisition time. This study supports the combination of eddy and topup as a superior correction tool in diffusion imaging rather than the eddy_correct tool, especially with trilinear interpolation, using
Evolution of physical and biological characteristics of mesoscale eddy in north-central Red Sea
Zarokanellos, Nikolaos; Jones, Burton
2015-04-01
Eddies appear to be important to both the physical and biogeochemical dynamics of the Red Sea. Numerical simulations of physical dynamics and remote sensing studies of chlorophyll concentration and sea surface height in the Red Sea indicate their importance to the upper portions of the sea (Raitsos et al., 2013; Yao et al., 2014; Zhan et al., 2014). Despite their apparent importance, process studies of these eddies have been lacking. In March 2013 we began an extended observational study of the north-central Red Sea (NCRS) where anticyclonic eddies have been observed. The study began with a ship-based characterization of the eddy and was followed by a three-month observational time series using an autonomous glider equipped with a CTD, oxygen sensor, and optical sensors for chlorophyll, CDOM and optical backscatter. The ship-based study captured an initial snapshot of an anticyclonic eddy and it's associated biological and bio-optical distributions. Initially, chlorophyll distributions tended to mirror the density distribution, with deeper isopycnals and chlorophyll maximum depth in the anticyclonic eddy center. The anticyclone eddy in March had an along basin diameter of 150 km, penetrated vertically less than 150 m and elevated near surface chlorophyll concentrations appeared along its outer boundary. The shallowing of the pycnocline of the outer boundaries of the anticyclone eddy on March may elevate nutrients into the lower euphotic zone, contributing to phytoplankton productivity and biomass within the eddy. This eddy contains most of the kinetic energy of the region with the maximum velocities up to 30 - 35 cm/s. The eddy appeared to interact with the coastal reefs where exchange particulate and dissolved matter may occur. The autonomous glider provided the spring-to-summer progression of the system with increasing stratification, shallowing of the subsurface chlorophyll maximum, and fluctuations in the position and intensity of the eddy. Our glider effort
Evolution of physical and biological characteristics of mesoscale eddy in north-central Red Sea
Zarokanellos, Nikolaos
2015-04-01
Eddies appear to be important to both the physical and biogeochemical dynamics of the Red Sea. Numerical simulations of physical dynamics and remote sensing studies of chlorophyll concentration and sea surface height in the Red Sea indicate their importance to the upper portions of the sea (Raitsos et al., 2013; Yao et al., 2014; Zhan et al., 2014). Despite their apparent importance, process studies of these eddies have been lacking. In March 2013 we began an extended observational study of the north-central Red Sea (NCRS) where anticyclonic eddies have been observed. The study began with a ship-based characterization of the eddy and was followed by a three-month observational time series using an autonomous glider equipped with a CTD, oxygen sensor, and optical sensors for chlorophyll, CDOM and optical backscatter. The ship-based study captured an initial snapshot of an anticyclonic eddy and it\\'s associated biological and bio-optical distributions. Initially, chlorophyll distributions tended to mirror the density distribution, with deeper isopycnals and chlorophyll maximum depth in the anticyclonic eddy center. The anticyclone eddy in March had an along basin diameter of 150 km, penetrated vertically less than 150 m and elevated near surface chlorophyll concentrations appeared along its outer boundary. The shallowing of the pycnocline of the outer boundaries of the anticyclone eddy on March may elevate nutrients into the lower euphotic zone, contributing to phytoplankton productivity and biomass within the eddy. This eddy contains most of the kinetic energy of the region with the maximum velocities up to 30 - 35 cm/s. The eddy appeared to interact with the coastal reefs where exchange particulate and dissolved matter may occur. The autonomous glider provided the spring-to-summer progression of the system with increasing stratification, shallowing of the subsurface chlorophyll maximum, and fluctuations in the position and intensity of the eddy. Our glider effort
Svatoš, J.
2016-11-01
This paper describes the design of a measuring chain for polyharmonic metal detectors used for education in laboratory exercises at Czech Technical University in Prague, Faculty of Electrical Engineering, Department of Measurement. The Measuring chain is composed of DDS signal generator, Digitiser and PC with software programmed in Labview. Eddy current principles or more specifically eddy current metal detectors are an important part of nondestructive testing, instrumentations and measurement. A short introduction to the background and principles of eddy current metal detectors are presented. Next part of the article deals with a brief description of the most common methods, as well as, non-traditional polyharmonic methods for eddy current metal detection. The following part contains an implementation of the proposed algorithms in LabVIEW graphical programming language. Finally, the created program for education of eddy current metal detectors and results obtained on the metal detector ATMID are discussed.
Estimation of turbulence dissipation rate by Large eddy PIV method in an agitated vessel
Kysela Bohuš
2015-01-01
Full Text Available The distribution of turbulent kinetic energy dissipation rate is important for design of mixing apparatuses in chemical industry. Generally used experimental methods of velocity measurements for measurement in complex geometries of an agitated vessel disallow measurement in resolution of small scales close to turbulence dissipation ones. Therefore, Particle image velocity (PIV measurement method improved by large eddy Ply approach was used. Large eddy PIV method is based on modeling of smallest eddies by a sub grid scale (SGS model. This method is similar to numerical calculations using Large Eddy Simulation (LES and the same SGS models are used. In this work the basic Smagorinsky model was employed and compared with power law approximation. Time resolved PIV data were processed by Large Eddy PIV approach and the obtained results of turbulent kinetic dissipation rate were compared in selected points for several operating conditions (impeller speed, operating liquid viscosity.
Iron flux induced by Haida eddies in the Gulf of Alaska
Xiu, Peng; Palacz, Artur P.; Chai, Fei; Roy, Eric G.; Wells, Mark L.
2011-07-01
Mesoscale anticyclonic Haida eddies are proposed to deliver a substantial amount of iron into the Gulf of Alaska (GOA) central gyre, where surface waters experience high-nitrate low-chlorophyll conditions. In this study we calculate an averaged upwelling flux of dissolved iron into the euphotic zone (100 m) of 1.17 μmol m-2 d-1 based on observed iron profiles and modeled eddy dynamics and resultant vertical velocities. This estimated eddy-derived iron supply rate is comparable with new estimates of pulsed iron fertilization rates from rare volcanic ash deposition events. Despite the relatively small area affected by Haida eddies, they are estimated to contribute about 4.6 × 106 moles of dissolved iron yearly to the GOA, which is equivalent to the annual atmospheric dust deposition. Haida eddies therefore represent a major iron source that should strongly influence the regional biological productivity and carbon budget of the GOA.
Calculation of Skin Depths and Eddy-Current Power Losses for Magnetic Position Sensors
2000-01-01
We present a theoretic model to calculate skin depths and eddy-current power losses for a magnetic position sensor. Eddy-current, arised from the operation of an alternating-current ex citation, induces secondary currents and fields between magnetic material and magnetic position sensor. In this paper, a magnetic position sensor system is simplified to be an outer-winding coil along the axial direction of a low carbon steel bar. The analytical model is derived from basic field and circuit theory considering a linear approximation for a nonlinear permeability. Thus the skin depths and eddy-current power losses from the model in eddy-current modeling techniques at various frequencies of an excited current source can be calculated. The proposed configuration is capable of predicting the skin depths and eddy-current power losses for a magnetic position sensor and has a consistence with experiments.
NONE
2000-02-29
The ultra-low inertia dynamometer equivalent to engines in inertia adopts a rare earth element magnet with large energy product, and simulates engine torque fluctuation by superimposing harmonic current on a stator coil. Since temperature rise is thus predicted by generation of fluctuating magnetic field due to the harmonic current or eddy current due to normal slot harmonics, sufficient study on eddy current loss is necessary for designs to prevent such performance drop. Eddy current analysis is under investigation by 3-D FEM for various size and shape magnets. The analysis example of an eddy current density distribution is illustrated for the one-pole section of the magnet stuck on a rotor surface which is divided into 4 parts along a rotor periphery. More precise analysis of such eddy current loss is scheduled for higher-reliability product design. (translated by NEDO)
Dissipative inertial transport patterns near coherent Lagrangian eddies in the ocean
Beron-Vera, F J; Haller, G; Farazmand, M; Trinanes, J; Wang, Y
2014-01-01
Recent developments in dynamical systems theory have revealed long-lived and coherent Lagrangian (i.e., material) eddies in incompressible, satellite-derived surface ocean velocity fields. Paradoxically, observed drifting buoys and floating matter tend to create dissipative-looking patterns near oceanic eddies, which appear to be inconsistent with the conservative fluid particle patterns created by coherent Lagrangian eddies. Here we show that inclusion of inertial effects (i.e., those produced by the buoyancy and size finiteness of an object) in a rotating two-dimensional incompressible flow context resolves this paradox. Specifically, we obtain that anticyclonic coherent Lagrangian eddies attract (repel) negatively (positively) buoyant finite-size particles, while cyclonic coherent Lagrangian eddies attract (repel) positively (negatively) buoyant finite-size particles. We show how these results explain dissipative-looking satellite-tracked surface drifter and subsurface float trajectories, as well as satell...
Benchmarking the mesoscale variability in global ocean eddy-permitting numerical systems
Cipollone, Andrea; Masina, Simona; Storto, Andrea; Iovino, Doroteaciro
2017-08-01
The role of data assimilation procedures on representing ocean mesoscale variability is assessed by applying eddy statistics to a state-of-the-art global ocean reanalysis (C-GLORS), a free global ocean simulation (performed with the NEMO system) and an observation-based dataset (ARMOR3D) used as an independent benchmark. Numerical results are computed on a 1/4 ∘ horizontal grid (ORCA025) and share the same resolution with ARMOR3D dataset. This "eddy-permitting" resolution is sufficient to allow ocean eddies to form. Further to assessing the eddy statistics from three different datasets, a global three-dimensional eddy detection system is implemented in order to bypass the need of regional-dependent definition of thresholds, typical of commonly adopted eddy detection algorithms. It thus provides full three-dimensional eddy statistics segmenting vertical profiles from local rotational velocities. This criterion is crucial for discerning real eddies from transient surface noise that inevitably affects any two-dimensional algorithm. Data assimilation enhances and corrects mesoscale variability on a wide range of features that cannot be well reproduced otherwise. The free simulation fairly reproduces eddies emerging from western boundary currents and deep baroclinic instabilities, while underestimates shallower vortexes that populate the full basin. The ocean reanalysis recovers most of the missing turbulence, shown by satellite products , that is not generated by the model itself and consistently projects surface variability deep into the water column. The comparison with the statistically reconstructed vertical profiles from ARMOR3D show that ocean data assimilation is able to embed variability into the model dynamics, constraining eddies with in situ and altimetry observation and generating them consistently with local environment.
Vertical heat and salt fluxes due to resolved and parameterized meso-scale Eddies
von Storch, Jin-Song; Haak, Helmuth; Hertwig, Eileen; Fast, Irina
2016-12-01
Using a suite of simulations with the Max Planck Institute Ocean Model (MPIOM) at resolutions of about 0.1°, 0.4° and 1.5°, we study the impact of resolved and parameterized vertical eddy fluxes on the long-standing biases obtained when running MPIOM at low resolutions. In the 0.1° simulation, the eddy heat and salt fluxes have three features in common. First, their horizontal area averages are both upward, counteracting the downward fluxes due to time-mean circulations. Second, their divergences at intermediate depths are both negative, acting to cool and to freshen water masses, thereby reducing the major long-standing warm and saline biases of the low-resolution MPIOM at these depths. Third, both the heat and salt budgets are dominated by a balance between the divergence of eddy flux and that of mean flux. The vertical profiles of the tendency forcing due to parameterized eddies resemble those due to resolved eddies. This resemblance does not guarantee a bias reduction, as the tendency forcing terms are much less well compensated in the 0.4°- and 1.5°-simulation than in the 0.1°-simulation. When concentrating on the eddy-induced transports, we identify two situations in which the eddy effect is not appropriately represented by the GM-parameterization. One emphasizes the importance of the mean tracer distribution and the other the importance of the simulated isoneutral slope in determining the eddy-induced transports. Given the mean salinity distribution in the Southern ocean, characterized by a tongue of fresh Antarctic Intermediate Water, the salinity advection via eddy-induced transport tends to strengthen, rather than to weaken, the saline biases. Due to the density biases in a widened region of the Agulhas current in the low-resolution runs, the isoneutral slope vectors are erroneous and the large parameterized eddy-induced transports do not occur where they should.
HU Zifeng; TAN Yehui; SONG Xingyu; ZHOU Linbin; LIAN Xiping; HUANG Liangmin; HE Yinghui
2014-01-01
Mesoscale eddies have been suggested to have an impact on biological carbon fixation in the South China Sea (SCS). However, their overall contribution to primary production during the spring inter-monsoon pe-riod is still unknown. Based on large-scale biological and environmental in situ observations and synchro-nous remote sensing data, the distribution patterns of phytoplankton biomass and the primary production, and the role of mesoscale eddies in regulating primary production in different eddy-controlled waters were investigated. The results suggested that the surface chlorophyll a concentrations and water column inte-grated primary production (IPP) are significantly higher in cyclonic eddies and lower in the anticyclonic eddies as compared to that in non-eddy waters. Although eddies could affect various environmental factors, such as nutrients, temperature and light availability, nutrient supply is suggested to be the most important one through which mesoscale eddies regulated the distribution patterns of phytoplankton biomass and pri-mary production. The estimated IPP in cyclonic and anticyclonic eddies are about 29.5%higher and 16.6%lower than the total average in the whole study area, respectively, indicating that the promotion effect of mesoscale cold eddies on the primary production was much stronger than the inhibition effect of the warm eddies per unit area. Overall, mesoscale eddies are crucial physical processes that affect the biological car-bon fixation and the distribution pattern of primary production in the SCS open sea, especially during the spring inter-monsoon period.
Sound-speed structure and propagational characteristics of a cold core eddy in the Bay of Bengal
PrasannaKumar, S.; Babu, M.T.; Murty, T.V.R.
reduces by about 20 m across the eddy. Simulation studies showed that the rays passing through the eddy undergoes a reduction in the path length thereby reducing the travel time. Travel time delay causEd. by the eddy is of the order of 200 milliseconds...
Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean
Cornejo D'Ottone, Marcela; Bravo, Luis; Ramos, Marcel; Pizarro, Oscar; Karstensen, Johannes; Gallegos, Mauricio; Correa-Ramirez, Marco; Silva, Nelson; Farias, Laura; Karp-Boss, Lee
2016-05-01
Mesoscale eddies are important, frequent, and persistent features of the circulation in the eastern South Pacific (ESP) Ocean, transporting physical, chemical and biological properties from the productive shelves to the open ocean. Some of these eddies exhibit subsurface hypoxic or suboxic conditions and may serve as important hotspots for nitrogen loss, but little is known about oxygen consumption rates and nitrogen transformation processes associated with these eddies. In the austral fall of 2011, during the Tara Oceans expedition, an intrathermocline, anticyclonic, mesoscale eddy with a suboxic (Water (ESSW) that at this latitude is normally restricted to an area near the coast. Measurements of nitrogen species within the eddy revealed undersaturation (below 44 %) of nitrous oxide (N2O) and nitrite accumulation (> 0.5 µM), suggesting that active denitrification occurred in this water mass. Using satellite altimetry, we were able to track the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). Field studies conducted in Chilean shelf waters close to the time of eddy formation provided estimates of initial O2 and N2O concentrations of the ESSW source water in the eddy. By the time of its offshore sighting, concentrations of both O2 and N2O in the subsurface oxygen minimum zone (OMZ) of the eddy were lower than concentrations in surrounding water and "source water" on the shelf, indicating that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L-1 d-1 and the rate of N2O consumption was 3.92 nmol L-1 d-1. These results show that mesoscale eddies affect open-ocean biogeochemistry in the ESP not only by transporting physical and chemical properties from the coast to the ocean interior but also during advection, local biological consumption of oxygen within an eddy further generates conditions favorable to
Detached Eddy Simulation of Flap Side-Edge Flow
Balakrishnan, Shankar K.; Shariff, Karim R.
2016-01-01
Detached Eddy Simulation (DES) of flap side-edge flow was performed with a wing and half-span flap configuration used in previous experimental and numerical studies. The focus of the study is the unsteady flow features responsible for the production of far-field noise. The simulation was performed at a Reynolds number (based on the main wing chord) of 3.7 million. Reynolds Averaged Navier-Stokes (RANS) simulations were performed as a precursor to the DES. The results of these precursor simulations match previous experimental and RANS results closely. Although the present DES simulations have not reached statistical stationary yet, some unsteady features of the developing flap side-edge flowfield are presented. In the final paper it is expected that statistically stationary results will be presented including comparisons of surface pressure spectra with experimental data.
Large-eddy simulation of transitional channel flow
Piomelli, Ugo; Zang, Thomas A.
1990-01-01
A large-eddy simulation (LES) of transition in plane channel flow was carried out. The LES results were compared with those of a fine direct numerical simulation (DNS), and with those of a coarse DNS that uses the same mesh as the LES, but does not use a residual stress model. While at the early stages of transition, LES and coarse DNS give the same results: the presence of the residual stress model was found to be necessary to predict accurately mean velocity and Reynolds stress profiles during the late stages of transition (after the second spike stage). The evolution of single Fourier modes is also predicted more accurately by the LES than by the DNS. As small scales are generated, the dissipative character of the residual stress starts to reproduce correctly the energy cascade. As transition progresses, the flow approaches its fully developed turbulent state, the subgrid scales tend towards equilibrium, and the model becomes more accurate.
Large-eddy simulation of atmospheric flow over complex terrain
Bechmann, Andreas
2007-01-01
layer transport processes. Velocity and turbulence profiles are in good agreement with measurements. Simulation of the flow over the Askervein hill is also performed. Speed-up and turbulence intensities show good agreement with measurements, except 400m downstream of the hill summit where speed......The present report describes the development and validation of a turbulence model designed for atmospheric flows based on the concept of Large-Eddy Simulation (LES). The background for the work is the high Reynolds number k - #epsilon# model, which has been implemented on a finite-volume code...... turbulence model is able to handle both engineering and atmospheric flows and can be run in both RANS or LES mode. For LES simulations a time-dependent wind field that accurately represents the turbulent structures of a wind environment must be prescribed at the computational inlet. A method is implemented...
Numerical studies towards practical large-eddy simulation
J. Boudet; J. Caro; L. Shao; E. Lévêque
2007-01-01
Large-eddy simulation developments and validations are presented for an improved simulation of turbulent internal flows. Numerical methods are proposed according to two competing criteria: numerical qualities (precision and spectral characteristics), and adaptability to complex configurations. First, methods are tested on academic test-cases, in order to abridge with fundamental studies. Consistent results are obtained using adaptable finite volume method, with higher order advection fluxes, implicit grid filtering and "low-cost" shear-improved Smagorinsky model. This analysis particularly focuses on mean flow, fluctuations, two-point correlations and spectra.Moreover, it is shown that exponential averaging is a promising tool for LES implementation in complex geometry with deterministic unsteadiness. Finally, adaptability of the method is demonstrated by application to a configuration representative of blade-tip clearance flow in a turbomachine.
Synthetic turbulence, fractal interpolation, and large-eddy simulation.
Basu, Sukanta; Foufoula-Georgiou, Efi; Porté-Agel, Fernando
2004-08-01
Fractal interpolation has been proposed in the literature as an efficient way to construct closure models for the numerical solution of coarse-grained Navier-Stokes equations. It is based on synthetically generating a scale-invariant subgrid-scale field and analytically evaluating its effects on large resolved scales. In this paper, we propose an extension of previous work by developing a multiaffine fractal interpolation scheme and demonstrate that it preserves not only the fractal dimension but also the higher-order structure functions and the non-Gaussian probability density function of the velocity increments. Extensive a priori analyses of atmospheric boundary layer measurements further reveal that this multiaffine closure model has the potential for satisfactory performance in large-eddy simulations. The pertinence of this newly proposed methodology in the case of passive scalars is also discussed.
Large Eddy Simulation of FDA's Idealized Medical Device.
Delorme, Yann T; Anupindi, Kameswararao; Frankel, Steven H
2013-12-01
A hybrid large eddy simulation (LES) and immersed boundary method (IBM) computational approach is used to make quantitative predictions of flow field statistics within the Food and Drug Administration's (FDA) idealized medical device. An in-house code is used, hereafter (W enoHemo(™) ), that combines high-order finite-difference schemes on structured staggered Cartesian grids with an IBM to facilitate flow over or through complex stationary or rotating geometries and employs a subgrid-scale (SGS) turbulence model that more naturally handles transitional flows [2]. Predictions of velocity and wall shear stress statistics are compared with previously published experimental measurements from Hariharan et al. [6] for the four Reynolds numbers considered.
Implicit large eddy simulation of shock-driven material mixing.
Grinstein, F F; Gowardhan, A A; Ristorcelli, J R
2013-11-28
Under-resolved computer simulations are typically unavoidable in practical turbulent flow applications exhibiting extreme geometrical complexity and a broad range of length and time scales. An important unsettled issue is whether filtered-out and subgrid spatial scales can significantly alter the evolution of resolved larger scales of motion and practical flow integral measures. Predictability issues in implicit large eddy simulation of under-resolved mixing of material scalars driven by under-resolved velocity fields and initial conditions are discussed in the context of shock-driven turbulent mixing. The particular focus is on effects of resolved spectral content and interfacial morphology of initial conditions on transitional and late-time turbulent mixing in the fundamental planar shock-tube configuration.
Large-eddy simulations of the Lillgrund wind farm
Nilsson, Karl; Ivanell, Stefan; Hansen, Kurt Schaldemose;
2015-01-01
The power production of the Lillgrund wind farm is determined numerically using large-eddy simulations and compared with measurements. In order to simulate realistic atmospheric conditions, pre-generated turbulence and wind shear are imposed in the computational domain. The atmospheric conditions...... are determined from data extracted from a met mast, which was erected prior to the establishment of the farm. In order to allocate most of the computational power to the simulations of the wake flow, the turbines are modeled using an actuator disc method where the discs are imposed in the computational domain...... ambient turbulence in the simulations. By introducing ambient atmospheric turbulence, the simulations compare very well with measurements at the studied inflow angles. A final study aiming at increasing the farm production by curtailing the power output of the front row turbines and thus letting more...
