Rotor wake characteristics of a transonic axial flow fan

NASA Technical Reports Server (NTRS)

Hathaway, M. D.; Gertz, J.; Epstein, A.; Strazisar, A. J.

1985-01-01

State of the art turbomachinery flow analysis codes are not capable of predicting the viscous flow features within turbomachinery blade wakes. Until efficient 3D viscous flow analysis codes become a reality there is therefore a need for models which can describe the generation and transport of blade wakes and the mixing process within the wake. To address the need for experimental data to support the development of such models, high response pressure measurements and laser anemometer velocity measurements were obtained in the wake of a transonic axial flow fan rotor.

Hawaiian Island Archipelago

NASA Image and Video Library

1988-10-03

STS026-43-082 (29 Sept. - 3 Oct. 1988) --- This 70mm northerly oriented frame over the Pacific Ocean features the Hawaiian Islands chain. The islands perturb the prevailing northeasterly winds producing extensive cloud wakes in the lee of the islands. Photo experts feel that atmospheric haze in the Hawaii wake is probably a result of the continuing eruptions of Kilauea volcano on the southeast coast. From the lower right corner in a diagonal directed upward to the north are the islands of Nihau, Kauai, Oahu, Molokai, Lanai, Maui, Kahoolawe, and Hawaii. This photo was shown during the post-flight press conference on October 11, 1988 by the STS-26 astronauts, who at one time during the flight wore Hawaiian attire to pay tribute to the working staff of the Hawaii tracking station.

32 CFR 935.139 - Motor vehicle operator qualifications.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Motor vehicle operator qualifications. 935.139... AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.139 Motor vehicle operator qualifications. (a) No person may operate a privately owned motor vehicle on Wake Island unless he has an island...

32 CFR 935.139 - Motor vehicle operator qualifications.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Motor vehicle operator qualifications. 935.139... AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.139 Motor vehicle operator qualifications. (a) No person may operate a privately owned motor vehicle on Wake Island unless he has an island...

Eastern Caribbean Circulation and Island Mass Effect on St. Croix, US Virgin Islands: A Mechanism for Relatively Consistent Recruitment Patterns

PubMed Central

Chérubin, Laurent Marcel; Garavelli, Lysel

2016-01-01

The northeastern Caribbean Sea is under the seasonal influence of the Trade Winds but also of the Orinoco/Amazon freshwater plume. The latter is responsible for intensification of the Caribbean Current in general and of its eddy activity in the northern part of the Caribbean Sea. More importantly, we show in this study that the front of the freshwater plume drives a northward flow that impinges directly on the island of St. Croix in the United States Virgin Islands. The angle of incidence of the incoming flow controls the nature of the wake on both sides and ends of the island, which changes from cyclonic to anticylonic wake flow, with either attached or shed eddies. Using an off-line bio-physical model, we simulated the dispersal and recruitment of an abundant Caribbean coral reef fish, the bluehead wrasse (Thalassoma bifasciatum) in the context of the wake flow variability around St. Croix. Our results revealed the role played by the consistent seasonal forcing of the wake flow on the recruitment patterns around the island at the interannual scale. The interannual variability of the timing of arrival and northward penetration of the plume instead controls the nature of the wake, hence the regional spatial recruitment patterns. PMID:26942575

Eastern Caribbean Circulation and Island Mass Effect on St. Croix, US Virgin Islands: A Mechanism for Relatively Consistent Recruitment Patterns.

PubMed

Chérubin, Laurent Marcel; Garavelli, Lysel

2016-01-01

The northeastern Caribbean Sea is under the seasonal influence of the Trade Winds but also of the Orinoco/Amazon freshwater plume. The latter is responsible for intensification of the Caribbean Current in general and of its eddy activity in the northern part of the Caribbean Sea. More importantly, we show in this study that the front of the freshwater plume drives a northward flow that impinges directly on the island of St. Croix in the United States Virgin Islands. The angle of incidence of the incoming flow controls the nature of the wake on both sides and ends of the island, which changes from cyclonic to anticylonic wake flow, with either attached or shed eddies. Using an off-line bio-physical model, we simulated the dispersal and recruitment of an abundant Caribbean coral reef fish, the bluehead wrasse (Thalassoma bifasciatum) in the context of the wake flow variability around St. Croix. Our results revealed the role played by the consistent seasonal forcing of the wake flow on the recruitment patterns around the island at the interannual scale. The interannual variability of the timing of arrival and northward penetration of the plume instead controls the nature of the wake, hence the regional spatial recruitment patterns.

Retinogeniculate transmission in wakefulness.

PubMed

Weyand, Theodore G

2007-08-01

Despite popular belief that the primary function of the thalamus is to "gate" sensory inputs by state, few studies have attempted to directly characterize the efficacy of such gating in the awake, behaving animal. I measured the efficacy of retinogeniculate transmission in the awake cat by taking advantage of the fact that many neurons in the lateral geniculate nucleus (LGN) are dominated by a single retinal input, and that this input produces a distinct event known as the S-potential. Retinal input failed to produce an LGN action potential half of the time. However, success or failure was powerfully tied to the recency of the S-potential. Short intervals tend to be successful and long intervals unsuccessful. For four of 12 neurons, the probability that a given S-potential could cause a spike exceeded 90% if that S-potential was preceded by an S-potential within the previous 10 ms (100 Hz). Whereas this temporal influence on efficacy has been demonstrated extensively in anesthetized animals, wakefulness is different in several ways. Overall efficacy is better in wakefulness than in anesthesia, the durations of facilitating effects are briefer in wakefulness, efficacy of long intervals is superior in wakefulness, and the temporal dependence can be briefly disrupted by altering background illumination. The last two observations may be particularly significant. Increased success at long intervals in wakefulness provides additional evidence that the spike code of the anesthetized animal is not the spike code of the awake animal. Altering retinogeniculate efficacy by altering visual conditions undermines the influence inter-S-potential interval might have in determining efficacy in the real world. Finally, S-potential amplitude, duration, and even slope are dynamic and systematic within wakefulness; providing further support that the S-potential is the extracellular signature of the retinal EPSP.

Far-Field Simulation of the Hawaiian Wake: Sea Surface Temperature and Orographic Effects(.

NASA Astrophysics Data System (ADS)

Hafner, Jan; Xie, Shang-Ping

2003-12-01

Recent satellite observations reveal far-reaching effects of the Hawaiian Islands on surface wind, cloud, ocean current, and sea surface temperature (SST) that extend leeward over an unusually long distance (>1000 km). A three-dimensional regional atmospheric model with full physics is used to investigate the cause of this long wake. While previous wind wake studies tend to focus on regions near the islands, the emphasis here is the far-field effects of SST and orography well away from the Hawaiian Islands. In response to an island-induced SST pattern, the model produces surface wind and cloud anomaly patterns that resemble those observed by satellites. In particular, anomalous surface winds are found to converge onto a zonal band of warmer water, with cloud liquid water content enhanced over it but reduced on the northern and southern sides. In the vertical, a two-cell meridional circulation develops of a baroclinic structure with the rising motion and thicker clouds over the warm water band. The model response in the wind and cloud fields supports the hypothesis that ocean atmosphere interaction is crucial for sustaining the island effects over a few thousand kilometers.Near Hawaii, mountains generate separate wind wakes in the model lee of individual islands as observed by satellites. Under orographic forcing, the model simulates the windward cloud line and the southwest-tilted cloud band leeward of the Big Island. In the far field, orographically induced wind perturbations are found to be in geostrophic balance with pressure anomalies, indicative of quasigeostrophic Rossby wave propagation. A shallow-water model is developed for disturbances trapped in the inversion-capped planetary boundary layer. The westward propagation of Rossby waves is found to increase the wake length significantly, consistent with the three-dimensional simulation.

Modeling the Wake of the Marquesas Archipelago

NASA Astrophysics Data System (ADS)

Raapoto, H.; Martinez, E.; Petrenko, A.; Doglioli, A. M.; Maes, C.

2018-02-01

In this study, a high-resolution (˜2.5 km) numerical model was set up to investigate the fine-scale activity within the region of the Marquesas archipelago. This has never been performed before. The robustness of the model results is assessed by comparison with remote sensing and in situ observations. Our results highlight regions of warm waters leeward of the different islands with high eddy kinetic energy (EKE) on their sides. The analysis of energy conversion terms reveals contributions to EKE variability by wind, baroclinic, and barotropic instabilities. The use of a geometry-based eddy detection algorithm reveals the generation of cyclonic and anticyclonic eddies in the wake of the largest islands, with both an inshore and offshore effect. Maximum eddy activity occurs in austral winter following the seasonality of both wind stress and EKE intensity. Most eddies have a radius between 20 and 30 km and are generally cyclonic rather than anticyclonic. Significant vertical velocities are observed in the proximity of the islands, associated with topographically induced flow separation. Eddy trapping inshore waters are advected offshore in the wake of the islands. The overall influence of these fine-scale dynamics could explain the strong biological enhancement of the archipelago.

Modelling the Wake of the Marquesas Archipelago

NASA Astrophysics Data System (ADS)

Raapoto, H.; Martinez, E. C.; Petrenko, A. A.; Doglioli, A. M.; Maes, C.

2017-12-01

In this study, a high-resolution ( 2.5 km) numerical model was set up to investigate the fine-scale activity within the region of the Marquesas archipelago where a strong biological enhancement occurs. This has never been performed before. The robustness of the model results is assessed by comparison with remote sensing and in situ observations. Our results highlight regions of warm waters leeward of the different islands with high eddy kinetic energy (EKE) on their sides. The analysis of energy conversion terms reveals contributions to EKE variability by wind, baroclinic and barotropic instabilities. The use of a geometry-based eddy detection algorithm reveals eddy generation in the wake of the largest islands, with both an inshore and offshore effect. Maximum eddy activity occurs in austral winter following the seasonality of both wind stress and EKE intensity. Most eddies have a radius between 20 and 30 km and are generally cyclonic rather than anticyclonic. Significant vertical velocities are observed in the proximity of the islands, associated with topography induced flow separation. Eddy trapping inshore waters are advected offshore in the wake of the islands. The overall influence of these fine-scale dynamics could explain the strong biological enhancement of the archipelago.

32 CFR 935.2 - Purpose.

Code of Federal Regulations, 2010 CFR

2010-07-01

... CODE General § 935.2 Purpose. The purpose of this part is to provide— (a) For the civil administration of Wake Island; (b) Civil laws for Wake Island not otherwise provided for; (c) Criminal laws for Wake...

32 CFR 935.2 - Purpose.

Code of Federal Regulations, 2013 CFR

2013-07-01

... CODE General § 935.2 Purpose. The purpose of this part is to provide— (a) For the civil administration of Wake Island; (b) Civil laws for Wake Island not otherwise provided for; (c) Criminal laws for Wake...

32 CFR 935.2 - Purpose.

Code of Federal Regulations, 2012 CFR

2012-07-01

... CODE General § 935.2 Purpose. The purpose of this part is to provide— (a) For the civil administration of Wake Island; (b) Civil laws for Wake Island not otherwise provided for; (c) Criminal laws for Wake...

32 CFR 935.2 - Purpose.

Code of Federal Regulations, 2011 CFR

2011-07-01

... CODE General § 935.2 Purpose. The purpose of this part is to provide— (a) For the civil administration of Wake Island; (b) Civil laws for Wake Island not otherwise provided for; (c) Criminal laws for Wake...

32 CFR 935.2 - Purpose.

Code of Federal Regulations, 2014 CFR

2014-07-01

... CODE General § 935.2 Purpose. The purpose of this part is to provide— (a) For the civil administration of Wake Island; (b) Civil laws for Wake Island not otherwise provided for; (c) Criminal laws for Wake...

A comprehensive comparison of turbulence models in the far wake

NASA Technical Reports Server (NTRS)

Cimbala, John M.

1993-01-01

In the present study, the far wake was examined numerically using an implicit, upwind, finite-volume, compressible Navier-Stokes code. The numerical grid started at 500 equivalent circular cylinder diameters in the wave, and extended to 4000 equivalent diameters. By concentrating only on the far wake, the numerical difficulties and fine mesh requirements near the wake-generating body were eliminated. At the time of this writing, results for the K-epsilon and K-omega turbulence models at low Mach number have been completed and show excellent agreement with previous incompressible results and far-wake similarity solutions. The code is presently being used to compare the performance of various other turbulence models, including Reynolds stress models and the new anisotropic two-equation turbulence models being developed at NASA Langley. By increasing our physical understanding of the deficiencies and limits of these models, it is hoped that improvements to the universality of the models can be made. Future plans include examination of two-dimensional momentumless wakes as well.

Submesoscale tidal eddies in the wake of coral islands and reefs: satellite data and numerical modelling

NASA Astrophysics Data System (ADS)

Delandmeter, Philippe; Lambrechts, Jonathan; Marmorino, George O.; Legat, Vincent; Wolanski, Eric; Remacle, Jean-François; Chen, Wei; Deleersnijder, Eric

2017-07-01

Interaction of tidal flow with a complex topography and bathymetry including headlands, islands, coral reefs and shoals create a rich submesoscale field of tidal jets, vortices, unsteady wakes, lee eddies and free shear layers, all of which impact marine ecology. A unique and detailed view of the submesoscale variability in a part of the Great Barrier Reef lagoon, Australia, that includes a number of small islands was obtained by using a "stereo" pair of 2-m-resolution visible-band images that were acquired just 54 s apart by the WorldView-3 satellite. Near-surface current and vorticity were extracted at a 50-m-resolution from those data using a cross-correlation technique and an optical-flow method, each yielding a similar result. The satellite-derived data are used to test the ability of the second-generation Louvain-la-Neuve ice-ocean model (SLIM), an unstructured-mesh, finite element model for geophysical and environmental flows, to reproduce the details of the currents in the region. The model succeeds in simulating the large-scale (> 1 km) current patterns, such as the main current and the width and magnitude of the jets developing in the gaps between the islands. Moreover, the order of magnitude of the vorticity and the occurrence of some vortices downstream of the islands are correctly reproduced. The smaller scales (< 500 m) are resolved by the model, although various discrepancies with the data are observed. The smallest scales (< 50 m) are unresolved by both the model- and image-derived velocity fields. This study shows that high-resolution models are able to a significant degree to simulate accurately the currents close to a rugged coast. Very-high-resolution satellite oceanography stereo images offer a new way to obtain snapshots of currents near a complex topography that has reefs, islands and shoals, and is a potential resource that could be more widely used to assess the predictive ability of coastal circulation models.

33 CFR 80.1495 - U.S. Pacific Island Possessions.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Island Possessions of American Samoa, Baker, Howland, Jarvis, Johnson, Palmyra, Swains and Wake Islands... 33 Navigation and Navigable Waters 1 2014-07-01 2014-07-01 false U.S. Pacific Island Possessions... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1495 U.S. Pacific Island...

33 CFR 80.1495 - U.S. Pacific Island Possessions.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Island Possessions of American Samoa, Baker, Howland, Jarvis, Johnson, Palmyra, Swains and Wake Islands... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false U.S. Pacific Island Possessions... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1495 U.S. Pacific Island...

33 CFR 80.1495 - U.S. Pacific Island Possessions.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Island Possessions of American Samoa, Baker, Howland, Jarvis, Johnson, Palmyra, Swains and Wake Islands... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false U.S. Pacific Island Possessions... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1495 U.S. Pacific Island...

33 CFR 80.1495 - U.S. Pacific Island Possessions.

Code of Federal Regulations, 2011 CFR

2011-07-01

... Island Possessions of American Samoa, Baker, Howland, Jarvis, Johnson, Palmyra, Swains and Wake Islands... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false U.S. Pacific Island Possessions... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1495 U.S. Pacific Island...

33 CFR 80.1495 - U.S. Pacific Island Possessions.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Island Possessions of American Samoa, Baker, Howland, Jarvis, Johnson, Palmyra, Swains and Wake Islands... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false U.S. Pacific Island Possessions... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Pacific Islands § 80.1495 U.S. Pacific Island...

32 CFR 935.140 - Motor vehicle maintenance and equipment.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Motor vehicle maintenance and equipment. 935.140... AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.140 Motor vehicle maintenance and equipment. (a) Each person who has custody of a motor vehicle on Wake Island shall present that vehicle for...

32 CFR 935.132 - Speed limits.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Speed limits. 935.132 Section 935.132 National... WAKE ISLAND CODE Motor Vehicle Code § 935.132 Speed limits. Each person operating a motor vehicle on Wake Island shall operate it at a speed— (a) That is reasonable, safe, and proper, considering time of...

32 CFR 935.132 - Speed limits.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Speed limits. 935.132 Section 935.132 National... WAKE ISLAND CODE Motor Vehicle Code § 935.132 Speed limits. Each person operating a motor vehicle on Wake Island shall operate it at a speed— (a) That is reasonable, safe, and proper, considering time of...

Secure Wake-Up Scheme for WBANs

NASA Astrophysics Data System (ADS)

Liu, Jing-Wei; Ameen, Moshaddique Al; Kwak, Kyung-Sup

Network life time and hence device life time is one of the fundamental metrics in wireless body area networks (WBAN). To prolong it, especially those of implanted sensors, each node must conserve its energy as much as possible. While a variety of wake-up/sleep mechanisms have been proposed, the wake-up radio potentially serves as a vehicle to introduce vulnerabilities and attacks to WBAN, eventually resulting in its malfunctions. In this paper, we propose a novel secure wake-up scheme, in which a wake-up authentication code (WAC) is employed to ensure that a BAN Node (BN) is woken up by the correct BAN Network Controller (BNC) rather than unintended users or malicious attackers. The scheme is thus particularly implemented by a two-radio architecture. We show that our scheme provides higher security while consuming less energy than the existing schemes.

32 CFR 935.131 - Right-hand side of the road.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Right-hand side of the road. 935.131 Section 935... INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.131 Right-hand side of the road. Each person driving a motor vehicle on Wake Island shall drive on the right-hand side of the road, except where...

32 CFR 935.131 - Right-hand side of the road.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Right-hand side of the road. 935.131 Section 935... INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.131 Right-hand side of the road. Each person driving a motor vehicle on Wake Island shall drive on the right-hand side of the road, except where...

32 CFR 935.131 - Right-hand side of the road.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Right-hand side of the road. 935.131 Section 935... INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.131 Right-hand side of the road. Each person driving a motor vehicle on Wake Island shall drive on the right-hand side of the road, except where...

32 CFR 935.131 - Right-hand side of the road.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Right-hand side of the road. 935.131 Section 935... INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.131 Right-hand side of the road. Each person driving a motor vehicle on Wake Island shall drive on the right-hand side of the road, except where...

32 CFR 935.131 - Right-hand side of the road.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Right-hand side of the road. 935.131 Section 935... INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.131 Right-hand side of the road. Each person driving a motor vehicle on Wake Island shall drive on the right-hand side of the road, except where...

Projected atoll shoreline and run-up changes in response to sea-level rise and varying large wave conditions at Wake and Midway Atolls, Northwestern Hawaiian Islands

USGS Publications Warehouse

Shope, James B.; Storlazzi, Curt; Hoeke, Ron

2017-01-01

Atoll islands are dynamic features that respond to seasonal alterations in wave conditions and sea level. It is unclear how shoreline wave run-up and erosion patterns along these low elevation islands will respond to projected sea-level rise (SLR) and changes in wave climate over the next century, hindering communities' preparation for the future. To elucidate how these processes may respond to climate change, extreme boreal winter and summer wave conditions under future sea-level rise (SLR) and wave climate scenarios were simulated at two atolls, Wake and Midway, using a shallow-water hydrodynamic model. Nearshore wave conditions were used to compute the potential longshore sediment flux along island shorelines via the CERC empirical formula and wave-driven erosion was calculated as the divergence of the longshore drift; run-up and the locations where the run-up exceed the berm elevation were also determined. SLR is projected to predominantly drive future island morphological change and flooding. Seaward shorelines (i.e., ocean fronted shorelines directly facing incident wave energy) were projected to experience greater erosion and flooding with SLR and in hypothetical scenarios where changes to deep water wave directions were altered, as informed by previous climate change forced Pacific wave modeling efforts. These changes caused nearshore waves to become more shore-normal, increasing wave attack along previously protected shorelines. With SLR, leeward shorelines (i.e., an ocean facing shoreline but sheltered from incident wave energy) became more accretive on windward islands and marginally more erosive along leeward islands. These shorelines became more accretionary and subject to more flooding with nearshore waves becoming more shore-normal. Lagoon shorelines demonstrated the greatest SLR-driven increase in erosion and run-up. They exhibited the greatest relative change with increasing wave heights where both erosion and run-up magnitudes increased. Wider

Projected atoll shoreline and run-up changes in response to sea-level rise and varying large wave conditions at Wake and Midway Atolls, Northwestern Hawaiian Islands

NASA Astrophysics Data System (ADS)

Shope, James B.; Storlazzi, Curt D.; Hoeke, Ron K.

2017-10-01

Atoll islands are dynamic features that respond to seasonal alterations in wave conditions and sea level. It is unclear how shoreline wave run-up and erosion patterns along these low elevation islands will respond to projected sea-level rise (SLR) and changes in wave climate over the next century, hindering communities' preparation for the future. To elucidate how these processes may respond to climate change, extreme boreal winter and summer wave conditions under future sea-level rise (SLR) and wave climate scenarios were simulated at two atolls, Wake and Midway, using a shallow-water hydrodynamic model. Nearshore wave conditions were used to compute the potential longshore sediment flux along island shorelines via the CERC empirical formula and wave-driven erosion was calculated as the divergence of the longshore drift; run-up and the locations where the run-up exceed the berm elevation were also determined. SLR is projected to predominantly drive future island morphological change and flooding. Seaward shorelines (i.e., ocean fronted shorelines directly facing incident wave energy) were projected to experience greater erosion and flooding with SLR and in hypothetical scenarios where changes to deep water wave directions were altered, as informed by previous climate change forced Pacific wave modeling efforts. These changes caused nearshore waves to become more shore-normal, increasing wave attack along previously protected shorelines. With SLR, leeward shorelines (i.e., an ocean facing shoreline but sheltered from incident wave energy) became more accretive on windward islands and marginally more erosive along leeward islands. These shorelines became more accretionary and subject to more flooding with nearshore waves becoming more shore-normal. Lagoon shorelines demonstrated the greatest SLR-driven increase in erosion and run-up. They exhibited the greatest relative change with increasing wave heights where both erosion and run-up magnitudes increased. Wider

Simulation of Rotary-Wing Near-Wake Vortex Structures Using Navier-Stokes CFD Methods

NASA Technical Reports Server (NTRS)

Kenwright, David; Strawn, Roger; Ahmad, Jasim; Duque, Earl; Warmbrodt, William (Technical Monitor)

1997-01-01

This paper will use high-resolution Navier-Stokes computational fluid dynamics (CFD) simulations to model the near-wake vortex roll-up behind rotor blades. The locations and strengths of the trailing vortices will be determined from newly-developed visualization and analysis software tools applied to the CFD solutions. Computational results for rotor nearwake vortices will be used to study the near-wake vortex roll up for highly-twisted tiltrotor blades. These rotor blades typically have combinations of positive and negative spanwise loading and complex vortex wake interactions. Results of the computational studies will be compared to vortex-lattice wake models that are frequently used in rotorcraft comprehensive codes. Information from these comparisons will be used to improve the rotor wake models in the Tilt-Rotor Acoustic Code (TRAC) portion of NASA's Short Haul Civil Transport program (SHCT). Accurate modeling of the rotor wake is an important part of this program and crucial to the successful design of future civil tiltrotor aircraft. The rotor wake system plays an important role in blade-vortex interaction noise, a major problem for all rotorcraft including tiltrotors.

PREFACE: Wake Conference 2015

NASA Astrophysics Data System (ADS)

Barney, Andrew; Nørkær Sørensen, Jens; Ivanell, Stefan

2015-06-01

The 44 papers in this volume constitute the proceedings of the 2015 Wake Conference, held in Visby on the island of Gotland in Sweden. It is the fourth time this conference has been held. The Wake Conference series started in Visby, where it was held in 2009 and 2011. In 2013 it took place in Copenhagen where it was combined with the International Conference on Offshore Wind Energy and Ocean Energy. In 2015 it is back where it started in Visby, where it takes place at Uppsala University Campus Gotland, June 9th-11th. The global yearly production of electrical energy by wind turbines has grown tremendously in the past decade and it now comprises more than 3% of the global electrical power consumption. Today the wind power industry has a global annual turnover of more than 50 billion USD and an annual average growth rate of more than 20%. State-of-the-art wind turbines have rotor diameters of up to 150 m and 8 MW installed capacity. These turbines are often placed in large wind farms that have a total production capacity corresponding to that of a nuclear power plant. In order to make a substantial impact on one of the most significant challenges of our time, global warming, the industry's growth has to continue for a decade or two yet. This in turn requires research into the physics of wind turbine wakes and wind farms. Modern wind turbines are today clustered in wind farms in which the turbines are fully or partially influenced by the wake of upstream turbines. As a consequence, the wake behind the wind turbines has a lower mean wind speed and an increased turbulence level, as compared to the undisturbed flow outside the farm. Hence, wake interaction results in decreased total production of power, caused by lower kinetic energy in the wind, and an increase in the turbulence intensity. Therefore, understanding the physical nature of the vortices and their dynamics in the wake of a turbine is important for the optimal design of a wind farm. This conference is aimed

Computer models of the spacecraft wake

NASA Technical Reports Server (NTRS)

Rubin, A. G.; Heinemann, M.; Tautz, M.; Cooke, D.

1986-01-01

Until recently, computations of space plasma flow over a spacecraft have been unstable for ratios of spacecraft dimension to Debye length typical of the low Earth orbit environment. Calculations are presented of the spacecraft/environment interaction based on two computer codes, MACH and POLAR. MACH, an inside-out particle tracking code, was developed for the purpose of validating the physics of POLAR in regimes where these are no comprehensive theoretical or experimental results. While the spacecraft which can be treated by MACH are restricted to simple geometries, the methodology is more fundamental than POLAR. MACH generates self-consistent solutions within the context of quasisteady Vlasov plasma flow and achieves Debye ratios previously unobtainable. POLAR uses a three-dimensional finite-element representation of the vehicle in a staggered mesh. The plasma sheath is modeled by outside-in particle tracking. Solutions for the plasma flow, wake and vehicle charging are obtained by Vlasov-Poisson iteration; charge stabilization techniques make the results virtually insensitive to the Debye ratio. POLAR reproduces the Laframboise static plasma solutions for sperical probes and fits the Makita-Kuriki probe data for spheres in a flowing plasma in regions where comparisons are valid. POLAR and MACH solutions for the particle and electrostatic potential structure of the wake of a charged disk in a low-altitude flow are shown for Mach numbers 4, 5, and 8. New features of the solutions include ion focussing in the wake and a definitive determination of the sheath edge in the wake which shows that the sheath is not an equipotential.

Modeling the air-sea feedback system of Madeira Island

NASA Astrophysics Data System (ADS)

Pullen, Julie; Caldeira, Rui; Doyle, James D.; May, Paul; Tomé, Ricardo

2017-07-01

A realistic nested data-assimilating two-way coupled ocean/atmosphere modeling study (highest resolution 2 km) of Madeira Island was conducted for June 2011, when conditions were favorable for atmospheric vortex shedding. The simulation's island lee region exhibited relatively cloud-free conditions, promoting warmer ocean temperatures (˜2°C higher than adjacent waters). The model reasonably reproduced measured fields at 14 meteorological stations, and matched the dimensions and magnitude of the warm sea surface temperature (SST) wake imaged by satellite. The warm SSTs in the wake are shown to imprint onto the atmospheric boundary layer (ABL) over several diurnal cycles by modulating the ABL depth up to ˜200-500 m. The erosion and dissipation of the warm ocean wake overnight was aided by atmospheric drainage flow and offshore advection of cold air (ΔT = 2°C) that produced strong upward heat fluxes (˜50 W/m2 sensible and ˜250 W/m2 latent) on an episodic basis. Nevertheless, the warm wake was never entirely eroded at night due to the cumulative effect of the diurnal cycle. The spatial pattern of the diurnal warming varied day-to-day in location and extent. Significant mutual interaction of the oceanic and atmospheric boundary layers was diagnosed via fluxes and temperature cross sections and reinforced by sensitivity runs. The simulation produces for the first time the interactive nature of the ocean and atmosphere boundary layers in the warm wake region of an island with complex terrain.

High-Order Numerical Simulations of Wind Turbine Wakes

NASA Astrophysics Data System (ADS)

Kleusberg, E.; Mikkelsen, R. F.; Schlatter, P.; Ivanell, S.; Henningson, D. S.

2017-05-01

Previous attempts to describe the structure of wind turbine wakes and their mutual interaction were mostly limited to large-eddy and Reynolds-averaged Navier-Stokes simulations using finite-volume solvers. We employ the higher-order spectral-element code Nek5000 to study the influence of numerical aspects on the prediction of the wind turbine wake structure and the wake interaction between two turbines. The spectral-element method enables an accurate representation of the vortical structures, with lower numerical dissipation than the more commonly used finite-volume codes. The wind-turbine blades are modeled as body forces using the actuator-line method (ACL) in the incompressible Navier-Stokes equations. Both tower and nacelle are represented with appropriate body forces. An inflow boundary condition is used which emulates homogeneous isotropic turbulence of wind-tunnel flows. We validate the implementation with results from experimental campaigns undertaken at the Norwegian University of Science and Technology (NTNU Blind Tests), investigate parametric influences and compare computational aspects with existing numerical simulations. In general the results show good agreement between the experiments and the numerical simulations both for a single-turbine setup as well as a two-turbine setup where the turbines are offset in the spanwise direction. A shift in the wake center caused by the tower wake is detected similar to experiments. The additional velocity deficit caused by the tower agrees well with the experimental data. The wake is captured well by Nek5000 in comparison with experiments both for the single wind turbine and in the two-turbine setup. The blade loading however shows large discrepancies for the high-turbulence, two-turbine case. While the experiments predicted higher thrust for the downstream turbine than for the upstream turbine, the opposite case was observed in Nek5000.

Turbulence Modelling in Wind Turbine Wakes =

NASA Astrophysics Data System (ADS)

Olivares Espinosa, Hugo

experiments. In addition, simulations are also carried out with EllipSys3D, a code widely used and tested for computations of wind turbine wakes, the results of which provide a useful reference. Despite a limited grid resolution with respect to the size of the inflow turbulence structures, the results show that the turbulence characteristics in both the decaying turbulence and in the wake field are aptly reproduced. These observations are accompanied by an assessment of the LES modelling, which is found to be adequate in the simulations. An analysis of the longitudinal evolution of the turbulence lengthscales shows that within the wake, they develop mostly as in the free decaying turbulence. Furthermore, both codes predict that the lengthscales of the ambience turbulence dominate across the wake, with little effect caused by the shear layer at the wake envelope. These remarks are supported by an examination of features in the energy spectra along the wake. Also in this thesis, the wake turbulence fields produced by two different AD models are compared: a uniformly loaded disk and a model that includes the effects of tangential velocities and considers airfoil blade properties. The latter includes a rotational velocity controller to simulate the real conditions of variable speed turbines. Results show that the differences observed between the models in the near wake field are reduced further downstream. Also, it is seen that these disparities decrease when a turbulent inflow is employed, in comparison with the non-turbulent case. These observations confirm the assumption that uniformly loaded disks are adequate to model the far wake. In addition, the control method is shown to adjust to the local inflow conditions, regulating the rotational speed accordingly, while the computed performance proves that the implementation represents well the modelled rotor design. The results obtained in this work show that the presented methodology can succesfuly be used in the modelling and

Free wake analysis of hover performance using a new influence coefficient method

NASA Technical Reports Server (NTRS)

Quackenbush, Todd R.; Bliss, Donald B.; Ong, Ching Cho; Ching, Cho Ong

1990-01-01

A new approach to the prediction of helicopter rotor performance using a free wake analysis was developed. This new method uses a relaxation process that does not suffer from the convergence problems associated with previous time marching simulations. This wake relaxation procedure was coupled to a vortex-lattice, lifting surface loads analysis to produce a novel, self contained performance prediction code: EHPIC (Evaluation of Helicopter Performance using Influence Coefficients). The major technical features of the EHPIC code are described and a substantial amount of background information on the capabilities and proper operation of the code is supplied. Sample problems were undertaken to demonstrate the robustness and flexibility of the basic approach. Also, a performance correlation study was carried out to establish the breadth of applicability of the code, with very favorable results.

Direct numerical simulations and modeling of a spatially-evolving turbulent wake

NASA Technical Reports Server (NTRS)

Cimbala, John M.

1994-01-01

Understanding of turbulent free shear flows (wakes, jets, and mixing layers) is important, not only for scientific interest, but also because of their appearance in numerous practical applications. Turbulent wakes, in particular, have recently received increased attention by researchers at NASA Langley. The turbulent wake generated by a two-dimensional airfoil has been selected as the test-case for detailed high-resolution particle image velocimetry (PIV) experiments. This same wake has also been chosen to enhance NASA's turbulence modeling efforts. Over the past year, the author has completed several wake computations, while visiting NASA through the 1993 and 1994 ASEE summer programs, and also while on sabbatical leave during the 1993-94 academic year. These calculations have included two-equation (K-omega and K-epsilon) models, algebraic stress models (ASM), full Reynolds stress closure models, and direct numerical simulations (DNS). Recently, there has been mutually beneficial collaboration of the experimental and computational efforts. In fact, these projects have been chosen for joint presentation at the NASA Turbulence Peer Review, scheduled for September 1994. DNS calculations are presently underway for a turbulent wake at Re(sub theta) = 1000 and at a Mach number of 0.20. (Theta is the momentum thickness, which remains constant in the wake of a two dimensional body.) These calculations utilize a compressible DNS code written by M. M. Rai of NASA Ames, and modified for the wake by J. Cimbala. The code employs fifth-order accurate upwind-biased finite differencing for the convective terms, fourth-order accurate central differencing for the viscous terms, and an iterative-implicit time-integration scheme. The computational domain for these calculations starts at x/theta = 10, and extends to x/theta = 610. Fully developed turbulent wake profiles, obtained from experimental data from several wake generators, are supplied at the computational inlet, along with

Documentation of Atmospheric Conditions During Observed Rising Aircraft Wakes

NASA Technical Reports Server (NTRS)

Zak, J. Allen; Rodgers, William G., Jr.

1997-01-01

Flight tests were conducted in the fall of 1995 off the coast of Wallops Island, Virginia in order to determine characteristics of wake vortices at flight altitudes. A NASA Wallops Flight Facility C130 aircraft equipped with smoke generators produced visible wakes at altitudes ranging from 775 to 2225 m in a variety of atmospheric conditions, orientations (head wind, cross wind), and airspeeds. Meteorological and aircraft parameters were collected continuously from a Langley Research Center OV-10A aircraft as it flew alongside and through the wake vortices at varying distances behind the C130. Meteorological data were also obtained from special balloon observations made at Wallops. Differential GPS capabilities were on each aircraft from which accurate altitude profiles were obtained. Vortices were observed to rise at distances beyond a mile behind the C130. The maximum altitude was 150 m above the C130 in a near neutral atmosphere with significant turbulence. This occurred from large vertical oscillations in the wakes. There were several cases when vortices did not descend after a very short initial period and remained near generation altitude in a variety of moderately stable atmospheres and wind shears.

Wake Management Strategies for Reduction of Turbomachinery Fan Noise

NASA Technical Reports Server (NTRS)

Waitz, Ian A.

1998-01-01

The primary objective of our work was to evaluate and test several wake management schemes for the reduction of turbomachinery fan noise. Throughout the course of this work we relied on several tools. These include 1) Two-dimensional steady boundary-layer and wake analyses using MISES (a thin-shear layer Navier-Stokes code), 2) Two-dimensional unsteady wake-stator interaction simulations using UNSFLO, 3) Three-dimensional, steady Navier-Stokes rotor simulations using NEWT, 4) Internal blade passage design using quasi-one-dimensional passage flow models developed at MIT, 5) Acoustic modeling using LINSUB, 6) Acoustic modeling using VO72, 7) Experiments in a low-speed cascade wind-tunnel, and 8) ADP fan rig tests in the MIT Blowdown Compressor.

32 CFR 935.161 - Fire hazards.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Fire hazards. 935.161 Section 935.161 National... WAKE ISLAND CODE Public Safety § 935.161 Fire hazards. (a) Each person engaged in a business or other activity on Wake Island shall, at his expense, provide and maintain (in an accessible location) fire...

32 CFR 935.161 - Fire hazards.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Fire hazards. 935.161 Section 935.161 National... WAKE ISLAND CODE Public Safety § 935.161 Fire hazards. (a) Each person engaged in a business or other activity on Wake Island shall, at his expense, provide and maintain (in an accessible location) fire...

32 CFR 935.161 - Fire hazards.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Fire hazards. 935.161 Section 935.161 National... WAKE ISLAND CODE Public Safety § 935.161 Fire hazards. (a) Each person engaged in a business or other activity on Wake Island shall, at his expense, provide and maintain (in an accessible location) fire...

32 CFR 935.161 - Fire hazards.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Fire hazards. 935.161 Section 935.161 National... WAKE ISLAND CODE Public Safety § 935.161 Fire hazards. (a) Each person engaged in a business or other activity on Wake Island shall, at his expense, provide and maintain (in an accessible location) fire...

32 CFR 935.161 - Fire hazards.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Fire hazards. 935.161 Section 935.161 National... WAKE ISLAND CODE Public Safety § 935.161 Fire hazards. (a) Each person engaged in a business or other activity on Wake Island shall, at his expense, provide and maintain (in an accessible location) fire...

Dynamic Hybrid Simulation of the Lunar Wake During ARTEMIS Crossing

NASA Astrophysics Data System (ADS)

Wiehle, S.; Plaschke, F.; Angelopoulos, V.; Auster, H.; Glassmeier, K.; Kriegel, H.; Motschmann, U. M.; Mueller, J.

2010-12-01

The interaction of the highly dynamic solar wind with the Moon is simulated with the A.I.K.E.F. (Adaptive Ion Kinetic Electron Fluid) code for the ARTEMIS P1 flyby on February 13, 2010. The A.I.K.E.F. hybrid plasma simulation code is the improved version of the Braunschweig code. It is able to automatically increase simulation grid resolution in areas of interest during runtime, which greatly increases resolution as well as performance. As the Moon has no intrinsic magnetic field and no ionosphere, the solar wind particles are absorbed at its surface, resulting in the formation of the lunar wake at the nightside. The solar wind magnetic field is basically convected through the Moon and the wake is slowly filled up with solar wind particles. However, this interaction is strongly influenced by the highly dynamic solar wind during the flyby. This is considered by a dynamic variation of the upstream conditions in the simulation using OMNI solar wind measurement data. By this method, a very good agreement between simulation and observations is achieved. The simulations show that the stationary structure of the lunar wake constitutes a tableau vivant in space representing the well-known Friedrichs diagram for MHD waves.

Studies of Particle Wake Potentials in Plasmas

NASA Astrophysics Data System (ADS)

Ellis, Ian; Graziani, Frank; Glosli, James; Strozzi, David; Surh, Michael; Richards, David; Decyk, Viktor; Mori, Warren

2011-10-01

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (PPPM) code ddcMD and the particle-in-cell (PIC) code BEPS to perform these simulations. As a starting point in our study, we examine the wake of a particle passing through a plasma in 3D electrostatic simulations performed with ddcMD and with BEPS using various cell sizes. In this poster, we compare the wakes we observe in these simulations with each other and predictions from Vlasov theory. Prepared by LLNL under Contract DE-AC52-07NA27344 and by UCLA under Grant DE-FG52-09NA29552.

Studies of particle wake potentials in plasmas

NASA Astrophysics Data System (ADS)

Ellis, Ian N.; Graziani, Frank R.; Glosli, James N.; Strozzi, David J.; Surh, Michael P.; Richards, David F.; Decyk, Viktor K.; Mori, Warren B.

2011-09-01

A detailed understanding of electron stopping and scattering in plasmas with variable values for the number of particles within a Debye sphere is still not at hand. Presently, there is some disagreement in the literature concerning the proper description of these processes. Theoretical models assume electrostatic (Coulomb force) interactions between particles and neglect magnetic effects. Developing and validating proper descriptions requires studying the processes using first-principle plasma simulations. We are using the particle-particle particle-mesh (PPPM) code ddcMD and the particle-in-cell (PIC) code BEPS to perform these simulations. As a starting point in our study, we examine the wake of a particle passing through a plasma in 3D electrostatic simulations performed with ddcMD and BEPS. In this paper, we compare the wakes observed in these simulations with each other and predictions from collisionless kinetic theory. The relevance of the work to Fast Ignition is discussed.

Molecular Dynamic Studies of Particle Wake Potentials in Plasmas

NASA Astrophysics Data System (ADS)

Ellis, Ian; Graziani, Frank; Glosli, James; Strozzi, David; Surh, Michael; Richards, David; Decyk, Viktor; Mori, Warren

2010-11-01

Fast Ignition studies require a detailed understanding of electron scattering, stopping, and energy deposition in plasmas with variable values for the number of particles within a Debye sphere. Presently there is disagreement in the literature concerning the proper description of these processes. Developing and validating proper descriptions requires studying the processes using first-principle electrostatic simulations and possibly including magnetic fields. We are using the particle-particle particle-mesh (P^3M) code ddcMD to perform these simulations. As a starting point in our study, we examined the wake of a particle passing through a plasma. In this poster, we compare the wake observed in 3D ddcMD simulations with that predicted by Vlasov theory and those observed in the electrostatic PIC code BEPS where the cell size was reduced to .03λD.

32 CFR 935.20 - Applicable law.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Applicable law. 935.20 Section 935.20 National... WAKE ISLAND CODE Civil Law § 935.20 Applicable law. Civil acts and deeds taking place on Wake Island... June 15, 1950 (64 Stat. 217) (48 U.S.C. 644a), according to the laws of the United States relating to...

32 CFR 935.20 - Applicable law.

Code of Federal Regulations, 2011 CFR

2011-07-01

... WAKE ISLAND CODE Civil Law § 935.20 Applicable law. Civil acts and deeds taking place on Wake Island... 32 National Defense 6 2011-07-01 2011-07-01 false Applicable law. 935.20 Section 935.20 National... June 15, 1950 (64 Stat. 217) (48 U.S.C. 644a), according to the laws of the United States relating to...

32 CFR 935.20 - Applicable law.

Code of Federal Regulations, 2013 CFR

2013-07-01

... WAKE ISLAND CODE Civil Law § 935.20 Applicable law. Civil acts and deeds taking place on Wake Island... 32 National Defense 6 2013-07-01 2013-07-01 false Applicable law. 935.20 Section 935.20 National... June 15, 1950 (64 Stat. 217) (48 U.S.C. 644a), according to the laws of the United States relating to...

32 CFR 935.20 - Applicable law.

Code of Federal Regulations, 2014 CFR

2014-07-01

... WAKE ISLAND CODE Civil Law § 935.20 Applicable law. Civil acts and deeds taking place on Wake Island... 32 National Defense 6 2014-07-01 2014-07-01 false Applicable law. 935.20 Section 935.20 National... June 15, 1950 (64 Stat. 217) (48 U.S.C. 644a), according to the laws of the United States relating to...

32 CFR 935.20 - Applicable law.

Code of Federal Regulations, 2012 CFR

2012-07-01

... WAKE ISLAND CODE Civil Law § 935.20 Applicable law. Civil acts and deeds taking place on Wake Island... 32 National Defense 6 2012-07-01 2012-07-01 false Applicable law. 935.20 Section 935.20 National... June 15, 1950 (64 Stat. 217) (48 U.S.C. 644a), according to the laws of the United States relating to...

Stability Impact on Wake Development in Moderately Complex Terrain

NASA Astrophysics Data System (ADS)

Infield, D.; Zorzi, G.

2017-05-01

This paper uses a year of SCADA data from Whitelee Wind Farm near Glasgow to investigate wind turbine wake development in moderately complex terrain. Atmospheric stability measurements in terms of Richardson number from a met mast at an adjoining site have been obtained and used to assess the impact of stability on wake development. Considerable filtering of these data has been undertaken to ensure that all turbines are working normally and are well aligned with the wind direction. A group of six wind turbines, more or less in a line, have been selected for analysis, and winds within a 2 degree direction sector about this line are used to ensure, as far as possible, that all the turbines investigated are fully immersed in the wake/s of the upstream turbine/s. Results show how the terrain effects combine with the wake effects, with both being of comparable importance for the site in question. Comparison has been made with results from two commercial CFD codes for neutral stability, and reasonable agreement is demonstrated. Richardson number has been plotted against wind shear and turbulence intensity at a met mast on the wind farm that for the selected wind direction is not in the wake of any turbines. Good correlations are found indicating that the Richardson numbers obtained are reliable. The filtered data used for wake analysis were split according to Richardson number into two groups representing slightly stable to neutral, and unstable conditions. Very little difference in wake development is apparent. A greater difference can be observed when the data are separated simply by turbulence intensity, suggesting that, although turbulence intensity is correlated with stability, of the two it is the parameter that most directly impacts on wake development through mixing of ambient and wake flows.

Wakes and differential charging of large bodies in low Earth orbit

NASA Technical Reports Server (NTRS)

Parker, L. W.

1985-01-01

Highlights of earlier results using the Inside-Out WAKE code on wake structures of LEO spacecraft are reviewed. For conducting bodies of radius large compared with the Debye length, a high Mach number wake develops a negative potential well. Quasineutrality is violated in the very near wake region, and the wake is relatively empty for a distance downstream of about one half of a Mach number of radii. There is also a suggestion of a core of high density along the axis. A comparison of rigorous numerical solutions with in situ wake data from the AE-C satellite suggests that the so called neutral approximation for ions (straight line trajectories, independent of fields) may be a reasonable approximation except near the center of the near wake. This approximation is adopted for very large bodies. Work concerned with the wake point potential of very large nonconducting bodies such as the shuttle orbiter is described. Using a cylindrical model for bodies of this size or larger in LEO (body radius up to 10 to the 5th power Debye lengths), approximate solutions are presented based on the neutral approximation (but with rigorous trajectory calculations for surface current balance). There is a negative potential well if the body is conducting, and no well if the body is nonconducting. In the latter case the wake surface itself becomes highly negative. The wake point potential is governed by the ion drift energy.

32 CFR 935.151 - Island permit for boat and vehicle.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Island permit for boat and vehicle. 935.151 Section 935.151 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL... boat and vehicle. (a) No person may use a privately owned motor vehicle or boat on Wake Island unless...

32 CFR 935.151 - Island permit for boat and vehicle.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Island permit for boat and vehicle. 935.151 Section 935.151 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL... boat and vehicle. (a) No person may use a privately owned motor vehicle or boat on Wake Island unless...

32 CFR 935.151 - Island permit for boat and vehicle.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Island permit for boat and vehicle. 935.151 Section 935.151 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL... boat and vehicle. (a) No person may use a privately owned motor vehicle or boat on Wake Island unless...

32 CFR 935.151 - Island permit for boat and vehicle.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Island permit for boat and vehicle. 935.151 Section 935.151 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL... boat and vehicle. (a) No person may use a privately owned motor vehicle or boat on Wake Island unless...

32 CFR 935.151 - Island permit for boat and vehicle.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Island permit for boat and vehicle. 935.151 Section 935.151 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL... boat and vehicle. (a) No person may use a privately owned motor vehicle or boat on Wake Island unless...

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

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.; Ahmad, Jasim U.

2012-01-01

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

Wake Vortex Advisory System (WakeVAS) Concept of Operations

NASA Technical Reports Server (NTRS)

Rutishauser, David; Lohr, Gary; Hamilton, David; Powers, Robert; McKissick, Burnell; Adams, Catherine; Norris, Edward

2003-01-01

NASA Langley Research Center has a long history of aircraft wake vortex research, with the most recent accomplishment of demonstrating the Aircraft VOrtex Spacing System (AVOSS) at Dallas/Forth Worth International Airport in July 2000. The AVOSS was a concept for an integration of technologies applied to providing dynamic wake-safe reduced spacing for single runway arrivals, as compared to current separation standards applied during instrument approaches. AVOSS included state-of-the-art weather sensors, wake sensors, and a wake behavior prediction algorithm. Using real-time data AVOSS averaged a 6% potential throughput increase over current standards. This report describes a Concept of Operations for applying the technologies demonstrated in the AVOSS to a variety of terminal operations to mitigate wake vortex capacity constraints. A discussion of the technological issues and open research questions that must be addressed to design a Wake Vortex Advisory System (WakeVAS) is included.

