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1

Maximum likelihood blood velocity estimator incorporating properties of flow physics.  

PubMed

The aspect of correlation among the blood velocities in time and space has not received much attention in previous blood velocity estimators. The theory of fluid mechanics predicts this property of the blood flow. Additionally, most estimators based on a cross-correlation analysis are limited on the maximum velocity detectable. This is due to the occurrence of multiple peaks in the cross-correlation function. In this study a new estimator (CMLE), which is based on correlation (C) properties inherited from fluid flow and maximum likelihood estimation (MLE), is derived and evaluated on a set of simulated and in vivo data from the carotid artery. The estimator is meant for two-dimensional (2-D) color flow imaging. The resulting mathematical relation for the estimator consists of two terms. The first term performs a cross-correlation analysis on the signal segment in the radio frequency (RF)-data under investigation. The flow physic properties are exploited in the second term, as the range of velocity values investigated in the cross-correlation analysis are compared to the velocity estimates in the temporal and spatial neighborhood of the signal segment under investigation. The new estimator has been compared to the cross-correlation (CC) estimator and the previously developed maximum likelihood estimator (MLE). The results show that the CMLE can handle a larger velocity search range and is capable of estimating even low velocity levels from tissue motion. The CC and the MLE produce incorrect velocity estimates due to the multiple peaks, when the velocity search range is increased above the maximum detectable velocity. The root-mean square error (RMS) on the velocity estimates for the simulated data is on the order of 7 cm/s (14%) for the CMLE, and it is comparable to the RMS for the CC and the MLE. When the velocity search range is set to twice the limit of the CC and the MLE, the number of incorrect velocity estimates are 0, 19.1, and 7.2% for the CMLE, CC, and MLE, respectively. The ability to handle a larger search range and estimating low velocity levels was confirmed on in vivo data. PMID:14995019

Schlaikjer, Malene; Jensen, Jørgen Arendt

2004-01-01

2

An improved Doppler model for obtaining accurate maximum blood velocities.  

PubMed

Maximum blood velocity estimates are frequently required in diagnostic applications, including carotid stenosis evaluation, arteriovenous fistula inspection, and maternal-fetal examinations. However, the currently used methods for ultrasound measurements are inaccurate and often rely on applying heuristic thresholds to a Doppler power spectrum. A new method that uses a mathematical model to predict the correct threshold that should be used for maximum velocity measurements has recently been introduced. Although it is a valuable and deterministic tool, this method is limited to parabolic flows insonated by uniform pressure fields. In this work, a more generalized technique that overcomes such limitations is presented. The new approach, which uses an extended Doppler spectrum model, has been implemented in an experimental set-up based on a linear array probe that transmits defocused steered waves. The improved model has been validated by Field II simulations and phantom experiments on tubes with diameters between 2mm and 8mm. Using the spectral threshold suggested by the new model significantly higher accuracy estimates of the peak velocity can be achieved than are now clinically attained, including for narrow beams and non-parabolic velocity profiles. In particular, an accuracy of +1.2±2.5cm/s has been obtained in phantom measurements for velocities ranging from 20 to 80cm/s. This result represents an improvement that can significantly affect the way maximum blood velocity is investigated today. PMID:24934798

Ricci, Stefano; Matera, Riccardo; Tortoli, Piero

2014-09-01

3

Maximum wind energy extraction strategies using power electronic converters  

Microsoft Academic Search

This thesis focuses on maximum wind energy extraction strategies for achieving the highest energy output of variable speed wind turbine power generation systems. Power electronic converters and controls provide the basic platform to accomplish the research of this thesis in both hardware and software aspects. In order to send wind energy to a utility grid, a variable speed wind turbine

Quincy Qing Wang

2003-01-01

4

Estimating maximum global wind power availability and associated climatic consequences  

Microsoft Academic Search

Estimating maximum global wind power availability and associated climatic consequences Wind speed reflects the continuous generation of kinetic energy and its dissipation, primarily in the atmospheric boundary layer. When wind turbines extract kinetic wind energy, less kinetic energy remains in the atmosphere in the mean state. While this effect does not play a significant role for a single turbine, it

Lee Miller; Fabian Gans; Axel Kleidon

2010-01-01

5

Latitudinal Variation of Solar Wind Velocity  

NASA Astrophysics Data System (ADS)

Single station solar wind velocity measurements using the Ooty Radio Telescope (ORT) in India (operating at 327 MHz) are reported for the period August 1992 to August 1993. Interplanetary scintillation (IPS) observations on a large number of compact radio sources covering a latitudinal range of ±80° were used to derive solar wind velocities using the method of fitting a power law model to the observed IPS spectra. The data shows a velocity versus heliographic latitude pattern which is similar to that reported by Rickett and Coles (1991) for the 1981 1982 period. However, the average of the measured equatorial velocities are higher, being about 470 km s-1 compared to their value of 400 km s-1. The distribution of electron density variations (?N e ) between 50R? and 90R? was also determined and it was found that ?N e was about 30% less at the poles as compared to the equator.

Ananthakrishnan, S.; Balasubramanian, V.; Janardhan, P.

1995-04-01

6

Satellite-tracked cumulus velocities. [for determining wind velocity  

NASA Technical Reports Server (NTRS)

The research indicates that extreme caution must be exercised in converting cloud velocities into winds. The motion of fair-weather cumuli obtained by tracking their shadows over Springfield, Missouri revealed that the standard deviation in the individual cloud motion is several times the tracking error. The motion of over-ocean cumuli near Barbados clearly indicated the complicated nature of cumulus velocities. Analysis of whole-sky images obtained near Tampa, Florida failed to show significant continuity and stability of cumulus plumes, less than 0.3 mile in diameter. Cumulus turrets with 0.3 to 2 mile in size appear to be the best target to infer the mean wind within the subcloud layers. Cumulus or stratocumulus cells consisting of x number of turrets do not always move with wind. The addition and deletion of turrets belonging to a specific cell appear to be the cause of the erratic motion of a tracer cell. It may by concluded that the accuracy of wind estimates is unlikely to be better than 2m/sec unless the physical and dynamical characteristics of cumulus motion is futher investigated.

Fujita, T. T.; Pearl, E. W.; Shenk, W. E.

1973-01-01

7

Probabilistic modelling of maximum wind pressure on structures  

Microsoft Academic Search

This paper formulates a probabilistic model which is able to represent the maximum equivalent pressure applied by the wind on a structural surface. Unlike the classical methods, where the randomness is circumscribed within the maximum mean loading component, this model relies also on the randomness of the maximum fluctuating action. Furthermore, it takes into account the presence of quadratic pressure

Evelia Schettini; Giovanni Solari

1998-01-01

8

An approximate, maximum terminal velocity descent to a point  

SciTech Connect

No closed form control solution exists for maximizing the terminal velocity of a hypersonic glider at an arbitrary point. As an alternative, this study uses neighboring extremal theory to provide a sampled data feedback law to guide the vehicle to a constrained ground range and altitude. The guidance algorithm is divided into two parts: 1) computation of a nominal, approximate, maximum terminal velocity trajectory to a constrained final altitude and computation of the resulting unconstrained groundrange, and 2) computation of the neighboring extremal control perturbation at the sample value of flight path angle to compensate for changes in the approximate physical model and enable the vehicle to reach the on-board computed groundrange. The trajectories are characterized by glide and dive flight to the target to minimize the time spent in the denser parts of the atmosphere. The proposed on-line scheme successfully brings the final altitude and range constraints together, as well as compensates for differences in flight model, atmosphere, and aerodynamics at the expense of guidance update computation time. Comparison with an independent, parameter optimization solution for the terminal velocity is excellent. 6 refs., 3 figs.

Eisler, G.R.; Hull, D.G.

1987-01-01

9

Maximum wind energy extraction strategies using power electronic converters  

NASA Astrophysics Data System (ADS)

This thesis focuses on maximum wind energy extraction strategies for achieving the highest energy output of variable speed wind turbine power generation systems. Power electronic converters and controls provide the basic platform to accomplish the research of this thesis in both hardware and software aspects. In order to send wind energy to a utility grid, a variable speed wind turbine requires a power electronic converter to convert a variable voltage variable frequency source into a fixed voltage fixed frequency supply. Generic single-phase and three-phase converter topologies, converter control methods for wind power generation, as well as the developed direct drive generator, are introduced in the thesis for establishing variable-speed wind energy conversion systems. Variable speed wind power generation system modeling and simulation are essential methods both for understanding the system behavior and for developing advanced system control strategies. Wind generation system components, including wind turbine, 1-phase IGBT inverter, 3-phase IGBT inverter, synchronous generator, and rectifier, are modeled in this thesis using MATLAB/SIMULINK. The simulation results have been verified by a commercial simulation software package, PSIM, and confirmed by field test results. Since the dynamic time constants for these individual models are much different, a creative approach has also been developed in this thesis to combine these models for entire wind power generation system simulation. An advanced maximum wind energy extraction strategy relies not only on proper system hardware design, but also on sophisticated software control algorithms. Based on literature review and computer simulation on wind turbine control algorithms, an intelligent maximum wind energy extraction control algorithm is proposed in this thesis. This algorithm has a unique on-line adaptation and optimization capability, which is able to achieve maximum wind energy conversion efficiency through continuously improving the performance of wind power generation systems. This algorithm is independent of wind power generation system characteristics, and does not need wind speed and turbine speed measurements. Therefore, it can be easily implemented into various wind energy generation systems with different turbine inertia and diverse system hardware environments. In addition to the detailed description of the proposed algorithm, computer simulation results are presented in the thesis to demonstrate the advantage of this algorithm. As a final confirmation of the algorithm feasibility, the algorithm has been implemented inside a single-phase IGBT inverter, and tested with a wind simulator system in research laboratory. Test results were found consistent with the simulation results. (Abstract shortened by UMI.)

Wang, Quincy Qing

2003-10-01

10

Spectroscopic mapping of solar wind velocities  

NASA Technical Reports Server (NTRS)

During the total solar eclipse of 1970, measurements of resonantly scattered Lyman-alpha radiation from the solar corona revealed a means to determine temperatures and densities in the solar corona beyond 1.5 R solar radii. A natural extension of this work is to use the Solar Probe to measure the spectral line profile of Lyman-alpha radiation backscattered toward the Sun from coronal regions between 4 R solar radii and 10 R solar radii. The backscattered profile would provide unique and quantitative determinations of the outlaw velocities of coronal material into the solar wind. Such information is of critical importance for understanding solar-wind formation and solar-terrestrial effects on the earth's climate. There is no known way to obtain this information without a Solar Probe-type mission.

Kohl, J. L.

1978-01-01

11

Three dimensional winds: A maximum cross-correlation application to elastic lidar data  

SciTech Connect

Maximum cross-correlation techniques have been used with satellite data to estimate winds and sea surface velocities for several years. Los Alamos National Laboratory (LANL) is currently using a variation of the basic maximum cross-correlation technique, coupled with a deterministic application of a vector median filter, to measure transverse winds as a function of range and altitude from incoherent elastic backscatter lidar (light detection and ranging) data taken throughout large volumes within the atmospheric boundary layer. Hourly representations of three-dimensional wind fields, derived from elastic lidar data taken during an air-quality study performed in a region of complex terrain near Sunland Park, New Mexico, are presented and compared with results from an Environmental Protection Agency (EPA) approved laser doppler velocimeter. The wind fields showed persistent large scale eddies as well as general terrain-following winds in the Rio Grande valley.

Buttler, W.T.

1996-05-01

12

Monitoring of wind pressure distribution at a supertall structure above maximum gradient wind level (presentation video)  

NASA Astrophysics Data System (ADS)

While the field measurement of wind speed at buildings and towers has been made by numerous investigators, the direct measurement of wind pressure at high-rise structures was seldom reported. Up to now, the information regarding wind pressure distribution above the maximum gradient wind level (it is 450 m stipulated in the Chinese code) has never been experimentally obtained. This paper presents a field monitoring investigation on the measurement of wind pressure and its distribution at the Canton Tower of 600 m high above the maximum gradient wind level during the typhoon Kaitak.

Ni, Y. Q.; Wang, Y. W.; Song, S. D.

2014-04-01

13

Estimating maximum global wind power availability and associated climatic consequences  

NASA Astrophysics Data System (ADS)

Estimating maximum global wind power availability and associated climatic consequences Wind speed reflects the continuous generation of kinetic energy and its dissipation, primarily in the atmospheric boundary layer. When wind turbines extract kinetic wind energy, less kinetic energy remains in the atmosphere in the mean state. While this effect does not play a significant role for a single turbine, it becomes a critical factor for the estimation of large-scale wind power availability. This extraction of kinetic energy by turbines also competes with the natural processes of kinetic energy dissipation, thus setting fundamental limits on extractability that are not considered in previous large-scale studies [1,2,3]. Our simple momentum balance model using ECMWF climate data illustrates a fundamental limit to global wind power extractability and thereby electricity potential (93TW). This is independent of engineering advances in turbine design and wind farm layout. These results are supported by similar results using a global climate model of intermediate complexity. Varying the surface drag coefficient with different simulations allows us to directly relate changes in atmospheric and boundary layer dissipation with resulting climate indices and wind power potential. These new estimates of the maximum power generation by wind turbines are well above the currently installed capacity. Hence, present day installations are unlikely to have a global impact. However, when compared to the current human energy demand of 17TW combined with plans by the US and EU to drastically increase onshore and offshore wind turbine installations [4,5,6], understanding the climatic response and ultimate limitations of wind power as a large-scale renewable energy source is critical. [1] Archer, C., and M.Z. Jacobson, (2005) Evaluation of global wind power, J. Geophys. Res. 110:D12110. [2] Lu, X., M.B. McElroy, and J. Kiviluoma, (2009) Global potential for wind-generated electricity, Proc Natl Acad Sci, 106. [3] Liu, W.T., W. Tang, and X. Xie, (2008) Wind power distribution over the ocean, Geophys. Res. Lett., 35 L13808. [4] IPCC, (2008) IPCC scoping meeting on renewable energy sources - proceedings, Intergovernmental Panel on Climate Change [5] U.S. Department of Energy, (2008) 20% wind energy by 2030: increasing wind energy's contribution to U.S. electricity supply, U.S. Dept. of Energy - Energy Information Administration. [6] EEA, (2009) Europe's onshore and offshore wind energy potential, European Environment Agency, ISSN 1725-2237.

Miller, Lee; Gans, Fabian; Kleidon, Axel

2010-05-01

14

High coronal structure of high velocity solar wind stream sources  

NASA Technical Reports Server (NTRS)

It is shown analytically that the transition from a high-speed stream source to the ambient coronal conditions is quite rapid in longitude in the high corona. This sharp eastern coronal boundary for the solar wind stream sources is strongly suggested by the solar wind 'dwells' which appear in plots of solar wind velocity against constant-radial-velocity-approximation source longitudes. The possibility of a systematic velocity-dependent effect in the constant-radial-velocity approximation, which would cause this boundary to appear sharper than it is, is investigated. A velocity-dependent interplanetary propagation effect or a velocity-dependent 'source altitude' are two possible sources of such a systematic effect. It is shown that, for at least some dwells, significant interplanetary effects are not likely. The variation of the Alfvenic critical radius in solar wind dwells is calculated, showing that the high-velocity stream originates from a significantly lower altitude than the ambient solar wind.

Nolte, J. T.; Krieger, A. S.; Roelof, E. C.; Gold, R. E.

1977-01-01

15

Method for assessing system impact of increasing wind farm sizes above their maximum limits  

Microsoft Academic Search

Current methods for determining wind farm maximum size use conservative voltage stability approach based on maximum wind speed occurring simultaneously with peak loading conditions. Wind patterns at a wind farm site may never allow the wind farm to produce its maximum capacity during the hours of heavy loading conditions. In this paper, a new method is proposed to determine wind

Ala A Tamimi; Anil Pahwa; Shelli Starrett

2011-01-01

16

Comprehensive review of wind energy maximum power extraction algorithms  

Microsoft Academic Search

With the advancements in the variable speed direct drive design and control of wind energy systems, the efficiency and energy capture of these systems is also increasing. As such, many maximum power point tracking methods have been developed and implemented. These MPPT algorithms can be broadly categorized into three types: Tip-Speed control, Power- Signal feedback, and Hill climb search based.

Shravana Musunuri; H. L. Ginn III

2011-01-01

17

Wind velocity profiles measured by the smoke-trail method at the Eastern Test Range, 1964  

NASA Technical Reports Server (NTRS)

Twenty-six detailed wind profiles measured by the smoke trail technique at the Eastern Test Range during the first seven months of 1964 are presented as plots of west-to-east and south-to-north velocity components at height intervals of 25 meters. The overall altitude ranges of the profiles vary from about 2.6 to 19.1 km. The wind measurements, which were made under a variety of conditions, include velocities in excess of the 90- and 95-percent highest values for the Eastern Test Range. The report also includes a listing of the wind profiles, their maximum velocities and direction of the maximum velocities, measured by the smoke trail method at the Eastern Test Range from 1962 to 1964.

Manning, J. C.; Rhyne, R. H.; Henry, R. M.

1972-01-01

18

Effect of velocity profile skewing on blood velocity and volume flow waveforms derived from maximum Doppler spectral velocity.  

PubMed

Given evidence that fully developed axisymmetric flow may be the exception rather than the rule, even in nominally straight arteries, maximum velocity (V(max)) can lie outside the Doppler sample volume (SV). The link between V(max) and derived quantities, such as volume flow (Q), may therefore be more complex than commonly thought. We performed idealized virtual Doppler ultrasound on data from image-based computational fluid dynamics (CFD) models of the normal human carotid artery and investigated how velocity profile skewing and choice of sample volume affected V(max) waveforms and derived Q variables, considering common assumptions about velocity profile shape (i.e., Poiseuille or Womersley). Severe velocity profile skewing caused substantial errors in V(max) waveforms when using a small, centered SV, although peak V(max) was reliably detected; errors with a long SV covering the vessel diameter were orientation dependent but lower overall. Cycle-averaged Q calculated from V(max) was typically within ±15%, although substantial skewing and use of a small SV caused 10%-25% underestimation. Peak Q derived from Womersley's theory was generally accurate to within ±10%. V(max) pulsatility and resistance indexes differed from Q-based values, although the Q-based resistance index could be predicted reliably. Skewing introduced significant error into V(max)-derived Q waveforms, particularly during mid-to-late systole. Our findings suggest that errors in the V(max) and Q waveforms related to velocity profile skewing and use of a small SV, or orientation-dependent errors for a long SV, could limit their use in wave analysis or for constructing characteristic or patient-specific flow boundary conditions for model studies. PMID:23453373

Mynard, Jonathan P; Steinman, David A

2013-05-01

19

Calibration of Instruments for Measuring Wind Velocity and Direction  

NASA Technical Reports Server (NTRS)

Signal Corps wind equipment AN/GMQ-1 consisting of a 3-cup anemometer and wind vane was calibrated for wind velocities from 1 to 200 miles per hour. Cup-shaft failure prevented calibration at higher wind velocities. The action of the wind vane was checked and found to have very poor directional accuracy below a velocity of 8 miles per hour. After shaft failure was reported to the Signal Corps, the cup rotors were redesigned by strengthening the shafts for better operation at high velocities. The anemometer with the redesigned cup rotors was recalibrated, but cup-shaft failure occurred again at a wind velocity of approximately 220 miles per hour. In the course of this calibration two standard generators were checked for signal output variation, and a wind-speed meter was calibrated for use with each of the redesigned cup rotors. The variation of pressure coefficient with air-flow direction at four orifices on a disk-shaped pitot head was obtained for wind velocities of 37.79 53.6, and 98.9 miles per hour. A pitot-static tube mounted in the nose of a vane was calibrated up to a dynamic pressure of 155 pounds per square foot, or approximately 256 miles per hour,

Vogler, Raymond D.; Pilny, Miroslav J.