Large-eddy simulation:Past, present and the future
Yang Zhiyin
2015-01-01
Large-eddy simulation (LES) was originally proposed for simulating atmospheric flows in the 1960s and has become one of the most promising and successful methodology for simulating turbulent flows with the improvement of computing power. It is now feasible to simulate complex engineering flows using LES. However, apart from the computing power, significant challenges still remain for LES to reach a level of maturity that brings this approach to the mainstream of engi-neering and industrial computations. This paper will describe briefly LES formalism first, present a quick glance at its history, review its current state focusing mainly on its applications in transi-tional flows and gas turbine combustor flows, discuss some major modelling and numerical chal-lenges/issues that we are facing now and in the near future, and finish with the concluding remarks.
Large-eddy simulation of an offshore Mediterranean area
Rizza, Umberto; Miglietta, Mario M.; Sempreviva, Anna Maria;
2014-01-01
in order to optimize the structural design of offshore large wind turbines that today reach heights up to 200 m. Large-eddy simulations (LESs) have been performed and compared with offshore experimental data collected during the LASIE campaign performed in the Mediterranean during summer 2007. Two...... simulations are performed: one where the LES is left free to evolve without any external forcing, and one where a force restoration nudging technique has been implemented in LES in order to force the model to the evolving large-scale situation. Model results have been compared against experimental soundings....... Results show that for all the calculated fields the nudged LES outperforms the simulation without nudging, demonstrating that incorporating changes in the large-scale features is necessary in order to provide a realistic evolution of the modelled meteorological fields at local scale. Thus, appropriately...
Large Eddy Simulation of Turbulent Flows in Wind Energy
Chivaee, Hamid Sarlak
This research is devoted to the Large Eddy Simulation (LES), and to lesser extent, wind tunnel measurements of turbulent flows in wind energy. It starts with an introduction to the LES technique associated with the solution of the incompressible Navier-Stokes equations, discretized using a finite...... Reynolds numbers, and thereafter, the fully-developed infinite wind farm boundary later simulations are performed. Sources of inaccuracy in the simulations are investigated and it is found that high Reynolds number flows are more sensitive to the choice of the SGS model than their low Reynolds number...... of attack. Laminar-turbulent transition, generation of laminar boundary layer separation, and formation of stall cells are investigated. The simulated airfoil characteristics are validated against measurements. It is concluded that the LES computations and wind tunnel measurements are in good agreement...
Large Eddy Simulation (LES for IC Engine Flows
Kuo Tang-Wei
2013-10-01
Full Text Available Numerical computations are carried out using an engineering-level Large Eddy Simulation (LES model that is provided by a commercial CFD code CONVERGE. The analytical framework and experimental setup consist of a single cylinder engine with Transparent Combustion Chamber (TCC under motored conditions. A rigorous working procedure for comparing and analyzing the results from simulation and high speed Particle Image Velocimetry (PIV experiments is documented in this work. The following aspects of LES are analyzed using this procedure: number of cycles required for convergence with adequate accuracy; effect of mesh size, time step, sub-grid-scale (SGS turbulence models and boundary condition treatments; application of the proper orthogonal decomposition (POD technique.
Lattice Boltzmann Large Eddy Simulation Model of MHD
Flint, Christopher
2016-01-01
The work of Ansumali \\textit{et al.}\\cite{Ansumali} is extended to Two Dimensional Magnetohydrodynamic (MHD) turbulence in which energy is cascaded to small spatial scales and thus requires subgrid modeling. Applying large eddy simulation (LES) modeling of the macroscopic fluid equations results in the need to apply ad-hoc closure schemes. LES is applied to a suitable mesoscopic lattice Boltzmann representation from which one can recover the MHD equations in the long wavelength, long time scale Chapman-Enskog limit (i.e., the Knudsen limit). Thus on first performing filter width expansions on the lattice Boltzmann equations followed by the standard small Knudsen expansion on the filtered lattice Boltzmann system results in a closed set of MHD turbulence equations provided we enforce the physical constraint that the subgrid effects first enter the dynamics at the transport time scales. In particular, a multi-time relaxation collision operator is considered for the density distribution function and a single rel...
Large Eddy Simulations of turbulent flows at supercritical pressure
Kunik, C.; Otic, I.; Schulenberg, T., E-mail: claus.kunik@kit.edu, E-mail: ivan.otic@kit.edu, E-mail: thomas.schulenberg@kit.edu [Karlsruhe Inst. of Tech. (KIT), Karlsruhe (Germany)
2011-07-01
A Large Eddy Simulation (LES) method is used to investigate turbulent heat transfer to CO{sub 2} at supercritical pressure for upward flows. At those pressure conditions the fluid undergoes strong variations of fluid properties in a certain temperature range, which can lead to a deterioration of heat transfer (DHT). In this analysis, the LES method is applied on turbulent forced convection conditions to investigate the influence of several subgrid scale models (SGS-model). At first, only velocity profiles of the so-called inflow generator are considered, whereas in the second part temperature profiles of the heated section are investigated in detail. The results are statistically analyzed and compared with DNS data from the literature. (author)
Aero-Acoustic Moldeling using Large Eddy Simulation
Shen, Wen Zhong; Sørensen, Jens Nørkær
2008-01-01
The flow-acoustic splitting technique for aero-acoustic computations is extended to simulate the propagation of acoustic waves generated by three-dimensional turbulent flows. In the flow part, a sub-grid-scale turbulence model (the mixed model) is employed for Large-Eddy Simulations. The obtained...... instantaneous flow solution is employed as input for the acoustic part. At low Mach numbers the differences in scales and propagation speed between the flow and the acoustic field are quite large, hence different meshes and time-steps can be utilized for the two parts. The model is applied to compute flows past...... characteristics for angles of attack up to stall. For the acoustic solutions, predicted noise spectra are validated quantitatively against the experimental data of Brook et al. A parametrical study of the noise pattern for flows at angles of attack between 4 deg and 12 deg shows that the noise level is small...
Gas turbine coatings eddy current quantitative and qualitative evaluation
Ribichini, Remo; Giolli, Carlo; Scrinzi, Erica
2017-02-01
Gas turbine blades (buckets) are among the most critical and expensive components of the engine. Buckets rely on protective coatings in order to withstand the harsh environment in which they operate. The thickness and the microstructure of coatings during the lifespan of a unit are fundamental to evaluate their fitness for service. A frequency scanning Eddy Current instrument can allow the measurement of the thickness and of physical properties of coatings in a Non-Destructive manner. The method employed relies on the acquisition of impedance spectra and on the inversion of the experimental data to derive the coating properties and structure using some assumptions. This article describes the experimental validation performed on several samples and real components in order to assess the performance of the instrument as a coating thickness gage. The application of the technique to support residual life assessment of serviced buckets is also presented.
Large eddy simulation requirements for the Richtmyer-Meshkov Instability
Olson, Britton J
2014-01-01
The shock induced mixing of two gases separated by a perturbed interface is investigated through Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS). In a simulation, physical dissipation of the velocity field and species mass fraction often compete with numerical dissipation arising from the errors of the numerical method. In a DNS the computational mesh resolves all physical gradients of the flow and the relative effect of numerical dissipation is small. In LES, unresolved scales are present and numerical dissipation can have a large impact on the flow, depending on the computational mesh. A suite of simulations explores the space between these two extremes by studying the effects of grid resolution, Reynolds number and numerical method on the mixing process. Results from a DNS are shown using two different codes, which use a high- and low-order numerical method and show convergence in the temporal and spectral dependent quantities associated with mixing. Data from a coarse LES are also presen...
Stray Field Reduction in ALS Eddy Current Septum Magnets
Shuman, Derek; Prestemon, Soren; Schlüter, Ross D; Steier, Christoph; Stover, Gregory D
2005-01-01
Stray field from an eddy current septum magnet adversely affects the circulating beam and can be reduced using several techniques. The stray field time history typically has a fast rise section followed by a long exponential decay section when pulsed with a half sine drive current. Changing the drive current pulse to a full sine has the effect of both reducing peak stray field magnitude by ~3x, and producing a quick decay from this peak to a lower field level which then has a similar long decay time constant as that from the half sine only drive current pulse. A method for tuning the second half sine (reverse) drive current pulse to eliminate the long exponential decay section is given.
LARGE EDDY SIMULATION OF PULSATING TURBULENT OPEN CHANNEL FLOW
ZOU Li-yong; LIU Nan-sheng; LU Xi-yun
2004-01-01
Pulsating turbulent open channel flow has been investigated by the use of Large Eddy Simulation (LES) technique coupled with dynamic Sub-Grid-Scale (SGS) model for turbulent SGS stress to closure the governing equations. Three-dimensional filtered Navier-Stokes equations are numerically solved by a fractional-step method. The objective of this study is to deal with the behavior of the pulsating turbulent open channel flow and to examine the reliability of the LES approach for predicting the pulsating turbulent flow. In this study, the Reynolds number (Reτ ) is chosen as 180 based on the friction velocity and the channel depth. The frequency of the driving pressure gradient for the pulsating turbulent flow ranges low, medium and high value. Statistical turbulence quantities as well as the flow structures are analyzed.
Large eddy simulation of urban features for Copenhagen metropolitan area
A. Mahura
2005-11-01
Full Text Available The large eddy simulations employing the SUBMESO model with the urban soil layer model SM2-U were performed for the model domain covering the Danish Island of Sealand and including the Copenhagen metropolitan area. Monthly and diurnal cycle variability were studied for the net radiation, sensible and storage heat fluxes, surface's temperatures, and others. These were evaluated for selected urban vs. non urban related types of covers/surfaces and urban districts such as city center, high buildings, industrial, and residential. Results showed strong effects of urban features on temporal and spatial variability. They are useful and applicable for verification of numerical weather prediction models and development of urban canopy parameterizations.
Eddy current characterization of magnetic treatment of nickel 200
Chern, E. J.
1993-01-01
Eddy current methods have been applied to characterize the effect of magnetic treatments on component service-life extension. Coil impedance measurements were acquired and analyzed on nickel 200 specimens that have been subjected to many mechanical and magnetic engineering processes: annealing, applied strain, magnetic field, shot peening, and magnetic field after peening. Experimental results have demonstrated a functional relationship between coil impedance, resistance and reactance, and specimens subjected to various engineering processes. It has shown that magnetic treatment does induce changes in electromagnetic properties of nickel 200 that then exhibit evidence of stress relief. However, further fundamental studies are necessary for a thorough understanding of the exact mechanism of the magnetic field processing effect on machine-tool service life.
Smoothed particle hydrodynamics method from a large eddy simulation perspective
Di Mascio, A.; Antuono, M.; Colagrossi, A.; Marrone, S.
2017-03-01
The Smoothed Particle Hydrodynamics (SPH) method, often used for the modelling of the Navier-Stokes equations by a meshless Lagrangian approach, is revisited from the point of view of Large Eddy Simulation (LES). To this aim, the LES filtering procedure is recast in a Lagrangian framework by defining a filter that moves with the positions of the fluid particles at the filtered velocity. It is shown that the SPH smoothing procedure can be reinterpreted as a sort of LES Lagrangian filtering, and that, besides the terms coming from the LES convolution, additional contributions (never accounted for in the SPH literature) appear in the equations when formulated in a filtered fashion. Appropriate closure formulas are derived for the additional terms and a preliminary numerical test is provided to show the main features of the proposed LES-SPH model.
Turbulent mixing, restratification, and phytoplankton growth at a submesoscale eddy
Taylor, J. R.
2016-06-01
High-resolution large-eddy simulations are used to study the influence of submesoscale mixed layer instability and small-scale turbulence on phytoplankton growth in light-limited conditions. Four simulations are considered with small-scale turbulence driven by varying levels of surface cooling. Significant small-scale turbulence is seen even without surface forcing, and the downward mixing of phytoplankton is sufficient to briefly delay the developing bloom. Moderate and strong values of the constant surface heat flux (Q =- 10,-100 W/m2) are sufficient to prevent a bloom. In contrast to the critical depth hypothesis, the growth rate for phytoplankton does not appear to be controlled by the mixed layer depth. Instead, a comparison between the turbulent diffusivity above the compensation depth and a critical value predicted by the critical turbulence hypothesis closely matches the timing and magnitude of phytoplankton growth.
Eddy Current Examination of Spent Nuclear Fuel Canister Closure Welds
Arthur D. Watkins; Dennis C. Kunerth; Timothy R. McJunkin
2006-04-01
The National Spent Nuclear Fuel Program (NSNFP) has developed standardized DOE SNF canisters for handling and interim storage of SNF at various DOE sites as well as SNF transport to and SNF handling and disposal at the repository. The final closure weld of the canister will be produced remotely in a hot cell after loading and must meet American Society of Mechanical Engineers (ASME) Section III, Division 3 code requirements thereby requiring volumetric and surface nondestructive evaluation to verify integrity. This paper discusses the use of eddy current testing (ET) to perform surface examination of the completed welds and repair cavities. Descriptions of integrated remote welding/inspection system and how the equipment is intended function will also be discussed.
Large-Eddy Simulations of Flapping-Induced Lift Enhancement
Franck, Jennifer; Swartz, Sharon; Breuer, Kenneth
2011-11-01
This work isolates the heaving motion of flapping flight in order to numerically investigate the fluid-structure interaction at Reynolds numbers relevant to birds and bats. Although there has been much focus on insect flight, larger vertebrates fly at a higher Reynolds number, which leads to different dynamics in terms of flow separation, reattachment, and high-lift mechanisms. In this work, an incompressible large-eddy simulation is used to simulate the periodic heaving of a flat plate at various angles of attack. It is found that the heaving motion can increase the average lift when compared with the steady flow, more so than is expected from the relative angle of attack. The additional lift is attributed to the vortex dynamics at the leading edge. The lift enhancement and flow features are compared with experimental results.
A laboratory activity on the eddy current brake
Molina-Bolívar, J. A.; Abella-Palacios, A. J.
2012-05-01
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 electromagnetic properties of the magnet on the magnetic drag force. This video-based experiment is ideal for the study of kinematic graphs and the application of Newton's laws. Video motion analysis software enables students to make precise measurements of the magnet's position at incremental times during its motion, thus allowing them to quantify electromagnetic induction phenomena. The equipment needed for this experiment and data collection software are present in most physics teaching laboratories or are inexpensive and available.
Quality and Reliability of Large-Eddy Simulations II
Salvetti, Maria Vittoria; Meyers, Johan; Sagaut, Pierre
2011-01-01
The second Workshop on "Quality and Reliability of Large-Eddy Simulations", QLES2009, was held at the University of Pisa from September 9 to September 11, 2009. Its predecessor, QLES2007, was organized in 2007 in Leuven (Belgium). The focus of QLES2009 was on issues related to predicting, assessing and assuring the quality of LES. The main goal of QLES2009 was to enhance the knowledge on error sources and on their interaction in LES and to devise criteria for the prediction and optimization of simulation quality, by bringing together mathematicians, physicists and engineers and providing a platform specifically addressing these aspects for LES. Contributions were made by leading experts in the field. The present book contains the written contributions to QLES2009 and is divided into three parts, which reflect the main topics addressed at the workshop: (i) SGS modeling and discretization errors; (ii) Assessment and reduction of computational errors; (iii) Mathematical analysis and foundation for SGS modeling.
Defect Automatic Identification of Eddy Current Pulsed Thermography
Kai Chen
2014-01-01
Full Text Available Eddy current pulsed thermography (ECPT is an effective nondestructive testing and evaluation (NDT&E technique, and has been applied for a wide range of conductive materials. Manual selected frames have been used for defects detection and quantification. Defects are indicated by high/low temperature in the frames. However, the variation of surface emissivity sometimes introduces illusory temperature inhomogeneity and results in false alarm. To improve the probability of detection, this paper proposes a two-heat balance states-based method which can restrain the influence of the emissivity. In addition, the independent component analysis (ICA is also applied to automatically identify defect patterns and quantify the defects. An experiment was carried out to validate the proposed methods.
Large-eddy simulation of turbulent circular jet flows
Jones, S. C. [Georgia Inst. of Technology, Atlanta, GA (United States); Sotiropoulos, F. [Georgia Inst. of Technology, Atlanta, GA (United States); Sale, M. J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2002-07-01
This report presents a numerical method for carrying out large-eddy simulations (LES) of turbulent free shear flows and an application of a method to simulate the flow generated by a nozzle discharging into a stagnant reservoir. The objective of the study was to elucidate the complex features of the instantaneous flow field to help interpret the results of recent biological experiments in which live fish were exposed to the jet shear zone. The fish-jet experiments were conducted at the Pacific Northwest National Laboratory (PNNL) under the auspices of the U.S. Department of Energy’s Advanced Hydropower Turbine Systems program. The experiments were designed to establish critical thresholds of shear and turbulence-induced loads to guide the development of innovative, fish-friendly hydropower turbine designs.
Wesseling, Joeri; Farla, J. C M; Hekkert, M. P.
2015-01-01
The ability of firms to influence environmental regulation has largely been overlooked in transition studies. We study how car manufacturers combine and change their innovation and political influence strategies in response to a technology-forcing regulation. We apply a conceptual framework on corpo
Ultra-high energy cosmic rays: from GeV to ZeV
Medina-Tanco, G A
2006-01-01
Cosmic ray (CR) particles arrive at the top of the Earth's atmosphere at a rate of around 1000 per square meter per second. They are mostly ionized nuclei - about 90% protons, 9% alpha particles traces of heavier nuclei and approximately 1% electrons. CRs are characterized by their high energies: most cosmic rays are relativistic, having kinetic energies comparable to or somewhat greater than their rest masses. A very few of them have ultra-relativistic energies extending beyond 100 EeV (tens of joules). In this series of lectures, delivered at the 2005 Mexican School of Astrophysics, an overview of the main experimental characteristics of the CR flux and their astrophysical significance is given. Particular emphasis is given to the upper end of the CR energy spectrum. Unfortunately, due to space limitations, only a fraction of the original content of the lectures is included in the present manuscript. In particular, the production mechanisms are not included and the fundamental topic of anisotropies is only ...
Wesseling, Joeri|info:eu-repo/dai/nl/357536320; Farla, J. C M|info:eu-repo/dai/nl/106857576; Hekkert, M. P.|info:eu-repo/dai/nl/143777629
2015-01-01
The ability of firms to influence environmental regulation has largely been overlooked in transition studies. We study how car manufacturers combine and change their innovation and political influence strategies in response to a technology-forcing regulation. We apply a conceptual framework on
Eddy damping effect of additional conductors in superconducting levitation systems
Jiang, Zhao-Fei; Gou, Xiao-Fan, E-mail: xfgou@hhu.edu.cn
2015-12-15
Highlights: • In this article, for the eddy current damper attached to the HTSC, we • quantitatively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. • presented four different arrangements of the copper damper, and comparatively studied their damping effects and Joule heating, and finally proposed the most advisable arrangement. - Abstract: Passive superconducting levitation systems consisting of a high temperature superconductor (HTSC) and a permanent magnet (PM) have demonstrated several fascinating applications such as the maglev system, flywheel energy storage. Generally, for the HTSC–PM levitation system, the HTSC with higher critical current density J{sub c} can obtain larger magnetic force to make the PM levitate over the HTSC (or suspended below the HTSC), however, the process of the vibration of the levitated PM, provides very limited inherent damping (essentially hysteresis). To improve the dynamic stability of the levitated PM, eddy damping of additional conductors can be considered as the most simple and effective approach. In this article, for the HTSC–PM levitation system with an additional copper damper attached to the HTSC, we numerically and comprehensively investigated the damping coefficient c, damping ratio, Joule heating of the copper damper, and the vibration frequency of the PM as well. Furthermore, we comparatively studied four different arrangements of the copper damper, on the comprehensive analyzed the damping effect, efficiency (defined by c/V{sub Cu}, in which V{sub Cu} is the volume of the damper) and Joule heating, and finally presented the most advisable arrangement.
Large eddy simulation subgrid model for soot prediction
El-Asrag, Hossam Abd El-Raouf Mostafa
Soot prediction in realistic systems is one of the most challenging problems in theoretical and applied combustion. Soot formation as a chemical process is very complicated and not fully understood. The major difficulty stems from the chemical complexity of the soot formation process as well as its strong coupling with the other thermochemical and fluid processes that occur simultaneously. Soot is a major byproduct of incomplete combustion, having a strong impact on the environment as well as the combustion efficiency. Therefore, innovative methods is needed to predict soot in realistic configurations in an accurate and yet computationally efficient way. In the current study, a new soot formation subgrid model is developed and reported here. The new model is designed to be used within the context of the Large Eddy Simulation (LES) framework, combined with Linear Eddy Mixing (LEM) as a subgrid combustion model. The final model can be applied equally to premixed and non-premixed flames over any required geometry and flow conditions in the free, the transition, and the continuum regimes. The soot dynamics is predicted using a Method of Moments approach with Lagrangian Interpolative Closure (MOMIC) for the fractional moments. Since no prior knowledge of the particles distribution is required, the model is generally applicable. The current model accounts for the basic soot transport phenomena as transport by molecular diffusion and Thermophoretic forces. The model is first validated against experimental results for non-sooting swirling non-premixed and partially premixed flames. Next, a set of canonical premixed sooting flames are simulated, where the effect of turbulence, binary diffusivity and C/O ratio on soot formation are studied. Finally, the model is validated against a non-premixed jet sooting flame. The effect of the flame structure on the different soot formation stages as well as the particle size distribution is described. Good results are predicted with
Toward a Mexican eddy covariance network for carbon cycle science
Vargas, Rodrigo; Yépez, Enrico A.
2011-09-01
First Annual MexFlux Principal Investigators Meeting; Hermosillo, Sonora, Mexico, 4-8 May 2011; The carbon cycle science community has organized a global network, called FLUXNET, to measure the exchange of energy, water, and carbon dioxide (CO2) between the ecosystems and the atmosphere using the eddy covariance technique. This network has provided unprecedented information for carbon cycle science and global climate change but is mostly represented by study sites in the United States and Europe. Thus, there is an important gap in measurements and understanding of ecosystem dynamics in other regions of the world that are seeing a rapid change in land use. Researchers met under the sponsorship of Red Temática de Ecosistemas and Consejo Nacional de Ciencia y Tecnologia (CONACYT) to discuss strategies to establish a Mexican eddy covariance network (MexFlux) by identifying researchers, study sites, and scientific goals. During the meeting, attendees noted that 10 study sites have been established in Mexico with more than 30 combined years of information. Study sites span from new sites installed during 2011 to others with 9 to 6 years of measurements. Sites with the longest span measurements are located in Baja California Sur (established by Walter Oechel in 2002) and Sonora (established by Christopher Watts in 2005); both are semiarid ecosystems. MexFlux sites represent a variety of ecosystem types, including Mediterranean and sarcocaulescent shrublands in Baja California; oak woodland, subtropical shrubland, tropical dry forest, and a grassland in Sonora; tropical dry forests in Jalisco and Yucatan; a managed grassland in San Luis Potosi; and a managed pine forest in Hidalgo. Sites are maintained with an individual researcher's funds from Mexican government agencies (e.g., CONACYT) and international collaborations, but no coordinated funding exists for a long-term program.