Night Waking, Sleep-Wake Organization, and Self-Soothing in the First Year of Life

PubMed Central

GOODLIN-JONES, BETH L.; BURNHAM, MELISSA M.; GAYLOR, ERIKA E.; ANDERS, THOMAS F.

2005-01-01

Few objective data are available regarding infants’ night waking behaviors and the development of self-soothing during the first year of life. This cross-sectional study examined 80 infants in one of four age groups (3, 6, 9, or 12 mo) for four nights by using videosomnography to code nighttime awakenings and parent-child interactions. A large degree of variability was observed in parents’ putting the infant to bed awake or asleep and in responding to vocalizations after nighttime awakenings. Most infants woke during the night at all ages observed. Younger infants tended to require parental intervention at night to return to sleep, whereas older infants exhibited a greater proportion of self-soothing after nighttime awakenings. However, even in the 12-month-old group, 50% of infants typically required parental intervention to get back to sleep after waking. Results emphasize the individual and contextual factors that effect the development of self-soothing behavior during the first year of life. PMID:11530895

Modeled atoll shoreline and run-up changes in response to sea-level rise and varying large wave conditions at Wake and Midway Atolls, Northwestern Hawaiian Islands

NASA Astrophysics Data System (ADS)

Shope, J. B.; Storlazzi, C. D.; Hoeke, R. K.

2016-12-01

Atoll islands are dynamic features that respond to seasonal alterations in wave conditions and sea level. With sea level and wave climates projected to change over the next century, it is unclear how shoreline wave runup and erosion patterns along these low elevation islands will respond, making it difficult for communities to prepare for the future. To investigate this, extreme boreal winter and summer wave conditions under a variety of future sea-level rise (SLR) scenarios were modeled at two atolls, Wake and Midway, using Delft3D. Nearshore wave conditions were used to find the potential longshore sediment flux, and wave-driven shoreline erosion was calculated as the divergence of the longshore drift; runup and the locations where runup exceed the berm elevation were also found. Of the aforementioned parameters, SLR is projected to be the dominant force driving future island morphological change and flooding. Increased sea level reduces depth-limited breaking by the atoll reef, allowing larger waves to reach the shoreline, increasing runup height and driving greater inland flooding along most coastlines. Previously protected shorelines, such as lagoon shorelines or shorelines with comparably wide reef flats, are projected see the greatest relative increases in runup. Increases in inland flooding extent were greatest along seaward shorelines due to increases in runup. Changes in incident wave directions had a smaller effect on runup, and the projected changes to incident wave heights had a negligible effect. SLR also drove the greatest changes to island shoreline morphology. Windward islands are projected to become thinner as seaward and lagoonal shorelines erode, accreting toward more leeward shorelines and shorelines with comparably wider reef flats. Similarly, leeward islands are anticipated to become thinner and longer, accreting towards their longitudinal ends. The shorelines of these islands will likely change dramatically over the next century as SLR and

The Effects of Double Diffusion and Background Turbulence on the Persistence of Submarine Wakes

DTIC Science & Technology

2016-03-01

acoustic detection of submerged objects. 14. SUBJECT TERMS fluid dynamics, submarine, wakes, turbulence 15. NUMBER OF PAGES 41 16. PRICE CODE...microstructure-based observations of stratified wakes offer a viable method for the non- acoustic detection of submerged objects. vi THIS PAGE...25 viii THIS PAGE INTENTIONALLY LEFT BLANK ix LIST OF FIGURES Figure 1. Velocity Profiles of Towed and Jet- Propelled Body

A stochastic wind turbine wake model based on new metrics for wake characterization: A stochastic wind turbine wake model based on new metrics for wake characterization

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

Doubrawa, Paula; Barthelmie, Rebecca J.; Wang, Hui

Understanding the detailed dynamics of wind turbine wakes is critical to predicting the performance and maximizing the efficiency of wind farms. This knowledge requires atmospheric data at a high spatial and temporal resolution, which are not easily obtained from direct measurements. Therefore, research is often based on numerical models, which vary in fidelity and computational cost. The simplest models produce axisymmetric wakes and are only valid beyond the near wake. Higher-fidelity results can be obtained by solving the filtered Navier-Stokes equations at a resolution that is sufficient to resolve the relevant turbulence scales. This work addresses the gap between thesemore » two extremes by proposing a stochastic model that produces an unsteady asymmetric wake. The model is developed based on a large-eddy simulation (LES) of an offshore wind farm. Because there are several ways of characterizing wakes, the first part of this work explores different approaches to defining global wake characteristics. From these, a model is developed that captures essential features of a LES-generated wake at a small fraction of the cost. The synthetic wake successfully reproduces the mean characteristics of the original LES wake, including its area and stretching patterns, and statistics of the mean azimuthal radius. The mean and standard deviation of the wake width and height are also reproduced. This preliminary study focuses on reproducing the wake shape, while future work will incorporate velocity deficit and meandering, as well as different stability scenarios.« less

Investigation of island formation due to RMPs in DIII-D plasmas with the SIESTA resistive MHD equilibrium code

NASA Astrophysics Data System (ADS)

Hirshman, S. P.; Shafer, M. W.; Seal, S. K.; Canik, J. M.

2016-04-01

> The SIESTA magnetohydrodynamic (MHD) equilibrium code has been used to compute a sequence of ideally stable equilibria resulting from numerical variation of the helical resonant magnetic perturbation (RMP) applied to an axisymmetric DIII-D plasma equilibrium. Increasing the perturbation strength at the dominant , resonant surface leads to lower MHD energies and increases in the equilibrium island widths at the (and sidebands) surfaces, in agreement with theoretical expectations. Island overlap at large perturbation strengths leads to stochastic magnetic fields which correlate well with the experimentally inferred field structure. The magnitude and spatial phase (around the dominant rational surfaces) of the resonant (shielding) component of the parallel current are shown to change qualitatively with the magnetic island topology.

Cosmic string wakes

NASA Technical Reports Server (NTRS)

Stebbins, Albert; Veeraraghavan, Shoba; Silk, Joseph; Brandenberger, Robert; Turok, Neil

1987-01-01

Accretion of matter onto wakes left behind by horizon-sized pieces of cosmic string is investigated, and the effects of wakes on the large-scale structure of the universe are determined. Accretion of cold matter onto wakes, the effects of a long string on fluids with finite velocity dispersion or sound speeds, the interactions between loops and wakes, and the conditions for wakes to survive disruption by loops are discussed. It is concluded that the most important wakes are those which were formed at the time of equal matter and radiation density. This leads to sheetlike overdense regions of galaxies with a mean separation in agreement with the scale of the bubbles of de Lapparent, Geller, and Huchra (1986). However, for the value of G(mu) favored from galaxy formation considerations in a universe with cold dark matter, a wake accretes matter from a distance of only about 1.5 Mpc, which is much less than the distance between the wakes.

Dust Storm Hits Canary Islands

NASA Technical Reports Server (NTRS)

2002-01-01

A thick pall of sand and dust blew out from the Sahara Desert over the Atlantic Ocean yesterday (January 6, 2002), engulfing the Canary Islands in what has become one of the worst sand storms ever recorded there. In this scene, notice how the dust appears particularly thick in the downwind wake of Tenerife, the largest of the Canary Islands. Perhaps the turbulence generated by the air currents flowing past the island's volcanic peaks is churning the dust back up into the atmosphere, rather than allowing it to settle toward the surface. This true-color image was captured by the Moderate-resolution Imaging Spectroradiometer (MODIS), flying aboard NASA's Terra satellite, on January 7, 2002. Image courtesy Jacques Descloitres, MODIS Land Rapid Response Team at NASA GSFC

Wind Turbine Wakes

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

Kelley, Christopher Lee; Maniaci, David Charles; Resor, Brian R.

2015-10-01

The total energy produced by a wind farm depends on the complex interaction of many wind turbines operating in proximity with the turbulent atmosphere. Sometimes, the unsteady forces associated with wind negatively influence power production, causing damage and increasing the cost of producing energy associated with wind power. Wakes and the motion of air generated by rotating blades need to be better understood. Predicting wakes and other wind forces could lead to more effective wind turbine designs and farm layouts, thereby reducing the cost of energy, allowing the United States to increase the installed capacity of wind energy. The Windmore » Energy Technologies Department at Sandia has collaborated with the University of Minnesota to simulate the interaction of multiple wind turbines. By combining the validated, large-eddy simulation code with Sandia’s HPC capability, this consortium has improved its ability to predict unsteady forces and the electrical power generated by an array of wind turbines. The array of wind turbines simulated were specifically those at the Sandia Scaled Wind Farm Testbed (SWiFT) site which aided the design of new wind turbine blades being manufactured as part of the National Rotor Testbed project with the Department of Energy.« less

Far-Field Turbulent Vortex-Wake/Exhaust Plume Interaction for Subsonic and HSCT Airplanes

NASA Technical Reports Server (NTRS)

Kandil, Osama A.; Adam, Ihab; Wong, Tin-Chee

1996-01-01

Computational study of the far-field turbulent vortex-wake/exhaust plume interaction for subsonic and high speed civil transport (HSCT) airplanes is carried out. The Reynolds-averaged Navier-Stokes (NS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The two-equation shear stress transport model of Menter is implemented with the NS solver for turbulent-flow calculation. For the far-field study, the computations of vortex-wake interaction with the exhaust plume of a single engine of a Boeing 727 wing in a holding condition and two engines of an HSCT in a cruise condition are carried out using overlapping zonal method for several miles downstream. These results are obtained using the computer code FTNS3D. The results of the subsonic flow of this code are compared with those of a parabolized NS solver known as the UNIWAKE code.

Free Wake Techniques for Rotor Aerodynamic Analylis. Volume 2: Vortex Sheet Models

NASA Technical Reports Server (NTRS)

Tanuwidjaja, A.

1982-01-01

Results of computations are presented using vortex sheets to model the wake and test the sensitivity of the solutions to various assumptions used in the development of the models. The complete codings are included.

Coalescing Wind Turbine Wakes

DOE PAGES

Lee, S.; Churchfield, M.; Sirnivas, S.; ...

2015-06-18

A team of researchers from the National Renewable Energy Laboratory and Statoil used large-eddy simulations to numerically investigate the merging wakes from upstream offshore wind turbines. Merging wakes are typical phenomena in wind farm flows in which neighboring turbine wakes consolidate to form complex flow patterns that are as yet not well understood. In the present study, three 6-MW turbines in a row were subjected to a neutrally stable atmospheric boundary layer flow. As a result, the wake from the farthest upstream turbine conjoined the downstream wake, which significantly altered the subsequent velocity deficit structures, turbulence intensity, and the globalmore » meandering behavior. The complexity increased even more when the combined wakes from the two upstream turbines mixed with the wake generated by the last turbine, thereby forming a "triplet" structure. Although the influence of the wake generated by the first turbine decayed with downstream distance, the mutated wakes from the second turbine continued to influence the downstream wake. Two mirror-image angles of wind directions that yielded partial wakes impinging on the downstream turbines yielded asymmetric wake profiles that could be attributed to the changing flow directions in the rotor plane induced by the Coriolis force. In conclusion, the turbine wakes persisted for extended distances in the present study, which is a result of low aerodynamic surface roughness typically found in offshore conditions« less

Computation of Turbulent Wake Flows in Variable Pressure Gradient

NASA Technical Reports Server (NTRS)

Duquesne, N.; Carlson, J. R.; Rumsey, C. L.; Gatski, T. B.

1999-01-01

Transport aircraft performance is strongly influenced by the effectiveness of high-lift systems. Developing wakes generated by the airfoil elements are subjected to strong pressure gradients and can thicken very rapidly, limiting maximum lift. This paper focuses on the effects of various pressure gradients on developing symmetric wakes and on the ability of a linear eddy viscosity model and a non-linear explicit algebraic stress model to accurately predict their downstream evolution. In order to reduce the uncertainties arising from numerical issues when assessing the performance of turbulence models, three different numerical codes with the same turbulence models are used. Results are compared to available experimental data to assess the accuracy of the computational results.

Evaluation of Fast-Time Wake Vortex Models using Wake Encounter Flight Test Data

NASA Technical Reports Server (NTRS)

Ahmad, Nashat N.; VanValkenburg, Randal L.; Bowles, Roland L.; Limon Duparcmeur, Fanny M.; Gloudesman, Thijs; van Lochem, Sander; Ras, Eelco

2014-01-01

This paper describes a methodology for the integration and evaluation of fast-time wake models with flight data. The National Aeronautics and Space Administration conducted detailed flight tests in 1995 and 1997 under the Aircraft Vortex Spacing System Program to characterize wake vortex decay and wake encounter dynamics. In this study, data collected during Flight 705 were used to evaluate NASA's fast-time wake transport and decay models. Deterministic and Monte-Carlo simulations were conducted to define wake hazard bounds behind the wake generator. The methodology described in this paper can be used for further validation of fast-time wake models using en-route flight data, and for determining wake turbulence constraints in the design of air traffic management concepts.

Beta EEG reflects sensory processing in active wakefulness and homeostatic sleep drive in quiet wakefulness.

PubMed

Grønli, Janne; Rempe, Michael J; Clegern, William C; Schmidt, Michelle; Wisor, Jonathan P

2016-06-01

Markers of sleep drive (<10 Hz; slow-wave activity and theta) have been identified in the course of slow-wave sleep and wakefulness. So far, higher frequencies in the waking electroencephalogram have not been examined thoroughly as a function of sleep drive. Here, electroencephalogram dynamics were measured in epochs of active wake (wake characterized by high muscle tone) or quiet wake (wake characterized by low muscle tone). It was hypothesized that the higher beta oscillations (15-35 Hz, measured by local field potential and electroencephalography) represent fundamentally different processes in active wake and quiet wake. In active wake, sensory stimulation elevated beta activity in parallel with gamma (80-90 Hz) activity, indicative of cognitive processing. In quiet wake, beta activity paralleled slow-wave activity (1-4 Hz) and theta (5-8 Hz) in tracking sleep need. Cerebral lactate concentration, a measure of cerebral glucose utilization, increased during active wake whereas it declined during quiet wake. Mathematical modelling of state-dependent dynamics of cortical lactate concentration was more precisely predictive when quiet wake and active wake were included as two distinct substates rather than a uniform state of wakefulness. The extent to which lactate concentration declined in quiet wake and increased in active wake was proportionate to the amount of beta activity. These data distinguish quiet wake from active wake. Quiet wake, particularly when characterized by beta activity, is permissive to metabolic and electrophysiological changes that occur in slow-wave sleep. These data urge further studies on state-dependent beta oscillations across species. © 2016 European Sleep Research Society.

Investigation of island formation due to RMPs in DIII-D plasmas with the SIESTA resistive MHD equilibrium code

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

Hirshman, S. P.; Shafer, M. W.; Seal, S. K.

The SIESTA magnetohydrodynamic (MHD) equilibrium code has been used to compute a sequence of ideally stable equilibria resulting from numerical variation of the helical resonant magnetic perturbation (RMP) applied to an axisymmetric DIII-D plasma equilibrium. Increasing the perturbation strength at the dominant m=2, n=-1 , resonant surface leads to lower MHD energies and increases in the equilibrium island widths at the m=2 (and sidebands) surfaces, in agreement with theoretical expectations. Island overlap at large perturbation strengths leads to stochastic magnetic fields which correlate well with the experimentally inferred field structure. The magnitude and spatial phase (around the dominant rational surfaces)more » of the resonant (shielding) component of the parallel current are shown to change qualitatively with the magnetic island topology.« less

Investigation of island formation due to RMPs in DIII-D plasmas with the SIESTA resistive MHD equilibrium code

DOE PAGES

Hirshman, S. P.; Shafer, M. W.; Seal, S. K.; ...

2016-03-03

The SIESTA magnetohydrodynamic (MHD) equilibrium code has been used to compute a sequence of ideally stable equilibria resulting from numerical variation of the helical resonant magnetic perturbation (RMP) applied to an axisymmetric DIII-D plasma equilibrium. Increasing the perturbation strength at the dominant m=2, n=-1 , resonant surface leads to lower MHD energies and increases in the equilibrium island widths at the m=2 (and sidebands) surfaces, in agreement with theoretical expectations. Island overlap at large perturbation strengths leads to stochastic magnetic fields which correlate well with the experimentally inferred field structure. The magnitude and spatial phase (around the dominant rational surfaces)more » of the resonant (shielding) component of the parallel current are shown to change qualitatively with the magnetic island topology.« less

[Melatonin, synthetic analogs, and the sleep/wake rhythm].

PubMed

Escames, G; Acuña-Castroviejo, D

Melatonin, a widespread hormone in the animal kingdom, is produced by several organs and tissues besides the pineal gland. Whilst extrapineal melatonin behaves as a cytoprotective molecule, the pineal produces the hormone in a rhythmic manner. The discovery of melatonin in 1958, and the characterization of its synthesis somewhat later, let to the description of its photoperiodic regulation and its relationship with the biological rhythms such as the sleep/wake rhythm. The suprachiasmatic nuclei are the anatomical seat of the biological clock, represented by the clock genes, which code for the period and frequency of the rhythms. The photoperiod synchronizes the activity of the auprachiasmatic biological clock, which in turn induces the melatonin's rhythm. The rhythm of melatonin, peaking at 2-3 am, acts as an endogenous synchronizer that translates the environmental photoperiodic signal in chemical information for the cells. The sleep/wake cycle is a typical biological rhythm synchronized by melatonin, and the sleep/wake cycle alterations of chronobiological origin, are very sensitive to melatonin treatment. Taking advantage of the chronobiotic and antidepressive properties of melatonin, a series of synthetic analogs of this hormone, with high interest in insomnia, are now available. Melatonin is a highly effective chronobiotic in the treatment of chronobiological alterations of the sleep/wake cycle. From a pharmacokinetic point of view, the synthetic drugs derived from melatonin are interesting tools in the therapy of these alterations.

Airloads, wakes, and aeroelasticity

NASA Technical Reports Server (NTRS)

Johnson, Wayne

1990-01-01

Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.

76 FR 78309 - Hawaiian and Pacific Islands National Wildlife Refuge Complex; Wilderness Review and Legislative...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-16

... Forest, Palmyra Atoll, Pearl Harbor, Rose Atoll, and Wake Atoll. These refuges are located in Hawai'i... the following national wildlife refuges: Baker Island, Guam, Hakalau Forest, Hanalei, Hawaiian Islands... identified a WSA on the Hakalau Forest Refuge, as part of the refuge's CCP completed in September 2010. The...

32 CFR 935.164 - Boat operations.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Boat operations. 935.164 Section 935.164 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Public Safety § 935.164 Boat operations. The operator of each boat used at Wake...

32 CFR 935.164 - Boat operations.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Boat operations. 935.164 Section 935.164 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Public Safety § 935.164 Boat operations. The operator of each boat used at Wake...

32 CFR 935.164 - Boat operations.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Boat operations. 935.164 Section 935.164 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Public Safety § 935.164 Boat operations. The operator of each boat used at Wake...

32 CFR 935.164 - Boat operations.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Boat operations. 935.164 Section 935.164 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Public Safety § 935.164 Boat operations. The operator of each boat used at Wake...

32 CFR 935.164 - Boat operations.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Boat operations. 935.164 Section 935.164 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Public Safety § 935.164 Boat operations. The operator of each boat used at Wake...

Recent NASA Wake-Vortex Flight Tests, Flow-Physics Database and Wake-Development Analysis

NASA Technical Reports Server (NTRS)

Vicroy, Dan D.; Vijgen, Paul M.; Reimer, Heidi M.; Gallegos, Joey L.; Spalart, Philippe R.

1998-01-01

A series of flight tests over the ocean of a four engine turboprop airplane in the cruise configuration have provided a data set for improved understanding of wake vortex physics and atmospheric interaction. An integrated database has been compiled for wake characterization and validation of wake-vortex computational models. This paper describes the wake-vortex flight tests, the data processing, the database development and access, and results obtained from preliminary wake-characterization analysis using the data sets.

Effect of Wind Turbine Wakes on the Performance of a Real Case WRF-LES Simulation

NASA Astrophysics Data System (ADS)

Doubrawa, P.; Montornès, A.; Barthelmie, R. J.; Pryor, S. C.; Giroux, G.; Casso, P.

2017-05-01

The main objective of this work is to estimate how much of the discrepancy between measured and modeled flow parameters can be attributed to wake effects. The real case simulations were performed for a period of 15 days with the Weather Research and Forecasting (WRF) model and nested down to a Large-Eddy Simulation (LES) scale of ∼ 100 m. Beyond the coastal escarpment, the site is flat and homogeneous and the study focuses on a meteorological mast and a northern turbine subjected to the wake of a southern turbine. The observational data set collected during the Prince Edward Island Wind Energy Experiment (PEIWEE) includes a sonic anemometer at 60 m mounted onto the mast, and measurements from the two turbines. Wake versus free stream conditions are distinguished based on measured wind direction while assuming constant expansion for the wake of the southern turbine. During the period considered the mast and northern turbine were under the southern turbine wake ∼ 16% and ∼ 11% of the time, respectively. Under these conditions, the model overestimates the wind speed and underestimates the turbulence intensity at the mast but not at the northern turbine, where the effect of wakes on the model error is unclear and other model limitations are likely more important. The wind direction difference between the southern and northern turbines is slightly underestimated by the model regardless of whether free stream or wake conditions are observed, indicating that it may be due to factors unrelated to the wake development such as surface forcings. Finally, coupling an inexpensive wake model to the high-fidelity simulation as a post-processing tool drives the simulated wind speeds at the mast significantly closer to the observed values, but the opposite is true at the coastal turbine which is in the far wake. This indicates that the application of a post-processing wake correction should be performed with caution and may increase the wind speed errors when other important

36 CFR 7.12 - Gulf Islands National Seashore.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 36 Parks, Forests, and Public Property 1 2013-07-01 2013-07-01 false Gulf Islands National Seashore. 7.12 Section 7.12 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... operated at greater than flat wake speed in the following locations: (i) Within 0.5 mile from the shoreline...

36 CFR 7.12 - Gulf Islands National Seashore.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 36 Parks, Forests, and Public Property 1 2011-07-01 2011-07-01 false Gulf Islands National Seashore. 7.12 Section 7.12 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... operated at greater than flat wake speed in the following locations: (i) Within 0.5 mile from the shoreline...

36 CFR 7.12 - Gulf Islands National Seashore.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 36 Parks, Forests, and Public Property 1 2010-07-01 2010-07-01 false Gulf Islands National Seashore. 7.12 Section 7.12 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... operated at greater than flat wake speed in the following locations: (i) Within 0.5 mile from the shoreline...

36 CFR 7.12 - Gulf Islands National Seashore.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 36 Parks, Forests, and Public Property 1 2014-07-01 2014-07-01 false Gulf Islands National Seashore. 7.12 Section 7.12 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... operated at greater than flat wake speed in the following locations: (i) Within 0.5 mile from the shoreline...

36 CFR 7.12 - Gulf Islands National Seashore.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 36 Parks, Forests, and Public Property 1 2012-07-01 2012-07-01 false Gulf Islands National Seashore. 7.12 Section 7.12 Parks, Forests, and Public Property NATIONAL PARK SERVICE, DEPARTMENT OF THE... operated at greater than flat wake speed in the following locations: (i) Within 0.5 mile from the shoreline...

TFaNS Tone Fan Noise Design/Prediction System. Volume 3; Evaluation of System Codes

NASA Technical Reports Server (NTRS)

Topol, David A.

1999-01-01

TFANS is the Tone Fan Noise Design/Prediction System developed by Pratt & Whitney under contract to NASA Lewis (presently NASA Glenn). The purpose of this system is to predict tone noise emanating from a fan stage including the effects of reflection and transmission by the rotor and stator and by the duct inlet and nozzle. These effects have been added to an existing annular duct/isolated stator noise prediction capability. TFANS consists of: The codes that compute the acoustic properties (reflection and transmission coefficients) of the various elements and write them to files. Cup3D: Fan Noise Coupling Code that reads these files, solves the coupling problem, and outputs the desired noise predictions. AWAKEN: CFD/Measured Wake Postprocessor which reformats CFD wake predictions and/or measured wake data so it can be used by the system. This volume of the report evaluates TFANS versus full-scale and ADP 22" fig data using the semi-empirical wake modelling in the system. This report is divided into three volumes: Volume 1: System Description, CUP3D Technical Documentation, and Manual for Code Developers; Volume II: User's Manual, TFANS Version 1.4; Volume III: Evaluation of System Codes.

A Study of Water Wave Wakes of Washington State Ferries

NASA Astrophysics Data System (ADS)

Perfect, Bradley; Riley, James; Thomson, Jim; Fay, Endicott

2015-11-01

Washington State Ferries (WSF) operates a ferry route that travels through a 600m-wide channel called Rich Passage. Concerns of shoreline erosion in Rich Passage have prompted this study of the generation and propagation of surface wave wakes caused by WSF vessels. The problem was addressed in three ways: analytically, using an extension of the Kelvin wake model by Darmon et al. (J. Fluid Mech., 738, 2014); computationally, employing a RANS Navier-Stokes model in the CFD code OpenFOAM which uses the Volume of Fluid method to treat the free surface; and with field data taken in Sept-Nov, 2014, using a suite of surface wave measuring buoys. This study represents one of the first times that model predictions of ferry boat-generated wakes can be tested against measurements in open waters. The results of the models and the field data are evaluated using direct comparison of predicted and measured surface wave height as well as other metrics. Furthermore, the model predictions and field measurements suggest differences in wake amplitudes for different class vessels. Finally, the relative strengths and weaknesses of each prediction method as well as of the field measurements will be discussed. Washington State Department of Transportation.

An integrated Navier-Stokes - full potential - free wake method for rotor flows

NASA Astrophysics Data System (ADS)

Berkman, Mert Enis

1998-12-01

The strong wake shed from rotary wings interacts with almost all components of the aircraft, and alters the flow field thus causing performance and noise problems. Understanding and modeling the behavior of this wake, and its effect on the aerodynamics and acoustics of helicopters have remained as challenges. This vortex wake and its effect should be accurately accounted for in any technique that aims to predict rotor flow field and performance. In this study, an advanced and efficient computational technique for predicting three-dimensional unsteady viscous flows over isolated helicopter rotors in hover and in forward flight is developed. In this hybrid technique, the advantages of various existing methods have been combined to accurately and efficiently study rotor flows with a single numerical method. The flow field is viewed in three parts: (i) an inner zone surrounding each blade where the wake and viscous effects are numerically captured, (ii) an outer zone away from the blades where wake is modeled, and (iii) a Lagrangean wake which induces wake effects in the outer zone. This technique was coded in a flow solver and compared with experimental data for hovering and advancing rotors including a two-bladed rotor, the UH-60A rotor and a tapered tip rotor. Detailed surface pressure, integrated thrust and torque, sectional thrust, and tip vortex position predictions compared favorably against experimental data. Results indicated that the hybrid solver provided accurate flow details and performance information typically in one-half to one-eighth cost of complete Navier-Stokes methods.

Aeroacoustic Codes For Rotor Harmonic and BVI Noise--CAMRAD.Mod1/HIRES

NASA Technical Reports Server (NTRS)

Brooks, Thomas F.; Boyd, D. Douglas, Jr.; Burley, Casey L.; Jolly, J. Ralph, Jr.

1996-01-01

This paper presents a status of non-CFD aeroacoustic codes at NASA Langley Research Center for the prediction of helicopter harmonic and Blade-Vortex Interaction (BVI) noise. The prediction approach incorporates three primary components: CAMRAD.Mod1 - a substantially modified version of the performance/trim/wake code CAMRAD; HIRES - a high resolution blade loads post-processor; and WOPWOP - an acoustic code. The functional capabilities and physical modeling in CAMRAD.Mod1/HIRES will be summarized and illustrated. A new multi-core roll-up wake modeling approach is introduced and validated. Predictions of rotor wake and radiated noise are compared with to the results of the HART program, a model BO-105 windtunnel test at the DNW in Europe. Additional comparisons are made to results from a DNW test of a contemporary design four-bladed rotor, as well as from a Langley test of a single proprotor (tiltrotor) three-bladed model configuration. Because the method is shown to help eliminate the necessity of guesswork in setting code parameters between different rotor configurations, it should prove useful as a rotor noise design tool.

Hypersonic merged layer blunt body flows with wakes

NASA Technical Reports Server (NTRS)

Jain, Amolak C.; Dahm, Werner K.

1991-01-01

An attempt is made here to understand the basic physics of the flowfield with wake on a blunt body of revolution under hypersonic rarefied conditions. A merged layer model of flow is envisioned. Full steady-state Navier-Stokes equations in spherical polar coordinate system are computed from the surface with slip and temperature jump conditions to the free stream by the Accelerated Successive Replacement method of numerical integration. Analysis is developed for bodies of arbitrary shape, but actual computations have been carried out for a sphere and sphere-cone body. Particular attention is paid to set the limit of the onset of separation, wake closure, shear-layer impingement, formation and dissipation of the shocks in the flowfield. Validity of the results is established by comparing the present results for sphere with the corresponding results of the SOFIA code in the common region of their validity and with the experimental data.

Development of Predictive Wake Vortex Transport Model for Terminal Area Wake Vortex Avoidance

DOT National Transportation Integrated Search

1976-05-01

The wake vortex transport program has been expanded to include viscous effects and the influence of initial roll-up, atmospheric turbulence, and wind shear on the persistence and motion of wake vortices in terminal areas. Analysis of wake characteris...

Connectivity of Sleep- and Wake-Promoting Regions of the Human Hypothalamus During Resting Wakefulness.

PubMed

Boes, Aaron D; Fischer, David; Geerling, Joel C; Bruss, Joel; Saper, Clifford B; Fox, Michael D

2018-05-29

The hypothalamus is a central hub for regulating sleep-wake patterns, the circuitry of which has been investigated extensively in experimental animals. This work has identified a wake-promoting region in the posterior hypothalamus, with connections to other wake-promoting regions, and a sleep-promoting region in the anterior hypothalamus, with inhibitory projections to the posterior hypothalamus. It is unclear whether a similar organization exists in humans. Here, we use anatomical landmarks to identify homologous sleep and wake-promoting regions of the human hypothalamus and investigate their functional relationships using resting-state functional connectivity MRI in healthy awake participants. First, we identify a negative correlation (anticorrelation) between the anterior and posterior hypothalamus, two regions with opposing roles in sleep-wake regulation. Next, we show that hypothalamic connectivity predicts a pattern of regional sleep-wake changes previously observed in humans. Specifically, regions that are more positively correlated with the posterior hypothalamus and more negatively correlated with the anterior hypothalamus correspond to regions with the greatest change in cerebral blood flow between sleep-wake states. Taken together, these findings provide preliminary evidence relating a hypothalamic circuit investigated in animals to sleep-wake neuroimaging results in humans, with implications for our understanding of human sleep-wake regulation and the functional significance of anticorrelations.

NWRA AVOSS Wake Vortex Prediction Algorithm. 3.1.1

NASA Technical Reports Server (NTRS)

Robins, R. E.; Delisi, D. P.; Hinton, David (Technical Monitor)

2002-01-01

This report provides a detailed description of the wake vortex prediction algorithm used in the Demonstration Version of NASA's Aircraft Vortex Spacing System (AVOSS). The report includes all equations used in the algorithm, an explanation of how to run the algorithm, and a discussion of how the source code for the algorithm is organized. Several appendices contain important supplementary information, including suggestions for enhancing the algorithm and results from test cases.

Characterization of plasma wake excitation and particle trapping in the nonlinear bubble regime

NASA Astrophysics Data System (ADS)

Benedetti, Carlo; Schroeder, Carl; Esarey, Eric; Leemans, Wim

2010-11-01

We investigate the excitation of nonlinear wake (bubble) formation by an ultra-short (kpL ˜2), intense (e Alaser/mc^2 > 2) laser pulse interacting with an underdense plasma. A detailed analysis of particle orbits in the wakefield is performed by using reduced analytical models and numerical simulations performed with the 2D cylindrical, envelope, ponderomotive, hybrid PIC/fluid code INF&RNO, recently developed at LBNL. In particular we study the requirements for injection and/or trapping of background plasma electrons in the nonlinear wake. Characterization of the phase-space properties of the injected particle bunch will also be discussed.

The Effect of Wake Passing on Turbine Blade Film Cooling

NASA Technical Reports Server (NTRS)

Heidmann, James David

1996-01-01

The effect of upstream blade row wake passing on the showerhead film cooling performance of a downstream turbine blade has been investigated through a combination of experimental and computational studies. The experiments were performed in a steady-flow annular turbine cascade facility equipped with an upstream rotating row of cylindrical rods to produce a periodic wake field similar to that found in an actual turbine. Spanwise, chordwise, and temporal resolution of the blade surface temperature were achieved through the use of an array of nickel thin-film surface gauges covering one unit cell of showerhead film hole pattern. Film effectiveness and Nusselt number values were determined for a test matrix of various injectants, injectant blowing ratios, and wake Strouhal numbers. Results indicated a demonstratable reduction in film effectiveness with increasing Strouhal number, as well as the expected increase in film effectiveness with blowing ratio. An equation was developed to correlate the span-average film effectiveness data. The primary effect of wake unsteadiness was found to be correlated well by a chordwise-constant decrement of 0.094-St. Measurable spanwise film effectiveness variations were found near the showerhead region, but meaningful unsteady variations and downstream spanwise variations were not found. Nusselt numbers were less sensitive to wake and injection changes. Computations were performed using a three-dimensional turbulent Navier-Stokes code which was modified to model wake passing and film cooling. Unsteady computations were found to agree well with steady computations provided the proper time-average blowing ratio and pressure/suction surface flow split are matched. The remaining differences were isolated to be due to the enhanced mixing in the unsteady solution caused by the wake sweeping normally on the pressure surface. Steady computations were found to be in excellent agreement with experimental Nusselt numbers, but to overpredict

Wake Vortex Research in the USA (WakeNet-USA)

NASA Technical Reports Server (NTRS)

Lang, Steve; Bryant, Wayne

2006-01-01

This viewgraph presentation reviews the cooperative work that FAA and NASA are engaged in to safely increase the capacity of the National Airspace System by studying the wake vortex operations. Wake vortex avoidance is a limiting factor in defining separation standards in the airport terminal area and could become a reducing separation standards in en route airspace.

Aircraft Wake RCS Measurement

NASA Technical Reports Server (NTRS)

Gilson, William H.

1994-01-01

A series of multi-frequency radar measurements of aircraft wakes at altitudes of 5,000 to 25,00 ft. were performed at Kwajalein, R.M.I., in May and June of 1990. Two aircraft were tested, a Learjet 35 and a Lockheed C-5A. The cross-section of the wake of the Learjet was too small for detection at Kwajalein. The wake of the C-5A, although also very small, was detected and measured at VHF, UHF, L-, S-, and C-bands, at distances behind the aircraft ranging from about one hundred meters to tens of kilometers. The data suggest that the mechanism by which aircraft wakes have detectable radar signatures is, contrary to previous expectations, unrelated to engine exhaust but instead due to turbulent mixing by the wake vortices of pre-existing index of refraction gradients in the ambient atmosphere. These measurements were of necessity performed with extremely powerful and sensitive instrumentation radars, and the wake cross-section is too small for most practical applications.

Aircraft wake RCS measurement

NASA Astrophysics Data System (ADS)

Gilson, William H.

1994-07-01

A series of multi-frequency radar measurements of aircraft wakes at altitudes of 5,000 to 25,00 ft. were performed at Kwajalein, R.M.I., in May and June of 1990. Two aircraft were tested, a Learjet 35 and a Lockheed C-5A. The cross-section of the wake of the Learjet was too small for detection at Kwajalein. The wake of the C-5A, although also very small, was detected and measured at VHF, UHF, L-, S-, and C-bands, at distances behind the aircraft ranging from about one hundred meters to tens of kilometers. The data suggest that the mechanism by which aircraft wakes have detectable radar signatures is, contrary to previous expectations, unrelated to engine exhaust but instead due to turbulent mixing by the wake vortices of pre-existing index of refraction gradients in the ambient atmosphere. These measurements were of necessity performed with extremely powerful and sensitive instrumentation radars, and the wake cross-section is too small for most practical applications.

Wake flowfields for Jovian probe

NASA Technical Reports Server (NTRS)

Engel, C. D.; Hair, L. M.

1980-01-01

The wake flow field developed by the Galileo probe as it enters the Jovian atmosphere was modeled. The wake produced by the probe is highly energetic, yielding both convective and radiative heat inputs to the base of the probe. A component mathematical model for the inviscid near and far wake, the viscous near and far wake, and near wake recirculation zone was developed. Equilibrium thermodynamics were used for both the ablation and atmospheric species. Flow fields for three entry conditions were calculated. The near viscous wave was found to exhibit a variable axial pressure distribution with the neck pressure approximately three times the base pressure. Peak wake flow field temperatures were found to be in proportion to forebody post shock temperatures.

32 CFR 935.130 - Applicability.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Applicability. 935.130 Section 935.130 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.130 Applicability. This subpart applies to self-propelled...

32 CFR 935.130 - Applicability.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Applicability. 935.130 Section 935.130 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.130 Applicability. This subpart applies to self-propelled...

32 CFR 935.130 - Applicability.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Applicability. 935.130 Section 935.130 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.130 Applicability. This subpart applies to self-propelled...

32 CFR 935.130 - Applicability.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Applicability. 935.130 Section 935.130 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.130 Applicability. This subpart applies to self-propelled...

32 CFR 935.130 - Applicability.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Applicability. 935.130 Section 935.130 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.130 Applicability. This subpart applies to self-propelled...

Self-preservation of turbulent wakes

NASA Technical Reports Server (NTRS)

Mehta, Jayesh M.

1989-01-01

The present experiment has ascertained the development of the wake flow behind NASA GA(W)-1 airfoils, showing that, in the far wake, the mean velocity profiles exhibit self-similar behavior irrespective of the upstream boundary layer's character. It is noted, however, that the processes by means of which different wakes reach the asymptotic stage can be very different for different types of wake generators.

32 CFR 935.102 - Information.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Information. 935.102 Section 935.102 National... WAKE ISLAND CODE Criminal Actions § 935.102 Information. (a) Any offense may be prosecuted by a written information signed by the Island Attorney. However, if the offense is one for which issue of a citation is...

32 CFR 935.102 - Information.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Information. 935.102 Section 935.102 National... WAKE ISLAND CODE Criminal Actions § 935.102 Information. (a) Any offense may be prosecuted by a written information signed by the Island Attorney. However, if the offense is one for which issue of a citation is...

32 CFR 935.102 - Information.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Information. 935.102 Section 935.102 National... WAKE ISLAND CODE Criminal Actions § 935.102 Information. (a) Any offense may be prosecuted by a written information signed by the Island Attorney. However, if the offense is one for which issue of a citation is...

32 CFR 935.102 - Information.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Information. 935.102 Section 935.102 National... WAKE ISLAND CODE Criminal Actions § 935.102 Information. (a) Any offense may be prosecuted by a written information signed by the Island Attorney. However, if the offense is one for which issue of a citation is...

32 CFR 935.102 - Information.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Information. 935.102 Section 935.102 National... WAKE ISLAND CODE Criminal Actions § 935.102 Information. (a) Any offense may be prosecuted by a written information signed by the Island Attorney. However, if the offense is one for which issue of a citation is...

32 CFR 935.138 - Motor bus operation.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Motor bus operation. 935.138 Section 935.138 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.138 Motor bus operation. Each person operating a motor...

32 CFR 935.138 - Motor bus operation.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Motor bus operation. 935.138 Section 935.138 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.138 Motor bus operation. Each person operating a motor...

Circadian Rhythm Sleep-Wake Disorders.

PubMed

Pavlova, Milena

2017-08-01

The endogenous circadian rhythms are one of the cardinal processes that control sleep. They are self-sustaining biological rhythms with a periodicity of approximately 24 hours that may be entrained by external zeitgebers (German for time givers), such as light, exercise, and meal times. This article discusses the physiology of the circadian rhythms, their relationship to neurologic disease, and the presentation and treatment of circadian rhythm sleep-wake disorders. Classic examples of circadian rhythms include cortisol and melatonin secretion, body temperature, and urine volume. More recently, the impact of circadian rhythm on several neurologic disorders has been investigated, such as the timing of occurrence of epileptic seizures as well as neurobehavioral functioning in dementia. Further updates include a more in-depth understanding of the symptoms, consequences, and treatment of circadian sleep-wake disorders, which may occur because of extrinsic misalignment with clock time or because of intrinsic dysfunction of the brain. An example of extrinsic misalignment occurs with jet lag during transmeridian travel or with intrinsic circadian rhythm sleep-wake disorders such as advanced or delayed sleep-wake phase disorders. In advanced sleep-wake phase disorder, which is most common in elderly individuals, sleep onset and morning arousal are undesirably early, leading to impaired evening function with excessive sleepiness and sleep-maintenance insomnia with early morning awakening. By contrast, delayed sleep-wake phase disorder is characterized by an inability to initiate sleep before the early morning hours, with subsequent delayed rise time, leading to clinical symptoms of severe sleep-onset insomnia coupled with excessive daytime sleepiness in the morning hours, as patients are unable to "sleep in" to attain sufficient sleep quantity. Irregular sleep-wake rhythm disorder is misentrainment with patches of brief sleep and wakefulness spread throughout the day

ASRS Reports on Wake Vortex Encounters

NASA Technical Reports Server (NTRS)

Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

2010-01-01

ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

Helicopter rotor wake geometry and its influence in forward flight. Volume 1: Generalized wake geometry and wake effect on rotor airloads and performance

NASA Technical Reports Server (NTRS)

Egolf, T. A.; Landgrebe, A. J.

1983-01-01

An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.

Spacecraft charging and ion wake formation in the near-Sun environment

NASA Astrophysics Data System (ADS)

Ergun, R. E.; Malaspina, D. M.; Bale, S. D.; McFadden, J. P.; Larson, D. E.; Mozer, F. S.; Meyer-Vernet, N.; Maksimovic, M.; Kellogg, P. J.; Wygant, J. R.

2010-07-01

A three-dimensional, self-consistent code is employed to solve for the static potential structure surrounding a spacecraft in a high photoelectron environment. The numerical solutions show that, under certain conditions, a spacecraft can take on a negative potential in spite of strong photoelectron currents. The negative potential is due to an electrostatic barrier near the surface of the spacecraft that can reflect a large fraction of the photoelectron flux back to the spacecraft. This electrostatic barrier forms if (1) the photoelectron density at the surface of the spacecraft greatly exceeds the ambient plasma density, (2) the spacecraft size is significantly larger than local Debye length of the photoelectrons, and (3) the thermal electron energy is much larger than the characteristic energy of the escaping photoelectrons. All of these conditions are present near the Sun. The numerical solutions also show that the spacecraft's negative potential can be amplified by an ion wake. The negative potential of the ion wake prevents secondary electrons from escaping the part of spacecraft in contact with the wake. These findings may be important for future spacecraft missions that go nearer to the Sun, such as Solar Orbiter and Solar Probe Plus.

32 CFR 935.132 - Speed limits.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Speed limits. 935.132 Section 935.132 National... WAKE ISLAND CODE Motor Vehicle Code § 935.132 Speed limits. Each person operating a motor vehicle on... day, road and weather conditions, the kind of motor vehicle, and the proximity to persons or buildings...

32 CFR 935.132 - Speed limits.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Speed limits. 935.132 Section 935.132 National... WAKE ISLAND CODE Motor Vehicle Code § 935.132 Speed limits. Each person operating a motor vehicle on... day, road and weather conditions, the kind of motor vehicle, and the proximity to persons or buildings...

32 CFR 935.132 - Speed limits.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Speed limits. 935.132 Section 935.132 National... WAKE ISLAND CODE Motor Vehicle Code § 935.132 Speed limits. Each person operating a motor vehicle on... day, road and weather conditions, the kind of motor vehicle, and the proximity to persons or buildings...

32 CFR 935.133 - Right-of-way.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Right-of-way. 935.133 Section 935.133 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.133 Right-of-way. (a) A pedestrian has the right-of-way over...

Dynamic wake prediction and visualization with uncertainty analysis

NASA Technical Reports Server (NTRS)

Holforty, Wendy L. (Inventor); Powell, J. David (Inventor)

2005-01-01

A dynamic wake avoidance system utilizes aircraft and atmospheric parameters readily available in flight to model and predict airborne wake vortices in real time. A novel combination of algorithms allows for a relatively simple yet robust wake model to be constructed based on information extracted from a broadcast. The system predicts the location and movement of the wake based on the nominal wake model and correspondingly performs an uncertainty analysis on the wake model to determine a wake hazard zone (no fly zone), which comprises a plurality of wake planes, each moving independently from another. The system selectively adjusts dimensions of each wake plane to minimize spatial and temporal uncertainty, thereby ensuring that the actual wake is within the wake hazard zone. The predicted wake hazard zone is communicated in real time directly to a user via a realistic visual representation. In an example, the wake hazard zone is visualized on a 3-D flight deck display to enable a pilot to visualize or see a neighboring aircraft as well as its wake. The system substantially enhances the pilot's situational awareness and allows for a further safe decrease in spacing, which could alleviate airport and airspace congestion.

Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.

2017-01-01

High-resolution simulations of rotor/vortex-wake interaction for a UH60-A rotor under BVI and dynamic stallconditions were carried out with the OVERFLOW Navier-Stokes code.a. The normal force and pitching moment variation with azimuth angle were in good overall agreementwith flight-test data, similar to other CFD results reported in the literature.b. The wake-grid resolution did not have a significant effect on the rotor-blade airloads. This surprisingresult indicates that a wake grid spacing of (Delta)S=10% ctip is sufficient for engineering airloads predictionfor hover and forward flight. This assumes high-resolution body grids, high-order spatial accuracy, anda hybrid RANS/DDES turbulence model.c. Three-dimensional dynamic stall was found to occur due the presence of blade-tip vortices passing overa rotor blade on the retreating side. This changed the local airfoil angle of attack, causing stall, unlikethe 2D perspective of pure pitch oscillation of the local airfoil section.

Simulating Wake Vortex Detection with the Sensivu Doppler Wind Lidar Simulator

NASA Technical Reports Server (NTRS)

Ramsey, Dan; Nguyen, Chi

2014-01-01

In support of NASA's Atmospheric Environment Safety Technologies NRA research topic on Wake Vortex Hazard Investigation, Aerospace Innovations (AI) investigated a set of techniques for detecting wake vortex hazards from arbitrary viewing angles, including axial perspectives. This technical report describes an approach to this problem and presents results from its implementation in a virtual lidar simulator developed at AI. Threedimensional data volumes from NASA's Terminal Area Simulation System (TASS) containing strong turbulent vortices were used as the atmospheric domain for these studies, in addition to an analytical vortex model in 3-D space. By incorporating a third-party radiative transfer code (BACKSCAT 4), user-defined aerosol layers can be incorporated into atmospheric models, simulating attenuation and backscatter in different environmental conditions and altitudes. A hazard detection algorithm is described that uses a twocomponent spectral model to identify vortex signatures observable from arbitrary angles.

Wake Turbulence Training Aid.

DOT National Transportation Integrated Search

1995-04-01

The goal of the Wake Turbulence Training Aid is to reduce the number of wake-turbulence related accidents and incidents by improving the pilot's and air traffic controller's decision making and situational awareness through increased and shared under...

Aeroacoustic Codes for Rotor Harmonic and BVI Noise. CAMRAD.Mod1/HIRES: Methodology and Users' Manual

NASA Technical Reports Server (NTRS)

Boyd, D. Douglas, Jr.; Brooks, Thomas F.; Burley, Casey L.; Jolly, J. Ralph, Jr.

1998-01-01

This document details the methodology and use of the CAMRAD.Mod1/HIRES codes, which were developed at NASA Langley Research Center for the prediction of helicopter harmonic and Blade-Vortex Interaction (BVI) noise. CANMAD.Mod1 is a substantially modified version of the performance/trim/wake code CANMAD. High resolution blade loading is determined in post-processing by HIRES and an associated indicial aerodynamics code. Extensive capabilities of importance to noise prediction accuracy are documented, including a new multi-core tip vortex roll-up wake model, higher harmonic and individual blade control, tunnel and fuselage correction input, diagnostic blade motion input, and interfaces for acoustic and CFD aerodynamics codes. Modifications and new code capabilities are documented with examples. A users' job preparation guide and listings of variables and namelists are given.