1950-01-01

20

Wind speed sensorless maximum power point tracking control of variable speed wind energy conversion systems  

Microsoft Academic Search

A maximum power point tracking (MPPT) controller for variable speed wind energy conversion system (WECS) is proposed. The proposed method, without requiring the knowledge of wind speed, air density or turbine parameters, generates at its output the optimum speed command for speed control loop of rotor flux oriented vector controlled machine side converter control system using only the instantaneous active

J. S. Thongam; P. Bouchard; H. Ezzaidi; M. Ouhrouche

2009-01-01

21

Novel Maximum Power Point Tracking Controller for Wind Turbine Driven Permanent Magnet Generator  

Microsoft Academic Search

This paper presents Maximum Power Point Control for variable speed wind turbine driven permanent-magnet generator. The wind turbine generator is operated such that the rotor speed varies according to wind speed to adjust the duty cycle of power converter and maximizes Wind Energy Conversion System (WECS) efficiency. The maximum power point for each speed value is traced using Maximum Power

R. Bharanikumar; A. C. Yazhini; A. N. Kumar

2008-01-01

22

Exploratory Meeting on Airborne Doppler Lidar Wind Velocity Measurements  

NASA Technical Reports Server (NTRS)

The scientific interests and applications of the Airborne Doppler Lidar Wind Velocity Measurement System to severe storms and local weather are discussed. The main areas include convective phenomena, local circulation, atmospheric boundary layer, atmospheric dispersion, and industrial aerodynamics.

Fichtel, G. H. (editor); Kaufman, J. W. (editor); Vaughan, W. W. (editor)

1980-01-01

23

An estimate of the maximum speed of the solar wind, 1938-1989  

NASA Technical Reports Server (NTRS)

In an effort to estimate the highest flow velocity that the solar wind has exhibited at earth during the past 50 years, geomagnetic storms that occurred from 1938 to 1989 were surveyed, and the storms that were preceded by a major proton flare were selected. For each identified flare-storm pair, the average speed ('transit speed') of the associated interplanetary shock from the interval between the flare onset and the sudden commencement of the geomagnetic storm was calculated. In each case, the maximum solar wind flow speed was inferred from an empirical relationship (derived for a sample of recent events) between the shock transit speed and the peak flow velocity of the associated transient stream, obtaining a distribution of maximum solar wind speeds, which presumably corresponds to a sample of the most energetic events of this 50-yr period. Results show no evidence for bulk flow velocities greater than the about 2000 km/sec value deduced by Zastenker et al. (1978) and Grunwaldt (1975) for the August 4, 1972 event.

Cliver, E. W.; Feynman, J.; Garrett, H. B.

1990-01-01

24

An estimate of the maximum speed of the solar wind, 1938-1989  

NASA Astrophysics Data System (ADS)

In an effort to estimate the highest flow velocity that the solar wind has exhibited at earth during the past 50 years, geomagnetic storms that occurred from 1938 to 1989 were surveyed, and the storms that were preceded by a major proton flare were selected. For each identified flare-storm pair, the average speed ('transit speed') of the associated interplanetary shock from the interval between the flare onset and the sudden commencement of the geomagnetic storm was calculated. In each case, the maximum solar wind flow speed was inferred from an empirical relationship (derived for a sample of recent events) between the shock transit speed and the peak flow velocity of the associated transient stream, obtaining a distribution of maximum solar wind speeds, which presumably corresponds to a sample of the most energetic events of this 50-yr period. Results show no evidence for bulk flow velocities greater than the about 2000 km/sec value deduced by Zastenker et al. (1978) and Grunwaldt (1975) for the August 4, 1972 event.

Cliver, E. W.; Feynman, J.; Garrett, H. B.

1990-10-01

25

Detonation velocity of pure and mixed CHNO explosives at maximum nominal density.  

PubMed

In this paper, a simple approach is introduced to predict detonation velocity of pure and mixed explosives at maximum nominal density. This technique may be applied to any pure or mixed explosives that contain elements of carbon, hydrogen, nitrogen and oxygen. The new method requires only elemental composition and some specific structural parameters. The introduced correlation can easily be applied for determining maximum expected detonation velocity of any new CHNO explosive without using its crystal density. Calculated detonation velocities by this procedure for both pure and composite explosive formulations show good agreement with respect to measured detonation velocity at maximum nominal density. PMID:16959409

Keshavarz, Mohammad Hossein

2007-03-22

26

Evidence of a velocity gradient in the solar wind  

NASA Technical Reports Server (NTRS)

Sector-boundary velocity data obtained by Mariner 5 near Venus and by Explorers 33, 34, and 35 near earth are analyzed to determine why higher velocities were measured at earth. Differences in the corresponding velocities are plotted as a function of the heliocentric latitude separation of Mariner and earth, and evidence of a significant latitude gradient in the solar wind is found. Several indirect arguments in support of a latitude gradient are presented, and it is concluded that if the solar wind velocity varies with latitude, latitudinal stresses may have a significant effect on the properties of the solar wind, such as the existence and character of the north-south component of the interplanetary magnetic field.

Smith, E. J.; Rhodes, E. J., Jr.

1974-01-01

27

Neural-network-based sensorless maximum wind energy capture with compensated power coefficient  

Microsoft Academic Search

This paper describes a small wind generation system where neural network principles are applied for wind speed estimation and robust control of maximum wind power extraction against potential drift of wind turbine power coefficient curve. The new control system will deliver maximum electric power to a customer with light weight, high efficiency, and high reliability without mechanical sensors. The concept

Hui Li; K. L. Shi; P. G. McLaren

2005-01-01

28

A unity power factor, maximum power point tracking battery charger for low power wind turbines  

Microsoft Academic Search

This paper proposes a unique implementation of power factor correction (PFC) and maximum power point tracking (MPPT) for low power wind turbines. For a given wind condition, there is a unique electrical load which will harvest the maximum power from a wind turbine, the proposed control algorithm actively tracks this electrical loading condition for maximum power. An active 3-phase rectifier

Gustavo Gamboa; John Elmes; Christopher Hamilton; Jonathan Baker; Michael Pepper; Issa Batarseh

2010-01-01

29

An intelligent maximum power extraction algorithm for inverter-based variable speed wind turbine systems  

Microsoft Academic Search

This paper focuses on the development of maximum wind power extraction algorithms for inverter-based variable speed wind power generation systems. A review of existing maximum wind power extraction algorithms is presented in this paper, based on which an intelligent maximum power extraction algorithm is developed by the authors to improve the system performance and to facilitate the control implementation. As

Quincy Wang; Liuchen Chang

2004-01-01

30

Relationships between wind velocity and underwater irradiance in a shallow lake (Lake Okeechobee, Florida, USA)  

USGS Publications Warehouse

Relationships between wind velocity and the vertical light attenuation coefficient (K0) were determined at two locations in a large, shallow lake (Lake Okeechobee, Florida, USA). K0 was significantly correlated with antecedent wind conditions, which explained as much as 90 percent of the daily variation in K0. Sub-surface irradiance began to change within 60 to 90 minutes of the time when wind velocity exceeded or dropped below a threshold value. Maximum one hour changes in K0 were > 50 percent, however, 20 to 30 percent changes were more common. The magnitude of change in K0 varied spatially based on differences in sediment type. K0 never exceeded 2.8 at a location where bottom sediments were dominated by a mixture of coarse sand and shells. In comparison, K0 exceeded 9 during episodic wind events where the bottom sediment was comprised of fine grain mud. Underwater irradiance data can be used to determine threshold wind velocity and account for the influence sediment type has on K0. Once a threshold velocity has been established, the frequency, rate, and duration of expected change in underwater irradiance can be evaluated. This is critical information for scientists who are studying algal productivity or other light-related phenomena.Relationships between wind velocity and the vertical light attenuation coefficient (K0) were determined at two locations in a large, shallow lake (Lake Okeechobee, Florida, USA). K0 was significantly correlated with antecedent wind conditions, which explained as much as 90 percent of the daily variation in K0. Sub-surface irradiance began to change within 60 to 90 minutes of the time when wind velocity exceeded or dropped below a threshold value. Maximum one hour changes in K0 were >50 percent, however, 20 to 30 percent changes were more common. The magnitude of change in K0 varied spatially based on differences in sediment type. K0 never exceeded 2.8 at a location where bottom sediments were dominated by a mixture of coarse sand and shells. In comparison, K0 exceeded 9 during episodic wind events where the bottom sediment was comprised of fine grain mud. Underwater irradiance data can be used to determine threshold wind velocity and account for the influence sediment type has on K0. Once a threshold velocity has been established, the frequency, rate, and duration of expected change in underwater irradiance can be evaluated. This is critical information for scientists who are studying algal productivity or other light-related phenomena.

Hanlon, C. G.; Miller, R. L.; McPherson, B. F.

1998-01-01

31

Determination of the envelope function (maximum velocity curve) in Doppler ultrasound flow velocity diagrams  

NASA Astrophysics Data System (ADS)

This paper presents a new approach for the evaluation of Doppler flow velocity diagrams, obtained during brachial artery flow mediated dilatation (FMD) studies. The velocity diagrams are stored as image sequences on VCR tape. For this reason standard signal processing methods can not be used. A method for determination of blood velocity envelopes from image data is reported that uses Doppler-data specific heuristic to achieve high accuracy and robustness. The approach was tested in 40 Doppler blood flow images. Comparisons with manually defined independent standards demonstrated a very good correlation in determined peak velocity values (r equals 0.993) and flow envelope areas (r equals 0.996). The method is currently tested in a large volume clinical study.

Tschirren, Juerg; Lauer, Ronald M.; Sonka, Milan

2000-06-01

32

Maximum power extraction from a small wind turbine using 4-phase interleaved boost converter  

Microsoft Academic Search

This paper describes a 4-phase interleaved boost converter in a small wind turbine application. The boost converter is placed between the wind turbine and the load and is controlled to extract the maximum power from wind turbine. The boost converter duty ratio adjusted, based on the wind speed and rotor speed values, so that the wind turbine would be operated

Liqin Ni; D. J. Patterson; J. L. Hudgins

2009-01-01

33

Velocity shear layers in solar winds affect Earth's magnetosphere  

NASA Astrophysics Data System (ADS)

Human society is increasingly reliant on technology that can be disrupted by space weather. For instance, geomagnetic storms can cause high-latitude air fights to be rerouted, costing as much as $100,000 per fight; induce errors of up to 46 meters in GPS systems; and affect satellites and the International Space Station. Space weather is determined by how the solar wind, a stream of hot plasma from the Sun, interacts with Earth's magnetic field. In studying space weather, scientists have largely neglected the fact that the solar wind contains layers of very strong velocity shear. Scientists understand very little about how these wind shears affect space weather.

Bhattacharya, Atreyee

2012-09-01

34

New Forecasting Factor for Solar Wind Velocity From EIT Observations  

NASA Astrophysics Data System (ADS)

Various solar wind velocity forecasting methods at 1AU have been developed during the last decade, such as Wang-sheeley model and Hakamada-Akasofu-Fry Version 2 (HAFv2) model. Some authors have found that Coronal hole(CH) areas can be used to forecast the solar wind velocity with better results in low CME activity periods(e.g. Vršnak et.al.). The property of the solar surface is a good indication of the following interplanetary and geomagnetic activities. We analyzed all EIT284Å images in almost the whole solar cycle 23 and developed a new forecasting factor(Pch) from the brightness of the solar Extreme Ultraviolet Images. and a good relationship was found between the Pch and solar wind velocity V three days later probed by ACE spacecraft. A simple method of forecasting the solar wind speed near earth in low CME activity periods is presented. For Pch and solar wind velocity, the linear correlation coefficients is R = 0.89 from 21 September until 26 December. For comparison we also analysed the same period data as Vršnak(2007) who using the coronal hole areas AM as input parameters for predicting solar wind velocity. The linear least-squares fit of Pch with the 3-day lag solar wind velocity showed a correlation coefficient R = 0.70, which is better than the result using AM(R = 0.62). The solar wind speed could be expressed as V (km s-1) = 337 + 0.00868 × Pch. The average of relative difference between the calculated and the observed values amounts to |?¯| ? 12.15%. Furthermore, for the ten peaks during the analysis period, AM and V just showed a correlation coefficient R = 0.32, much worse than using Pch factor which showed R = 0.75. Moreover, the Pch factor exterminated personal bias in the forecasting process, which existed in the method using AM as input parameters because the coronal hole boundary can not be easily determined since no quantitative criteria can be used to precisely locate coronal holes from observation. Finally, the expression of V by Pch is analysed, which showed the variation of background solar wind speed during the whole solar cycle 23.

Luo, B.; Liu, S.; Zhong, Q.; Gong, J.

2007-12-01

35

Quartz crystal microbalances to measure wind velocity and air humidity  

NASA Technical Reports Server (NTRS)

Instrument includes four temperature-sensing, Y-cut quartz crystals to determine wind direction, velocity, and temperature. Two additional AT-cut crystals are used to determine air humidity. Entire signal processing is provided by built-in electronics circuits.

Stephens, J. B.; Lave, E. G.

1975-01-01

36

Measurement of turbulent wind velocities using a rotating boom apparatus  

SciTech Connect

The present report covers both the development of a rotating-boom facility and the evaluation of the spectral energy of the turbulence measured relative to the rotating boom. The rotating boom is composed of a helicopter blade driven through a pulley speed reducer by a variable speed motor. The boom is mounted on a semiportable tower that can be raised to provide various ratios of hub height to rotor diameter. The boom can be mounted to rotate in either the vertical or horizontal plane. Probes that measure the three components of turbulence can be mounted at any location along the radius of the boom. Special hot-film sensors measured two components of the turbulence at a point directly in front of the rotating blade. By using the probe rotated 90/sup 0/ about its axis, the third turbulent velocity component was measured. Evaluation of the spectral energy distributions for the three components of velocity indicates a large concentration of energy at the rotational frequency. At frequencies slightly below the rotational frequency, the spectral energy is greatly reduced over that measured for the nonrotating case measurements. Peaks in the energy at frequencies that are multiples of the rotation frequency were also observed. We conclude that the rotating boom apparatus is suitable and ready to be used in experiments for developing and testing sensors for rotational measurement of wind velocity from wind turbine rotors. It also can be used to accurately measure turbulent wind for testing theories of rotationally sampled wind velocity.

Sandborn, V.A.; Connell, J.R.

1984-04-01

37

Threshold velocity for wind erosion: the effects of porous fences  

Microsoft Academic Search

Porous fence is a kind of artificial windbreak that has many practical applications. The threshold wind velocities at different distances downwind from porous fences were measured and the corresponding characteristics of particle movement observed to assess their shelter effect. It is found that the fence’s porosity is the key factor that determines the resulting shelter effect. The area near a

Zhibao Dong; Guangqiang Qian; Wanyin Luo; Hongtao Wang

2006-01-01

38

Maximum Velocity of a Boulder Ejected From an Impact Crater Formed on a Regolith Covered Surface  

NASA Astrophysics Data System (ADS)

We investigate the effect of regolith depth on boulder ejection velocity. A "boulder" refers to an apparently intact rock or rock fragment lying on a planetary surface, regardless of emplacement mechanism. Boulders appear in planetary images as positive relief features --- bright, sun-facing pixels adjacent to dark, shadowed pixels. We studied 12 lunar craters in high resolution (1~m) photographs from Lunar Orbiter III and V. Local regolith depth was measured using the method of small crater morphology. Ejection velocities of boulders were calculated assuming a ballistic trajectory to the final boulder location. A plot of regolith depth/crater diameter vs. maximum boulder ejection velocity shows that craters formed in deeper regolith (with respect to crater size) eject boulders at lower velocities. When ejection velocity (EjV) is in m/s, and regolith depth (Dr) and crater diameter (Dc) are in meters, the data fit the relation Dr / Dc = 1053 × EjVmax-2.823. To explain the data, we turn to impact cratering theory. An ejected particle will follow a streamline from its place of origin to its ejection point (the Z-model), and then follow a ballistic trajectory. Material ejected along more shallow streamlines is ejected at greater velocities. If shallow regolith covers the surface, the most shallow (greatest velocity) streamlines will travel only through the regolith. Boulders, however, must be ejected from the bedrock below the regolith. Thus, the boulder ejected with the greatest velocity originates just below the regolith, along the most shallow streamline through the bedrock. If the regolith is deeper, the most shallow streamline through the bedrock will be deeper, and the maximum velocity of an ejected boulder will be lower. Hence, the regolith depth and maximum ejection velocity of a boulder are correlated: greater boulder ejection velocities correspond to thinner regolith. We observe this correlation in the data.

Bart, G. D.; Melosh, H. J.

2007-12-01

39

A wind tunnel simulation of the mean velocity fields behind upright porous fences  

Microsoft Academic Search

Porosity is the most important parameter that determines the efficiency of wind fences. The present study provided a deeper understanding of mean flow regime behind fences with different porosities at different wind velocities by means of a scaled wind tunnel simulation. Velocities were measured using particle image velocimetry and the mean velocity field was obtained and discussed. The mean velocity

Zhibao Dong; Wanyin Luo; Guangqiang Qian; Hongtao Wang

2007-01-01

40

Fluid velocity actuated structure for a wind mill\\/water wheel  

Microsoft Academic Search

A fluid velocity actuated structure for a wind mill\\/water wheel, comprising an elongated cylinder with blades\\/fins hingedly supported thereon. When exposed to the driving force the one blade\\/fin will respond by assuming a position of least resistance thereto whereas the 180° opposite blade\\/fin will assume a position of maximum resistance thereto. The hinge supports for the fins\\/blades has a swivel

1981-01-01

41

Wind velocity-change (gust rise) criteria for wind turbine design  

Microsoft Academic Search

A closed-form equation is derived for root mean square (rms) value of velocity change (gust rise) that occurs over the swept area of wind turbine rotor systems and an equation for rms value of velocity change that occurs at a single point in space. These formulas confirm the intuitive assumption that a large system will encounter a less severe environment

W. C. Cliff; G. H. Fichtl

1978-01-01

42

[Wind tunnel experiment on canopy structural parameters of isolated tree and wind velocity field characters nearby].  

PubMed

The canopy structural parameters(porosity beta and permeability alpha) of isolated tree, and the wind velocity field character nearby were analyzed by wind tunnel experiment. The results show that alpha and beta fitted the function of alpha = beta 0.6, and the wind velocity nearby decreased in ellipsoid contour. The contour increased with increasing tree height and canopy width, and decreased with increasing permeability (or porosity). The isotach became the shape of ellipses or elliptic segments in horizontal and vertical plans. PMID:11767595

Guan, D; Zhu, T

2000-04-01

43

Visibility-Graph Analysis of the Solar Wind Velocity  

NASA Astrophysics Data System (ADS)

We analyze in situ measurements of the solar wind velocity obtained by the Advanced Composition Explorer (ACE) and the Helios spacecraft during the years 1998 - 2012 and 1975 - 1983, respectively. The data mainly belong to solar cycles 23 (1996 - 2008) and 21 (1976 - 1986). We used the directed horizontal-visibility-graph (DHVg) algorithm and estimated a graph functional, namely, the degree distance ( D), which is defined using the Kullback-Leibler divergence (KLD) to understand the time irreversibility of solar wind time-series. We estimated this degree-distance irreversibility parameter for these time-series at different phases of the solar activity cycle. The irreversibility parameter was first established for known dynamical data and was then applied to solar wind velocity time-series. It is observed that irreversibility in solar wind velocity fluctuations show a similar behavior at 0.3 AU ( Helios data) and 1 AU (ACE data). Moreover, the fluctuations change over the phases of the activity cycle.