An improved, SSH-based method to automatically identify mesoscale eddies in the ocean
WANG Xin; DU Yun-yan; ZHOU Cheng-hu; FAN Xing; YI Jia-wei
2013-01-01
Mesoscale eddies are an important component of oceanic features. How to automatically identify these mesoscale eddies from available data has become an important research topic. Through careful examination of existing methods, we propose an improved, SSH-based automatic identification method. Using the inclusion relation of enclosed SSH contours, the mesoscale eddy boundary and core(s) can be automatically identified. The time evolution of eddies can be examined by a threshold search algorithm and a tracking algorithm based on similarity. Sea-surface height (SSH) data from Naval Research Laboratory Layered Ocean Model (NLOM) and sea-level anomaly (SLA) data from altimeter are used in the many experiments, in which different automatic identification methods are compared. Our results indicate that the improved method is able to extract the mesoscale eddy boundary more precisely, retaining the multiple-core structure. In combination with the tracking algorithm, this method can capture complete mesoscale eddy processes. It can thus provide reliable information for further study of reconstructing eddy dynamics, merging, splitting, and evolution of a multi-core structure.
Key factors of eddy current separation for recovering aluminum from crushed e-waste.
Ruan, Jujun; Dong, Lipeng; Zheng, Jie; Zhang, Tao; Huang, Mingzhi; Xu, Zhenming
2017-02-01
Recovery of e-waste in China had caused serious pollutions. Eddy current separation is an environment-friendly technology of separating nonferrous metallic particles from crushed e-waste. However, due to complex particle characters, separation efficiency of traditional eddy current separator was low. In production, controllable operation factors of eddy current separation are feeding speed, (ωR-v), and Sp. There is little special information about influencing mechanism and critical parameters of these factors in eddy current separation. This paper provided the special information of these key factors in eddy current separation of recovering aluminum particles from crushed waste refrigerator cabinets. Detachment angles increased as the increase of (ωR-v). Separation efficiency increased with the growing of detachment angles. Aluminum particles were completely separated from plastic particles in critical parameters of feeding speed 0.5m/s and detachment angles greater than 6.61deg. Sp/Sm of aluminum particles in crushed waste refrigerators ranged from 0.08 to 0.51. Separation efficiency increased as the increase of Sp/Sm. This enlightened us to develop new separator to separate smaller nonferrous metallic particles in e-waste recovery. High feeding speed destroyed separation efficiency. However, greater Sp of aluminum particles brought positive impact on separation efficiency. Greater Sp could increase critical feeding speed to offer greater throughput of eddy current separation. This paper will guide eddy current separation in production of recovering nonferrous metals from crushed e-waste.
Students, Scientists, and Family Commemorate the Life and Diverse Works of Jack Eddy
Judge, Philip
2011-02-01
Eddy Cross-Disciplinary Symposium on Sun-Climate Research; Aspen, Colorado, 22-24 October 2010; In 1976, John Allen Eddy published a seminal article (see Science, 192(4245), 1189-1202) revealing a link between the Little Ice Age, which occurred during the sixteenth through nineteenth centuries, and a period of low sunspot activity, which Eddy called the “Maunder Minimum.” This work placed Sun-climate research on a firm scientific footing. Eddy passed away on 10 June 2009. Following Eddy's passions for education and cross-disciplinary research, a symposium was held to expose talented college students to the science and politics of Sun-climate research. Funding from NASA's Living With a Star Targeted Research and Technology program and from the High Altitude Observatory, Advanced Study Program, and Integrated Science Program of the National Center for Atmospheric Research (NCAR) supported keynote speakers and provided scholarships for 30 students (junior year to Ph.D.) from diverse disciplines. Eddy's wife, Barbara, led a session devoted to personal recollections. Spencer Weart (American Institute of Physics) gave an after-dinner tribute using recordings of Eddy from a 1999 interview.
Zhang, Zhiwei; Tian, Jiwei; Qiu, Bo; Zhao, Wei; Chang, Ping; Wu, Dexing; Wan, Xiuquan
2016-04-01
Oceanic mesoscale eddies with horizontal scales of 50–300 km are the most energetic form of flows in the ocean. They are the oceanic analogues of atmospheric storms and are effective transporters of heat, nutrients, dissolved carbon, and other biochemical materials in the ocean. Although oceanic eddies have been ubiquitously observed in the world oceans since 1960s, our understanding of their three-dimensional (3D) structure, generation, and dissipation remains fragmentary due to lack of systematic full water-depth measurements. To bridge this knowledge gap, we designed and conducted a multi-months field campaign, called the South China Sea Mesoscale Eddy Experiment (S-MEE), in the northern South China Sea in 2013/2014. The S-MEE for the first time captured full-depth 3D structures of an anticyclonic and cyclonic eddy pair, which are characterized by a distinct vertical tilt of their axes. By observing the eddy evolution at an upstream versus downstream location and conducting an eddy energy budget analysis, the authors further proposed that generation of submesoscale motions most likely constitutes the dominant dissipation mechanism for the observed eddies.
Dynamical analysis of mesoscale eddy-induced ocean internal waves using linear theories
XU Qing; ZHENG Quanan; LIN Hui; LIU Yuguang; SONG YTony; YUAN Yeli
2008-01-01
This study aims to explore generation mechanisms of the ocean internal wave using the dynamical analysis methods based on linear theories. Historical cruise measurements and recent synthetic aperture radar (SAR) observations of mesoscale eddies with diame-ter of several tens of kilometers to hundreds of kilometers show that the internal wave packets with wavelength of hundreds of me-ters to kilometer exist inside the mesoscale eddies. This coexistence phenomenon and inherent links between the two different scale processes are revealed in the solutions of governing equations and boundary conditions for the internal wave disturbance with a horizontally slowly variable amplitude in a cylindrical coordinate system. The theoretical solutions indicate that the instability of eddy current field provides the dynamical mechanism to internal wave generation. The derived dispersion relation indicates that the internal wave propagation is modified by the eddy current field structure. The energy equation of the internal waves clearly shows the internal wave energy increment comes from the eddy. The theoretical models are used to explain the observation of the mesoscale ed-dy-induced internal waves off the Norwegian coast. The two-dimensional waveform solution of the anticyclonic eddy-induced internal wave packet appears as ring-shaped curves, which contains the typical features of eddy stream lines. The comparison of theoretical solutions to the structure of the internal wave packets on SAR image shows a good agreement on the major features.
Mesoscale Ocean Large Eddy Simulations Using High-resolution Ocean Models
Pearson, B.; Fox-Kemper, B.; Bachman, S.; Bryan, F.; Bailey, D. A.
2016-02-01
Inaccurate parameterization of sub-grid eddies can cause excessive damping and spurious diapycnal mixing, especially in high-resolution [O(10km)] ocean models. The Mesoscale Ocean Large Eddy Simulation (MOLES) approach provides a framework for developing resolution- and flow-adaptive parameterizations of eddy effects. Large eddy simulation techniques are commonly used to simulate 3D turbulence, and MOLES is modified to be appropriate for the more two-dimensional nature of mesoscale ocean turbulence. However, the effect of MOLES in high-resolution ocean models has not been investigated extensively. We will contrast results, and cost, from a suite of idealized simulations of frontal spin-down (MITgcm) and from high-resolution global climate models (0.1o, POP2), under a variety of eddy parameterizations. These include MOLES based upon 2D turbulence theory, MOLES based upon quasi-geostrophic (QG) turbulence theory, and traditional biharmonic schemes. The idealized simulations show that MOLES (particularly QG) improves the spectral slopes of energy and enstrophy near the grid-scale when compared to more traditional eddy parameterizations, across a range of grid resolutions. In the high-resolution global climate model we compare the effect of different parameterizations on the spectral characteristics of the simulated flow, and on the large-scale transport. Using MOLES in a climate model results in greater energy and variability near the grid scale, and this produces a flow, which, spectrally, is more consistent with an inertial turbulent cascade and observations of eddy behavior.
Vertical scales and dynamics of eddies in the Arctic Ocean's Canada Basin
Zhao, Mengnan; Timmermans, Mary-Louise
2015-12-01
A decade of moored measurements from the Arctic Ocean's northwestern Beaufort Gyre (collected as a component of the Beaufort Gyre Exploration Project) are analyzed to examine the range of mesoscale eddies over the water column and the dynamical processes that set eddy vertical scales. A total of 58 eddies were identified in the moored record, all anticyclones with azimuthal velocities ranging from 10 to 43 cm/s. These are divided into three classes based on core depths. Shallow eddies (core depths around 120 m) are shown to be vertically confined by the strong stratification of the halocline; typical thicknesses are around 100 m. Deep eddies (core depths around 1200 m) are much taller (thicknesses around 1300 m) owing to the weaker stratification at depth, consistent with a previous study. Eddies centered around mid-depths all have two cores (vertically aligned and separated in depth) characterized by velocity maxima and anomalous temperature and salinity properties. One core is located at the base of the halocline (around 200 m depth) and the other at the depth of the Atlantic Water layer (around 400 m depth). These double-core eddies have vertical scales between those of the shallow and deep eddies. The strongly decreasing stratification in their depth range motivates a derivation for the quasi-geostrophic adjustment of a nonuniformly stratified water column to a potential vorticity anomaly. The result aids in interpreting the dynamics and origins of the double-core eddies, providing insight into transport across a major water mass front separating Canadian and Eurasian Water.
Particle aggregation in anticyclonic eddies and implications for distribution of biomass
A. Samuelsen
2012-01-01
Full Text Available Acoustic measurements show that the biomass of zooplankton and mesopelagic fish is redistributed by mesoscale variability and that the signal extends over several hundred meters depth. The mechanisms governing this distribution are not well understood, but influences from both physical (i.e. physical redistribution and biological processes (i.e. nutrient transport, primary production, active swimming, etc. are likely. This study examines how hydrodynamic conditions and basic vertical swimming behavior act to distribute biomass in an anticyclonic eddy. Using an eddy-resolving 2.3 km-resolution physical ocean model as forcing for a particle-tracking module, particles representing passively floating organisms and organisms with vertical swimming behavior are released within an eddy and monitored for 20 to 30 days. The role of hydrodynamic conditions on the distribution of biomass is discussed in relation to the acoustic measurements. Particles released close to the surfaces tend, in agreement with the observations, to accumulate around the edge of the eddy, whereas particles released at depth tend to distribute along the isopycnals. After a month they are displaced several hundreds meters in the vertical with the deepest particles found close to the eddy center, but there is no evidence of aggregation of particles along the eddy rim. All in all, the particle redistribution appears to result from a complex mixture of strain and vertical velocity. The simplified view where the vertical velocity in eddies is regarded as uniform and symmetric around the eddy center is therefore not a reliable representation of the eddy dynamics.
Pulsed Excitation in Eddy Current Non-Destructive Testing of Conductive Materials
Ladislav Janousek
2008-01-01
Full Text Available The paper deals with eddy current non-destructive testing of conductive materials. Basic principle of the method is explained. Two types of eddy current excitation, the harmonic one and the pulsed one, are discussed. The characteristics, advantages as well as disadvantages of the two excitation methods are compared. It is explained that the pulsed excitation gives more complex information about a tested object. Experimental results of the pulsed eddy current testing of a defect in an Aluminium plate are presented
Development of eddy current testing system using magnetic saturation in ferromagnetic materials
Sung, Je Joong; Ahn, Hyung Keun; Shin, Yong Hoon [Sae An Engineering Corperation, Seoul (Korea, Republic of); Seo, Dong Man [Kunjang College, Kunsan (Korea, Republic of)
2002-11-15
Ferromagnetic materials have difficulties of eddy current test using traditional eddy current equipment due to their electric character of high permeability and anomalous magnetic flux. Development of on-line eddy current test equipment for ferromagnetic materials is a goal of this research. as the first step for it, in this paper, a prove for ferromagnetic materials was developed and practical test was performed with it at a manufactory. For magnetic saturation of inside of ferromagnetic material, DC power supply was used. As increasement of applied voltage, signals of defects were distinguished.
Karstensen, Johannes; Schütte, Florian; Pietri, Alice
2017-01-01
finestructure is seen between the surface and 140m just outside the maximum mesoscale flow but also in a layer underneath the eddy centre, between 250 and 450m. For both regions a cyclonic rotation of the velocity finestructure with depth suggests the vertical propagation of near-inertial wave (NIW) energy....... Modification of the planetary vorticity by anticyclonic (eddy core) and cyclonic (eddy periphery) relative vorticity is most likely impacting the NIW energy propagation. Below the low oxygen core salt-finger type double diffusive layers are found that align with the velocity finestructure. Apparent oxygen...
A LARGE EDDY SIMULATION TURBULENCE MODEL FOR COASTAL SEAS AND SHALLOW WATER PROBLEMS
无
2001-01-01
In large scale motions of circulations in coastal seas and shallow-water problems, different characteristics of flow in the horizontal plane and in the vertical direction are expected. In this paper, a new large eddy simulation model was proposed. There are some differences between the present method and the other LES models. The philosophy of the large eddy simulation and the directional eddy viscosity method were applied in the horizontal plane and in the vertical direction, respectively. Comparied with the other LES models in which there is no difference between horizontal viscosity and vertical viscosity, the proposed method is resonable.
Patnaik, K.V.K.R.K.; Maneesha, K.; Sadhuram, Y.; Prasad, K.V.S.R.; Murty, T.V.R.; Rao, V.B.
feedback to the atmosphere (Namias and Canyan, 1981). For example the hurricane “Opal” that occurred in 1995 intensified rapidly from Category 1 to Category 4 status within 14 hours as it passed over a warm core eddy and encountered a deeper and warmer...’s negative feedback, helps to maintain and even boost the TC intensity. Though Bay of Bengal is well known for eddies, quantitative analysis on the role of these eddies in the intensification of storms is still lacking. Ali et al. (2007...
Behavior of magnetic field and eddy current in a magnetostriction based bi-layered composite
Kewei Zhang
2016-12-01
Full Text Available In this paper, we presented a theoretical method for studying the behavior of magnetic field intensity and eddy current inside a magnetostriction based bi-layered composite. Firstly, the mathematical model for the electromagnetic field in the composite was established. Then, the governing equation for determining the magnetic field intensity and eddy current was solved. Furthermore, the effect of the composite’s conductivity on the magnetic field intensity and eddy current were discussed. Lastly, by comparing with the well known R.L. Stoll’s equation, the magnetic field intensity calculated based on our equation showed a less than 0.5% error.
Behavior of magnetic field and eddy current in a magnetostriction based bi-layered composite
Zhang, Kewei; Zhang, Kehao; Liu, Huifeng; Li, Junlin
2016-12-01
In this paper, we presented a theoretical method for studying the behavior of magnetic field intensity and eddy current inside a magnetostriction based bi-layered composite. Firstly, the mathematical model for the electromagnetic field in the composite was established. Then, the governing equation for determining the magnetic field intensity and eddy current was solved. Furthermore, the effect of the composite's conductivity on the magnetic field intensity and eddy current were discussed. Lastly, by comparing with the well known R.L. Stoll's equation, the magnetic field intensity calculated based on our equation showed a less than 0.5% error.
Significant Atmospheric Boundary Layer Change Observed above an Agulhas Current Warm Cored Eddy
C. Messager
2016-01-01
Full Text Available The air-sea impact of a warm cored eddy ejected from the Agulhas Retroflection region south of Africa was assessed through both ocean and atmospheric profiling measurements during the austral summer. The presence of the eddy causes dramatic atmospheric boundary layer deepening, exceeding what was measured previously over such a feature in the region. This deepening seems mainly due to the turbulent heat flux anomaly above the warm eddy inducing extensive deep and persistent changes in the atmospheric boundary layer thermodynamics. The loss of heat by turbulent processes suggests that this kind of oceanic feature is an important and persistent source of heat for the atmosphere.
Empirical models of the eddy heat flux and vertical shear on short time scales
Ghan, S. J.
1984-01-01
An intimate relation exists between the vertical shear and the horizontal eddy heat flux within the atmosphere. In the present investigation empirical means are employed to provide clues concerning the relationship between the shear and eddy heat flux. In particular, linear regression models are applied to individual and joint time series of the shear and eddy heat flux. These discrete models are used as a basis to infer continuous models. A description is provided of the observed relationship between the flux and the shear, taking into account means, standard deviations, and lag correction functions.
A simple model for the interaction between vertical eddy heat fluxes and static stability
Gutowski, W. J., Jr.
1985-01-01
A numerical model for studying the interaction of vertical eddy heat fluxes and vertical temperature structure in midlatitude regions is described. The temperature profile for the model was derived from calculations of the equilibrium among heating rates in simplified representations of large-scale vertical eddy heat flux, moist convection and radiation. An eddy flux profile is calculated based on the quasi-geostrophic, liner baroclinic instability of a single wave. Model equilibrium states for summer and winter conditions are compared with observations, and the results are discussed in detail.
Innovative CO2 Analyzer Technology for the Eddy Covariance Flux Monitor Project
National Aeronautics and Space Administration — We propose to build and evaluate NDIR Analyzers that can observe eddy covariance flux of CO2 from unmanned airborne platforms. For both phases, a total of four...
On the Eddy Isopycnal Thickness Diffusivity of the Gent-McWilliams Subgrid Mixing Parameterization.
Nakamura, Mototaka; Chao, Yi
2000-01-01
Output of an eddy-resolving model of the North Atlantic Ocean is used to diagnose the eddy thickness diffusivity coefficient, , defined by Gent and McWilliams in their quasi-adiabatic parameterization for transports by mesoscale eddies. The results suggest that has large spatial and temporal variations, with negative values about half of the time. The order of magnitude of shows a wide range in the western North Atlantic, varying from 10 m2 s1 to 107 m2 s1. Also, the value of is considerably affected by the timescale used to define the high-frequency and low-frequency components. The results suggest that should be a diagnosed variable that reflects the strength of eddy mixing during a model integration.
Sabbagh, Harold A; Sabbagh, Elias H; Aldrin, John C; Knopp, Jeremy S
2013-01-01
Computational Electromagnetics and Model-Based Inversion: A Modern Paradigm for Eddy Current Nondestructive Evaluation describes the natural marriage of the computer to eddy-current NDE. Three distinct topics are emphasized in the book: (a) fundamental mathematical principles of volume-integral equations as a subset of computational electromagnetics, (b) mathematical algorithms applied to signal-processing and inverse scattering problems, and (c) applications of these two topics to problems in which real and model data are used. By showing how mathematics and the computer can solve problems more effectively than current analog practices, this book defines the modern technology of eddy-current NDE. This book will be useful to advanced students and practitioners in the fields of computational electromagnetics, electromagnetic inverse-scattering theory, nondestructive evaluation, materials evaluation and biomedical imaging. Users of eddy-current NDE technology in industries as varied as nuclear power, aerospace,...
Robust High Fidelity Large Eddy Simulation Tool for Gas Turbine Combustors Project
National Aeronautics and Space Administration — The objective is to develop and demonstrate the use of Large Eddy Simulation (LES) for computations of gas turbine combustor flow and transport processes, using the...
Detached-eddy simulation of flow around the NREL phase VI blade
Johansen, Jeppe; Sørensen, Niels N.; Michelsen, J.A.;
2002-01-01
–Stokes method in the boundary layer with a large-eddy simulation in the free shear flow. The present study focuses on static and dynamic stall regions highly relevant for stall-regulated wind turbines. Computations do predict force coefficients and pressure distributions fairly well. Results using detached-eddy......The detached-eddy simulation model implemented in the computational fluid dynamics code EllipSys3D is used to calculate the flow around the non-rotating NREL Phase VI wind turbine blade. Results are presented for flow around a parked blade at fixed angle of attack and a blade pitching along...... the blade axis. Computed blade characteristics are compared with experimental data from the NREL/NASA Ames Phase VI unsteady experiment. The detached-eddy simulation model is a method for predicting turbulence in computational fluid dynamics computations, which combines a Reynolds-averaged Navier...
Lagrangian study of transport and mixing in a mesoscale eddy street
Prants, S V; Ponomarev, V I; Uleysky, M Yu; 10.1016/j.ocemod.2011.02.008
2012-01-01
We use dynamical systems approach and Lagrangian tools to study surface transport and mixing of water masses in a selected coastal region of the Japan Sea with moving mesoscale eddies associated with the Primorskoye Current. Lagrangian trajectories are computed for a large number of particles in an interpolated velocity field generated by a numerical regional multi-layer eddy-resolving circulation model. We compute finite-time Lyapunov exponents for a comparatively long period of time by the method developed and plot the Lyapunov synoptic map quantifying surface transport and mixing in that region. This map uncovers the striking flow structures along the coast with a mesoscale eddy street and repelling material lines. We propose new Lagrangian diagnostic tools --- the time of exit of particles off a selected box, the number of changes of the sign of zonal and meridional velocities --- to study transport and mixing by a pair of strongly interacting eddies often visible at sea-surface temperature satellite imag...
A Renewed Approach for Large Eddy Simulation of Complex Geometries Project
National Aeronautics and Space Administration — The potential benefits of Large Eddy Simulation (LES) for aerodynamics and combustion simulation hvae largely been missed, due to the complexity of generating grids...
Detection of Bay of Bengal eddies from TOPEX and in situ observations
Gopalan, A.K.S.; Gopalakrishna, V.V.; Ali, M.M.; Sharma, R.
good qualitative agreement with the subsurface isotherm features (troughs and ridges) of the in situ temperature profiles. However, this agreement does not extend to the surface and hence SST patterns are not good indicators of eddy positions in the Bay...
Are eddies nature’s trigger to enhance biological productivity in the Bay of Bengal?
PrasannaKumar, S.; Nuncio, M.; Kumar, A.; Sardessai, S.; DeSouza, S.N.; Gauns, M.; Ramaiah, N.; Madhupratap, M.
and augments the subsurface nutrient injection to the euphotic zone by eddy pumping. Notwithstanding this, the lower than expected primary production in the north suggests the possible role of riverine sediment in limiting the sunlight for photosynthesis....
Estimates of vertical velocities and eddy coefficients in the Bay of Bengal
Varkey, M.J.; Sastry, J.S.
Vertical velocities and eddy coefficients in the intermediate depths of the Bay of Bengal are calculated from mean hydrographic data for 300 miles-squares. The linear current density (sigma- O) versus log-depth plots show steady balance between...