Separation of circadian and wake duration-dependent modulation of EEG activation during wakefulness

NASA Technical Reports Server (NTRS)

Cajochen, C.; Wyatt, J. K.; Czeisler, C. A.; Dijk, D. J.

2002-01-01

The separate contribution of circadian rhythmicity and elapsed time awake on electroencephalographic (EEG) activity during wakefulness was assessed. Seven men lived in an environmental scheduling facility for 4 weeks and completed fourteen 42.85-h 'days', each consisting of an extended (28.57-h) wake episode and a 14.28-h sleep opportunity. The circadian rhythm of plasma melatonin desynchronized from the 42.85-h day. This allowed quantification of the separate contribution of circadian phase and elapsed time awake to variation in EEG power spectra (1-32 Hz). EEG activity during standardized behavioral conditions was markedly affected by both circadian phase and elapsed time awake in an EEG frequency- and derivation-specific manner. The nadir of the circadian rhythm in alpha (8-12 Hz) activity in both fronto-central and occipito-parietal derivations occurred during the biological night, close to the crest of the melatonin rhythm. The nadir of the circadian rhythm of theta (4.5-8 Hz) and beta (20-32 Hz) activity in the fronto-central derivation was located close to the onset of melatonin secretion, i.e. during the wake maintenance zone. As time awake progressed, delta frequency (1-4.5 Hz) and beta (20-32 Hz) activity rose monotonically in frontal derivations. The interaction between the circadian and wake-dependent increase in frontal delta was such that the intrusion of delta was minimal when sustained wakefulness coincided with the biological day, but pronounced during the biological night. Our data imply that the circadian pacemaker facilitates frontal EEG activation during the wake maintenance zone, by generating an arousal signal that prevents the intrusion of low-frequency EEG components, the propensity for which increases progressively during wakefulness.

Dynamics and control of hydrofoil wakes

NASA Astrophysics Data System (ADS)

Kjeldsen, Morten; Wosnik, Martin; Arndt, Roger

2008-11-01

The problem of rotor-stator interaction (RSI) is an issue within the field of turbomachinery. The flow field entering the rotor cascade will depend on the stator blade to blade velocity distributions, and the viscous wake trailing cascade blades. This flow field is also dependent on the mode of operation, e.g by changing the angle of each blade in hydroturbines. Manipulating the stator viscous wakes is one method to minimize the problems associated RSI; i.e. noise and vibration. In order to explore this concept, a comprehensive experimental program was carried out in a high-speed water tunnel utilizing a series of NACA 0015 hydrofoils. Baseline wake data were collected with a hydraulically smooth foil and compared with two foils modified with two sizes of vortex generators (VG) positioned close to the leading edge of the foil. Not only was the effect of the modifications on wake spreading investigated but also the effect on wake dynamics such as vortex shedding was studied. A high frame-rate PIV system was used at recording rates of 1 and 10 kHz to map the near wake region, extending roughly 1 chord-length downstream the trailing edge, over a range of angles of attack and velocities. The results show that wake dynamics and wake characteristics, i.e. velocity deficit and width, scale with average drag. It was demonstrated that the use of VGs can improve both the dynamics and spreading characteristics of the wake.

32 CFR 935.140 - Motor vehicle maintenance and equipment.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Motor vehicle maintenance and equipment. 935.140 Section 935.140 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Motor Vehicle Code § 935.140 Motor vehicle maintenance and equipment. (a) Each person who has custod...

32 CFR 935.134 - Arm signals.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Arm signals. 935.134 Section 935.134 National... WAKE ISLAND CODE Motor Vehicle Code § 935.134 Arm signals. (a) Any person operating a motor vehicle and... signal for a turn or stop is made by fully extending the left arm as follows: (1) Left turn—extend left...

32 CFR 935.134 - Arm signals.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Arm signals. 935.134 Section 935.134 National... WAKE ISLAND CODE Motor Vehicle Code § 935.134 Arm signals. (a) Any person operating a motor vehicle and... signal for a turn or stop is made by fully extending the left arm as follows: (1) Left turn—extend left...

32 CFR 935.134 - Arm signals.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Arm signals. 935.134 Section 935.134 National... WAKE ISLAND CODE Motor Vehicle Code § 935.134 Arm signals. (a) Any person operating a motor vehicle and... signal for a turn or stop is made by fully extending the left arm as follows: (1) Left turn—extend left...

Cosmic string wakes and large-scale structure

NASA Technical Reports Server (NTRS)

Charlton, Jane C.

1988-01-01

The formation of structure from infinite cosmic string wakes is modeled for a universe dominated by cold dark matter (CDM). Cross-sectional slices through the wake distribution tend to outline empty regions with diameters which are not inconsistent with the range of sizes of the voids in the CfA slice of the universe. The topology of the wake distribution is found to be spongy rather than cell-like. Correlations between CDM wakes do not extend much beyond a horizon length, so it is unlikely that CDM wakes are responsible for the correlations between clusters of galaxies. An estimate of the fraction of matter to accrete onto CDM wakes indicates that wakes could be more important in galaxy formation than previously anticipated.

Self-similarity and turbulence characteristics of wind turbine wakes via large-eddy simulation (Invited)

NASA Astrophysics Data System (ADS)

Xie, S.; Archer, C. L.

2013-12-01

In this study, a new large-eddy simulation code, the Wind Turbine and Turbulence Simulator (WiTTS), is developed to study the wake generated from a single wind turbine in the neutral ABL. The WiTTS formulation is based on a scale-dependent Lagrangian dynamical model of the sub-grid shear stress and uses actuator lines to simulate the effects of the rotating blades. WiTTS is first tested against wind tunnel experiments and then used to study the commonly-used assumptions of self-similarity and axis-symmetry of the wake under neutral conditions for a variety of wind speeds and turbine properties. The mean velocity deficit shows good self-similarity properties following a normal distribution in the horizontal plane at the hub-height level. Self-similarity is a less valid approximation in the vertical near the ground, due to strong wind shear and ground effects. The mean velocity deficit is strongly dependent on the thrust coefficient or induction factor. A new relationship is proposed to model the mean velocity deficit along the centerline at the hub-height level to fit the LES results piecewise throughout the wake. A logarithmic function is used in the near and intermediate wake regions whereas a power function is used in the far-wake. These two functions provide a better fit to both simulated and observed wind velocity deficits than other functions previously used in wake models such as WAsP. The wind shear and impact with the ground cause an anisotropy in the expansion of the wake such that the wake grows faster horizontally than vertically. The wake deforms upon impact with the ground and spreads laterally. WiTTS is also used to study the turbulence characteristics in the wake. Aligning with the mean wind direction, the streamwise component of turbulence intensity is the dominant among the three components and thus it is further studied. The highest turbulence intensity occurs near the top-tip level. The added turbulence intensity increases fast in the near-wake

Foraging behavior of Long-tailed Ducks in a ferry wake

USGS Publications Warehouse

Perry, Matthew C.

2012-01-01

Clangula hyemalis (Long-tailed Ducks) were observed diving in the wake of the Nantucket Island ferry during December over a 5-year period (2005–2009). The unusual diving behavior appeared to be related to foraging, but could not be confirmed. Long-tailed Ducks typically feed on more mobile prey than most other diving ducks, and it is speculated that the propeller wash in shallow water dislodged or disturbed prey and provided an enhanced feeding opportunity. Long-tailed Ducks collected while feeding in a disturbed area near a clamming boat not far from the ferry channel were feeding predominantly on Crangon septemspinosa (Sand Shrimp) that apparently had been dislodged by the clamming operation.

Wake Vortex Advisory System (WakeVAS) Evaluation of Impacts on the National Airspace System

NASA Technical Reports Server (NTRS)

Smith, Jeremy C.; Dollyhigh, Samuel M.

2005-01-01

This report is one of a series that describes an ongoing effort in high-fidelity modeling/simulation, evaluation and analysis of the benefits and performance metrics of the Wake Vortex Advisory System (WakeVAS) Concept of Operations being developed as part of the Virtual Airspace Modeling and Simulation (VAMS) project. A previous study, determined the overall increases in runway arrival rates that could be achieved at 12 selected airports due to WakeVAS reduced aircraft spacing under Instrument Meteorological Conditions. This study builds on the previous work to evaluate the NAS wide impacts of equipping various numbers of airports with WakeVAS. A queuing network model of the National Airspace System, built by the Logistics Management Institute, Mclean, VA, for NASA (LMINET) was used to estimate the reduction in delay that could be achieved by using WakeVAS under non-visual meteorological conditions for the projected air traffic demand in 2010. The results from LMINET were used to estimate the total annual delay reduction that could be achieved and from this, an estimate of the air carrier variable operating cost saving was made.

Extreme changes to barrier islands along the central Gulf of Mexico coast during Hurricane Katrina: Chapter 5C in Science and the storms-the USGS response to the hurricanes of 2005

USGS Publications Warehouse

Sallenger, Asbury; Wright, Wayne; Lillycrop, Jeff; Howd, Peter; Stockdon, Hilary; Guy, Kristy K.; Morgan, Karen

2007-01-01

Hurricane Katrina caused extreme changes to the barrier islands of the central Gulf of Mexico coast. Dauphin Island, Ala., migrated landward and stranded the remains of its oceanfront row homes in the sea. Chandeleur Islands, La., were completely stripped of their sand, leaving only marshy outcrops in the storm's wake.

Wake-Vortex Hazards During Cruise

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.; James, Kevin D.; Nixon, David (Technical Monitor)

1998-01-01

Even though the hazard posed by lift-generated wakes of subsonic transport aircraft has been studied extensively for approach and departure at airports, only a small amount of effort has gone into the potential hazard at cruise altitude. This paper reports on a studio of the wake-vortex hazard during cruise because encounters may become more prevalent when free-flight becomes available and each aircraft, is free to choose its own route between destinations. In order to address the problem, the various fluid-dynamic stages that vortex wakes usually go through as they age will be described along with estimates of the potential hazard that each stage poses. It appears that a rolling-moment hazard can be just as severe at cruise as for approach at airports, but it only persists for several minutes. However, the hazard posed by the downwash in the wake due to the lift on the generator aircraft persists for tens of minutes in a long narrow region behind the generating aircraft. The hazard consists of severe vertical loads when an encountering aircraft crosses the wake. A technique for avoiding vortex wakes at cruise altitude will be described. To date the hazard posed by lift-generated vortex wakes and their persistence at cruise altitudes has been identified and subdivided into several tasks. Analyses of the loads to be encounter and are underway and should be completed shortly. A review of published literature on the subject has been nearly completed (see text) and photographs of vortex wakes at cruise altitudes have been taken and the various stages of decay have been identified. It remains to study and sort the photographs for those that best illustrate the various stages of decay after they are shed by subsonic transport aircraft at cruise altitudes. The present status of the analysis and the paper are described.

The Effect of Flow Curvature on the Axisymmetric Wake

NASA Astrophysics Data System (ADS)

Holmes, Marlin; Naughton, Jonathan

2016-11-01

The swirling turbulent wake is a perturbation to the canonical axisymmetric turbulent wake. Past studies of the axisymmetric turbulent wake have increased understanding of wake Reynolds number influence on wake characteristics such as centerline wake velocity deficit and wake width. In comparison, the axisymmetric turbulent swirling wake has received little attention. Earlier work by our group has shown that the addition of swirl can change the characteristics of the wake. The goal of this current work is to examine how wake mean flow quantities are related to the wake Reynolds number and the swirl number, where the latter quantity is the ratio of the angular momentum flux to the axial momentum deficit flux. A custom designed swirling wake generator is used in a low turbulence intensity wind tunnel flow to study the turbulent swirling wake in isolation. Stereoscopic Particle Image Velocimetry is used to obtain three component velocity fields in the axial-radial plane. From this data, the wake Reynolds number, the swirl number, centerline velocity decay, wake width, and other relevant wake mean flow quantities are determined. Using these results, the impact of swirl on wake development is discussed. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award # DE-SC0012671.

Three-Phased Wake Vortex Decay

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Ahmad, Nashat N.; Switzer, George S.; LimonDuparcmeur, Fanny M.

2010-01-01

A detailed parametric study is conducted that examines vortex decay within turbulent and stratified atmospheres. The study uses a large eddy simulation model to simulate the out-of-ground effect behavior of wake vortices due to their interaction with atmospheric turbulence and thermal stratification. This paper presents results from a parametric investigation and suggests improvements for existing fast-time wake prediction models. This paper also describes a three-phased decay for wake vortices. The third phase is characterized by a relatively slow rate of circulation decay, and is associated with the ringvortex stage that occurs following vortex linking. The three-phased decay is most prevalent for wakes imbedded within environments having low-turbulence and near-neutral stratification.

Application of a Two-dimensional Unsteady Viscous Analysis Code to a Supersonic Throughflow Fan Stage

NASA Technical Reports Server (NTRS)

Steinke, Ronald J.

1989-01-01

The Rai ROTOR1 code for two-dimensional, unsteady viscous flow analysis was applied to a supersonic throughflow fan stage design. The axial Mach number for this fan design increases from 2.0 at the inlet to 2.9 at the outlet. The Rai code uses overlapped O- and H-grids that are appropriately packed. The Rai code was run on a Cray XMP computer; then data postprocessing and graphics were performed to obtain detailed insight into the stage flow. The large rotor wakes uniformly traversed the rotor-stator interface and dispersed as they passed through the stator passage. Only weak blade shock losses were computerd, which supports the design goals. High viscous effects caused large blade wakes and a low fan efficiency. Rai code flow predictions were essentially steady for the rotor, and they compared well with Chima rotor viscous code predictions based on a C-grid of similar density.

Wake shed by an accelerating carangiform fish

NASA Astrophysics Data System (ADS)

Ting, Shang-Chieh; Yang, Jing-Tang

2008-11-01

We reveal an important fact that momentum change observed in the wake of an accelerating carangiform fish does not necessarily elucidate orientations of propulsive forces produced. An accelerating Crucian Carp (Carassius auratus) was found to shed a wake with net forward fluid momentum, which seemed drag-producing. Based on Newton's law, however, an accelerating fish is expected to shed a thrust wake with net rearward fluid momentum, rather than a drag wake. The unusual wake pattern observed is considered to be resulted primarily from the effect of pressure gradient created by accelerating movements of the fish. Ambient fluids tend to be sucked into low pressure zones behind an accelerating fish, resulting in forward orientations of jets recognizable in the wake. Accordingly, as to an accelerating fish, identifying force orientations from the wake requires considering also the effect of pressure gradient.

Multi-Model Ensemble Wake Vortex Prediction

NASA Technical Reports Server (NTRS)

Koerner, Stephan; Holzaepfel, Frank; Ahmad, Nash'at N.

2015-01-01

Several multi-model ensemble methods are investigated for predicting wake vortex transport and decay. This study is a joint effort between National Aeronautics and Space Administration and Deutsches Zentrum fuer Luft- und Raumfahrt to develop a multi-model ensemble capability using their wake models. An overview of different multi-model ensemble methods and their feasibility for wake applications is presented. The methods include Reliability Ensemble Averaging, Bayesian Model Averaging, and Monte Carlo Simulations. The methodologies are evaluated using data from wake vortex field experiments.

Contributions of the stochastic shape wake model to predictions of aerodynamic loads and power under single wake conditions

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

Doubrawa, P.; Barthelmie, R. J.; Wang, H.

The contribution of wake meandering and shape asymmetry to load and power estimates is quantified by comparing aeroelastic simulations initialized with different inflow conditions: an axisymmetric base wake, an unsteady stochastic shape wake, and a large-eddy simulation with rotating actuator-line turbine representation. Time series of blade-root and tower base bending moments are analyzed. We find that meandering has a large contribution to the fluctuation of the loads. Moreover, considering the wake edge intermittence via the stochastic shape model improves the simulation of load and power fluctuations and of the fatigue damage equivalent loads. Furthermore, these results indicate that the stochasticmore » shape wake simulator is a valuable addition to simplified wake models when seeking to obtain higher-fidelity computationally inexpensive predictions of loads and power.« less

Contributions of the stochastic shape wake model to predictions of aerodynamic loads and power under single wake conditions

DOE PAGES

Doubrawa, P.; Barthelmie, R. J.; Wang, H.; ...

2016-10-03

The contribution of wake meandering and shape asymmetry to load and power estimates is quantified by comparing aeroelastic simulations initialized with different inflow conditions: an axisymmetric base wake, an unsteady stochastic shape wake, and a large-eddy simulation with rotating actuator-line turbine representation. Time series of blade-root and tower base bending moments are analyzed. We find that meandering has a large contribution to the fluctuation of the loads. Moreover, considering the wake edge intermittence via the stochastic shape model improves the simulation of load and power fluctuations and of the fatigue damage equivalent loads. Furthermore, these results indicate that the stochasticmore » shape wake simulator is a valuable addition to simplified wake models when seeking to obtain higher-fidelity computationally inexpensive predictions of loads and power.« less

Orexin Gene Therapy Restores the Timing and Maintenance of Wakefulness in Narcoleptic Mice

PubMed Central

Kantor, Sandor; Mochizuki, Takatoshi; Lops, Stefan N.; Ko, Brian; Clain, Elizabeth; Clark, Erika; Yamamoto, Mihoko; Scammell, Thomas E.

2013-01-01

Study Objectives: Narcolepsy is caused by selective loss of the orexin/hypocretin-producing neurons of the hypothalamus. For patients with narcolepsy, chronic sleepiness is often the most disabling symptom, but current therapies rarely normalize alertness and do not address the underlying orexin deficiency. We hypothesized that the sleepiness of narcolepsy would substantially improve if orexin signaling were restored in specific brain regions at appropriate times of day. Design: We used gene therapy to restore orexin signaling in a mouse model of narcolepsy. In these Atx mice, expression of a toxic protein (ataxin-3) selectively kills the orexin neurons. Interventions: To induce ectopic expression of the orexin neuropeptides, we microinjected an adeno-associated viral vector coding for prepro-orexin plus a red fluorescence protein (AAV-orexin) into the mediobasal hypothalamus of Atx and wild-type mice. Control mice received an AAV coding only for red fluorescence protein. Two weeks later, we recorded sleep/wake behavior, locomotor activity, and body temperature and examined the patterns of orexin expression. Measurements and Results: Atx mice rescued with AAV-orexin produced long bouts of wakefulness and had a normal diurnal pattern of arousal, with the longest bouts of wake and the highest amounts of locomotor activity in the first hours of the night. In addition, AAV-orexin improved the timing of rapid eye movement sleep and the consolidation of nonrapid eye movement sleep in Atx mice. Conclusions: These substantial improvements in sleepiness and other symptoms of narcolepsy demonstrate the effectiveness of orexin gene therapy in a mouse model of narcolepsy. Additional work is needed to optimize this approach, but in time, AAV-orexin could become a useful therapeutic option for patients with narcolepsy. Citation: Kantor S; Mochizuki T; Lops SN; Ko B; Clain E; Clark E; Yamamoto M; Scammell TE. Orexin gene therapy restores the timing and maintenance of wakefulness

Discharge properties of upper airway motor units during wakefulness and sleep.

PubMed

Trinder, John; Jordan, Amy S; Nicholas, Christian L

2014-01-01

Upper airway muscle motoneurons, as assessed at the level of the motor unit, have a range of different discharge patterns, varying as to whether their activity is modulated in phase with the respiratory cycle, are predominantly inspiratory or expiratory, or are phasic as opposed to tonic. Two fundamental questions raised by this observation are: how are synaptic inputs from premotor neurons distributed over motoneurons to achieve these different discharge patterns; and how do different discharge patterns contribute to muscle function? We and others have studied the behavior of genioglossus (GG) and tensor palatini (TP) single motor units at transitions from wakefulness to sleep (sleep onset), from sleep to wakefulness (arousal from sleep), and during hypercapnia. Results indicate that decreases or increases in GG and TP muscle activity occur as a consequence of derecruitment or recruitment, respectively, of phasic and tonic inspiratory-modulated motoneurons, with only minor changes in rate coding. Further, sleep-wake state and chemical inputs to this "inspiratory system" appear to be mediated through the respiratory pattern generator. In contrast, phasic and tonic expiratory units and units with a purely tonic pattern, the "tonic system," are largely unaffected by sleep-wake state, and are only weakly influenced by chemical stimuli and the respiratory cycle. We speculate that the "inspiratory system" produces gross changes in upper airway muscle activity in response to changes in respiratory drive, while the "tonic system" fine tunes airway configuration with activity in this system being determined by local mechanical conditions. © 2014 Elsevier B.V. All rights reserved.

Wake measurements in a strong adverse pressure gradient

NASA Technical Reports Server (NTRS)

Hoffenberg, R.; Sullivan, John P.; Schneider, S. P.

1994-01-01

The behavior of wakes in adverse pressure gradients is critical to the performance of high-lift systems for transport aircraft. Wake deceleration is known to lead to sudden thickening and the onset of reversed flow; this 'wake bursting' phenomenon can occur while surface flows remain attached. Although 'wake bursting' is known to be important for high-lift systems, no detailed measurements of 'burst' wakes have ever been reported. Wake bursting has been successfully achieved in the wake of a flat plate as it decelerated in a two-dimensional diffuser, whose sidewalls were forced to remain attached by use of slot blowing. Pilot probe surveys, L.D.V. measurements, and flow visualization have been used to investigate the physics of this decelerated wake, through the onset of reversed flow.

Evolution of Rotor Wake in Swirling Flow

NASA Technical Reports Server (NTRS)

El-Haldidi, Basman; Atassi, Hafiz; Envia, Edmane; Podboy, Gary

2000-01-01

A theory is presented for modeling the evolution of rotor wakes as a function of axial distance in swirling mean flows. The theory, which extends an earlier work to include arbitrary radial distributions of mean swirl, indicates that swirl can significantly alter the wake structure of the rotor especially at large downstream distances (i.e., for moderate to large rotor-stator spacings). Using measured wakes of a representative scale model fan stage to define the mean swirl and initial wake perturbations, the theory is used to predict the subsequent evolution of the wakes. The results indicate the sensitivity of the wake evolution to the initial profile and the need to have complete and consistent initial definition of both velocity and pressure perturbations.

Spatial Linear Instability of Confluent Wake/Boundary Layers

NASA Technical Reports Server (NTRS)

Liou, William W.; Liu, Feng-Jun; Rumsey, C. L. (Technical Monitor)

2001-01-01

The spatial linear instability of incompressible confluent wake/boundary layers is analyzed. The flow model adopted is a superposition of the Blasius boundary layer and a wake located above the boundary layer. The Orr-Sommerfeld equation is solved using a global numerical method for the resulting eigenvalue problem. The numerical procedure is validated by comparing the present solutions for the instability of the Blasius boundary layer and for the instability of a wake with published results. For the confluent wake/boundary layers, modes associated with the boundary layer and the wake, respectively, are identified. The boundary layer mode is found amplified as the wake approaches the wall. On the other hand, the modes associated with the wake, including a symmetric mode and an antisymmetric mode, are stabilized by the reduced distance between the wall and the wake. An unstable mode switching at low frequency is observed where the antisymmetric mode becomes more unstable than the symmetric mode when the wake velocity defect is high.

Absolute instability of the Gaussian wake profile

NASA Technical Reports Server (NTRS)

Hultgren, Lennart S.; Aggarwal, Arun K.

1987-01-01

Linear parallel-flow stability theory has been used to investigate the effect of viscosity on the local absolute instability of a family of wake profiles with a Gaussian velocity distribution. The type of local instability, i.e., convective or absolute, is determined by the location of a branch-point singularity with zero group velocity of the complex dispersion relation for the instability waves. The effects of viscosity were found to be weak for values of the wake Reynolds number, based on the center-line velocity defect and the wake half-width, larger than about 400. Absolute instability occurs only for sufficiently large values of the center-line wake defect. The critical value of this parameter increases with decreasing wake Reynolds number, thereby indicating a shrinking region of absolute instability with decreasing wake Reynolds number. If backflow is not allowed, absolute instability does not occur for wake Reynolds numbers smaller than about 38.

Effects of magnetic islands on drift wave instability

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

Jiang, P., E-mail: jiangp@pku.edu.cn; Department of Physics and Astronomy, University of California, Irvine, California 92697; Lin, Z., E-mail: zhihongl@uci.edu

2014-12-15

Magnetic islands have been implemented in the gyrokinetic toroidal code to study the effects of the islands on microturbulence. The pressure profile flattening is verified in the simulation with the islands. Simulations of ion temperature gradient instability find that different toroidal modes are linearly coupled together and that toroidal spectra become broader when the island width increases. The real frequencies and growth rates of different toroidal modes approach each other with the averaged value independent of the island width. The linear mode structures are enhanced at the island separatrices and weakened at the island centers, consistent with the flattening ofmore » the pressure profile inside the islands.« less

Coupled wake boundary layer model of windfarms

NASA Astrophysics Data System (ADS)

Stevens, Richard; Gayme, Dennice; Meneveau, Charles

2014-11-01

We present a coupled wake boundary layer (CWBL) model that describes the distribution of the power output in a windfarm. The model couples the traditional, industry-standard wake expansion/superposition approach with a top-down model for the overall windfarm boundary layer structure. Wake models capture the effect of turbine positioning, while the top-down approach represents the interaction between the windturbine wakes and the atmospheric boundary layer. Each portion of the CWBL model requires specification of a parameter that is unknown a-priori. The wake model requires the wake expansion rate, whereas the top-down model requires the effective spanwise turbine spacing within which the model's momentum balance is relevant. The wake expansion rate is obtained by matching the mean velocity at the turbine from both approaches, while the effective spanwise turbine spacing is determined from the wake model. Coupling of the constitutive components of the CWBL model is achieved by iterating these parameters until convergence is reached. We show that the CWBL model predictions compare more favorably with large eddy simulation results than those made with either the wake or top-down model in isolation and that the model can be applied successfully to the Horns Rev and Nysted windfarms. The `Fellowships for Young Energy Scientists' (YES!) of the Foundation for Fundamental Research on Matter supported by NWO, and NSF Grant #1243482.

Cloud patterns lee of Hawaii Island: A synthesis of satellite observations and numerical simulation

NASA Astrophysics Data System (ADS)

Yang, Yang; Xie, Shang-Ping; Hafner, Jan

2008-08-01

Standing well above the trade wind inversion, Hawaii Island (maximum elevation ˜4.2 km) splits the northeast trade winds and induces a westerly reverse flow in the wake. Satellite observations and regional model simulations are used to investigate circulation effects on lee cloud formation during summer. Over the island, the cloud distribution is consistent with orographic-induced vertical motions. Over the lee ocean, our analysis reveals a cloud band that extends southwestward over a few tens of kilometers from the southwest coast of the island. This southwest lee cloud band is most pronounced in the afternoon, anchored by strong convergence and maintained by in situ cloud production in the upward motion. Such an offshore cloud band is not found off the northwest coast, an asymmetry possibly due to the Coriolis effect on the orographic flow. Off the Kona coast, the dynamically induced westerly reverse flow keeps the wake cool and nearly free of clouds during the day. Along the Kona coast, clouds are blown offshore from the island by the easterly trades in the afternoon in a layer above the reverse flow. Deprived of in situ production, these afternoon Kona coast clouds dissipate rapidly offshore. At night, the offshore land/valley breezes converge onto the onshore reverse flow, and a cloud deck forms on and off the Kona coast, bringing nighttime rain as observed at land stations. To illustrate the circulation effect, lee cloud formation is compared between tall Hawaii and short Kauai/Oahu Islands, which feature the flow-around and flow-over regimes, respectively. Effects of trade wind strength on the leeside cloudiness are also studied.

Orexin gene therapy restores the timing and maintenance of wakefulness in narcoleptic mice.

PubMed

Kantor, Sandor; Mochizuki, Takatoshi; Lops, Stefan N; Ko, Brian; Clain, Elizabeth; Clark, Erika; Yamamoto, Mihoko; Scammell, Thomas E

2013-08-01

Narcolepsy is caused by selective loss of the orexin/hypocretin-producing neurons of the hypothalamus. For patients with narcolepsy, chronic sleepiness is often the most disabling symptom, but current therapies rarely normalize alertness and do not address the underlying orexin deficiency. We hypothesized that the sleepiness of narcolepsy would substantially improve if orexin signaling were restored in specific brain regions at appropriate times of day. We used gene therapy to restore orexin signaling in a mouse model of narcolepsy. In these Atx mice, expression of a toxic protein (ataxin-3) selectively kills the orexin neurons. To induce ectopic expression of the orexin neuropeptides, we microinjected an adeno-associated viral vector coding for prepro-orexin plus a red fluorescence protein (AAV-orexin) into the mediobasal hypothalamus of Atx and wild-type mice. Control mice received an AAV coding only for red fluorescence protein. Two weeks later, we recorded sleep/wake behavior, locomotor activity, and body temperature and examined the patterns of orexin expression. Atx mice rescued with AAV-orexin produced long bouts of wakefulness and had a normal diurnal pattern of arousal, with the longest bouts of wake and the highest amounts of locomotor activity in the first hours of the night. In addition, AAV-orexin improved the timing of rapid eye movement sleep and the consolidation of nonrapid eye movement sleep in Atx mice. These substantial improvements in sleepiness and other symptoms of narcolepsy demonstrate the effectiveness of orexin gene therapy in a mouse model of narcolepsy. Additional work is needed to optimize this approach, but in time, AAV-orexin could become a useful therapeutic option for patients with narcolepsy.

Calculation of wake vortex structures in the near-field wake behind cruising aircraft

NASA Astrophysics Data System (ADS)

Ehret, T.; Oertel, H.

Wake flows behind cruising aircraft influence the distribution of the exhaust gases. A three-dimensional vortex filament method was developed to calculate the vortex structures and the velocity field of the vorticity dominated wake flows as an integration of the Biot-Savart law. For three-dimensional vortex filament calculations, self-induction singularities were prevented using a finite vortex core for each vortex filament. Numerical simulations show the vortex structures and the velocity field in the wake behind a cruising Boeing 747 as a result of the integration of the Biot-Savart law. It is further shown how the structures of the fully rolled-up trailing vortices depend on the wing span loading, i.e. the circulation distribution.

Validation of Vortex-Lattice Method for Loads on Wings in Lift-Generated Wakes

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.

1995-01-01

A study is described that evaluates the accuracy of vortex-lattice methods when they are used to compute the loads induced on aircraft as they encounter lift-generated wakes. The evaluation is accomplished by the use of measurements made in the 80 by 120 ft Wind Tunnel of the lift, rolling moment, and downwash in the wake of three configurations of a model of a subsonic transport aircraft. The downwash measurements are used as input for a vortex-lattice code in order to compute the lift and rolling moment induced on wings that have a span of 0.186, 0.510, or 1.022 times the span of the wake-generating model. Comparison of the computed results with the measured lift and rolling-moment distributions the vortex-lattice method is very reliable as long as the span of the encountering or following wing is less than about 0.2 of the generator span. As the span of the following wing increases above 0.2, the vortex-lattice method continues to correctly predict the trends and nature of the induced loads, but it overpredicts the magnitude of the loads by increasing amounts.

Vortex wake control via smart structures technology

NASA Astrophysics Data System (ADS)

Quackenbush, Todd R.; Bilanin, Alan J.; McKillip, Robert M., Jr.

1996-05-01

Control of trailing vortex wakes is an important challenges for both military and civilian applications. This paper summarizes an assessment of the feasibility of mitigating adverse vortex wake effects using control surfaces actuated via Shape Memory Alloy (SMA) technology. The assessment involved a combined computational/design analysis that identified methods for introducing small secondary vortices to promote the deintensification of vortex wakes of submarines and aircraft. Computational analyses of wake breakup using this `vortex leveraging' strategy were undertaken, and showed dramatic increases in the dissipation rate of concentrated vortex wakes. This paper briefly summarizes these results and describes the preliminary design of actuation mechanisms for the deflectable surfaces that effect the required time-varying wake perturbations. These surfaces, which build on the high-force, high- deflection capabilities of SMA materials, are shown to be well suited for the very low frequency actuation requirements of the wake deintensification mission. The paper outlines the assessment of device performance capabilities and describes the sizing studies undertaken for full-scale Vortex Leveraging Tabs (VLTs) designed for use in hydrodynamic and aerodynamic applications. Results obtained to date indicate that the proposed VLTs can accelerate wake breakup by over a factor of three and can be implemented using deflectable surfaces actuated using SMAs.

Nonlinear Kinetic Instabilities in Plasma Wakes

NASA Astrophysics Data System (ADS)

Hutchinson, I. H.; Haakonsen, C. B.

2015-12-01

Relative motion of a plasma and an embedded perturbing solid objectproduces a plasma wake, which is kinetically unstable. For moons,asteroids, spacecraft, probes, and planets without a magnetosphere theresponse is dominantly electrostatic, although generally with abackground magnetic field. Using high-fidelity particle-in-cellsimulations, we have observed the development of kinetic instabilitiesand their non-linear consequences in representative wakes. We havealso explained the observations with semi-analytical non-lineartheory. The ion and electron distribution function shapes are stronglyperturbed in the wake region. The ions form two opposite beamsdirected inward along the guiding magnetic field, in part because ofthe attraction of the wake's electric potential well. The electrondistribution forms a notch or dimple (of reduced phase space density)localized in velocity to orbits that dwell near the wake axis (becauseof repulsion). Those orbits are de-energized by cross-field drift downthe potential-energy ridge. The resulting Langmuir instability spawnselectron holes. The holes that move faster than the ion beams areaccelerated out of the wake by its electrostatic field without growingsubstantially. Some holes, however, remain in the wake at essentiallyzero parallel velocity. They grow, as a result of the same mechanismthat formed the notch: cross-field drift from a lower to a higherdensity. When the density rises by a factor of order two or three,they grow large enough to perturb the ions, tap their free energy, anddisrupt the ion streams well before they would become ion-ionunstable. Crucially, these processes depend strongly on theion/electron mass ratio and require close to physical ratio (1836) insimulations, to reveal their characteristics. Electron holes arisingfrom these processes may be widely present and observable in spaceplasma wakes.

Probes, Moons, and Kinetic Plasma Wakes

NASA Astrophysics Data System (ADS)

Hutchinson, I. H.; Malaspina, D.; Zhou, C.

2017-10-01

Nonmagnetic objects as varied as probes in tokamaks or moons in space give rise to flowing plasma wakes in which strong distortions of the ion and electron velocity distributions cause electrostatic instabilities. Non-linear phenomena such as electron holes are then produced. Historic probe theory largely ignores the resulting unstable character of the wake, but since we can now simulate computationally the non-linear wake phenomena, a timely challenge is to reassess the influence of these instabilities both on probe measurements and on the wakes themselves. Because the electron instability wavelengths are very short (typically a few Debye-lengths), controlled laboratory experiments face serious challenges in diagnosing them. That is one reason why they have long been neglected as an influence in probe interpretation. Space-craft plasma observations, by contrast, easily obtain sub-Debye-length resolution, but have difficulty with larger-scale reconstruction of the plasma spatial variation. In addition to surveying our developing understanding of wakes in magnetized plasmas, ongoing analysis of Artemis data concerning electron holes observed in the solar-wind lunar wake will be featured. Work partially supported by NASA Grant NNX16AG82G.

Dopaminergic Modulation of Sleep-Wake States.

PubMed

Herrera-Solis, Andrea; Herrera-Morales, Wendy; Nunez-Jaramillo, Luis; Arias-Carrion, Oscar

2017-01-01

The role of dopamine in sleep-wake regulation is considered as a wakefulness-promoting agent. For the clinical treatment of excessive daytime sleepiness, drugs have been commonly used to increase dopamine release. However, sleep disorders or lack of sleep are related to several dopaminerelated disorders. The effects of dopaminergic agents, nevertheless, are mediated by two families of dopamine receptors, D1 and D2-like receptors; the first family increases adenylyl cyclase activity and the second inhibits adenylyl cyclase. For this reason, the dopaminergic agonist effects on sleep-wake cycle are complex. Here, we review the state-of-the-art and discuss the different effects of dopaminergic agonists in sleep-wake states, and propose that these receptors account for the affinity, although not the specificity, of several effects on the sleep-wake cycle. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Evaluation of a Wake Vortex Upset Model Based on Simultaneous Measurements of Wake Velocities and Probe-Aircraft Accelerations

NASA Technical Reports Server (NTRS)

Short, B. J.; Jacobsen, R. A.

1979-01-01

Simultaneous measurements were made of the upset responses experienced and the wake velocities encountered by an instrumented Learjet probe aircraft behind a Boeing 747 vortex-generating aircraft. The vortex-induced angular accelerations experienced could be predicted within 30% by a mathematical upset response model when the characteristics of the wake were well represented by the vortex model. The vortex model used in the present study adequately represented the wake flow field when the vortices dissipated symmetrically and only one vortex pair existed in the wake.

ARCHITECTURAL DRAWING, MILITARY AIR COMMAND COMMUNICATION CENTER PRECAST CONCRETE WALL ...

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

ARCHITECTURAL DRAWING, MILITARY AIR COMMAND COMMUNICATION CENTER PRECAST CONCRETE WALL DETAILS. DATED 03/15/1971 - Wake Island Airfield, Terminal Building, West Side of Wake Avenue, Wake Island, Wake Island, UM

Clinical Practice Guideline for the Treatment of Intrinsic Circadian Rhythm Sleep-Wake Disorders: Advanced Sleep-Wake Phase Disorder (ASWPD), Delayed Sleep-Wake Phase Disorder (DSWPD), Non-24-Hour Sleep-Wake Rhythm Disorder (N24SWD), and Irregular Sleep-Wake Rhythm Disorder (ISWRD). An Update for 2015

PubMed Central

Auger, R. Robert; Burgess, Helen J.; Emens, Jonathan S.; Deriy, Ludmila V.; Thomas, Sherene M.; Sharkey, Katherine M.

2015-01-01

A systematic literature review and meta-analyses (where appropriate) were performed and the GRADE approach was used to update the previous American Academy of Sleep Medicine Practice Parameters on the treatment of intrinsic circadian rhythm sleep-wake disorders. Available data allowed for positive endorsement (at a second-tier degree of confidence) of strategically timed melatonin (for the treatment of DSWPD, blind adults with N24SWD, and children/ adolescents with ISWRD and comorbid neurological disorders), and light therapy with or without accompanying behavioral interventions (adults with ASWPD, children/adolescents with DSWPD, and elderly with dementia). Recommendations against the use of melatonin and discrete sleep-promoting medications are provided for demented elderly patients, at a second- and first-tier degree of confidence, respectively. No recommendations were provided for remaining treatments/ populations, due to either insufficient or absent data. Areas where further research is needed are discussed. Citation: Auger RR, Burgess HJ, Emens JS, Deriy LV, Thomas SM, Sharkey KM. Clinical practice guideline for the treatment of intrinsic circadian rhythm sleep-wake disorders: advanced sleep-wake phase disorder (ASWPD), delayed sleep-wake phase disorder (DSWPD), non-24-hour sleep-wake rhythm disorder (N24SWD), and irregular sleep-wake rhythm disorder (ISWRD). An update for 2015. J Clin Sleep Med 2015;11(10):1199–1236. PMID:26414986

Large HAWT wake measurement and analysis

NASA Technical Reports Server (NTRS)

Miller, A. H.; Wegley, H. L.; Buck, J. W.

1995-01-01

From the theoretical fluid dynamics point of view, the wake region of a large horizontal-axis wind turbine has been defined and described, and numerical models of wake behavior have been developed. Wind tunnel studies of single turbine wakes and turbine array wakes have been used to verify the theory and further refine the numerical models. However, the effects of scaling, rotor solidity, and topography on wake behavior are questions that remain unanswered. In the wind tunnel studies, turbines were represented by anything from scaled models to tea strainers or wire mesh disks whose solidity was equivalent to that of a typical wind turbine. The scale factor compensation for the difference in Reynolds number between the scale model and an actual turbine is complex, and not typically accounted for. Though it is wise to study the simpler case of wakes in flat topography, which can be easily duplicated in the wind tunnel, current indications are that wind turbine farm development is actually occurring in somewhat more complex terrain. Empirical wake studies using large horizontal-axis wind turbines have not been thoroughly composited, and, therefore, the results have not been applied to the well-developed theory of wake structure. The measurement programs have made use of both in situ sensor systems, such as instrumented towers, and remote sensors, such as kites and tethered, balloonborne anemometers. We present a concise overview of the work that has been performed, including our own, which is based on the philosophy that the MOD-2 turbines are probably their own best detector of both the momentum deficit and the induced turbulence effect downwind. Only the momentum deficit aspects of the wake/machine interactions have been addressed. Both turbine power output deficits and wind energy deficits as measured by the onsite meteorological towers have been analyzed from a composite data set. The analysis has also evidenced certain topographic influences on the operation of

Large HAWT wake measurement and analysis

NASA Astrophysics Data System (ADS)

Miller, A. H.; Wegley, H. L.; Buck, J. W.

1995-05-01

From the theoretical fluid dynamics point of view, the wake region of a large horizontal-axis wind turbine has been defined and described, and numerical models of wake behavior have been developed. Wind tunnel studies of single turbine wakes and turbine array wakes have been used to verify the theory and further refine the numerical models. However, the effects of scaling, rotor solidity, and topography on wake behavior are questions that remain unanswered. In the wind tunnel studies, turbines were represented by anything from scaled models to tea strainers or wire mesh disks whose solidity was equivalent to that of a typical wind turbine. The scale factor compensation for the difference in Reynolds number between the scale model and an actual turbine is complex, and not typically accounted for. Though it is wise to study the simpler case of wakes in flat topography, which can be easily duplicated in the wind tunnel, current indications are that wind turbine farm development is actually occurring in somewhat more complex terrain. Empirical wake studies using large horizontal-axis wind turbines have not been thoroughly composited, and, therefore, the results have not been applied to the well-developed theory of wake structure. The measurement programs have made use of both in situ sensor systems, such as instrumented towers, and remote sensors, such as kites and tethered, balloonborne anemometers. We present a concise overview of the work that has been performed, including our own, which is based on the philosophy that the MOD-2 turbines are probably their own best detector of both the momentum deficit and the induced turbulence effect downwind. Only the momentum deficit aspects of the wake/machine interactions have been addressed. Both turbine power output deficits and wind energy deficits as measured by the onsite meteorological towers have been analyzed from a composite data set. The analysis has also evidenced certain topographic influences on the operation of

Performance and wake conditions of a rotor located in the wake of an obstacle

NASA Astrophysics Data System (ADS)

Naumov, I. V.; Kabardin, I. K.; Mikkelsen, R. F.; Okulov, V. L.; Sørensen, J. N.

2016-09-01

Obstacles like forests, ridges and hills can strongly affect the velocity profile in front of a wind turbine rotor. The present work aims at quantifying the influence of nearby located obstacles on the performance and wake characteristics of a downstream located wind turbine. Here the influence of an obstacle in the form of a cylindrical disk was investigated experimentally in a water flume. A model of a three-bladed rotor, designed using Glauert's optimum theory at a tip speed ratio λ = 5, was placed in the wake of a disk with a diameter close to the one of the rotor. The distance from the disk to the rotor was changed from 4 to 8 rotor diameters, with the vertical distance from the rotor axis varied 0.5 and 1 rotor diameters. The associated turbulent intensity of the incoming flow to the rotor changed 3 to '6% due to the influence of the disk wake. In the experiment, thrust characteristics and associated pulsations as a function of the incoming flow structures were measured by strain gauges. The flow condition in front of the rotor was measured with high temporal accuracy using LDA and power coefficients were determine as function of tip speed ratio for different obstacle positions. Furthermore, PIV measurements were carried out to study the development of the mean velocity deficit profiles of the wake behind the wind turbine model under the influence of the wake generated by the obstacle. By use of regression techniques to fit the velocity profiles it was possible to determine velocity deficits and estimate length scales of the wake attenuation.

Endoplasmic reticulum stress in wake-active neurons progresses with aging.

PubMed

Naidoo, Nirinjini; Zhu, Jingxu; Zhu, Yan; Fenik, Polina; Lian, Jie; Galante, Ray; Veasey, Sigrid

2011-08-01

Fragmentation of wakefulness and sleep are expected outcomes of advanced aging. We hypothesize that wake neurons develop endoplasmic reticulum dyshomeostasis with aging, in parallel with impaired wakefulness. In this series of experiments, we sought to more fully characterize age-related changes in wakefulness and then, in relevant wake neuronal populations, explore functionality and endoplasmic reticulum homeostasis. We report that old mice show greater sleep/wake transitions in the active period with markedly shortened wake periods, shortened latencies to sleep, and less wake time in the subjective day in response to a novel social encounter. Consistent with sleep/wake instability and reduced social encounter wakefulness, orexinergic and noradrenergic wake neurons in aged mice show reduced c-fos response to wakefulness and endoplasmic reticulum dyshomeostasis with increased nuclear translocation of CHOP and GADD34. We have identified an age-related unfolded protein response injury to and dysfunction of wake neurons. It is anticipated that these changes contribute to sleep/wake fragmentation and cognitive impairment in aging. © 2011 The Authors. Aging Cell © 2011 Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland.

Analysis of Hypersonic Vehicle Wakes

DTIC Science & Technology

2015-09-17

factor used with viscous Jacobian matrix of left eigenvectors for A R specific gas constant Re Reynolds number Recell cell Reynolds number......focus was shifted to characterizing other wake phenomena. The aerothermal phenomena of interest in the wake include: gas properties, chemical species

Droplet depinning in a wake

NASA Astrophysics Data System (ADS)

Hooshanginejad, Alireza; Lee, Sungyon

2017-03-01

Pinning and depinning of a windswept droplet on a surface is familiar yet deceptively complex for it depends on the interaction of the contact line with the microscopic features of the solid substrate. This physical picture is further compounded when wind of the Reynolds number greater than 100 blows over pinned drops, leading to the boundary layer separation and wake generation. In this Rapid Communication, we incorporate the well-developed ideas of the classical boundary layer to study partially wetting droplets in a wake created by a leader object. Depending on its distance from the leader, the droplet is observed to exhibit drafting, upstream motion, and splitting, due to the wake-induced hydrodynamic coupling that is analogous to drafting of moving bodies. We successfully rationalize the onset of the upstream motion regime using a reduced model that computes the droplet shape governed by the pressure field inside the wake.

Apparatus for Control of Stator Wakes

DTIC Science & Technology

2009-09-18

wake deficit . This has the effect of reducing the blade rate tonal noise of the propulsion rotor. 11 o CN 6 ...upstream of propeller propulsors the sharp wake deficits behind the stators result in unsteady loading and distinguishable peaks in the noise spectra at...trailing edge of a stator blade in order to fill its mean wake deficit to reduce unsteady loading on the rotor blades . Interaction between

Introduction to the Arizona Sky Island Arthropod Project (ASAP): Systematics, Biogeography, Ecology, and Population Genetics of Arthropods of the Madrean Sky Islands.

PubMed

Moore, Wendy; Meyer, Wallace M; Eble, Jeffrey A; Franklin, Kimberly; Wiens, John F; Brusca, Richard C

2013-01-01

The Arizona Sky Island Arthropod Project (ASAP) is a new multi-disciplinary research program at the University of Arizona that combines systematics, biogeography, ecology, and population genetics to study origins and patterns of arthropod diversity along elevation gradients and among mountain ranges in the Madrean Sky Island Region. Arthropods represent taxonomically and ecologically diverse organisms that drive key ecosystem processes in this mountain archipelago. Using data from museum specimens and specimens we obtain during long-term collecting and monitoring programs, ASAP will document arthropod species across Arizona's Sky Islands to address a number of fundamental questions about arthropods of this region. Baseline data will be used to determine climatic boundaries for target species, which will then be integrated with climatological models to predict future changes in arthropod communities and distributions in the wake of rapid climate change. ASAP also makes use of the natural laboratory provided by the Sky Islands to investigate ecological and genetic factors that influence diversification and patterns of community assembly. Here, we introduce the project, outline overarching goals, and describe preliminary data from the first year of sampling ground-dwelling beetles and ants in the Santa Catalina Mountains.

Introduction to the Arizona Sky Island Arthropod Project (ASAP): Systematics, Biogeography, Ecology, and Population Genetics of Arthropods of the Madrean Sky Islands

PubMed Central

Moore, Wendy; Meyer, Wallace M.; Eble, Jeffrey A.; Franklin, Kimberly; Wiens, John F.; Brusca, Richard C.