Suyal, Vinita; Prasad, Awadhesh; Singh, Harinder P.

2014-01-01

44

Velocity-Space Proton Diffusion in the Solar Wind Turbulence  

NASA Astrophysics Data System (ADS)

We study the velocity-space quasi-linear diffusion of the solar wind protons driven by oblique Alfvén turbulence at proton kinetic scales. Turbulent fluctuations at these scales possess the properties of kinetic Alfvén waves (KAWs) that are efficient in Cherenkov-resonant interactions. The proton diffusion proceeds via Cherenkov kicks and forms a quasi-linear plateau - the nonthermal proton tail in the velocity distribution function (VDF). The tails extend in velocity space along the mean magnetic field from 1 to (1.5 - 3) V A, depending on the spectral break position, on the turbulence amplitude at the spectral break, and on the spectral slope after the break. The most favorable conditions for the tail generation occur in the regions where the proton thermal and Alfvén velocities are about equal, V Tp/ V A?1. The estimated formation times are within 1 - 2 h for typical tails at 1 AU, which is much shorter than the solar wind expansion time. Our results suggest that the nonthermal proton tails, observed in situ at all heliocentric distances > 0.3 AU, are formed locally in the solar wind by the KAW turbulence. We also suggest that the bump-on-tail features - proton beams, often seen in the proton VDFs, can be formed at a later evolutional stage of the nonthermal tails by the time-of-flight effects.

Voitenko, Y.; Pierrard, V.

2013-11-01

45

An analysis of maximum horizontal wind speeds recorded since 1961 at Kennedy Space Center, Florida  

NASA Technical Reports Server (NTRS)

Tabulations of maximum horizontal wind speed values are reported that were recorded at the Kennedy Space Center. Maximum wind speeds were recorded during the eight hurricanes which have affected the area--Cleo in August 1964 through Agnes in June 1972. Detailed tabulations and frequency distributions of daily maximum horizontal wind speeds recorded at NASA's 150 m ground tower facility at nine levels from December 1965 through March 1970 are also included.

Alexander, M. B.

1978-01-01

46

Long-term variations of the solar wind density - velocity relation.  

NASA Astrophysics Data System (ADS)

The relation between density and velocity of the solar wind is determined for the individual phases of solar activity cycles 20 and 21, using daily averaged values of the solar wind parameters (November 1963 -- May 1980, Bartels rotations No.s 1783-2006). It was found that the particle concentration decreases in all analysed phases of the two solar cycles with increasing solar wind velocity. In most phases of cycles 20 and 21 (with the exception of the ascending branch of cycle 20), the density decreases as n ˜V-1.5. As regards the quiescent solar wind with no marked velocity gradients, it was found that n ˜V(1.6-1.7). During the ascending phase, it appears that n ˜V-1.1 is realistic. In both cycles, 20 and 21, it was found that the particle density of the solar wind is higher on the average (about 1.5 times) in the solar activity minimum than in its maximum.

Kul?ár, L.

47

An experimental study of a plasma actuator in absence of free airflow: Ionic wind velocity profile  

SciTech Connect

In this study, we are interested in the direct current electrical corona discharge created between two wire electrodes. The experimental results are related to some electroaerodynamic actuators based on the direct current corona discharge at the surface of a dielectric material. Several geometrical forms are selected for the dielectric surface, such as a plate, a cylinder, and a NACA 0015 aircraft wing. The current density-electric field characteristics are presented for different cases in order to determine the discharge regimes. The corona discharge produces nonthermal plasma, so it is called plasma discharge. Plasma discharge creates a tangential ionic wind above the surface at the vicinity of the wall. The ionic wind induced by the corona discharge is measured in absence of free external airflow. The ionic wind velocity profiles and the maximum induced tangential force are given for different surface forms, so it is possible to compare the actuators effect based on the span of the ionic wind velocity and thrust values. The higher ionic wind velocity is obtained with the NACA profile, which shows the effectiveness of this actuator for the airflow control.

Mestiri, R.; Hadaji, R.; Ben Nasrallah, S. [Ecole Nationale d'Ingenieurs de Monastir, Monastir 5019 (Tunisia)

2010-08-15

48

Efficient wind turbine design for low velocity air flow  

Microsoft Academic Search

Six rows of radial blades, arranged to extend in a spiral (in the direction of axial rotation) covering 55 degrees of arc about a hollow support section, constitute an optimum blade arrangement for maximum efficiency in low velocity airflows. Each blade in the rows is contoured to receive both direct flow pressure as well as airfoil lift in order to

Fosdick

1984-01-01

49

Maximum-likelihood estimation of range, velocity, and acceleration using a linear FM train radar waveform  

Microsoft Academic Search

An efficient implementation of the maximum likelihood estimator (MLE) is presented for the estimation of target range, radial velocity and acceleration when the radar waveform consists of a wideband linear frequency modulated (LFM) pulse train. Analytic properties of the associated wideband ambiguity function are derived; in particular the ambiguity function, with acceleration set to zero, is derived in closed form.

Theagenis J. Abatzoglou; Gregory O. Gheen

1997-01-01

50

Observations of Rapid Velocity Variations in the Slow Solar Wind  

NASA Astrophysics Data System (ADS)

The technique of interplanetary scintillation (IPS) is the observation of rapid fluctuations of the radio signal from an astronomical compact source as the signal passes through the ever-changing density of the solar wind. Cross-correlation of simultaneous observations of IPS from a single radio source, received at multiple sites of the European Incoherent SCATter (EISCAT) radio antenna network, is used to determine the velocity of the solar wind material passing over the lines of sight of the antennas. Calculated velocities reveal the slow solar wind to contain rapid velocity variations when viewed on a time-scale of several minutes. Solar TErrestrial RElations Observatory (STEREO) Heliospheric Imager (HI) observations of white-light intensity have been compared with EISCAT observations of IPS to identify common density structures that may relate to the rapid velocity variations in the slow solar wind. We have surveyed a one-year period, starting in April 2007, of the EISCAT IPS observing campaigns beginning shortly after the commencement of full science operations of the STEREO mission in a bid to identify common density structures in both EISCAT and STEREO HI datasets. We provide a detailed investigation and presentation of joint IPS/HI observations from two specific intervals on 23 April 2007 and 19 May 2007 for which the IPS P-Point (point of closest approach of the line of sight to the Sun) was between 72 and 87 solar radii out from the Sun's centre. During the 23 April interval, a meso-scale (of the order of 105 km or larger) transient structure was observed by HI-1A to pass over the IPS ray path near the P-Point; the observations of IPS showed a micro-scale structure (of the order of 102 km) within the meso-scale transient. Observations of IPS from the second interval, on 19 May, revealed similar micro-scale velocity changes, however, no transient structures were detected by the HIs during that period. We also pose some fundamental thoughts on the slow solar wind structure itself.

Hardwick, S. A.; Bisi, M. M.; Davies, J. A.; Breen, A. R.; Fallows, R. A.; Harrison, R. A.; Davis, C. J.

2013-07-01

51

How did the solar wind structure change around the solar maximum? From interplanetary scintillation observation  

Microsoft Academic Search

Observations from the second Ulysses fast latitude scan show that the global structure of solar wind near solar maximum is much more complex than at solar minimum. Soon after solar maximum, Ulysses observed a polar coronal hole (high speed) plasma with magnetic polarity of the new solar cycle in the Northern Hemisphere. We analyze the solar wind structure at and

K. Fujiki; M. Kojima; M. Tokumaru; T. Ohmi; A. Yokobe; K. Hayashi; D. J. McComas; H. A. Elliott

2003-01-01

52

CFD wind tunnel test: Field velocity patterns of wind on a building with a refuge floor  

NASA Astrophysics Data System (ADS)

This paper reports a CFD wind tunnel study of wind patterns on a square-plan building with a refuge floor at its mid-height level. In this study, a technique of using calibrated power law equations of velocity and turbulent intensity applied as the boundary conditions in CFD wind tunnel test is being evaluated by the physical wind tunnel data obtained by the Principal Author with wind blowing perpendicularly on the building without a refuge floor. From the evaluated results, an optimised domain of flow required to produce qualitative agreement between the wind tunnel data and simulated results is proposed in this paper. Simulated results with the evaluated technique are validated by the wind tunnel data obtained by the Principal Author. The results contribute to an understanding of the fundamental behaviour of wind flow in a refuge floor when wind is blowing perpendicularly on the building. Moreover, the results reveal that the designed natural ventilation of a refuge floor may not perform desirably when the wind speed on the level is low. Under this situation, the refuge floor may become unsafe if smoke was dispersed in the leeward side of the building at a level immediately below the refuge floor.

Cheng, C. K.; Yuen, K. K.; Lam, K. M.; Lo, S. M.

2005-10-01

53

Study and effect of IMF and solar wind velocity in CR modulation  

NASA Astrophysics Data System (ADS)

The high amplitude wave train events HAEs of cosmic ray intensity observed during 1981-1994 were analyzed We have studied the effect of southward component Bz of interplanetary magnetic field IMF and solar wind velocity on cosmic ray diurnal anisotropy The neutron monitor data of Deep River station has been used in the present analysis It has been observed that HAEs are weakly dependent on high-speed solar wind velocity The occurrence of HAE is dominant for positive polarity of southward component Bz of IMF The diurnal time of maximum significantly shifts towards earlier hours as compared to the azimuthal corotational direction for majority of the HAEs during the period of investigation

Mishra, R. K.; Mishra, R. A.

54

Accuracy of aircraft velocities from inertial navigation systems for application to airborne wind measurements  

NASA Technical Reports Server (NTRS)

An experimental assessment was made of two commercially available inertial navigation systems (INS) with regard to their velocity measuring capability for use in wind, shear, and long-wavelength atmospheric turbulence research. The assessment was based on 52 sets of postflight measurements of velocity (error) during a "Schuler cycle" (84 minutes) while the INS was still operating but the airplane was motionless. Four INS units of one type and two units of another were tested over a period of 2 years after routine research flights similar to air-linetype operations of from 1 to 6 hours duration. The maximum postflight errors found for the 52 cases had a root mean square value of 2.82 m/sec with little or no correlation of error magnitude with flight duration. Using an INS for monitoring ground speed during landway in a predicted high wind shear situation could lead to landing speeds which are dangerously high or low.

Rhyne, R. H.

1980-01-01

55

Low-level nocturnal wind maximum over the Central Amazon Basin  

NASA Technical Reports Server (NTRS)

A low-level nocturnal wind maximum is shown to exist over extensive and nearly undisturbed rainforest near the central Amazon city of Manaus. Meteorological data indicate the presence of this nocturnal wind maximum during both the wet and dry seasons of the Central Amazon Basin. Daytime wind speeds which are characteristically 3-7 m/s between 300 and 1000 m increase to 10-15 m/s shortly after sunset. The wind-speed maximum is reached in the early evening, with wind speeds remaining high until several hours after sunrise. The nocturnal wind maximum is closely linked to a strong low-level inversion formed by radiational cooling of the rainforest canopy. Surface and low-level pressure gradients between the undisturbed forest and the large Amazon river system and the city of Manaus are shown to be responsible for much of the nocturnal wind increase. The pressure gradients are interpreted as a function of the thermal differences between undisturbed forest and the river/city. The importance of both the frictional decoupling and the horizontal pressure gradient suggest that the nocturnal wind maximum does not occur uniformly over all Amazonia. Low-level winds are thought to be pervasive under clear skies and strong surface cooling and that, in many places (i.e., near rivers), local pressure gradients enhance the low-level nocturnal winds.

Greco, Steven; Ulanski, Stanley; Garstang, Michael; Houston, Samuel

1992-01-01

56

On the relation between winds, current velocities and transports in the Yucatan Channel  

NASA Astrophysics Data System (ADS)

A mooing array deployed from February 2008 to May 2011 by the Canek project indicates the flow at 50 m depth and transport through the western Yucatan Channel have two separate maxima in spring and summer, that are significantly correlated with the anticyclonic wind stress curl leading in Yucatan Channel by 0~2 months. The wind stress curl over the Cayman Sea derived from the ERA-interim reanalysis, has a strong semiannual signal with two anti-cyclonic maxima in January and July. Transport through the whole Channel, however, has a clear maximum in summer and a weaker one in winter. Our results partially agree with previous findings from model experiments, but indicate that the relation between Loop Current extension, maximum velocity and transport in Yucatan Channel may not be a simple one.

Romero Arteaga, A. M.; Sheinbaum, J.; Athié, G.; Ochoa-de-La-Torre, J. L.; Candela, J.

2013-05-01

57

Velocity fields in a low-latitude coronal hole - Results from the Solar Maximum Mission  

NASA Technical Reports Server (NTRS)

The Solar Maximum Mission (SMM) satellite has been used to observe Doppler signatures in C IV in a low-latitude coronal hole as it crossed the central meridian (1985 February 2-8). Scatter plots of C IV emission intensity versus velocity do not show the pronounced positive correlation which has been reported in other regions on the sun. These data suggest that the coronal hole may control the gross velocity field in the solar atmosphere at the level where C IV is formed. Some localized regions of upflow coincide with EUV bright points in the coronal hole.

Mullan, D. J.; Waldron, W. L.

1987-01-01

58

Relationship between the IMF azimuthal angle and solar wind velocity  

NASA Astrophysics Data System (ADS)

The relationship between the IMF azimuthal angle and plasma velocity has been studied independently for three types of solar wind streams (recurrent and transient high-speed streams and low-speed background wind) based on the interplanetary medium parameters measured in the near-Earth orbits in 1964-1996. The relationships between the IMF azimuthal angle cotangent and plasma velocity are close to linear but strongly differ from one another and from the theoretical relationship for all types of streams. These differences area caused by the magnetic field disturbance on the time scales smaller than a day, and the effect of this disturbance has been studied quantitatively. The effective periods of rotation of the IMF sources on the Sun, depending on the solar cycle phase, have been obtained from the relations between the IMF azimuthal angle cotangent and plasma velocity. During the most part of the solar cycle, the periods of rotation of the IMF sources are close to the period of rotation of the solar equator but abruptly increase to the values typical of the solar circumpolar zones in the years of solar minimums.

Erofeev, D. V.

2008-04-01

59

Solar wind collimation of the Jupiter high velocity dust streams  

NASA Astrophysics Data System (ADS)

The dust bursts discovered by the Ulysses dust sensor when approaching Jupiter in 1992 were later confirmed as collimated streams of high velocity (~200 km/s) charged (~5V) dust grains escaping from Jupiter and dominated by the interplanetary Magnetic field (IMF). With Cassini, a similar phenomenon was observed in Saturn. It was demonstrated that the Jovian dust streams are closely related to the solar wind compressed regions, either Corotating interaction regions (CIRs) or Coronal mass ejections (CMEs) ¨Cto a minor extent-. Actually the dust streams seem ultimately to be generated by such events. This can be explained considering that dust grains are accelerated as they gain substantial energy while compressed at the forward and reverse shocks that bound or precede these solar wind regions.

Flandes, A.; Krueger, H.

2006-12-01

60

Potential for coherent Doppler wind velocity lidar using neodymium lasers  

NASA Technical Reports Server (NTRS)

Existing techniques for the frequency stabilization of Nd:YAG lasers operating at 1.06 micron, and the high-gain amplification of radiation at that wavelength, make possible the construction of a coherent Doppler wind velocity lidar using Nd:YAG. Velocity accuracy and range resolution are better at 1.06 micron than at 10.6 microns at the same level of the SNR. Backscatter from the atmosphere at 1.06 micron is greater than that at 10.6 microns by about 2 orders of magnitude, but the quantum-limited noise is higher by 100 also. Near-field attenuation and turbulent effects are more severe at 1.06 micron. In some configurations and environments, the 1.06-micron wavelength may be the better choice, and there may be technological advantages favoring the use of solid-state lasers in satellite systems.

Kane, T. J.; Byer, R. L.; Zhou, B.

1984-01-01

61

The analysis and kinetic energy balance of an upper-level wind maximum during intense convection  

NASA Technical Reports Server (NTRS)

The purpose of this paper is to analyze the formation and maintenance of the upper-level wind maximum which formed between 1800 and 2100 GMT, April 10, 1979, during the AVE-SESAME I period, when intense storms and tornadoes were experienced (the Red River Valley tornado outbreak). Radiosonde stations participating in AVE-SESAME I are plotted (centered on Oklahoma). National Meteorological Center radar summaries near the times of maximum convective activity are mapped, and height and isotach plots are given, where the formation of an upper-level wind maximum over Oklahoma is the most significant feature at 300 mb. The energy balance of the storm region is seen to change dramatically as the wind maximum forms. During much of its lifetime, the upper-level wind maximum is maintained by ageostrophic flow that produces cross-contour generation of kinetic energy and by the upward transport of midtropospheric energy. Two possible mechanisms for the ageostrophic flow are considered.

Fuelberg, H. E.; Jedlovec, G. J.

1982-01-01

62

Sensitivity of estuarine turbidity maximum to settling velocity, tidal mixing, and sediment supply  

USGS Publications Warehouse

Estuarine turbidity maximum, numerical modeling, settling velocity, stratification The spatial and temporal distribution of suspended material in an Estuarine Turbidity Maxima (ETM) is primarily controlled by particle settling velocity, tidal mixing, shear-stress thresholds for resuspension, and sediment supply. We vary these parameters in numerical experiments of an idealized two-dimensional (x-z) estuary to demonstrate their affects on the development and retention of particles in an ETM. Parameters varied are the settling velocity (0.01, 0.1, and 0.5 mm/s), tidal amplitude (0.4 m 12 hour tide and 0.3 to 0.6 m 14 day spring neap cycle), and sediment availability (spatial supply limited or unlimited; and temporal supply as a riverine pulse during spring vs. neap tide). Results identify that particles with a low settling velocity are advected out of the estuary and particles with a high settling velocity provide little material transport to an ETM. Particles with an intermediate settling velocity develop an ETM with the greatest amount of material retained. For an unlimited supply of sediment the ETM and limit of salt intrusion co-vary during the spring neap cycle. The ETM migrates landward of the salt intrusion during spring tides and seaward during neap tides. For limited sediment supply the ETM does not respond as an erodible pool of sediment that advects landward and seaward with the salt front. The ETM is maintained seaward of the salt intrusion and controlled by the locus of sediment convergence in the bed. For temporal variability of sediment supplied from a riverine pulse, the ETM traps more sediment if the pulse encounters the salt intrusion at neap tides than during spring tides. ?? 2007 Elsevier B.V. All rights reserved.