Analysis of eddy current induced in track on medium-low speed maglev train
Li, Guanchun; Jia, Zhen; He, Guang; Li, Jie
2017-06-01
Electromagnetic levitation (EMS) maglev train relies on the attraction between the electromagnets and rails which are mounted on the train to achieve suspension. During the movement, the magnetic field generated by the electromagnet will induce the eddy current in the orbit and the eddy current will weaken the suspended magnetic field. Which leads to the attenuation of the levitation force, the increases of suspension current and the degradation the suspension performance. In this paper, the influence of eddy current on the air gap magnetic field is solved by theoretical analysis, and the correction coefficient of air gap magnetic field is fitted according to the finite element data. The levitation force and current are calculated by the modified formula, and the velocity curves of the levitation force and current are obtained. The results show that the eddy current effect increases the load power by 61.9% in the case of heavy loads.
Observing subsurface changes of two anticyclonic eddies passing over the Izu-Ogasawara Ridge
Xu, Lixiao; Xie, Shang-Ping; Jing, Zhao; Wu, Lixin; Liu, Qinyu; Li, Peiliang; Du, Yan
2017-02-01
Eddy-bathymetry interactions are common in the ocean, but the full evolution of the interaction is difficult to observe below the surface. Using 17 Iridium Argo floats, we continually track two anticyclonic eddies (AEs) in the North Pacific that migrate westward and encounter the Izu-Ogasawara Ridge. Based on over 5000 Argo profiles following the two AEs, this study presents the first detailed descriptions of changes in eddy vertical structure and diapycnal mixing as the two AEs pass the Ridge. There, we find that isopycnals dome up and the eddy diameter increases, while the diapycnal mixing is enhanced—to the order of 10-4 m2 s-1 or larger, in comparison with an ambient of 10-5 m2 s-1. The enhanced mixing around the AE center in the upper -1000 m appears where the underlying bathymetry is shallower than -4000 m and is mainly sustained by tidally generated internal waves.
Innovative CO2 Analyzer Technology for the Eddy Covariance Flux Monitor Project
National Aeronautics and Space Administration — We propose to build and evaluate NDIR Analyzers that can be used to observe Eddy Covariance Flux and Absolute Dry Mole Fraction of CO2 from stationary and airborne...
In the past two decades, research interest has focused on the eddy ...
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Current results in meandering, with the formation of eddies that can ... forced by a number of oceanic and meteorological boundary conditions, none of which is entirely predictable. ...... invade the South Atlantic: evidence from Geosat altimeter.
Eddy current imaging for electrical characterization of silicon solar cells and TCO layers
Hwang, Byungguk; Hillmann, Susanne; Schulze, Martin; Klein, Marcus; Heuer, Henning
2015-03-01
Eddy Current Testing has been mainly used to determine defects of conductive materials and wall thicknesses in heavy industries such as construction or aerospace. Recently, high frequency Eddy Current imaging technology was developed. This enables the acquirement of information of different depth level in conductive thin-film structures by realizing proper standard penetration depth. In this paper, we summarize the state of the art applications focusing on PV industry and extend the analysis implementing achievements by applying spatially resolved Eddy Current Testing. The specific state of frequency and complex phase angle rotation demonstrates diverse defects from front to back side of silicon solar cells and characterizes homogeneity of sheet resistance in Transparent Conductive Oxide (TCO) layers. In order to verify technical feasibility, measurement results from the Multi Parameter Eddy Current Scanner, MPECS are compared to the results from Electroluminescence.
Mathematical Modeling of Eddy-Current Loss for a New Induction Heating Device
Hai Du
2014-01-01
Full Text Available A new induction heating device is presented in this paper. This device can convert mechanical energy into heat energy by utilizing eddy currents, which are induced by rotating permanent magnets. A mathematical model is established for estimating eddy-current loss of the device. The distribution of induced currents and the resultant magnetic field intensity are considered in the process of modeling the eddy-current loss and so is the mutual influence of the electric field between neighborhood pole projection areas. Particularly, the skin effect is considered by correcting the numerical integral domain of eddy current density, which has great effect on the calculating results. Based on specific examples, the effectiveness and correctness of proposed model are proved by finite element analysis. The results show that the mathematical model can provide important reference for design and structure optimization of the device.
Dare, P. M.; Smith, P. J.
1983-01-01
The eddy kinetic energy budget is calculated for a 48-hour forecast of an intense occluding winter cyclone associated with a strong well-developed jet stream. The model output consists of the initialized (1200 GMT January 9, 1975) and the 12, 24, 36, and 48 hour forecast fields from the Drexel/NCAR Limited Area Mesoscale Prediction System (LAMPS) model. The LAMPS forecast compares well with observations for the first 24 hours, but then overdevelops the low-level cyclone while inadequately developing the upper-air wave and jet. Eddy kinetic energy was found to be concentrated in the upper-troposphere with maxima flanking the primary trough. The increases in kinetic energy were found to be due to an excess of the primary source term of kinetic energy content, which is the horizontal flux of eddy kinetic energy over the primary sinks, and the generation and dissipation of eddy kinetic energy.
Measurement of toroidal vessel eddy current during plasma disruption on J-TEXT
Liu, L. J.; Yu, K. X.; Zhang, M., E-mail: zhangming@hust.edu.cn; Zhuang, G.; Li, X.; Yuan, T.; Rao, B.; Zhao, Q. [State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China)
2016-01-15
In this paper, we have employed a thin, printed circuit board eddy current array in order to determine the radial distribution of the azimuthal component of the eddy current density at the surface of a steel plate. The eddy current in the steel plate can be calculated by analytical methods under the simplifying assumptions that the steel plate is infinitely large and the exciting current is of uniform distribution. The measurement on the steel plate shows that this method has high spatial resolution. Then, we extended this methodology to a toroidal geometry with the objective of determining the poloidal distribution of the toroidal component of the eddy current density associated with plasma disruption in a fusion reactor called J-TEXT. The preliminary measured result is consistent with the analysis and calculation results on the J-TEXT vacuum vessel.
Eddy current loss calculation and thermal analysis of axial-flux permanent magnet couplers
Di Zheng
2017-02-01
Full Text Available A three-dimensional magnetic field analytical model of axial-flux permanent magnet couplers is presented to calculate the eddy current loss, and the prediction of the copper plate temperature under various loads is analyzed. The magnetic field distribution is calculated, and then the eddy current loss is obtained, with the magnetic field analytical model established in cylindrical coordinate. The influence of various loads on eddy current loss is analyzed. Furthermore, a thermal model of axial-flux permanent magnet couplers is established by taking the eddy current loss as the heat source, using the electromagnetic-thermal coupled method. With the help of the thermal model, the influence of various loads on copper plate temperature rise is also analyzed. The calculated results are compared with the results of finite element method and measurement. The comparison results confirm the validity of the magnetic field analytical model and thermal model.
High Temperature, Through the Case Eddy Current Sensor for Blade Vibration Measurements Project
National Aeronautics and Space Administration — Preliminary results have shown that low temperature eddy current sensors can provide excellent resolution for blade tip timing, and have the ability to see ?through...
Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean
M. Cornejo
2015-09-01
Full Text Available Eastern boundary upwelling systems are characterized by high productivity that often leads to subsurface hypoxia on the shelf. Mesoscale eddies are important, frequent, and persistent features of circulation in these regions, transporting physical, chemical and biological properties from shelves to the open ocean. In austral fall of 2011, during the Tara Oceans expedition, a subsurface layer (200–400 m in which the concentration of oxygen was very low (−1 of O2 was observed in the eastern South Pacific, ~ 900 km offshore (30° S, 81° W. Satellite altimetry combined with CTD observations associated the local oxygen anomaly with an intrathermocline, anticyclonic, mesoscale eddy with a diameter of about 150 km. The eddy contained Equatorial Subsurface Water (ESSW that at this latitude is normally restricted near the coast. Undersaturation (44 % of nitrous oxide (N2O and nitrite accumulation (> 0.5 μM gave evidence for denitrification in this water mass. Based on satellite altimetry, we tracked the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W. We estimate that the eddy formed in April 2010. Field studies conducted on the Chilean shelf in June 2010 provided approximate information on initial O2 and N2O concentrations of "source water" in the region at the time of eddy formation. Concentrations of both O2 and N2O in the oxygen minimum zone (OMZ of the offshore eddy were lower than its surroundings or "source water" on the shelf, suggesting that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. Our results show that mesoscale eddies in the ESP not only transport physical properties of the ESSW from the coast to the ocean interior, but also export and transform biogeochemical properties, creating suboxic environments in the
Adjoint sensitivity studies of loop current and eddy shedding in the Gulf of Mexico
Gopalakrishnan, Ganesh
2013-07-01
Adjoint model sensitivity analyses were applied for the loop current (LC) and its eddy shedding in the Gulf of Mexico (GoM) using the MIT general circulation model (MITgcm). The circulation in the GoM is mainly driven by the energetic LC and subsequent LC eddy separation. In order to understand which ocean regions and features control the evolution of the LC, including anticyclonic warm-core eddy shedding in the GoM, forward and adjoint sensitivities with respect to previous model state and atmospheric forcing were computed using the MITgcm and its adjoint. Since the validity of the adjoint model sensitivities depends on the capability of the forward model to simulate the real LC system and the eddy shedding processes, a 5 year (2004–2008) forward model simulation was performed for the GoM using realistic atmospheric forcing, initial, and boundary conditions. This forward model simulation was compared to satellite measurements of sea-surface height (SSH) and sea-surface temperature (SST), and observed transport variability. Despite realistic mean state, standard deviations, and LC eddy shedding period, the simulated LC extension shows less variability and more regularity than the observations. However, the model is suitable for studying the LC system and can be utilized for examining the ocean influences leading to a simple, and hopefully generic LC eddy separation in the GoM. The adjoint sensitivities of the LC show influences from the Yucatan Channel (YC) flow and Loop Current Frontal Eddy (LCFE) on both LC extension and eddy separation, as suggested by earlier work. Some of the processes that control LC extension after eddy separation differ from those controlling eddy shedding, but include YC through-flow. The sensitivity remains stable for more than 30 days and moves generally upstream, entering the Caribbean Sea. The sensitivities of the LC for SST generally remain closer to the surface and move at speeds consistent with advection by the high-speed core of
The eddy performance: Contemporary ethnography of Mount Tlaloc
Lorente Fernández, David
2010-12-01
Full Text Available Mount Tlaloc was a very important religious place in the prehispanic age: it was the place where request ceremonies for rain took place on the Mexica Empire. This is the reason for the increasing interest in this place among archaeologists and ethnohistorians. However, systematic ethnography in the region is almost inexistent and the accurate meaning of the offerings and rituals which are still being carried out nowadays is unknown. The article shows the conclusions of a long fieldwork on the region which describes a therapeutic ceremony where the offering consists in the performing of an eddy —an identification with the water spirits to copy their behavior. Such eddy is related to another array of offerings which includes the donation of seeds or their smell as food. With the analysis of the ritual, the complex contemporary cosmology is explored showing a link between Mount Tlaloc and the local irrigation system: their irrigation channels and the springs are a whole from a conceptual and geographic point of view.
El Monte Tláloc constituyó un importante sitio ceremonial regional en la época prehispánica: era el lugar en el que se realizaban los ritos petitorios de lluvia del Imperio mexica. Por ello ha despertado el interés creciente de arqueólogos y etnohistoriadores. Sin embargo, la etnografía sistemática de la zona es prácticamente inexistente, al grado de que desconocemos exactamente el sentido de las ofrendas y los rituales que continúan realizándose allí. En este sentido, el artículo presenta las conclusiones de un prolongado trabajo de campo en el área y describe un rito terapéutico en el que la ofrenda es la teatralización de un «remolino actuado», es decir, una identificación con los espíritus del agua por el recurso de imitar sus acciones. Dicho remolino se asocia también con otra variedad de ofrendas que incluyen la donación de semillas o sus aromas como alimento. A partir de un análisis del rito se
Improved engine wall models for Large Eddy Simulation (LES)
Plengsaard, Chalearmpol
Improved wall models for Large Eddy Simulation (LES) are presented in this research. The classical Werner-Wengle (WW) wall shear stress model is used along with near-wall sub-grid scale viscosity. A sub-grid scale turbulent kinetic energy is employed in a model for the eddy viscosity. To gain better heat flux results, a modified classical variable-density wall heat transfer model is also used. Because no experimental wall shear stress results are available in engines, the fully turbulent developed flow in a square duct is chosen to validate the new wall models. The model constants in the new wall models are set to 0.01 and 0.8, respectively and are kept constant throughout the investigation. The resulting time- and spatially-averaged velocity and temperature wall functions from the new wall models match well with the law-of-the-wall experimental data at Re = 50,000. In order to study the effect of hot air impinging walls, jet impingement on a flat plate is also tested with the new wall models. The jet Reynolds number is equal to 21,000 and a fixed jet-to-plate spacing of H/D = 2.0. As predicted by the new wall models, the time-averaged skin friction coefficient agrees well with experimental data, while the computed Nusselt number agrees fairly well when r/D > 2.0. Additionally, the model is validated using experimental data from a Caterpillar engine operated with conventional diesel combustion. Sixteen different operating engine conditions are simulated. The majority of the predicted heat flux results from each thermocouple location follow similar trends when compared with experimental data. The magnitude of peak heat fluxes as predicted by the new wall models is in the range of typical measured values in diesel combustion, while most heat flux results from previous LES wall models are over-predicted. The new wall models generate more accurate predictions and agree better with experimental data.
Large-Eddy Simulation Code Developed for Propulsion Applications
DeBonis, James R.
2003-01-01
A large-eddy simulation (LES) code was developed at the NASA Glenn Research Center to provide more accurate and detailed computational analyses of propulsion flow fields. The accuracy of current computational fluid dynamics (CFD) methods is limited primarily by their inability to properly account for the turbulent motion present in virtually all propulsion flows. Because the efficiency and performance of a propulsion system are highly dependent on the details of this turbulent motion, it is critical for CFD to accurately model it. The LES code promises to give new CFD simulations an advantage over older methods by directly computing the large turbulent eddies, to correctly predict their effect on a propulsion system. Turbulent motion is a random, unsteady process whose behavior is difficult to predict through computer simulations. Current methods are based on Reynolds-Averaged Navier- Stokes (RANS) analyses that rely on models to represent the effect of turbulence within a flow field. The quality of the results depends on the quality of the model and its applicability to the type of flow field being studied. LES promises to be more accurate because it drastically reduces the amount of modeling necessary. It is the logical step toward improving turbulent flow predictions. In LES, the large-scale dominant turbulent motion is computed directly, leaving only the less significant small turbulent scales to be modeled. As part of the prediction, the LES method generates detailed information on the turbulence itself, providing important information for other applications, such as aeroacoustics. The LES code developed at Glenn for propulsion flow fields is being used to both analyze propulsion system components and test improved LES algorithms (subgrid-scale models, filters, and numerical schemes). The code solves the compressible Favre-filtered Navier- Stokes equations using an explicit fourth-order accurate numerical scheme, it incorporates a compressible form of
Pulsed eddy current inspection of CF-188 inner wing spar
Horan, Peter Francis
Royal Canadian Air Force (RCAF) CF-188 Hornet aircraft engineering authorities have stated a requirement for a Non-Destructive Evaluation (NDE) technique to detect Stress Corrosion Cracking (SCC) in the inner wing spars without fastener or composite wing skin removal. Current radiographic inspections involve significant aircraft downtime, and Pulsed Eddy Current (PEC) inspection is proposed as a solution. The aluminum inner wing spars of CF-188 Hornet aircraft may undergo stress corrosion cracking (SCC) along the spar between the fasteners that secure carbon-fiber/ epoxy composite skin to the wing. Inspection of the spar through the wing skin is required to avoid wing disassembly. The thickness of the wing skin varies between 8 and 20 mm (0.3 to 0.8 inch) and fasteners may be either titanium or ferrous. PEC generated by a probe centered over a fastener, demonstrates capability of detecting simulated cracks within spars with the wing skin present. Comparison of signals from separate sensors, mounted to either side of the excitation coil, is used to detect differences in induced eddy current fields, which arise in the presence of cracks. To overcome variability in PEC signal response due to variation in 1) skin thickness, 2) fastener material and size, and 3) centering over fasteners, a large calibration data set is acquired. Multi-dimensional scores from a Modified Principal Components Analysis (PCA) of the data are reduced to one dimension (1D) using a Discriminant Analysis method. Under inspection conditions, calibrated PCA scores combined with discriminant analysis permit rapid real time go/no-go PEC detection of cracks in CF-188 inner wing spar. Probe designs using both pickup coils and Giant Magnetoresistive (GMR) sensors were tested on samples with the same ferrous and titanium fasteners found on the CF-188. Flaws were correctly detected at lift-offs of up to 21mm utilizing a variety of insulating skin materials simulating the carbon-fibre reinforced polymer
Soil Respiration in Eddy Covariance Footprints using Forced Diffusion
Nickerson, N.; Gabriel, C. E.; Creelman, C.
2016-12-01
Eddy covariance (EC) has been widely used across the globe for more than 20 years, offering researchers invaluable measurements of parameters including Net Ecosystem Exchange and ecosystem respiration. However, research suggests that EC assumptions and technical obstacles can cause biased gas exchange estimates. Measurements of soil respiration (RS) at the ground level may help alleviate these biases; for example, by allowing researchers to reconcile nocturnal EC flux data with RS or by providing a means to inform gap-filling models. RS measurements have been used sparingly alongside EC towers because of the large cost required to scale chamber systems to the EC footprint and data integration and processing burdens. Here we present the Forced Diffusion (FD) method for the measurement of RS at EC sites. The FD method allows for inexpensive and autonomous measurements, providing a scalable approach to matching the EC footprint compared to other RS systems. A pilot study at the Howland Forest AmeriFlux site was carried out from July 15, 2016 to Dec., 2016 using EC, custom-made automated chambers, and FD chambers in tandem. These results emphasize how RS measurements, like those from the eosFD, can identify decoupling of above and below canopy air masses and assist in informing and parameterizing gap-filling techniques. Uncertainty in nocturnal EC fluxes has been extensively characterized at Howland Forest with EC measurements spanning more than 20 years. Similarly, long term automated measurements of RS are also made at Howland, and have already been used to inform EC gap-filling models, making Howland the ideal site for such a study. This study has been designed to reproduce previous findings from Howland using the FD approach, aiming to demonstrate that the measurements taken using the eosFD correlate well with the existing chamber systems and can be used with equal efficacy to inform gap filling models or for other other eddy covariance QA/QC procedures, including
Observational evidence of seasonality in the timing of loop current eddy separation
Hall, Cody A.; Leben, Robert R.
2016-12-01
Observational datasets, reports and analyses over the time period from 1978 through 1992 are reviewed to derive pre-altimetry Loop Current (LC) eddy separation dates. The reanalysis identified 20 separation events in the 15-year record. Separation dates are estimated to be accurate to approximately ± 1.5 months and sufficient to detect statistically significant LC eddy separation seasonality, which was not the case for previously published records because of the misidentification of separation events and their timing. The reanalysis indicates that previously reported LC eddy separation dates, determined for the time period before the advent of continuous altimetric monitoring in the early 1990s, are inaccurate because of extensive reliance on satellite sea surface temperature (SST) imagery. Automated LC tracking techniques are used to derive LC eddy separation dates in three different altimetry-based sea surface height (SSH) datasets over the time period from 1993 through 2012. A total of 28-30 LC eddy separation events were identified in the 20-year record. Variations in the number and dates of eddy separation events are attributed to the different mean sea surfaces and objective-analysis smoothing procedures used to produce the SSH datasets. Significance tests on various altimetry and pre-altimetry/altimetry combined date lists consistently show that the seasonal distribution of separation events is not uniform at the 95% confidence level. Randomization tests further show that the seasonal peak in LC eddy separation events in August and September is highly unlikely to have occurred by chance. The other seasonal peak in February and March is less significant, but possibly indicates two seasons of enhanced probability of eddy separation centered near the spring and fall equinoxes. This is further quantified by objectively dividing the seasonal distribution into two seasons using circular statistical techniques and a k-means clustering algorithm. The estimated
Detached eddy simulation of unsteady cavitation and pressure fluctuation around 3-D NACA66 hydrofoil
Zhang De-Sheng
2015-01-01
Full Text Available The unsteady cavitating flow and pressure fluctuation around the 3-D NACA66 hydrofoil were simulated and validated based on detached eddy simulation turbulence model and a homogeneous cavitation model. Numerical results show that detached eddy simulation can predict the evolution of cavity inception, sheet cavitation growth, cloud cavitation shedding, and breakup, as well as the pressure fluctuation on the surface of hydrofoil. The sheet cavitation growth, detachment, cloud cavitation shedding are responsible for the features of the pressure fluctuation.
Implementation of a Large Eddy Simulation Method Applied to Recirculating Flow in a Ventilated Room
Davidson, Lars
In the present work Large Eddy Simulations are presented. The flow in a ventilated enclosure is studied. We use an explicit, two-steps time-advancement scheme where the pressure is solved from a Poisson equation.......In the present work Large Eddy Simulations are presented. The flow in a ventilated enclosure is studied. We use an explicit, two-steps time-advancement scheme where the pressure is solved from a Poisson equation....
Modeling Studies of Eddies in the Leeuwin Current: The Role of Thermal Forcing
Batteen, Mary L.; Rutherford, Martin J.
1990-01-01
A high resolution, multilevel, primitive equation (PE) model is used to investigate the generation and stability of the Leeuwin Current and eddies off the west coast of Australia. Two numerical experiments are conducted to investigate the roles of the Indian Ocean temperature field and the North West (NW) Shelf waters in generating both the current and eddies. In the first experiment an alongshore temperature gradient, typical of the Indian Ocean temperature field, is imposed, whi...
2014-10-01
coatings using eddy current techniques”, AIP Conference Proceedings , Vol. 1430, 2012, pp 441. 7. F. M. Smits, “Measurement of sheet resistivities with... Conference 2014: 27 October - 30 October, Charleston, SC, USA. “High-Frequency Eddy Current System for Analyzing Wet Conductive Coatings during...Processing”. 3. QNDE 2014 (ORAL PRESENTATION), 41st Annual Review of Progress in Quantitative Nondestructive Evaluation: Conference Boise Centre
Tilt-shift eddy current probe impact on information value of response signal
Chudacik Vladimir; Smetana Milan
2016-01-01
This article deals with the possibility for increasing of the informational value of a response signal using tilt-shift eddy current probe. Numerical simulations based on the FEM method using the OPERA 3D software as well as gained experimental results are presented. The simulated cracks are evaluated at the selected eddy current probe tilts and shifts with respect to conductive plate to obtain additional data needed for its evaluation and localization. Obtained simulation results are compare...