2014-01-01

The Arizona Sky Island Arthropod Project (ASAP) is a new multi-disciplinary research program at the University of Arizona that combines systematics, biogeography, ecology, and population genetics to study origins and patterns of arthropod diversity along elevation gradients and among mountain ranges in the Madrean Sky Island Region. Arthropods represent taxonomically and ecologically diverse organisms that drive key ecosystem processes in this mountain archipelago. Using data from museum specimens and specimens we obtain during long-term collecting and monitoring programs, ASAP will document arthropod species across Arizona's Sky Islands to address a number of fundamental questions about arthropods of this region. Baseline data will be used to determine climatic boundaries for target species, which will then be integrated with climatological models to predict future changes in arthropod communities and distributions in the wake of rapid climate change. ASAP also makes use of the natural laboratory provided by the Sky Islands to investigate ecological and genetic factors that influence diversification and patterns of community assembly. Here, we introduce the project, outline overarching goals, and describe preliminary data from the first year of sampling ground-dwelling beetles and ants in the Santa Catalina Mountains. PMID:25505938

Full-Scale Field Test of Wake Steering

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

Fleming, Paul; Annoni, Jennifer; Scholbrock, Andrew

Wind farm control, in which turbine controllers are coordinated to improve farmwide performance, is an active field of research. One form of wind farm control is wake steering, in which a turbine is yawed to the inflow to redirect its wake away from downstream turbines. Wake steering has been studied in depth in simulations as well as in wind tunnels and scaled test facilities. This work performs a field test of wake steering on a full-scale turbine. In the campaign, the yaw controller of the turbine has been set to track different yaw misalignment set points while a nacelle-mounted lidarmore » scans the wake at several ranges downwind. The lidar measurements are combined with turbine data, as well as measurements of the inflow made by a highly instrumented meteorological mast. In conclusion, these measurements are then compared to the predictions of a wind farm control-oriented model of wakes.« less

Full-Scale Field Test of Wake Steering

DOE PAGES

Fleming, Paul; Annoni, Jennifer; Scholbrock, Andrew; ...

2017-06-13

Wind farm control, in which turbine controllers are coordinated to improve farmwide performance, is an active field of research. One form of wind farm control is wake steering, in which a turbine is yawed to the inflow to redirect its wake away from downstream turbines. Wake steering has been studied in depth in simulations as well as in wind tunnels and scaled test facilities. This work performs a field test of wake steering on a full-scale turbine. In the campaign, the yaw controller of the turbine has been set to track different yaw misalignment set points while a nacelle-mounted lidarmore » scans the wake at several ranges downwind. The lidar measurements are combined with turbine data, as well as measurements of the inflow made by a highly instrumented meteorological mast. In conclusion, these measurements are then compared to the predictions of a wind farm control-oriented model of wakes.« less

32 CFR 707.10 - Wake illumination light.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 5 2013-07-01 2013-07-01 false Wake illumination light. 707.10 Section 707.10... RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS § 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the wake. ...

32 CFR 707.10 - Wake illumination light.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 5 2014-07-01 2014-07-01 false Wake illumination light. 707.10 Section 707.10... RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS § 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the wake. ...

32 CFR 707.10 - Wake illumination light.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 5 2011-07-01 2011-07-01 false Wake illumination light. 707.10 Section 707.10... RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS § 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the wake. ...

32 CFR 707.10 - Wake illumination light.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 5 2012-07-01 2012-07-01 false Wake illumination light. 707.10 Section 707.10... RESPECT TO ADDITIONAL STATION AND SIGNAL LIGHTS § 707.10 Wake illumination light. Naval vessels may display a white spot light located near the stern to illuminate the wake. ...

Implementation and validation of a wake model for low-speed forward flight

NASA Technical Reports Server (NTRS)

Komerath, Narayanan M.; Schreiber, Olivier A.

1987-01-01

The computer implementation and calculations of the induced velocities produced by a wake model consisting of a trailing vortex system defined from a prescribed time averaged downwash distribution are detailed. Induced velocities are computed by approximating each spiral turn by a pair of large straight vortex segments positioned at critical points relative to where the induced velocity is required. A remainder term for the rest of the spiral is added. This approach results in decreased computation time compared to classical models where each spiral turn is broken down in small straight vortex segments. The model includes features such a harmonic variation of circulation, downwash outside of the blade and/or outside the tip path plane, blade bound vorticity induced velocity with harmonic variation of circulation and time averaging. The influence of various options and parameters on the results are investigated and results are compared to experimental field measurements with which, a resonable agreement is obtained. The capabilities of the model as well as its extension possibilities are studied. The performance of the model in predicting the recently-acquired NASA Langley Inflow data base for a four-bladed rotor is compared to that of the Scully Free Wake code, a well-established program which requires much greater computational resources. It is found that the two codes predict the experimental data with essentially the same accuracy, and show the same trends.

Comparing offshore wind farm wake observed from satellite SAR and wake model results

NASA Astrophysics Data System (ADS)

Bay Hasager, Charlotte

2014-05-01

Offshore winds can be observed from satellite synthetic aperture radar (SAR). In the FP7 EERA DTOC project, the European Energy Research Alliance project on Design Tools for Offshore Wind Farm Clusters, there is focus on mid- to far-field wind farm wakes. The more wind farms are constructed nearby other wind farms, the more is the potential loss in annual energy production in all neighboring wind farms due to wind farm cluster effects. It is of course dependent upon the prevailing wind directions and wind speed levels, the distance between the wind farms, the wind turbine sizes and spacing. Some knowledge is available within wind farm arrays and in the near-field from various investigations. There are 58 offshore wind farms in the Northern European seas grid connected and in operation. Several of those are spaced near each other. There are several twin wind farms in operation including Nysted-1 and Rødsand-2 in the Baltic Sea, and Horns Rev 1 and Horns Rev 2, Egmond aan Zee and Prinses Amalia, and Thompton 1 and Thompton 2 all in the North Sea. There are ambitious plans of constructing numerous wind farms - great clusters of offshore wind farms. Current investigation of offshore wind farms includes mapping from high-resolution satellite SAR of several of the offshore wind farms in operation in the North Sea. Around 20 images with wind farm wake cases have been retrieved and processed. The data are from the Canadian RADARSAT-1/-2 satellites. These observe in microwave C-band and have been used for ocean surface wind retrieval during several years. The satellite wind maps are valid at 10 m above sea level. The wakes are identified in the raw images as darker areas downwind of the wind farms. In the SAR-based wind maps the wake deficit is found as areas of lower winds downwind of the wind farms compared to parallel undisturbed flow in the flow direction. The wind direction is clearly visible from lee effects and wind streaks in the images. The wind farm wake cases

Wind turbine wake measurement in complex terrain

NASA Astrophysics Data System (ADS)

Hansen, KS; Larsen, GC; Menke, R.; Vasiljevic, N.; Angelou, N.; Feng, J.; Zhu, WJ; Vignaroli, A.; W, W. Liu; Xu, C.; Shen, WZ

2016-09-01

SCADA data from a wind farm and high frequency time series measurements obtained with remote scanning systems have been analysed with focus on identification of wind turbine wake properties in complex terrain. The analysis indicates that within the flow regime characterized by medium to large downstream distances (more than 5 diameters) from the wake generating turbine, the wake changes according to local atmospheric conditions e.g. vertical wind speed. In very complex terrain the wake effects are often “overruled” by distortion effects due to the terrain complexity or topology.

Near wakes of advanced turbopropellers

NASA Technical Reports Server (NTRS)

Hanson, D. B.; Patrick, W. P.

1989-01-01

The flow in the wake of a model single rotation Prop-Fan rotor operating in a wind tunnel was traversed with a hot-wire anemometer system designed to determine the 3 periodic velocity components. Special data acquisition and data reduction methods were required to deal with the high data frequency, narrow wakes, and large fluctuating air angles in the tip vortex region. The model tip helical Mach number was 1.17, simulating the cruise condition. Although the flow field is complex, flow features such as viscous velocity defects, vortex sheets, tip vortices, and propagating acoustic pulses are clearly identified with the aid of a simple analytical wake theory.

Ship wakes and their manifestations on the sea surface

NASA Astrophysics Data System (ADS)

Ermakov, Stanislav; Kapustin, Ivan; Kalimulin, Rashid

2013-04-01

Spatial/temporal evolution of turbulence generated by surface ships and the effect of the wake on short wind waves has been studied on the Black Sea and on the Gorky Water Reservoir. Measurements of currents in ship wakes were conducted using an Acoustic Doppler Current Profiler deployed from a motor boat. It was obtained that the temporal/spatial evolution of the wake width could be described approximately by a 0.4-power dependence, and the wake depth remained nearly constant at its initial stage. This allowed one to consider the wake widening as a one-dimensional process. We have developed a simple one-dimensional model of ship wake evolution using a semi-empirical theory of turbulence, and the initial stage of the wake widening (when neglecting dissipation) was described by the equation of turbulent energy balance with the pulse initial condition. Mean circulating currents in the wake zone resulting in the wind wave intensification ("suloi" areas) at the boundaries of the wake were detected in experiment. The asymmetry of the "suloi" bands was observed when the wind was blowing nearly perpendicular to the wake axis. It was shown that the later stage of the wake evolution is characterized by the formation of slick bands at the edges of the wake. The slick bands is a result of the transport of surfactants to the water surface by air bubbles in the wake and their compression due to the mean circulating currents. The work was supported by RFBR (projects 12-05-31237, 11-05-00295), the Program RAN Radiophysics, and by the Russian Government (Grants No. 11.G34.31.0048 and 11.G34.31.0078).

Multiple Near Wake Patterns Behind Annular Rings

NASA Astrophysics Data System (ADS)

Zhang, Jinzhong; Higuchi, Hiroshi; Muzas, Brian K.; Furuya, Shojiro

1996-11-01

Wake interactions behind concentric annular rings at different spacing ratios were experimentally investigated. The flow visualization, laser Doppler velocimetry data and results from the particle tracking velocimetry are presented and discussed. Jets through individual slots merged in multiply-stable, axisymmetric manners. Most flow patterns were persistent unless the flow was strongly disturbed. The vortex interactions from individual annular elements were also axisymmetric in the near wake. This is in contrast to the asymmetric flows observed earlier behind two-dimensional slotted plates (Higuchi et al. J. Aircraft 26 1989, Phys. Fluids 6(1), 1994). The intermediate wake, however, was dominated by large scale, three-dimensional wake motions even at moderate porosity. Onset of the specific flow patterns was associated with the interactions among start-up vortices. Given model geometry, different turbulent structures and mean velocity profiles were observed in the intermediate wake depending on the near wake pattern. *BKM was a NSF-REU Program undergrad. from Princeton U. and SF was from Mitsubishi Heavy Industries. This work was suppoted in part by the Naval Air Warfare Center.

Wind-tunnel measurements in the wakes of structures

NASA Technical Reports Server (NTRS)

Woo, H. G. C.; Peterka, J. A.; Cermak, J. E.

1977-01-01

Detailed measurements of longitudinal mean velocity, turbulence intensity, space correlations, and spectra made in the wake of two rectangular scaled models in simulated atmospheric boundary-layer winds are presented. The model buildings were 1:50 scale models of two trailers. Results of a flow visualization study of the wake geometry are analyzed with some singular point theorems. Two hypothetical flow patterns of the detailed wake geometry are proposed. Some preliminary studies of the vortex wake, effects of the model size, model aspect ratios, and boundary layer characteristics on the decay rate and extent of the wake are also presented and discussed.

32 CFR 935.13 - Revocation or suspension of permits and registrations.

Code of Federal Regulations, 2010 CFR

2010-07-01

... registrations. 935.13 Section 935.13 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Civil Administration Authority § 935.13... reasons, within 30 days thereafter. (d) If a hearing is not granted within 30 days, a written decision is...

Active Wake Redirection Control to Improve Energy Yield (Poster)

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

Churchfield, M. J.; Fleming, P.; DeGeorge, E.

Wake effects can dramatically reduce the efficiency of waked turbines relative to the unwaked turbines. Wakes can be deflected, or 'redirected,' by applying yaw misalignment to the turbines. Yaw misalignment causes part of the rotor thrust vector to be pointed in the cross-stream direction, deflecting the flow and the wake. Yaw misalignment reduces power production, but the global increase in wind plant power due to decreased wake effect creates a net increase in power production. It is also a fairly simple control idea to implement at existing or new wind plants. We performed high-fidelity computational fluid dynamics simulations of themore » wake flow of the proposed Fishermen's Atlantic City Windfarm (FACW) that predict that under certain waking conditions, wake redirection can increase plant efficiency by 10%. This means that by applying wake redirection control, for a given watersheet area, a wind plant can either produce more power, or the same amount of power can be produced with a smaller watersheet area. With the power increase may come increased loads, though, due to the yaw misalignment. If misalignment is applied properly, or if layered with individual blade pitch control, though, the load increase can be mitigated. In this talk we will discuss the concept of wake redirection through yaw misalignment and present our CFD results of the FACW project. We will also discuss the implications of wake redirection control on annual energy production, and finally we will discuss plans to implement wake redirection control at FACW when it is operational.« less

Wake Turbulence

DOT National Transportation Integrated Search

1997-07-06

THIS IS A SAFETY NOTICE. The guidance contained herein supersedes : the guidance provided in the current edition of Order 7110.65, Air Traffic Control, relating to selected wake turbulence separations and aircraft weight classifications. This Notice ...

Dreaming and waking: similarities and differences revisited.

PubMed

Kahan, Tracey L; LaBerge, Stephen P

2011-09-01

Dreaming is often characterized as lacking high-order cognitive (HOC) skills. In two studies, we test the alternative hypothesis that the dreaming mind is highly similar to the waking mind. Multiple experience samples were obtained from late-night REM sleep and waking, following a systematic protocol described in Kahan (2001). Results indicated that reported dreaming and waking experiences are surprisingly similar in their cognitive and sensory qualities. Concurrently, ratings of dreaming and waking experiences were markedly different on questions of general reality orientation and logical organization (e.g., the bizarreness or typicality of the events, actions, and locations). Consistent with other recent studies (e.g., Bulkeley & Kahan, 2008; Kozmová & Wolman, 2006), experiences sampled from dreaming and waking were more similar with respect to their process features than with respect to their structural features. Copyright © 2010 Elsevier Inc. All rights reserved.

Wake Vortex and Groundwind Meteorological Measurements

DOT National Transportation Integrated Search

1976-05-01

Wake vortex groundwind and meteorological measurements obtained by DOT-TSC at John F. Kennedy (JKF) International Airport have been reduced, analyzed, and correlated with a theoretical vortex transport model. The predictive Wake Vortex Transport Mode...

Development of a Linearized Unsteady Euler Analysis with Application to Wake/Blade-Row Interactions

NASA Technical Reports Server (NTRS)

Verdon, Joseph M.; Montgomery, Matthew D.; Chuang, H. Andrew

1999-01-01

A three-dimensional, linearized, Euler analysis is being developed to provide a comprehensive and efficient unsteady aerodynamic analysis for predicting the aeroacoustic and aeroelastic responses of axial-flow turbomachinery blading. The mathematical models needed to describe nonlinear and linearized, inviscid, unsteady flows through a blade row operating within a cylindrical annular duct are presented in this report. A numerical model for linearized inviscid unsteady flows, which couples a near-field, implicit, wave-split, finite volume analysis to far-field eigen analyses, is also described. The linearized aerodynamic and numerical models have been implemented into the three-dimensional unsteady flow code, LINFLUX. This code is applied herein to predict unsteady subsonic flows driven by wake or vortical excitations. The intent is to validate the LINFLUX analysis via numerical results for simple benchmark unsteady flows and to demonstrate this analysis via application to a realistic wake/blade-row interaction. Detailed numerical results for a three-dimensional version of the 10th Standard Cascade and a fan exit guide vane indicate that LINFLUX is becoming a reliable and useful unsteady aerodynamic prediction capability that can be applied, in the future, to assess the three-dimensional flow physics important to blade-row, aeroacoustic and aeroelastic responses.

Detailed field test of yaw-based wake steering

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

Fleming, Paul; Churchfield, Matt; Scholbrock, Andrew

This study describes a detailed field-test campaign to investigate yaw-based wake steering. In yaw-based wake steering, an upstream turbine intentionally misaligns its yaw with respect to the inflow to deflect its wake away from a downstream turbine, with the goal of increasing total power production. In the first phase, a nacelle-mounted scanning lidar was used to verify wake deflection of a misaligned turbine and calibrate wake deflection models. In the second phase, these models were used within a yaw controller to achieve a desired wake deflection. This paper details the experimental design and setup. Lastly, all data collected as partmore » of this field experiment will be archived and made available to the public via the U.S. Department of Energy's Atmosphere to Electrons Data Archive and Portal.« less

Detailed field test of yaw-based wake steering

DOE PAGES

Fleming, Paul; Churchfield, Matt; Scholbrock, Andrew; ...

2016-10-03

This study describes a detailed field-test campaign to investigate yaw-based wake steering. In yaw-based wake steering, an upstream turbine intentionally misaligns its yaw with respect to the inflow to deflect its wake away from a downstream turbine, with the goal of increasing total power production. In the first phase, a nacelle-mounted scanning lidar was used to verify wake deflection of a misaligned turbine and calibrate wake deflection models. In the second phase, these models were used within a yaw controller to achieve a desired wake deflection. This paper details the experimental design and setup. Lastly, all data collected as partmore » of this field experiment will be archived and made available to the public via the U.S. Department of Energy's Atmosphere to Electrons Data Archive and Portal.« less

Impact of Wake Dispersion on Axial Compressor Performance

NASA Technical Reports Server (NTRS)

Hah, Chunill

2017-01-01

Detailed development of wakes and their impact on the performance of a low-speed one and half stage axial compressor are investigated with a large eddy simulation (LES). To investigate effects of wake mixing recovery and wake interaction with the boundary layer of the downstream blade, spacing between the rotor blade and the stator is varied. The calculated LES flow fields based on a fine computational grid are compared with related measurements and analyzed in detail at several radial locations. The current LES calculates the effects of wake recovery very well. The effects of wake recovery vary significantly in the radial direction. Loss generation is higher on the pressure side at the stator exit at both near design and near stall condition. The current investigation indicates that better management of wake development can be achieved for improved compressor performance.

Stability analysis of shallow wake flows

NASA Astrophysics Data System (ADS)

Kolyshkin, A. A.; Ghidaoui, M. S.

2003-11-01

Experimentally observed periodic structures in shallow (i.e. bounded) wake flows are believed to appear as a result of hydrodynamic instability. Previously published studies used linear stability analysis under the rigid-lid assumption to investigate the onset of instability of wakes in shallow water flows. The objectives of this paper are: (i) to provide a preliminary assessment of the accuracy of the rigid-lid assumption; (ii) to investigate the influence of the shape of the base flow profile on the stability characteristics; (iii) to formulate the weakly nonlinear stability problem for shallow wake flows and show that the evolution of the instability is governed by the Ginzburg Landau equation; and (iv) to establish the connection between weakly nonlinear analysis and the observed flow patterns in shallow wake flows which are reported in the literature. It is found that the relative error in determining the critical value of the shallow wake stability parameter induced by the rigid-lid assumption is below 10% for the practical range of Froude number. In addition, it is shown that the shape of the velocity profile has a large influence on the stability characteristics of shallow wakes. Starting from the rigid-lid shallow-water equations and using the method of multiple scales, an amplitude evolution equation for the most unstable mode is derived. The resulting equation has complex coefficients and is of Ginzburg Landau type. An example calculation of the complex coefficients of the Ginzburg Landau equation confirms the existence of a finite equilibrium amplitude, where the unstable mode evolves with time into a limit-cycle oscillation. This is consistent with flow patterns observed by Ingram & Chu (1987), Chen & Jirka (1995), Balachandar et al. (1999), and Balachandar & Tachie (2001). Reasonable agreement is found between the saturation amplitude obtained from the Ginzburg Landau equation under some simplifying assumptions and the numerical data of Grubi

Wake curvature and trailing edge interaction effects in viscous flow over airfoils

NASA Technical Reports Server (NTRS)

Melnik, R. E.

1979-01-01

A theory developed for analyzing viscous flows over airfoils at high Reynolds numbers is described. The theory includes a complete treatment of viscous interaction effects induced by the curved wake behind the airfoil and accounts for normal pressure gradients across the boundary layer in the trailing edge region. A brief description of a computer code that was developed to solve the extended viscous interaction equations is given. Comparisons of the theoretical results with wind tunnel data for two rear loaded airfoils at supercritical conditions are presented.

Dissipation of Turbulence in the Wake of a Wind Turbine

NASA Astrophysics Data System (ADS)

Lundquist, J. K.; Bariteau, L.

2015-02-01

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behaviour of an individual wake as it merges with other wakes and propagates downwind is critical in assessing wind-farm power production. This evolution depends on the rate of turbulence dissipation in the wind-turbine wake, which has not been previously quantified in field-scale measurements. In situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine were collected using a tethered lifting system (TLS) carrying a payload of high-rate turbulence probes. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located near the turbine. Good agreement between the tower measurements and the TLS measurements was established for a case without a wind-turbine wake. When an operating wind turbine is located between the tower and the TLS so that the wake propagates to the TLS, the TLS measures dissipation rates one to two orders of magnitude higher in the wake than outside of the wake. These data, collected between two and three rotor diameters downwind of the turbine, document the significant enhancement of turbulent kinetic energy dissipation rate within the wind-turbine wake. These wake measurements suggest that it may be useful to pursue modelling approaches that account for enhanced dissipation. Comparisons of wake and non-wake dissipation rates to mean wind speed, wind-speed variance, and turbulence intensity are presented to facilitate the inclusion of these measurements in wake modelling schemes.

Wind tunnel measurements for dispersion modelling of vehicle wakes

NASA Astrophysics Data System (ADS)

Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

2012-12-01

Wind tunnel measurements downwind of reduced scale car models have been made to study the wake regions in detail, test the usefulness of existing vehicle wake models, and draw key information needed for dispersion modelling in vehicle wakes. The experiments simulated a car moving in still air. This is achieved by (i) the experimental characterisation of the flow, turbulence and concentration fields in both the near and far wake regions, (ii) the preliminary assessment of existing wake models using the experimental database, and (iii) the comparison of previous field measurements in the wake of a real diesel car with the wind tunnel measurements. The experiments highlighted very large gradients of velocities and concentrations existing, in particular, in the near-wake. Of course, the measured fields are strongly dependent on the geometry of the modelled vehicle and a generalisation for other vehicles may prove to be difficult. The methodology applied in the present study, although improvable, could constitute a first step towards the development of mathematical parameterisations. Experimental results were also compared with the estimates from two wake models. It was found that they can adequately describe the far-wake of a vehicle in terms of velocities, but a better characterisation in terms of turbulence and pollutant dispersion is needed. Parameterised models able to predict velocity and concentrations with fine enough details at the near-wake scale do not exist.

Quantitative three-dimensional low-speed wake surveys

NASA Technical Reports Server (NTRS)

Brune, G. W.

1992-01-01

Theoretical and practical aspects of conducting three-dimensional wake measurements in large wind tunnels are reviewed with emphasis on applications in low-speed aerodynamics. Such quantitative wake surveys furnish separate values for the components of drag, such as profile drag and induced drag, but also measure lift without the use of a balance. In addition to global data, details of the wake flowfield as well as spanwise distributions of lift and drag are obtained. The paper demonstrates the value of this measurement technique using data from wake measurements conducted by Boeing on a variety of low-speed configurations including the complex high-lift system of a transport aircraft.

Direct Numerical Simulations of Transitional/Turbulent Wakes

NASA Technical Reports Server (NTRS)

Rai, Man Mohan

2011-01-01

The interest in transitional/turbulent wakes spans the spectrum from an intellectual pursuit to understand the complex underlying physics to a critical need in aeronautical engineering and other disciplines to predict component/system performance and reliability. Cylinder wakes have been studied extensively over several decades to gain a better understanding of the basic flow phenomena that are encountered in such flows. Experimental, computational and theoretical means have been employed in this effort. While much has been accomplished there are many important issues that need to be resolved. The physics of the very near wake of the cylinder (less than three diameters downstream) is perhaps the most challenging of them all. This region comprises the two detached shear layers, the recirculation region and wake flow. The interaction amongst these three components is to some extent still a matter of conjecture. Experimental techniques have generated a large percentage of the data that have provided us with the current state of understanding of the subject. More recently computational techniques have been used to simulate cylinder wakes, and the data from such simulations are being used to both refine our understanding of such flows as well as provide new insights. A few large eddy and direct numerical simulations (LES and DNS) of cylinder wakes have appeared in the literature in the recent past. These investigations focus on the low Reynolds number range where the cylinder boundary layer is laminar (sub-critical range). However, from an engineering point of view, there is considerable interest in the situation where the upper and/or lower boundary layer of an airfoil is turbulent, and these turbulent boundary layers separate from the airfoil to contribute to the formation of the wake downstream. In the case of cylinders, this only occurs at relatively large unit Reynolds numbers. However, in the case of airfoils, the boundary layer has the opportunity to transition

32 CFR 935.101 - Seizure of property.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Seizure of property. 935.101 Section 935.101 National Defense Department of Defense (Continued) DEPARTMENT OF THE AIR FORCE TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Criminal Actions § 935.101 Seizure of property. Any property seized in connection...

Wake vortex separation standards : analysis methods

DOT National Transportation Integrated Search

1997-01-01

Wake vortex separation standards are used to prevent hazardous wake vortex encounters. A "safe" separation model can be used to assess the safety of proposed changes in the standards. A safe separation model can be derived from an encounter hazard mo...

Simulation of wind turbine wakes using the actuator line technique

PubMed Central

Sørensen, Jens N.; Mikkelsen, Robert F.; Henningson, Dan S.; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J.

2015-01-01

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. PMID:25583862

Interaction of Aircraft Wakes From Laterally Spaced Aircraft

NASA Technical Reports Server (NTRS)

Proctor, Fred H.

2009-01-01

Large Eddy Simulations are used to examine wake interactions from aircraft on closely spaced parallel paths. Two sets of experiments are conducted, with the first set examining wake interactions out of ground effect (OGE) and the second set for in ground effect (IGE). The initial wake field for each aircraft represents a rolled-up wake vortex pair generated by a B-747. Parametric sets include wake interactions from aircraft pairs with lateral separations of 400, 500, 600, and 750 ft. The simulation of a wake from a single aircraft is used as baseline. The study shows that wake vortices from either a pair or a formation of B-747 s that fly with very close lateral spacing, last longer than those from an isolated B-747. For OGE, the inner vortices between the pair of aircraft, ascend, link and quickly dissipate, leaving the outer vortices to decay and descend slowly. For the IGE scenario, the inner vortices ascend and last longer, while the outer vortices decay from ground interaction at a rate similar to that expected from an isolated aircraft. Both OGE and IGE scenarios produce longer-lasting wakes for aircraft with separations less than 600 ft. The results are significant because concepts to increase airport capacity have been proposed that assume either aircraft formations and/or aircraft pairs landing on very closely spaced runways.

EEG microstates of wakefulness and NREM sleep.

PubMed

Brodbeck, Verena; Kuhn, Alena; von Wegner, Frederic; Morzelewski, Astrid; Tagliazucchi, Enzo; Borisov, Sergey; Michel, Christoph M; Laufs, Helmut

2012-09-01

EEG-microstates exploit spatio-temporal EEG features to characterize the spontaneous EEG as a sequence of a finite number of quasi-stable scalp potential field maps. So far, EEG-microstates have been studied mainly in wakeful rest and are thought to correspond to functionally relevant brain-states. Four typical microstate maps have been identified and labeled arbitrarily with the letters A, B, C and D. We addressed the question whether EEG-microstate features are altered in different stages of NREM sleep compared to wakefulness. 32-channel EEG of 32 subjects in relaxed wakefulness and NREM sleep was analyzed using a clustering algorithm, identifying the most dominant amplitude topography maps typical of each vigilance state. Fitting back these maps into the sleep-scored EEG resulted in a temporal sequence of maps for each sleep stage. All 32 subjects reached sleep stage N2, 19 also N3, for at least 1 min and 45 s. As in wakeful rest we found four microstate maps to be optimal in all NREM sleep stages. The wake maps were highly similar to those described in the literature for wakefulness. The sleep stage specific map topographies of N1 and N3 sleep showed a variable but overall relatively high degree of spatial correlation to the wake maps (Mean: N1 92%; N3 87%). The N2 maps were the least similar to wake (mean: 83%). Mean duration, total time covered, global explained variance and transition probabilities per subject, map and sleep stage were very similar in wake and N1. In wake, N1 and N3, microstate map C was most dominant w.r.t. global explained variance and temporal presence (ratio total time), whereas in N2 microstate map B was most prominent. In N3, the mean duration of all microstate maps increased significantly, expressed also as an increase in transition probabilities of all maps to themselves in N3. This duration increase was partly--but not entirely--explained by the occurrence of slow waves in the EEG. The persistence of exactly four main microstate

Application of laser velocimetry to aircraft wake-vortex measurements

NASA Technical Reports Server (NTRS)

Ciffone, D. L.; Orloff, K. L.

1977-01-01

The theory and use of a laser velocimeter that makes simultaneous measurements of vertical and longitudinal velocities while rapidly scanning a flow field laterally are described, and its direct application to trailing wake-vortex research is discussed. Pertinent measurements of aircraft wake-vortex velocity distributions obtained in a wind tunnel and water towing tank are presented. The utility of the velocimeter to quantitatively assess differences in wake velocity distributions due to wake dissipating devices and span loading changes on the wake-generating model is also demonstrated.

Dissipation of turbulence in the wake of a wind turbine

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

Lundquist, J. K.; Bariteau, L.

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behaviour of an individual wake as it merges with other wakes and propagates downwind is critical in assessing wind-farm power production. This evolution depends on the rate of turbulence dissipation in the wind-turbine wake, which has not been previously quantified in field-scale measurements. In situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine were collected using a tethered lifting system (TLS) carrying a payload of high-ratemore » turbulence probes. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located near the turbine. Good agreement between the tower measurements and the TLS measurements was established for a case without a wind-turbine wake. When an operating wind turbine is located between the tower and the TLS so that the wake propagates to the TLS, the TLS measures dissipation rates one to two orders of magnitude higher in the wake than outside of the wake. These data, collected between two and three rotor diameters D downwind of the turbine, document the significant enhancement of turbulent kinetic energy dissipation rate within the wind-turbine wake. These wake measurements suggest that it may be useful to pursue modelling approaches that account for enhanced dissipation. Furthermore. comparisons of wake and non-wake dissipation rates to mean wind speed, wind-speed variance, and turbulence intensity are presented to facilitate the inclusion of these measurements in wake modelling schemes.« less

Dissipation of turbulence in the wake of a wind turbine

DOE PAGES

Lundquist, J. K.; Bariteau, L.

2014-11-06

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behaviour of an individual wake as it merges with other wakes and propagates downwind is critical in assessing wind-farm power production. This evolution depends on the rate of turbulence dissipation in the wind-turbine wake, which has not been previously quantified in field-scale measurements. In situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine were collected using a tethered lifting system (TLS) carrying a payload of high-ratemore » turbulence probes. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located near the turbine. Good agreement between the tower measurements and the TLS measurements was established for a case without a wind-turbine wake. When an operating wind turbine is located between the tower and the TLS so that the wake propagates to the TLS, the TLS measures dissipation rates one to two orders of magnitude higher in the wake than outside of the wake. These data, collected between two and three rotor diameters D downwind of the turbine, document the significant enhancement of turbulent kinetic energy dissipation rate within the wind-turbine wake. These wake measurements suggest that it may be useful to pursue modelling approaches that account for enhanced dissipation. Furthermore. comparisons of wake and non-wake dissipation rates to mean wind speed, wind-speed variance, and turbulence intensity are presented to facilitate the inclusion of these measurements in wake modelling schemes.« less

One-Dimensional Czedli-Type Islands

ERIC Educational Resources Information Center

Horvath, Eszter K.; Mader, Attila; Tepavcevic, Andreja

2011-01-01

The notion of an island has surfaced in recent algebra and coding theory research. Discrete versions provide interesting combinatorial problems. This paper presents the one-dimensional case with finitely many heights, a topic convenient for student research.

Use of high order, periodic orbits in the PIES code

NASA Astrophysics Data System (ADS)

Monticello, Donald; Reiman, Allan

2010-11-01

We have implemented a version of the PIES code (Princeton Iterative Equilibrium SolverootnotetextA. Reiman et al 2007 Nucl. Fusion 47 572) that uses high order periodic orbits to select the surfaces on which straight magnetic field line coordinates will be calculated. The use of high order periodic orbits has increase the robustness and speed of the PIES code. We now have more uniform treatment of in-phase and out-of-phase islands. This new version has better convergence properties and works well with a full Newton scheme. We now have the ability to shrink islands using a bootstrap like current and this includes the m=1 island in tokamaks.

Wake Vortex Avoidance System and Method

NASA Technical Reports Server (NTRS)

Shams, Qamar A. (Inventor); Zuckerwar, Allan J. (Inventor); Knight, Howard K. (Inventor)

2017-01-01

A wake vortex avoidance system includes a microphone array configured to detect low frequency sounds. A signal processor determines a geometric mean coherence based on the detected low frequency sounds. A display displays wake vortices based on the determined geometric mean coherence.

Lidar-based wake tracking for closed-loop wind farm control

NASA Astrophysics Data System (ADS)

Raach, Steffen; Schlipf, David; Cheng, Po Wen

2016-09-01

This work presents two advancements towards closed-loop wake redirecting of a wind turbine. First, a model-based estimation approach is presented which uses a nacelle-based lidar system facing downwind to obtain information about the wake. A reduced order wake model is described which is then used in the estimation to track the wake. The tracking is demonstrated with lidar measurement data from an offshore campaign and with simulated lidar data from a SOWFA simulation. Second, a controller for closed-loop wake steering is presented. It uses the wake tracking information to set the yaw actuator of the wind turbine to redirect the wake to a desired position. Altogether, this paper aims to present the concept of closed-loop wake redirecting and gives a possible solution to it.

Turbulent Plane Wakes Subjected to Successive Strains

NASA Technical Reports Server (NTRS)

Rogers, Michael M.

2003-01-01

Six direct numerical simulations of turbulent time-evolving strained plane wakes have been examined to investigate the response of a wake to successive irrotational plane strains of opposite sign. The orientation of the applied strain field has been selected so that the flow is the time-developing analogue of a spatially developing wake evolving in the presence of either a favourable or an adverse streamwise pressure gradient. The magnitude of the applied strain rate a is constant in time t until the total strain e(sup at) reaches about four. At this point, a new simulation is begun with the sign of the applied strain being reversed (the original simulation is continued as well). When the total strain is reduced back to its original value of one, yet another simulation is begun with the sign of the strain being reversed again back to its original sign. This process is done for both initially "favourable" and initially "adverse" strains, providing simulations for each of these strain types from three different initial conditions. The evolution of the wake mean velocity deficit and width is found to be very similar for all the adversely strained cases, with both measures rapidly achieving exponential growth at the rate associated with the cross-stream expansive strain e(sup at). In the "favourably" strained cases, the wake widths approach a constant and the velocity deficits ultimately decay rapidly as e(sup -2at). Although all three of these cases do exhibit the same asymptotic exponential behaviour, the time required to achieve this is longer for the cases that have been previously adversely strained (by at approx. equals 1). These simulations confirm the generality of the conclusions drawn in Rogers (2002) regarding the response of plane wakes to strain. The evolution of strained wakes is not consistent with the predictions of classical self-similar analysis; a more general equilibrium similarity solution is required to describe the results. At least for the cases

Simulation of wind turbine wakes using the actuator line technique.

PubMed

Sørensen, Jens N; Mikkelsen, Robert F; Henningson, Dan S; Ivanell, Stefan; Sarmast, Sasan; Andersen, Søren J

2015-02-28

The actuator line technique was introduced as a numerical tool to be employed in combination with large eddy simulations to enable the study of wakes and wake interaction in wind farms. The technique is today largely used for studying basic features of wakes as well as for making performance predictions of wind farms. In this paper, we give a short introduction to the wake problem and the actuator line methodology and present a study in which the technique is employed to determine the near-wake properties of wind turbines. The presented results include a comparison of experimental results of the wake characteristics of the flow around a three-bladed model wind turbine, the development of a simple analytical formula for determining the near-wake length behind a wind turbine and a detailed investigation of wake structures based on proper orthogonal decomposition analysis of numerically generated snapshots of the wake. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Interfacing comprehensive rotorcraft analysis with advanced aeromechanics and vortex wake models

NASA Astrophysics Data System (ADS)

Liu, Haiying

This dissertation describes three aspects of the comprehensive rotorcraft analysis. First, a physics-based methodology for the modeling of hydraulic devices within multibody-based comprehensive models of rotorcraft systems is developed. This newly proposed approach can predict the fully nonlinear behavior of hydraulic devices, and pressure levels in the hydraulic chambers are coupled with the dynamic response of the system. The proposed hydraulic device models are implemented in a multibody code and calibrated by comparing their predictions with test bench measurements for the UH-60 helicopter lead-lag damper. Predicted peak damping forces were found to be in good agreement with measurements, while the model did not predict the entire time history of damper force to the same level of accuracy. The proposed model evaluates relevant hydraulic quantities such as chamber pressures, orifice flow rates, and pressure relief valve displacements. This model could be used to design lead-lag dampers with desirable force and damping characteristics. The second part of this research is in the area of computational aeroelasticity, in which an interface between computational fluid dynamics (CFD) and computational structural dynamics (CSD) is established. This interface enables data exchange between CFD and CSD with the goal of achieving accurate airloads predictions. In this work, a loose coupling approach based on the delta-airloads method is developed in a finite-element method based multibody dynamics formulation, DYMORE. To validate this aerodynamic interface, a CFD code, OVERFLOW-2, is loosely coupled with a CSD program, DYMORE, to compute the airloads of different flight conditions for Sikorsky UH-60 aircraft. This loose coupling approach has good convergence characteristics. The predicted airloads are found to be in good agreement with the experimental data, although not for all flight conditions. In addition, the tight coupling interface between the CFD program, OVERFLOW

Review of Idealized Aircraft Wake Vortex Models

NASA Technical Reports Server (NTRS)

Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don

2014-01-01

Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.

Vortex wakes of a flapping foil in a flowing soap film

NASA Astrophysics Data System (ADS)

Schnipper, Teis; Andersen, Anders; Bohr, Tomas

2008-11-01

We present an experimental study of an oscillating, symmetric foil in a vertically flowing soap film. By varying frequency and amplitude of the oscillation we explore and visualize a variety of wake structures, including von Kármán wake, reverse von Kármán wake, 2P wake, and 2P+2S wake. We characterize the transition from the von Kármán wake (drag) to the reverse von Kármán wake (thrust) and discuss the results in relation to fish swimming. We visualize the time evolution of the vortex shedding in detail, identify the origins of the vortices comprising the wake, and propose a simple model to account for the transition from von Kármán like wakes to more exotic wake structures.

Separation of Lift-Generated Vortex Wakes Into Two Diverging Parts

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.; Brown, Anthony P.

2010-01-01

As part of an ongoing study of the spreading rate of lift-generated vortex wakes, the present investigation considers possible reasons as to why segments of lift-generated wakes sometimes depart from the main part of the wake to move rapidly in either an upward or downward direction. It is assumed that deficiencies or enhancements of the lift carry over across the fuselage-shrouded wing are the driving mechanism for departures of wake-segments. The computations presented first indicate that upwardly departing wake segments that were observed and photographed could have been produced by a deficiency in lift carryover across the fuselage-shrouded part of the wing. Computations made of idealized vortex wakes indicate that upward departure of a wake segment requires a centerline reduction in the span loading of 70% or more, whether the engines are at idle or robust thrust. Similarly, it was found that downward departure of wake segments is produced when the lift over the center part of the wing is enhanced. However, it was also found that downward departures do not occur without the presence of robust engine-exhaust streams (i.e., engines must NOT be at idle). In those cases, downward departures of a wake segment occurs when the centerline value of the loading is enhanced by any amount between about 10% to 100%. Observations of condensation trails indicate that downward departure of wake segments is rare. Upward departures of wake segments appears to be more common but still rare. A study to determine the part of the aircraft that causes wake departures has not been carried out. However, even though departures of wake segments rarely occur, some aircraft do regularly shed these wake structures. If aircraft safety is to be assured to a high degree of reliability, and a solution for eliminating them is not implemented, existing guidelines for the avoidance of vortex wakes [1,3] may need to be broadened to include possible increases in wake sizes caused by vertical

Characterization of forced response of density stratified reacting wake

NASA Astrophysics Data System (ADS)

Pawar, Samadhan A.; Sujith, Raman I.; Emerson, Benjamin; Lieuwen, Tim

2018-02-01

The hydrodynamic stability of a reacting wake depends primarily on the density ratio [i.e., ratio of unburnt gas density (ρu) to burnt gas density (ρb)] of the flow across the wake. The variation of the density ratio from high to low value, keeping ρ u / ρ b > 1 , transitions dynamical characteristics of the reacting wake from a linearly globally stable (or convectively unstable) to a globally unstable mode. In this paper, we propose a framework to analyze the effect of harmonic forcing on the deterministic and synchronization characteristics of reacting wakes. Using the recurrence quantification analysis of the forced wake response, we show that the deterministic behaviour of the reacting wake increases as the amplitude of forcing is increased. Furthermore, for different density ratios, we found that the synchronization of the top and bottom branches of the wake with the forcing signal is dependent on whether the mean frequency of the natural oscillations of the wake (fn) is lesser or greater than the frequency of external forcing (ff). We notice that the response of both branches (top and bottom) of the reacting wake to the external forcing is asymmetric and symmetric for the low and high density ratios, respectively. Furthermore, we characterize the phase-locking behaviour between the top and bottom branches of the wake for different values of density ratios. We observe that an increase in the density ratio results in a gradual decrease in the relative phase angle between the top and bottom branches of the wake, which leads to a change in the vortex shedding pattern from a sinuous (anti-phase) to a varicose (in-phase) mode of the oscillations.

Effects of Aircraft Wake Dynamics on Measured and Simulated NO(x) and HO(x) Wake Chemistry. Appendix B

NASA Technical Reports Server (NTRS)

Lewellen, D. C.; Lewellen, W. S.

2001-01-01

High-resolution numerical large-eddy simulations of the near wake of a B757 including simplified NOx and HOx chemistry were performed to explore the effects of dynamics on chemistry in wakes of ages from a few seconds to several minutes. Dilution plays an important basic role in the NOx-O3 chemistry in the wake, while a more interesting interaction between the chemistry and dynamics occurs for the HOx species. These simulation results are compared with published measurements of OH and HO2 within a B757 wake under cruise conditions in the upper troposphere taken during the Subsonic Aircraft Contrail and Cloud Effects Special Study (SUCCESS) mission in May 1996. The simulation provides a much finer grained representation of the chemistry and dynamics of the early wake than is possible from the 1 s data samples taken in situ. The comparison suggests that the previously reported discrepancy of up to a factor of 20 - 50 between the SUCCESS measurements of the [HO2]/[OH] ratio and that predicted by simplified theoretical computations is due to the combined effects of large mixing rates around the wake plume edges and averaging over volumes containing large species fluctuations. The results demonstrate the feasibility of using three-dimensional unsteady large-eddy simulations with coupled chemistry to study such phenomena.

Optimization Under Uncertainty for Wake Steering Strategies

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

Quick, Julian; Annoni, Jennifer; King, Ryan N.

Here, wind turbines in a wind power plant experience significant power losses because of aerodynamic interactions between turbines. One control strategy to reduce these losses is known as 'wake steering,' in which upstream turbines are yawed to direct wakes away from downstream turbines. Previous wake steering research has assumed perfect information, however, there can be significant uncertainty in many aspects of the problem, including wind inflow and various turbine measurements. Uncertainty has significant implications for performance of wake steering strategies. Consequently, the authors formulate and solve an optimization under uncertainty (OUU) problem for finding optimal wake steering strategies in themore » presence of yaw angle uncertainty. The OUU wake steering strategy is demonstrated on a two-turbine test case and on the utility-scale, offshore Princess Amalia Wind Farm. When we accounted for yaw angle uncertainty in the Princess Amalia Wind Farm case, inflow-direction-specific OUU solutions produced between 0% and 1.4% more power than the deterministically optimized steering strategies, resulting in an overall annual average improvement of 0.2%. More importantly, the deterministic optimization is expected to perform worse and with more downside risk than the OUU result when realistic uncertainty is taken into account. Additionally, the OUU solution produces fewer extreme yaw situations than the deterministic solution.« less

Optimization Under Uncertainty for Wake Steering Strategies

NASA Astrophysics Data System (ADS)

Quick, Julian; Annoni, Jennifer; King, Ryan; Dykes, Katherine; Fleming, Paul; Ning, Andrew

2017-05-01

Wind turbines in a wind power plant experience significant power losses because of aerodynamic interactions between turbines. One control strategy to reduce these losses is known as “wake steering,” in which upstream turbines are yawed to direct wakes away from downstream turbines. Previous wake steering research has assumed perfect information, however, there can be significant uncertainty in many aspects of the problem, including wind inflow and various turbine measurements. Uncertainty has significant implications for performance of wake steering strategies. Consequently, the authors formulate and solve an optimization under uncertainty (OUU) problem for finding optimal wake steering strategies in the presence of yaw angle uncertainty. The OUU wake steering strategy is demonstrated on a two-turbine test case and on the utility-scale, offshore Princess Amalia Wind Farm. When we accounted for yaw angle uncertainty in the Princess Amalia Wind Farm case, inflow-direction-specific OUU solutions produced between 0% and 1.4% more power than the deterministically optimized steering strategies, resulting in an overall annual average improvement of 0.2%. More importantly, the deterministic optimization is expected to perform worse and with more downside risk than the OUU result when realistic uncertainty is taken into account. Additionally, the OUU solution produces fewer extreme yaw situations than the deterministic solution.

Optimization Under Uncertainty for Wake Steering Strategies

DOE PAGES

Quick, Julian; Annoni, Jennifer; King, Ryan N.; ...

2017-06-13

Here, wind turbines in a wind power plant experience significant power losses because of aerodynamic interactions between turbines. One control strategy to reduce these losses is known as 'wake steering,' in which upstream turbines are yawed to direct wakes away from downstream turbines. Previous wake steering research has assumed perfect information, however, there can be significant uncertainty in many aspects of the problem, including wind inflow and various turbine measurements. Uncertainty has significant implications for performance of wake steering strategies. Consequently, the authors formulate and solve an optimization under uncertainty (OUU) problem for finding optimal wake steering strategies in themore » presence of yaw angle uncertainty. The OUU wake steering strategy is demonstrated on a two-turbine test case and on the utility-scale, offshore Princess Amalia Wind Farm. When we accounted for yaw angle uncertainty in the Princess Amalia Wind Farm case, inflow-direction-specific OUU solutions produced between 0% and 1.4% more power than the deterministically optimized steering strategies, resulting in an overall annual average improvement of 0.2%. More importantly, the deterministic optimization is expected to perform worse and with more downside risk than the OUU result when realistic uncertainty is taken into account. Additionally, the OUU solution produces fewer extreme yaw situations than the deterministic solution.« less

Crosswind Shear Gradient Affect on Wake Vortices

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Ahmad, Nashat N.

2011-01-01

Parametric simulations with a Large Eddy Simulation (LES) model are used to explore the influence of crosswind shear on aircraft wake vortices. Previous studies based on field measurements, laboratory experiments, as well as LES, have shown that the vertical gradient of crosswind shear, i.e. the second vertical derivative of the environmental crosswind, can influence wake vortex transport. The presence of nonlinear vertical shear of the crosswind velocity can reduce the descent rate, causing a wake vortex pair to tilt and change in its lateral separation. The LES parametric studies confirm that the vertical gradient of crosswind shear does influence vortex trajectories. The parametric results also show that vortex decay from the effects of shear are complex since the crosswind shear, along with the vertical gradient of crosswind shear, can affect whether the lateral separation between wake vortices is increased or decreased. If the separation is decreased, the vortex linking time is decreased, and a more rapid decay of wake vortex circulation occurs. If the separation is increased, the time to link is increased, and at least one of the vortices of the vortex pair may have a longer life time than in the case without shear. In some cases, the wake vortices may never link.

Dog EEG for wake-promotion studies.