J. C. , W.; Sherwood, C. R.; Geyer, W. R.

2007-01-01

63

An intelligent maximum power extraction algorithm for hybrid wind–diesel-storage system  

Microsoft Academic Search

This paper focuses on the development of maximum wind power extraction algorithms for variable speed wind turbines in hybrid wind–diesel storage system (HWDSS). The propose algorithm utilizes Takagi–Sugeno (T–S) fuzzy controller. This algorithm combines the merits of: (i) the capability for dealing with nonlinear systems; (ii) the powerful LMI approach to obtain control gains; (iii) the high performance of integral

Elkhatib Kamal; Magdy Koutb; Abdul Azim Sobaih; Belal Abozalam

2010-01-01

64

Fuzzy logic control based maximum power tracking of a wind energy system  

Microsoft Academic Search

In this paper a utility interactive wind energy conversion system (WECS) with an asynchronous (AC–DC–AC) link is described. The control system has the objective of identifying and extracting the maximum power from the wind energy system and transferring this power to utility. A fuzzy logic control (FLC) technique has been implemented to design the tracking controller of the WECS. A

Amal Z. Mohamed; Mona N. Eskander; Fadia A. Ghali

2001-01-01

65

Doubly Fed Induction Generator Maximum Wind Power Extraction Study Through Integrated Steady-state and Close-loop Control Evaluation  

Microsoft Academic Search

A doubly fed induction generator wind turbine is a variable-speed wind turbine widely used in the modern wind power industry. Unlike a fixed-speed wind turbine, the maximum power extraction of the turbine is affected by (1) electrical characteristics of the generator, (2) aerodynamic characteristics of the turbine blades, and (3) maximum power extraction control strategies. This article presents a doubly

Shuhui Li; Timothy A. Haskew; Eduard Muljadi

2010-01-01

66

The epoch state navigation filter. [for maximum likelihood estimates of position and velocity vectors  

NASA Technical Reports Server (NTRS)

The formulation of a recursive maximum likelihood navigation system employing reference position and velocity vectors as state variables is presented. Convenient forms of the required variational equations of motion are developed together with an explicit form of the associated state transition matrix needed to refer measurement data from the measurement time to the epoch time. Computational advantages accrue from this design in that the usual forward extrapolation of the covariance matrix of estimation errors can be avoided without incurring unacceptable system errors. Simulation data for earth orbiting satellites are provided to substantiate this assertion.

Battin, R. H.; Croopnick, S. R.; Edwards, J. A.

1977-01-01

67

A multiyear global surface wind velocity dataset using SSM/I wind observations  

SciTech Connect

The Special Sensor Microwave Imagers (SSM/I) aboard three DMSP satellites have improved a large dataset of surface wind speeds over the global oceans from July 1987 to the present. These data are characterized by high resolution, coverage, and accuracy, but their application has been limited by the lack of directional information. In an effort to extend the applicability of these data , methodology has been developed to assign directions to the SSM/I wind speeds and to produce analyses using these data. Following extensive testing, this methodology has been used to generate a seven and one-half year dataset (from July 1987 through December 1994) of global SSM/I wind vectors. These data are currently being used in a variety of atmospheric and oceanic applications and are available to interested investigators. Recent results presented in this paper show the accuracy of the SSM/I wind velocities, the ability of these data to improve surface wind analyses, and the propagation of a synoptic-scale convergent cortex in the Tropics that can be tracked from year to year in annual mean SSM/I wind fields. 11 refs., 5 figs., 2 tabs.

Atlas, R. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)] [NASA Goddard Space Flight Center, Greenbelt, MD (United States); Bloom, S.C.; Ardizzone, J. [Goddard Space Flight Center, Greenbelt, MD (United States)] [and others] [Goddard Space Flight Center, Greenbelt, MD (United States); and others

1996-05-01

68

The wind potential impact on the maximum wind energy penetration in autonomous electrical grids  

Microsoft Academic Search

According to long-term wind speed measurements the Aegean Archipelago possesses excellent wind potential, hence properly designed wind energy applications can substantially contribute to fulfill the energy requirements of the island societies. On top of this, in most islands the electricity production cost is extremely high, while significant insufficient power supply problems are often encountered, especially during the summer. Unfortunately, the

J. K. Kaldellis

2008-01-01

69

Pulsar Wind Nebulae, Space Velocities and Supernova Remnant  

NASA Technical Reports Server (NTRS)

The original proposal for this LTSA grant was for X-ray studies of pulsars, and especially pulsar wind nebulae and what they could tell us about pulsar properties, especially their space velocities. By any metric, this program has been very successful. No fewer than 14 papers on directly related topics (and several dozen more on related topics) have been published in refereed journals with the PI as lead or co-author, all observational results that have had significant impact on the field. These include the first X-ray detection of the "Duck" pulsar, a clear demonstration that estimated pulsar ages can be off by over an order of magnitude (via observations of the young supernova remnant G11.2-0.3) and the detection of the first pulsar wind nebula around a millisecond pulsar. These publications have also resulted in 4 press releases. Moreover, they also represent the thesis work of two PhD students at MIT (Froney Crawford and Mike Pivovaroff) and one postdoctoral fellow, Bryan Gaensler, now Assistant Professor at Harvard.

2005-01-01

70

Loop Current variability due to wind stress and reduced sea level during the Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

One of the most prominent features of the circulation in the Gulf of Mexico is the Loop Current (LC). It is of special interest as it influences not only the climate in the Gulf of Mexico. Although causation is not well understood yet, dynamical relationships between LC retraction and extension, seasonal migrations of the Intertropical Convergence Zone (ITCZ) and the related wind stress curl over the subtropical North Atlantic, and changes in the thermohaline circulation are indicated by model simulations. A characteristic feature of the LC is the shedding of anticyclonic eddies. These eddies can have depth signatures of up to 1000 m and are of special interest as they supply heat and moisture into the western and northern Gulf. The eddies are generated aperiodically every 3 to 21 months, with an average shedding time of 9.5 months. Eddy shedding appears to be related to a suite of oceanographic forcing fields such as the Yucatan Channel throughflow, the Florida Current and North Brazil Current variability, as well as synoptic meteorological forcing variability. By combining state-of-the-art paleoceanographic and meso-scale eddy-resolving numerical modeling techniques, we examined the Loop Current dynamics and hydrographic changes in the Gulf going back in time up to ~21,000 years. To assess the impact of Last Glacial Maximum (LGM) wind stress and reduced sea level we have re-configured an existing hierarchy of models of the North Atlantic Ocean (FLAME) with a horizontal grid resolution of ca. 30 km (wind stress was taken from the PMIP-II database). The sea level was lowered compared to the CONTROL run by 110 m and 67 m. These sea level changes have been chosen according to the cold-deglacial periods Heinrich I and Younger Dryas. The result of our model simulations is a continuous increase in eddy shedding from the LGM to the Holocene. This increase is predominantly controlled by the continuous deglacial sea level rise. Changes in wind stress curl related to the southward displacement of the ITCZ tend to produce larger Yucatan and Florida Strait throughflow but do not play a dominant role in controlling the eddy shedding, and appear thus of minor importance for the regional climate in the Gulf of Mexico. Comparing our results to observations we found that mean sortable silt values from Florida Strait depict an increase in bottom current velocities during cold climatic periods and times of lowered sea level, too. This is in contrast to recent hydrographic estimates pointing to reduced transports through the Florida Straits.

Mildner, T. C.; Eden, C.; Nuernberg, D.; Schoenfeld, J.

2011-12-01

71

A new control method of permanent magnet generator for maximum power tracking in wind turbine application  

Microsoft Academic Search

This paper discusses a new and simple control method for maximum power tracking in a variable speed wind turbine by using a step-up dc-dc converter. The output voltage of permanent magnet generator is connected to a fixed dc-link through a three-phase rectifier and the dc-dc converter. A maximum power-tracking algorithm calculates the speed command that corresponds to maximum power output

R. Esmaili; L. Xu; D. K. Nichols

2005-01-01

72

A new method for determining the meridional wind velocity during an ionospheric storm  

NASA Astrophysics Data System (ADS)

This paper introduces a new method for determining the meridional wind velocity during an ionospheric storm based on a sequence of Doppler ionograms. By this new method, the height- and time-dependent meridional wind velocity in the F2 layer was obtained during the magnetic substorm on April 17, 2002. The peak velocity of meridional wind at 300 km altitude is about 300 m/s, the deduced propagation velocity of traveling atmospheric disturbances (TADs) is about 520 m/s. Furthermore, not only the amplitude but also the onset time and phase velocity of the TAD-associated wind perturbation can be explained by the present theories and observations of meridional winds. This work offers a new method to investigate the propagation and morphology of meridional wind during a magnetic substorm by using Digisonde routine observations.

Yuan, Zhigang; Ning, Baiqi; Liu, Libo; Wan, Weixing; Zhao, Biqiang

2003-03-01

73

Simultaneous PIV and PTV measurements of wind and sand particle velocities  

NASA Astrophysics Data System (ADS)

Wind-blown sand is a typical example of two-phase particle-laden flows. Owing to lack of simultaneous measured data of the wind and wind-blown sand, interactions between them have not yet been fully understood. In this study, natural sand of 100-125 ?m taken from Taklimakan Desert was tested at the freestream wind speed of 8.3 m/s in an atmospheric boundary layer wind tunnel. The captured flow images containing both saltating sand and small wind tracer particles, were separated by using a digital phase mask technique. The 2-D PIV (particle imaging velocimetry) and PTV (particle tracking velocimetry) techniques were employed to extract simultaneously the wind velocity field and the velocity field of dispersed sand particles, respectively. Comparison of the mean streamwise wind velocity profile and the turbulence statistics with and without sand transportation reveal a significant influence of sand movement on the wind field, especially in the dense saltating sand layer ( y/ ? < 0.1). The ensemble-averaged streamwise velocity profile of sand particles was also evaluated to investigate the velocity lag between the sand and the wind. This study would be helpful in improving the understanding of interactions between the wind and the wind-blown sand.

Zhang, Wei; Wang, Yuan; Lee, Sang Joon

2008-08-01

74

Effect of Wind Tunnel Air Velocity on VOC Flux Rates from CAFO Manure and Wastewater  

Microsoft Academic Search

Wind tunnels and flux chambers are often used to measure volatile organic compound (VOC) emissions and estimate emission factors from animal feeding operations (AFOs) without regard to air velocity or sweep air flow rates. Laboratory experiments were conducted to evaluate the effect of wind tunnel air velocity on VOC emission rates. VOC emissions were measured on standard solutions of VOCs

David B. Parker; Edward Caraway; Marty Rhoades; Chanci Donnell; Jan Spears; N. Andy Cole; Richard W. Todd; Kenneth D. Casey

2008-01-01

75

Estimating random transverse velocities in the fast solar wind from EISCAT Interplanetary Scintillation measurements  

Microsoft Academic Search

Interplanetary scintillation measurements can yield estimates of a large number of solar wind parameters, including bulk flow speed, variation in bulk velocity along the observing path through the solar wind and random variation in transverse velocity. This last parameter is of particular interest, as it can indicate the flux of low-frequency Alfvén waves, and the dissipation of these waves has

A. Canals; A. R. Breen; L. Ofman; P. J. Moran; R. A. Fallows

2002-01-01

76

Gas transfer velocities measured at low wind speed over a lake  

USGS Publications Warehouse

The relationship between gas transfer velocity and wind speed was evaluated at low wind speeds by quantifying the rate of evasion of the deliberate tracer, SF6, from a small oligotrophic lake. Several possible relationships between gas transfer velocity and low wind speed were evaluated by using 1-min-averaged wind speeds as a measure of the instantaneous wind speed values. Gas transfer velocities in this data set can be estimated virtually equally well by assuming any of three widely used relationships between k600 and winds referenced to 10-m height, U10: (1) a bilinear dependence with a break in the slope at ???3.7 m s-1, which resulted in the best fit; (2) a power dependence; and (3) a constant transfer velocity for U10 3.7 m s-1 which, coupled with the typical variability in instantaneous wind speeds observed in the field, leads to average transfer velocity estimates that are higher than those predicted for steady wind trends. The transfer velocities predicted by the bilinear steady wind relationship for U10 < ???3.7 m s-1 are virtually identical to the theoretical predictions for transfer across a smooth surface.

Crusius, J.; Wanninkhof, R.

2003-01-01

77

Maximum shortening velocity of lymphatic muscle approaches that of striated muscle.  

PubMed

Lymphatic muscle (LM) is widely considered to be a type of vascular smooth muscle, even though LM cells uniquely express contractile proteins from both smooth muscle and cardiac muscle. We tested the hypothesis that LM exhibits an unloaded maximum shortening velocity (Vmax) intermediate between that of smooth muscle and cardiac muscle. Single lymphatic vessels were dissected from the rat mesentery, mounted in a servo-controlled wire myograph, and subjected to isotonic quick release protocols during spontaneous or agonist-evoked contractions. After maximal activation, isotonic quick releases were performed at both the peak and plateau phases of contraction. Vmax was 0.48 ± 0.04 lengths (L)/s at the peak: 2.3 times higher than that of mesenteric arteries and 11.4 times higher than mesenteric veins. In cannulated, pressurized lymphatic vessels, shortening velocity was determined from the maximal rate of constriction [rate of change in internal diameter (-dD/dt)] during spontaneous contractions at optimal preload and minimal afterload; peak -dD/dt exceeded that obtained during any of the isotonic quick release protocols (2.14 ± 0.30 L/s). Peak -dD/dt declined with pressure elevation or activation using substance P. Thus, isotonic methods yielded Vmax values for LM in the mid to high end (0.48 L/s) of those the recorded for phasic smooth muscle (0.05-0.5 L/s), whereas isobaric measurements yielded values (>2.0 L/s) that overlapped the midrange of values for cardiac muscle (0.6-3.3 L/s). Our results challenge the dogma that LM is classical vascular smooth muscle, and its unusually high Vmax is consistent with the expression of cardiac muscle contractile proteins in the lymphatic vessel wall. PMID:23997104

Zhang, Rongzhen; Taucer, Anne I; Gashev, Anatoliy A; Muthuchamy, Mariappan; Zawieja, David C; Davis, Michael J

2013-11-15

78

Effects of forward velocity on noise for a J85 turbojet engine with multitube suppressor from wind tunnel and flight tests  

NASA Technical Reports Server (NTRS)

Flight and wind tunnel noise tests were conducted using a J85 turbojet engine as a part of comprehensive programs to obtain an understanding of forward velocity effects on jet exhaust noise. Nozzle configurations of primary interest were a 104-tube suppressor with and without an acoustically-treated shroud. The installed configuration of the engine was as similar as possible in the flight and wind tunnel tests. Exact simultaneous matching of engine speed, exhaust velocity, and exhaust temperature was not possible, and the wind tunnel maximum Mach number was approximately 0.27, while the flight Mach number was approximately 0.37. The nominal jet velocity range was 450 to 640 m/sec. For both experiments, background noise limited the jet velocity range for which significant data could be obtained. In the present tests the observed directivity and forward velocity effects for the suppressor are more similar to predicted trends for internally-generated noise than unsuppressed jet noise.

Stone, J. R.; Miles, J. H.; Sargent, N. B.

1976-01-01

79

Maximum Peak Power Tracking-Based Control Algorithms with Stall Regulation for Optimal Wind Energy Capture  

NASA Astrophysics Data System (ADS)

This paper presents three control strategies for maximum peak power tracking (MPPT) based algorithm to optimize the captured wind energy. The first control strategy uses a predetermined peak torque-speed characteristic as a system command. The second strategy employs perturbation and observation (P&O) technique to determine the optimal operating points based on the slope of the power-rotational speed curve. The calculated torque references are used in conjunction with the fuzzy logic control in the third control strategy to derive the torque command. Stall regulation is employed to limit the output power of the wind generator. The MPPT- based algorithm with all three strategies was implemented on a low cost digital signal controller and was tested with a system consisting of a wind turbine controller and a wind turbine simulator. The experimental results confirm that all strategies can attain the maximum power for any wind speeds below-rated speed but with different control performances in terms of power fluctuation, rotational speed fluctuation and tracking time. The stall regulation was very effective in limiting the output power of the system at the wind speeds above-rated speed.

Neammanee, Bunlung; Krajangpan, Korawit; Sirisumrannukul, Somporn; Chatratana, Somchai

80

Sensorless Maximum Power Point Tracking of Wind by DFIG Using Rotor Position Phase Lock Loop (PLL)  

Microsoft Academic Search

This paper presents an invention, the rotor position phase lock loop (PLL), which enables maximum power point (MPPT) tracking of wind by doubly-fed induction generators without needing a tachometer, an absolute position encoder, or an anemometer. The rotor position PLL is parameter variation insensitive, requiring only an estimate of the magnetization inductance for it to operate. It is also insensitive

Baike Shen; Bakari Mwinyiwiwa; Yongzheng Zhang; Boon-Teck Ooi

2009-01-01

81

An estimate of the maximum speed of the solar wind, 1938-1989  

Microsoft Academic Search

Beginning with a list of severe geomagnetic storms, the authors obtain an estimate of the maximum solar wind flow speed at Earth during the past â¼50 years. They do this by (1) focusing on the subset of severe storms that followed major proton flares (since large proton events are strongly associated with fast coronal mass ejections), (2) calculating the average

E. W. Cliver; J. Feynman; H. B. Garrett

1990-01-01

82

Sensorless maximum power point tracking control in wind energy generation using permanent magnet synchronous generator  

Microsoft Academic Search

This paper proposes a control strategy for variable speed wind energy conversion system (WECS), incorporating maximum power point tracking (MPPT) algorithm, using direct driven permanent magnet synchronous generator (PMSG). The generator is operated in the speed control mode below the base speed by controlling the terminal voltage using three phase front-end active-rectifier feeding power to the DC bus. The voltage

N. Srighakollapu; P. S. Sensarma

2008-01-01

83

Fine Structure in the Corona and Solar Wind at High Heliographic Latitudes at Solar Maximum  

NASA Technical Reports Server (NTRS)

Microstreams and pressure balance structures in fast solar wind were more easily detected at Ulysses at 2.2 AU over the poles than at Helios at 0.3 AU. This is because solar rotation brings sources of fast solar wind beneath sources of slow solar wind at a rate that depends on latitude, for the same size features. Dynamic interaction between the fast and slow wind tends to mix the flows and make features more difficult to detect with increasing distance from the Sun. A given sized feature takes proportionally longer to pass a longitude when it is at 80 degrees latitude than when it is at the equator. At solar maximum, Ulysses will mainly be sampling solar wind coming from above streamers and from near streamers. The data will provide information on fine structure at the tops of streamers - the stalks - and on the source of slow solar wind, The visibility of the boundaries between fast and slow wind and of the stalk will increase with increasing latitude. We will present quantitative calculations of the visibility of various sized features, with various differences in flow speed, at the location of Ulysses when it is over the south (in 2000) and north (in 2001) polar regions of the Sun.

Suess. S. T.; Poletto, G.

2000-01-01

84

Fine Structure in the Corona and Solar Wind at High Heliographic Latitudes at Solar Maximum  

NASA Technical Reports Server (NTRS)

Microstreams and pressure balance structures in fast solar wind were more easily detected at Ulysses at 2.2 AU over the poles than at Helios at 0.3 AU. This is because solar rotation brings sources of fast solar wind beneath sources of slow solar wind at a rate that depends on latitude, for the same size features. Dynamic interaction between the fast and slow wind tends to mix the flows and make features more difficult to detect with increasing distance from the Sun. A given sized feature takes proportionally longer to pass a longitude when it is at 80 degrees latitude than when it is at the equator. At solar maximum, Ulysses will mainly be sampling solar wind coming from above streamers and from near streamers. The data will provide information on fine structure at the tops of streamers - the stalks - and on the source of slow solar wind. The visibility of the boundaries between fast and slow wind and of the stalk will increase with increasing latitude. I will present quantitative calculations of the visibility of various sized features, with various differences in flow speed, at the location of Ulysses when it is over the south (in 2000) and north (in 2001) polar regions of the Sun.