Two Dimensional Steady State Eddy Current Analysis of a Spinning Conducting Cylinder
2017-03-09
UNCLASSIFIED UNCLASSIFIED AD-E403 855 Technical Report ARMET-TR-16045 TWO-DIMENSIONAL STEADY-STATE EDDY CURRENT ANALYSIS OF A ...any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN...August 2014 4. TITLE AND SUBTITLE TWO-DIMENSIONAL STEADY-STATE EDDY CURRENT ANALYSIS OF A SPINNING CONDUCTING CYLINDER 5a. CONTRACT NUMBER 5b
Influence of spatial exclusion on the statistical behavior of attached eddies
de Silva, Charitha M.; Woodcock, James D.; Hutchins, Nicholas; Marusic, Ivan
2016-06-01
Recent studies have shown Townsend's attached eddy hypothesis to be a promising basis for modeling the velocity statistics in the logarithmic region of turbulent wall flows. Accordingly, the attached eddy model is able to reliably estimate the functional forms of the mean velocity, second-order moments of the velocity fluctuations, and recently structure functions and higher-order moments of the velocity fluctuations. However, detailed quantitative comparisons with experimental results reveal differences, particularly for the higher-order moments. Specifically, the predicted flatness (kurtosis) is found to be invariably greater than 3 (i.e., super-Gaussian behavior) for all velocity components, while experimental results show sub-Gaussian behavior for the streamwise component of velocity. In this study, we show that this and other discrepancies can be resolved by considering the finite space occupied by each eddy. Earlier models had allowed each eddy to be perfectly randomly located, with no consideration for the locations of neighboring eddies (in other words, their locations can be described as a Poisson point process). Here we investigate the effect of mandating a minimum distance between any two eddies of the same height. We demonstrate that this spatial exclusion, when combined with an experimentally observed shape for the representative eddy, produces predictions that are now in better agreement with experimental observations. In particular, sub-Gaussian behavior is now attained for the streamwise component, while super-Gaussian behavior is maintained for the other velocity components, qualitatively matching experimental findings. Therefore, our findings infer that spatial exclusion between eddies is likely to play an important role in the laws that govern their spatial arrangement, which is likely to be more disperse than a Poisson point process.
Piomelli, Ugo; Zang, Thomas A.; Speziale, Charles G.; Lund, Thomas S.
1990-01-01
An eddy viscosity model based on the renormalization group theory of Yakhot and Orszag (1986) is applied to the large-eddy simulation of transition in a flat-plate boundary layer. The simulation predicts with satisfactory accuracy the mean velocity and Reynolds stress profiles, as well as the development of the important scales of motion. The evolution of the structures characteristic of the nonlinear stages of transition is also predicted reasonably well.
Validation of Finite Element Solutions of Nonlinear, Periodic Eddy Current Problems
Plasser René
2014-12-01
Full Text Available An industrial application is presented to validate a finite element analysis of 3-dimensional, nonlinear eddy-current problems with periodic excitation. The harmonic- balance method and the fixed-point technique are applied to get the steady state solution using the finite element method. The losses occurring in steel reinforcements underneath a reactor due to induced eddy-currents are computed and compared to measurements.
Observation of Oceanic Eddy in the Northeastern Arabian Sea Using Multisensor Remote Sensing Data
R. K. Sarangi
2012-01-01
Full Text Available An oceanic eddy of size about 150 kilometer diameter observed in the northeastern Arabian Sea using remote sensing satellite sensors; IRS-P4 OCM, NOAA-AVHRR and NASA Quickscat Scatterometer data. The eddy was detected in the 2nd week of February in Indian Remote Sensing satellite (IRS-P4 Ocean Color Monitor (OCM sensor retrieved chlorophyll image on 10th February 2002, between latitude 16°90′–18°50′N and longitude 66°05′–67°60′E. The chlorophyll concentration was higher in the central part of eddy (~1.5 mg/m3 than the peripheral water (~0.8 mg/m3. The eddy lasted till 10th March 2002. NOAA-AVHRR sea surface temperature (SST images generated during 15th February-15th March 2002. The SST in the eddy’s center (~23°C was lesser than the surrounding water (~24.5°C. The eddy was of cold core type with the warmer water in periphery. Quickscat Scatterometer retrieved wind speed was 8–10 m/sec. The eddy movement observed southeast to southwest direction and might helped in churning. The eddy seemed evident due to convective processes in water column. The processes like detrainment and entrainment play role in bringing up the cooler water and the bottom nutrient to surface and hence the algal blooming. This type of cold core/anti-cyclonic eddy is likely to occur during late winter/spring as a result of the prevailing climatic conditions.
Siebicke, Lukas
2017-04-01
The eddy covariance (EC) method is state-of-the-art in directly measuring vegetation-atmosphere exchange of CO2 and H2O at ecosystem scale. However, the EC method is currently limited to a small number of atmospheric tracers by the lack of suitable fast-response analyzers or poor signal-to-noise ratios. High resource and power demands may further restrict the number of spatial sampling points. True eddy accumulation (TEA) is an alternative method for direct and continuous flux observations. Key advantages are the applicability to a wider range of air constituents such as greenhouse gases, isotopes, volatile organic compounds and aerosols using slow-response analyzers. In contrast to relaxed eddy accumulation (REA), true eddy accumulation (Desjardins, 1977) has the advantage of being a direct method which does not require proxies. True Eddy Accumulation has the potential to overcome above mentioned limitations of eddy covariance but has hardly ever been successfully demonstrated in practice in the past. This study presents flux measurements using an innovative approach to true eddy accumulation by directly, continuously and automatically measuring trace gas fluxes using a flow-through system. We merge high-frequency flux contributions from TEA with low-frequency covariances from the same sensors. We show flux measurements of CO2, CH4 and H2O by TEA and EC above an old-growth forest at the ICOS flux tower site "Hainich" (DE-Hai). We compare and evaluate the performance of the two direct turbulent flux measurement methods eddy covariance and true eddy accumulation using side-by-side trace gas flux observations. We further compare performance of seven instrument complexes, i.e. combinations of sonic anemometers and trace gas analyzers. We compare gas analyzers types of open-path, enclosed-path and closed-path design. We further differentiate data from two gas analysis technologies: infrared gas analysis (IRGA) and laser spectrometry (open path and CRDS closed
SAR Analysis of the Terra Nova Bay Ice Eddy of Summer 2015
Moctezuma Flores, Miguel; Parmiggiani, Flavio; Fragiacomo, Corrado; Guerrieri, Lorenzo
2016-08-01
In the framework of a study of new-ice formation in Antarctica, SAR image acquisitions were planned over Terra Nova Bay (TNB). Thanks to the ESA Third Party Mission program, Cosmo-SkyMed and Radarsat-2 images were obtained for the period 20 February20 March, 2015; in addition, available Sentinel-1 images over TNB for the same period were retrieved from the ESA Scientific Data Hub. The first inspection of the images revealed the presence of a prominent eddy of surface ice, presumably induced by the wind blowing from the continent. Our first goal was to investigate the correlation between eddy area and wind field. Wind data were obtained from the AWS 'Eneide' located near the Italian Antarctic Base "Mario Zucchelli Station" at TNB.For measuring the eddy area, we developed a specific processing scheme which consists of the following stages: 1. Non-linear filtering; 2. Segmentation, based on the Markov Random Field theory, which uses a contextual approach applied to both the original and the filtered image; 3. Extraction of the eddy parameters, area and perimeter, by means of an active contour detection algorithm which works in an iterative way.The correlation between eddy area and wind field was analysed by means of the Running Correlation Coefficient function Rcc which can reveal the consistency between the two variables. Rcc attained high values in the period 20 February 12 March; after March 15, a powerful katabatic wind completely disrupted the surface ice eddy and displayed a well-defined polynya.
Scale-aware deterministic and stochastic parametrizations of eddy-mean flow interaction
Zanna, Laure; Porta Mana, PierGianLuca; Anstey, James; David, Tomos; Bolton, Thomas
2017-03-01
The role of mesoscale eddies is crucial for the ocean circulation and its energy budget. The sub-grid scale eddy variability needs to be parametrized in ocean models, even at so-called eddy permitting resolutions. Porta Mana and Zanna (2014) propose an eddy parametrization based on a non-Newtonian stress which depends on the partially resolved scales and their variability. In the present study, we test two versions of the parametrization, one deterministic and one stochastic, at coarse and eddy-permitting resolutions in a double gyre quasi-geostrophic model. The parametrization leads to drastic improvements in the mean state and variability of the ocean state, namely in the jet rectification and the kinetic-energy spectra as a function of wavenumber and frequency for eddy permitting models. The parametrization also appears to have a stabilizing effect on the model, especially the stochastic version. The parametrization possesses attractive features for implementation in global models: very little computational cost, it is flow aware and uses the properties of the underlying flow. The deterministic coefficient is scale-aware, while the stochastic parameter is scale- and flow-aware with dependence on resolution, stratification and wind forcing.
Numerical Study of Eddy Shedding By The Loop Current With Ogcm
Tanahara, S.; Crèpon, M.
The high resolution CLIPPER model for the Atlantic Ocean running at 1/6o was used to study the dynamic of the Gulf of Mexico. The model was daily forced with the ECMWF re-analysis air-sea fluxes during 20 years. A spin-up phase of 10 years is done in the experience. The results show the formation of the Loop Current in the interior of the Gulf of Mexico. This loop detach an anticyclonic eddy northward to Yucatan shelf Peninsula. The size of the eddy is close to 290 Km and 1000 m depth. The eddy shedding periodicity is between 7 to 9 months for the 5 first years of numer- ical forcing simulation. After that, the eddy shedding is blocked and an intensification and deepening of the loop happens. It is found that barotropic transport through Yu- catan channel and vertical structure of cross velocity's Yucatan current are important for eddy shedding process. A hypothesis for the generation and blocking of westward propagation of eddies in the Gulf of Mexico is proposed according to the numerical results.
Detecting and tracking eddies in oceanic flows: A vorticity based Euler-Lagrangian method
Vortmeyer-Kley, Rahel; Gräwe, Ulf; Feudel, Ulrike
2016-04-01
Algae blooms as recurrent events in the Baltic Sea are an increasing natural hazard. Sandulescu et al. show in numerical simulation in [1] that eddies can play the role of an incubator for an algae bloom. Inside the eddy nutrients and plankton are trapped and can then be transported across rather long distances. To gain insight in mechanisms of algae bloom evolution detection and tracking of eddies is of interest. Based on the idea to interpret an eddy as a region that is bounded by manifolds and has an elliptic fixed point inside them, we develop an Euler-Lagrangian eddytracking tool using the idea of Lagrangian descriptors [2] and the vorticity. To test how well the tool detects eddy tracks and shapes, and estimates eddy lifetimes, the method is applied to a synthetic van Karman-Vortex Street. The results are compared to an eddytracking tool by Nencioli et al. [3]. Even velocity fields incorporated with different types of noise are taken into account to test the robustness of the tool. Finally, both methods are applied to velocity fields of the Baltic Sea. [1] M. Sandulescu, C. Lopez, E. Hernandez-Garcia and U. Feudel, Nonlinear Proc. Geophys., 14, 443-454, (2007). [2] J. Jimenez-Madrid and A. Mancho, Chaos, 19, 013111-1-18, (2009). [3] F. Nencioli, C. Dong, T. Dickey, L. Washburn, and J.C. McWilliams, J. Atmos. Ocean Tech., 27, 564-579, (2010).
Gaube, Peter; Barceló, Caren; McGillicuddy, Dennis J; Domingo, Andrés; Miller, Philip; Giffoni, Bruno; Marcovaldi, Neca; Swimmer, Yonat
2017-01-01
Marine animals, such as turtles, seabirds and pelagic fishes, are observed to travel and congregate around eddies in the open ocean. Mesoscale eddies, large swirling ocean vortices with radius scales of approximately 50-100 km, provide environmental variability that can structure these populations. In this study, we investigate the use of mesoscale eddies by 24 individual juvenile loggerhead sea turtles (Caretta caretta) in the Brazil-Malvinas Confluence region. The influence of eddies on turtles is assessed by collocating the turtle trajectories to the tracks of mesoscale eddies identified in maps of sea level anomaly. Juvenile loggerhead sea turtles are significantly more likely to be located in the interiors of anticyclones in this region. The distribution of surface drifters in eddy interiors reveals no significant association with the interiors of cyclones or anticyclones, suggesting higher prevalence of turtles in anticyclones is a result of their behavior. In the southern portion of the Brazil-Malvinas Confluence region, turtle swimming speed is significantly slower in the interiors of anticyclones, when compared to the periphery, suggesting that these turtles are possibly feeding on prey items associated with anomalously low near-surface chlorophyll concentrations observed in those features.
A. Samuelsen
2012-06-01
Full Text Available Acoustic measurements show that the biomass of zooplankton and mesopelagic fish is redistributed by mesoscale variability and that the signal extends over several hundred meters depth. The mechanisms governing this distribution are not well understood, but influences from both physical (i.e. redistribution and biological processes (i.e. nutrient transport, primary production, active swimming, etc. are likely. This study examines how hydrodynamic conditions and basic vertical swimming behavior act to distribute biomass in an anticyclonic eddy. Using an eddy-resolving 2.3 km-resolution physical ocean model as forcing for a particle-tracking module, particles representing passively floating organisms and organisms with vertical swimming behavior are released within an eddy and monitored for 20 to 30 days. The role of hydrodynamic conditions on the distribution of biomass is discussed in relation to the acoustic measurements. Particles released close to the surface tend, in agreement with the observations, to accumulate around the edge of the eddy, whereas particles released at depth gradually become distributed along the isopycnals. After a month they are displaced several hundreds meters in the vertical with the deepest particles found close to the eddy center and the shallowest close to the edge. There is no evidence of aggregation of particles along the eddy rim in the last simulation. The model results points towards a physical mechanism for aggregation at the surface, however biological processes cannot be ruled out using the current modeling tool.
Final Report: "Large-Eddy Simulation of Anisotropic MHD Turbulence"
Zikanov, Oleg
2008-06-23
To acquire better understanding of turbulence in flows of liquid metals and other electrically conducting fluids in the presence of steady magnetic fields and to develop an accurate and physically adequate LES (large-eddy simulation) model for such flows. The scientific objectives formulated in the project proposal have been fully completed. Several new directions were initiated and advanced in the course of work. Particular achievements include a detailed study of transformation of turbulence caused by the imposed magnetic field, development of an LES model that accurately reproduces this transformation, and solution of several fundamental questions of the interaction between the magnetic field and fluid flows. Eight papers have been published in respected peer-reviewed journals, with two more papers currently undergoing review, and one in preparation for submission. A post-doctoral researcher and a graduate student have been trained in the areas of MHD, turbulence research, and computational methods. Close collaboration ties have been established with the MHD research centers in Germany and Belgium.
XLES Part II: From Extended Large Eddy Simulation to ODTLES
Glawe, Christoph; Kerstein, Alan R; Klein, Rupert
2015-01-01
In turbulence research and flow applications, turbulence models like RaNS (Reynolds averaged Navier-Stokes) models and LES (Large Eddy Simulation) are used. Both models filter the governing flow equations. Thus a scale separation approach is introduced for modeling purposes with the large scales simulated using a numerical scheme while smaller scales are assumed to be less important and might be modeled more or less easily. Unfortunately small scales are frequently of big importance, e.g. in reactive flows, wall bounded flows, or flows with significant Prandtl or Schmidt number effects. Recent alternatives to these standard models are the class of models based on the one-dimensional turbulence (ODT) idea, like ODTLES. The ability of ODT to capture highly turbulent flows (recently up to $Re_\\tau = 6\\times 10^5$) allows ODTLES to realize 3D resolutions basically independent of the turbulent intensity. In two papers we provide a formal theory and application of an innovative modeling strategy for highly turbulen...
Large-eddy simulation of the very stable boundary layer
Chinita, M. J.; Matheou, G.
2016-12-01
The stable boundary layer is ubiquitous and typically forms at night when the ground radiatively cools and in polar regions throughout the day. Stable stratification and the associated reduction in the energetic scales in combination with the large anisotropy of turbulent motions challenge numerical models. This modeling difficulty also affects large-eddy simulation (LES) methods leading to scarce LES results for very stable conditions. In contrast, the NWP of convective flows has greatly benefited from the ample availability of high quality LES data. In order to overcome these limitations, a novel LES model setup is developed to enable the modeling of very stable boundary layers. A series of Ekman layer-type boundary layers at various surface cooling rates, geotropic winds and latitudes (rotation rates) is presented. A temperature surface condition is applied in the LES. The surface heat flux is dynamically computed byresolving the surface layer since the often-used Monin-Obukhov similarity theory cannot represent very stable conditions. Depending on the conditions, the LES gracefully transitions to a direct numerical simulation (DNS) where the flow becomes fully resolved. Two stability regimes can be discerned based on vertical profiles of the Richardson number. Overall, the model predicts that turbulence is very resilient with respect to stability. Temperature and velocity fluctuations persist even at high Richardson numbers. The nature of the fluctuations, i.e., due to turbulence/overturning or waves, is discussed. Scaling relations and spectra are also presented and discussed.
Large eddy simulation modelling of combustion for propulsion applications.
Fureby, C
2009-07-28
Predictive modelling of turbulent combustion is important for the development of air-breathing engines, internal combustion engines, furnaces and for power generation. Significant advances in modelling non-reactive turbulent flows are now possible with the development of large eddy simulation (LES), in which the large energetic scales of the flow are resolved on the grid while modelling the effects of the small scales. Here, we discuss the use of combustion LES in predictive modelling of propulsion applications such as gas turbine, ramjet and scramjet engines. The LES models used are described in some detail and are validated against laboratory data-of which results from two cases are presented. These validated LES models are then applied to an annular multi-burner gas turbine combustor and a simplified scramjet combustor, for which some additional experimental data are available. For these cases, good agreement with the available reference data is obtained, and the LES predictions are used to elucidate the flow physics in such devices to further enhance our knowledge of these propulsion systems. Particular attention is focused on the influence of the combustion chemistry, turbulence-chemistry interaction, self-ignition, flame holding burner-to-burner interactions and combustion oscillations.
Large Eddy Simulation and Study of the Urban Boundary Layer
苗世光; 蒋维楣
2004-01-01
Based on a pseudo-spectral large eddy simulation (LES) model, an LES model with an anisotropy turbulent kinetic energy (TKE) closure model and an explicit multi-stage third-order Runge-Kutta scheme is established. The modeling and analysis show that the LES model can simulate the planetary boundary layer (PBL) with a uniform underlying surface under various stratifications very well. Then, similar to the description of a forest canopy, the drag term on momentum and the production term of TKE by subgrid city buildings are introduced into the LES equations to account for the area-averaged effect of the subgrid urban canopy elements and to simulate the meteorological fields of the urban boundary layer (UBL). Numerical experiments and comparison analysis show that: (1) the result from the LES of the UBL with a proposed formula for the drag coefficient is consistent and comparable with that from wind tunnel experiments and an urban subdomain scale model; (2) due to the effect of urban buildings, the wind velocity near the canopy is decreased, turbulence is intensified, TKE, variance, and momentum flux are increased, the momentum and heat flux at the top of the PBL are increased, and the development of the PBL is quickened; (3) the height of the roughness sublayer (RS) of the actual city buildings is the maximum building height (1.5-3 times the mean building height), and a constant flux layer (CFL) exists in the lower part of the UBL.
Large eddy simulation of city micro-atmospheric environment
2008-01-01
Air quality is one of the important conditions for a better residence life in the populated urban area and it is closed related to the micro-atmospheric environment. Atmospheric environment is controlled by air motion with multi-scales in the city,while air flows in the residence area are of micro-scale atmospheric motion. This paper introduces a modern numerical simulation method,i.e. large eddy simulation(LES) ,for studying micro-atmospheric flows in the city residence area. For the complex flow features in the residence area,the proper application of LES is studied and various numerical methods are compared in order to investigate their effects on the prediction accuracy of micro-atmospheric flows,for instance,roughness elements and immersed boundary method for complex terrain,different subgrid models and so on. The wind field(including turbulence properties) and contaminant dispersion are computed by the proposed method for a model and a realistic residence area,and the numerical results are in good agreement with the experimental measurements.
Large-Eddy simulation of pulsatile blood flow.
Paul, Manosh C; Mamun Molla, Md; Roditi, Giles
2009-01-01
Large-Eddy simulation (LES) is performed to study pulsatile blood flow through a 3D model of arterial stenosis. The model is chosen as a simple channel with a biological type stenosis formed on the top wall. A sinusoidal non-additive type pulsation is assumed at the inlet of the model to generate time dependent oscillating flow in the channel and the Reynolds number of 1200, based on the channel height and the bulk velocity, is chosen in the simulations. We investigate in detail the transition-to-turbulent phenomena of the non-additive pulsatile blood flow downstream of the stenosis. Results show that the high level of flow recirculation associated with complex patterns of transient blood flow have a significant contribution to the generation of the turbulent fluctuations found in the post-stenosis region. The importance of using LES in modelling pulsatile blood flow is also assessed in the paper through the prediction of its sub-grid scale contributions. In addition, some important results of the flow physics are achieved from the simulations, these are presented in the paper in terms of blood flow velocity, pressure distribution, vortices, shear stress, turbulent fluctuations and energy spectra, along with their importance to the relevant medical pathophysiology.
Preconditioning method and engineering application of large eddy simulation
2008-01-01
On applying large eddy simulation (LES) to engineering interest, one of the keys is to obtain two-order low-dissipation shock-capturing schemes adapted to LES. Therefore, the preconditioning method for all speed flows is adopted. However, the accuracy of preconditioned schemes is not satisfactory because of the poor per-formance of stability of preconditioning techniques especially in viscous flows. The reason of unstability is attributed to the unstability structure in the preconditioned eigenvalue matrix. Based on Roe scheme and two assumptions for low-Mach- Number flows, the new scheme named Low-Speed-Roe scheme is deduced for removing the unstability structure. Numerical experiments show that this scheme has the reasonable computational stability. For general-precision problems, Low-Speed-Roe scheme has similar behavior as the classical preconditioned Roe scheme. For simulations of high-accuracy requirement such as LES, Low-Speed- Roe scheme can obtain better results of complex flows, such as the laminar sepa-ration bubble on the suction surface of the high-loaded turbine blade T106.