PubMed

Parmentier, Régis; Bricout, Denis; Brousseau, Emmanuel; Giboulot, Thierry

2006-10-01

Described in this unit is a protocol for investigating the wake-promoting activity of new chemical entities (NCEs) in dog. The experimental approach is based on scoring of sleep/wake stages in animals implanted with a telemetry device for recording EMG and cortical EEG signals. A major advantage of this procedure is that it is conducted in nontethered animals, limiting possible bias and complications encountered with conventional recording systems. In this procedure, polygraphic recording is conducted using four implanted beagles. Results of studies with modafinil, a wake-promoting agent, are described to demonstrate the utility of this test procedure.

Ship-wave-shaped wave clouds induced by the Crozet Islands, south Indian Ocean

NASA Image and Video Library

2017-12-08

There are special places on Earth that sometimes write their personal signature in the clouds. The Crozet Islands are one such place, thanks to the tall volcanic peaks that grace the islands. When air flows around these tall peaks, it gets pushed around the islands as well as up and over the peak. The net effect of the flowing air flowing around the solid, tall peaks is much like the solid bow of a ship cutting through standing water. In each case v-shaped waves are formed behind the motion. In liquid, this is called a wake; in the atmosphere, when clouds are present or created, they are known as ship-wave-shaped clouds. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured this true-color image as it passed over the Crozet Islands on November 26, 2014. Three distinct waves are seen behind the three largest islands. From west to east these are Pig Island, Possession Island and East Island. Credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Investigation to Study the Aerodynamic Ship Wake Turbulence Generated by a DD963 Destroyer.

DTIC Science & Technology

1979-10-01

development of aircraft control systems and aerodynamics and ship interfacing hardware. The DD 963 had previously been designated as the smallest non...P AD-AOA3 663 BOEING VERTOL CO PHILADELPHIA PA F/6 20/4 INVESTI6ATION To STUDY THE AERODYNAMIC SHIP WAKE TURBULENCE GEN-ETCIU) OCT 79 T S GARNETT...16s9o * PHILADELPHIA. PENNSYLVANIA 10142 4 April 1980 8-1162-6192 Naval Air Development Center Warminster, Pennsylvania 18974 Attention: Code 6053

32 CFR 935.51 - Motor vehicle violations.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Motor vehicle violations. 935.51 Section 935.51... REGULATIONS WAKE ISLAND CODE Penalties § 935.51 Motor vehicle violations. Whoever is found guilty of a... than 30 days, or suspension or revocation of his motor vehicle operator's permit, or any combination or...

32 CFR 935.51 - Motor vehicle violations.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Motor vehicle violations. 935.51 Section 935.51... REGULATIONS WAKE ISLAND CODE Penalties § 935.51 Motor vehicle violations. Whoever is found guilty of a... than 30 days, or suspension or revocation of his motor vehicle operator's permit, or any combination or...

From Wake Steering to Flow Control

DOE PAGES

Fleming, Paul A.; Annoni, Jennifer; Churchfield, Matthew J.; ...

2017-11-22

In this article, we investigate the role of flow structures generated in wind farm control through yaw misalignment. A pair of counter-rotating vortices are shown to be important in deforming the shape of the wake and in explaining the asymmetry of wake steering in oppositely signed yaw angles. We motivate the development of new physics for control-oriented engineering models of wind farm control, which include the effects of these large-scale flow structures. Such a new model would improve the predictability of control-oriented models. Results presented in this paper indicate that wind farm control strategies, based on new control-oriented models withmore » new physics, that target total flow control over wake redirection may be different, and perhaps more effective, than current approaches. We propose that wind farm control and wake steering should be thought of as the generation of large-scale flow structures, which will aid in the improved performance of wind farms.« less

Analysis of Predicted Aircraft Wake Vortex Transport and Comparison with Experiment Volume I -- Wake Vortex Predictive System Study

DOT National Transportation Integrated Search

1974-04-01

A unifying wake vortex transport model is developed and applied to a wake vortex predictive system concept. The fundamentals of vortex motion underlying the predictive model are discussed including vortex decay, bursting and instability phenomena. A ...

Why Does Sleep Slow-Wave Activity Increase After Extended Wake? Assessing the Effects of Increased Cortical Firing During Wake and Sleep

PubMed Central

Rodriguez, Alexander V.; Funk, Chadd M.; Vyazovskiy, Vladyslav V.; Nir, Yuval; Tononi, Giulio

2016-01-01

During non-rapid eye movement (NREM) sleep, cortical neurons alternate between ON periods of firing and OFF periods of silence. This bi-stability, which is largely synchronous across neurons, is reflected in the EEG as slow waves. Slow-wave activity (SWA) increases with wake duration and declines homeostatically during sleep, but the underlying mechanisms remain unclear. One possibility is neuronal “fatigue”: high, sustained firing in wake would force neurons to recover with more frequent and longer OFF periods during sleep. Another possibility is net synaptic potentiation during wake: stronger coupling among neurons would lead to greater synchrony and therefore higher SWA. Here, we obtained a comparable increase in sustained firing (6 h) in cortex by: (1) keeping mice awake by exposure to novel objects to promote plasticity and (2) optogenetically activating a local population of cortical neurons at wake-like levels during sleep. Sleep after extended wake led to increased SWA, higher synchrony, and more time spent OFF, with a positive correlation between SWA, synchrony, and OFF periods. Moreover, time spent OFF was correlated with cortical firing during prior wake. After local optogenetic stimulation, SWA and cortical synchrony decreased locally, time spent OFF did not change, and local SWA was not correlated with either measure. Moreover, laser-induced cortical firing was not correlated with time spent OFF afterward. Overall, these results suggest that high sustained firing per se may not be the primary determinant of SWA increases observed after extended wake. SIGNIFICANCE STATEMENT A long-standing hypothesis is that neurons fire less during slow-wave sleep to recover from the “fatigue” accrued during wake, when overall synaptic activity is higher than in sleep. This idea, however, has rarely been tested and other factors, namely increased cortical synchrony, could explain why sleep slow-wave activity (SWA) is higher after extended wake. We forced

Why Does Sleep Slow-Wave Activity Increase After Extended Wake? Assessing the Effects of Increased Cortical Firing During Wake and Sleep.

PubMed

Rodriguez, Alexander V; Funk, Chadd M; Vyazovskiy, Vladyslav V; Nir, Yuval; Tononi, Giulio; Cirelli, Chiara

2016-12-07

During non-rapid eye movement (NREM) sleep, cortical neurons alternate between ON periods of firing and OFF periods of silence. This bi-stability, which is largely synchronous across neurons, is reflected in the EEG as slow waves. Slow-wave activity (SWA) increases with wake duration and declines homeostatically during sleep, but the underlying mechanisms remain unclear. One possibility is neuronal "fatigue": high, sustained firing in wake would force neurons to recover with more frequent and longer OFF periods during sleep. Another possibility is net synaptic potentiation during wake: stronger coupling among neurons would lead to greater synchrony and therefore higher SWA. Here, we obtained a comparable increase in sustained firing (6 h) in cortex by: (1) keeping mice awake by exposure to novel objects to promote plasticity and (2) optogenetically activating a local population of cortical neurons at wake-like levels during sleep. Sleep after extended wake led to increased SWA, higher synchrony, and more time spent OFF, with a positive correlation between SWA, synchrony, and OFF periods. Moreover, time spent OFF was correlated with cortical firing during prior wake. After local optogenetic stimulation, SWA and cortical synchrony decreased locally, time spent OFF did not change, and local SWA was not correlated with either measure. Moreover, laser-induced cortical firing was not correlated with time spent OFF afterward. Overall, these results suggest that high sustained firing per se may not be the primary determinant of SWA increases observed after extended wake. A long-standing hypothesis is that neurons fire less during slow-wave sleep to recover from the "fatigue" accrued during wake, when overall synaptic activity is higher than in sleep. This idea, however, has rarely been tested and other factors, namely increased cortical synchrony, could explain why sleep slow-wave activity (SWA) is higher after extended wake. We forced neurons in the mouse cortex to fire

First Lunar Wake Passage of ARTEMIS: Discrimination of Wake Effects and Solar Wind Fluctuations by 3D Hybrid Simulations

NASA Technical Reports Server (NTRS)

Wiehle, S.; Plaschke, F.; Motschmann, U.; Glassmeier, K. H.; Auster, H. U.; Angelopoulos, V.; Mueller, J.; Kriegel, H.; Georgescu, E.; Halekas, J.;

Direct Simulation and Theoretical Study of Sub- and Supersonic Wakes

NASA Astrophysics Data System (ADS)

Hickey, Jean-Pierre

Wakes are constitutive components of engineering, aeronautical and geophysical flows. Despite their canonical nature, many fundamental questions surrounding wakes remain unanswered. The present work studies the nature of archetypal planar splitter-plate wakes in the sub- and supersonic regimes from a theoretical as well as a numerical perspective. A highly-parallelizable computational fluid dynamic solver was developed, from scratch, for the very-large scale direct numerical simulations of high-speed free shear flows. Wakes maintain a near indelible memory of their origins; thus, changes to the state of the flow on the generating body lead to multiple self-similar states in the far wake. To understand the source of the lack of universality, three distinct wake evolution scenarios are investigated in the incompressible limit: the Kelvin-Helmholtz transition, the bypass transition in an asymmetric wake and the initially turbulent wake. The multiplicity of self-similar states is the result of a plurality of far wake structural organizations, which maintains the memory of the flow. The structural organization is predicated on the presence or absence of near wake anti-symmetric perturbations (as a result of shedding, instability modes and/or trailing edge receptivity). The plurality of large-scale structural organization contrasts with the commonality observed in the mid-sized structures, which are dominated by inclined vortical rods, and not, as previously assumed, by horseshoe structures. The compressibility effects are a direct function of the maximal velocity defect in the wake and are therefore only important in the transitional region - the far wake having an essentially incompressible character. The compressibility simultaneously modifies the growth rate and wavelength of the primary instability mode with a concomitant effect on the emerging transitional structures. As a direct result, the spanwise rollers have an increasing ellipticity and cross-wake domain of

Verification of a magnetic island in gyro-kinetics by comparison with analytic theory

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

Zarzoso, D., E-mail: david.zarzoso-fernandez@polytechnique.org; Casson, F. J.; Poli, E.

A rotating magnetic island is imposed in the gyrokinetic code GKW, when finite differences are used for the radial direction, in order to develop the predictions of analytic tearing mode theory and understand its limitations. The implementation is verified against analytics in sheared slab geometry with three numerical tests that are suggested as benchmark cases for every code that imposes a magnetic island. The convergence requirements to properly resolve physics around the island separatrix are investigated. In the slab geometry, at low magnetic shear, binormal flows inside the island can drive Kelvin-Helmholtz instabilities which prevent the formation of the steadymore » state for which the analytic theory is formulated.« less

Volumetric LiDAR scanning of a wind turbine wake and comparison with a 3D analytical wake model

NASA Astrophysics Data System (ADS)

Carbajo Fuertes, Fernando; Porté-Agel, Fernando

2016-04-01

A correct estimation of the future power production is of capital importance whenever the feasibility of a future wind farm is being studied. This power estimation relies mostly on three aspects: (1) a reliable measurement of the wind resource in the area, (2) a well-established power curve of the future wind turbines and, (3) an accurate characterization of the wake effects; the latter being arguably the most challenging one due to the complexity of the phenomenon and the lack of extensive full-scale data sets that could be used to validate analytical or numerical models. The current project addresses the problem of obtaining a volumetric description of a full-scale wake of a 2MW wind turbine in terms of velocity deficit and turbulence intensity using three scanning wind LiDARs and two sonic anemometers. The characterization of the upstream flow conditions is done by one scanning LiDAR and two sonic anemometers, which have been used to calculate incoming vertical profiles of horizontal wind speed, wind direction and an approximation to turbulence intensity, as well as the thermal stability of the atmospheric boundary layer. The characterization of the wake is done by two scanning LiDARs working simultaneously and pointing downstream from the base of the wind turbine. The direct LiDAR measurements in terms of radial wind speed can be corrected using the upstream conditions in order to provide good estimations of the horizontal wind speed at any point downstream of the wind turbine. All this data combined allow for the volumetric reconstruction of the wake in terms of velocity deficit as well as turbulence intensity. Finally, the predictions of a 3D analytical model [1] are compared to the 3D LiDAR measurements of the wind turbine. The model is derived by applying the laws of conservation of mass and momentum and assuming a Gaussian distribution for the velocity deficit in the wake. This model has already been validated using high resolution wind-tunnel measurements

EEG power during waking and NREM sleep in primary insomnia.

PubMed

Wu, You Meme; Pietrone, Regina; Cashmere, J David; Begley, Amy; Miewald, Jean M; Germain, Anne; Buysse, Daniel J

2013-10-15

Pathophysiological models of insomnia invoke the concept of 24-hour hyperarousal, which could lead to symptoms and physiological findings during waking and sleep. We hypothesized that this arousal could be seen in the waking electroencephalogram (EEG) of individuals with primary insomnia (PI), and that waking EEG power would correlate with non-REM (NREM) EEG. Subjects included 50 PI and 32 good sleeper controls (GSC). Five minutes of eyes closed waking EEG were collected at subjects' usual bedtimes, followed by polysomnography (PSG) at habitual sleep times. An automated algorithm and visual editing were used to remove artifacts from waking and sleep EEGs, followed by power spectral analysis to estimate power from 0.5-32 Hz. We did not find significant differences in waking or NREM EEG spectral power of PI and GSC. Significant correlations between waking and NREM sleep power were observed across all frequency bands in the PI group and in most frequency bands in the GSC group. The absence of significant differences between groups in waking or NREM EEG power suggests that our sample was not characterized by a high degree of cortical arousal. The consistent correlations between waking and NREM EEG power suggest that, in samples with elevated NREM EEG beta activity, waking EEG power may show a similar pattern.

Inlet Guide Vane Wakes Including Rotor Effects

NASA Astrophysics Data System (ADS)

Johnston, R. T.; Fleeter, S.

2001-02-01

Fundamental experiments are described directed at the investigation of forcing functions generated by an inlet guide vane (IGV) row, including interactions with the downstream rotor, for application to turbomachine forced response design systems. The experiments are performed in a high-speed research fan facility comprised of an IGV row upstream of a rotor. IGV-rotor axial spacing is variable, with the IGV row able to be indexed circumferentially, thereby allowing measurements to be made across several IGV wakes. With an IGV relative Mach number of 0.29, measurements include the IGV wake pressure and velocity fields for three IGV-rotor axial spacings. The decay characteristics of the IGV wakes are compared to the Majjigi and Gliebe empirical correlations. After Fourier decomposition, a vortical-potential gust splitting analysis is implemented to determine the vortical and potential harmonic wake gust forcing functions both upstream and downstream of the rotor. Higher harmonics of the vortical gust component of the IGV wakes are found to decay at a uniform rate due to viscous diffusion.

Radar Reflectivity in Wingtip-Generated Wake Vortices

NASA Technical Reports Server (NTRS)

Marshall, Robert E.; Mudukutore, Ashok; Wissel, Vicki

1997-01-01

This report documents new predictive models of radar reflectivity, with meter-scale resolution, for aircraft wakes in clear air and fog. The models result from a radar design program to locate and quantify wake vortices from commercial aircraft in support of the NASA Aircraft Vortex Spacing System (AVOSS). The radar reflectivity model for clear air assumes: 1) turbulent eddies in the wake produce small discontinuities in radar refractive index; and 2) these turbulent eddies are in the 'inertial subrange' of turbulence. From these assumptions, the maximum radar frequency for detecting a particular aircraft wake, as well as the refractive index structure constant and radar volume reflectivity in the wake can be obtained from the NASA Terminal Area Simulation System (TASS) output. For fog conditions, an empirical relationship is used to calculate radar reflectivity factor from TASS output of bulk liquid water. Currently, two models exist: 1) Atlas-based on observations of liquid water and radar reflectivity factor in clouds; and 2) de Wolf- specifically tailored to a specific measured dataset (1992 Vandenberg Air Force Base).

Wake loss and energy spread factor of the LEReC Booster cavity caused by short range wake field

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

Xiao, Binping; Blaskiewicz, Michael; Fedotov, Alexei

LEReC project uses a DC photoemission gun with multi-alkali (CsK 2Sb or NaK 2Sb) cathode [1]. To get 24 mm “flat-top” distribution, 32 Gaussian laser bunches with 0.6 mm rms length are stacked together with 0.75 mm distance [2]. In this case one cannot simply use a 1 cm rms length Gaussian/step/delta bunch for short range wake field simulation since a 0.6 mm bunch contains frequency much higher than the 1 cm bunch. A short range wake field simulation was done using CST Particle Studio™ with 0.6 mm rms Gaussian bunch at the speed of light, and this result wasmore » compared with the result for 1 cm rms Gaussian bunch in Figure 1, from where one notice that the wake potential for the 0.6 mm bunch is ~10 times higher than that of the 1 cm bunch. The wake potential of the 0.6 mm bunch, as well as the charge distribution, was then “shift and stack” every 0.75 mm, the normalized results are shown in Figure 2. The wake loss factor (WLF) is the integration of the product of wake potential and normalized bunch charge, and the energy spread factor (ESF) is the rms deviation from the average energy loss. It is calculated by summing the weighted squares of the differences and taking the square root of the sum. These two factors were then divided by β 2 for 1.6 MV beam energy. The wake loss factor is at 0.86 V/pC and energy spread factor is at 0.54 V/pC rms. With 100 pC electron bunch, the energy spread inter-bunch is 54 V rms.« less

Solar-wind proton access deep into the near-Moon wake

NASA Astrophysics Data System (ADS)

Nishino, M. N.; Fujimoto, M.; Maezawa, K.; Saito, Y.; Yokota, S.; Asamura, K.; Tanaka, T.; Tsunakawa, H.; Matsushima, M.; Takahashi, F.; Terasawa, T.; Shibuya, H.; Shimizu, H.

2009-08-01

We study solar wind (SW) entry deep into the near-Moon wake using SELENE (KAGUYA) data. It has been known that SW protons flowing around the Moon access the central region of the distant lunar wake, while their intrusion deep into the near-Moon wake has never been expected. We show that SW protons sneak into the deepest lunar wake (anti-subsolar region at ˜100 km altitude), and that the entry yields strong asymmetry of the near-Moon wake environment. Particle trajectory calculations demonstrate that these SW protons are once scattered at the lunar dayside surface, picked-up by the SW motional electric field, and finally sneak into the deepest wake. Our results mean that the SW protons scattered at the lunar dayside surface and coming into the night side region are crucial for plasma environment in the wake, suggesting absorption of ambient SW electrons into the wake to maintain quasi-neutrality.

On the investigation of cascade and turbomachinery rotor wake characteristics

NASA Technical Reports Server (NTRS)

Raj, R.; Lakshminarayana, B.

1975-01-01

The objective of the investigation reported in this thesis is to study the characteristics of a turbomachinery rotor wake, both analytically and experimentally. The constitutive equations for the rotor wake are developed using generalized tensors and a non-inertial frame of reference. Analytical and experimental investigation is carried out in two phases; the first phase involved the study of a cascade wake in the absence of rotation and three dimensionality. In the second phase the wake of a rotor is studied. Simplified two- and three-dimensional models are developed for the prediction of the mean velocity profile of the cascade and the rotor wake, respectively, using the principle of self-similarity. The effect of various major parameters of the rotor and the flow geometry is studied on the development of a rotor wake. Laws governing the decay of the wake velocity defect in a cascade and rotor wake as a function of downstream distance from the trailing edge, pressure gradient and other parameters are derived.

Helicopter rotor wake geometry and its influence in forward flight. Volume 2: Wake geometry charts

NASA Technical Reports Server (NTRS)

Egolf, T. A.; Landgrebe, A. J.

1983-01-01

Isometric and projection view plots, inflow ratio nomographs, undistorted axial displacement nomographs, undistorted longitudinal and lateral coordinates, generalized axial distortion nomographs, blade/vortex passage charts, blade/vortex intersection angle nomographs, and fore and aft wake boundary charts are discussed. Example condition, in flow ratio, undistorted axial location, longitudinal and lateral coordinates, axial coordinates distortions, blade/tip vortex intersections, angle of intersection, and fore and aft wake boundaries are also discussed.

On the wake of a Darrieus turbine

NASA Technical Reports Server (NTRS)

Base, T. E.; Phillips, P.; Robertson, G.; Nowak, E. S.

1981-01-01

The theory and experimental measurements on the aerodynamic decay of a wake from high performance vertical axis wind turbine are discussed. In the initial experimental study, the wake downstream of a model Darrieus rotor, 28 cm diameter and a height of 45.5 cm, was measured in a Boundary Layer Wind Tunnel. The wind turbine was run at the design tip speed ratio of 5.5. It was found that the wake decayed at a slower rate with distance downstream of the turbine, than a wake from a screen with similar troposkein shape and drag force characteristics as the Darrieus rotor. The initial wind tunnel results indicated that the vertical axis wind turbines should be spaced at least forty diameters apart to avoid mutual power depreciation greater than ten per cent.

Role of the locus coeruleus in the emergence of power law wake bouts in a model of the brainstem sleep-wake system through early infancy.

PubMed

Patel, Mainak; Rangan, Aaditya

2017-08-07

Infant rats randomly cycle between the sleeping and waking states, which are tightly correlated with the activity of mutually inhibitory brainstem sleep and wake populations. Bouts of sleep and wakefulness are random; from P2-P10, sleep and wake bout lengths are exponentially distributed with increasing means, while during P10-P21, the sleep bout distribution remains exponential while the distribution of wake bouts gradually transforms to power law. The locus coeruleus (LC), via an undeciphered interaction with sleep and wake populations, has been shown experimentally to be responsible for the exponential to power law transition. Concurrently during P10-P21, the LC undergoes striking physiological changes - the LC exhibits strong global 0.3 Hz oscillations up to P10, but the oscillation frequency gradually rises and synchrony diminishes from P10-P21, with oscillations and synchrony vanishing at P21 and beyond. In this work, we construct a biologically plausible Wilson Cowan-style model consisting of the LC along with sleep and wake populations. We show that external noise and strong reciprocal inhibition can lead to switching between sleep and wake populations and exponentially distributed sleep and wake bout durations as during P2-P10, with the parameters of inhibition between the sleep and wake populations controlling mean bout lengths. Furthermore, we show that the changing physiology of the LC from P10-P21, coupled with reciprocal excitation between the LC and wake population, can explain the shift from exponential to power law of the wake bout distribution. To our knowledge, this is the first study that proposes a plausible biological mechanism, which incorporates the known changing physiology of the LC, for tying the developing sleep-wake circuit and its interaction with the LC to the transformation of sleep and wake bout dynamics from P2-P21. Copyright © 2017 Elsevier Ltd. All rights reserved.

Tomographic particle image velocimetry of desert locust wakes: instantaneous volumes combine to reveal hidden vortex elements and rapid wake deformation

PubMed Central

Bomphrey, Richard J.; Henningsson, Per; Michaelis, Dirk; Hollis, David

2012-01-01

Aerodynamic structures generated by animals in flight are unstable and complex. Recent progress in quantitative flow visualization has advanced our understanding of animal aerodynamics, but measurements have hitherto been limited to flow velocities at a plane through the wake. We applied an emergent, high-speed, volumetric fluid imaging technique (tomographic particle image velocimetry) to examine segments of the wake of desert locusts, capturing fully three-dimensional instantaneous flow fields. We used those flow fields to characterize the aerodynamic footprint in unprecedented detail and revealed previously unseen wake elements that would have gone undetected by two-dimensional or stereo-imaging technology. Vortex iso-surface topographies show the spatio-temporal signature of aerodynamic force generation manifest in the wake of locusts, and expose the extent to which animal wakes can deform, potentially leading to unreliable calculations of lift and thrust when using conventional diagnostic methods. We discuss implications for experimental design and analysis as volumetric flow imaging becomes more widespread. PMID:22977102

Evolution of plasma wakes in density up- and down-ramps

NASA Astrophysics Data System (ADS)

Zhang, C. J.; Joshi, C.; Xu, X. L.; Mori, W. B.; Li, F.; Wan, Y.; Hua, J. F.; Pai, C. H.; Wang, J.; Lu, W.

2018-02-01

The time evolution of plasma wakes in density up- and down-ramps is examined through theory and particle-in-cell simulations. Motivated by observation of the reversal of a linear plasma wake in a plasma density upramp in a recent experiment (Zhang et al 2017 Phys. Rev. Lett. 119 064801) we have examined the behaviour of wakes in plasma ramps that always accompany any plasma source used for plasma-based acceleration. In the up-ramp case it is found that, after the passage of the drive pulse, the wavnumber/wavelength of the wake starts to decrease/increase with time until it eventually tends to zero/infinity, then the wake reverses its propagation direction and the wavenunber/wavelength of the wake begins to increase/shrink. The evolutions of the wavenumber and the phase velocity of the wake as functions of time are shown to be significantly different in the up-ramp and the down-ramp cases. In the latter case the wavenumber of the wake at a particular position in the ramp increases until the wake is eventually damped. It is also shown that the waveform of the wake at a particular time after being excited can be precisely controlled by tuning the initial plasma density profile, which may enable a new type of plasma-based ultrafast optics.

Proceedings of the NASA First Wake Vortex Dynamic Spacing Workshop

NASA Technical Reports Server (NTRS)

Creduer, Leonard (Editor); Perry, R. Brad (Editor)

1997-01-01

A Government and Industry workshop on wake vortex dynamic spacing systems was conducted on May 13-15, 1997, at the NASA Langley Research Center. The purpose of the workshop was to disclose the status of ongoing NASA wake vortex R&D to the international community and to seek feedback on the direction of future work to assure an optimized research approach. Workshop sessions examined wake vortex characterization and physics, wake sensor technologies, aircraft/wake encounters, terminal area weather characterization and prediction, and wake vortex systems integration and implementation. A final workshop session surveyed the Government and Industry perspectives on the NASA research underway and related international wake vortex activities. This document contains the proceedings of the workshop including the presenters' slides, the discussion following each presentation, the wrap-up panel discussion, and the attendees' evaluation feedback.

Dissipation of turbulence in the wake of a wind turbine

NASA Astrophysics Data System (ADS)

Lundquist, J. K.; Bariteau, L.

2013-12-01

The wake of a wind turbine is characterized by increased turbulence and decreased wind speed. Turbines are generally deployed in large groups in wind farms, and so the behavior of an individual wake as it merges with other wakes and propagates downwind is of great importance in assessing wind farm power production as well as impacts of wind energy deployment on local and regional environments. The rate of turbulence dissipation in the wake quantifies the wake behavior as it propagates. In situ field measurements of turbulence dissipation rate in the wake of wind turbines have not been previously collected although correct modeling of dissipation rate is required for accurate simulations of wake evolution. In Fall 2012, we collected in situ measurements of winds and turbulence dissipation from the wake region of a multi-MW turbine, using the University of Colorado at Boulder's Tethered Lifting System (TLS). The TLS is a unique state-of-the-art tethersonde, proven in numerous boundary-layer field experiments to be able to measure turbulence kinetic energy dissipation rates. Ambient flow measurements were provided from sonic anemometers on a meteorological tower located upwind of the turbine, from a profiling lidar upwind, and from a scanning lidar measuring both inflow to and wake from the turbine. Measurements collected within the wake indicate that dissipation rates are higher in the turbine wake than in the ambient flow. Profiles of dissipation and turbulence throughout the rotor disk suggest that dissipation peaks near the hub height of the turbine. Suggestions for incorporating this information into wind turbine modeling approaches will be provided.

Cavitation and Wake Structure of Unsteady Tip Vortex Flows

DTIC Science & Technology

1992-12-10

wake structure generated by three-dimensional lifting surfaces. No longer can the wake be modeled as a simple horseshoe vortex structure with the tip...first initiates. -13- Z Strtn vortex "~Bound vortex "’ ; b Wake 2 Figure 1.5 Far-Field Horseshoe Model of a Finite Wing This figure shows a finite wing...Figure 1.11 Simplified Illustration of Wake Structure Behind an Oscillating Wing This schematic shows a simplified model of the trailing vortex

Numerical analyses of evolution of unsteady flow structures in the wake of flapping starling wing model

NASA Astrophysics Data System (ADS)

Krishnan, Krishnamoorthy; Naqavi, Iftekhar Z.; Gurka, Roi

2017-11-01

Understanding the physics of flapping wings at moderate Reynolds number flows takes on greater importance in the context of avian aerodynamics as well as in the design of miniature-aerial-vehicles. Analyzing the characteristics of wake vortices generated downstream of flapping wings can help to explain the unsteady contribution to the aerodynamics loads. In this study, numerical simulations of flow over a bio-inspired pseudo-2D flapping wing model was conducted to characterize the evolution of unsteady flow structures in the downstream wake of flapping wing. The wing model was based on a European starling's wing and wingbeat kinematics were incorporated to simulate a free-forward flight. The starling's wingbeat kinematics were extracted from experiments conducted in a wind tunnel where freely flying starling was measured using high-speed PIV as well as high-speed imaging yielding a series of kinematic images sampled at 500 Hz. The average chord of the wing section was 6 cm and simulations were carried out at a Reynolds number of 54,000, reduced frequency of 0.17, and Strouhal number of 0.16. Large eddy simulation was performed using a second order, finite difference code ParLES. Characteristics of wake vortex structures during the different phases of the wing strokes were examined. The role of wingbeat kinematics in the configuration of downstream vortex patterns is discussed. Evaluated wake topology and lift-drag characteristics are compared with the starling's wind tunnel results.

Dream to Predict? REM Dreaming as Prospective Coding

PubMed Central

Llewellyn, Sue

2016-01-01

The dream as prediction seems inherently improbable. The bizarre occurrences in dreams never characterize everyday life. Dreams do not come true! But assuming that bizarreness negates expectations may rest on a misunderstanding of how the predictive brain works. In evolutionary terms, the ability to rapidly predict what sensory input implies—through expectations derived from discerning patterns in associated past experiences—would have enhanced fitness and survival. For example, food and water are essential for survival, associating past experiences (to identify location patterns) predicts where they can be found. Similarly, prediction may enable predator identification from what would have been only a fleeting and ambiguous stimulus—without prior expectations. To confront the many challenges associated with natural settings, visual perception is vital for humans (and most mammals) and often responses must be rapid. Predictive coding during wake may, therefore, be based on unconscious imagery so that visual perception is maintained and appropriate motor actions triggered quickly. Speed may also dictate the form of the imagery. Bizarreness, during REM dreaming, may result from a prospective code fusing phenomena with the same meaning—within a particular context. For example, if the context is possible predation, from the perspective of the prey two different predators can both mean the same (i.e., immediate danger) and require the same response (e.g., flight). Prospective coding may also prune redundancy from memories, to focus the image on the contextually-relevant elements only, thus, rendering the non-relevant phenomena indeterminate—another aspect of bizarreness. In sum, this paper offers an evolutionary take on REM dreaming as a form of prospective coding which identifies a probabilistic pattern in past events. This pattern is portrayed in an unconscious, associative, sensorimotor image which may support cognition in wake through being mobilized as a

The sleep-wake-cycle: basic mechanisms.

PubMed

Jones, B E

1989-11-01

The physiologic characteristics of the sleep-wake states have been well defined and some of the chemical and neuron systems that participate in the cyclic generation and maintenance of these states have been identified. The actual dynamic process by which these systems interact to generate the basic sleep-wake cycle, however, remains a mystery.

Acoustic imaging of aircraft wake vortex dynamics

DOT National Transportation Integrated Search

2005-06-01

The experience in utilizing a phased microphone array to passively image aircraft wake : vortices is highlighted. It is demonstrated that the array can provide visualization of wake : dynamics similar to smoke release or natural condensation of vorti...

The NASA-LeRC wind turbine sound prediction code

NASA Technical Reports Server (NTRS)

Viterna, L. A.

1981-01-01

Development of the wind turbine sound prediction code began as part of an effort understand and reduce the noise generated by Mod-1. Tone sound levels predicted with this code are in good agreement with measured data taken in the vicinity Mod-1 wind turbine (less than 2 rotor diameters). Comparison in the far field indicates that propagation effects due to terrain and atmospheric conditions may amplify the actual sound levels by 6 dB. Parametric analysis using the code shows that the predominant contributors to Mod-1 rotor noise are (1) the velocity deficit in the wake of the support tower, (2) the high rotor speed, and (3) off-optimum operation.

Circadian Rhythm Sleep-Wake Disorders in Older Adults.

PubMed

Kim, Jee Hyun; Duffy, Jeanne F

2018-03-01

The timing, duration, and consolidation of sleep result from the interaction of the circadian timing system with a sleep-wake homeostatic process. When aligned and functioning optimally, this allows wakefulness throughout the day and a long consolidated sleep episode at night. Mismatch between the desired timing of sleep and the ability to fall and remain asleep is a hallmark of the circadian rhythm sleep-wake disorders. This article discusses changes in circadian regulation of sleep with aging; how age influences the prevalence, diagnosis, and treatment of circadian rhythm sleep-wake disorders; and how neurologic diseases in older patients affect circadian rhythms and sleep. Copyright © 2017 Elsevier Inc. All rights reserved.

Aircraft Wake Vortices : An Assessment of the Current Situation

DOT National Transportation Integrated Search

1991-01-01

The state of knowledge about aircraft wake vortices in the summer of 1990 is summarized. With the advent of a new FAA wake vortex program, the current situation was assessed by answering five questions: (1) What do we know about wake vortices, (2) wh...

Direct Numerical Simulation of a Weakly Stratified Turbulent Wake

NASA Technical Reports Server (NTRS)

Redford, J. A.; Lund, T. S.; Coleman, Gary N.

2014-01-01

Direct numerical simulation (DNS) is used to investigate a time-dependent turbulent wake evolving in a stably stratified background. A large initial Froude number is chosen to allow the wake to become fully turbulent and axisymmetric before stratification affects the spreading rate of the mean defect. The uncertainty introduced by the finite sample size associated with gathering statistics from a simulation of a time-dependent flow is reduced, compared to earlier simulations of this flow. The DNS reveals the buoyancy-induced changes to the turbulence structure, as well as to the mean-defect history and the terms in the mean-momentum and turbulence-kinetic-energy budgets, that characterize the various states of this flow - namely the three-dimensional (essentially unstratified), non-equilibrium (or 'wake-collapse') and quasi-two-dimensional (or 'two-component') regimes observed elsewhere for wakes embedded in both weakly and strongly stratified backgrounds. The wake-collapse regime is not accompanied by transfer (or 'reconversion') of the potential energy of the turbulence to the kinetic energy of the turbulence, implying that this is not an essential feature of stratified-wake dynamics. The dependence upon Reynolds number of the duration of the wake-collapse period is demonstrated, and the effect of the details of the initial/near-field conditions of the wake on its subsequent development is examined.

The HART II International Workshop: An Assessment of the State-of-the-Art in Comprehensive Code Prediction

NASA Technical Reports Server (NTRS)

vanderWall, Berend G.; Lim, Joon W.; Smith, Marilyn J.; Jung, Sung N.; Bailly, Joelle; Baeder, James D.; Boyd, D. Douglas, Jr.

2013-01-01

Significant advancements in computational fluid dynamics (CFD) and their coupling with computational structural dynamics (CSD, or comprehensive codes) for rotorcraft applications have been achieved recently. Despite this, CSD codes with their engineering level of modeling the rotor blade dynamics, the unsteady sectional aerodynamics and the vortical wake are still the workhorse for the majority of applications. This is especially true when a large number of parameter variations is to be performed and their impact on performance, structural loads, vibration and noise is to be judged in an approximate yet reliable and as accurate as possible manner. In this article, the capabilities of such codes are evaluated using the HART II International Workshop database, focusing on a typical descent operating condition which includes strong blade-vortex interactions. A companion article addresses the CFD/CSD coupled approach. Three cases are of interest: the baseline case and two cases with 3/rev higher harmonic blade root pitch control (HHC) with different control phases employed. One setting is for minimum blade-vortex interaction noise radiation and the other one for minimum vibration generation. The challenge is to correctly predict the wake physics-especially for the cases with HHC-and all the dynamics, aerodynamics, modifications of the wake structure and the aero-acoustics coming with it. It is observed that the comprehensive codes used today have a surprisingly good predictive capability when they appropriately account for all of the physics involved. The minimum requirements to obtain these results are outlined.

An Assessment of Comprehensive Code Prediction State-of-the-Art Using the HART II International Workshop Data

NASA Technical Reports Server (NTRS)

vanderWall, Berend G.; Lim, Joon W.; Smith, Marilyn J.; Jung, Sung N.; Bailly, Joelle; Baeder, James D.; Boyd, D. Douglas, Jr.

2012-01-01

Despite significant advancements in computational fluid dynamics and their coupling with computational structural dynamics (= CSD, or comprehensive codes) for rotorcraft applications, CSD codes with their engineering level of modeling the rotor blade dynamics, the unsteady sectional aerodynamics and the vortical wake are still the workhorse for the majority of applications. This is especially true when a large number of parameter variations is to be performed and their impact on performance, structural loads, vibration and noise is to be judged in an approximate yet reliable and as accurate as possible manner. In this paper, the capabilities of such codes are evaluated using the HART II Inter- national Workshop data base, focusing on a typical descent operating condition which includes strong blade-vortex interactions. Three cases are of interest: the baseline case and two cases with 3/rev higher harmonic blade root pitch control (HHC) with different control phases employed. One setting is for minimum blade-vortex interaction noise radiation and the other one for minimum vibration generation. The challenge is to correctly predict the wake physics - especially for the cases with HHC - and all the dynamics, aerodynamics, modifications of the wake structure and the aero-acoustics coming with it. It is observed that the comprehensive codes used today have a surprisingly good predictive capability when they appropriately account for all of the physics involved. The minimum requirements to obtain these results are outlined.

Long-term oscillations in the sleep/wake cycle of infants

NASA Astrophysics Data System (ADS)

Diambra, L.; Malta, C. P.; Capurro, A.

2009-11-01

The development of circadian sleep-wakefulness rhythm was investigated by a longitudinal study of six normal infants. We propose an entropy based measure for the sleep/wake cycle fragmentation. Our results confirm that the sleep/wake cycle fragmentation and the sleep/wake ratio decrease, while the circadian power increases during the maturation process of infants. In addition to these expected linear trends in the variables devised to quantify sleep consolidation, circadian power and sleep/wake ratio, we found that they present infradian rhythms in the monthly range.

Three-dimensional structure of wind turbine wakes as measured by scanning lidar

NASA Astrophysics Data System (ADS)

Bodini, Nicola; Zardi, Dino; Lundquist, Julie K.

2017-08-01

The lower wind speeds and increased turbulence that are characteristic of turbine wakes have considerable consequences on large wind farms: turbines located downwind generate less power and experience increased turbulent loads. The structures of wakes and their downwind impacts are sensitive to wind speed and atmospheric variability. Wake characterization can provide important insights for turbine layout optimization in view of decreasing the cost of wind energy. The CWEX-13 field campaign, which took place between June and September 2013 in a wind farm in Iowa, was designed to explore the interaction of multiple wakes in a range of atmospheric stability conditions. Based on lidar wind measurements, we extend, present, and apply a quantitative algorithm to assess wake parameters such as the velocity deficits, the size of the wake boundaries, and the location of the wake centerlines. We focus on wakes from a row of four turbines at the leading edge of the wind farm to explore variations between wakes from the edge of the row (outer wakes) and those from turbines in the center of the row (inner wakes). Using multiple horizontal scans at different elevations, a three-dimensional structure of wakes from the row of turbines can be created. Wakes erode very quickly during unstable conditions and can in fact be detected primarily in stable conditions in the conditions measured here. During stable conditions, important differences emerge between the wakes of inner turbines and the wakes of outer turbines. Further, the strong wind veer associated with stable conditions results in a stretching of the wake structures, and this stretching manifests differently for inner and outer wakes. These insights can be incorporated into low-order wake models for wind farm layout optimization or for wind power forecasting.

Three-dimensional structure of wind turbine wakes as measured by scanning lidar

DOE PAGES

Bodini, Nicola; Zardi, Dino; Lundquist, Julie K.

2017-08-14

The lower wind speeds and increased turbulence that are characteristic of turbine wakes have considerable consequences on large wind farms: turbines located downwind generate less power and experience increased turbulent loads. The structures of wakes and their downwind impacts are sensitive to wind speed and atmospheric variability. Wake characterization can provide important insights for turbine layout optimization in view of decreasing the cost of wind energy. The CWEX-13 field campaign, which took place between June and September 2013 in a wind farm in Iowa, was designed to explore the interaction of multiple wakes in a range of atmospheric stability conditions.more » Based on lidar wind measurements, we extend, present, and apply a quantitative algorithm to assess wake parameters such as the velocity deficits, the size of the wake boundaries, and the location of the wake centerlines. We focus on wakes from a row of four turbines at the leading edge of the wind farm to explore variations between wakes from the edge of the row (outer wakes) and those from turbines in the center of the row (inner wakes). Using multiple horizontal scans at different elevations, a three-dimensional structure of wakes from the row of turbines can be created. Wakes erode very quickly during unstable conditions and can in fact be detected primarily in stable conditions in the conditions measured here. During stable conditions, important differences emerge between the wakes of inner turbines and the wakes of outer turbines. Further, the strong wind veer associated with stable conditions results in a stretching of the wake structures, and this stretching manifests differently for inner and outer wakes. As a result, these insights can be incorporated into low-order wake models for wind farm layout optimization or for wind power forecasting.« less

Three-dimensional structure of wind turbine wakes as measured by scanning lidar

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

Bodini, Nicola; Zardi, Dino; Lundquist, Julie K.

The lower wind speeds and increased turbulence that are characteristic of turbine wakes have considerable consequences on large wind farms: turbines located downwind generate less power and experience increased turbulent loads. The structures of wakes and their downwind impacts are sensitive to wind speed and atmospheric variability. Wake characterization can provide important insights for turbine layout optimization in view of decreasing the cost of wind energy. The CWEX-13 field campaign, which took place between June and September 2013 in a wind farm in Iowa, was designed to explore the interaction of multiple wakes in a range of atmospheric stability conditions.more » Based on lidar wind measurements, we extend, present, and apply a quantitative algorithm to assess wake parameters such as the velocity deficits, the size of the wake boundaries, and the location of the wake centerlines. We focus on wakes from a row of four turbines at the leading edge of the wind farm to explore variations between wakes from the edge of the row (outer wakes) and those from turbines in the center of the row (inner wakes). Using multiple horizontal scans at different elevations, a three-dimensional structure of wakes from the row of turbines can be created. Wakes erode very quickly during unstable conditions and can in fact be detected primarily in stable conditions in the conditions measured here. During stable conditions, important differences emerge between the wakes of inner turbines and the wakes of outer turbines. Further, the strong wind veer associated with stable conditions results in a stretching of the wake structures, and this stretching manifests differently for inner and outer wakes. As a result, these insights can be incorporated into low-order wake models for wind farm layout optimization or for wind power forecasting.« less

Brief wakeful resting can eliminate directed forgetting.

PubMed

Schlichting, Andreas; Bäuml, Karl-Heinz T

2017-02-01

When cued to intentionally forget previously encoded memories, participants typically show reduced recall of the memories on a later recall test. We examined how such directed forgetting is affected by a brief period of wakeful resting between encoding and test. Encoding was followed by a "passive" wakeful resting period in which subjects heard emotionally neutral music or perceived neutral pictures, or it was followed by an "active" distraction period in which subjects were engaged in counting or calculation tasks. Whereas typical directed forgetting was present after active distraction, the forgetting was absent after wakeful resting. The findings indicate that the degree to which people can intentionally forget memories is influenced by the cognitive activity that people engage in shortly after learning takes place. The results provide first evidence on the interplay between wakeful resting and intentional forgetting.

Sleep-wake disturbances after traumatic brain injury.

PubMed

Ouellet, Marie-Christine; Beaulieu-Bonneau, Simon; Morin, Charles M

2015-07-01

Sleep-wake disturbances are extremely common after a traumatic brain injury (TBI). The most common disturbances are insomnia (difficulties falling or staying asleep), increased sleep need, and excessive daytime sleepiness that can be due to the TBI or other sleep disorders associated with TBI, such as sleep-related breathing disorder or post-traumatic hypersomnia. Sleep-wake disturbances can have a major effect on functional outcomes and on the recovery process after TBI. These negative effects can exacerbate other common sequelae of TBI-such as fatigue, pain, cognitive impairments, and psychological disorders (eg, depression and anxiety). Sleep-wake disturbances associated with TBI warrant treatment. Although evidence specific to patients with TBI is still scarce, cognitive-behavioural therapy and medication could prove helpful to alleviate sleep-wake disturbances in patients with a TBI. Copyright © 2015 Elsevier Ltd. All rights reserved.

A new methodology for free wake analysis using curved vortex elements

NASA Technical Reports Server (NTRS)

Bliss, Donald B.; Teske, Milton E.; Quackenbush, Todd R.

1987-01-01

A method using curved vortex elements was developed for helicopter rotor free wake calculations. The Basic Curve Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with a scheme to fit the elements along a vortex filament contour, this method has a significant advantage in overall accuracy and efficiency when compared to the traditional straight-line element approach. A theoretical and numerical analysis shows that free wake flows involving close interactions between filaments should utilize curved vortex elements in order to guarantee a consistent level of accuracy. The curved element method was implemented into a forward flight free wake analysis, featuring an adaptive far wake model that utilizes free wake information to extend the vortex filaments beyond the free wake regions. The curved vortex element free wake, coupled with this far wake model, exhibited rapid convergence, even in regions where the free wake and far wake turns are interlaced. Sample calculations are presented for tip vortex motion at various advance ratios for single and multiple blade rotors. Cross-flow plots reveal that the overall downstream wake flow resembles a trailing vortex pair. A preliminary assessment shows that the rotor downwash field is insensitive to element size, even for relatively large curved elements.

Circadian Sleep-Wake Rhythm of Older Adults with Intellectual Disabilities

ERIC Educational Resources Information Center

Maaskant, Marijke; van de Wouw, Ellen; van Wijck, Ruud; Evenhuis, Heleen M.; Echteld, Michael A.

2013-01-01

The circadian sleep-wake rhythm changes with aging, resulting in a more fragmented sleep-wake pattern. In individuals with intellectual disabilities (ID), brain structures regulating the sleep-wake rhythm might be affected. The aims of this study were to compare the sleep-wake rhythm of older adults with ID to that of older adults in the general…

Disruption of hierarchical predictive coding during sleep

PubMed Central

Strauss, Melanie; Sitt, Jacobo D.; King, Jean-Remi; Elbaz, Maxime; Azizi, Leila; Buiatti, Marco; Naccache, Lionel; van Wassenhove, Virginie; Dehaene, Stanislas

2015-01-01

When presented with an auditory sequence, the brain acts as a predictive-coding device that extracts regularities in the transition probabilities between sounds and detects unexpected deviations from these regularities. Does such prediction require conscious vigilance, or does it continue to unfold automatically in the sleeping brain? The mismatch negativity and P300 components of the auditory event-related potential, reflecting two steps of auditory novelty detection, have been inconsistently observed in the various sleep stages. To clarify whether these steps remain during sleep, we recorded simultaneous electroencephalographic and magnetoencephalographic signals during wakefulness and during sleep in normal subjects listening to a hierarchical auditory paradigm including short-term (local) and long-term (global) regularities. The global response, reflected in the P300, vanished during sleep, in line with the hypothesis that it is a correlate of high-level conscious error detection. The local mismatch response remained across all sleep stages (N1, N2, and REM sleep), but with an incomplete structure; compared with wakefulness, a specific peak reflecting prediction error vanished during sleep. Those results indicate that sleep leaves initial auditory processing and passive sensory response adaptation intact, but specifically disrupts both short-term and long-term auditory predictive coding. PMID:25737555

TFaNS Tone Fan Noise Design/Prediction System. Volume 1; System Description, CUP3D Technical Documentation and Manual for Code Developers

NASA Technical Reports Server (NTRS)

Topol, David A.

1999-01-01

TFaNS is the Tone Fan Noise Design/Prediction System developed by Pratt & Whitney under contract to NASA Lewis (presently NASA Glenn). The purpose of this system is to predict tone noise emanating from a fan stage including the effects of reflection and transmission by the rotor and stator and by the duct inlet and nozzle. These effects have been added to an existing annular duct/isolated stator noise prediction capability. TFaNS consists of: The codes that compute the acoustic properties (reflection and transmission coefficients) of the various elements and write them to files. Cup3D: Fan Noise Coupling Code that reads these files, solves the coupling problem, and outputs the desired noise predictions. AWAKEN: CFD/Measured Wake Postprocessor which reformats CFD wake predictions and/or measured wake data so it can be used by the system. This volume of the report provides technical background for TFaNS including the organization of the system and CUP3D technical documentation. This document also provides information for code developers who must write Acoustic Property Files in the CUP3D format. This report is divided into three volumes: Volume I: System Description, CUP3D Technical Documentation, and Manual for Code Developers; Volume II: User's Manual, TFaNS Vers. 1.4; Volume III: Evaluation of System Codes.