Suess, S. T.; Rose, M. Franklin (Technical Monitor)

2001-01-01

85

Dependence of velocity fluctuations on solar wind speeds: A simple analysis with IPS method  

NASA Technical Reports Server (NTRS)

A number of theoretical works have suggested that MHD plasma fluctuations in solar winds should play an important role particularly in the acceleration of high speed winds inside or near 0.1 AU from the sun. Since velocity fluctuations in solar winds are expected to be caused by the MHD plasma fluctuations, measurements of the velocity fluctuations give clues to reveal the acceleration process of solar winds. We made interplanetary scintillation (IPS) observations at the region out of 0.1 AU to investigate dependence of velocity fluctuations on flow speeds. For evaluating the velocity fluctuation of a flow, we selected the IPS data-set acquired at 2 separate antennas which located in the projected flow direction onto the baseline plane, and tried to compare skewness of the observed cross correlation function(CCF) with skewness of modeled CCFs in which velocity fluctuations were parametrized. The integration effect of IPS along a ray path was also taken into account in the estimation of modeled CCFs. Although this analysis method is significant to derive only parallel fluctuation components to the flow directions, preliminary analyses show following results: (1) High speed winds (Vsw greater than or equal to 500 km/s out of 0.3 AU) indicate enhancement of velocity fluctuations near 0.1 AU; and (2) Low speed winds (Vsw less than or equal to 400 Km/s out of 0.3 AU) indicate small velocity fluctuations at any distances.

Misawa, H.; Kojima, M.

1995-01-01

86

The stellar wind velocity function for red supergiants determined in eclipsing binaries  

NASA Technical Reports Server (NTRS)

The potential for direct measurement of the acceleration of stellar winds from the supergiant component of Zeta Aurigae-type binary stars is discussed. The aberration angle of the interaction shock cone centered on the hot star provides a measure of the velocity of the cool star wind at the orbit of the secondary. This is confirmed by direct observations of stellar wind (P Cygni) line profile variations. This velocity is generally smaller than the final (terminal) velocity of the wind, deduced from the P Cygni line profiles. The contrast between these results and previously published supergiant wind models is discussed. The implication on the physics of energy source dissipation predicted in the theoretical models is considered.

Ahmad, Imad A.; Stencel, Robert E.

1988-01-01

87

Airside velocity measurements over the wind-sheared water surface using particle image velocimetry  

Microsoft Academic Search

An experimental investigation of the airflow structure in the near surface region over the wind-sheared air–water interface\\u000a is reported. The two-dimensional velocity fields in a plane perpendicular to the water surface were measured using particle\\u000a image velocimetry (PIV) technique over a wind speed range from 1.5 to 4.4 m s?1. The results show a reduction in the mean velocity magnitudes and

Nasiruddin Shaikh; Kamran Siddiqui

2008-01-01

88

Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus  

NASA Technical Reports Server (NTRS)

Strong 10-micron line emission from (C-12)(O-16)2 in the upper atmosphere of Venus has been detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicated mean zonal wind velocities less than 10 m/s in the upper atmosphere near the equator. No evidence was found for the 100-m/s wind velocity implied by the apparent four-day rotation period of ultraviolet cloud features.

Betz, A. L.; Johnson, M. A.; Mclaren, R. A.; Sutton, E. C.

1976-01-01

89

Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus  

NASA Technical Reports Server (NTRS)

Strong 10 micrometer line emission from (C-12)(O-16)2 in the upper atmosphere of Venus was detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicate mean zonal wind velocities less than 10 m/sec in the upper atmosphere near the equator. No evidence was found of the 100 m/sec wind velocity implied by the apparent 4-day rotation period of ultraviolet cloud features.

Betz, A. L.; Johnson, M. A.; Mclaren, R. A.; Sutton, E. C.

1975-01-01

90

Heterodyne detection of CO2 emission lines and wind velocities in the atmosphere of Venus  

NASA Technical Reports Server (NTRS)

Strong 10 micrometer line emission from (c-12)(o-16)2 in the upper atmosphere of Venus was detected by heterodyne techniques. Observations of the absolute Doppler shift of the emission features indicate mean zonal wind velocities less than 10 m/sec in the upper atmosphere near the equator. No evidence was found of the 100 m/sec wind velocity implied by the apparent 4-day rotation period of ultraviolet cloud features.

Betz, A. L.; Johnson, M. A.; Mclaren, R. A.; Sutton, E. C.

1975-01-01

91

Umbilical artery waveform analysis based on maximum, mean and mode velocity in early human pregnancy  

Microsoft Academic Search

The objective of this study was to identify the best method for reconstructing blood-flow velocities from the early human umbilical artery to determine the physiological changes in fetal blood-flow velocity and heart rate. Pulsed Doppler recordings from the umbilical artery with a duration of approximately 7 s were made at 10–20 weeks of gestation. For reconstruction of the blood-flow velocity

Nicolette T. C. Ursem; Hans J. F. Brinkman; Piet C. Struijk; Wim C. J. Hop; Mark H. Kempski; Bradley B. Keller; Juriy W. Wladimiroff

1998-01-01

92

Wind tunnel experimental investigation of sand velocity in aeolian sand transport  

NASA Astrophysics Data System (ADS)

Sand velocity in aeolian sand transport was measured using the laser Doppler technique of PDPA (Phase Doppler Particle Analyzer) in a wind tunnel. The sand velocity profile, probability distribution of particle velocity, particle velocity fluctuation and particle turbulence were analyzed in detail. The experimental results verified that the sand horizontal velocity profile can be expressed by a logarithmic function above 0.01 m, while a deviation occurs below 0.01 m. The mean vertical velocity of grains generally ranges from - 0.2 m/s to 0.2 m/s, and is downward at the lower height, upward at the higher height. The probability distributions of the horizontal velocity of ascending and descending particles have a typical peak and are right-skewed at a height of 4 mm in the lower part of saltation layer. The vertical profile of the horizontal RMS velocity fluctuation of particles shows a single peak. The horizontal RMS velocity fluctuation of sand particles is generally larger than the vertical RMS velocity fluctuation. The RMS velocity fluctuations of grains in both horizontal and vertical directions increase with wind velocity. The particle turbulence intensity decreases with height. The present investigation is helpful in understanding the sand movement mechanism in windblown sand transport and also provides a reference for the study of blowing sand velocity.

Kang, Liqiang; Guo, Liejin; Gu, Zhengmeng; Liu, Dayou

2008-05-01

93

An Estimate of Solar Wind Velocity Profiles in a Coronal Hole and a Coronal Streamer Area (6-40 R(radius symbol)  

NASA Technical Reports Server (NTRS)

Total electron content data obtained from the Ulysses Solar Corona Experiment (SCE) in 1991 were used to select two data sets, one associated with a coronal hole and the other with coronal streamer crossings. (This is largely equatorial data shortly after solar maximum.) The solar wind velocity profile is estimated for these areas.

Patzold, M.; Tsurutani, B. T.; Bird, M. K.

1995-01-01

94

The heavy ions of the solar wind: pseudo-heating by velocity filtration and acceleration  

Microsoft Academic Search

Due to their different mass and charge states, heavy solar coronal and solar wind ions provide invaluable information on the physical mechanisms responsible for the heating of the corona and for the solar wind acceleration. In the present work, it is shown that key characteristics observed in the corona are predicted by the velocity filtration effect. This mechanism originally proposed

V. Pierrard; H. Lamy; J. Lemaire

2003-01-01

95

Vortex-induced cable vibration of cable-stayed bridges at high reduced wind velocity  

Microsoft Academic Search

In this paper, mechanisms of vortex-induced vibration of inclined cables at high reduced wind velocity region are discussed using results from a series of wind tunnel tests. As a conclusion, this aerodynamic instability of inclined cables would occur by the fluid interaction between Karman vortex and axial vortex. Also, the axial flow along the cable axis and the upper water

Masaru Matsumoto; Tomomi Yagi; Yoshinori Shigemura; Daisuke Tsushima

2001-01-01

96

Thermal iron ions in high speed solar wind streams. II - Temperatures and bulk velocities  

NASA Technical Reports Server (NTRS)

Mitchel and Roelof (1980) reported the detection of iron in high speed solar wind flows using the small, but finite sensitivity of solid state detectors to Fe ions in the low energy (50-200 keV protons) L1 channel of the NOAA/JHU energetic particle experiment (EPE). In the current investigation, the EPE response is modeled to a convected Maxwellian to obtain the thermal velocity, flow angle, and bulk velocity of the iron distribution. It is assumed that the iron bulk flow velocity can be represented as a vector sum of the hydrogen bulk velocity and an interplanetary magnetic field (IMF) aligned velocity increment. It is found that the velocity increment is smaller than the local Alfven speed in magnitude, and that the iron thermal velocity is comparable with or greater than the proton thermal velocity, with the 'thermal' velocity defined as the square root of 2kT/m.

Mitchell, D. G.; Roelof, E. C.; Feldman, W. C.; Bame, S. J.; Williams, D. J.

1981-01-01

97

Southern Hemisphere Westerly Wind Changes during the Last Glacial Maximum: Paleo-data Synthesis  

NASA Astrophysics Data System (ADS)

Changes in the strength and position of Southern Hemisphere westerly winds during the last glacial cycle have been invoked to explain glacial-interglacial climate fluctuations. However, neither paleo models nor paleodata agree on the magnitude, or even the sign, of the change in wind strength and latitude during the Last Glacial Maximum (LGM), compared to the recent past. This study synthesizes paleo-environmental data that have been used to infer changes in winds during the LGM compared with the late Holocene. These compilations include changes in terrestrial moisture, dust deposition, and ocean productivity, along with summaries of previously published information on sea surface temperatures (SSTs) and ocean dynamics in the Southern Hemisphere. Our compilations of terrestrial moisture from 94 sites and dust deposition from 87 sites show generally drier conditions for the LGM between 0 and 40°S, with wetter conditions along the west coasts and drying along the east coasts of continents. LGM dust deposition rates ranged from 2 to 4.5 times higher over the Southern Ocean and about 13 times higher over the Antarctic continent. For the oceans, reconstructed changes in SSTs show maximum cooling (>4°C) in the modern-day Subantarctic Zone, coincident with a region of enhanced export production during the LGM compared with today. We find that any hypothesis of LGM wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents, cooler temperatures and higher productivity in the Subantarctic Zone, and reductions in Agulhas leakage around southern Africa. Our comparison suggests that an overall strengthening, an equatorward displacement, or no change at all in winds could all be interpreted as consistent with observations. If a single cause related to the southern westerlies is sought for all the evidence presented, then an equatorward displacement or strengthening of the winds would be consistent with the largest proportion of the data evidence. However, other processes, such as weakening or poleward shifts in winds, a weakened hydrological cycle, extended sea-ice cover, and changed buoyancy fluxes, cannot be ruled out as potential explanations of observed changes in moisture, surface temperature, and productivity. We contend that resolving the position and strength of westerly winds during the LGM remains elusive based on data reconstructions alone. However, we believe that these data reconstructions of environmental conditions can be used in conjunction with model simulations to identify which processes best represent westerly wind conditions during the LGM.

Kohfeld, Karen; Graham, Robert; De Boer, Agatha; Sime, Louise; Wolff, Eric; Le Quéré, Corinne; Bopp, Laurent

2013-04-01

98

RW Sextantis, a disk with a hot, high-velocity wind  

NASA Technical Reports Server (NTRS)

The continuum spectrum of the flickering blue variable RW Sex was observed from 10,000 to 1150 A. The star is a cataclysmic variable currently stabilized at maximum, and the spectrum is dominated by an accretion disk, with flat spectrum in the ultraviolet, except at more than 5000 A, where a blackbody near 7000 K is seen. A distance of 400 pc is derived, if the latter arises from an F type main sequence star. The accretion rate required is near 10 to the -8th solar masses per year. Only weak emission is seen, except for Lyman alpha; strong, broad UV absorption lines are seen with centers displaced up to -3000 km/s, with terminal velocities up to -4500 km/s, the velocity of escape from a white dwarf. The low X-ray flux may arise from absorption within an unusually dense, hot wind from the innermost portions of the disk. The estimated mass loss rate is nearly 10 to the -12th solar masses per year.

Greenstein, J. L.; Oke, J. B.

1982-01-01

99

Do Inner Planets Modulate the Solar Wind Velocity at 1 AU from the Sun?  

NASA Astrophysics Data System (ADS)

Quite recently, it has been suggested that the interaction of the solar wind with Mercury results in the variation in the solar wind velocity in the Earth's neighborhood during inferior conjunctions with Mercury. This suggestion has important implications both on the plasma physics of the interplanetary space and on the space weather forecast. In this study we have attempted to answer a question of whether the claim is properly tested. We confirm that there are indeed ups and downs in the profile of the solar wind velocity measured at the distance of 1 AU from the Sun. However, the characteristic attribute of the variation in the solar wind velocity during the inferior conjunctions with Mercury is found to be insensitive to the phase of the solar cycles, contrary to an earlier suggestion. We have found that the cases of the superior conjunctions with Mercury and of even randomly chosen data sets rather result in similar features. Cases of Venus are also examined, where it is found that the ups and downs with a period of ~ 10 to 15 days can be also seen. We conclude, therefore, that those variations in the solar wind velocity turn out to be a part of random fluctuations and have nothing to do with the relative position of inner planets. At least, one should conclude that the solar wind velocity is not a proper observable modulated by inner planets at the distance of 1 AU from the Sun in the Earth's neighborhood during inferior conjunctions.

Kim, Jung-Hee; Chang, Heon-Young

2014-03-01

100

Density, Velocity and Ionization Structure in Accretion-Disc Winds  

NASA Technical Reports Server (NTRS)

This was a project to exploit the unique capabilities of FUSE to monitor variations in the wind- formed spectral lines of the luminous, low-inclination, cataclysmic variables(CV) -- RW Sex. (The original proposal contained two additional objects but these were not approved.) These observations were intended to allow us to determine the relative roles of density and ionization state changes in the outflow and to search for spectroscopic signatures of stochastic small-scale structure and shocked gas. By monitoring the temporal behavior of blue-ward extended absorption lines with a wide range of ionization potentials and excitation energies, we proposed to track the changing physical conditions in the outflow. We planned to use a new Monte Carlo code to calculate the ionization structure of and radiative transfer through the CV wind. The analysis therefore was intended to establish the wind geometry, kinematics and ionization state, both in a time-averaged sense and as a function of time.

Sonneborn, George (Technical Monitor); Long, Knox

2004-01-01

101

The influence of velocity variability on the determination of wind profiles  

NASA Technical Reports Server (NTRS)

High sensitivity radars allow the determination of velocity estimates at time resolutions down to one minute or better. Because of the variability introduced to the mean wind due to turbulence and waves, the high resolution profiles may not be too useful for forecasting applications, although they yield the most realistic estimate of the instantaneous wind profile. Profiles of wind speed and direction, vertical velocity and echo power, which were deduced in real-time on 23 August 1981 with the spaced antenna drift mode of the SOUSY-VHF-Radar are shown. Whereas these profiles were measured within 1 minute, the operating routine allowed the selection of variable (longer) measuring periods, and one has to search for the optimum duration of the data averaging period. A high time resolution wind vector diagram is given which gives an idea of the temporal variability. The data were obtained with the spaced antenna technique, which allows a good estimate of the horizontal wind without having to correct for the vertical velocity component. The wind vectors specifically indicate a quasi-periodic variation in direction. This is assumed to be due to gravity waves since the vertical velocity also shows periodical variations with the same period. The consistency of these spaced-antenna VHF radar results along with the radiosonde data convinced researchers that the method is quite suitable for wind profiling applications.

Rottger, J.

1986-01-01

102

Computer simulation of coherent Doppler lidar measurement of wind velocity and retrieval of turbulent wind statistics  

Microsoft Academic Search

We describe the algorithms for the simulation of cw and pulsed coherent Doppler wind lidar operation in a turbulent atmosphere and the methods to estimate the mean wind and the parameters of small-scale wind turbulence from lidar data. The algorithms are realized as LabView computer codes, which include parts simulating the atmospheric turbulent wind fields based on the Karman model,

Viktor A. Banakh; Christian Werner

2005-01-01

103

Dispersion in Neptune's zonal wind velocities from NIR Keck AO observations in July 2009  

NASA Astrophysics Data System (ADS)

We report observations of Neptune made in H-(1.4-1.8 ?m) and K'-(2.0-2.4 ?m) bands on 14 and 16 July 2009 from the 10-m W.M. Keck II Telescope using the near-infrared camera NIRC2 coupled to the Adaptive Optics (AO) system. We track the positions of 54 bright atmospheric features over a few hours to derive their zonal and latitudinal velocities, and perform radiative transfer modeling to measure the cloud-top pressures of 50 features seen simultaneously in both bands. We observe one South Polar Feature (SPF) on 14 July and three SPFs on 16 July at ˜65 °S. The SPFs observed on both nights are different features, consistent with the high variability of Neptune's storms. There is significant dispersion in Neptune's zonal wind velocities about the smooth Voyager wind profile fit of Sromovsky et al. (Icarus, 105:140, 1993), much greater than the upper limit we expect from vertical wind shear, with the largest dispersion seen at equatorial and southern mid-latitudes. Comparison of feature pressures vs. residuals in zonal velocity from the smooth Voyager wind profile also directly reveals the dominance of mechanisms over vertical wind shear in causing dispersion in the zonal winds. Vertical wind shear is not the primary cause of the difference in dispersion and deviation in zonal velocities between features tracked in H-band on 14 July and those tracked in K'-band on 16 July. Dispersion in the zonal velocities of features tracked over these short time periods is dominated by one or more mechanisms, other than vertical wind shear, that can cause changes in the dispersion and deviation in the zonal velocities on timescales of hours to days.

Fitzpatrick, Patrick J.; de Pater, Imke; Luszcz-Cook, Statia; Wong, Michael H.; Hammel, Heidi B.

2014-03-01

104

Relationships among daily mean and maximum wind speeds, with application to data quality assurance  

NASA Astrophysics Data System (ADS)

A growing number of climate change and variability studies, as well as applied research toward improving engineering design climatographies, require high-quality, long-term, extreme-value climate data sets for accurate and reliable estimates and assessments. As part of a historical weather data rescue project of the US government, new data quality control procedures are being developed and applied for daily maximum wind speeds. Not only are existing quality assurance procedures mostly lacking for such data but the climatological relationships upon which such quality checks may be based are also grossly underexploited. Therefore, this study seeks to elucidate relationships among peak-gust, fastest-mile, and fastest 5-min wind speeds, utilizing the peak gust factor model but generalizing it for these and other extreme wind-speed elements. The relationship between peak-gust factor and daily mean wind speed is also adapted for quality assurance and for a wider range of climates than previously studied. Fastest-interval wind-speed factors are found to follow Gaussian, gamma, or Weibull probability distributions, included within mixed models to handle zeros. Resistant prediction interval estimates about a resistant regression were developed for quality assurance of peak-gust factor, given the daily mean wind speed. Flagging thresholds were estimated using parametric bootstrapping. Flag rates from 0.05 to 0.5% are in line with rates reported in the literature, from work with similar data sets; overall Type I and Type II error rates are in the range 0.03-0.3%. The approach outlined lends itself straightforwardly to application in data quality assurance.

Graybeal, Daniel Y.