Large eddy simulation for aerodynamics: status and perspectives.
Sagaut, Pierre; Deck, Sébastien
2009-07-28
The present paper provides an up-to-date survey of the use of large eddy simulation (LES) and sequels for engineering applications related to aerodynamics. Most recent landmark achievements are presented. Two categories of problem may be distinguished whether the location of separation is triggered by the geometry or not. In the first case, LES can be considered as a mature technique and recent hybrid Reynolds-averaged Navier-Stokes (RANS)-LES methods do not allow for a significant increase in terms of geometrical complexity and/or Reynolds number with respect to classical LES. When attached boundary layers have a significant impact on the global flow dynamics, the use of hybrid RANS-LES remains the principal strategy to reduce computational cost compared to LES. Another striking observation is that the level of validation is most of the time restricted to time-averaged global quantities, a detailed analysis of the flow unsteadiness being missing. Therefore, a clear need for detailed validation in the near future is identified. To this end, new issues, such as uncertainty and error quantification and modelling, will be of major importance. First results dealing with uncertainty modelling in unsteady turbulent flow simulation are presented.
Analysis of errors occurring in large eddy simulation.
Geurts, Bernard J
2009-07-28
We analyse the effect of second- and fourth-order accurate central finite-volume discretizations on the outcome of large eddy simulations of homogeneous, isotropic, decaying turbulence at an initial Taylor-Reynolds number Re(lambda)=100. We determine the implicit filter that is induced by the spatial discretization and show that a higher order discretization also induces a higher order filter, i.e. a low-pass filter that keeps a wider range of flow scales virtually unchanged. The effectiveness of the implicit filtering is correlated with the optimal refinement strategy as observed in an error-landscape analysis based on Smagorinsky's subfilter model. As a point of reference, a finite-volume method that is second-order accurate for both the convective and the viscous fluxes in the Navier-Stokes equations is used. We observe that changing to a fourth-order accurate convective discretization leads to a higher value of the Smagorinsky coefficient C(S) required to achieve minimal total error at given resolution. Conversely, changing only the viscous flux discretization to fourth-order accuracy implies that optimal simulation results are obtained at lower values of C(S). Finally, a fully fourth-order discretization yields an optimal C(S) that is slightly lower than the reference fully second-order method.
An ink-jet printed eddy current position sensor.
Jeranče, Nikola; Bednar, Nikola; Stojanović, Goran
2013-04-18
An eddy current sensor with an ink-jet printed flexible inductor has been designed and fabricated. The inductor has been designed by means of software developed in-house. It has been fabricated by ink-jet printing with silver ink on a flexible substrate. The inductor is a part of the oscillator circuit whose oscillating frequency is measured by a microcontroller. The sensor characteristics have been analyzed for two types of application. The first considered application is the displacement of a large conductive target in a direction perpendicular to the inductor plane. The second considered application is the displacement of a small steel ball parallel to the inductor plane. Inductance and oscillating frequency have been measured in order to completely characterize the sensor. The obtained results validate the use of the sensor for both considered applications, and are in good agreement with the simulations. The advantages of this type of sensor are low cost, the possibility for the inductor to match any curved surface and flexibility and precision of the inductor design.
An Ink-Jet Printed Eddy Current Position Sensor
Goran Stojanović
2013-04-01
Full Text Available An eddy current sensor with an ink-jet printed flexible inductor has been designed and fabricated. The inductor has been designed by means of software developed in-house. It has been fabricated by ink-jet printing with silver ink on a flexible substrate. The inductor is a part of the oscillator circuit whose oscillating frequency is measured by a microcontroller. The sensor characteristics have been analyzed for two types of application. The first considered application is the displacement of a large conductive target in a direction perpendicular to the inductor plane. The second considered application is the displacement of a small steel ball parallel to the inductor plane. Inductance and oscillating frequency have been measured in order to completely characterize the sensor. The obtained results validate the use of the sensor for both considered applications, and are in good agreement with the simulations. The advantages of this type of sensor are low cost, the possibility for the inductor to match any curved surface and flexibility and precision of the inductor design.
XLES Part I: Introduction to Extended Large Eddy Simulation
Glawe, Christoph; Kerstein, Alan R; Klein, Rupert
2015-01-01
Direct numerical simulation (DNS), mostly used in fundamental turbulence research, is limited to low turbulent intensities due the current and future computer resources. Standard turbulence models, like RaNS (Reynolds averaged Navier-Stokes) and LES (Large Eddy Simulation), are applied to flows in engineering, but they miss small scale effects, which are frequently of importance, see e.g. the whole area of reactive flows, flows with apparent Prandtl or Schmidt number effects, or even wall bounded flows. A recent alternative to these standard approaches is the one-dimensional turbulence (ODT) model, which is limited to 1D sub-domains. In two papers we will provide a generalized filter strategy, called XLES (extended LES), including a formal theory (part I) and one special approach in the XLES family of models, called ODTLES (in part II (see Glawe et al. (2015))). ODTLES uses an ODT sub-grid model to describe all turbulent scales not represented by XLES, which leaves the larger scales to be simulated in 3D. Thi...
Diffusion of electromagnetic eddy currents in unconsolidated alluvium
Gilliland, E. S.; Weiss, C. J.
2007-12-01
Recent studies on the diffusive transport of electromagnetic eddy currents in complex geologic materials have invited speculation on novel theoretical frameworks to encapsulate the macroscopic effects of multi-scale geologic complexity. These ideas have been based on a limited amount of data from a restricted suite of geologic environments. To test the veracity of the various diffusion theories proposed in the literature, a new data set is presented here which consists of transient electromagnetic data collected over an alluvial fill aquifer in the Estancia Basin of central New Mexico. Geologic mapping and correlation of historical well-log data show the experiment site to consist of mainly unconsolidated felsic alluvium with intermittent cobble horizons. Analysis of the electromagnetic data in terms of its diagnostic move-out behavior of the source wavelet shows some similarity to previously obtained results in floodplain environments. Further analysis of the data shows that this behavior is dominated by the alluvial texture and not influenced by the underlying basement rock.
Large eddy simulation of a pumped- storage reservoir
Launay, Marina; Leite Ribeiro, Marcelo; Roman, Federico; Armenio, Vincenzo
2016-04-01
The last decades have seen an increasing number of pumped-storage hydropower projects all over the world. Pumped-storage schemes move water between two reservoirs located at different elevations to store energy and to generate electricity following the electricity demand. Thus the reservoirs can be subject to important water level variations occurring at the daily scale. These new cycles leads to changes in the hydraulic behaviour of the reservoirs. Sediment dynamics and sediment budgets are modified, sometimes inducing problems of erosion and deposition within the reservoirs. With the development of computer performances, the use of numerical techniques has become popular for the study of environmental processes. Among numerical techniques, Large Eddy Simulation (LES) has arisen as an alternative tool for problems characterized by complex physics and geometries. This work uses the LES-COAST Code, a LES model under development in the framework of the Seditrans Project, for the simulation of an Upper Alpine Reservoir of a pumped-storage scheme. Simulations consider the filling (pump mode) and emptying (turbine mode) of the reservoir. The hydraulic results give a better understanding of the processes occurring within the reservoir. They are considered for an assessment of the sediment transport processes and of their consequences.
Large Eddy Simulation of isothermal cruciform jet flow: Preliminary results
B.T. Kannan
2016-09-01
Full Text Available The present work is a numerical study of a turbulent isothermal jet issuing from cruciform nozzle into still air at a high Reynolds number of 1.7 × 105. The numerical simulation was carried out by using open source CFD tool OpenFOAM®. Three-dimensional cuboid shaped domain was used to simulate the unsteady turbulent flow field. The simulation was carried out by solving the filtered Navier–Stokes equations along with Smagorinsky sub-grid scale model. The Large Eddy Simulation (LES solutions are compared with experimental data for validation of the jet flow physics. The flow field of turbulent jet from cruciform nozzle are described in terms of inverse mean axial velocity decay and visualizations. The vortical structures are visualized using iso-surface contours of vorticity magnitude. The vortical structures develop from the cruciform nozzle is significantly different from axisymmetric nozzles. The vortical structures show changes in shape as they move downstream from the nozzle. The cruciform jet shows complex vorticity dynamics in the near field region.
Large-eddy simulations of contrails in a turbulent atmosphere
J. Picot
2014-11-01
Full Text Available In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES coupled to a Lagrangian particle tracking method to treat the ice phase. This is the first paper where fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere lower stratosphere. The initial flow-field is composed by the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail decent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex break-up dominates over background turbulence at the end of the vortex regime and dominates the mixing with ambient air. This results in global microphysical characteristics such as ice mass and optical depth that are be slightly affected by the intensity of atmospheric turbulence. On the other hand, the background humidity and temperature have a first order effect on the survival of ice crystals and particle size distribution, which is in line with recent and ongoing studies in the literature.
Eddy-Current Sensors with Asymmetrical Point Spread Function
Janusz Gajda
2016-10-01
Full Text Available This paper concerns a special type of eddy-current sensor in the form of inductive loops. Such sensors are applied in the measuring systems classifying road vehicles. They usually have a rectangular shape with dimensions of 1 × 2 m, and are installed under the surface of the traffic lane. The wide Point Spread Function (PSF of such sensors causes the information on chassis geometry, contained in the measurement signal, to be strongly averaged. This significantly limits the effectiveness of the vehicle classification. Restoration of the chassis shape, by solving the inverse problem (deconvolution, is also difficult due to the fact that it is ill-conditioned. An original approach to solving this problem is presented in this paper. It is a hardware-based solution and involves the use of inductive loops with an asymmetrical PSF. Laboratory experiments and simulation tests, conducted with models of an inductive loop, confirmed the effectiveness of the proposed solution. In this case, the principle applies that the higher the level of sensor spatial asymmetry, the greater the effectiveness of the deconvolution algorithm.
Indonesian Throughflow in an eddy-permitting oceanic GCM
LI Wei; LIU Hailong; ZHANG Xuehong
2004-01-01
An eddy-permitting quasi-global oceanic GCM was driven by wind stresses from reanalysis data for the period of 1958-2001 to get the time series of the upper circulation in the Indonesian Sea. The model represents a reasonable pathway of Indonesian Throughflow (ITF) with Makassar Strait making the major passage transfer the North Pacific water southward. The simulated annual mean ITF transport is 14.5 Sv, with 13.2 Sv in the upper 700 m. Annual cycle is the dominant signal for the seasonal climatology of the upper layer transport. Both the annual mean and seasonal cycle agree well with the observation. The overall correlation between the interannual anomaly of the ITF transport and Nino 3.4 index reaches -0.65 in the simulation, which indicates that ENSO-related interannual variability in the Pacific is dominant in controlling the ITF transport. The relationship between the interannual anomalies of ITF and sea surface temperature in the Pacific, the Indian Ocean is not fixed in the simulation. In 1994, for instance, the intensive Indian Ocean sea surface temperature anomaly plays a dominant role in the formation of an impressive large transport of ITF.
Large eddy simulation of unsteady lean stratified premixed combustion
Duwig, C. [Division of Fluid Mechanics, Department of Energy Sciences, Lund University, SE 221 00 Lund (Sweden); Fureby, C. [Division of Weapons and Protection, Warheads and Propulsion, The Swedish Defense Research Agency, FOI, SE 147 25 Tumba (Sweden)
2007-10-15
Premixed turbulent flame-based technologies are rapidly growing in importance, with applications to modern clean combustion devices for both power generation and aeropropulsion. However, the gain in decreasing harmful emissions might be canceled by rising combustion instabilities. Unwanted unsteady flame phenomena that might even destroy the whole device have been widely reported and are subject to intensive studies. In the present paper, we use unsteady numerical tools for simulating an unsteady and well-documented flame. Computations were performed for nonreacting, perfectly premixed and stratified premixed cases using two different numerical codes and different large-eddy-simulation-based flamelet models. Nonreacting simulations are shown to agree well with experimental data, with the LES results capturing the mean features (symmetry breaking) as well as the fluctuation level of the turbulent flow. For reacting cases, the uncertainty induced by the time-averaging technique limited the comparisons. Given an estimate of the uncertainty, the numerical results were found to reproduce well the experimental data in terms both of mean flow field and of fluctuation levels. In addition, it was found that despite relying on different assumptions/simplifications, both numerical tools lead to similar predictions, giving confidence in the results. Moreover, we studied the flame dynamics and particularly the response to a periodic pulsation. We found that above a certain excitation level, the flame dynamic changes and becomes rather insensitive to the excitation/instability amplitude. Conclusions regarding the self-growth of thermoacoustic waves were drawn. (author)
Eddy current septum magnets for injection and extraction at SSRF
Ouyang, Lian-Hua; Gu, Ming; Liu, Bo; Chen, Rong
2010-03-01
There are 6 in-vacuum eddy current septum magnets used for booster injection, extraction, and storage ring injection in SSRF. Special attention was paid to coils and their support designs because of the shock force they bear in the magnetic fields and the high heat which is hard to be dissipated in vacuum environment. For the storage ring magnets, good transverse homogeneity in the gap was achieved by careful design, precise machining and accurate assembly; and an extremely low leakage field on the stored beam is another key feature thanks to the high permeability Mu metal. Magnetic field measurement was conducted with both a point coil and a long integral coil, and the results agree well with the OPERA-2d/3d simulations. An inner tube is added to keep the continuity of impedance for the circulating beam with two RF finger flanges at each end. There is no vacuum separation between the inner tube and the magnet chamber. Sputter ion pumps integrated with NEG are used to acquire the UHV for the chamber.
Inverse problem of pulsed eddy current field of ferromagnetic plates
Chen, Xing-Le; Lei, Yin-Zhao
2015-03-01
To determine the wall thickness, conductivity and permeability of a ferromagnetic plate, an inverse problem is established with measured values and calculated values of time-domain induced voltage in pulsed eddy current testing on the plate. From time-domain analytical expressions of the partial derivatives of induced voltage with respect to parameters, it is deduced that the partial derivatives are approximately linearly dependent. Then the constraints of these parameters are obtained by solving a partial linear differential equation. It is indicated that only the product of conductivity and wall thickness, and the product of relative permeability and wall thickness can be determined accurately through the inverse problem with time-domain induced voltage. In the practical testing, supposing the conductivity of the ferromagnetic plate under test is a fixed value, and then the relative variation of wall thickness between two testing points can be calculated via the ratio of the corresponding inversion results of the product of conductivity and wall thickness. Finally, this method for wall thickness measurement is verified by the experiment results of a carbon steel plate. Project supported by the National Defense Basic Technology Research Program of China (Grant No. Z132013T001).
Three dimensional boundary element solutions for eddy current nondestructive evaluation
Yang, Ming; Song, Jiming; Nakagawa, Norio
2014-02-01
The boundary integral equations (BIE) method is a numerical computational method of solving linear partial differential equations which have been formulated as integral equations. It can be applied in many areas of engineering and science including fluid mechanics, acoustics, electromagnetics, and fracture mechanics. The eddy current problem is formulated by the BIE and discretized into matrix equations by the method of moments (MoM) or the boundary element method (BEM). The three dimensional arbitrarily shaped objects are described by a number of triangular patches. The Stratton-Chu formulation is specialized for the conductive medium. The equivalent electric and magnetic surface currents are expanded in terms of Rao-Wilton-Glisson (RWG) vector basis function while the normal component of magnetic field is expanded in terms of the pulse basis function. Also, a low frequency approximation is applied in the external medium. Additionally, we introduce Auld's impedance formulas to calculate impedance variation. There are very good agreements between numerical results and those from theory and/or experiments for a finite cross-section above a wedge.
Investigation of casing inspection through tubing with pulsed eddy current
Fu, Yuewen; Yu, Runqiao; Peng, Xuewen; Ren, Shangkun
2012-12-01
Corrosion and cracks of casing string in oil wells is a serious problem on which little research has been done when inspecting casing through tubing. In this study, inspecting casing through tubing with pulsed eddy current is investigated. Longitudinal and transverse probes are centred inside the tubing to detect wall thinnings and cracks in casing. A time slice of induced voltage in the receiving coil of the probe is used as the feature to recognise defects. The experimental results show that large area wall thinnings and long cracks in casing are detected successfully through the tubing with appropriate inspection parameters. The probe's orientation to the crack is important and a particular discovery is that the transverse probe should be parallel to the transverse crack and not be perpendicular to it when inspecting. A method based on linear regression is proposed to estimate flaws in casing while wall thinning in the tubing occurs at the same location. The method is effective for large area thinning in casing when tubing thinning is wide.
Eddy current testing system for bottom mounted instrumentation welds
Kobayashi Noriyasu
2015-01-01
Full Text Available The capability of eddy current testing (ECT for the bottom mounted instrumentation (BMI weld area of reactor vessel in a pressurized water reactor was demonstrated by the developed ECT system and procedure. It is difficult to position and move the probe on the BMI weld area because the area has complexly curved surfaces. The space coordinates and the normal vectors at the scanning points were calculated as the scanning trajectory of probe based on the measured results of surface shape on the BMI mock-up. The multi-axis robot was used to move the probe on the mock-up. Each motion-axis position of the robot corresponding to each scanning point was calculated by the inverse kinematic algorithm. In the mock-up test, the probe was properly contacted with most of the weld surfaces. The artificial stress corrosion cracking of approximately 6 mm in length and the electrical-discharge machining slit of 0.5 mm in length, 1 mm in depth and 0.2 mm in width given on the weld surface were detected. From the probe output voltage, it was estimated that the average probe tilt angle on the surface under scanning was 2.6°.
Detection of localized damage by eddy currents technique
Aoukili A.
2014-01-01
Full Text Available Non destructive evaluation techniques based on eddy currents (EC are largely used for quality control of the castings in a lot of industries. The principle of detection by EC consists in using an adequate inductive coil to generate them by a variable magnetic field, and measuring their effects by using one or several sensors. These effects result from the interaction between the induced magnetic field and the excited conductive material. A local variation of the physical properties or geometry of the tested sample, due to a singularity or a flaw, causes a modification of the EC distribution, enabling thus detection. In order to optimize the capacity of defect revealing by means of EC based probes, an accurate modelling of the problem is essential. This can be used to perform simulation of the EC distribution under different circumstances and to analyze the EC sensitivity to the various implicated parameters. In this work, the modelling of EC is made by using the finite element method. Using a B-scan strategy was used, detection of a small defect having the shape of an open cavity is shown to be correctly indicated via monitoring variations of the induced voltage in the receiver coil.
Unsteady RANS and Large Eddy simulations of multiphase diesel injection
Philipp, Jenna; Green, Melissa; Akih-Kumgeh, Benjamin
2015-11-01
Unsteady Reynolds Averaged Navier-Stokes (URANS) and Large Eddy Simulations (LES) of two-phase flow and evaporation of high pressure diesel injection into a quiescent, high temperature environment is investigated. Unsteady RANS and LES are turbulent flow simulation approaches used to determine complex flow fields. The latter allows for more accurate predictions of complex phenomena such as turbulent mixing and physio-chemical processes associated with diesel combustion. In this work we investigate a high pressure diesel injection using the Euler-Lagrange method for multiphase flows as implemented in the Star-CCM+ CFD code. A dispersed liquid phase is represented by Lagrangian particles while the multi-component gas phase is solved using an Eulerian method. Results obtained from the two approaches are compared with respect to spray penetration depth and air entrainment. They are also compared with experimental data taken from the Sandia Engine Combustion Network for ``Spray A''. Characteristics of primary and secondary atomization are qualitatively evaluated for all simulation modes.
A Large Eddy Simulation Study for upstream wind energy conditioning
Sharma, V.; Calaf, M.; Parlange, M. B.
2013-12-01
The wind energy industry is increasingly focusing on optimal power extraction strategies based on layout design of wind farms and yaw alignment algorithms. Recent field studies by Mikkelsen et al. (Wind Energy, 2013) have explored the possibility of using wind lidar technology installed at hub height to anticipate incoming wind direction and strength for optimizing yaw alignment. In this work we study the benefits of using remote sensing technology for predicting the incoming flow by using large eddy simulations of a wind farm. The wind turbines are modeled using the classic actuator disk concept with rotation, together with a new algorithm that permits the turbines to adapt to varying flow directions. This allows for simulations of a more realistic atmospheric boundary layer driven by a time-varying geostrophic wind. Various simulations are performed to investigate possible improvement in power generation by utilizing upstream data. Specifically, yaw-correction of the wind-turbine is based on spatio-temporally averaged wind values at selected upstream locations. Velocity and turbulence intensity are also considered at those locations. A base case scenario with the yaw alignment varying according to wind data measured at the wind turbine's hub is also used for comparison. This reproduces the present state of the art where wind vanes and cup anemometers installed behind the rotor blades are used for alignment control.
Large Eddy Simulation of High-Speed, Premixed Ethylene Combustion
Ramesh, Kiran; Edwards, Jack R.; Chelliah, Harsha; Goyne, Christopher; McDaniel, James; Rockwell, Robert; Kirik, Justin; Cutler, Andrew; Danehy, Paul
2015-01-01
A large-eddy simulation / Reynolds-averaged Navier-Stokes (LES/RANS) methodology is used to simulate premixed ethylene-air combustion in a model scramjet designed for dual mode operation and equipped with a cavity for flameholding. A 22-species reduced mechanism for ethylene-air combustion is employed, and the calculations are performed on a mesh containing 93 million cells. Fuel plumes injected at the isolator entrance are processed by the isolator shock train, yielding a premixed fuel-air mixture at an equivalence ratio of 0.42 at the cavity entrance plane. A premixed flame is anchored within the cavity and propagates toward the opposite wall. Near complete combustion of ethylene is obtained. The combustor is highly dynamic, exhibiting a large-scale oscillation in global heat release and mass flow rate with a period of about 2.8 ms. Maximum heat release occurs when the flame front reaches its most downstream extent, as the flame surface area is larger. Minimum heat release is associated with flame propagation toward the cavity and occurs through a reduction in core flow velocity that is correlated with an upstream movement of the shock train. Reasonable agreement between simulation results and available wall pressure, particle image velocimetry, and OH-PLIF data is obtained, but it is not yet clear whether the system-level oscillations seen in the calculations are actually present in the experiment.