International Survey on the Management of Wake-Up Stroke.

PubMed

de Castro-Afonso, Luís Henrique; Nakiri, Guilherme Seizem; Pontes-Neto, Octávio Marques; dos Santos, Antônio Carlos; Abud, Daniel Giansante

2016-01-01

Patients who wake up having experienced a stroke while asleep represent around 20% of acute stroke admissions. According to international guidelines for the management of acute stroke, patients presenting with wake-up stroke are not currently eligible to receive revascularization treatments. In this study, we aimed to assess the opinions of stroke experts about the management of patients with wake-up stroke by using an international multicenter electronic survey. This study consisted of 8 questions on wake-up stroke treatment. Two hundred invitations to participate in the survey were sent by e-mail. Fifty-nine participants started the survey, 4 dropped out before completing it, and 55 completed the full questionnaire. We had 55 participants from 22 countries. In this study, most stroke experts recommended a recanalization treatment for wake-up stroke. However, there was considerable disagreement among experts regarding the best brain imaging method and the best recanalization treatment. The results of ongoing randomized trials on wake-up stroke are urgently needed.

Vortex Wakes of Subsonic Transport Aircraft

NASA Technical Reports Server (NTRS)

Rossow, Vernon J.; Nixon, David (Technical Monitor)

1999-01-01

A historical overview will be presented of the research conducted on the structure and modification of the vortices generated by the lifting surfaces of subsonic transport aircraft. The seminar will describe the three areas of vortex research; namely, the magnitude of the hazard posed, efforts to reduce the hazard to an acceptable level, and efforts to develop a systematic means for avoiding vortex wakes. It is first pointed out that the characteristics of lift-generated vortices are related to the aerodynamic shapes that produce them and that various arrangements of surfaces can be used to produce different vortex structures. The largest portion of the research conducted to date has been directed at finding ways to reduce the hazard potential of lift-generated vortices shed by subsonic transport aircraft in the vicinity of airports during landing and takeoff operations. It is stressed that lift-generated vortex wakes are so complex that progress towards a solution requires application of a combined theoretical and experimental research program because either alone often leads to incorrect conclusions. It is concluded that a satisfactory aerodynamic solution to the wake-vortex problem at airports has not yet been found but a reduction in the impact of the wake-vortex hazard on airport capacity may become available in the foreseeable future through wake-vortex avoidance concepts currently under study. The material to be presented in this overview is drawn from articles published in aerospace journals that are available publicly.

Forecasting behavior in smart homes based on sleep and wake patterns.

PubMed

Williams, Jennifer A; Cook, Diane J

2017-01-01

The goal of this research is to use smart home technology to assist people who are recovering from injuries or coping with disabilities to live independently. We introduce an algorithm to model and forecast wake and sleep behaviors that are exhibited by the participant. Furthermore, we propose that sleep behavior is impacted by and can be modeled from wake behavior, and vice versa. This paper describes the Behavior Forecasting (BF) algorithm. BF consists of 1) defining numeric values that reflect sleep and wake behavior, 2) forecasting wake and sleep values from past behavior, 3) analyzing the effect of wake behavior on sleep and vice versa, and 4) improving prediction performance by using both wake and sleep scores. The BF method was evaluated with data collected from 20 smart homes. We found that regardless of the forecasting method utilized, wake behavior and sleep behavior can be modeled with a minimum accuracy of 84%. Additionally, normalizing the wake and sleep scores drastically improves the accuracy to 99%. The results show that we can effectively model wake and sleep behaviors in a smart environment. Furthermore, wake behaviors can be predicted from sleep behaviors and vice versa.

CONTROL OF SLEEP AND WAKEFULNESS

PubMed Central

Brown, Ritchie E.; Basheer, Radhika; McKenna, James T.; Strecker, Robert E.; McCarley, Robert W.

2013-01-01

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making. PMID:22811426

Abnormal Sleep/Wake Dynamics in Orexin Knockout Mice

PubMed Central

Diniz Behn, Cecilia G.; Klerman, Elizabeth B.; Mochizuki, Takatoshi; Lin, Shih-Chieh; Scammell, Thomas E.

2010-01-01

Study Objectives: Narcolepsy with cataplexy is caused by a loss of orexin (hypocretin) signaling, but the physiologic mechanisms that result in poor maintenance of wakefulness and fragmented sleep remain unknown. Conventional scoring of sleep cannot reveal much about the process of transitioning between states or the variations within states. We developed an EEG spectral analysis technique to determine whether the state instability in a mouse model of narcolepsy reflects abnormal sleep or wake states, faster movements between states, or abnormal transitions between states. Design: We analyzed sleep recordings in orexin knockout (OXKO) mice and wild type (WT) littermates using a state space analysis technique. This non-categorical approach allows quantitative and unbiased examination of sleep/wake states and state transitions. Measurements and Results: OXKO mice spent less time in deep, delta-rich NREM sleep and in active, theta-rich wake and instead spent more time near the transition zones between states. In addition, while in the midst of what should be stable wake, OXKO mice initiated rapid changes into NREM sleep with high velocities normally seen only in transition regions. Consequently, state transitions were much more frequent and rapid even though the EEG progressions during state transitions were normal. Conclusions: State space analysis enables visualization of the boundaries between sleep and wake and shows that narcoleptic mice have less distinct and more labile states of sleep and wakefulness. These observations provide new perspectives on the abnormal state dynamics resulting from disrupted orexin signaling and highlight the usefulness of state space analysis in understanding narcolepsy and other sleep disorders. Citation: Diniz Behn CG; Klerman EB; Mochizuki T; Lin S; Scammell TE. Abnormal sleep/wake dynamics in orexin knockout mice. SLEEP 2010;33(3):297-306. PMID:20337187

32 CFR 935.21 - Civil rights, powers, and duties.

Code of Federal Regulations, 2010 CFR

2010-07-01

... INSULAR REGULATIONS WAKE ISLAND CODE Civil Law § 935.21 Civil rights, powers, and duties. In any case in... the laws of the United States or this part, the civil rights, powers, and duties as they obtain under... 32 National Defense 6 2010-07-01 2010-07-01 false Civil rights, powers, and duties. 935.21 Section...

32 CFR 935.21 - Civil rights, powers, and duties.

Code of Federal Regulations, 2011 CFR

2011-07-01

... INSULAR REGULATIONS WAKE ISLAND CODE Civil Law § 935.21 Civil rights, powers, and duties. In any case in... the laws of the United States or this part, the civil rights, powers, and duties as they obtain under... 32 National Defense 6 2011-07-01 2011-07-01 false Civil rights, powers, and duties. 935.21 Section...

32 CFR 935.21 - Civil rights, powers, and duties.

Code of Federal Regulations, 2012 CFR

2012-07-01

... INSULAR REGULATIONS WAKE ISLAND CODE Civil Law § 935.21 Civil rights, powers, and duties. In any case in... the laws of the United States or this part, the civil rights, powers, and duties as they obtain under... 32 National Defense 6 2012-07-01 2012-07-01 false Civil rights, powers, and duties. 935.21 Section...

32 CFR 935.21 - Civil rights, powers, and duties.

Code of Federal Regulations, 2014 CFR

2014-07-01

... INSULAR REGULATIONS WAKE ISLAND CODE Civil Law § 935.21 Civil rights, powers, and duties. In any case in... the laws of the United States or this part, the civil rights, powers, and duties as they obtain under... 32 National Defense 6 2014-07-01 2014-07-01 false Civil rights, powers, and duties. 935.21 Section...

32 CFR 935.21 - Civil rights, powers, and duties.

Code of Federal Regulations, 2013 CFR

2013-07-01

... INSULAR REGULATIONS WAKE ISLAND CODE Civil Law § 935.21 Civil rights, powers, and duties. In any case in... the laws of the United States or this part, the civil rights, powers, and duties as they obtain under... 32 National Defense 6 2013-07-01 2013-07-01 false Civil rights, powers, and duties. 935.21 Section...

A phase code for memory could arise from circuit mechanisms in entorhinal cortex

PubMed Central

Hasselmo, Michael E.; Brandon, Mark P.; Yoshida, Motoharu; Giocomo, Lisa M.; Heys, James G.; Fransen, Erik; Newman, Ehren L.; Zilli, Eric A.

2009-01-01

Neurophysiological data reveals intrinsic cellular properties that suggest how entorhinal cortical neurons could code memory by the phase of their firing. Potential cellular mechanisms for this phase coding in models of entorhinal function are reviewed. This mechanism for phase coding provides a substrate for modeling the responses of entorhinal grid cells, as well as the replay of neural spiking activity during waking and sleep. Efforts to implement these abstract models in more detailed biophysical compartmental simulations raise specific issues that could be addressed in larger scale population models incorporating mechanisms of inhibition. PMID:19656654

Canary Islands

NASA Image and Video Library

2013-12-30

On December 10, 2013 the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite flew across the central Atlantic Ocean and captured a true-color image of the Canary Islands. Lying off of the coast of Western Sahara and Morocco, the islands were created by successive submarine volcanic eruptions which raised the ocean floor vertically until some of land rose above sea level. The oldest islands lie in the east and the youngest in the west. From east to west, the major islands seen in this image are: Lanzarote, Fuerteventura, Gran Canaria, Tenerife, La Gomera, La Palmera and El Hierro. While the creation of the islands began in the Late Cretaceous Period (70 – 80 million years ago), active volcanic activity continues. In 2011, a spectacular submarine eruption occurred just off the shore of El Hierro. The volcano became quiet again, but very recently increasing earthquakes and changing height of El Hierro suggested the volcano may again be entering an active eruptive phase. On December 27 the island’s volcano monitoring agency had raised the volcanic eruption risk for El Hierro to “yellow” – a code that means increasing activity but no eruption imminent. That afternoon a magnitude 5.1 earthquake struck offshore at El Hierro. The epicenter was 9 miles (15 km) deep, and it was one of the largest quakes ever recorded at the island. Credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Experimental study on wake structure of single rising clean bubble

NASA Astrophysics Data System (ADS)

Sato, Ayaka; Takedomi, Yuta; Shirota, Minori; Sanada, Toshiyuki; Watanabe, Masao

2007-11-01

Wake structure of clean bubble rising in quiescent silicone oil solution of photochromic dye is experimentally studied. A single bubble is generated, immediately after UV sheet light illuminates the part of the liquid just above the bubble generation nozzle in order to activate photochromic dye. Once the bubble passes across the colored part of the liquid, the bubble is accompanied by some portion of activated dye tracers; hence the flow structure in the rear of the single rising bubble is visualized. We capture stereo images of both wake structure and bubble motion. We study how wake structure changes with the increase in bubble size. We observe the stable axisymmetric wake structure, which is called `standing eddy' when bubble size is relatively small, and then wake structure becomes unstable and starts to oscillate with the increase in bubble size. With further increase in bubble size, a pair of streamwise vortices, which is called `double thread', is observed. We discuss in detail this transition from the steady wake to unsteady wake structure, especially double thread wake development and hairpin vortices shedding, in relation to the transition from rectilinear to spiral or zigzag bubble motions.

Optimization Under Uncertainty for Wake Steering Strategies: Preprint

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

Quick, Julian; Annoni, Jennifer; King, Ryan N

Wind turbines in a wind power plant experience significant power losses because of aerodynamic interactions between turbines. One control strategy to reduce these losses is known as 'wake steering,' in which upstream turbines are yawed to direct wakes away from downstream turbines. Previous wake steering research has assumed perfect information, however, there can be significant uncertainty in many aspects of the problem, including wind inflow and various turbine measurements. Uncertainty has significant implications for performance of wake steering strategies. Consequently, the authors formulate and solve an optimization under uncertainty (OUU) problem for finding optimal wake steering strategies in the presencemore » of yaw angle uncertainty. The OUU wake steering strategy is demonstrated on a two-turbine test case and on the utility-scale, offshore Princess Amalia Wind Farm. When we accounted for yaw angle uncertainty in the Princess Amalia Wind Farm case, inflow-direction-specific OUU solutions produced between 0% and 1.4% more power than the deterministically optimized steering strategies, resulting in an overall annual average improvement of 0.2%. More importantly, the deterministic optimization is expected to perform worse and with more downside risk than the OUU result when realistic uncertainty is taken into account. Additionally, the OUU solution produces fewer extreme yaw situations than the deterministic solution.« less

Visualization of the wake behind a sliding bubble

NASA Astrophysics Data System (ADS)

O'Reilly Meehan, R.; Grennan, K.; Davis, I.; Nolan, K.; Murray, D. B.

2017-10-01

In this work, Schlieren measurements are presented for the wake of an air bubble sliding under a heated, inclined surface in quiescent water to provide new insights into the intricate sliding bubble wake structure and the associated convective cooling process. This is a two-phase flow configuration that is pertinent to thermal management solutions, where the fundamental flow physics have yet to be fully described. In this work, we present an experimental apparatus that enables high-quality Schlieren images for different bubble sizes and measurement planes. By combining these visualizations with an advanced bubble tracking technique, we can simultaneously quantify the symbiotic relationship that exists between the sliding bubble dynamics and its associated wake. An unstable, dynamic wake structure is revealed, consisting of multiple hairpin-shaped vortex structures interacting within the macroscopic area affected by the bubble. As vorticity is generated in the near wake, the bubble shape is observed to recoil and rebound. This also occurs normal to the surface and is particularly noticeable for larger bubble sizes, with a periodic ejection of material from the near wake corresponding to significant shape changes. These findings, along with their implications from a thermal management perspective, provide information on the rich dynamics of this natural flow that cannot be obtained using alternate experimental techniques.

Sleep-wake disturbances in sporadic Creutzfeldt-Jakob disease.

PubMed

Landolt, H-P; Glatzel, M; Blättler, T; Achermann, P; Roth, C; Mathis, J; Weis, J; Tobler, I; Aguzzi, A; Bassetti, C L

2006-05-09

The prevalence and characteristics of sleep-wake disturbances in sporadic Creutzfeldt-Jakob disease (sCJD) are poorly understood. Seven consecutive patients with definite sCJD underwent a systematic assessment of sleep-wake disturbances, including clinical history, video-polysomnography, and actigraphy. Extent and distribution of neurodegeneration was estimated by brain autopsy in six patients. Western blot analyses enabling classification and quantification of the protease-resistant isoform of the prion protein, PrPSc, in thalamus and occipital cortex was available in four patients. Sleep-wake symptoms were observed in all patients, and were prominent in four of them. All patients had severe sleep EEG abnormalities with loss of sleep spindles, very low sleep efficiency, and virtual absence of REM sleep. The correlation between different methods to assess sleep-wake functions (history, polysomnography, actigraphy, videography) was generally poor. Brain autopsy revealed prominent changes in cortical areas, but only mild changes in the thalamus. No mutation of the PRNP gene was found. This study demonstrates in sporadic Creutzfeldt-Jakob disease, first, the existence of sleep-wake disturbances similar to those reported in fatal familial insomnia in the absence of prominent and isolated thalamic neuronal loss, and second, the need of a multimodal approach for the unambiguous assessment of sleep-wake functions in these patients.

Wind Wake Watcher v. 1.0

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

Martin, Shawn

This software enables the user to produce Google Earth visualizations of turbine wake effects for wind farms. The visualizations are based on computations of statistical quantities that vary with wind direction and help quantify the effects on power production of upwind turbines on turbines in their wakes. The results of the software are plot images and kml files that can be loaded into Google Earth. The statistics computed are described in greater detail in the paper: S. Martin, C. H. Westergaard, and J. White (2016), Visualizing Wind Farm Wakes Using SCADA Data, in Wither Turbulence and Big Data in themore » 21st Century? Eds. A. Pollard, L. Castillo, L. Danaila, and M. Glauser. Springer, pgs. 231-254.« less

Wind turbine wake characterization using long-range Doppler lidar

NASA Astrophysics Data System (ADS)

Aitken, M.; Lundquist, J. K.; Hestmark, K.; Banta, R. M.; Pichugina, Y.; Brewer, A.

2012-12-01

Wind turbines extract energy from the freestream flow, resulting in a waked region behind the rotor which is characterized by reduced wind speed and increased turbulence. The velocity deficit in the wake diminishes with distance, as faster-moving air outside is gradually entrained. In a concentrated group of turbines, then, downwind machines experience very different inflow conditions compared to those in the front row. As utility-scale turbines rarely exist in isolation, detailed knowledge of the mean flow and turbulence structure inside wakes is needed to correctly model both power production and turbine loading at modern wind farms. To this end, the Turbine Wake and Inflow Characterization Study (TWICS) was conducted in the spring of 2011 to determine the reduction in wind speeds downstream from a multi-MW turbine located at the National Renewable Energy Laboratory's National Wind Technology Center (NWTC) near Boulder, Colorado. Full-scale measurements of wake dynamics are hardly practical or even possible with conventional sensors, such as cup anemometers mounted on meteorological (met) masts. Accordingly, the High Resolution Doppler Lidar (HRDL) developed by the National Oceanic and Atmospheric Administration's Earth System Research Laboratory was employed to investigate the formation and propagation of wakes under varying levels of ambient wind speed, shear, atmospheric stability, and turbulence. HRDL remotely senses line-of-sight wind velocities and has been used in several previous studies of boundary layer aerodynamics. With a fully steerable beam and a maximum range up to about 5 km, depending on atmospheric conditions, HRDL performed a comprehensive survey of the wind flow in front of and behind the turbine to study the shape, meandering, and attenuation of wakes. Due in large part to limited experimental data availability, wind farm wake modeling is still subject to an unacceptable amount of uncertainty, particularly in complex terrain. Here, analytical

Codes for the identification of aquifer names and geologic units in the United States and the Caribbean outlying areas

USGS Publications Warehouse

,

1988-01-01

This standard provides codes to be used for the identification of aquifer names and geologic units in the United States, the Caribbean and other outlying areas. Outlying areas include Puerto Rico, the Virgin Islands, American Samoa, the Midway Islands, Trust Territories of the Pacific Islands, and miscellaneous Pacific Islands. Each code identifies an aquifer or rock-stratigraphic unit and its age designation. The codes provide a standardized base for use by organizations in the storage, retrieval, and exchange of ground-water data; the indexing and inventory of ground-water data and information; the cataloging of ground-water data acquisition activities; and a variety of other applications.

Codes for the identification of aquifer names and geologic units in the United States and the Caribbean outlying areas

USGS Publications Warehouse

,

1985-01-01

This standard provides codes to be used for the identification of aquifer names and geologic units in the United States, the Caribbean and other outlying areas. Outlying areas include Puerto Rico, the Virgin Islands, American Samoa, the Midway Islands, Trust Territories of the Pacific Islands, and miscellaneous Pacific Islands. Each code identifies an aquifer or rock-stratigraphic unit and its age designation. The codes provide a standardized base for use by organizations in the storage, retrieval, and exchange of ground-water data; the indexing and inventory of ground-water data and information; the cataloging of ground-water data acquisition activities; and a variety of other applications.

Evaluation of Fast-Time Wake Vortex Prediction Models

NASA Technical Reports Server (NTRS)

Proctor, Fred H.; Hamilton, David W.

2009-01-01

Current fast-time wake models are reviewed and three basic types are defined. Predictions from several of the fast-time models are compared. Previous statistical evaluations of the APA-Sarpkaya and D2P fast-time models are discussed. Root Mean Square errors between fast-time model predictions and Lidar wake measurements are examined for a 24 hr period at Denver International Airport. Shortcomings in current methodology for evaluating wake errors are also discussed.

Neuroligin-1 links neuronal activity to sleep-wake regulation.

PubMed

El Helou, Janine; Bélanger-Nelson, Erika; Freyburger, Marlène; Dorsaz, Stéphane; Curie, Thomas; La Spada, Francesco; Gaudreault, Pierre-Olivier; Beaumont, Éric; Pouliot, Philippe; Lesage, Frédéric; Frank, Marcos G; Franken, Paul; Mongrain, Valérie

2013-06-11

Maintaining wakefulness is associated with a progressive increase in the need for sleep. This phenomenon has been linked to changes in synaptic function. The synaptic adhesion molecule Neuroligin-1 (NLG1) controls the activity and synaptic localization of N-methyl-d-aspartate receptors, which activity is impaired by prolonged wakefulness. We here highlight that this pathway may underlie both the adverse effects of sleep loss on cognition and the subsequent changes in cortical synchrony. We found that the expression of specific Nlg1 transcript variants is changed by sleep deprivation in three mouse strains. These observations were associated with strain-specific changes in synaptic NLG1 protein content. Importantly, we showed that Nlg1 knockout mice are not able to sustain wakefulness and spend more time in nonrapid eye movement sleep than wild-type mice. These changes occurred with modifications in waking quality as exemplified by low theta/alpha activity during wakefulness and poor preference for social novelty, as well as altered delta synchrony during sleep. Finally, we identified a transcriptional pathway that could underlie the sleep/wake-dependent changes in Nlg1 expression and that involves clock transcription factors. We thus suggest that NLG1 is an element that contributes to the coupling of neuronal activity to sleep/wake regulation.

Vitamin B12 treatment for sleep-wake rhythm disorders.

PubMed

Okawa, M; Mishima, K; Nanami, T; Shimizu, T; Iijima, S; Hishikawa, Y; Takahashi, K

1990-02-01

Vitamin B12 (VB12) was administered to two patients suffering for many years from different sleep-wake rhythm disorders. One patient was a 15-year-old blind girl suffering from a free-running sleep-wake rhythm (hypernychthemeral syndrome) with a period of about 25 h. In spite of repeated trials to entrain her sleep-wake cycle to the environmental 24-h rhythm, her free-running rhythm persisted for about 13 years. When she was 14 years old, administration of VB12 per os was started at the daily dose of 1.5 mg t.i.d. Shortly thereafter, her sleep-wake rhythm was entrained to the environmental 24-h rhythm, and her 24-h sleep-wake rhythm was maintained while she was on the medication. Within 2 months of the withholding of VB12, her free-running sleep-wake rhythm reappeared. The VB12 level in the serum was within the normal range both before and after treatment. The other patient was a 55-year-old man suffering from delayed sleep phase syndrome since 18 years of age. After administration of VB12 at the daily doses of 1.5 mg, his sleep-wake rhythm disorder was improved. The good therapeutic effect lasted for more than 6 months while he was on the medication.

Neuroligin-1 links neuronal activity to sleep-wake regulation

PubMed Central

El Helou, Janine; Bélanger-Nelson, Erika; Freyburger, Marlène; Dorsaz, Stéphane; Curie, Thomas; La Spada, Francesco; Gaudreault, Pierre-Olivier; Beaumont, Éric; Pouliot, Philippe; Lesage, Frédéric; Frank, Marcos G.; Franken, Paul; Mongrain, Valérie

2013-01-01

Maintaining wakefulness is associated with a progressive increase in the need for sleep. This phenomenon has been linked to changes in synaptic function. The synaptic adhesion molecule Neuroligin-1 (NLG1) controls the activity and synaptic localization of N-methyl-d-aspartate receptors, which activity is impaired by prolonged wakefulness. We here highlight that this pathway may underlie both the adverse effects of sleep loss on cognition and the subsequent changes in cortical synchrony. We found that the expression of specific Nlg1 transcript variants is changed by sleep deprivation in three mouse strains. These observations were associated with strain-specific changes in synaptic NLG1 protein content. Importantly, we showed that Nlg1 knockout mice are not able to sustain wakefulness and spend more time in nonrapid eye movement sleep than wild-type mice. These changes occurred with modifications in waking quality as exemplified by low theta/alpha activity during wakefulness and poor preference for social novelty, as well as altered delta synchrony during sleep. Finally, we identified a transcriptional pathway that could underlie the sleep/wake-dependent changes in Nlg1 expression and that involves clock transcription factors. We thus suggest that NLG1 is an element that contributes to the coupling of neuronal activity to sleep/wake regulation. PMID:23716671

Vortex wake alleviation studies with a variable twist wing

NASA Technical Reports Server (NTRS)

Holbrook, G. T.; Dunham, D. M.; Greene, G. C.

1985-01-01

Vortex wake alleviation studies were conducted in a wind tunnel and a water towing tank using a multisegmented wing model which provided controlled and measured variations in span load. Fourteen model configurations are tested at a Reynolds number of one million and a lift coefficient of 0.6 in the Langley 4- by 7-Meter Tunnel and the Hydronautics Ship Model Basin water tank at Hydronautics, Inc., Laurel, Md. Detailed measurements of span load and wake velocities at one semispan downstream correlate well with each other, with inviscid predictions of span load and wake roll up, and with peak trailing-wing rolling moments measured in the far wake. Average trailing-wing rolling moments are found to be an unreliable indicator of vortex wake intensity because vortex meander does not scale between test facilities and free-air conditions. A tapered-span-load configuration, which exhibits little or no drag penalty, is shown to offer significant downstream wake alleviation to a small trailing wing. The greater downstream wake alleviation achieved with the addition of spoilers to a flapped-wing configuration is shown to result directly from the high incremental drag and turbulence associated with the spoilers and not from the span load alteration they cause.

Aircraft Vortex Wake Descent and Decay under Real Atmospheric Effects

DOT National Transportation Integrated Search

1973-10-01

Aircraft vortex wake descent and decay in a real atmosphere is studied analytically. Factors relating to encounter hazard, wake generation, wake descent and stability, and atmospheric dynamics are considered. Operational equations for encounter hazar...

Abnormal sleep/wake dynamics in orexin knockout mice.

PubMed

Diniz Behn, Cecilia G; Klerman, Elizabeth B; Mochizuki, Takatoshi; Lin, Shih-Chieh; Scammell, Thomas E

2010-03-01

Narcolepsy with cataplexy is caused by a loss of orexin (hypocretin) signaling, but the physiologic mechanisms that result in poor maintenance of wakefulness and fragmented sleep remain unknown. Conventional scoring of sleep cannot reveal much about the process of transitioning between states or the variations within states. We developed an EEG spectral analysis technique to determine whether the state instability in a mouse model of narcolepsy reflects abnormal sleep or wake states, faster movements between states, or abnormal transitions between states. We analyzed sleep recordings in orexin knockout (OXKO) mice and wild type (WT) littermates using a state space analysis technique. This non-categorical approach allows quantitative and unbiased examination of sleep/wake states and state transitions. OXKO mice spent less time in deep, delta-rich NREM sleep and in active, theta-rich wake and instead spent more time near the transition zones between states. In addition, while in the midst of what should be stable wake, OXKO mice initiated rapid changes into NREM sleep with high velocities normally seen only in transition regions. Consequently, state transitions were much more frequent and rapid even though the EEG progressions during state transitions were normal. State space analysis enables visualization of the boundaries between sleep and wake and shows that narcoleptic mice have less distinct and more labile states of sleep and wakefulness. These observations provide new perspectives on the abnormal state dynamics resulting from disrupted orexin signaling and highlight the usefulness of state space analysis in understanding narcolepsy and other sleep disorders.

Tracking and Characterization of Aircraft Wakes Using Acoustic and Lidar Measurements

NASA Technical Reports Server (NTRS)

Booth, Earl R., Jr.; Humphreys, William M., Jr.

2005-01-01

Data from the 2003 Denver International Airport Wake Acoustics Test are further examined to discern spectral content of aircraft wake signatures, and to compare three dimensional wake tracking from acoustic data to wake tracking data obtained through use of continuous wave and pulsed lidar. Wake tracking data derived from acoustic array data agree well with both continuous wave and pulsed lidar in the horizontal plane, but less well with pulsed lidar in the vertical direction. Results from this study show that the spectral distribution of acoustic energy in a wake signature varies greatly with aircraft type.

Simulated Wake Characteristics Data for Closely Spaced Parallel Runway Operations Analysis

NASA Technical Reports Server (NTRS)

Guerreiro, Nelson M.; Neitzke, Kurt W.

2012-01-01

A simulation experiment was performed to generate and compile wake characteristics data relevant to the evaluation and feasibility analysis of closely spaced parallel runway (CSPR) operational concepts. While the experiment in this work is not tailored to any particular operational concept, the generated data applies to the broader class of CSPR concepts, where a trailing aircraft on a CSPR approach is required to stay ahead of the wake vortices generated by a lead aircraft on an adjacent CSPR. Data for wake age, circulation strength, and wake altitude change, at various lateral offset distances from the wake-generating lead aircraft approach path were compiled for a set of nine aircraft spanning the full range of FAA and ICAO wake classifications. A total of 54 scenarios were simulated to generate data related to key parameters that determine wake behavior. Of particular interest are wake age characteristics that can be used to evaluate both time- and distance- based in-trail separation concepts for all aircraft wake-class combinations. A simple first-order difference model was developed to enable the computation of wake parameter estimates for aircraft models having weight, wingspan and speed characteristics similar to those of the nine aircraft modeled in this work.

Forecasting Behavior in Smart Homes Based on Sleep and Wake Patterns

PubMed Central

Williams, Jennifer A.; Cook, Diane J.

2017-01-01

Background The goal of this research is to use smart home technology to assist people who are recovering from injuries or coping with disabilities to live independently. Objective We introduce an algorithm to model and forecast wake and sleep behaviors that are exhibited by the participant. Furthermore, we propose that sleep behavior is impacted by and can be modeled from wake behavior, and vice versa. Methods This paper describes the Behavior Forecasting (BF) algorithm. BF consists of 1) defining numeric values that reflect sleep and wake behavior, 2) forecasting wake and sleep values from past behavior, 3) analyzing the effect of wake behavior on sleep and vice versa, and 4) improving prediction performance by using both wake and sleep scores. Results The BF method was evaluated with data collected from 20 smart homes. We found that regardless of the forecasting method utilized, wake behavior and sleep behavior can be modeled with a minimum accuracy of 84%. Additionally, normalizing the wake and sleep scores drastically improves the accuracy to 99%. Conclusions The results show that we can effectively model wake and sleep behaviors in a smart environment. Furthermore, wake behaviors can be predicted from sleep behaviors and vice versa. PMID:27689555

Adaptive sleep-wake discrimination for wearable devices.

PubMed

Karlen, Walter; Floreano, Dario

2011-04-01

Sleep/wake classification systems that rely on physiological signals suffer from intersubject differences that make accurate classification with a single, subject-independent model difficult. To overcome the limitations of intersubject variability, we suggest a novel online adaptation technique that updates the sleep/wake classifier in real time. The objective of the present study was to evaluate the performance of a newly developed adaptive classification algorithm that was embedded on a wearable sleep/wake classification system called SleePic. The algorithm processed ECG and respiratory effort signals for the classification task and applied behavioral measurements (obtained from accelerometer and press-button data) for the automatic adaptation task. When trained as a subject-independent classifier algorithm, the SleePic device was only able to correctly classify 74.94 ± 6.76% of the human-rated sleep/wake data. By using the suggested automatic adaptation method, the mean classification accuracy could be significantly improved to 92.98 ± 3.19%. A subject-independent classifier based on activity data only showed a comparable accuracy of 90.44 ± 3.57%. We demonstrated that subject-independent models used for online sleep-wake classification can successfully be adapted to previously unseen subjects without the intervention of human experts or off-line calibration.

Effect of Nearshore Islands on Tsunami Inundation in Shadow Zones

NASA Astrophysics Data System (ADS)

Goertz, J.; Kaihatu, J. M.; Kalligeris, N.; Lynett, P. J.; Synolakis, C.

2017-12-01

Field surveys performed in the wake of the 2010 Mentawai tsunami event have described the belief of local residents that offshore islands serve as possible tsunami sheltering mechanisms, reducing the corresponding inundation on beaches behind the islands, despite the fact that deduced inundation from debris lines show this to be in fact untrue (Hill et al. 2012). Recent numerical model studies (Stefanakis et al. 2014) have shown that inundation levels on beaches behind conical islands are indeed higher than they are on open coastlines. While work has been done on tsunami amplification on the lee side of islands (Briggs et al. 1995), no work has been done concerning tsunami inundation on beach areas behind the islands. A series of experiments to address this were conducted in the Directional Wave Basin (DWB) at the O.H. Hinsdale Wave Research Laboratory at Oregon State University in summer 2016. A series of four sheet metal islands (two with a full conical section, two truncated at the water line) were placed at varying distances from the toe of a 1/10 sloping beach. Incident wave conditions consisting of solitary waves and full-stroke "dam break" waves were run over the islands. Free surface elevations, velocities, and beach runup were measured, with the intent of determining relationships between the wave condition, the island geometry and distance from the beach, and the tsunami characteristics. A series of runup measurements from a particular set of experiments can be seen in Figure 1. Based on these preliminary analyses, it was determined that: A) inundation was always amplified behind the island relative to areas outside this shadow zone; and B) inundation was generally highest with the island closest to the beach, except in the case where the tsunami wave broke prior to reaching the island. In this latter scenario, the inundation behind the island increased with island distance from the beach. The development of relationships between the inundation levels

Blunt body near wake flow field at Mach 6

NASA Technical Reports Server (NTRS)

Horvath, Thomas J.; McGinley, Catherine B.; Hannemann, Klaus

1996-01-01

Tests were conducted in a Mach 6 flow to examine the reattachment process of an axisymmetric free shear layer associated with the near wake of a 70 deg. half angle, spherically blunted cone with a cylindrical after body. Model angle of incidence was fixed at 0 deg. and free-stream Reynolds numbers based on body diameter ranged from 0.5 x 10(exp 6) to 4 x 10(exp 6). The sensitivity of wake shear layer transition on reattachment heating was investigated. The present perfect gas study was designed to compliment results obtained previously in facilities capable of producing real gas effects. The instrumented blunted cone model was designed primarily for testing in high enthalpy hypervelocity shock tunnels in both this country and abroad but was amenable for testing in conventional hypersonic blowdown wind tunnels as well. Surface heating rates were inferred from temperature - time histories from coaxial surface thermocouples on the model forebody and thin film resistance gages along the model base and cylindrical after body. General flow feature (bow shock, wake shear layer, and recompression shock) locations were visually identified by schlieren photography. Mean shear layer position and growth were determined from intrusive pitot pressure surveys. In addition, wake surveys with a constant temperature hot-wire anemometer were utilized to qualitatively characterize the state of the shear layer prior to reattachment. Experimental results were compared to laminar perfect gas predictions provided by a 3-D Navier Stokes code (NSHYP). Shear layer impingement on the instrumented cylindrical after body resulted in a localized heating maximum that was 21 to 29 percent of the forebody stagnation point heating. Peak heating resulting from the reattaching shear layer was found to be a factor of 2 higher than laminar predictions, which suggested a transitional shear layer. Schlieren flow visualization and fluctuating voltage time histories and spectra from the hot wire surveys

Functional anatomy of the sleep-wakefulness cycle: wakefulness.

PubMed

Reinoso-Suárez, Fernando; de Andrés, Isabel; Garzón, Miguel

2011-01-01

Sleep is a necessary, diverse, periodic, and an active condition circadian and homeostatically regulated and precisely meshed with waking time into the sleep-wakefulness cycle (SWC). Photic retinal stimulation modulates the suprachiasmatic nucleus, which acts as the pacemaker for SWC rhythmicity. Both the light period and social cues adjust the internal clock, making the SWC a circadian, 24-h period in the adult human. Bioelectrical and behavioral parameters characterize the different phases of the SWC. For a long time, lesions and electrical stimulation of brain structures, as well as connection studies, were the main methods used to decipher the foundations of the functional anatomy of the SWC. That is why the first section of this review presents these early historical studies to then discuss the current state of our knowledge based on our understanding of the functional anatomy of the structures underlying the SWC. Supported by this description, we then present a detailed review and update of the structures involved in the phase of wakefulness (W), including their morphological, functional, and chemical characteristics, as well as their anatomical connections. The structures for W generation are known as the "ascending reticular activating system", and they keep and maintain the "thalamo-cerebral cortex unit" awake. This system originates from the neuronal groups located within the brainstem, hypothalamus, and basal forebrain, which use known neurotransmitters and whose neurons are more active during W than during the other SWC states. Thus, synergies among several of these neurotransmitters are necessary to generate the cortical and thalamic activation that is characteristic of the W state, with all the plastic qualities and nuances present in its different behavioral circumstances. Each one of the neurotransmitters exerts powerful influences on the information and cognitive processes as well as attentional, emotional, motivational, behavioral, and arousal

32 CFR 707.10 - Wake illumination light.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 5 2010-07-01 2010-07-01 false Wake illumination light. 707.10 Section 707.10 National Defense Department of Defense (Continued) DEPARTMENT OF THE NAVY NAVIGATION SPECIAL RULES WITH... display a white spot light located near the stern to illuminate the wake. ...

Some wake-related operational limitations of rotorcraft

NASA Technical Reports Server (NTRS)

Heyson, H. H.

1980-01-01

Wind tunnel measurements show that the wake of a rotor, except at near hovering speeds, is not like that of a propeller. The wake is more like that of a wing except that, because of the slow speeds, the wake velocities may be much greater. The helicopter can produce a wake hazard to following light aircraft that is disproportionately great compared to an equivalent fixed wing aircraft. This hazard should be recognized by both pilots and airport controllers when operating in congested areas. Ground effect is generally counted as a blessing since it allows overloaded takeoffs; however, it also introduces additional operation problems. These problems include premature blade stall in hover, settling in forward transition, shuddering in approach to touchdown and complicatons with yaw control. Some of these problems were treated analytically in an approximate manner and reasonable experiment agreement was obtained. An awareness of these effects can prepare the user for their appearance and their consequences.

Wind Turbine Wake Experiment - Wieringermeer (WINTWEX-W)

NASA Astrophysics Data System (ADS)

Kumer, V. M.; Reuder, J.; Svardal, B.; Eecen, P.

2014-12-01

WINTWEX-W is a cooperative wake measurement campaign conducted by the Norwegian Centre of Offshore Wind Energy (Norcowe) and the Energy Research Centre of the Netherlands (ECN). A scanning, four static Windcubes as well as a downstream looking nacelle LiDAR were placed for half a year downstream of one of five research wind turbines in ECNs' wind turbine test farm Wieringermeer. In order to capture wake characteristics under different weather conditions we scanned a 60˚ sector at three different elevations and two vertical cross-sections every minute. Windcubes v1 measured wind profiles every second at 2, 5 and 12 rotor diameter downstream distances. Another static Windcube, a forward-looking nacelle LiDAR and three Sonics were placed upstream to measure the undisturbed approaching flow field. The aim of the campaign is a qualitative and quantitative description of single wind turbine wake propagation and persistency, as well as to improve CFD wake models by delivering a detailed data set of several real atmospheric conditions.

A Study of Wake Development and Structure in Constant Pressure Gradients

NASA Technical Reports Server (NTRS)

Thomas, Flint O.; Nelson, R. C.; Liu, Xiaofeng

2000-01-01

Motivated by the application to high-lift aerodynamics for commercial transport aircraft, a systematic investigation into the response of symmetric/asymmetric planar turbulent wake development to constant adverse, zero, and favorable pressure gradients has been conducted. The experiments are performed at a Reynolds number of 2.4 million based on the chord of the wake generator. A unique feature of this wake study is that the pressure gradients imposed on the wake flow field are held constant. The experimental measurements involve both conventional LDV and hot wire flow field surveys of mean and turbulent quantities including the turbulent kinetic energy budget. In addition, similarity analysis and numerical simulation have also been conducted for this wake study. A focus of the research has been to isolate the effects of both pressure gradient and initial wake asymmetry on the wake development. Experimental results reveal that the pressure gradient has a tremendous influence on the wake development, despite the relatively modest pressure gradients imposed. For a given pressure gradient, the development of an initially asymmetric wake is different from the initially symmetric wake. An explicit similarity solution for the shape parameters of the symmetric wake is obtained and agrees with the experimental results. The turbulent kinetic energy budget measurements of the symmetric wake demonstrate that except for the convection term, the imposed pressure gradient does not change the fundamental flow physics of turbulent kinetic energy transport. Based on the turbulent kinetic energy budget measurements, an approach to correct the bias error associated with the notoriously difficult dissipation estimate is proposed and validated through the comparison of the experimental estimate with a direct numerical simulation result.

Modeling the effects of caffeine on the sleep/ wake cycle.

PubMed

Daniello, Allison; Fievisohn, Elizabeth; Gregory, T Stan

2012-01-01

Caffeine is present in many products consumed daily, including coffee, soda, and chocolate, and is known to delay the onset of sleepiness and cause sleep disturbances. It is an adenosine antagonist, inhibiting some hormones that promote sleep, and therefore promoting wakefulness. This paper proposes a model to incorporate the effects of caffeine on the sleep/wake cycle. The “flip-flop” model was used to model the sleep cycle, where switching between a sleep state and a wake state was nearly instantaneous. Sleep patterns were modeled based on the circadian rhythm and homeostatic drive, as was done by Rempe et al. (2010). The model demonstrated how the homeostatic drive and circadian rhythm interact to cause sleep and wakefulness. The effects of caffeine were incorporated to have a masking effect on the homeostatic drive, promoting wakefulness. Preliminary results showed that caffeine intake late in the evening caused the switch from wake to sleep to occur later than if no caffeine was present in the system. Additionally, the switch from wake to sleep was increasingly delayed with increased caffeine intake at the same time. This model is not yet validated, though potential studies for validation are proposed. This model presents an interesting method for incorporating the effects of caffeine on the sleep/wake cycle.

Saturated Widths of Magnetic Islands in Tokamak Discharges

NASA Astrophysics Data System (ADS)

Halpern, F.; Pankin, A. Y.

2005-10-01

The new ISLAND module described in reference [1] implements a quasi-linear model to compute the widths of multiple magnetic islands driven by saturated tearing modes in toroidal plasmas of arbitrary aspect ratio and cross sectional shape. The distortion of the island shape caused by the radial variation in the perturbation is computed in the new module. In transport simulations, the enhanced transport caused by the magnetic islands has the effect of flattening the pressure and current density profiles. This self consistent treatment of the magnetic islands alters the development of the plasma profiles. In addition, it is found that islands closer to the magnetic axis influence the evolution of islands further out in the plasma. In order to investigate such phenomena, the ISLAND module is used within the BALDUR predictive modeling code to compute the widths of multiple magnetic islands in tokamak discharges. The interaction between the islands and sawtooth crashes is examined in simulations of DIII-D and JET discharges. The module is used to compute saturated neoclassical tearing mode island widths for multiple modes in ITER. Preliminary results for island widths in ITER are consistent with those presented [2] by Hegna. [1] F.D. Halpern, G. Bateman, A.H. Kritz and A.Y. Pankin, ``The ISLAND Module for Computing Magnetic Island Widths in Tokamaks,'' submitted to J. Plasma Physics (2005). [2] C.C. Hegna, 2002 Fusion Snowmass Meeting.

On the Effects of Wind Turbine Wake Skew Caused by Wind Veer

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

Churchfield, Matthew J; Sirnivas, Senu

Because of Coriolis forces caused by the Earth's rotation, the structure of the atmospheric boundary layer often contains wind-direction change with height, also known as wind-direction veer. Under low turbulence conditions, such as in stably stratified atmospheric conditions, this veer can be significant, even across the vertical extent of a wind turbine's rotor disk. The veer then causes the wind turbine wake to skew as it advects downstream. This wake skew has been observed both experimentally and numerically. In this work, we attempt to examine the wake skewing process in some detail, and quantify how differently a skewed wake versusmore » a non skewed wake affects a downstream turbine. We do this by performing atmospheric large-eddy simulations to create turbulent inflow winds with and without veer. In the veer case, there is a roughly 8 degree wind direction change across the turbine rotor. We then perform subsequent large-eddy simulations using these inflow data with an actuator line rotor model to create wakes. The turbine modeled is a large, modern, offshore, multimegawatt turbine. We examine the unsteady wake data in detail and show that the skewed wake recovers faster than the non skewed wake. We also show that the wake deficit does not skew to the same degree that a passive tracer would if subject to veered inflow. Last, we use the wake data to place a hypothetical turbine 9 rotor diameters downstream by running aeroelastic simulations with the simulated wake data. We see differences in power and loads if this downstream turbine is subject to a skewed or non skewed wake. We feel that the differences observed between the skewed and nonskewed wake are important enough that the skewing effect should be included in engineering wake models.« less

Investigating the interaction between the homeostatic and circadian processes of sleep-wake regulation for the prediction of waking neurobehavioural performance

NASA Technical Reports Server (NTRS)

Van Dongen, Hans P A.; Dinges, David F.

2003-01-01

The two-process model of sleep regulation has been applied successfully to describe, predict, and understand sleep-wake regulation in a variety of experimental protocols such as sleep deprivation and forced desynchrony. A non-linear interaction between the homeostatic and circadian processes was reported when the model was applied to describe alertness and performance data obtained during forced desynchrony. This non-linear interaction could also be due to intrinsic non-linearity in the metrics used to measure alertness and performance, however. Distinguishing these possibilities would be of theoretical interest, but could also have important implications for the design and interpretation of experiments placing sleep at different circadian phases or varying the duration of sleep and/or wakefulness. Although to date no resolution to this controversy has been found, here we show that the issue can be addressed with existing data sets. The interaction between the homeostatic and circadian processes of sleep-wake regulation was investigated using neurobehavioural performance data from a laboratory experiment involving total sleep deprivation. The results provided evidence of an actual non-linear interaction between the homeostatic and circadian processes of sleep-wake regulation for the prediction of waking neurobehavioural performance.

Sleep/wake dependent changes in cortical glucose concentrations.

PubMed

Dash, Michael B; Bellesi, Michele; Tononi, Giulio; Cirelli, Chiara

2013-01-01

Most of the energy in the brain comes from glucose and supports glutamatergic activity. The firing rate of cortical glutamatergic neurons, as well as cortical extracellular glutamate levels, increase with time spent awake and decline throughout non rapid eye movement sleep, raising the question whether glucose levels reflect behavioral state and sleep/wake history. Here chronic (2-3 days) electroencephalographic recordings in the rat cerebral cortex were coupled with fixed-potential amperometry to monitor the extracellular concentration of glucose ([gluc]) on a second-by-second basis across the spontaneous sleep-wake cycle and in response to 3 h of sleep deprivation. [Gluc] progressively increased during non rapid eye movement sleep and declined during rapid eye movement sleep, while during wake an early decline in [gluc] was followed by an increase 8-15 min after awakening. There was a significant time of day effect during the dark phase, when rats are mostly awake, with [gluc] being significantly lower during the last 3-4 h of the night relative to the first 3-4 h. Moreover, the duration of the early phase of [gluc] decline during wake was longer after prolonged wake than after consolidated sleep. Thus, the sleep/wake history may affect the levels of glucose available to the brain upon awakening. © 2012 The Authors Journal of Neurochemistry © 2012 International Society for Neurochemistry.

Rotor cascade shape optimization with unsteady passing wakes using implicit dual time stepping method

NASA Astrophysics Data System (ADS)

Lee, Eun Seok

2000-10-01

An improved aerodynamics performance of a turbine cascade shape can be achieved by an understanding of the flow-field associated with the stator-rotor interaction. In this research, an axial gas turbine airfoil cascade shape is optimized for improved aerodynamic performance by using an unsteady Navier-Stokes solver and a parallel genetic algorithm. The objective of the research is twofold: (1) to develop a computational fluid dynamics code having faster convergence rate and unsteady flow simulation capabilities, and (2) to optimize a turbine airfoil cascade shape with unsteady passing wakes for improved aerodynamic performance. The computer code solves the Reynolds averaged Navier-Stokes equations. It is based on the explicit, finite difference, Runge-Kutta time marching scheme and the Diagonalized Alternating Direction Implicit (DADI) scheme, with the Baldwin-Lomax algebraic and k-epsilon turbulence modeling. Improvements in the code focused on the cascade shape design capability, convergence acceleration and unsteady formulation. First, the inverse shape design method was implemented in the code to provide the design capability, where a surface transpiration concept was employed as an inverse technique to modify the geometry satisfying the user specified pressure distribution on the airfoil surface. Second, an approximation storage multigrid method was implemented as an acceleration technique. Third, the preconditioning method was adopted to speed up the convergence rate in solving the low Mach number flows. Finally, the implicit dual time stepping method was incorporated in order to simulate the unsteady flow-fields. For the unsteady code validation, the Stokes's 2nd problem and the Poiseuille flow were chosen and compared with the computed results and analytic solutions. To test the code's ability to capture the natural unsteady flow phenomena, vortex shedding past a cylinder and the shock oscillation over a bicircular airfoil were simulated and compared with

Effect of wakes on land-atmosphere fluxes

NASA Astrophysics Data System (ADS)

Markfort, C. D.; Zhang, W.; Porte-Agel, F.; Stefan, H. G.