2006-01-01

105

Scaling of maximum velocity, body force, and power consumption of dielectric barrier discharge plasma actuators via particle image velocimetry  

NASA Astrophysics Data System (ADS)

This study presents Particle Image Velocimetry (PIV) measurements of the induced flow characteristics generated by single dielectric barrier discharge (DBD) actuators in quiescent conditions. The primary aim is to establish accurate empirical trends for model development on both the maximum induced velocity and body force with voltage and consumed power. The results reveal a power law variation for the maximum velocity at low voltages which is followed by an asymptotic behavior. In contrast, the body force is characterized by two power law regions. The power law exponent is shown to be a function of the dielectric thickness, frequency and dielectric constant. Reducing the former or increasing the latter two result in a higher coefficient and lower voltage at which the trend changes. The onset of the second region occurs at a Re ~ 100 (based on the maximum velocity, um, and corresponding half height, y1/2) and is characterized by a velocity profile which no longer agrees with the laminar profile of Glauert whilst moving increasingly towards the turbulent case. Phase locked PIV measurements show that as the voltage increases the peak momentum transfer shifts from the middle of the AC cycle to the latter end of the forward stroke. Lissajous plots of um? against the corresponding x location and plasma length ?x demonstrate that the peak momentum transfer remains relatively fixed in space as the voltage and plasma length increase.

Murphy, J. P.; Kriegseis, J.; Lavoie, P.

2013-06-01

106

Comparison of vertical velocities analyzed by a numerical model and measured by a VHF wind profiler  

NASA Technical Reports Server (NTRS)

The use of wind profilers for measuring vertical velocities in the troposphere and lower stratosphere is potentially of great interest for verification of forecasts, diagnosis of mesoscale circulations, and studies of wave motions. The studies of profiler vertical velocities to date have shown that the observed patterns of ascent and subsidence are reasonable when compared to the synoptic conditions. However, difficulties arise when a direct verification of the profiler vertical winds is sought. Since no other technique can measure the vertical velocities over the same height range and with the same claimed accuracy as the profilers, direct comparisons are impossible. The only alternative is to compare the measurements to analyzed vertical velocity fields. Here, researchers compare vertical measurements made with the SOUSY VHF radar over a period of 11 days at the beginning of November 1981 to the analyzed vertical velocities produced by the European Center for Medium-range Weather Forecasting (ECMWF) model for grid points near the radar site.

Larsen, M. F.; Rottger, J.; Dennis, T. S.

1986-01-01

107

Low-velocity variability in the stellar wind of HD 152408 (O8: Iafpe)  

NASA Technical Reports Server (NTRS)

We describe high-quality, spectroscopic time series observations of variability at low velocities in the stellar wind of the extreme O-supergiant HD 152408. These observations were obtained during a monitoring campaign coordinated between Australia and Chile in 1992 July. Systematic variability on hourly time scales is particularly apparent in the He I lambda 5876 P Cygni profile, which diagnoses the deeper, denser region of the wind. These changes indicate the presence of evolving wind structure, which takes the form of blueward-migrating, discrete optical depth enhancements. Four distinct features are identified over approximately 5 days, spanning a velocity range of about -50 km/s at formation to about -500 km/s (i.e., greater than or approximately equal to 0.5 of the terminal velocity) at the blue edge of the He I absorption trough. Sympathetic variations are also apparent in the Balmer emission lines of HD 152408. The characteristics of these features, including their widths, column densities, and accelerations, suggest similarities to discrete absorption components commonly seen at larger velocities in UV P Cygni profiles of other O-type stars. These optical results demonstrate that frequent, systematic wind variability is present down to very large depths, and provide constraints on the stability of the low-velocity regime of hot-star winds.

Prinja, Raman K.; Fullerton, A. W.

1994-01-01

108

Measurements of dust deposition velocity in a wind-tunnel experiment  

NASA Astrophysics Data System (ADS)

In this study, we present the results of a wind-tunnel experiment on dust deposition. A new method is proposed to derive dust deposition velocity from the PDA (Particle Dynamics Analysis) particle-velocity and particle-size measurements. This method has the advantage that the motions of individual dust particles are directly observed and all relevant data for computing dust deposition velocity is collected using a single instrument, and therefore the measurement uncertainties are reduced. The method is used in the wind-tunnel experiment to measure the dust deposition velocities for different particle sizes, wind speeds and surface conditions. For a sticky-smooth wood surface and a water surface, the observed dust deposition velocities are compared with the predictions using a dust deposition scheme, and the entire dataset is compared with the data found in the literature. From the wind-tunnel experiments, a relatively reliable dataset of dust deposition velocity is obtained, which is of considerable value for the development and validation of dust deposition schemes.

Zhang, J.; Shao, Y.; Huang, N.

2014-04-01

109

A complementary review of maximum power point tracking methods for wind generators  

NASA Astrophysics Data System (ADS)

Maximum power point tracking (MPPT) is a very important necessity in a system of energy conversion from a renewable energy source. In this paper, is made an attempt to provide a brief review of 12 very recent publications, not analyzed in the last surveys appeared in 2010 and 2011, and to make a comparative analyze and a classification of all available MPPT algorithms, highlighting their strength and drawbacks. After addressing the reasons for use of MPPT techniques, various power optimization schemes are surveyed. The comparative analysis and a classification of the MPPT algorithms are useful for the designers of wind energy power systems.

Cr?ciunescu, Aurelian; Popescu, Claudia; Popescu, Mihai

2012-09-01

110

Reynolds-number-dependence of the maximum in the streamwise velocity fluctuations in wall turbulence  

Microsoft Academic Search

A survey is made of the standard deviation of the streamwise velocity fluctuations in near-wall turbulence and in particular\\u000a of the Reynolds-number-dependency of its peak value. The following canonical flow geometries are considered: an incompressible\\u000a turbulent boundary layer under zero pressure gradient, a fully developed two-dimensional channel and a cylindrical pipe flow.\\u000a Data were collected from 47 independent experimental and

S. Mochizuki; F. T. M. Nieuwstadt

1996-01-01

111

Dependence of velocity fluctuations on solar wind speeds from an IPS analysis method  

SciTech Connect

Interplanetary scintillation (IPS) observations were made with radio telescopes of the STE Lab. (327 MHz) and the EISCAT facilities (932 MHz) in 1993 and 1994 to investigate the dependence of the parallel component of velocity fluctuation ({delta}V{sub parallel}) on flow speeds. Preliminary analyses show the following results; 1) {delta}V{sub parallel} in high speed winds (V{sub IPS}> or approx. 500 km/s at distances beyond 0.3 AU) increases with approaching the sun, 2) Low speed winds (V{sub IPS} < or approx. 400 km/s at distances beyond 0.3AU) have a small {delta}V{sub parallel} at all distances. Here, V{sub IPS} is the solar wind velocity observed with the IPS method. Since the parallel fluctuation component is expected to be related to magnetoacoustic waves near the sun, the results infer that magnetoacoustic waves have some relation to the acceleration of high speed solar winds.

Misawa, Hiroaki; Kojima, Masayoshi [Solar-Terrestrial Environment Laboratory, Nagoya University (Japan); Upper Atmosphere and Space Research Laboratory, Tohoku University (Japan); Solar-Terrestrial Environment Laboratory, Nagoya University (Japan)

1996-07-20

112

A wind tunnel study of air flow in waving wheat: Single-point velocity statistics  

Microsoft Academic Search

We analyse single-point velocity statistics obtained in a wind tunnel within and above a model of a waving wheat crop, consisting of nylon stalks 47 mm high and 0.25 mm wide in a square array with frontal area index 0.47. The variability of turbulence measurements in the wind tunnel is illustrated by using a set of 71 vertical traverses made

Y. Brunet; J. J. Finnigan; M. R. Raupach

1994-01-01

113

Comparison of CO2 Doppler lidar and GPS rawinsonde wind velocity measurements  

NASA Astrophysics Data System (ADS)

A comparison of CO2 Doppler lidar and GPS rawinsonde measurements of horizontal wind velocity was conducted during May 2000 at Hanscom AFB, Massachusetts. Seven days of side-by-side measurements using both lidar and GPS sondes were achieved comparing wind velocity as a function of altitude up to 6 km. The horizontal wind velocity was determined by the CO2 Doppler lidar using the Velocity Azimuth Display (VAD) method. Horizontal winds were also determined simultaneously using a differential GPS-tracked rawinsonde which provides GPS position coordinates once per second. Both lidar VAD wind speed Root Mean Squared Difference (RMS) and lidar vs. GPS sonde RMS were calculated and compared as a function of altitude, time, and stability regime. On average, significant increases in both the lidar VAD RMS and lidar vs. GPS RMS were observed during unstable conditions compared to stable conditions. Analyses of lidar VAD RMS show the smallest typical values average near 0.5 m/s over a single profile.

Roadcap, John R.; McNicholl, Patrick J.; Teets, Edward H., Jr.; Laird, Mitchell H.

2001-09-01

114

Correlated studies at activity maximum: The Sun and the solar wind  

NASA Technical Reports Server (NTRS)

The breadth and power of the set of solar and heliospheric observatories presently in space is unprecedented. Their observations generally began at solar minimum or in the declining phase of the past maximum, but it is anticipated that most of the instruments will be able to observe the rise to the next maximum and that the events will happen then. The second orbit of Ulysses will be especially interesting and the Yokhoh orbital decay is not projected until 2002. New spacecraft, including TRACE, HESSI, and SOLAR-B, may also become available. The current remote sensing and in situ measurements are characterized by a much stronger understanding of how the solar and interplanetary phenomena match. The novel discoveries from the current data are reviewed, and speculations are expressed on how to take advantage of the future data, emphasizing the use of heliospheric observations to help probe the connectivity of the corona/solar wind interface region. It is suggested that there now exists a possibility of understanding the heliospheric structure empirically in new ways: by using particles as tracers of the field, and by correlating multi-point measurements of structures in the solar wind with solar images.

Hudson, H. S.; Galvin, A. B.

1997-01-01

115

IPS observations of the solar wind velocity and the acceleration mechanism  

NASA Technical Reports Server (NTRS)

Coronal holes are well know sources of high speed solar wind, however, the exact acceleration mechanism of the wind is still unknown. Interplanetary scintillation (IPS) observations indicate that the fast solar wind reaches an average velocity of 800 km s(exp -1) within several solar radii with large velocity fluctuations. However, the origin of the IPS velocity spread below 10 solar radii is unclear. A previously developed coronal home model with a more realistic initial state is applied, and time-dependent, nonlinear, resistive 2.5-DMHD equations are numerically solved. It is found that nonlinear solitary-like waves with a supersonic phase speed are generated in coronal holes by torisonal Alfven waves in the radial flow velocity. The outward propagating nonlinear waves are similar in properties to sound solitons. When these waves are present, the solar wind speed and density fluctuate considerably on a time scale of an hour and on spatial scales of several solar radii in addition to the Alfvenic fluctuations. This is in qualitative agreement with the IPS velocity observations beyond 10 solar radii.

Ofman, L.; Davila, J. M.; Coles, W. A.; Grall, R. R.; Klinglesmith, M. T.

1997-01-01

116

Effect of Wind Velocity on Flame Spread in Microgravity  

NASA Technical Reports Server (NTRS)

A three-dimensional, time-dependent model is developed describing ignition and subsequent transition to flame spread over a thermally thin cellulosic sheet heated by external radiation in a microgravity environment. A low Mach number approximation to the Navier Stokes equations with global reaction rate equations describing combustion in the gas phase and the condensed phase is numerically solved. The effects of a slow external wind (1-20 cm/s) on flame transition are studied in an atmosphere of 35% oxygen concentration. The ignition is initiated at the center part of the sample by generating a line-shape flame along the width of the sample. The calculated results are compared with data obtained in the 10s drop tower. Numerical results exhibit flame quenching at a wind speed of 1.0 cm/s, two localized flames propagating upstream along the sample edges at 1.5 cm/s, a single line-shape flame front at 5.0 cm/s, three flames structure observed at 10.0 cm/s (consisting of a single line-shape flame propagating upstream and two localized flames propagating downstream along sample edges) and followed by two line-shape flames (one propagating upstream and another propagating downstream) at 20.0 cm/s. These observations qualitatively compare with experimental data. Three-dimensional visualization of the observed flame complex, fuel concentration contours, oxygen and reaction rate isosurfaces, convective and diffusive mass flux are used to obtain a detailed understanding of the controlling mechanism, Physical arguments based on lateral diffusive flux of oxygen, fuel depletion, oxygen shadow of the flame and heat release rate are constructed to explain the various observed flame shapes.

Prasad, Kuldeep; Olson, Sandra L.; Nakamura, Yuji; Fujita, Osamu; Nishizawa, Katsuhiro; Ito, Kenichi; Kashiwagi, Takashi; Simons, Stephen N. (Technical Monitor)

2002-01-01

117

A wind tunnel study of air flow in waving wheat: Two-point velocity statistics  

Microsoft Academic Search

Two-point, space-time correlations of streamwise and vertical velocity were obtained from a wind tunnel simulation of an atmospheric surface layer with an underlying model wheat canopy constructed of flexible nylon stalks. Velocity data extend from 1\\/6 canopy height to several canopy heights, with in excess of 2000 three-dimensional vector separations of the two x-wire probes. Isocorrelation contours over anx, z

R. H. Shaw; Y. Brunet; J. J. Finnigan; M. R. Raupach

1995-01-01

118

Reproduction of wind velocity history in a multiple fan wind tunnel  

Microsoft Academic Search

An actively controlled wind tunnel for simulating the atmospheric boundary layer is described. The air flows are generated by 99 frequency-controlled fans arranged in a 9 wide by 11 high matrix. Various fluctuating flows can be reproduced in this wind tunnel by altering the input data of the fans through computer control. In this paper the method used to reproduce

Shuyang Cao; Akira Nishi; Hironori Kikugawa; Yuji Matsuda

2002-01-01

119

Neutral Wind Velocities Calculated from Temperature Measurements During a Magnetic Storm and the Observed Ionospheric Effects.  

National Technical Information Service (NTIS)

Neutral temperature measurements on the OGO 6 satellite are used to calculate the neutral wind velocities during the magnetic storm of Sept. 27, 1969. The neutral densities required for these calculations are taken from the Jacchia 1971 model and the elec...

O. P. Saxena K. K. Mahajan

1973-01-01

120

Prediction of daily average solar wind velocity from solar magnetic field observations using hybrid intelligent systems  

Microsoft Academic Search

A hybrid intelligent system, combining theory driven and data driven models, is used to predict the daily solar wind velocity at 1 AU from solar magnetic field observations. The Potential Field Model (theory driven) is used to calculate the coronal magnetic field up to the source surface placed at 2.5R?. The Earth's position is projected onto the source surface using

P. Wintoft; H. Lundstedt

1997-01-01

121

Remote Sensing of Solar Wind Velocities using Interplanetary Scintillation with MEXART and STELab Stations  

NASA Astrophysics Data System (ADS)

Radio signals from compact radio sources are scattered by electron density irregularities in the solar wind. This effect is registered by radio telescopes as intensity fluctuations of the observed radio source amplitude and known as Interplanetary Scintillation (IPS). The Mexican Array Radio Telescope (MEXART) and the antennas of Solar Terrestrial Environment Laboratory (STELab) are instruments dedicated to studies of IPS signals. In this work we present a technique (Manoharan and Ananthakrishnan, 1990) used to estimate solar wind velocities applied to observations of MEXART and STELab using single station spectra. Currently STELab uses a multi-station IPS technique to determinate solar wind speeds. Here we compare velocities obtained with a single station to those obtained using the multi-station technique for a few strong radio sources using both techniques and with both instruments. At the Center for Astrophysics and Space Sciences - University of California, San Diego (CASS-UCSD), a tomography program is able to reconstruct the dynamics of the inner heliosphere globally using IPS measurements to give solar wind densities and velocities. We show the incorporation of velocities provided by MEXART into this program that has been used successfully for over a decade with STELab IPS measurements.

Mejia-Ambriz, J. C.; Jackson, B. V.; Gonzalez-Esparza, A.; Tokumaru, M.; Yu, H.; Buffington, A.; Hick, P.

2013-05-01

122

Wind Velocity Profiles Measured by the Smoke-Trail Method at Wallops Island, Virginia, 1965 - 1969.  

National Technical Information Service (NTIS)

Thirty-nine detailed wind profiles measured by the smoke-trail method at the Wallops Island Test Range during the years 1965 through 1969 are presented as west-to-east and south-to-north velocity components at height intervals of 25 meters. The overall al...

R. H. Rhyne J. C. Manning R. M. Henry

1972-01-01

123

Aerosol particle microstructure dependence of accuracy of cw Doppler lidar estimate of wind velocity  

Microsoft Academic Search

The effect of aerosol microstructure on the estimation error of wind velocity measured by cw CO2 Doppler lidar is analyzed in the paper. Based on the numerical simulation of a lidar return is has been shown that aerosol particles, due to their difference in size, make essentially different contribution to a measured lidar return power that leads to deviation of

Viktor A. Banakh; Igor N. Smalikho; Christian H. Werner

2001-01-01

124

The winds of O-stars. II - The terminal velocities of stellar winds of O-type stars  

NASA Technical Reports Server (NTRS)

The SEI method (Lamers et al., 1987) is used to obtain P Cygni profiles of the UV resonance lines of C IV, N V, and S IV and of the subordinate UV lines of N IV and C III observed in the spectra of 27 O-type stars. Theoretical profiles which include the turbulence effects agree well with the observations, and they can account for the deep absorption troughs, the shape of the violet absorption wings, and the wavelength of the emission peak. The resulting terminal velocities of the stellar winds are found to be systematically lower by about 400 km/s than previous estimates obtained using the Sobolev approximation (Castor and Lamers, 1979), suggesting that the narrow absorption components, observed in the UV resonance lines of O and B stars, reach the terminal velocity of the winds.

Groenewegen, M. A. T.; Lamers, H. J. G. L. M.; Pauldrach, A. W. A.

1989-01-01

125

The winds of O-stars. II - The terminal velocities of stellar winds of O-type stars  

NASA Astrophysics Data System (ADS)

The SEI method (Lamers et al., 1987) is used to obtain P Cygni profiles of the UV resonance lines of C IV, N V, and S IV and of the subordinate UV lines of N IV and C III observed in the spectra of 27 O-type stars. Theoretical profiles which include the turbulence effects agree well with the observations, and they can account for the deep absorption troughs, the shape of the violet absorption wings, and the wavelength of the emission peak. The resulting terminal velocities of the stellar winds are found to be systematically lower by about 400 km/s than previous estimates obtained using the Sobolev approximation (Castor and Lamers, 1979), suggesting that the narrow absorption components, observed in the UV resonance lines of O and B stars, reach the terminal velocity of the winds.

Groenewegen, M. A. T.; Lamers, H. J. G. L. M.; Pauldrach, A. W. A.

1989-08-01

126

Comparing Solar Wind Velocity Measurements Derived from Sun-grazing Comet Lovejoy (C/2011 W3) with Solar Wind Models  

NASA Astrophysics Data System (ADS)

Comets' plasma (type I) tails have been studied as natural probes of the solar wind since the mid-20th century. Local solar wind conditions directly control the morphology and dynamics of a comet's plasma tail. During ideal observing geometries, the orientation and structure of the plasma tail can reveal large-scale and small-scale variations in the local solar wind structure. We present solar wind velocity measurements derived from multiple observing locations of comet Lovejoy (C/2011 W3) from the 14th - 19th December 2011 using recent images from the SECCHI and LASCO heliospheric imagers and coronagraphs aboard STEREO A and B, and SOHO. Overlapping observation sessions from the three spacecraft provided the perfect opportunity to use comet Lovejoy as a diagnostic tool to understand solar wind variability close to the Sun. Our unique analysis technique [submitted] allows us to determine the latitudinal variations of the solar wind, heliospheric current sheet sector boundaries and the boundaries of transient features as comet Lovejoy probes the Sun's atmosphere. We plan to compare our observations to results of suitable simulations of plasma conditions in the corona and inner heliosphere during the time of Lovejoy's perihelion passage.