Mathematics of large eddy simulation of turbulent flows
Berselli, L.C. [Pisa Univ. (Italy). Dept. of Applied Mathematics ' ' U. Dini' ' ; Iliescu, T. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Mathematics; Layton, W.J. [Pittsburgh Univ., PA (United States). Dept. of Mathematics
2006-07-01
Large eddy simulation (LES) is a method of scientific computation seeking to predict the dynamics of organized structures in turbulent flows by approximating local, spatial averages of the flow. Since its birth in 1970, LES has undergone an explosive development and has matured into a highly-developed computational technology. It uses the tools of turbulence theory and the experience gained from practical computation. This book focuses on the mathematical foundations of LES and its models and provides a connection between the powerful tools of applied mathematics, partial differential equations and LES. Thus, it is concerned with fundamental aspects not treated so deeply in the other books in the field, aspects such as well-posedness of the models, their energy balance and the connection to the Leray theory of weak solutions of the Navier-Stokes equations. The authors give a mathematically informed and detailed treatment of an interesting selection of models, focusing on issues connected with understanding and expanding the correctness and universality of LES. This volume offers a useful entry point into the field for PhD students in applied mathematics, computational mathematics and partial differential equations. Non-mathematicians will appreciate it as a reference that introduces them to current tools and advances in the mathematical theory of LES. (orig.)
L. Stramma
2013-06-01
Full Text Available 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.
The Solomon Sea eddy activity from a 1/36° regional model
Djath, Bughsin; Babonneix, Antoine; Gourdeau, Lionel; Marin, Frédéric; Verron, Jacques
2013-04-01
In the South West Pacific, the Solomon Sea exhibits the highest levels of eddy kinetic energy but relatively little is known about the eddy activity in this region. This Sea is directly influenced by a monsoonal regime and ENSO variability, and occupies a strategical location as the Western Boundary Currents exiting it are known to feed the warm pool and to be the principal sources of the Equatorial UnderCurrent. During their transit in the Solomon Sea, meso-scale eddies are suspected to notably interact and influence these water masses. The goal of this study is to give an exhaustive description of this eddy activity. A dual approach, based both on altimetric data and high resolution modeling, has then been chosen for this purpose. First, an algorithm is applied on nearly 20 years of 1/3° x 1/3° gridded SLA maps (provided by the AVISO project). This allows eddies to be automatically detected and tracked, thus providing some basic eddy properties. The preliminary results show that two main and distinct types of eddies are detected. Eddies in the north-eastern part shows a variability associated with the mean structure, while those in the southern part are associated with generation/propagation processes. However, the resolution of the AVISO dataset is not very well suited to observe fine structures and to match with the numerous islands bordering the Solomon Sea. For this reason, we will confront these observations with the outputs of a 1/36° resolution realistic model of the Solomon Sea. The high resolution numerical model (1/36°) indeed permits to reproduce very fine scale features, such as eddies and filaments. The model is two-way embedded in a 1/12° regional model which is itself one-way embedded in the DRAKKAR 1/12° global model. The NEMO code is used as well as the AGRIF software for model nestings. Validation is realized by comparison with AVISO observations and available in situ data. In preparing the future wide-swath altimetric SWOT mission that is
Zhang, S.; Rem, P.C.; Forssberg, E.
1999-01-01
Owing to the growing emergence of the end-of-life electrical and electronic products with complex material structures and an ever-diminishing particle size of the valuable metals involved, development of eddy current separators (ECS) has been targeting selective separation of small non-ferrous metal
Karstensen, Johannes; Schütte, Florian; Pietri, Alice; Krahmann, Gerd; Fiedler, Björn; Grundle, Damian; Hauss, Helena; Körtzinger, Arne; Löscher, Carolin R.; Testor, Pierre; Vieira, Nuno; Visbeck, Martin
2017-04-01
The temporal evolution of the physical and biogeochemical structure of an oxygen-depleted anticyclonic modewater eddy is investigated over a 2-month period using high-resolution glider and ship data. A weakly stratified eddy core (squared buoyancy frequency N2 ˜ 0.1 × 10-4 s-2) at shallow depth is identified with a horizontal extent of about 70 km and bounded by maxima in N2. The upper N2 maximum (3-5 × 10-4 s-2) coincides with the mixed layer base and the lower N2 maximum (0.4 × 10-4 s-2) is found at about 200 m depth in the eddy centre. The eddy core shows a constant slope in temperature/salinity (T/S) characteristic over the 2 months, but an erosion of the core progressively narrows down the T/S range. The eddy minimal oxygen concentrations decreased by about 5 µmol kg-1 in 2 months, confirming earlier estimates of oxygen consumption rates in these eddies. Separating the mesoscale and perturbation flow components reveals oscillating velocity finestructure ( ˜ 0.1 m s-1) underneath the eddy and at its flanks. The velocity finestructure is organized in layers that align with layers in properties (salinity, temperature) but mostly cross through surfaces of constant density. The largest magnitude in velocity finestructure is seen between the surface and 140 m just outside the maximum mesoscale flow but also in a layer underneath the eddy centre, between 250 and 450 m. For both regions a cyclonic rotation of the velocity finestructure with depth suggests the vertical propagation of near-inertial wave (NIW) energy. Modification of the planetary vorticity by anticyclonic (eddy core) and cyclonic (eddy periphery) relative vorticity is most likely impacting the NIW energy propagation. Below the low oxygen core salt-finger type double diffusive layers are found that align with the velocity finestructure. Apparent oxygen utilization (AOU) versus dissolved inorganic nitrate (NO3-) ratios are about twice as high (16) in the eddy core compared to surrounding waters (8
Anticyclonic eddy energy and pathways in the Algerian basin (1993-2007)
Pessini, Federica; Perilli, Angelo; Olita, Antonio
2016-04-01
The Algero-Provençal basin plays a key role in the circulation of the entire Mediterranean Sea. Consequently, in the past its hydrodynamics has been intensively studied with infrared and colour satellite imagery, moorings, surface drifters and altimetry observations. The basin is divided into two sub-basins by the North Balearic front, a thermal front characterized by a high seasonal variability: the Provençal sub-basin in the north and the Algerian sub-basin in the south. The Algerian basin is dominated by mesoscale phenomena, especially anti-cyclonic eddies. The Algerian current becomes unstable and meanders; often giving rise to mesoscale eddies of both signs. The anti-cyclonic eddies (hereafter Algerian Eddies or AEs) can grow rapidly in horizontal and vertical extension. They can also detach from the Algerian slope and circulate for several months within the sub-basin, while the cyclonic ones quickly disappear. In spite of its limited dimensions, the Algerian sub-basin can contain as many as three long-life AEs, which can interact with each other and with sub-basin dynamics. In spite of the current body of research, a study on the tracking, energy and interaction of these long-life eddies in time and space is still lacking. In order to fill this gap, we applied the automated eddy detection and tracking method created by Penven (2005), which reveals the complex movements and dynamics of eddies in the Algerian sub-basin. The Penven algorithm combines the detection of the largest closed contours in SSH (Sea Surface Height) with a positive value of the relevant Okubo-Weiss parameter. The latter has already been successfully used in the Algerian Basin by Isern-Fontanet et al. (2003). The eddy-tracking algorithm is based on the minimization of a general distance that takes into account the difference in coordinates, radius, vorticity, mean height and amplitude between eddies of consecutive temporal steps. The code was modified and adapted in order to optimize its
Lei Wang
Full Text Available It is widely recognized that the mesoscale eddies play an important part in the biogeochemical cycle in ocean ecosystem, especially in the oligotrophic tropical zones. So here a heterogeneous cyclonic eddy in its flourishing stage was detected using remote sensing and in situ biogeochemical observation in the western South China Sea (SCS in early September, 2007. The high-performance liquid chromatography method was used to identify the photosynthetic pigments. And the CHEMical TAXonomy (CHEMTAX was applied to calculate the contribution of nine phytoplankton groups to the total chlorophyll a (TChl a biomass. The deep chlorophyll a maximum layer (DCML was raised to form a dome structure in the eddy center while there was no distinct enhancement for TChl a biomass. The integrated TChl a concentration in the upper 100 m water column was also constant from the eddy center to the surrounding water outside the eddy. However the TChl a biomass in the surface layer (at 5 m in the eddy center was promoted 2.6-fold compared to the biomass outside the eddy (p < 0.001. Thus, the slight enhancement of TChl a biomass of euphotic zone integration within the eddy was mainly from the phytoplankton in the upper mixed zone rather than the DCML. The phytoplankton community was primarily contributed by diatoms, prasinophytes, and Synechococcus at the DCML within the eddy, while less was contributed by haptophytes_8 and Prochlorococcus. The TChl a biomass for most of the phytoplankton groups increased at the surface layer in the eddy center under the effect of nutrient pumping. The doming isopycnal within the eddy supplied nutrients gently into the upper mixing layer, and there was remarkable enhancement in phytoplankton biomass at the surface layer with 10.5% TChl a biomass of water column in eddy center and 3.7% at reference stations. So the slight increasing in the water column integrated phytoplankton biomass might be attributed to the stimulated phytoplankton
Evaluation of a scalar eddy transport coefficient based on geometric constraints
Bachman, S. D.; Marshall, D. P.; Maddison, J. R.; Mak, J.
2017-01-01
A suite of idealized models is used to evaluate and compare several previously proposed scalings for the eddy transport coefficient in downgradient mesoscale eddy closures. Of special interest in this comparison is a scaling introduced as part of the eddy parameterization framework of Marshall et al. (2012), which is derived using the inherent geometry of the Eliassen-Palm eddy flux tensor. The primary advantage of using this coefficient in a downgradient closure is that all dimensional terms are explicitly specified and the only uncertainty is a nondimensional parameter, α, which is bounded by one in magnitude. In each model a set of passive tracers is initialized, whose flux statistics are used to invert for the eddy-induced tracer transport. Unlike previous work, where this technique has been employed to diagnose the tensor coefficient of a linear flux-gradient relationship, the idealization of these models allows the lateral eddy transport to be described by a scalar coefficient. The skill of the extant scalings is then measured by comparing their predicted values against the coefficients diagnosed using this method. The Marshall et al. (2012), scaling is shown to scale most closely with the diagnosed coefficients across all simulations. It is shown that the skill of this scaling is due to its functional dependence on the total eddy energy, and that this scaling provides an excellent match to the diagnosed fluxes even in the limit of constant α. Possible extensions to this work, including how to incorporate the resultant transport coefficient into the Gent and McWilliams parameterization, are discussed.
SUN; Xiaomin; ZHU; Zhilin; XU; Jinping; YUAN; Guofu
2005-01-01
It is more and more popular to estimate the exchange of water vapor, heat and CO2fluxes between the land surface and the atmosphere using the eddy covariance technique. To get believable fluxes, it is necessary to correct the observations based on the different surface conditions and to determine relevant techinical parameters. The raw 10 Hz eddy covariance data observed in the Yucheng and Changbai Mountains stations were recalculated by various averaging periods (from 1 to 720 min) respectively, and the recalculated results were compared with the results calculated by the averaging period of 30 mins. Meanwhile, the distinctions of fluxes calculated by different averaging periods were analyzed. The continuous 15 days observations over wheat fields in the Yucheng station were mainly analyzed. The results are shown that: (i) In the Yucheng station, compared with the observations by 30 min, when the averaging period changes from 10 to 60 min, the variations of the eddy-covariance estimates of fluxes were less than 2%; when the averaging period changes less than 10 min, the estimate of fluxes reduced obviously with the reduction of the averaging period (the max relative error was -12%); and when the averaging period exceeds 120 min, the eddy covariance estimates of fluxes will be increased and become unsteady (the max relative error is over 10%); (ii) the eddy covariance estimates of fluxes over wheat field in the Yucheng station suggusted that it is much better to take 10 min as an averaging period in studying diurnal change of fluxes, and take 30min for a long-term flux observation; and (iii) normalized ratio was put forward to determine the range of averaging period of eddy covariance measurements. By comparing the observations over farmlands and those over forests, it is indicated that the increase of eddy covariance estimates over tall forest was more than that over short vegetation when the averaging period increased.
Large-Eddy Simulation of Maritime Deep Tropical Convection
Khairoutdinov, Marat F.; Krueger, Steve K.; Moeng, Chin-Hoh; Bogenschutz, Peter A.; Randall, David A.
2009-04-01
This study represents an attempt to apply Large-Eddy Simulation (LES) resolution to simulate deep tropical convection in near equilibrium for 24 hours over an area of about 205 × 205 km2, which is comparable to that of a typical horizontal grid cell in a global climate model. The simulation is driven by large-scale thermodynamic tendencies derived from mean conditions during the GATE Phase III field experiment. The LES uses 2048 × 2048 × 256 grid points with horizontal grid spacing of 100 m and vertical grid spacing ranging from 50 m in the boundary layer to 100 m in the free troposphere. The simulation reaches a near equilibrium deep convection regime in 12 hours. The simulated vertical cloud distribution exhibits a tri-modal vertical distribution of deep, middle and shallow clouds similar to that often observed in Tropics. A sensitivity experiment in which cold pools are suppressed by switching off the evaporation of precipitation results in much lower amounts of shallow and congestus clouds. Unlike the benchmark LES where the new deep clouds tend to appear along the edges of spreading cold pools, the deep clouds in the no-cold-pool experiment tend to reappear at the sites of the previous deep clouds and tend to be surrounded by extensive areas of sporadic shallow clouds. The vertical velocity statistics of updraft and downdraft cores below 6 km height are compared to aircraft observations made during GATE. The comparison shows generally good agreement, and strongly suggests that the LES simulation can be used as a benchmark to represent the dynamics of tropical deep convection on scales ranging from large turbulent eddies to mesoscale convective systems. The effect of horizontal grid resolution is examined by running the same case with progressively larger grid sizes of 200, 400, 800, and 1600 m. These runs show a reasonable agreement with the benchmark LES in statistics such as convective available potential energy, convective inhibition, cloud fraction
Large-eddy simulation of maritime deep tropical convection
Peter A Bogenschutz
2009-12-01
Full Text Available This study represents an attempt to apply Large-Eddy Simulation (LES resolution to simulate deep tropical convection in near equilibrium for 24 hours over an area of about 205 x 205 km2, which is comparable to that of a typical horizontal grid cell in a global climate model. The simulation is driven by large-scale thermodynamic tendencies derived from mean conditions during the GATE Phase III field experiment. The LES uses 2048 x 2048 x 256 grid points with horizontal grid spacing of 100 m and vertical grid spacing ranging from 50 m in the boundary layer to 100 m in the free troposphere. The simulation reaches a near equilibrium deep convection regime in 12 hours. The simulated vertical cloud distribution exhibits a trimodal vertical distribution of deep, middle and shallow clouds similar to that often observed in Tropics. A sensitivity experiment in which cold pools are suppressed by switching off the evaporation of precipitation results in much lower amounts of shallow and congestus clouds. Unlike the benchmark LES where the new deep clouds tend to appear along the edges of spreading cold pools, the deep clouds in the no-cold-pool experiment tend to reappear at the sites of the previous deep clouds and tend to be surrounded by extensive areas of sporadic shallow clouds. The vertical velocity statistics of updraft and downdraft cores below 6 km height are compared to aircraft observations made during GATE. The comparison shows generally good agreement, and strongly suggests that the LES simulation can be used as a benchmark to represent the dynamics of tropical deep convection on scales ranging from large turbulent eddies to mesoscale convective systems. The effect of horizontal grid resolution is examined by running the same case with progressively larger grid sizes of 200, 400, 800, and 1600 m. These runs show a reasonable agreement with the benchmark LES in statistics such as convective available potential energy, convective inhibition
Large eddy simulation of the flow through a swirl generator
Conway, Stephen
1998-12-01
The advances made in computer technology over recent years have led to a great increase in the engineering problems that can be studied using CFD. The computation of flows over and through complex geometries at relatively high Reynolds numbers is becoming more common using the Large Eddy Simulation (LES) technique. Direct numerical simulations of such flows is still beyond the capacity of todays fastest supercomputers, requiring excessive computational times and memory. In addition, traditional Reynolds Averaged Navier Stokes (RANS) methods are known to have limited applicability in a wide range of engineering flow situations. In this thesis LES has been used to simulate the flow through a cascade of guidance vanes, more commonly known as a swirl generator, positioned at the inlet to a gas turbine combustion chamber. This flow case is of interest because of the complex flow phenomena which occur within the swirl generator, which include compressibility effects, different types of flow instabilities, transition, laminar and turbulent separation and near wall turbulence. It is also of interest because it fits very well into the range of engineering applications that can be studied using LES. Two computational grids with different resolutions and two subgrid scale stress models were used in the study. The effects of separation and transition are investigated. A vortex shedding frequency from the guidance vanes is determined which is seen to be dependent on the angle of incident air flow. Interaction between the movement of the separation region and the shedding frequency is also noted. Such vortex shedding phenomena can directly affect the quality of fuel and air mixing within the combustion chamber and can in some cases induce vibrations in the gas turbine structure. Comparisons between the results obtained using different grid resolutions with an implicit and a dynamic divergence (DDM) subgrid scale stress models are also made 32 refs, 35 figs, 2 tabs
Project EDDIE: Improving Big Data skills in the classroom
Soule, D. C.; Bader, N.; Carey, C.; Castendyk, D.; Fuller, R.; Gibson, C.; Gougis, R.; Klug, J.; Meixner, T.; Nave, L. E.; O'Reilly, C.; Richardson, D.; Stomberg, J.
2015-12-01
High-frequency sensor-based datasets are driving a paradigm shift in the study of environmental processes. The online availability of high-frequency data creates an opportunity to engage undergraduate students in primary research by using large, long-term, and sensor-based, datasets for science courses. Project EDDIE (Environmental Data-Driven Inquiry & Exploration) is developing flexible classroom activity modules designed to (1) improve quantitative and reasoning skills; (2) develop the ability to engage in scientific discourse and argument; and (3) increase students' engagement in science. A team of interdisciplinary faculty from private and public research universities and undergraduate institutions have developed these modules to meet a series of pedagogical goals that include (1) developing skills required to manipulate large datasets at different scales to conduct inquiry-based investigations; (2) developing students' reasoning about statistical variation; and (3) fostering accurate student conceptions about the nature of environmental science. The modules cover a wide range of topics, including lake physics and metabolism, stream discharge, water quality, soil respiration, seismology, and climate change. Assessment data from questionnaire and recordings collected during the 2014-2015 academic year show that our modules are effective at making students more comfortable analyzing data. Continued development is focused on improving student learning outcomes with statistical concepts like variation, randomness and sampling, and fostering scientific discourse during module engagement. In the coming year, increased sample size will expand our assessment opportunities to comparison groups in upper division courses and allow for evaluation of module-specific conceptual knowledge learned. This project is funded by an NSF TUES grant (NSF DEB 1245707).
Large Eddy Simulation of Vertical Axis Wind Turbine Wakes
Sina Shamsoddin
2014-02-01
Full Text Available In this study, large eddy simulation (LES is combined with a turbine model to investigate the wake behind a vertical-axis wind turbine (VAWT in a three-dimensional turbulent flow. Two methods are used to model the subgrid-scale (SGS stresses: (a the Smagorinsky model; and (b the modulated gradient model. To parameterize the effects of the VAWT on the flow, two VAWT models are developed: (a the actuator swept-surface model (ASSM, in which the time-averaged turbine-induced forces are distributed on a surface swept by the turbine blades, i.e., the actuator swept surface; and (b the actuator line model (ALM, in which the instantaneous blade forces are only spatially distributed on lines representing the blades, i.e., the actuator lines. This is the first time that LES has been applied and validated for the simulation of VAWT wakes by using either the ASSM or the ALM techniques. In both models, blade-element theory is used to calculate the lift and drag forces on the blades. The results are compared with flow measurements in the wake of a model straight-bladed VAWT, carried out in the Institute de Méchanique et Statistique de la Turbulence (IMST water channel. Different combinations of SGS models with VAWT models are studied, and a fairly good overall agreement between simulation results and measurement data is observed. In general, the ALM is found to better capture the unsteady-periodic nature of the wake and shows a better agreement with the experimental data compared with the ASSM. The modulated gradient model is also found to be a more reliable SGS stress modeling technique, compared with the Smagorinsky model, and it yields reasonable predictions of the mean flow and turbulence characteristics of a VAWT wake using its theoretically-determined model coefficient.
Properties of shallow convection from Large-Eddie simulations
Denby, Leif; Herzog, Michael
2017-04-01
Utilizing Large-Eddie simulations (LES) of isolated individual convective clouds in an idealised conditionally unstable atmosphere and large-domain LES simulations of radiative-convective equilibrium (RCE) from the RICO measuring campaign (Rauber et al. 2007), vertical profiles of individual clouds and statistical properties of the cloud ensemble have been extracted and compared against predictions by an 1D entraining parcel model and against the cloud-ensemble model of the CCFM (Wagner and Graf 2010) convection scheme (which comprises a solution of a Lotka-Volterra population dynamics system). For the simulations of isolated clouds it was possible to achieve agreement with the entraining parcel model when simulations were carried out with 2D axisymmetry and the entrainment rate was prescribed using an entraining profile estimated from LES simulation using a passive tracer (in place of the traditional Morton- Turner entrainment rate parameterisation), this agreement was not achieved when comparing against 3D simulations. Integrating the entraining parcel model using the horizontal mean environment profile of the RCE simulation (and so the vertical profile as would be predicted by a climate model) it was not possible to achieve the variation in cloud-top height seen in the RCE simulation, even when greatly increasing the entrainment rate. However, if the near-environment of a convective cloud was used as the environmental profile the variation in cloud-top height was achieved (by varying the cloud-base state variables within values extracted from RCE simulation). This indicates that the near-cloud environment is significantly different that the horizontal mean environment and must be taken into account if the effect of entrainment is to be correctly captured in parameterisations for convection. Finally, size-distribution of convective clouds extracted from RCE simulation showed qualitative agreement with predictions of CCFM's spectrum model.
Regional Scaling of Airborne Eddy Covariance Flux Observation
Sachs, T.; Serafimovich, A.; Metzger, S.; Kohnert, K.; Hartmann, J.