2011-12-01

Wakes affect land-atmosphere fluxes of momentum and scalars, including water vapor and trace gases. Canopies and bluff bodies, including forests, buildings and topography, cause boundary layer flow separation, significantly extend flow recovery, and lead to a break down of standard Monin-Obukhov similarity relationships in the atmospheric boundary layer (ABL). Wakes generated by these land surface features persist for significant distances affecting a large fraction of the Earth's terrestrial surface. This effect is currently not accounted for in land-atmosphere modeling, and little is known about how heterogeneity of wake-generating features effect land surface fluxes. Additionally flux measurements, made in wake-affected regions, do not satisfy the homogeneous requirements for the standard eddy correlation (EC) method. This phenomenon often referred to as sheltering has been shown to affect momentum and kinetic energy fluxes into lakes from the atmosphere (Markfort et al. 2010). This presentation will highlight results from controlled wind tunnel experiments of neutral and thermally stratified boundary layers, using PIV and custom x-wire/cold-wire anemometry, designed to understand how the physical structure of upstream bluff bodies or porous canopies and thermal stability affect the separation zone, boundary layer recovery and surface fluxes. We also compare these results to field measurements taken with a Doppler LiDAR in the wake of a canopy and a building. We have found that there is a nonlinear relationship between porosity and flow separation behind a canopy to clearing transition. Results will provide the basis for new parameterizations to account for wake effects on land-atmosphere fluxes and corrections for EC measurements over open fields, lakes, and wetlands.

A late wake time phase delays the human dim light melatonin rhythm.

PubMed

Burgess, Helen J; Eastman, Charmane I

2006-03-13

Short sleep/dark durations, due to late bedtimes or early wake times or both, are common in modern society. We have previously shown that a series of days with a late bedtime phase delays the human dim light melatonin rhythm, as compared to a series of days with an early bedtime, despite a fixed wake time. Here we compared the effect of an early versus late wake time with a fixed bedtime on the human dim light melatonin rhythm. Fourteen healthy subjects experienced 2 weeks of short 6h nights with an early wake time fixed at their habitual weekday wake time and 2 weeks of long 9 h nights with a wake time that occurred 3h later than the early wake time, in counterbalanced order. We found that after 2 weeks with the late wake time, the dim light melatonin onset delayed by 2.4 h and the dim light melatonin offset delayed by 2.6 h (both p < 0.001), as compared to after 2 weeks with the early wake time. These results highlight the substantial influence that wake time, likely via the associated morning light exposure, has on the timing of the human circadian clock. Furthermore, the results suggest that when people truncate their sleep by waking early their circadian clocks phase advance and when people wake late their circadian clocks phase delay.

Rotor boundary layer development with inlet guide vane (IGV) wake impingement

NASA Astrophysics Data System (ADS)

Jia, Lichao; Zou, Tengda; Zhu, Yiding; Lee, Cunbiao

2018-04-01

This paper examines the transition process in a boundary layer on a rotor blade under the impingement of an inlet guide vane wake. The effects of wake strengths and the reduced frequency on the unsteady boundary layer development on a low-speed axial compressor were investigated using particle image velocimetry. The measurements were carried out at two reduced frequencies (fr = fIGVS0/U2i, fr = 1.35, and fr = 0.675) with the Reynolds number, based on the blade chord and the isentropic inlet velocity, being 97 500. At fr = 1.35, the flow separated at the trailing edge when the wake strength was weak. However, the separation was almost totally suppressed as the wake strength increased. For the stronger wake, both the wake's high turbulence and the negative jet behavior of the wake dominated the interaction between the unsteady wake and the separated boundary layer on the suction surface of the airfoil. The boundary layer displacement thickened first due to the negative jet effect. Then, as the disturbances developed underneath the wake, the boundary layer thickness reduced gradually. The high disturbance region convected downstream at a fraction of the free-stream velocity and spread in the streamwise direction. The separation on the suction surface was suppressed until the next wake's arrival. Because of the long recovery time at fr = 0.675, the boundary layer thickened gradually as the wake convected further downstream and finally separated due to the adverse pressure gradient. The different boundary layer states in turn affected the development of disturbances.

Progressive Loss of the Orexin Neurons Reveals Dual Effects on Wakefulness

PubMed Central

Branch, Abigail F.; Navidi, William; Tabuchi, Sawako; Terao, Akira; Yamanaka, Akihiro; Scammell, Thomas E.; Diniz Behn, Cecilia

2016-01-01

Study Objectives: Narcolepsy is caused by loss of the orexin (also known as hypocretin) neurons. In addition to the orexin peptides, these neurons release additional neurotransmitters, which may produce complex effects on sleep/wake behavior. Currently, it remains unknown whether the orexin neurons promote the initiation as well as the maintenance of wakefulness, and whether the orexin neurons influence initiation or maintenance of sleep. To determine the effects of the orexin neurons on the dynamics of sleep/wake behavior, we analyzed sleep/wake architecture in a novel mouse model of acute orexin neuron loss. Methods: We used survival analysis and other statistical methods to analyze sleep/wake architecture in orexin-tTA ; TetO diphtheria toxin A mice at different stages of orexin neuron degeneration. Results: Progressive loss of the orexin neurons dramatically reduced survival of long wake bouts, but it also improved survival of brief wake bouts. In addition, with loss of the orexin neurons, mice were more likely to wake during the first 30 sec of nonrapid eye movement sleep and then less likely to return to sleep during the first 60 sec of wakefulness. Conclusions: These findings help explain the sleepiness and fragmented sleep that are characteristic of narcolepsy. Orexin neuron loss impairs survival of long wake bouts resulting in poor maintenance of wakefulness, but this neuronal loss also fragments sleep by increasing the risk of awakening at the beginning of sleep and then reducing the likelihood of quickly returning to sleep. Citation: Branch AF, Navidi W, Tabuchi S, Terao A, Yamanaka A, Scammell TE, Diniz Behn C. Progressive loss of the orexin neurons reveals dual effects on wakefulness. SLEEP 2016;39(2):369–377. PMID:26446125

Low-Dimensional Model of a Cylinder Wake

NASA Astrophysics Data System (ADS)

Luchtenburg, Mark; Cohen, Kelly; Siegel, Stefan; McLaughlin, Tom

2003-11-01

In a two-dimensional cylinder wake, self-excited oscillations in the form of periodic shedding of vortices are observed above a critical Reynolds number of about 47. These flow-induced non-linear oscillations lead to some undesirable effects associated with unsteady pressures such as fluid-structure interactions. An effective way of suppressing the self-excited flow oscillations is by the incorporation of closed-loop flow control. In this effort, a low dimensional, proper orthogonal decomposition (POD) model is based on data obtained from direct numerical simulations of the Navier Stokes equations for the two dimensional circular cylinder wake at a Reynolds number of 100. Three different conditions are examined, namely, the unforced wake experiencing steady-state vortex shedding, the transient behavior of the unforced wake at the startup of the simulation, and transient response to open-loop harmonic forcing by translation. We discuss POD mode selection and the number of modes that need to be included in the low-dimensional model. It is found that the transient dynamics need to be represented by a coupled system that includes an aperiodic mean-flow mode, an aperiodic shift mode and the periodic von Karman modes. Finally, a least squares mapping method is introduced to develop the non-linear state equations. The predictive capability of the state equations demonstrates the ability of the above approach to model the transient dynamics of the wake.

The Plasma Wake Downstream of Lunar Topographic Obstacles: Preliminary Results from 2D Particle Simulations

NASA Technical Reports Server (NTRS)

Zimmerman, Michael I.; Farrell, W. M.; Snubbs, T. J.; Halekas, J. S.

2011-01-01

Anticipating the plasma and electrical environments in permanently shadowed regions (PSRs) of the moon is critical in understanding local processes of space weathering, surface charging, surface chemistry, volatile production and trapping, exo-ion sputtering, and charged dust transport. In the present study, we have employed the open-source XOOPIC code [I] to investigate the effects of solar wind conditions and plasma-surface interactions on the electrical environment in PSRs through fully two-dimensional pattic1e-in-cell simulations. By direct analogy with current understanding of the global lunar wake (e.g., references) deep, near-terminator, shadowed craters are expected to produce plasma "mini-wakes" just leeward of the crater wall. The present results (e.g., Figure I) are in agreement with previous claims that hot electrons rush into the crater void ahead of the heavier ions, fanning a negative cloud of charge. Charge separation along the initial plasma-vacuum interface gives rise to an ambipolar electric field that subsequently accelerates ions into the void. However, the situation is complicated by the presence of the dynamic lunar surface, which develops an electric potential in response to local plasma currents (e.g., Figure Ia). In some regimes, wake structure is clearly affected by the presence of the charged crater floor as it seeks to achieve current balance (i.e. zero net current to the surface).

Use of Plasma Actuators as a Moving-Wake Generator

NASA Technical Reports Server (NTRS)

Corke, Thomas C.; Thomas, Flint O.; Klapetzky Michael J.

2007-01-01

The work documented in this report tests the concept of using plasma actuators as a simple and easy way to generate a simulated moving-wake and the disturbances associated with it in turbines. This wake is caused by the blades of the upstream stages of the turbine. Two types of devices, one constructed of arrays of NACA 0018 airfoils, and the one constructed of flat plates were studied. The airfoils or plates were equipped with surface mounted dielectric barrier discharge (DBD) plasma actuators, which were used to generate flow disturbances resembling moving-wakes. CTA hot-wire anemometry and flow visualization using a smoke-wire were used to investigate the wake independence at various spacings and downstream locations. The flat plates were found to produce better results than the airfoils in creating large velocity fluctuations in the free-stream flow. Different dielectric materials, plasma actuator locations, leading edge contours, angles of attack and plate spacings were investigated, some with positive results. The magnitudes of the velocity fluctuations were found to be comparable to existing mechanical moving-wake generators, thus proving the feasibility of using plasma actuators as a moving-wake generator.

Dynamics of the vortex wakes of flying and swimming vertebrates.

PubMed

Rayner, J M

1995-01-01

The vortex wakes of flying and swimming animals provide evidence of the history of aero- and hydrodynamic force generation during the locomotor cycle. Vortex-induced momentum flux in the wake is the reaction of forces the animal imposes on its environment, which must be in equilibrium with inertial and external forces. In flying birds and bats, the flapping wings generate lift both to provide thrust and to support the weight. Distinct wingbeat and wake movement patterns can be identified as gaits. In flow visualization experiments, only two wake patterns have been identified: a vortex ring gait with inactive upstroke, and a continuous vortex gait with active upstroke. These gaits may be modelled theoretically by free vortex and lifting line theory to predict mechanical energy consumption, aerodynamic forces and muscle activity. Longer-winged birds undergo a distinct gait change with speed, but shorter-winged species use the vortex ring gait at all speeds. In swimming fish, the situation is more complex: the wake vortices form a reversed von Kármán vortex street, but little is known about the mechanism of generation of the wake, or about how it varies with speed and acceleration or with body form and swimming mode. An unresolved complicating factor is the interaction between the drag wake of the flapping fish body and the thrusting wake from the tail.

The plasma wake of mesosonic conducting bodies. II - An experimental parametric study of the mid-wake ion density peak

NASA Technical Reports Server (NTRS)

Stone, N. H.

1981-01-01

An experimental investigation of the disturbed flow field created by conducting bodies in a mesosonic, collisionless plasma stream is reported. The mid-wake region is investigated, where, for bodies of the order of a Debye length in size, the focused ion streams converge to form a significant current density peak on the wake axis. A parametric description is obtained of the behavior of the amplitude, width, and position of this peak. The results also indicate that portions of the axial ion peak are created by additional mechanisms and that body geometry affects the mid-wake structure only when the sheath is sufficiently thin to conform to the shape of the body.

Aircraft wake vortex measurements at Denver International Airport

DOT National Transportation Integrated Search

2004-05-10

Airport capacity is constrained, in part, by spacing requirements associated with the wake vortex hazard. NASA's Wake Vortex Avoidance Project has a goal to establish the feasibility of reducing this spacing while maintaining safety. Passive acoustic...

Kelvin-Mach Wake in a Two-Dimensional Fermi Sea

NASA Astrophysics Data System (ADS)

Kolomeisky, Eugene B.; Straley, Joseph P.

2018-06-01

The dispersion law for plasma oscillations in a two-dimensional electron gas in the hydrodynamic approximation interpolates between Ω ∝√{q } and Ω ∝q dependences as the wave vector q increases. As a result, downstream of a charged impurity in the presence of a uniform supersonic electric current flow, a wake pattern of induced charge density and potential is formed whose geometry is controlled by the Mach number M . For 1 wake consists of transverse wave fronts confined within a sector, whose angle is given by the classic Mach condition. An additional wake of a larger angle resembling the Kelvin ship wake, and consisting of both transverse and diverging wave fronts, is found outside the Mach sector for M >√{2 }. These wakes also trail an external charge, traveling supersonically, a fixed distance away from the electron gas.

Linear instability of supersonic plane wakes

NASA Technical Reports Server (NTRS)

Papageorgiou, D. T.

1989-01-01

In this paper we present a theoretical and numerical study of the growth of linear disturbances in the high-Reynolds-number and laminar compressible wake behind a flat plate which is aligned with a uniform stream. No ad hoc assumptions are made as to the nature of the undisturbed flow (in contrast to previous investigations) but instead the theory is developed rationally by use of proper wake-profiles which satisfy the steady equations of motion. The initial growth of near wake perturbation is governed by the compressible Rayleigh equation which is studied analytically for long- and short-waves. These solutions emphasize the asymptotic structures involved and provide a rational basis for a nonlinear development. The evolution of arbitrary wavelength perturbations is addressed numerically and spatial stability solutions are presented that account for the relative importance of the different physical mechanisms present, such as three-dimensionality, increasing Mach numbers enough (subsonic) Mach numbers, there exists a region of absolute instability very close to the trailing-edge with the majority of the wake being convectively unstable. At higher Mach numbers (but still not large-hypersonic) the absolute instability region seems to disappear and the maximum available growth-rates decrease considerably. Three-dimensional perturbations provide the highest spatial growth-rates.

Assessment of a wake vortex flight test program

NASA Technical Reports Server (NTRS)

Spangler, S. B.; Dillenius, M. F. E.; Schwind, R. G.; Nielsen, J. N.

1974-01-01

A proposed flight test program to measure the characteristics of wake vortices behind a T-33 aircraft was investigated. A number of facets of the flight tests were examined to define the parameters to be measured, the anticipated vortex characteristics, the mutual interference between the probe aircraft and the wake, the response of certain instruments to be used in obtaining measurements, the effect of condensation on the wake vortices, and methods of data reduction. Recommendations made as a result of the investigation are presented.

Analysis of noise measured from a propeller in a wake

NASA Technical Reports Server (NTRS)

Block, P. J. W.

1984-01-01

In this experimental study, the acoustic characteristics of a propeller operating in a wake were studied. The propeller performance and noise were measured from two 0.25 scale propellers operating in an open jet anechoic flow environment with and without a wake. One propeller had NACA 16 series sections; the other, ARA-D. Wake thicknesses of 1 and 3 propeller chords were generated by an airfoil which spanned the full diameter of the propeller. The airfoil wake profiles were measured. Noise measurements were made in and out of the flow. The propellers were operated at 40, 83, and 100 inf of thrust. The acoustic data are analyzed, and the effects on the overall sound pressure level (OASPL) and scaled A weighted sound level L sub A with propeller thrust, wake thickness, and observer location are presented. The analysis showed that, generally, the wake increased the overall noise (OASPL) produced by the propeller; increased the harmonic content of the noise, thus the scaled L sub a; and produced an azimuthal dependence. With few exceptions, both propellers generally produced the same trends in delta OASPL and delta L sub a with thrust and wake thickness.

Wake Vortex Field Measurement Program at Memphis, Tennessee: Data Guide

NASA Technical Reports Server (NTRS)

Campbell, S. D.; Dasey, T. J.; Freehart, R. E.; Heinrichs, R. M.; Mathews, M. P.; Perras, G. H.; Rowe, G. S.

1997-01-01

Eliminating or reducing current restrictions in the air traffic control system due to wake vortex considerations would yield increased capacity, decreased delays, and cost savings. Current wake vortex separation standards are widely viewed as very conservative under most conditions. However, scientific uncertainty about wake vortex behavior under different atmospheric conditions remains a barrier to development of an adaptive vortex spacing system. The objective of the wake vortex field measurement efforts during December, 1994 and August, 1995 at Memphis, TN were to record wake vortex behavior for varying atmospheric conditions and types of aircraft. This effort is part of a larger effort by the NASA Langley Research Center to develop an Aircraft Vortex Spacing System (AVOSS) as an element of the Terminal Area Productivity (TAP) program. The TAP program is being performed in concert with the FAA Terminal Air Traffic Control Automation (TATCA) program and ATC Automation. Wake vortex behavior was observed using a mobile continuous-wave (CW) coherent laser Doppler radar (lidar) developed at Lincoln Laboratory. This lidar features a number of improvements over previous systems, including the first-ever demonstration of an automatic wake vortex detection and tracking algorithm.

Passive propulsion in vortex wakes

NASA Astrophysics Data System (ADS)

Beal, D. N.; Hover, F. S.; Triantafyllou, M. S.; Liao, J. C.; Lauder, G. V.

A dead fish is propelled upstream when its flexible body resonates with oncoming vortices formed in the wake of a bluff cylinder, despite being well outside the suction region of the cylinder. Within this passive propulsion mode, the body of the fish extracts sufficient energy from the oncoming vortices to develop thrust to overcome its own drag. In a similar turbulent wake and at roughly the same distance behind a bluff cylinder, a passively mounted high-aspect-ratio foil is also shown to propel itself upstream employing a similar flow energy extraction mechanism. In this case, mechanical energy is extracted from the flow at the same time that thrust is produced. These results prove experimentally that, under proper conditions, a body can follow at a distance or even catch up to another upstream body without expending any energy of its own. This observation is also significant in the development of low-drag energy harvesting devices, and in the energetics of fish dwelling in flowing water and swimming behind wake-forming obstacles.

Initialization and Simulation of Three-Dimensional Aircraft Wake Vortices

NASA Technical Reports Server (NTRS)

Ash, Robert L.; Zheng, Z. C.

1997-01-01

This paper studies the effects of axial velocity profiles on vortex decay, in order to properly initialize and simulate three-dimensional wake vortex flow. Analytical relationships are obtained based on a single vortex model and computational simulations are performed for a rather practical vortex wake, which show that the single vortex analytical relations can still be applicable at certain streamwise sections of three-dimensional wake vortices.

Wind Turbine Wake-Redirection Control at the Fishermen's Atlantic City Windfarm: Preprint

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

Churchfield, M.; Fleming, P.; Bulder, B.

2015-05-06

In this paper, we will present our work towards designing a control strategy to mitigate wind turbine wake effects by redirecting the wakes, specifically applied to the Fishermen’s Atlantic City Windfarm (FACW), proposed for deployment off the shore of Atlantic City, New Jersey. As wind turbines extract energy from the air, they create low-speed wakes that extend behind them. Full wake recovery Full wake recovery to the undisturbed wind speed takes a significant distance. In a wind energy plant the wakes of upstream turbines may travel downstream to the next row of turbines, effectively subjecting them to lower wind speeds,more » meaning these waked turbines will produce less power.« less

Tracking wakefulness as it fades: Micro-measures of alertness.

PubMed

Jagannathan, Sridhar R; Ezquerro-Nassar, Alejandro; Jachs, Barbara; Pustovaya, Olga V; Bareham, Corinne A; Bekinschtein, Tristan A

2018-08-01

A major problem in psychology and physiology experiments is drowsiness: around a third of participants show decreased wakefulness despite being instructed to stay alert. In some non-visual experiments participants keep their eyes closed throughout the task, thus promoting the occurrence of such periods of varying alertness. These wakefulness changes contribute to systematic noise in data and measures of interest. To account for this omnipresent problem in data acquisition we defined criteria and code to allow researchers to detect and control for varying alertness in electroencephalography (EEG) experiments under eyes-closed settings. We first revise a visual-scoring method developed for detection and characterization of the sleep-onset process, and adapt the same for detection of alertness levels. Furthermore, we show the major issues preventing the practical use of this method, and overcome these issues by developing an automated method (micro-measures algorithm) based on frequency and sleep graphoelements, which are capable of detecting micro variations in alertness. The validity of the micro-measures algorithm was verified by training and testing using a dataset where participants are known to fall asleep. In addition, we tested generalisability by independent validation on another dataset. The methods developed constitute a unique tool to assess micro variations in levels of alertness and control trial-by-trial retrospectively or prospectively in every experiment performed with EEG in cognitive neuroscience under eyes-closed settings. Copyright © 2018. Published by Elsevier Inc.

Canopy wake measurements using multiple scanning wind LiDARs

NASA Astrophysics Data System (ADS)

Markfort, C. D.; Carbajo Fuertes, F.; Iungo, V.; Stefan, H. G.; Porte-Agel, F.

2014-12-01

Canopy wakes have been shown, in controlled wind tunnel experiments, to significantly affect the fluxes of momentum, heat and other scalars at the land and water surface over distances of ˜O(1 km), see Markfort et al. (EFM, 2013). However, there are currently no measurements of the velocity field downwind of a full-scale forest canopy. Point-based anemometer measurements of wake turbulence provide limited insight into the extent and details of the wake structure, whereas scanning Doppler wind LiDARs can provide information on how the wake evolves in space and varies over time. For the first time, we present measurements of the velocity field in the wake of a tall patch of forest canopy. The patch consists of two uniform rows of 40-meter tall deciduous, plane trees, which border either side of the Allée de Dorigny, near the EPFL campus. The canopy is approximately 250 m long, and it is approximately 40 m wide, along the direction of the wind. A challenge faced while making field measurements is that the wind rarely intersects a canopy normal to the edge. The resulting wake flow may be deflected relative to the mean inflow. Using multiple LiDARs, we measure the evolution of the wake due to an oblique wind blowing over the canopy. One LiDAR is positioned directly downwind of the canopy to measure the flow along the mean wind direction and the other is positioned near the canopy to evaluate the transversal component of the wind and how it varies with downwind distance from the canopy. Preliminary results show that the open trunk space near the base of the canopy results in a surface jet that can be detected just downwind of the canopy and farther downwind dissipates as it mixes with the wake flow above. A time-varying recirculation zone can be detected by the periodic reversal of the velocity near the surface, downwind of the canopy. The implications of canopy wakes for measurement and modeling of surface fluxes will be discussed.

Canopy wake measurements using multiple scanning wind LiDARs

NASA Astrophysics Data System (ADS)

Markfort, Corey D.; Carbajo Fuertes, Fernando; Valerio Iungo, Giacomo; Stefan, Heinz; Porté-Agel, Fernando

2014-05-01

Canopy wakes have been shown, in controlled wind tunnel experiments, to significantly affect the fluxes of momentum, heat and other scalars at the land and water surface over distances of ~O(1 km), see Markfort et al. (EFM, 2013). However, there are currently no measurements of the velocity field downwind of a full-scale forest canopy. Point-based anemometer measurements of wake turbulence provide limited insight into the extent and details of the wake structure, whereas scanning Doppler wind LiDARs can provide information on how the wake evolves in space and varies over time. For the first time, we present measurements of the velocity field in the wake of a tall patch of forest canopy. The patch consists of two uniform rows of 35-meter tall deciduous, plane trees, which border either side of the Allée de Dorigny, near the EPFL campus. The canopy is approximately 250 m long, and it is 35 m wide, along the direction of the wind. A challenge faced while making field measurements is that the wind rarely intersects a canopy normal to the edge. The resulting wake flow may be deflected relative to the mean inflow. Using multiple LiDARs, we measure the evolution of the wake due to an oblique wind blowing over the canopy. One LiDAR is positioned directly downwind of the canopy to measure the flow along the mean wind direction and the other is positioned near the canopy to evaluate the transversal component of the wind and how it varies with downwind distance from the canopy. Preliminary results show that the open trunk space near the base of the canopy results in a surface jet that can be detected just downwind of the canopy and farther downwind dissipates as it mixes with the wake flow above. A time-varying recirculation zone can be detected by the periodic reversal of the velocity vector near the surface, downwind of the canopy. The implications of canopy wakes for measurement and modeling of surface fluxes will be discussed.

32 CFR 935.52 - Violations of Subpart O or P of this part.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 32 National Defense 6 2014-07-01 2014-07-01 false Violations of Subpart O or P of this part. 935... TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Penalties § 935.52 Violations of Subpart O or P of this part. (a) Whoever is found guilty of a violation of subpart O or P of this part is subject to a fine of...

32 CFR 935.52 - Violations of Subpart O or P of this part.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 32 National Defense 6 2013-07-01 2013-07-01 false Violations of Subpart O or P of this part. 935... TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Penalties § 935.52 Violations of Subpart O or P of this part. (a) Whoever is found guilty of a violation of subpart O or P of this part is subject to a fine of...

32 CFR 935.52 - Violations of Subpart O or P of this part.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 32 National Defense 6 2012-07-01 2012-07-01 false Violations of Subpart O or P of this part. 935... TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Penalties § 935.52 Violations of Subpart O or P of this part. (a) Whoever is found guilty of a violation of subpart O or P of this part is subject to a fine of...

32 CFR 935.52 - Violations of Subpart O or P of this part.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 32 National Defense 6 2011-07-01 2011-07-01 false Violations of Subpart O or P of this part. 935... TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Penalties § 935.52 Violations of Subpart O or P of this part. (a) Whoever is found guilty of a violation of subpart O or P of this part is subject to a fine of...

32 CFR 935.52 - Violations of Subpart O or P of this part.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 32 National Defense 6 2010-07-01 2010-07-01 false Violations of Subpart O or P of this part. 935... TERRITORIAL AND INSULAR REGULATIONS WAKE ISLAND CODE Penalties § 935.52 Violations of Subpart O or P of this part. (a) Whoever is found guilty of a violation of subpart O or P of this part is subject to a fine of...

Wake characteristics of wind turbines in utility-scale wind farms

NASA Astrophysics Data System (ADS)

Yang, Xiaolei; Foti, Daniel; Sotiropoulos, Fotis

2017-11-01

The dynamics of turbine wakes is affected by turbine operating conditions, ambient atmospheric turbulent flows, and wakes from upwind turbines. Investigations of the wake from a single turbine have been extensively carried out in the literature. Studies on the wake dynamics in utility-scale wind farms are relatively limited. In this work, we employ large-eddy simulation with an actuator surface or actuator line model for turbine blades to investigate the wake dynamics in utility-scale wind farms. Simulations of three wind farms, i.e., the Horns Rev wind farm in Denmark, Pleasant Valley wind farm in Minnesota, and the Vantage wind farm in Washington are carried out. The computed power shows a good agreement with measurements. Analysis of the wake dynamics in the three wind farms is underway and will be presented in the conference. This work was support by Xcel Energy (RD4-13). The computational resources were provided by National Renewable Energy Laboratory.

Large-eddy simulation of propeller wake at design operating conditions

NASA Astrophysics Data System (ADS)

Kumar, Praveen; Mahesh, Krishnan

2016-11-01

Understanding the propeller wake is crucial for efficient design and optimized performance. The dynamics of the propeller wake are also central to physical phenomena such as cavitation and acoustics. Large-eddy simulation is used to study the evolution of the wake of a five-bladed marine propeller from near to far field at design operating condition. The computed mean loads and phase-averaged flow field show good agreement with experiments. The propeller wake consisting of tip and hub vortices undergoes streamtube contraction, which is followed by the onset of instabilities as evident from the oscillations of the tip vortices. Simulation results reveal a mutual induction mechanism of instability where instead of the tip vortices interacting among themselves, they interact with the smaller vortices generated by the roll-up of the blade trailing edge wake in the near wake. Phase-averaged and ensemble-averaged flow fields are analyzed to explain the flow physics. This work is supported by ONR.

Computer program documentation for a subcritical wing design code using higher order far-field drag minimization

NASA Technical Reports Server (NTRS)

Kuhlman, J. M.; Shu, J. Y.

1981-01-01

A subsonic, linearized aerodynamic theory, wing design program for one or two planforms was developed which uses a vortex lattice near field model and a higher order panel method in the far field. The theoretical development of the wake model and its implementation in the vortex lattice design code are summarized and sample results are given. Detailed program usage instructions, sample input and output data, and a program listing are presented in the Appendixes. The far field wake model assumes a wake vortex sheet whose strength varies piecewise linearly in the spanwise direction. From this model analytical expressions for lift coefficient, induced drag coefficient, pitching moment coefficient, and bending moment coefficient were developed. From these relationships a direct optimization scheme is used to determine the optimum wake vorticity distribution for minimum induced drag, subject to constraints on lift, and pitching or bending moment. Integration spanwise yields the bound circulation, which is interpolated in the near field vortex lattice to obtain the design camber surface(s).

Acoustic characterization of wake vortices in ground effect

DOT National Transportation Integrated Search

2005-01-01

The experience and findings of an exploratory effort to characterize the sound emitted by : aircraft wake vortices near the ground are presented. A line array of four directional : microphones was deployed and recorded the wakes of several commercial...

Controlled Wake of a Moving Axisymmetric Bluff Body

NASA Astrophysics Data System (ADS)

Lee, E.; Vukasinovic, B.; Glezer, A.

2017-11-01

The aerodynamic loads exerted on a wire-mounted axisymmetric bluff body in prescribed rigid motion are controlled by fluidic manipulation of its near wake. The body is supported by a six-degree of freedom eight-wire traverse and its motion is controlled using a dedicated servo actuator and inline load cell for each wire. The instantaneous aerodynamic forces and moments on the moving body are manipulated by controlled interactions of an azimuthal array of integrated synthetic jet actuators with the cross flow to induce localized flow attachment over the body's aft end and thereby alter the symmetry of the wake. The coupled interactions between the wake structure and the effected aerodynamic loads during prescribed time-periodic and transitory (gust like) motions are investigated with emphasis on enhancing or diminishing the loads for maneuver control, and decoupling the body's motion from its far wake.

Noise generated by a propeller in a wake

NASA Technical Reports Server (NTRS)

Block, P. J. W.

1984-01-01

Propeller performance and noise were measured on two model scale propellers operating in an anechoic flow environment with and without a wake. Wake thickness of one and three propeller chords were generated by an airfoil which spanned the full diameter of the propeller. Noise measurements were made in the relative near field of the propeller at three streamwise and three azimuthal positions. The data show that as much as 10 dB increase in the OASPL results when a wake is introduced into an operating propeller. Performance data are also presented for completeness.

An Aeroelastic Perspective of Floating Offshore Wind Turbine Wake Formation and Instability

NASA Astrophysics Data System (ADS)

Rodriguez, Steven N.; Jaworski, Justin W.

2015-11-01

The wake formation and wake stability of floating offshore wind turbines are investigated from an aeroelastic perspective. The aeroelastic model is composed of the Sebastian-Lackner free-vortex wake aerodynamic model coupled to the nonlinear Hodges-Dowell beam equations, which are extended to include the effects of blade profile asymmetry, higher-order torsional effects, and kinetic energy components associated with periodic rigid-body motions of floating platforms. Rigid-body platform motions are also assigned to the aerodynamic model as varying inflow conditions to emulate operational rotor-wake interactions. Careful attention is given to the wake formation within operational states where the ratio of inflow velocity to induced velocity is over 50%. These states are most susceptible to aerodynamic instabilities, and provide a range of states about which a wake stability analysis can be performed. In addition, the stability analysis used for the numerical framework is implemented into a standalone free-vortex wake aerodynamic model. Both aeroelastic and standalone aerodynamic results are compared to evaluate the level of impact that flexible blades have on the wake formation and wake stability.

Ship heading and velocity analysis by wake detection in SAR images

NASA Astrophysics Data System (ADS)

Graziano, Maria Daniela; D'Errico, Marco; Rufino, Giancarlo

2016-11-01

With the aim of ship-route estimation, a wake detection method is developed and applied to COSMO/SkyMed and TerraSAR-X Stripmap SAR images over the Gulf of Naples, Italy. In order to mitigate the intrinsic limitations of the threshold logic, the algorithm identifies the wake features according to the hydrodynamic theory. A post-detection validation phase is performed to classify the features as real wake structures by means of merit indexes defined in the intensity domain. After wake reconstruction, ship heading is evaluated on the basis of turbulent wake direction and ship velocity is estimated by both techniques of azimuth shift and Kelvin pattern wavelength. The method is tested over 34 ship wakes identified by visual inspection in both HH and VV images at different incidence angles. For all wakes, no missed detections are reported and at least the turbulent and one narrow-V wakes are correctly identified, with ship heading successfully estimated. Also, the azimuth shift method is applied to estimate velocity for the 10 ships having route with sufficient angular separation from the satellite ground track. In one case ship velocity is successfully estimated with both methods, showing agreement within 14%.

Measuremants in the wake of an infinite swept airfoil

NASA Technical Reports Server (NTRS)

Novak, C. J.; Ramaprian, B. R.

1982-01-01

This is a report of the measurements in the trailing edge region as well as in the report of the developing wake behind a swept NACA 0012 airfoil at zero incidence and a sweep angle of 30 degrees. The measurements include both the mean and turbulent flow properties. The mean flow velocities, flow inclination and static pressure are measured using a calibrated three-hole yaw probe. The measurements of all the relevant Reynolds stress components in the wake are made using a tri-axial hot-wire probe and a digital data processing technique developed by the authors. The development of the three dimensional near-wake into a nearly two dimensional far-wake is discussed in the light of the experimental data. A complete set of wake data along with the data on the initial boundary layer in the trailing edge region of the airfoil are tabulated in an appendix to the report.

Circadian Rhythm Sleep-Wake Disorders.

PubMed

Abbott, Sabra M; Reid, Kathryn J; Zee, Phyllis C

2015-12-01

The circadian system regulates the timing and expression of nearly all biological processes, most notably, the sleep-wake cycle, and disruption of this system can result in adverse effects on both physical and mental health. The circadian rhythm sleep-wake disorders (CRSWDs) consist of 5 disorders that are due primarily to pathology of the circadian clock or to a misalignment of the timing of the endogenous circadian rhythm with the environment. This article outlines the nature of these disorders, the association of many of these disorders with psychiatric illness, and available treatment options. Copyright © 2015 Elsevier Inc. All rights reserved.

Rotating Wheel Wake

NASA Astrophysics Data System (ADS)

Lombard, Jean-Eloi; Xu, Hui; Moxey, Dave; Sherwin, Spencer

2016-11-01

For open wheel race-cars, such as Formula One, or IndyCar, the wheels are responsible for 40 % of the total drag. For road cars, drag associated to the wheels and under-carriage can represent 20 - 60 % of total drag at highway cruise speeds. Experimental observations have reported two, three or more pairs of counter rotating vortices, the relative strength of which still remains an open question. The near wake of an unsteady rotating wheel. The numerical investigation by means of direct numerical simulation at ReD =400-1000 is presented here to further the understanding of bifurcations the flow undergoes as the Reynolds number is increased. Direct numerical simulation is performed using Nektar++, the results of which are compared to those of Pirozzoli et al. (2012). Both proper orthogonal decomposition and dynamic mode decomposition, as well as spectral analysis are leveraged to gain unprecedented insight into the bifurcations and subsequent topological differences of the wake as the Reynolds number is increased.

Canopy-wake dynamics: the failure of the constant flux layer

NASA Astrophysics Data System (ADS)

Stefan, H. G.; Markfort, C. D.; Porte-Agel, F.

2013-12-01

The atmospheric boundary layer adjustment at the abrupt transition from a canopy (forest) to a flat surface (land or water) was investigated in a wind tunnel experiment. Detailed measurements examining the effect of canopy turbulence on flow separation, reduced surface shear stress and wake recovery are compared to data for the classical case of a solid backward-facing step. Results provide new insights into the data interpretation for flux estimation by eddy-covariance and flux gradient methods and for the assessment of surface boundary conditions in turbulence models of the atmospheric boundary layer in complex landscapes and over water bodies affected by canopy wakes. The wind tunnel results indicate that the wake of a forest canopy strongly affects surface momentum flux within a distance of 35 - 100 times the step or canopy height, and mean turbulence quantities require distances of at least 100 times the canopy height to adjust to the new surface. The near-surface mixing length in the wake exhibits characteristic length scales of canopy flows at the canopy edge, of the flow separation in the near wake and adjusts to surface layer scaling in the far wake. Components of the momentum budget are examined individually to determine the impact of the wake. The results demonstrate why a constant flux layer does not form until far downwind in the wake. An empirical model for surface shear stress distribution from a forest to a clearing or lake is proposed.

Approaches to Measuring the Effects of Wake-Promoting Drugs: A Focus on Cognitive Function

PubMed Central

Edgar, Christopher J.; Pace-Schott, Edward F.; Wesnes, Keith A.

2009-01-01

Objectives In clinical drug development, wakefulness and wake-promotion maybe assessed by a large number of scales and questionnaires. Objective assessment of wakefulness is most commonly made using sleep latency/maintenance of wakefulness tests, polysomnography and/or behavioral measures. The purpose of the present review is to highlight the degree of overlap in the assessment of wakefulness and cognition, with consideration of assessment techniques and the underlying neurobiology of both concepts. Design Reviews of four key areas were conducted: commonly used techniques in the assessment of wakefulness; neurobiology of sleep/wake and cognition; targets of wake promoting and/or cognition enhancing drugs; and ongoing clinical trials investigating wake promoting effects. Results There is clear overlap between the assessment of wakefulness and cognition. There are common techniques which may be used to assess both concepts; aspects of the neurobiology of both concepts may be closely related; and wake promoting drugs may have nootropic properties (and vice-versa). Clinical trials of wake promoting drugs often, though not routinely, assess aspects of cognition. Conclusions Routine and broad assessment of cognition in the development of wake promoting drugs may reveal important nootropic effects, which are not secondary to alertness/wakefulness, whilst existing cognitive enhancers may have under explored or unknown wake promoting properties. PMID:19565524

Comparative study on the wake deflection behind yawed wind turbine models

NASA Astrophysics Data System (ADS)

Schottler, Jannik; Mühle, Franz; Bartl, Jan; Peinke, Joachim; Adaramola, Muyiwa S.; Sætran, Lars; Hölling, Michael

2017-05-01

In this wind tunnel campaign, detailed wake measurements behind two different model wind turbines in yawed conditions were performed. The wake deflections were quantified by estimating the rotor-averaged available power within the wake. By using two different model wind turbines, the influence of the rotor design and turbine geometry on the wake deflection caused by a yaw misalignment of 30° could be judged. It was found that the wake deflections three rotor diameters downstream were equal while at six rotor diameters downstream insignificant differences were observed. The results compare well with previous experimental and numerical studies.

The wake of hovering flight in bats

PubMed Central

Håkansson, Jonas; Hedenström, Anders; Winter, York; Johansson, L. Christoffer

2015-01-01

Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down- and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%. PMID:26179990

Mesoscale wake clouds in Skylab pictures.

NASA Technical Reports Server (NTRS)

Fujita, T. T.; Tecson, J. J.

1974-01-01

The recognition of cloud patterns formed in the wake of orographic obstacles was investigated using pictures from Skylab, for the purpose of estimating atmospheric motions. The existence of ship-wake-type wave clouds in contrast to vortex sheets were revealed during examination of the pictures, and an attempt was made to characterize the pattern of waves as well as the transition between waves and vortices. Examples of mesoscale cloud patterns which were analyzed photogrammetrically and meteorologically are presented.

Measurements of Aircraft Wake Vortex Separation at High Arrival Rates and a Proposed New Wake Vortex Separation Philosophy

NASA Technical Reports Server (NTRS)

Rutishauser, David; Donohue, George L.; Haynie, Rudolph C.

2003-01-01

This paper presents data and a proposed new aircraft wake vortex separation standard that argues for a fundamental re-thinking of international practice. The current static standard, under certain atmospheric conditions, presents an unnecessary restriction on system capacity. A new approach, that decreases aircraft separation when atmospheric conditions dictate, is proposed based upon the availability of new instrumentation and a better understanding of wake physics.

Airfoil-Wake Modification with Gurney Flap at Low Reynolds Number

NASA Astrophysics Data System (ADS)

Gopalakrishnan Meena, Muralikrishnan; Taira, Kunihiko; Asai, Keisuke

2018-04-01

The complex wake modifications produced by a Gurney flap on symmetric NACA airfoils at low Reynolds number are investigated. Two-dimensional incompressible flows over NACA 0000 (flat plate), 0006, 0012 and 0018 airfoils at a Reynolds number of $Re = 1000$ are analyzed numerically to examine the flow modifications generated by the flaps for achieving lift enhancement. While high lift can be attained by the Gurney flap on airfoils at high angles of attack, highly unsteady nature of the aerodynamic forces are also observed. Analysis of the wake structures along with the lift spectra reveals four characteristic wake modes (steady, 2S, P and 2P), influencing the aerodynamic performance. The effects of the flap over wide range of angles of attack and flap heights are considered to identify the occurrence of these wake modes, and are encapsulated in a wake classification diagram. Companion three-dimensional simulations are also performed to examine the influence of three-dimensionality on the wake regimes. The spanwise instabilities that appear for higher angles of attack are found to suppress the emergence of the 2P mode. The use of the wake classification diagram as a guidance for Gurney flap selection at different operating conditions to achieve the required aerodynamic performance is discussed.

Cost-Effectiveness Analysis of the Residential Provisions of the 2015 IECC for Rhode Island

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

Mendon, Vrushali V.; Zhao, Mingjie; Taylor, Zachary T.

The 2015 IECC provides cost-effective savings for residential buildings in Rhode Island. Moving to the 2015 IECC from the 2012 IECC base code is cost-effective for residential buildings in all climate zones in Rhode Island.

An Operational Wake Vortex Sensor Using Pulsed Coherent Lidar

NASA Technical Reports Server (NTRS)

Barker, Ben C., Jr.; Koch, Grady J.; Nguyen, D. Chi

1998-01-01

NASA and FAA initiated a program in 1994 to develop methods of setting spacings for landing aircraft by incorporating information on the real-time behavior of aircraft wake vortices. The current wake separation standards were developed in the 1970's when there was relatively light airport traffic and a logical break point by which to categorize aircraft. Today's continuum of aircraft sizes and increased airport packing densities have created a need for re-evaluation of wake separation standards. The goals of this effort are to ensure that separation standards are adequate for safety and to reduce aircraft spacing for higher airport capacity. Of particular interest are the different requirements for landing under visual flight conditions and instrument flight conditions. Over the years, greater spacings have been established for instrument flight than are allowed for visual flight conditions. Preliminary studies indicate that the airline industry would save considerable money and incur fewer passenger delays if a dynamic spacing system could reduce separations at major hubs during inclement weather to the levels routinely achieved under visual flight conditions. The sensor described herein may become part of this dynamic spacing system known as the "Aircraft VOrtex Spacing System" (AVOSS) that will interface with a future air traffic control system. AVOSS will use vortex behavioral models and short-term weather prediction models in order to predict vortex behavior sufficiently into the future to allow dynamic separation standards to be generated. The wake vortex sensor will periodically provide data to validate AVOSS predictions. Feasibility of measuring wake vortices using a lidar was first demonstrated using a continuous wave (CW) system from NASA Marshall Space Flight Sensor and tested at the Volpe National Transportation Systems Center's wake vortex test site at JFK International Airport. Other applications of CW lidar for wake vortex measurement have been made

19 CFR 7.2 - Insular possessions of the United States other than Puerto Rico.

Code of Federal Regulations, 2011 CFR

2011-04-01

... possessions are the U.S. Virgin Islands, Guam, American Samoa, Wake Island, Midway Islands, and Johnston Atoll...) Importations into Guam, American Samoa, Wake Island, Midway Islands, Johnston Atoll, and the Commonwealth of... no customs authority on Johnston Atoll, which is under the operational control of the Defense Nuclear...

19 CFR 7.2 - Insular possessions of the United States other than Puerto Rico.

Code of Federal Regulations, 2012 CFR

2012-04-01

... possessions are the U.S. Virgin Islands, Guam, American Samoa, Wake Island, Midway Islands, and Johnston Atoll...) Importations into Guam, American Samoa, Wake Island, Midway Islands, Johnston Atoll, and the Commonwealth of... no customs authority on Johnston Atoll, which is under the operational control of the Defense Nuclear...

19 CFR 7.2 - Insular possessions of the United States other than Puerto Rico.

Code of Federal Regulations, 2013 CFR

2013-04-01

... possessions are the U.S. Virgin Islands, Guam, American Samoa, Wake Island, Midway Islands, and Johnston Atoll...) Importations into Guam, American Samoa, Wake Island, Midway Islands, Johnston Atoll, and the Commonwealth of... no customs authority on Johnston Atoll, which is under the operational control of the Defense Nuclear...

19 CFR 7.2 - Insular possessions of the United States other than Puerto Rico.

Code of Federal Regulations, 2014 CFR

2014-04-01

... possessions are the U.S. Virgin Islands, Guam, American Samoa, Wake Island, Midway Islands, and Johnston Atoll...) Importations into Guam, American Samoa, Wake Island, Midway Islands, Johnston Atoll, and the Commonwealth of... no customs authority on Johnston Atoll, which is under the operational control of the Defense Nuclear...

19 CFR 7.2 - Insular possessions of the United States other than Puerto Rico.

Code of Federal Regulations, 2010 CFR

2010-04-01

... possessions are the U.S. Virgin Islands, Guam, American Samoa, Wake Island, Midway Islands, and Johnston Atoll...) Importations into Guam, American Samoa, Wake Island, Midway Islands, Johnston Atoll, and the Commonwealth of... no customs authority on Johnston Atoll, which is under the operational control of the Defense Nuclear...

Potential flow theory and operation guide for the panel code PMARC

NASA Technical Reports Server (NTRS)

Ashby, Dale L.; Dudley, Michael R.; Iguchi, Steve K.; Browne, Lindsey; Katz, Joseph

1991-01-01

The theoretical basis for PMARC, a low-order potential-flow panel code for modeling complex three-dimensional geometries, is outlined. Several of the advanced features currently included in the code, such as internal flow modeling, a simple jet model, and a time-stepping wake model, are discussed in some detail. The code is written using adjustable size arrays so that it can be easily redimensioned for the size problem being solved and the computer hardware being used. An overview of the program input is presented, with a detailed description of the input available in the appendices. Finally, PMARC results for a generic wing/body configuration are compared with experimental data to demonstrate the accuracy of the code. The input file for this test case is given in the appendices.

Differences in harm from legal BZP/TFMPP party pills between North Island and South Island users in New Zealand: a case of effective industry self-regulation?