Ramanjooloo, Y.; Jones, G. H.; Coates, A. J.; Owens, M. J.; Battams, K.

2012-12-01

127

An analysis of maximum horizontal wind speeds and associated parameters recorded at NASA's 150-Meter Ground Winds Tower facility at Kennedy Space Center, Florida  

NASA Technical Reports Server (NTRS)

Continuous horizontal wind speed measurements were processed and classified as a function of tower level (10, 18, 60, and 150 meters) and period of reference day, month, season: winter (October through March) and summer (April through September), and annual. Tabulations were made of the daily maximum horizontal wind speed, time of ocurrence, and five associated parameters: mean horizontal wind speed, maximum vertical gusts (i.e., updraft and downdraft), and mean and instantaneous directions. Analyses using these data included means, extremes, standard deviations, and frequency distributions. Comparisons of intensity of maximum horizontal wind speeds determined in this year of data are made with maximum values recorded at Kennedy Space Center during another non-hurricane-occurrence year (1967) and with values during 1966 through 1972 when six hurricanes affected the area after the Ground Winds Tower facility became operational. Wind flow in the lowest 150 meters of the atmosphere was measured for the identification of hazards involved in wind shear encounter relative to ascent and descent of the space shuttle and conventional aircraft.

Alexander, M. B.

1978-01-01

128

Active removal of wind noise from outdoor microphones using local velocity measurements  

NASA Astrophysics Data System (ADS)

Wind noise in outdoor microphone measurements can significantly degrade acoustic data. Since acoustic and wind spectra often overlap when low frequency acoustic sources are observed, wind noise is generally impossible to remove by band selective filtering. This research examines active removal of wind noise from an outdoor microphone. Measurements performed outdoors on a horizontally positioned microphone demonstrate that a major part of unscreened microphone wind noise is flow noise caused by interaction between the microphone and adjacent air flow. It is concluded that pressure fluctuations in the passing air volume are a second significant contributor. While wind noise contamination is most often treated with passive spherical foam windscreens, an active wind noise reduction system based upon local velocity measurements applied to a passively screened or unscreened microphone is proposed. A simple relationship, developed from the Bernoulli equation, is used to transform these wind velocity measurements into microphone wind pressure estimates. Extensive measurements of coherence between these anemometer derived pressure estimates and wind noise in screened and unscreened microphones are performed for a variety of anemometer positions. These measurements indicate the dominant source of wind noise in a passively screened microphone is local pressure fluctuations that are not correlated with pressure estimates based on local velocity fluctuations. This important observation indicates than an active system based upon velocity measurements is unlikely to quiet a microphone that has convential passive screening by a substantial amount and that an active system based upon velocity measurements applied to an unscreened microphone is unlikely to surpass the performance of a passively screened microphone. An outdoor active wind noise cancellation system is demonstrated for a horizontally positioned unscreened microphone. A signal space approach is used to determine the effectiveness of single and multiple anemometer channels in the system and it is shown that while additional quieting is obtained with additional anemometers the additional quieting achieved diminishes rapidly with new channels. The active system transfer functions are observed to possess significant stability of over periods of tens of minutes to hours. This stability apparently depends upon the stability of the wind environment. It is concluded that adaptive active quieting systems would require only infrequent updates in such an environment. System performance with a four channel anemometer system is observed to be similar to that using a small passive screen. Wind energy reduction performance of the active windscreen is shown to be between 10 and 13 dB for frequencies below 200Hz and this performance decreases smoothly to approximately 5 dB at 500 Hz. The active system has application when the presence or physical size of the passive windscreen is undesirable. Further, it is concluded that the concepts presented also provide an effective approach for studying the behavior of passive wind screens and outdoor microphone wind noise.

Shust, Michael Ray

1998-07-01

129

The Evolution of the Spectrum of Velocity Fluctuations in the Solar Wind  

NASA Technical Reports Server (NTRS)

Previous studies have shown that the power spectra of the magnetic field and velocity in the solar wind do not evolve in the same way with heliocentric distance. In particular, the velocity spectrum remains flatter for a substantial distance. However, Voyager observations of the velocity spectrum have demonstrated a likely asymptotic state in which the spectrum steepens to having a spectral index of -5/3, finally matching the magnetic spectrum and the theoretical expectation of Kolmogoroff turbulence. Here we examine evidence from other spacecraft, in particular studying Ulysses spectra to determine if the Voyager result, based on a very few sufficiently complete intervals, is correct. Preliminary results confirm the -5/3 slope for velocity fluctuations at -5 AU from the Sun in the ecliptic. We will examine many intervals to develop a more general picture of the spectral evolution in various conditions, and how magnetic and velocity spectra differ in these cases.

Roberts, Dana Aaron

2007-01-01

130

An evaluation of errors observed in the measurement of low wind velocities  

NASA Technical Reports Server (NTRS)

Measurements of low wind velocities (the absolute value of V sub H is approx. equal to 6 m/s) with a VHF wind profiler can be difficult if ground clutter or other biases in the system dominate in altering the position of the perceived peak in the calculated power spectrum. A variety of methods for ground clutter suppression are used in profiler systems today (Cornish, 1983). An editing method called zero suppression takes the spectral value of selectable number of points (N) on each side of 0 velocity (one point on either side, in this study) and sets them equal to the mean value of the points exterior to the specified N points on either side of 0. Analysis done with the PSU VHF(1) radar, shows that this zero-suppression method can systematically bias horizontal wings V sub H below 6 m/s. With the zero suppression, an artificial increase in absolute wind velocities occurs when the spectral peaks fall within the plus or minus N points of the FFT (personal communication, Strauch, 1985). It was also established that the method artificially decreases the absolute wind velocities inferred from spectral peaks that are outside but near the suppressed region. Comparisons of wind profiles observed with and without zero suppression are given. The range of the biased velocities extends to about plus or minus 6 m/s. Biases have been deduced to be as much as 2 m/s, but more commonly they are on the order of 1.0 m/s.

Williams, S. R.; Thomson, D. W.

1986-01-01

131

An investigation into the contraction of the hurricane radius of maximum wind  

NASA Astrophysics Data System (ADS)

The radius of the maximum tangential wind (RMW) associated with the hurricane primary circulation has been long known to undergo continuous contraction during the hurricane development. In this study, we document some characteristic behaviors of the RMW contraction in a series of ensemble real-time simulations of Hurricane Katrina (2005) and in idealized experiments using the Rotunno and Emanuel (Mon Weather Rev 137:1770-1789, 1987) axisymmetric hurricane model. Of specific interest is that the contraction appears to slow down abruptly at the middle of the hurricane intensification, and the RMW becomes nearly stationary subsequently, despite the rapidly strengthening rotational flows. A kinematic model is then presented to examine such behaviors of the RMW in which necessary conditions for the RMW to stop contracting are examined. Further use of the Emanuel's (J Atmos Sci 43:585-605, 1986) analytical hurricane theory reveals a connection between the hurricane maximum potential intensity and the hurricane eye size, an issue that has not been considered adequately in previous studies.

Kieu, Chanh Q.

2012-01-01

132

The Evolution of the Spectrum of Velocity Fluctuations in the Solar Wind  

NASA Technical Reports Server (NTRS)

Recent work has shown that at 1AU from the Sun the power spectrum of the solar wind magnetic field has the -5/3 spectral slope expected for Kolmogorov turbulence, but that the velocity has closer to a -3/2 spectrum. This paper traces the changes in solar wind velocity spectra from 0.3 to 5 AU using data from the Helios and Ulysses spacecraft to show that this is a transient stage in the evolution. The spectrum of the velocity is found to be flatter than that of the magnetic field for the higher frequencies examined for all cases until the slopes become equal (at -5/3) well past 1 AU when the wind is relatively nonAlfvenic. In some respects, in particular in the evolution of the frequency at which the spectrum changes from flatter at larger scales to a traditionally turbulent spectrum at smaller scales, the velocity field evolves more rapidly that the magnetic, and this is associated with the dominance of the magnetic energy over the kinetic at "inertial range" scales. The Alfvenicity of the fluctuations, not the speed of the flow, is shown to control the rate of the spectral evolution. This study shows that, for the solar wind ., the idea of a simple "inertial range" with uniform spectral properties is not realistic, and new phenomenologies will be needed to capture the true situation. In addition a flattening of the velocity spectrum persists at times for small scales, which may provide a clue to the nature of the small-scale interactions.

Roberts, D. Aaron

2010-01-01

133

The wind-induced drift velocity of the freshwater layer on the sea's surface  

NASA Astrophysics Data System (ADS)

The effect of an unsteady river plume on the wind drift was studied. Initially, the plume occurs as a horizontal homogeneous near-surface layer with a low density and different thicknesses being washed around by the wind in the course of time due to the vertical mixing with the underlying waters. This process is described using the one-dimensional Princeton Ocean Model (POM) with the integrated turbulence submodel. A series of numerical experiments yielded the empirical dependence of the normalized surface drift velocity modulus on the nondimensional parameters: the Ekman numbers and the relations between the buoyancy and Coriolis forces.

Zhurbas, N. V.

2013-03-01

134

Single-pulse measurement of wind velocities using an Er:Yb:glass coherent laser radar  

NASA Astrophysics Data System (ADS)

Many wind-field mapping applications require range-resolved atmospheric velocity measurements at long range and/or with a temporal resolution sufficient to investigate turbulence. We argue that this capability can be achieved only by coherent laser radar systems that transmit energetic (>1mJ) pulses. We describe such a system and describe single-pulse measurement of the range-resolved line-of-sight velocities, and show that the instrument-limited reproducibility of the measurements is 0.4ms-1.

Heintze, Matthew C.; Chang, Nick W. H.; Jeanneret, Francois; Munch, Jesper; Ottaway, David J.; Veitch, Peter J.

2011-07-01

135

Single-pulse measurement of wind velocities using an Er:Yb:glass coherent laser radar.  

PubMed

Many wind-field mapping applications require range-resolved atmospheric velocity measurements at long range and/or with a temporal resolution sufficient to investigate turbulence. We argue that this capability can be achieved only by coherent laser radar systems that transmit energetic (>1 mJ) pulses. We describe such a system and describe single-pulse measurement of the range-resolved line-of-sight velocities, and show that the instrument-limited reproducibility of the measurements is 0.4 ms(-1). PMID:21772386

Heintze, Matthew C; Chang, Nick W H; Jeanneret, Francois; Munch, Jesper; Ottaway, David J; Veitch, Peter J

2011-07-20

136

CO2 lidar for measurements of trace gases and wind velocities  

NASA Technical Reports Server (NTRS)

CO2 lidar systems technology and signal processing requirements relevant to measurement needs and sensitivity are discussed. Doppler processing is similar to microwave radar, with signal reception controlled by a computer capable of both direct and heterodyne operations. Trace gas concentrations have been obtained with the NASA DIAL system, and trace gas transport has been determined with Doppler lidar measurements for wind velocity and turbulence. High vertical resolution measurement of trace gases, wind velocity, and turbulence are most important in the planetary boundary layer and in regions between the PBL and the lower stratosphere. Shear measurements are critical for airport operational safety. A sensitivity analysis for heterodyne detection with the DIAL system and for short pulses using a Doppler lidar system is presented. The development of transient injection locking techniques, as well as frequency stability by reducing chirp and catalytic control of closed cycle CO2 laser chemistry, is described.

Hess, R. V.

1982-01-01

137

Cascade-like and scaling behavior of wind velocity increments in the atmospheric surface layer  

NASA Astrophysics Data System (ADS)

By using a large amount of data collected in the atmospheric surface layer, we analyze the probability density functions (PDFs), the probability of return and the moments of wind velocity increments. Results show that the PDFs change from the non-Gaussian long-tailed distributions to Gaussian with the increase of time scales. This is similar to what has been observed and interpreted as an indication of cascade in the fully developed homogeneous and isotropic turbulence. Besides, both the probability of return and the moments are found to be scaling with time scales. We then compare above results with the truncated Lévy flights and the log-normal PDF model. It is found that although both models show the cascade-like behavior in the PDFs and the scaling behavior in the probability of return and the moments under some conditions, they are not good enough for quantitatively describing the random process of wind velocity increments.

Liu, Lei; Hu, Fei

2013-12-01

138

The power associated with density fluctuations and velocity fluctuations in the solar wind  

NASA Technical Reports Server (NTRS)

Direct observations from Pioneer 6 of solar-wind-proton fluctuations have been used to obtain the power spectra associated with solar-wind-proton number density and velocity fluctuations in the frequency range of 0.001 to 0.01 Hz, extending previous analyses by an order of magnitude at the higher frequencies. The slopes of the power spectra associated with the density fluctuations and the velocity fluctuations are similar and are in agreement with the shape of the power spectra found at the lower frequencies. The power spectra indicate that the power-law density spectrum observed at lower frequencies extends to at least 0.01 Hz. This smooth variation in the spectrum at these frequencies is consistent with previous extrapolations of both spacecraft and interplanetary scintillation observations.

Intriligator, D. S.

1974-01-01

139

Interpretation of solar wind reconnection exhaust in terms of kinetic Alfvén wave group-velocity cones  

Microsoft Academic Search

Recent multi-satellite measurements of reconnection exhausts in the solar wind have allowed for the first time to determine the reconnection rate (R) and the exhaust wedge angle 2$\\\\theta$w. We compare such observations of R and $\\\\theta$w with the theoretical predictions based on the half-cone angles ($\\\\theta$g) of the group velocity vectors (Vg) of the kinetic Alfvén (KA) and slow MHD

Nagendra Singh

2007-01-01

140

Remote measurement of the transverse wind velocity component using a laser Doppler velocimeter  

NASA Technical Reports Server (NTRS)

The wind speed transverse to the line-of-sight of a laser Doppler radar has been measured using the intensity fluctuations of the returned signal. These measurements were made at a range of 100 m with a CO2 CW laser Doppler velocimeter, which was simultaneously performing its design function of determining the radial velocity component. The transverse component measurements are compared with those obtained using a u, v, w Gill propeller anemometer.

Kennedy, L. Z.; Bilbro, J. W.

1979-01-01

141

Controlled Velocity Testing of an 8-kW Wind Turbine  

SciTech Connect

This paper describes a case study of the controlled-velocity test of an 8-kW wind turbine. The turbine was developed in response to the U.S. Department of Energy's small wind turbine program. As background, the prototype development is discussed. The turbine mechanical and electrical components are described. The turbine was tested on a flatbed truck and driven down an airfield runway at constant relative wind speed. Horizontal furling was used to control over-speed. Various parameters were changed to determine their effects on furling. The testing showed that the machine had insufficient rotor offset for adequate furling. Also, a rotor resonance problem was discovered and remedied. Problems associated with taking the measurements made it difficult to determine if the truck test was a suitable method for code validation. However, qualitative observations gleaned from the testing justified the effort.

Larwood, S.; Sencenbaugh, J.; Acker, B.

2001-07-31

142

Comparison of solar wind velocity measurements with a theoretical acceleration model  

SciTech Connect

Interplanetary radio scintillation (IPS) measurements of the solar wind velocity were made using the receiving antennas of the European Incoherent Scatter Facility (EISCAT) radar system in northern Scandinavia from June through October 1990. The observations, which cover the distance range from 11 to 90 R{sub s} from Sun center, were taken with sufficient density to measure the same stream at two (or more) different distances. The deduced velocities are in the range 100 {approx lt} U {approx lt} 540 km s{sup {minus}1}. The authors selected from 192 observations, 16 examples of streams observed with good radial alignment, of which 12 were observed unchanged for several days. The measured velocities are compared with calculations based on a two-fluid solar wind model with Alfven waves. In eight cases the measurements are in good agreement with the model when a moderate amount of wave energy is added to the flow. In four cases the observed streams show low or moderate velocities below, say, 20 R{sub s} but then accelerate fast at larger distances from the Sun. This delayed acceleration is much steeper than the acceleration in the model at these distances. In the remaining four cases the streams seem to reach their final velocities much closer to the base than in other cases, and they are not observed to accelerate much between 10 and 90 R{sub s}. At these distances all related solar wind models they have seen give the same results; they all fit half the data, and none can fit the other half.

Coles, W.A. (Univ. of California, La Jolla (United States)); Esser, R. (Univ. of Tromsoe (Norway)); Loevhaug, U.P. (EISCAT, Ramfjordbotn (Norway)); Markkanen, J. (Geophysical Observatory, Sodankyla (Finland))

1991-08-01

143

Monthly means and trends in maximum 2-minute winds at coastal stations in the conterminous U.S  

NASA Astrophysics Data System (ADS)

Near-coastal ocean buoys and remote sensing platforms provide evidence for an increase in significant wave heights over the last several decades (e.g., Komar and Allan 2008, Menéndez et al. 2008), which may be caused (at least in part) by an increase in extreme wind speeds (e.g., Young et al. 2011, Arinaga and Cheung 2012). I use observations of maximum 2-minute winds at coastal stations in the conterminous U.S. to determine if similar trends appear in the land-based records. Analyses of both wind speed and direction provide insight into the causes of these extreme events (e.g., Bromirski and Kossin 2008, Wang et al. 2009). Maximum 2-minute wind measurements began with the installation of ASOS in the mid-1990s. Maximum 1-minute winds were recorded prior to the ASOS, so I used only the 2-minute data. I compiled the maximum 2-minute winds for each month at 40 stations along the Pacific, Atlantic, and Gulf Coasts. Record lengths range from 12 years to over 17 years, with most stations having 15-16 years of data. ASOS stations switched from mechanical to sonic anemometers in the mid- to late 2000s but the short record length makes it difficult to determine if this created inhomogeneities in the measurements. The fastest sustained wind speeds for west coast stations have a winter maximum and a summer minimum. Directions typically are south or southwesterly in winter and west or northwesterly in summer, consistent with seasonal changes in the Pacific High. Northeastern stations also have a winter maximum and summer minimum in the fastest speeds. Winter wind directions primarily are from the northwest, north, or northeast, consistent with the predominant winter storm track. Summer wind directions vary considerably across the stations as storm tracks become more variable. In contrast, the fastest sustained wind speeds at southeastern and Gulf Coast stations have a winter/early spring minimum and a summer/early fall maximum, as expected when the fastest speeds derive from hurricanes. Directions are predominantly from the east, northeast, and southeast from June to October. Winter/early spring wind directions are variable across the stations. Linear trends in the fastest wind speeds show no uniform pattern across stations and months, though positive trends are more common than are negative trends. Given the climatologically short period of record, I used bootstrapping to assess the significance of each station's monthly trend. Along the west coast, significant positive trends are common in May and August. There are few significant negative trends. In the northeast, significant positive trends are common in June and December, as are significant negative trends in September. In the southeastern U.S. and along the Gulf Coast, significant positive trends appear at many stations in March, June, and December with significant negative trends in September. Overall, like ocean-based observations, the land-based maximum 2-minute wind record shows some evidence for an increase in the fastest speeds over the past 12-17 years, though with a high degree of spatial heterogeneity. Significant negative trends do occur in the record, and are particularly prominent in September along the East and Gulf Coasts.

Klink, K.