2014-12-01
The earth's surface is tightly coupled to the global climate system by the vertical exchange of energy and matter. Thus, to better understand and potentially predict changes to our climate system, it is critical to quantify the surface-atmosphere exchange of heat, water vapor, and greenhouse gases on climate-relevant spatial and temporal scales. Currently, most flux observations consist of ground-based, continuous but local measurements. These provide a good basis for temporal integration, but may not be representative of the larger regional context. This is particularly true for the Arctic, where site selection is additionally bound by logistical constraints, among others. Airborne measurements can overcome this limitation by covering distances of hundreds of kilometers over time periods of a few hours. The Airborne Measurements of Methane Fluxes (AIRMETH) campaigns are designed to quantitatively and spatially explicitly address this issue: The research aircraft POLAR 5 is used to acquire thousands of kilometers of eddy-covariance flux data. During the AIRMETH-2012 and AIRMETH-2013 campaigns we measured the turbulent exchange of energy, methane, and (in 2013) carbon dioxide over the North Slope of Alaska, USA, and the Mackenzie Delta, Canada. Here, we present the potential of environmental response functions (ERFs) for quantitatively linking flux observations to meteorological and biophysical drivers in the flux footprints. We use wavelet transforms of the original high-frequency data to improve spatial discretization of the flux observations. This also enables the quantification of continuous and biophysically relevant land cover properties in the flux footprint of each observation. A machine learning technique is then employed to extract and quantify the functional relationships between flux observations and the meteorological and biophysical drivers. The resulting ERFs are used to extrapolate fluxes over spatio-temporally explicit grids of the study area. The
DU Yunyan; YI Jiawei; WU Di; HE Zhigang; WANG Dongxiao; LIANG Fuyuan
2014-01-01
Automated identification and tracking of mesoscale ocean eddies has recently become one research hotspot in physical oceanography. Several methods have been developed and applied to survey the general kinetic and geometric characteristics of the ocean eddies in the South China Sea (SCS). However, very few studies attempt to examine eddies’ internal evolution processes. In this study, we reported a hybrid method to trace eddies’ propagation in the SCS based on their internal structures, which are characterized by eddy centers, footprint borders, and composite borders. Eddy identification and tracking results were represented by a GIS-based spatiotemporal model. Information on instant states, dynamic evolution processes, and events of disappearance, reappearance, split, and mergence is stored in a GIS database. Results were validated by comparing against the ten Dongsha Cyclonic Eddies (DCEs) and the three long-lived anticyclonic eddies (ACEs) in the northern SCS, which were reported in previous literature. Our study confirmed the develop-ment of these eddies. Furthermore, we found more DCE-like and ACE-like eddies in these areas from 2005 to 2012 in our database. Spatial distribution analysis of disappearing, reappearing, splitting, and merging activities shows that eddies in the SCS tend to cluster to the northwest of Luzon Island, southwest of Luzon Strait, and around the marginal sea of Vietnam. Kuroshio intrusions and the complex sea floor topography in these areas are the possible factors that lead to these spatial clusters.
Zhai, X.; Johnson, H. L.; Marshall, D. P.; Saenko, O. A.
2012-04-01
Ocean eddies generated through instability of the mean flow play a vital role in balancing the energy budget of the global ocean. In equilibrium, the sources and sinks of eddy energy have to be balanced. However, where and how eddy energy is removed remains a large source of uncertainty. Ocean eddies are observed to propagate westward at speeds similar to the phase speeds of classical Rossby waves, but what happens to the eddies when they encounter the western boundary is unclear. Using a simple reduced-gravity model and satellite altimetry data, we show that the western boundary acts as a ``graveyard'' for the westward-propagating ocean eddies. We estimate a convergence of eddy energy near the western boundary of approximately 0.1~0.3 terawatts, poleward of 10 degree of latitude. This energy is most likely scattered into high-wavenumber vertical modes, resulting in energy dissipation and diapycnal mixing. A set of sensitivity experiments are conducted using an ocean general circulation model to investigate the effect of this eddy energy sink on ocean stratification and large-scale circulation, through the impact of energy dissipation on diapycnal mixing. It is found that with the addition of the eddy energy sink, the deep ocean thermal structure becomes closer to that observed, and the overturning circulation and stratification in the abyss become stronger. The Drake Passage transport also increases and becomes closer to its observational estimates.
Kuo, Yi-Chun; Chern, Ching-Sheng; Zheng, Zhe-Wen
2017-02-01
The Luzon Strait (LS) connects the northwestern Pacific Ocean and the South China Sea (SCS) and is the western boundary gap for the Kuroshio current (KC). Satellite observations indicate that a cyclonic mesoscale eddy can trigger westward extension of the KC into the SCS and shed a smaller anticyclonic eddy to the west of the LS. We used a nonlinear reduced-gravity (primitive equation) model to study this phenomenon and analyzed the dynamic process. The location of the collision between the eddy and the KC could be critical for varying the circulation in the LS. The eddy's deformation rate, associated with its decaying speed, is also closely related to the location of the eddy during collision. When a cyclonic eddy moved from a region to the east of the Luzon Island toward the LS, the KC intruded into the SCS with growing negative vorticity during the collision of the eddy and KC. This tendency for negative vorticity is attributed to the beta effect and squeezing of the planetary vorticity caused by the flow divergence. As the eddy dissipated, the KC in the LS recovered its original pattern. When the collision of the eddy occurred at the center of the LS, the momentum balance of the KC loop was dominated by the inertial term, and the circulation in the LS remained in a leaping state.
Coria-Monter, Erik; Monreal-Gómez, María. Adela; Salas-de-León, David Alberto; Aldeco-Ramírez, Javier; Merino-Ibarra, Martín.
2014-09-01
The differential distribution of diatoms and dinoflagellates in the Bay of La Paz, Gulf of California, Mexico, was analyzed in summer of 2009, when a cyclonic eddy confined in the bay dominated the circulation. An uplift of the nutricline in the eddy drove high concentrations of nutrients to the euphotic layer. A differential phytoplankton distribution was observed to be associated with the eddy: there was an abundance of dinoflagellates close to the center of the cyclonic eddy, whereas diatoms were more abundant at the periphery. A significant inverse correlation (R = -0.62, p < 0.002) was found between the temperature at 25 m depth and the dinoflagellates abundance. Based on the temporal evolution of chlorophyll measured by MODIS satellite images, and a conceptual model proposed for the lifecycle of eddies, the cyclonic eddy may have been an old decaying structure. The effect of the cyclonic eddy on the phytoplankton distribution in this small semienclosed region was apparently similar to that found in larger eddies in the open ocean, but this is the first time such a differential distribution has been found associated to a confined eddy.
Baurle, R. A.
2015-01-01
Steady-state and scale-resolving simulations have been performed for flow in and around a model scramjet combustor flameholder. The cases simulated corresponded to those used to examine this flowfield experimentally using particle image velocimetry. A variety of turbulence models were used for the steady-state Reynolds-averaged simulations which included both linear and non-linear eddy viscosity models. The scale-resolving simulations used a hybrid Reynolds-averaged / large eddy simulation strategy that is designed to be a large eddy simulation everywhere except in the inner portion (log layer and below) of the boundary layer. Hence, this formulation can be regarded as a wall-modeled large eddy simulation. This effort was undertaken to formally assess the performance of the hybrid Reynolds-averaged / large eddy simulation modeling approach in a flowfield of interest to the scramjet research community. The numerical errors were quantified for both the steady-state and scale-resolving simulations prior to making any claims of predictive accuracy relative to the measurements. The steady-state Reynolds-averaged results showed a high degree of variability when comparing the predictions obtained from each turbulence model, with the non-linear eddy viscosity model (an explicit algebraic stress model) providing the most accurate prediction of the measured values. The hybrid Reynolds-averaged/large eddy simulation results were carefully scrutinized to ensure that even the coarsest grid had an acceptable level of resolution for large eddy simulation, and that the time-averaged statistics were acceptably accurate. The autocorrelation and its Fourier transform were the primary tools used for this assessment. The statistics extracted from the hybrid simulation strategy proved to be more accurate than the Reynolds-averaged results obtained using the linear eddy viscosity models. However, there was no predictive improvement noted over the results obtained from the explicit
An experimental study on the formation and survival of stratified subsurface eddies
Bormans, Myriam
1992-12-01
We report the results of laboratory experiments on the formation and survival of internally stratified subsurface eddies in a rotating fluid. The eddies were created by injecting a dense turbulent plume at the surface of a linearly stratified environment. The relative vorticity of the lenses was always negative but larger than that of homogeneous lenses created by laminar injection. During the first 100 revolutions, the eddies shed fluid in two symmetric arms. The shedding which is believed to result from shear instabilities always resulted in a stationary axisymmetric eddy. After the eddy had spun down, the remnant fluid persisted for thousands of rotations as a circular feature with internal stratification identical to that of the environment. We created eddies with and without double diffusive convective instabilities and compared the volume of dyed fluid and the evolution of their aspect ratios. Sugar and salt were used as laboratory analogues of salt and heat, respectively. The Burger number of the lenses decreased rapidly within the first 200 revolutions and then much more slowly to reach a value between 0.2 and 0.4, These latter values are larger than those predicted by Gill (1981) for a homogeneous lens due to the internal stratification of the lenses. Radial spreading of the lens due to double diffusive intrusions was found to be larger, but of the same order of magnitude, as that induced by the vertical exchange of momentum in the absence of double diffusive convection. We formed eddies internally stratified in the diffusive sense (stable sugar gradient and unstable salt gradient) or doubly stable (stable sugar and salt gradients) by changing the ratio of the volume flux at the source to the volume flux at the spreading level as described by Bormans and Turner (1990). When the stratification in the eddies was doubly stable, three distinctive regions were observed: a region of convective layers and diffusive density interfaces at the top, a central region
Hunt, Julian C. R.; Moustaoui, Mohamed; Mahalov, Alex
2015-09-01
High resolution three-dimensional simulations are presented of the interactions between turbulent shear flows moving with mean relative velocity ΔU below a stably stratified region with buoyancy frequency (N+). An artificial forcing in the simulation, with a similar effect as a small negative eddy viscosity, leads to a steady state flow which models thin interfaces. Characteristic eddies of the turbulence have length scale L. If the bulk Richardson number Rib=(LN+/ΔU)2 lies between lower and upper critical values denoted as Ri∗(temperature. Comparisons are made with shear turbulent interfaces with no stratification. When Rib>R~i, vertical propagating waves are generated, with shear stresses carrying significant momentum flux and progressively less as Rib increases. Simulations for a jet and a turbulent mixing layer show similar results. A perturbation analysis, using inhomogeneous Rapid Distortion Theory, models the transition zone between shear eddies below the interface and the fluctuations in the stratified region, consistent with the simulations. It demonstrates how the wave-momentum-flux has a maximum when Rib˜2 and then decreases as Rib increases. This coupling mechanism between eddies and waves, which is neglected in eddy viscosity models for shear layers, can drive flows in the stratosphere and the deeper ocean, with significant consequences for short- and long-term flow phenomena. The "detached layer" is a mechanism that contributes to the formation of stratus clouds and polluted layers above the atmospheric boundary layer.
New subgrid-scale models for large-eddy simulation of Rayleigh-Bénard convection
Dabbagh, F.; Trias, F. X.; Gorobets, A.; Oliva, A.
2016-09-01
At the crossroad between flow topology analysis and the theory of turbulence, a new eddy-viscosity model for Large-eddy simulation has been recently proposed by Trias et al.[PoF, 27, 065103 (2015)]. The S3PQR-model has the proper cubic near-wall behaviour and no intrinsic limitations for statistically inhomogeneous flows. In this work, the new model has been tested for an air turbulent Rayleigh-Benard convection in a rectangular cell of aspect ratio unity and n span-wise open-ended distance. To do so, direct numerical simulation has been carried out at two Rayleigh numbers Ra = 108 and 1010, to assess the model performance and investigate a priori the effect of the turbulent Prandtl number. Using an approximate formula based on the Taylor series expansion, the turbulent Prandtl number has been calculated and revealed a constant and Ra-independent value across the bulk region equals to 0.55. It is found that the turbulent components of eddy-viscosity and eddy-diffusivity are positively prevalent to maintain a turbulent wind essentially driven by the mean buoyant force at the sidewalls. On the other hand, the new eddy-viscosity model is preliminary tested for the case of Ra = 108 and showed overestimation of heat flux within the boundary layer but fairly good prediction of turbulent kinetics at this moderate turbulent flow.
An alternative eddy-viscosity representation and its implication to turbulence modeling
Jakirlic, Suad; Jovanovic, Jovan; Basara, Branislav
2013-11-01
Large majority of turbulence models in the RANS framework (it holds also in the case of the LES method) is based on the eddy-viscosity rationale. The principle task of modeling the Reynolds stress tensor reduces to modeling the eddy-viscosity, representing, according to Boussinesq (1877), the ``coefficient of proportionality'' between the Reynolds stress and mean rate of strain tensors. In the present contribution an extended formulation based on the least square approach applied to the Boussinesq's correlation is presented. Furthermore, a Taylor-microscale-based formulation is derived originating from the equilibrium assumption related to the equality between the production and dissipation rates of kinetic energy of turbulence. Finally, an expression is proposed reflecting the Reynolds stress anisotropy influence on the eddy-viscosity damping by approaching the solid wall as well as including an appropriate length-scale switch accounting for the viscosity effects through inclusion of the Kolmogorov scales blended with those of the energy-containing eddies. The latter formulation is successfully applied in the framework of an instability-sensitive Reynolds stress model of turbulence. The afore-mentioned eddy-viscosity definitions are comparatively assessed in a series of wall-bounded flow configurations (including separation) in a Reynolds number range.
McGloin, Ryan; McGowan, Hamish; McJannet, David; Cook, Freeman; Sogachev, Andrey; Burn, Stewart
2014-01-01
Accurate quantification of evaporation from small water storages is essential for water management and planning, particularly in water-scarce regions. In order to ascertain suitable methods for direct measurement of evaporation from small water bodies, this study presents a comparison of eddy covariance and scintillometry measurements from a reservoir in southeast Queensland, Australia. The work presented expands on a short study presented by McJannet et al. (2011) to include comparisons of eddy covariance measurements and scintillometer-derived predictions of surface energy fluxes under a wide range of seasonal weather conditions. In this study, analysis was undertaken to ascertain whether important theoretical assumptions required for both techniques are valid in the complex environment of a small reservoir. Statistical comparison, energy balance closure, and the relationship between evaporation measurements and key environmental controls were used to compare the results of the two techniques. Reasonable agreement was shown between the sensible heat flux measurements from eddy covariance and scintillometry, while scintillometer-derived estimates of latent heat flux were approximately 21% greater than eddy covariance measurements. We suggest possible reasons for this difference and provide recommendations for further research for improving measurements of surface energy fluxes over small water bodies using eddy covariance and scintillometry.
Zevenhoven, Koos C. J.; Busch, Sarah; Hatridge, Michael; Öisjöen, Fredrik; Ilmoniemi, Risto J.; Clarke, John
2014-03-01
Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field—applied before each signal acquisition sequence to increase the signal—induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6 ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures.
Akuetevi, C. Q. C.; Barnier, B.; Verron, J.; Molines, J.-M.; Lecointre, A.
2016-02-01
Three hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Donohue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations.
Zevenhoven, Koos C J; Busch, Sarah; Hatridge, Michael; Oisjöen, Fredrik; Ilmoniemi, Risto J; Clarke, John
2014-03-14
Eddy currents induced by applied magnetic-field pulses have been a common issue in ultra-low-field magnetic resonance imaging. In particular, a relatively large prepolarizing field-applied before each signal acquisition sequence to increase the signal-induces currents in the walls of the surrounding conductive shielded room. The magnetic-field transient generated by the eddy currents may cause severe image distortions and signal loss, especially with the large prepolarizing coils designed for in vivo imaging. We derive a theory of eddy currents in thin conducting structures and enclosures to provide intuitive understanding and efficient computations. We present detailed measurements of the eddy-current patterns and their time evolution in a previous-generation shielded room. The analysis led to the design and construction of a new shielded room with symmetrically placed 1.6-mm-thick aluminum sheets that were weakly coupled electrically. The currents flowing around the entire room were heavily damped, resulting in a decay time constant of about 6 ms for both the measured and computed field transients. The measured eddy-current vector maps were in excellent agreement with predictions based on the theory, suggesting that both the experimental methods and the theory were successful and could be applied to a wide variety of thin conducting structures.
Spatial variation of eddy-diffusion coefficients in the turbulent plasma sheet during substorms
M. Stepanova
2009-04-01
Full Text Available Study of the plasma turbulence in the central plasma sheet was performed using the Interball-Tail satellite data. Fluctuations of the plasma bulk velocity in the plasma sheet were deduced from the measurements taken by the Corall instrument for different levels of geomagnetic activity and different locations inside the plasma sheet. The events that satisfied the following criteria were selected for analysis: number density 0.1–10 cm^{−3}, ion temperature T≥0.3 keV, and average bulk velocity ≤100 km/s. It was found that the plasma sheet flow generally appears to be strongly turbulent, i.e. is dominated by fluctuations that are unpredictable. Corresponding eddy-diffusion coefficients in Y- and Z-direction in the GSM coordinate system were derived using the autocorrelation time and rms velocity. Statistical studies of variation of the eddy-diffusion coefficients with the location inside the plasma sheet showed a significant increase in these coefficients in the tailward direction. During substorms this dependence shows strong increase of eddy-diffusion in the central part of the plasma sheet at the distances of 10–30 Earth's radii. This effect is much stronger for Y-components of the eddy-diffusion coefficient, which could be related to the geometry of the plasma sheet, allowing more room for development of eddies in this direction.
Short-term fluctuations in the eddy heat flux and baroclinic stability of the atmosphere
Stone, P. H.; Ghan, S. J.; Spiegel, D.; Rambaldi, S.
1982-01-01
National Meteorological Center data from midlatitudes for three Januaries is used in calculating time series of the zonal mean meridional eddy heat flux and the zonal mean baroclinic stability, as measured by the difference between the zonal wind shear and the critical value of the shear in two-level models. Time-lagged correlations between the two series reveal a highly significant negative correlation for short time lags, peaking at approximately -0.4 when the stability parameter lags one half day behind the eddy flux. They also reveal that strongly unstable conditions are not followed by significant increases in the eddy flux. These results are seen as indicating that the synoptic variations of the zonal mean eddy flux are not closely related to the degree of baroclinic instability of the zonal mean flow. The autocorrelation of the eddy flux is then compared with those expected for autoregressive processes. A Bayesian information criterion suggests that the behavior is represented best by a damped oscillation, with a damping time of 0.8 day and a period of five days.
Rail temperature rise characteristics caused by linear eddy current brake of high-speed train
Xiaoshan Lu
2014-12-01
Full Text Available The rail temperature rises when the linear eddy current brake of high-speed train is working, which may lead to a change of rail physical characteristics or an effect on train operations. Therefore, a study concerning the characteristics of rail temperature rise caused by eddy current has its practical necessity. In the research, the working principle of a linear eddy current brake is introduced and its FEA model is established. According to the generation mechanism of eddy current, the theoretical formula of the internal energy which is produced by the eddy current is deduced and the thermal load on the rail is obtained. ANSYS is used to simulate the rail temperature changes under different conditions of thermal loads. The research result shows the main factors which contribute to the rising of rail temperature are the train speed, brake gap and exciting current. The rail temperature rises non-linearly with the increase of train speed. The rail temperature rise curve is more sensitive to the exciting current than the air gap. Moreover, the difference stimulated by temperature rising between rails of 60 kg/m and 75 kg/m is presented as well.
Characteristic Analysis and Control of a Hybrid Excitation Linear Eddy Current Brake
Baoquan Kou
2015-07-01
Full Text Available In this paper, a novel hybrid excitation linear eddy current brake is presented as a braking system for high-speed road and rail vehicles. The presence of the permanent magnets (PMs, whose flux lines in the primary core are oppositely directed with respect to the flux lines by the excitation windings, has the effect of mitigating the saturation of the iron in the teeth of the primary core. This allows the brake to be fed with more intense currents, improving the braking force. First, using the magnetic equivalent circuit method and the layer theory approach, the analytical model of the hybrid excitation linear eddy current brake was developed, which can account for the saturation effects occurring in the iron parts. The saturation effects make the design and control of eddy current brakes more difficult. Second, the relationship between the braking force characteristics and the design parameters were analyzed to provide useful information to the designers of eddy current brakes. Then, the controller of the hybrid excitation linear eddy current brake was designed to control the amplitude of the braking force. Finally, experimental measurements were conducted to verify the validity of the theoretical analysis.
A clustering analysis of eddies' spatial distribution in the South China Sea
J. Yi
2012-11-01
Full Text Available Spatial variation is important for studying the mesoscale eddies in the South China Sea (SCS. To investigate such spatial variations, this study made a clustering analysis on eddies' distribution using the K-means approach. Results showed that clustering tendency of anticyclonic eddies (AEs and cyclonic eddies (CEs were weak but not random, and the number of clusters were proved greater than four. Finer clustering results showed 10 regions where AEs densely populated and 6 regions for CEs in the SCS. Previous studies confirmed these partitions and possible generation mechanisms were related. Comparisons between AEs and CEs revealed that patterns of AE are relatively more aggregated than those of CE, and specific distinctions were summarized: (1 to the southwest of Luzon Island, AEs and CEs are generated spatially apart; AEs are likely located north of 14° N and closer to shore, while CEs are to the south and further offshore; (2 the Central SCS and Nansha Trough are mostly dominated by AEs; (3 along 112° E, clusters of AEs and CEs are located sequentially apart, and the pair off Vietnam represents the dipole eddies; (4 to the southwest of Dongsha Islands, AEs are concentrated to the east of CEs. Overlaps of AEs and CEs in the northeastern and Southern SCS were further examined considering seasonal variations. The northeastern overlap represented near-concentric distributions while the southern one was a mixed effect of seasonal variations, complex circulations and topography influences.
Rifai, Damhuji; Abdalla, Ahmed N.; Razali, Ramdan; Ali, Kharudin; Faraj, Moneer A.
2017-01-01
The use of the eddy current technique (ECT) for the non-destructive testing of conducting materials has become increasingly important in the past few years. The use of the non-destructive ECT plays a key role in the ensuring the safety and integrity of the large industrial structures such as oil and gas pipelines. This paper introduce a novel ECT probe design integrated with the distributed ECT inspection system (DSECT) use for crack inspection on inner ferromagnetic pipes. The system consists of an array of giant magneto-resistive (GMR) sensors, a pneumatic system, a rotating magnetic field excitation source and a host PC acting as the data analysis center. Probe design parameters, namely probe diameter, an excitation coil and the number of GMR sensors in the array sensor is optimized using numerical optimization based on the desirability approach. The main benefits of DSECT can be seen in terms of its modularity and flexibility for the use of different types of magnetic transducers/sensors, and signals of a different nature with either digital or analog outputs, making it suited for the ECT probe design using an array of GMR magnetic sensors. A real-time application of the DSECT distributed system for ECT inspection can be exploited for the inspection of 70 mm carbon steel pipe. In order to predict the axial and circumference defect detection, a mathematical model is developed based on the technique known as response surface methodology (RSM). The inspection results of a carbon steel pipe sample with artificial defects indicate that the system design is highly efficient. PMID:28335399