PubMed

Wilkins, Chris; Sweetsur, Paul

2010-01-01

'Party' pills containing benzylpiperazine (BZP) and trifluoromethylphenylpiperazine (TFMPP) were sold legally in New Zealand until early 2008. Prospective studies of hospital emergency department admissions appeared to suggest that the harm from party pills was greater among South Island than North Island users. The party pill industry association (the Social Tonics Association of New Zealand or STANZ) claimed these differences were due to the voluntary code of practice adopted by their members in the North Island. The aims of this study were to examine differences in harm from party pills between North and South Island users in New Zealand, and to investigate possible reasons for any differences in harm, including the impact of industry self-regulation. A national household survey of BZP/TFMPP party pill use was conducted in New Zealand. Information on the ingredients of party pills was provided by the National Poisons Centre. In a number of instances last year users of party pills from the South Island were more likely than last year users from the North Island to report harm from party pills. There were no differences between the North and South Island users with regard to the mean number of BZP/TFMPP party pills taken, mean total milligrams of BZP/TFMPP ingested or prevalence of use of other drug types in combination with party pills. A minority of users in the South Island reported using extremely high numbers of BZP/TFMPP party pills in a single session and using extremely high potency brands of party pills. Last year party pill users from the South Island were more likely than those from the North Island to be students. A number of factors may have contributed to the greater harm from BZP/TFMPP party pills among South Island users including a higher proportion of student users with higher consumption of alcohol and other drugs. Users from both Islands commonly exceeded the dosage of BZP/TFMPP recommended by STANZ suggesting the STANZ code of conduct was

On the Effects of Wind Turbine Wake Skew Caused by Wind Veer: Preprint

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

Churchfield, Matthew J; Sirnivas, Senu

Because of Coriolis forces caused by the Earth's rotation, the structure of the atmospheric boundary layer often contains wind-direction change with height, also known as wind-direction veer. Under low turbulence conditions, such as in stably stratified atmospheric conditions, this veer can be significant, even across the vertical extent of a wind turbine's rotor disk. The veer then causes the wind turbine wake to skew as it advects downstream. This wake skew has been observed both experimentally and numerically. In this work, we attempt to examine the wake skewing process in some detail, and quantify how differently a skewed wake versusmore » a non skewed wake affects a downstream turbine. We do this by performing atmospheric large-eddy simulations to create turbulent inflow winds with and without veer. In the veer case, there is a roughly 8 degree wind direction change across the turbine rotor. We then perform subsequent large-eddy simulations using these inflow data with an actuator line rotor model to create wakes. The turbine modeled is a large, modern, offshore, multimegawatt turbine. We examine the unsteady wake data in detail and show that the skewed wake recovers faster than the non skewed wake. We also show that the wake deficit does not skew to the same degree that a passive tracer would if subject to veered inflow. Last, we use the wake data to place a hypothetical turbine 9 rotor diameters downstream by running aeroelastic simulations with the simulated wake data. We see differences in power and loads if this downstream turbine is subject to a skewed or non skewed wake. We feel that the differences observed between the skewed and nonskewed wake are important enough that the skewing effect should be included in engineering wake models.« less

Brain Energetics During the Sleep-Wake Cycle

PubMed Central

DiNuzzo, Mauro; Nedergaard, Maiken

2017-01-01

Brain activity during wakefulness is associated with high metabolic rates that are believed to support information processing and memory encoding. In spite of loss of consciousness, sleep still carries a substantial energy cost. Experimental evidence supports a cerebral metabolic shift taking place during sleep that suppresses aerobic glycolysis, a hallmark of environment-oriented waking behavior and synaptic plasticity. Recent studies reveal that glial astrocytes respond to the reduction of wake-promoting neuromodulators by regulating volume, composition and glymphatic drainage of interstitial fluid. These events are accompanied by changes in neuronal discharge patterns, astrocyte-neuron interactions, synaptic transactions and underlying metabolic features. Internally-generated neuronal activity and network homeostasis are proposed to account for the high sleep-related energy demand. PMID:29024871

CFD Simulations for the Effect of Unsteady Wakes on the Boundary Layer of a Highly Loaded Low-Pressure Turbine Airfoil (L1A)

NASA Technical Reports Server (NTRS)

Vinci, Samuel, J.

2012-01-01

This report is the third part of a three-part final report of research performed under an NRA cooperative Agreement contract. The first part was published as NASA/CR-2012-217415. The second part was published as NASA/CR-2012-217416. The study of the very high lift low-pressure turbine airfoil L1A in the presence of unsteady wakes was performed computationally and compared against experimental results. The experiments were conducted in a low speed wind tunnel under high (4.9%) and then low (0.6%) freestream turbulence intensity for Reynolds number equal to 25,000 and 50,000. The experimental and computational data have shown that in cases without wakes, the boundary layer separated without reattachment. The CFD was done with LES and URANS utilizing the finite-volume code ANSYS Fluent (ANSYS, Inc.) under the same freestream turbulence and Reynolds number conditions as the experiment but only at a rod to blade spacing of 1. With wakes, separation was largely suppressed, particularly if the wake passing frequency was sufficiently high. This was validated in the 3D CFD efforts by comparing the experimental results for the pressure coefficients and velocity profiles, which were reasonable for all cases examined. The 2D CFD efforts failed to capture the three dimensionality effects of the wake and thus were less consistent with the experimental data. The effect of the freestream turbulence intensity levels also showed a little more consistency with the experimental data at higher intensities when compared with the low intensity cases. Additional cases with higher wake passing frequencies which were not run experimentally were simulated. The results showed that an initial 25% increase from the experimental wake passing greatly reduced the size of the separation bubble, nearly completely suppressing it.

A review of recent wake vortex research for increasing airport capacity

NASA Astrophysics Data System (ADS)

Hallock, James N.; Holzäpfel, Frank

2018-04-01

This paper is a brief review of recent wake vortex research as it affects the operational problem of spacing aircraft to increase airport capacity and throughput. The paper addresses the questions of what do we know about wake vortices and what don't we know about wake vortices. The introduction of Heavy jets in the late 1960s stimulated the study of wake vortices for safety reasons and the use of pulsed lidars and the maturity of computational fluid dynamics in the last three decades have led to extensive data collection and analyses which are now resulting in the development and implementation of systems to safely decrease separations in the terminal environment. Although much has been learned about wake vortices and their behavior, there is still more to be learned about the phenomena of aircraft wake vortices.

Comparison of four large-eddy simulation research codes and effects of model coefficient and inflow turbulence in actuator-line-based wind turbine modeling

DOE PAGES

Martinez-Tossas, Luis A.; Churchfield, Matthew J.; Yilmaz, Ali Emre; ...

2018-05-16

Here, large-eddy simulation (LES) of a wind turbine under uniform inflow is performed using an actuator line model (ALM). Predictions from four LES research codes from the wind energy community are compared. The implementation of the ALM in all codes is similar and quantities along the blades are shown to match closely for all codes. The value of the Smagorinsky coefficient in the subgrid-scale turbulence model is shown to have a negligible effect on the time-averaged loads along the blades. Conversely, the breakdown location of the wake is strongly dependent on the Smagorinsky coefficient in uniform laminar inflow. Simulations aremore » also performed using uniform mean velocity inflow with added homogeneous isotropic turbulence from a public database. The time-averaged loads along the blade do not depend on the inflow turbulence. Moreover, and in contrast to the uniform inflow cases, the Smagorinsky coefficient has a negligible effect on the wake profiles. It is concluded that for LES of wind turbines and wind farms using ALM, careful implementation and extensive cross-verification among codes can result in highly reproducible predictions. Moreover, the characteristics of the inflow turbulence appear to be more important than the details of the subgrid-scale modeling employed in the wake, at least for LES of wind energy applications at the resolutions tested in this work.« less

Comparison of four large-eddy simulation research codes and effects of model coefficient and inflow turbulence in actuator-line-based wind turbine modeling

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

Martinez-Tossas, Luis A.; Churchfield, Matthew J.; Yilmaz, Ali Emre

Here, large-eddy simulation (LES) of a wind turbine under uniform inflow is performed using an actuator line model (ALM). Predictions from four LES research codes from the wind energy community are compared. The implementation of the ALM in all codes is similar and quantities along the blades are shown to match closely for all codes. The value of the Smagorinsky coefficient in the subgrid-scale turbulence model is shown to have a negligible effect on the time-averaged loads along the blades. Conversely, the breakdown location of the wake is strongly dependent on the Smagorinsky coefficient in uniform laminar inflow. Simulations aremore » also performed using uniform mean velocity inflow with added homogeneous isotropic turbulence from a public database. The time-averaged loads along the blade do not depend on the inflow turbulence. Moreover, and in contrast to the uniform inflow cases, the Smagorinsky coefficient has a negligible effect on the wake profiles. It is concluded that for LES of wind turbines and wind farms using ALM, careful implementation and extensive cross-verification among codes can result in highly reproducible predictions. Moreover, the characteristics of the inflow turbulence appear to be more important than the details of the subgrid-scale modeling employed in the wake, at least for LES of wind energy applications at the resolutions tested in this work.« less

Wake meandering of a model wind turbine operating in two different regimes

NASA Astrophysics Data System (ADS)

Foti, Daniel; Yang, Xiaolei; Campagnolo, Filippo; Maniaci, David; Sotiropoulos, Fotis

2018-05-01

The flow behind a model wind turbine under two different turbine operating regimes (region 2 for turbine operating at optimal condition with the maximum power coefficient and 1.4-deg pitch angle and region 3 for turbine operating at suboptimal condition with a lower power coefficient and 7-deg pitch angle) is investigated using wind tunnel experiments and numerical experiments using large-eddy simulation (LES) with actuator surface models for turbine blades and nacelle. Measurements from the model wind turbine experiment reveal that the power coefficient and turbine wake are affected by the operating regime. Simulations with and without a nacelle model are carried out for each operating condition to study the influence of the operating regime and nacelle on the formation of the hub vortex and wake meandering. Statistics and energy spectra of the simulated wakes are in good agreement with the measurements. For simulations with a nacelle model, the mean flow field is composed of an outer wake, caused by energy extraction by turbine blades, and an inner wake directly behind the nacelle, while for the simulations without a nacelle model, the central region of the wake is occupied by a jet. The simulations with the nacelle model reveal an unstable helical hub vortex expanding outward toward the outer wake, while the simulations without a nacelle model show a stable and columnar hub vortex. Because of the different interactions of the inner region of the wake with the outer region of the wake, a region with higher turbulence intensity is observed in the tip shear layer for the simulation with a nacelle model. The hub vortex for the turbine operating in region 3 remains in a tight helical spiral and intercepts the outer wake a few diameters further downstream than for the turbine operating in region 2. Wake meandering, a low-frequency large-scale motion of the wake, commences in the region of high turbulence intensity for all simulations with and without a nacelle model

CFD three dimensional wake analysis in complex terrain

NASA Astrophysics Data System (ADS)

Castellani, F.; Astolfi, D.; Terzi, L.

2017-11-01

Even if wind energy technology is nowadays fully developed, the use of wind energy in very complex terrain is still challenging. In particular, it is challenging to characterize the combination effects of wind ow over complex terrain and wake interactions between nearby turbines and this has a practical relevance too, for the perspective of mitigating anomalous vibrations and loads as well improving the farm efficiency. In this work, a very complex terrain site has been analyzed through a Reynolds-averaged CFD (Computational Fluid Dynamics) numerical wind field model; in the simulation the inuence of wakes has been included through the Actuator Disk (AD) approach. In particular, the upstream turbine of a cluster of 4 wind turbines having 2.3 MW of rated power is studied. The objective of this study is investigating the full three-dimensional wind field and the impact of three-dimensionality on the evolution of the waked area between nearby turbines. A post-processing method of the output of the CFD simulation is developed and this allows to estimate the wake lateral deviation and the wake width. The reliability of the numerical approach is inspired by and crosschecked through the analysis of the operational SCADA (Supervisory Control and Data Acquisition) data of the cluster of interest.

Mach-like capillary-gravity wakes.

PubMed

Moisy, Frédéric; Rabaud, Marc

2014-08-01

We determine experimentally the angle α of maximum wave amplitude in the far-field wake behind a vertical surface-piercing cylinder translated at constant velocity U for Bond numbers Bo(D)=D/λ(c) ranging between 0.1 and 4.2, where D is the cylinder diameter and λ(c) the capillary length. In all cases the wake angle is found to follow a Mach-like law at large velocity, α∼U(-1), but with different prefactors depending on the value of Bo(D). For small Bo(D) (large capillary effects), the wake angle approximately follows the law α≃c(g,min)/U, where c(g,min) is the minimum group velocity of capillary-gravity waves. For larger Bo(D) (weak capillary effects), we recover a law α∼√[gD]/U similar to that found for ship wakes at large velocity [Rabaud and Moisy, Phys. Rev. Lett. 110, 214503 (2013)]. Using the general property of dispersive waves that the characteristic wavelength of the wave packet emitted by a disturbance is of order of the disturbance size, we propose a simple model that describes the transition between these two Mach-like regimes as the Bond number is varied. We show that the new capillary law α≃c(g,min)/U originates from the presence of a capillary cusp angle (distinct from the usual gravity cusp angle), along which the energy radiated by the disturbance accumulates for Bond numbers of order of unity. This model, complemented by numerical simulations of the surface elevation induced by a moving Gaussian pressure disturbance, is in qualitative agreement with experimental measurements.

Capacity and Wake Vortices

DOT National Transportation Integrated Search

2002-09-08

Aircraft wake vortices can pose a threat, especially in the terminal environment where aircraft operate in close proximity. Vortex separation standards preclude hazardous encounters, but are oftentimes very conservative. A key to increasing airport c...

Radiative Forcing Over Ocean by Ship Wakes

NASA Technical Reports Server (NTRS)

Gatebe, Charles K.; Wilcox, E.; Poudyal, R.; Wang, J.

2011-01-01

Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be -0.00014 plus or minus 53% Watts per square meter assuming a global distribution of 32331 ships of size of greater than or equal to 100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Watts per square meter), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.

Exploiting Concurrent Wake-Up Transmissions Using Beat Frequencies

PubMed Central

2017-01-01

Wake-up receivers are the natural choice for wireless sensor networks because of their ultra-low power consumption and their ability to provide communications on demand. A downside of ultra-low power wake-up receivers is their low sensitivity caused by the passive demodulation of the carrier signal. In this article, we present a novel communication scheme by exploiting purposefully-interfering out-of-tune signals of two or more wireless sensor nodes, which produce the wake-up signal as the beat frequency of superposed carriers. Additionally, we introduce a communication algorithm and a flooding protocol based on this approach. Our experiments show that our approach increases the received signal strength up to 3 dB, improving communication robustness and reliability. Furthermore, we demonstrate the feasibility of our newly-developed protocols by means of an outdoor experiment and an indoor setup consisting of several nodes. The flooding algorithm achieves almost a 100% wake-up rate in less than 20 ms. PMID:28933749

Exploiting Concurrent Wake-Up Transmissions Using Beat Frequencies.

PubMed

Kumberg, Timo; Schindelhauer, Christian; Reindl, Leonhard

2017-07-26

Wake-up receivers are the natural choice for wireless sensor networks because of their ultra-low power consumption and their ability to provide communications on demand. A downside of ultra-low power wake-up receivers is their low sensitivity caused by the passive demodulation of the carrier signal. In this article, we present a novel communication scheme by exploiting purposefully-interfering out-of-tune signals of two or more wireless sensor nodes, which produce the wake-up signal as the beat frequency of superposed carriers. Additionally, we introduce a communication algorithm and a flooding protocol based on this approach. Our experiments show that our approach increases the received signal strength up to 3 dB, improving communication robustness and reliability. Furthermore, we demonstrate the feasibility of our newly-developed protocols by means of an outdoor experiment and an indoor setup consisting of several nodes. The flooding algorithm achieves almost a 100% wake-up rate in less than 20 ms.

Flow Structures within a Helicopter Rotor Hub Wake

NASA Astrophysics Data System (ADS)

Elbing, Brian; Reich, David; Schmitz, Sven

2015-11-01

A scaled model of a notional helicopter rotor hub was tested in the 48'' Garfield Thomas Water Tunnel at the Applied Research Laboratory Penn State. The measurement suite included total hub drag and wake velocity measurements (LDV, PIV, stereo-PIV) at three downstream locations. The main objective was to understand the spatiotemporal evolution of the unsteady wake between the rotor hub and the nominal location of the empennage (tail). Initial analysis of the data revealed prominent two- and four-per-revolution fluid structures linked to geometric hub features persisting into the wake far-field. In addition, a six-per-revolution fluid structure was observed in the far-field, which is unexpected due to the lack of any hub feature with the corresponding symmetry. This suggests a nonlinear interaction is occurring within the wake to generate these structures. This presentation will provide an overview of the experimental data and analysis with particular emphasis on these six-per-revolution structures.

Dynamics of sleep/wake determination--Normal and abnormal

NASA Astrophysics Data System (ADS)

Mahowald, Mark W.; Schenck, Carlos H.; O'Connor, Kevin A.

1991-10-01

Virtually all members of the animal kingdom experience a relentless and powerful cycling of states of being: wakefulness, rapid eye movement sleep, and nonrapid eye movement sleep. Each of these states is composed of a number of physiologic variables generated in a variety of neural structures. The predictable oscillations of these states are driven by presumed neural pacemakers which are entrained to the 24 h geophysical environment by the light/dark cycle. Experiments in nature have indicated that wake/sleep rhythm perturbations may occur either involving desynchronization of the basic 24 h wake/sleep cycle within the geophysical 24 h cycle (circadian rhythm disturbances) or involving the rapid oscillation or incomplete declaration of state (such as narcolepsy). The use of phase spaces to describe states of being may be of interest in the description of state determination in both illness and health. Some fascinating clinical and experimental phenomena may represent bifurcations in the sleep/wake control system.

Aircraft Wake Vortex Measurements at Denver International Airport

NASA Technical Reports Server (NTRS)

Dougherty, Robert P.; Wang, Frank Y.; Booth, Earl R.; Watts, Michael E.; Fenichel, Neil; D'Errico, Robert E.

2004-01-01

Airport capacity is constrained, in part, by spacing requirements associated with the wake vortex hazard. NASA's Wake Vortex Avoidance Project has a goal to establish the feasibility of reducing this spacing while maintaining safety. Passive acoustic phased array sensors, if shown to have operational potential, may aid in this effort by detecting and tracking the vortices. During August/September 2003, NASA and the USDOT sponsored a wake acoustics test at the Denver International Airport. The central instrument of the test was a large microphone phased array. This paper describes the test in general terms and gives an overview of the array hardware. It outlines one of the analysis techniques that is being applied to the data and gives sample results. The technique is able to clearly resolve the wake vortices of landing aircraft and measure their separation, height, and sinking rate. These observations permit an indirect estimate of the vortex circulation. The array also provides visualization of the vortex evolution, including the Crow instability.

LES of an Advancing Helicopter Rotor, and Near to Far Wake Assessment

NASA Astrophysics Data System (ADS)

Caprace, Denis-Gabriel; Duponcheel, Matthieu; Chatelain, Philippe; Winckelmans, Grégoire

2017-11-01

Helicopter wake physics involve complex, unsteady vortical flows which have been only scarcely addressed in past studies. The present work focuses on LES of the wake flow behind an advancing rotor, to support the investigation of rotorcraft wake physics and decay mechanisms. A hybrid Vortex Particle-Mesh (VPM) method is employed to simulate the wake of an articulated four-bladed rotor in trimmed conditions, at an advance ratio of 0.41. The simulation domain extends to 30 rotor diameters downstream. The coarse scale aerodynamics of the blades are accounted for through enhanced immersed lifting lines. The vorticity generation mechanisms, the roll-up of the near wake and the resulting established far wake are described (i) qualitatively in terms of vortex dynamics using rotor polar plots and 3D visualizations; (ii) quantitatively using classical integral diagnostics. The power spectra measured by velocity probes in the wake are also presented. The analysis shows that the wake reaches a fully turbulent equilibrium state at a distance of about 30 diameters downstream. This work is supported by the Belgian french community F.R.S.-FNRS.

Aerodynamic interaction between vortical wakes and lifting two-dimensional bodies

NASA Technical Reports Server (NTRS)

Stremel, Paul M.

1989-01-01

Unsteady rotor wake interactions with the empennage, tail boom, and other aerodynamic surfaces of a helicopter have a significant influence on its aerodynamic performance, the ride quality, and vibration. A numerical method for computing the aerodynamic interaction between an interacting vortex wake and the viscous flow about arbitrary two-dimensional bodies was developed to address this helicopter problem. The method solves for the flow field velocities on a body-fitted computational mesh using finite-difference techniques. The interacting vortex wake is represented by an array of discrete vortices which, in turn, are represented by a finite-core model. The evolution of the interacting vortex wake is calculated by Lagrangian techniques. The viscous flow field of the two-dimensional body is calculated on an Eulerian grid. The flow around circular and elliptic cylinders in the absence of an interacting vortex wake was calculated. These results compare very well with other numerical results and with results obtained from experiment and thereby demonstrate the accuracy of the viscous solution. The interaction of a rotor wake with the flow about a 4 to 1 elliptic cylinder at 45 degree incidence was calculated for a Reynolds number of 3000. The results demonstrate the significant variations in the lift and drag on the elliptic cylinder in the presence of the interacting rotor wake.

A wind-tunnel investigation of wind-turbine wakes in yawed conditions

NASA Astrophysics Data System (ADS)

Bastankhah, Majid; Porté-Agel, Fernando

2015-06-01

Wind-tunnel experiments were performed to study the performance of a model wind turbine and its wake characteristics in a boundary layer under different operating conditions, including different yaw angles and tip speed ratios. High-resolution particle image- velocimetry (PIV) was used to measure the three velocity components in a horizontal plane at hub height covering a broad streamwise range from upstream of the turbine to the far- wake region. Additionally, thrust and power coefficients of the turbine were measured under different conditions. These power and thrust measurements, together with the highly-resolved flow measurements, enabled us to systematically study different wake properties. The near-wake region is found to have a highly complex structure influenced by different factors such as tip speed ratio and wake rotation. In particular, for higher tip speed ratios, a noticeable speed-up region is observed in the central part of near wake, which greatly affects the flow distribution in this region. In this regard, the behavior of the near wake for turbines with similar thrust coefficients but different tip speed ratios can vary widely. In contrast, it is shown that the mean streamwise velocity in the far wake of the turbine with zero yaw angle has a self-similar Gaussian distribution, and the strength of wake in this region is consistent with the magnitude of the thrust coefficient. With increasing yaw angle, as expected, the power and thrust coefficients decrease, and the wake deflection increases. The measurements also reveal that, in addition to turbulent momentum flux, lateral mean momentum flux boosts the flow entrainment in only one side of the wake, which results in a faster wake recovery in that side. It is also found that the induced velocity upstream of a yawed turbine has a non-symmetric distribution, and its distribution is in agreement with the available model in the literature. Moreover, the results suggest that in order to accurately

The Neutral Islands during the Late Epoch of Reionization

NASA Astrophysics Data System (ADS)

Xu, Yidong; Yue, Bin; Chen, Xuelei

2018-05-01

The large-scale structure of the ionization field during the epoch of reionization (EoR) can be modeled by the excursion set theory. While the growth of ionized regions during the early stage are described by the ``bubble model'', the shrinking process of neutral regions after the percolation of the ionized region calls for an ``island model''. An excursion set based analytical model and a semi-numerical code (islandFAST) have been developed. The ionizing background and the bubbles inside the islands are also included in the treatment. With two kinds of absorbers of ionizing photons, i.e. the large-scale under-dense neutral islands and the small-scale over-dense clumps, the ionizing background are self-consistently evolved in the model.

A Physiologically Based Model of Orexinergic Stabilization of Sleep and Wake

PubMed Central

Fulcher, Ben D.; Phillips, Andrew J. K.; Postnova, Svetlana; Robinson, Peter A.

2014-01-01

The orexinergic neurons of the lateral hypothalamus (Orx) are essential for regulating sleep-wake dynamics, and their loss causes narcolepsy, a disorder characterized by severe instability of sleep and wake states. However, the mechanisms through which Orx stabilize sleep and wake are not well understood. In this work, an explanation of the stabilizing effects of Orx is presented using a quantitative model of important physiological connections between Orx and the sleep-wake switch. In addition to Orx and the sleep-wake switch, which is composed of mutually inhibitory wake-active monoaminergic neurons in brainstem and hypothalamus (MA) and the sleep-active ventrolateral preoptic neurons of the hypothalamus (VLPO), the model also includes the circadian and homeostatic sleep drives. It is shown that Orx stabilizes prolonged waking episodes via its excitatory input to MA and by relaying a circadian input to MA, thus sustaining MA firing activity during the circadian day. During sleep, both Orx and MA are inhibited by the VLPO, and the subsequent reduction in Orx input to the MA indirectly stabilizes sustained sleep episodes. Simulating a loss of Orx, the model produces dynamics resembling narcolepsy, including frequent transitions between states, reduced waking arousal levels, and a normal daily amount of total sleep. The model predicts a change in sleep timing with differences in orexin levels, with higher orexin levels delaying the normal sleep episode, suggesting that individual differences in Orx signaling may contribute to chronotype. Dynamics resembling sleep inertia also emerge from the model as a gradual sleep-to-wake transition on a timescale that varies with that of Orx dynamics. The quantitative, physiologically based model developed in this work thus provides a new explanation of how Orx stabilizes prolonged episodes of sleep and wake, and makes a range of experimentally testable predictions, including a role for Orx in chronotype and sleep inertia. PMID

Numerical study on wake characteristics of high-speed trains

NASA Astrophysics Data System (ADS)

Yao, Shuan-Bao; Sun, Zhen-Xu; Guo, Di-Long; Chen, Da-Wei; Yang, Guo-Wei

2013-12-01

Intensive turbulence exists in the wakes of high speed trains, and the aerodynamic performance of the trailing car could deteriorate rapidly due to complicated features of the vortices in the wake zone. As a result, the safety and amenity of high speed trains would face a great challenge. This paper considers mainly the mechanism of vortex formation and evolution in the train flow field. A real CRH2 model is studied, with a leading car, a middle car and a trailing car included. Different running speeds and cross wind conditions are considered, and the approaches of unsteady Reynold-averaged Navier-Stokes (URANS) and detached eddy simulation (DES) are utilized, respectively. Results reveal that DES has better capability of capturing small eddies compared to URANS. However, for large eddies, the effects of two approaches are almost the same. In conditions without cross winds, two large vortex streets stretch from the train nose and interact strongly with each other in the wake zone. With the reinforcement of the ground, a complicated wake vortex system generates and becomes strengthened as the running speed increases. However, the locations of flow separations on the train surface and the separation mechanism keep unchanged. In conditions with cross winds, three large vortices develop along the leeward side of the train, among which the weakest one has no obvious influence on the wake flow while the other two stretch to the tail of the train and combine with the helical vortices in the train wake. Thus, optimization of the aerodynamic performance of the trailing car should be aiming at reducing the intensity of the wake vortex system.

Sleep-Wake Concordance in Couples Is Inversely Associated With Cardiovascular Disease Risk Markers.

PubMed

Gunn, Heather E; Buysse, Daniel J; Matthews, Karen A; Kline, Christopher E; Cribbet, Matthew R; Troxel, Wendy M

2017-01-01

To determine whether interdependence in couples' sleep (sleep-wake concordance i.e., whether couples are awake or asleep at the same time throughout the night) is associated with two markers of cardiovascular disease (CVD) risk, ambulatory blood pressure (BP) and systemic inflammation. This community-based study is a cross-sectional analysis of 46 adult couples, aged 18-45 years, without known sleep disorders. Percent sleep-wake concordance, the independent variable, was calculated for each individual using actigraphy. Ambulatory BP monitors measured BP across 48 h. Dependent variables included mean sleep systolic BP (SBP) and diastolic BP (DBP), mean wake SBP and DBP, sleep-wake SBP and DBP ratios, and C-reactive protein (CRP). Mixed models were used and were adjusted for age, sex, education, race, and body mass index. Higher sleep-wake concordance was associated with lower sleep SBP (b = -.35, SE = .01) and DBP (b = -.22, SE = .10) and lower wake SBP (b = -.26, SE = .12; all p values < .05). Results were moderated by sex; for women, high concordance was associated with lower BP. Men and women with higher sleep-wake concordance also had lower CRP values (b = -.15, SE = .03, p < .05). Sleep-wake concordance was not associated with wake DBP or sleep/wake BP ratios. Significant findings remained after controlling for individual sleep quality, duration, and wake after sleep onset. Sleep-wake concordance was associated with sleep BP, and this association was stronger for women. Higher sleep-wake concordance was associated with lower systemic inflammation for men and women. Sleep-wake concordance may be a novel mechanism by which marital relationships are associated with long-term CVD outcomes. © Sleep Research Society 2016. Published by Oxford University Press on behalf of the Sleep Research Society. All rights reserved. For permissions, please e-mail journals.permissions@oup.com.

RGS Proteins and Gαi2 Modulate Sleep, Wakefulness, and Disruption of Sleep/ Wake States after Isoflurane and Sevoflurane Anesthesia.

PubMed

Zhang, Hao; Wheat, Heather; Wang, Peter; Jiang, Sha; Baghdoyan, Helen A; Neubig, Richard R; Shi, X Y; Lydic, Ralph

2016-02-01

This study tested the hypothesis that Regulators of G protein Signaling (RGS) proteins contribute to the regulation of wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep, and to sleep disruption caused by volatile anesthetics. The three groups used in this study included wild-type (WT; n = 7) mice and knock-in mice that were heterozygous (+/GS; n = 7) or homozygous (GS/GS; n = 7) for an RGS-insensitive allele that causes prolonged Gαi2 signaling. Mice were implanted with electrodes for recording sleep and conditioned for 1 week or more to sleep in the laboratory. Using within and between groups designs, 24-h recordings of wakefulness, NREM sleep, and REM sleep were compared across three interventions: (1) baseline (control) and after 3 h of being anesthetized with (2) isoflurane or (3) sevoflurane. Baseline recordings during the light phase revealed that relative to WT mice, homozygous RGS-insensitive (GS/GS) mice exhibit significantly increased wakefulness and decreased NREM and REM sleep. During the dark phase, these state-specific differences remained significant but reversed direction of change. After cessation of isoflurane and sevoflurane anesthesia there was a long-lasting and significant disruption of sleep and wakefulness. The durations of average episodes of wakefulness, NREM sleep, and REM sleep were significantly altered as a function of genotype and isoflurane and sevoflurane anesthesia. RGS proteins and Gαi2 play a significant role in regulating states of wakefulness, NREM sleep, and REM sleep. Genotype-specific differences demonstrate that RGS proteins modulate sleep disruption caused by isoflurane and sevoflurane anesthesia. The results also support the conclusion that isoflurane and sevoflurane anesthesia do not satisfy the homeostatic drive for sleep. © 2016 Associated Professional Sleep Societies, LLC.

Determination of Wind Turbine Near-Wake Length Based on Stability Analysis

NASA Astrophysics Data System (ADS)

Sørensen, Jens N.; Mikkelsen, Robert; Sarmast, Sasan; Ivanell, Stefan; Henningson, Dan

2014-06-01

A numerical study on the wake behind a wind turbine is carried out focusing on determining the length of the near-wake based on the instability onset of the trailing tip vortices shed from the turbine blades. The numerical model is based on large-eddy simulations (LES) of the Navier-Stokes equations using the actuator line (ACL) method. The wake is perturbed by applying stochastic or harmonic excitations in the neighborhood of the tips of the blades. The flow field is then analyzed to obtain the stability properties of the tip vortices in the wake of the wind turbine. As a main outcome of the study it is found that the amplification of specific waves (traveling structures) along the tip vortex spirals is responsible for triggering the instability leading to wake breakdown. The presence of unstable modes in the wake is related to the mutual inductance (vortex pairing) instability where there is an out-of-phase displacement of successive helix turns. Furthermore, using the non-dimensional growth rate, it is found that the pairing instability has a universal growth rate equal to π/2. Using this relationship, and the assumption that breakdown to turbulence occurs once a vortex has experienced sufficient growth, we provide an analytical relationship between the turbulence intensity and the stable wake length. The analysis leads to a simple expression for determining the length of the near wake. This expression shows that the near wake length is inversely proportional to thrust, tip speed ratio and the logarithmic of the turbulence intensity.

Influence of short rear end tapers on the wake of a simplified square-back vehicle: wake topology and rear drag

NASA Astrophysics Data System (ADS)

Perry, Anna-Kristina; Pavia, Giancarlo; Passmore, Martin

2016-11-01

As vehicle manufacturers work to reduce energy consumption of all types of vehicles, external vehicle aerodynamics has become increasingly important. Whilst production vehicle shape optimisation methods are well developed, the need to make further advances requires deeper understanding of the highly three-dimensional flow around bluff bodies. In this paper, the wake flow of a generic bluff body, the Windsor body, based on a square-back car geometry, was investigated by means of balance measurements, surface pressure measurements and 2D particle image velocimetry planes. Changes in the wake topology are triggered by the application of short tapers (4 % of the model length) to the top and bottom edges of the base, representing a shape optimisation that is realistic for many modern production vehicles. The base drag is calculated and correlated with the aerodynamic drag data. The results not only show the effectiveness of such small devices in modifying the time average topology of the wake but also shed some light on the effects produced by different levels of upwash and downwash on the bi-stable nature of the wake itself.

Atmospheric Turbulence Effects on Near-Ground Wake Vortex Demise

DOT National Transportation Integrated Search

2008-01-20

The Federal Aviation Administration (FAA) and National Aeronautics and Space Administration (NASA) have been working jointly on a phased approach to implement wake avoidance solutions designed to safely reduce wake turbulence separation standards in ...

Flight Data Reduction of Wake Velocity Measurements Using an Instrumented OV-10 Airplane

NASA Technical Reports Server (NTRS)

Vicroy, Dan D.; Stuever, Robert A.; Stewart, Eric C.; Rivers, Robert A.

1999-01-01

A series of flight tests to measure the wake of a Lockheed C- 130 airplane and the accompanying atmospheric state have been conducted. A specially instrumented North American Rockwell OV-10 airplane was used to measure the wake and atmospheric conditions. An integrated database has been compiled for wake characterization and validation of wake vortex computational models. This paper describes the wake- measurement flight-data reduction process.

Running Promotes Wakefulness and Increases Cataplexy in Orexin Knockout Mice

PubMed Central

España, Rodrigo A.; McCormack, Sarah L.; Mochizuki, Takatoshi; Scammell, Thomas E.

2007-01-01

Study Objective: People with narcolepsy and mice lacking orexin/hypocretin have disrupted sleep/wake behavior and reduced physical activity. Our objective was to identify physiologic mechanisms through which orexin deficiency reduces locomotor activity. Design: We examined spontaneous wheel running activity and its relationship to sleep/wake behavior in wild type (WT) and orexin knockout (KO) mice. Additionally, given that physical activity promotes alertness, we also studied whether orexin deficiency reduces the wake-promoting effects of exercise. Measurements and Results: Orexin KO mice ran 42% less than WT mice. Their ability to run appeared normal as they initiated running as often as WT mice and ran at normal speeds. However, their running bouts were considerably shorter, and they often had cataplexy or quick transitions into sleep after running. Wheel running increased the total amount of wakefulness in WT and orexin KO mice similarly, however, KO mice continued to have moderately fragmented sleep/wake behavior. Wheel running also doubled the amount of cataplexy by increasing the probability of transitioning into cataplexy. Conclusions: Orexin KO mice run significantly less than normal, likely due to sleepiness, imminent cataplexy, or a reduced motivation to run. Orexin is not required for the wake-promoting effects of wheel running given that both WT and KO mice had similar increases in wakefulness with running wheels. In addition, the clear increase in cataplexy with wheel running suggests the possibility that positive emotions or reward can trigger murine cataplexy, similar to that seen in people and dogs with narcolepsy. Citation: España RA; McCormack SL; Mochizuki T; Scammell TE. Running promotes wakefulness and increases cataplexy in orexin knockout mice. SLEEP 2007;30(11):1417-1425. PMID:18041476

The Windy Island Soliton Experiment (WISE): Shallow Water and Basin Experiment Configuration and Preliminary Observations

DTIC Science & Technology

2009-02-19

Virginia 22203-1995 The Windy Island Soliton Experiment (WISE): Shallow Water and Basin Experiment Configuration and Preliminary Observations...case letters) The Windy Island Soliton Experiment (WISE): Shallow water and Basin Experiment Configuration and Preliminary Observations 5. FUNDING...release; distribution is unlimited 12b. DISTRIBUTION CODE 13. ABSTRACT (maximum 200 words) The Windy Islands Soliton Experiment (WISE) was

Simulation of magnetic island dynamics under resonant magnetic perturbation with the TEAR code and validation of the results on T-10 tokamak data

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

Ivanov, N. V.; Kakurin, A. M.

2014-10-15

Simulation of the magnetic island evolution under Resonant Magnetic Perturbation (RMP) in rotating T-10 tokamak plasma is presented with intent of TEAR code experimental validation. In the T-10 experiment chosen for simulation, the RMP consists of a stationary error field, a magnetic field of the eddy current in the resistive vacuum vessel and magnetic field of the externally applied controlled halo current in the plasma scrape-off layer (SOL). The halo-current loop consists of a rail limiter, plasma SOL, vacuum vessel, and external part of the circuit. Effects of plasma resistivity, viscosity, and RMP are taken into account in the TEARmore » code based on the two-fluid MHD approximation. Radial distribution of the magnetic flux perturbation is calculated with account of the externally applied RMP. A good agreement is obtained between the simulation results and experimental data for the cases of preprogrammed and feedback-controlled halo current in the plasma SOL.« less

Stereo-Video Data Reduction of Wake Vortices and Trailing Aircrafts

NASA Technical Reports Server (NTRS)

Alter-Gartenberg, Rachel

1998-01-01

This report presents stereo image theory and the corresponding image processing software developed to analyze stereo imaging data acquired for the wake-vortex hazard flight experiment conducted at NASA Langley Research Center. In this experiment, a leading Lockheed C-130 was equipped with wing-tip smokers to visualize its wing vortices, while a trailing Boeing 737 flew into the wake vortices of the leading airplane. A Rockwell OV-10A airplane, fitted with video cameras under its wings, flew at 400 to 1000 feet above and parallel to the wakes, and photographed the wake interception process for the purpose of determining the three-dimensional location of the trailing aircraft relative to the wake. The report establishes the image-processing tools developed to analyze the video flight-test data, identifies sources of potential inaccuracies, and assesses the quality of the resultant set of stereo data reduction.

3D equilibrium reconstruction with islands

DOE PAGES

Cianciosa, M.; Hirshman, S. P.; Seal, S. K.; ...

2018-02-15

This study presents the development of a 3D equilibrium reconstruction tool and the results of the first-ever reconstruction of an island equilibrium. The SIESTA non-nested equilibrium solver has been coupled to the V3FIT 3D equilibrium reconstruction code. Computed from a coupled VMEC and SIESTA model, synthetic signals are matched to measured signals by finding an optimal set of equilibrium parameters. By using the normalized pressure in place of normalized flux, non-equilibrium quantities needed by diagnostic signals can be efficiently mapped to the equilibrium. The effectiveness of this tool is demonstrated by reconstructing an island equilibrium of a DIII-D inner wallmore » limited L-mode case with an n = 1 error field applied. Finally, flat spots in Thomson and ECE temperature diagnostics show the reconstructed islands have the correct size and phase.« less

3D equilibrium reconstruction with islands

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

Cianciosa, M.; Hirshman, S. P.; Seal, S. K.

This study presents the development of a 3D equilibrium reconstruction tool and the results of the first-ever reconstruction of an island equilibrium. The SIESTA non-nested equilibrium solver has been coupled to the V3FIT 3D equilibrium reconstruction code. Computed from a coupled VMEC and SIESTA model, synthetic signals are matched to measured signals by finding an optimal set of equilibrium parameters. By using the normalized pressure in place of normalized flux, non-equilibrium quantities needed by diagnostic signals can be efficiently mapped to the equilibrium. The effectiveness of this tool is demonstrated by reconstructing an island equilibrium of a DIII-D inner wallmore » limited L-mode case with an n = 1 error field applied. Finally, flat spots in Thomson and ECE temperature diagnostics show the reconstructed islands have the correct size and phase.« less

3D equilibrium reconstruction with islands

NASA Astrophysics Data System (ADS)

Cianciosa, M.; Hirshman, S. P.; Seal, S. K.; Shafer, M. W.

2018-04-01

This paper presents the development of a 3D equilibrium reconstruction tool and the results of the first-ever reconstruction of an island equilibrium. The SIESTA non-nested equilibrium solver has been coupled to the V3FIT 3D equilibrium reconstruction code. Computed from a coupled VMEC and SIESTA model, synthetic signals are matched to measured signals by finding an optimal set of equilibrium parameters. By using the normalized pressure in place of normalized flux, non-equilibrium quantities needed by diagnostic signals can be efficiently mapped to the equilibrium. The effectiveness of this tool is demonstrated by reconstructing an island equilibrium of a DIII-D inner wall limited L-mode case with an n = 1 error field applied. Flat spots in Thomson and ECE temperature diagnostics show the reconstructed islands have the correct size and phase. ).

Deciphering Neural Codes of Memory during Sleep

PubMed Central

Chen, Zhe; Wilson, Matthew A.

2017-01-01

Memories of experiences are stored in the cerebral cortex. Sleep is critical for consolidating hippocampal memory of wake experiences into the neocortex. Understanding representations of neural codes of hippocampal-neocortical networks during sleep would reveal important circuit mechanisms on memory consolidation, and provide novel insights into memory and dreams. Although sleep-associated ensemble spike activity has been investigated, identifying the content of memory in sleep remains challenging. Here, we revisit important experimental findings on sleep-associated memory (i.e., neural activity patterns in sleep that reflect memory processing) and review computational approaches for analyzing sleep-associated neural codes (SANC). We focus on two analysis paradigms for sleep-associated memory, and propose a new unsupervised learning framework (“memory first, meaning later”) for unbiased assessment of SANC. PMID:28390699

Boat, wake, and wave real-time simulation

NASA Astrophysics Data System (ADS)

Świerkowski, Leszek; Gouthas, Efthimios; Christie, Chad L.; Williams, Owen M.

2009-05-01

We describe the extension of our real-time scene generation software VIRSuite to include the dynamic simulation of small boats and their wakes within an ocean environment. Extensive use has been made of the programmabilty available in the current generation of GPUs. We have demonstrated that real-time simulation is feasible, even including such complexities as dynamical calculation of the boat motion, wake generation and calculation of an FFTgenerated sea state.

Sleep/Wakefulness Management in Continuous/Sustained Operations

DTIC Science & Technology

2002-11-01

SEINE CEDEX, FRANCE RTO LECTURE SERIES 223 Sleep/Wakefulness Management in Continuous/Sustained Operations (La gestion des rythmes veille/sommeil lors... Management in Continuous/Sustained Operations (La gestion des rythmes veille/sommeil lors des opérations continues/soutenues) The material in this...St. Joseph Print Group Inc. (A St. Joseph Corporation Company) 1165 Kenaston Street, Ottawa, Ontario, Canada K1G 6S1 ii Sleep/Wakefulness Management in

Cylinder wakes in flowing soap films

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

Vorobieff, P.; Ecke, R.E.; Vorobieff, P.

1999-09-01

We present an experimental characterization of cylinder wakes in flowing soap films. From instantaneous velocity and thickness fields, we find the vortex-shedding frequency, mean-flow velocity, and mean-film thickness. Using the empirical relationship between the Reynolds and Strouhal numbers obtained for cylinder wakes in three dimensions, we estimate the effective soap-film viscosity and its dependence on film thickness. We also compare the decay of vorticity with that in a simple Rankine vortex model with a dissipative term to account for air drag. [copyright] [ital 1999] [ital The American Physical Society

Running promotes wakefulness and increases cataplexy in orexin knockout mice.

PubMed

España, Rodrigo A; McCormack, Sarah L; Mochizuki, Takatoshi; Scammell, Thomas E

2007-11-01

People with narcolepsy and mice lacking orexin/hypocretin have disrupted sleep/wake behavior and reduced physical activity. Our objective was to identify physiologic mechanisms through which orexin deficiency reduces locomotor activity. We examined spontaneous wheel running activity and its relationship to sleep/wake behavior in wild type (WT) and orexin knockout (KO) mice. Additionally, given that physical activity promotes alertness, we also studied whether orexin deficiency reduces the wake-promoting effects of exercise. Orexin KO mice ran 42% less than WT mice. Their ability to run appeared normal as they initiated running as often as WT mice and ran at normal speeds. However, their running bouts were considerably shorter, and they often had cataplexy or quick transitions into sleep after running. Wheel running increased the total amount of wakefulness in WT and orexin KO mice similarly, however, KO mice continued to have moderately fragmented sleep/wake behavior. Wheel running also doubled the amount of cataplexy by increasing the probability of transitioning into cataplexy. Orexin KO mice run significantly less than normal, likely due to sleepiness, imminent cataplexy, or a reduced motivation to run. Orexin is not required for the wake-promoting effects of wheel running given that both WT and KO mice had similar increases in wakefulness with running wheels. In addition, the clear increase in cataplexy with wheel running suggests the possibility that positive emotions or reward can trigger murine cataplexy, similar to that seen in people and dogs with narcolepsy.

Extrasynaptic GABAA receptors in rat pontine reticular formation increase wakefulness.

PubMed

Vanini, Giancarlo; Baghdoyan, Helen A

2013-03-01

Gamma-aminobutyric acid (GABA) causes phasic inhibition via synaptic GABAA receptors and tonic inhibition via extrasynaptic GABAA receptors. GABA levels in the extracellular space regulate arousal state and cognition by volume transmission via extrasynaptic GABAA receptors. GABAergic transmission in the pontine reticular formation promotes wakefulness. No previous studies have determined whether an agonist at extrasynaptic GABAA receptors administered into the pontine reticular formation alters sleep and wakefulness. Therefore, this study used gaboxadol (THIP; agonist at extrasynaptic GABAA receptors that contain a δ subunit) to test the hypothesis that extrasynaptic GABAA receptors within the pontine reticular formation modulate sleep and wakefulness. Within/between subjects. University of Michigan. Adult male Crl:CD*(SD) (Sprague-Dawley) rats (n = 10). Microinjection of gaboxadol, the nonsubtype selective GABAA receptor agonist muscimol (positive control), and saline (negative control) into the rostral pontine reticular formation. Gaboxadol significantly increased wakefulness and decreased both nonrapid eye movement sleep and rapid eye movement sleep in a concentration-dependent manner. Relative to saline, gaboxadol did not alter electroencephalogram power. Microinjection of muscimol into the pontine reticular formation of the same rats that received gaboxadol increased wakefulness and decreased sleep. Tonic inhibition via extrasynaptic GABAA receptors that contain a δ subunit may be one mechanism by which the extracellular pool of endogenous GABA in the rostral pontine reticular formation promotes wakefulness. Vanini G; Baghdoyan HA. Extrasynaptic GABAA receptors in rat pontine reticular formation increase wakefulness. SLEEP 2013;36(3):337-343.

Theoretical evaluation of a V/STOL fighter model utilizing the PAN AIR code

NASA Technical Reports Server (NTRS)

Howell, G. A.; Bhateley, I. C.

1982-01-01

The PAN AIR computer code was investigated as a tool for predicting closely coupled aerodynamic and propulsive flowfields of arbitrary configurations. The NASA/Ames V/STOL fighter model, a configuration of complex geometry, was analyzed with the PAN AIR code. A successful solution for this configuration was obtained when the nozzle exit was treated as an impermeable surface and no wakes were included around the nozzle exit. When separated flow was simulated from the end of the nacelle, requiring the use of wake networks emanating from the nozzle exit, a number of problems were encountered. A circular body nacelle model was used to investigate various techniques for simulating the exhaust plume in PAN AIR. Several approaches were tested and eliminated because they could not correctly simulate the interference effects. Only one plume modeling technique gave good results. A PAN AIR computation that used a plume shape and inflow velocities obtained from the Navier-Stokes solution for the plume produced results for the effects of power that compared well with experimental data.

On the wake flow of asymmetrically beveled trailing edges

NASA Astrophysics Data System (ADS)

Guan, Yaoyi; Pröbsting, Stefan; Stephens, David; Gupta, Abhineet; Morris, Scott C.

2016-05-01

Trailing edge and wake flows are of interest for a wide range of applications. Small changes in the design of asymmetrically beveled or semi-rounded trailing edges can result in significant difference in flow features which are relevant for the aerodynamic performance, flow-induced structural vibration and aerodynamically generated sound. The present study describes in detail the flow field characteristics around a family of asymmetrically beveled trailing edges with an enclosed trailing-edge angle of 25° and variable radius of curvature R. The flow fields over the beveled trailing edges are described using data obtained by particle image velocimetry (PIV) experiments. The flow topology for different trailing edges was found to be strongly dependent on the radius of curvature R, with flow separation occurring further downstream as R increases. This variation in the location of flow separation influences the aerodynamic force coefficients, which were evaluated from the PIV data using a control volume approach. Two-point correlations of the in-plane velocity components are considered to assess the structure in the flow field. The analysis shows large-scale coherent motions in the far wake, which are associated with vortex shedding. The wake thickness parameter yf is confirmed as an appropriate length scale to characterize this large-scale roll-up motion in the wake. The development in the very near wake was found to be critically dependent on R. In addition, high-speed PIV measurements provide insight into the spectral characteristics of the turbulent fluctuations. Based on the time-resolved flow field data, the frequency range associated with the shedding of coherent vortex pairs in the wake is identified. By means of time-correlation of the velocity components, turbulent structures are found to convect from the attached or separated shear layers without distinct separation point into the wake.

Wake flow control using a dynamically controlled wind turbine

NASA Astrophysics Data System (ADS)