2012-12-01

144

An analysis of maximum vertical gusts recorded at NASA's 150-meter ground winds tower facility at Kennedy Space Center, Florida  

NASA Technical Reports Server (NTRS)

A statistical summary is presented of vertical wind speed data recorded at NASA's 150-Meter Ground Winds Tower Facility on Merritt Island, Kennedy Space Center, Florida. One year of continuous around-the-clock vertical wind speed measurements processed by the Automatic Data Acquisition System (ADAS) is classified as a function of tower level (10, 18, 60, and 150 meters) and period of reference day, month, season: winter (October through March) and summer (April through September), and annual. Intensity, frequency, time of occurrence, prevailing conditions, etc., of the daily maximum vertical gusts (i.e., updraft and downdraft) are determined. The results are compared with the vertical gusts associated with the daily maximum horizontal gust. The intent of this summarization of vertical wind speed data is to provide a general description of wind flow in the lower 150 meters of the atmosphere for the identification of hazards involved in wind shear encounters relative to ascent and descent of the Space Shuttle and conventional aircraft.

Alexander, M. B.

1977-01-01

145

A new apparatus for continuous measuring the falling velocity of the wind-dispersal seeds  

NASA Astrophysics Data System (ADS)

A new apparatus for continuous measuring the falling velocity of wind-dispersal seeds is presented in this paper. The key unit of this apparatus is the photo-detectors installed on the ends of a vertical tube. The photodetector is composed of a LED and a photo-sensor. The LED light goes through a horizontal slit to from a flat light plane, which be received by the photo-sensors on the opposite side. When a plant seed falls down and passes through the flat light plane, a pulse signal will be detected by the photo-sensor. The average falling velocity of the seed is calculated according to the falling time and the distance from the starting point to the testing point. By using several tubes and photo-detectors, the apparatus can continuously measure the velocity of a seed falling down to different height. This apparatus avoids the affect of the static electricity and airflow to the seeds.

Ji, Huihua; Wang, Shoubing; Chen, Huacai; Zhu, Zhouhong; Zhu, Min

2011-11-01

146

Kinetic Alfvén wave and ion velocity distribution functions in the solar wind  

NASA Astrophysics Data System (ADS)

Using 1D test particle simulations, the effect of a kinetic Alfvén wave on the velocity distribution function of protons in the collisionless solar wind is investigated. We first use linear Vlasov theory to obtain the property of a kinetic Alfvén wave numerically (the wave propagates in the direction almost perpendicular to the background magnetic field). We then numerically simulate how the wave will shape the proton velocity distribution function. It is found that Landau resonance may be able to generate two components in the initially Maxwellian proton velocity distribution function: a tenuous beam component along the direction of the background magnetic field and a core component. The streaming speed of the beam relative to the core proton component is about 1.2 -- 1.3 Alfvén speed. However, no perpendicular ion heating is observed from the simulation. Reference: Li, X., Lu, Q.M., Chen, Y., Li, B., Xia, L.D., ApJ, 719, L190, 2010.

Li, X.; Lu, Q.; Chen, Y.; Li, B.; Xia, L.

2010-12-01

147

Comparative flight and full-scale wind-tunnel measurements of the maximum lift of an airplane  

NASA Technical Reports Server (NTRS)

Determinations of the power-off maximum lift of a Fairchild 22 airplane were made in the NACA full-scale wind tunnel and in flight. The results from the two types of test were in satisfactory agreement. It was found that, when the airplane was rotated positively in pitch through the angle of stall at rates of the order of 0.1 degree per second, the maximum lift coefficient was considerably higher than that obtained in the standard tests, in which the forces are measured with the angles of attack fixed. Scale effect on the maximum lift coefficient was also investigated.

Silverstein, Abe; Katzoff, S; Hootman, James A

1938-01-01

148

An empirical model to forecast solar wind velocity through statistical modeling  

NASA Astrophysics Data System (ADS)

The accurate prediction of the solar wind velocity has been a major challenge in the space weather community. Previous studies proposed many empirical and semi-empirical models to forecast the solar wind velocity based on either the historical observations, e.g. the persistence model, or the instantaneous observations of the sun, e.g. the Wang-Sheeley-Arge model. In this study, we use the one-minute WIND data from January 1995 to August 2012 to investigate and compare the performances of 4 models often used in literature, here referred to as the null model, the persistence model, the one-solar-rotation-ago model, and the Wang-Sheeley-Arge model. It is found that, measured by root mean square error, the persistence model gives the most accurate predictions within two days. Beyond two days, the Wang-Sheeley-Arge model serves as the best model, though it only slightly outperforms the null model and the one-solar-rotation-ago model. Finally, we apply the least-square regression to linearly combine the null model, the persistence model, and the one-solar-rotation-ago model to propose a 'general persistence model'. By comparing its performance against the 4 aforementioned models, it is found that the accuracy of the general persistence model outperforms the other 4 models within five days. Due to its great simplicity and superb performance, we believe that the general persistence model can serve as a benchmark in the forecast of solar wind velocity and has the potential to be modified to arrive at better models.

Gao, Y.; Ridley, A. J.

2013-12-01

149

Southern Hemisphere westerly wind strength at sub-Antarctic Macquarie Island since the end of the Last Glacial Maximum  

NASA Astrophysics Data System (ADS)

Recent climate changes have been attributed to increasing atmospheric greenhouse gas concentrations (e.g. CO2). Atmospheric CO2 concentrations are partly controlled by changes in the oceans' capacity to absorb or release CO2 at the surface. These increases are partly controlled by changes in the oceans' capacity to absorb CO2 at the surface vs. upwelling of deep-water old carbon. The Southern Ocean is considered to play a major role in this, particularly on glacial-interglacial timescales. Southern Ocean circulation is strongly influenced by changes in Southern Hemisphere westerly wind strength. Understanding past changes in the Southern Hemisphere westerly winds is needed for interpreting past variations in atmospheric CO2 concentrations. Most palaeoclimate reconstructions disagree on past Southern Hemisphere westerly wind strength. The main reasons include the location of sites, assumptions made and methods used. Sub-Antarctic islands such as Macquarie Island (54°S, 158°E) are ideally located to address these limitations. They occur at latitudes where the Southern Hemisphere westerly winds are strongest. Strong winds cause a west-east conductivity gradient in lakes as ions are delivered by wind-derived sea spray. A diatom-conductivity model for Macquarie Island was applied to a lake sediment core on the western side of the island to infer past lake water conductivity (sea spray), where more/less sea spray is related to stronger/weaker Southern Hemisphere westerly winds. This showed the Southern Hemisphere westerly winds were stronger at Macquarie Island during the Last Glacial Maximum, then abruptly decreased at the a similar time to decreases in dust flux and increases in CO2 concentrations recorded at EPICA Dome C, Antarctica. The winds were generally weaker during the Holocene. An increase in the lake's sedimentation rate during the mid Holocene revealed distinct oscillations and high variability similar to those observed in the Dome C dust flux record. This is the first direct Southern Hemisphere westerly wind strength reconstruction from their core belt.

Saunders, Krystyna; Hodgson, Dominic; Grosjean, Martin

2014-05-01

150

MAXIMUM WIND-HYDRO POWER PENETRATION IN SMALL & MEDIUM SIZED ISLANDS  

Microsoft Academic Search

The prospect of creating a combined wind-hydro energy production station is hereby analyzed, in an attempt to fulfil the electricity demand of small and medium-sized remote Aegean islands. According to results obtained, a properly sized wind-hydro solution not only may realize a high wind penetration in the autonomous electrical systems but it is additionally the best way to handle the

E. Christinakis; K. Kavadias; J. K. Kaldellis

151

No evidence for the localized heating of solar wind protons at intense velocity shear zones  

NASA Astrophysics Data System (ADS)

measurements from the Wind spacecraft at 1 AU, the heating of protons in the solar wind at locations of intense velocity shear is examined. The 4321 sites of intense shear in fast coronal hole origin plasma are analyzed. The proton temperature, the proton specific entropy, and the proton number density at the locations of the shears are compared with the same quantities in the plasmas adjacent to the shears. A very slight but statistically significant enhancement of the proton temperature is seen at the sites of the shears, but it is accompanied by a larger enhancement of the proton number density at the sites of the shears. Consequently, there is no enhancement of the proton specific entropy at the shear sites, indicating no production of entropy; hence, no evidence for plasma heating is found at the sites of the velocity shears. Since the shearing velocities have appreciable Mach numbers, the authors suggest that there can be a slight adiabatic compression of the plasma at the shear zones.

Borovsky, Joseph E.; Steinberg, John T.

2014-03-01

152

The Velocity Induced by the Wake of a Wind Turbine in a Shear Layer, Including Ground Effect.  

National Technical Information Service (NTIS)

A theory is developed for the calculation of the velocity field induced by the wake of a horizontal axis wind turbine in a wind shear layer and in the vicinity of a plane ground surface, when the force distribution of the turbine is known. The turbine is ...

B. C. A. Johansson

1980-01-01

153

Modeling of Wind Turbine Driving Permanent Magnet Generator with Maximum Power Point Tracking System  

Microsoft Academic Search

This paper elaborates on the analysis and simulation of 15 kW Wind Turbine Generator (WTG) driving low speed Permanent Magnet Synchronous Generator (PMSG) using PSIM computer simulation program. The system consists of wind turbine, permanent magnet generator, three-phase diode rectifier, boost converter, and voltage source inverter models. In the WTG model, the best performance coefficient has been determined according to

Ali M. Eltamaly

2007-01-01

154

Assessing the maximum fuel savings obtainable in simple wind-diesel systems  

Microsoft Academic Search

We present a statistical method to derive the upper limit of the obtainalbe fuel savings in simple wind-diesel systems applying fixed control rules. The fuel savings when using the optimal control may be estimated from the statistical properties of the time series of the power balance: wind turbine power-load. The method is validated by comparison with a time step simulation

Hans Georg Beyer; Thomas Degner

1997-01-01

155

Five-Spacecraft Observations of Solar Wind Structure and Interplanetary Shocks Approaching Solar Maximum  

Microsoft Academic Search

We combined solar wind observations from five different spacecraft: Helios 1, Helios 2, OMNI tape, Voyager 1, and Voyager 2, from November 1977 to February 1978, to study the structure of the solar wind streams and the propagation of interplanetary shocks and ejecta. We identified 12 shock events of different origin: 7 transient forward shocks (TFSs) and 5 corotating interaction

A. Gonzalez-Esparza

2001-01-01

156

Maximum energy of cosmic-ray particles accelerated by supernova remnant shocks in stellar wind cavities  

Microsoft Academic Search

Diffusive shock acceleration, balanced by adiabatic losses, leads readily to particle energies of more than 10 to the 15th eV in the case of a supernova shock freely expanding into a stellar wind cavity. This process accelerates particles early on out of stellar wind material which is often enriched in certain elements (isotopes), and may thus contribute to explain elemental

Heinrich J. Voelk; Peter L. Biermann

1988-01-01

157

A coronal hole and its identification as the source of a high velocity solar wind stream  

NASA Technical Reports Server (NTRS)

X-ray images of the solar corona showed a magnetically open structure in the low corona which extended from N20W20 to the south pole. Analysis of the measured X-ray intensities shows the density scale heights within the structure to be typically a factor of two less than that in the surrounding large scale magnetically closed regions. The structure is identified as a coronal hole. Wind measurements for the appropriate period were traced back to the sun by the method of instantaneous ideal spirals. A striking agreement was found between the Carrington longitude of the solar source of a recurrent high velocity solar wind stream and the position of the hole.

Krieger, A. S.; Timothy, A. F.; Roelof, E. C.

1973-01-01

158

Sensory and motor maximum nerve conduction velocity in the peripheral and central nervous system of the beagle dog.  

PubMed

Sensory maximum nerve conduction velocity (MNCV) and motor MNCV were monitored in altogether 14 beagle dogs anaesthetized with pentobarbital. Sensory MNCV was determined by averaging cortically evoked potentials from somatosensory area I (SS I) in response to repeated electrical stimulation of digital paw pads, tibial nerve at calcaneus or sciatic nerve at trochanter. Sensory MNCV determined from paw to tibial nerve at calcaneus was 53 m/sec, from tibial nerve at calcaneus to sciatic nerve at trochanter 64 m/sec and from sciatic nerve at trochanter to crotex SS I 53 m/sec. Motor peripheral MNCV determined in the customary way from sciatic nerve at trochanter to tibial nerve at calcaneus was 68 m/sec and distal latency 3.6 msec. Motor central MNCV from motor cortex to the sciatic nerve at the trochanter in 5 unanaesthetized dogs was 57 m/sec. These testing procedures serve for quantitative assessment of possible impairment of impulse transmission in the central and peripheral sensory and motor pathway of beagle dogs used in routine toxicity studies. PMID:7180741

Schaeppi, U; Teste, M; Siegenthaler, U

1982-10-01

159

The velocity of the tip vortex of a horizontal-axis wind turbine at high tip speed ratio  

Microsoft Academic Search

An equation is derived for the streamwise velocity of the tip vortex of a horizontal-axis wind turbine as the pitch of the vortex tends to zero. The equation is applicable at high tip speed ratios provided the vortex core remains of constant size and there is no flow along the vortex axis. Under these conditions, the vortex velocity is the

D. H. Wood

1998-01-01

160

Interplanetary Shocks and Solar Wind Structure Approaching Solar Maximum: Helios, IMP8 and Voyager Observations  

Microsoft Academic Search

We studied solar wind observations of five different spacecraft: Helios 1, Helios 2, IMP-8, Voyager 1 and Voyager 2, from November 1977 to February 1978. In this period the large-scale dynamics of the solar wind near of the ecliptic plane\\u000a was characterized by transient forward shocks (TFSs), ejecta, unstable corotating interaction regions (CIRs), and complex\\u000a and variable magnetic sector structures.

A. González-Esparza

2001-01-01

161

Global Solar Wind Structure from Solar Minimum to Solar Maximum: Sources and Evolution  

Microsoft Academic Search

During the past few years, significant progress has been made in identifying the coronal sources of structures observed in\\u000a the solar wind. This recent work has been facilitated by the relative simplicity and stability of structures during solar\\u000a minimum. The challenge now is to continue to use coordinated coronal\\/solar wind observations to study the far more complicated\\u000a and time-evolving structures

S. E. Gibson

2001-01-01

162

Scintillation Measurements of the Solar Wind Velocity in Strong Scattering near the Sun  

NASA Astrophysics Data System (ADS)

The multi-antenna scintillation method of measuring the solar-wind velocity has been very effective, particularly near the Sun and at high heliographic latitudes where direct measurements are rare or non-existent. However, scintillation observations inherently involve an LOS integration. Several methods have been used to deal with this problem, but they all require the basic assumption that contributions from different parts of the LOS add linearly. This assumption is valid for weak scintillations where the Born approximation holds, but it is not correct for strong scintillations. In this article we compare simultaneous observations of the same radio source, and therefore the same solar wind, at radio wavelengths of 32 cm and 92 cm. The 32-cm observations at the European Incoherent Scatter Radar (EISCAT) were made in weak-scattering and those at 92 cm at the Solar-Terrestrial Environment Laboratory (STEL) were made in strong-scattering mode. The results showed no significant bias in velocity caused by strong scattering, confirming that the LOS inversion techniques can be extended into the strong-scattering regime.

Kojima, M.; Coles, W. A.; Tokumaru, M.; Fujiki, K.

2013-04-01

163

Estimation of Venus wind velocities from high-resolution infrared spectra. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

Zonal velocity profiles in the Venus atmosphere above the clouds were estimated from measured asymmetries of HCl and HF infrared absorption lines in high-resolution Fourier interferometer spectra of the planet. These asymmetries are caused by both pressure-induced shifts in the positions of the hydrogen-halide lines perturbed by CO2 and Doppler shifts due to atmospheric motions. Particularly in the case of the HCl 2-0 band, the effects of the two types of line shifts can be easily isolated, making it possible to estimate a profile of average Venus equatorial zonal velocity as a function of pressure in the region roughly 60 to 70 km above the surface of the planet. The mean profiles obtained show strong vertical shear in the Venus zonal winds near the cloud-top level, and both the magnitude and direction of winds at all levels in this region appear to vary greatly with longitude relative to the sub-solar point.

Smith, M. A. H.

1978-01-01

164

Remote Sensing Data in Wind Velocity Field Modelling: a Case Study from the Sudetes (SW Poland)  

NASA Astrophysics Data System (ADS)

The phenomena of wind-field deformation above complex (mountainous) terrain is a popular subject of research related to numerical modelling using GIS techniques. This type of modelling requires, as input data, information on terrain roughness and a digital terrain/elevation model. This information may be provided by remote sensing data. Consequently, its accuracy and spatial resolution may affect the results of modelling. This paper represents an attempt to conduct wind-field modelling in the area of the ?nie?nik Massif (Eastern Sudetes). The modelling process was conducted in WindStation 2.0.10 software (using the computable fluid dynamics solver Canyon). Two different elevation models were used: the Global Land Survey Digital Elevation Model (GLS DEM) and Digital Terrain Elevation Data (DTED) Level 2. The terrain roughness raster was generated on the basis of Corine Land Cover 2006 (CLC 2006) data. The output data were post-processed in ArcInfo 9.3.1 software to achieve a high-quality cartographic presentation. Experimental modelling was conducted for situations from 26 November 2011, 25 May 2012, and 26 May 2012, based on a limited number of field measurements and using parameters of the atmosphere boundary layer derived from the aerological surveys provided by the closest meteorological stations. The model was run in a 100-m and 250-m spatial resolution. In order to verify the model's performance, leave-one-out cross-validation was used. The calculated indices allowed for a comparison with results of former studies pertaining to WindStation's performance. The experiment demonstrated very subtle differences between results in using DTED or GLS DEM elevation data. Additionally, CLC 2006 roughness data provided more noticeable improvements in the model's performance, but only in the resolution corresponding to the original roughness data. The best input data configuration resulted in the following mean values of error measure: root mean squared error of velocity = 1.0 m/s and mean absolute error of direction = 30°. The author concludes that, within specific meteorological conditions (relatively strong and constant synoptic forcing) and using the aforementioned input data, the Canyon model provides fairly acceptable results. Similarly, the quality of the presented remote sensing data is suitable for wind velocity modelling in the proposed resolution. However, CLC 2006 land use data should be first verified with a higher-resolution satellite or aerial imagery.

Jancewicz, Kacper

2013-08-01

165

Remote Sensing Data in Wind Velocity Field Modelling: a Case Study from the Sudetes (SW Poland)  

NASA Astrophysics Data System (ADS)

The phenomena of wind-field deformation above complex (mountainous) terrain is a popular subject of research related to numerical modelling using GIS techniques. This type of modelling requires, as input data, information on terrain roughness and a digital terrain/elevation model. This information may be provided by remote sensing data. Consequently, its accuracy and spatial resolution may affect the results of modelling. This paper represents an attempt to conduct wind-field modelling in the area of the ?nie?nik Massif (Eastern Sudetes). The modelling process was conducted in WindStation 2.0.10 software (using the computable fluid dynamics solver Canyon). Two different elevation models were used: the Global Land Survey Digital Elevation Model (GLS DEM) and Digital Terrain Elevation Data (DTED) Level 2. The terrain roughness raster was generated on the basis of Corine Land Cover 2006 (CLC 2006) data. The output data were post-processed in ArcInfo 9.3.1 software to achieve a high-quality cartographic presentation. Experimental modelling was conducted for situations from 26 November 2011, 25 May 2012, and 26 May 2012, based on a limited number of field measurements and using parameters of the atmosphere boundary layer derived from the aerological surveys provided by the closest meteorological stations. The model was run in a 100-m and 250-m spatial resolution. In order to verify the model's performance, leave-one-out cross-validation was used. The calculated indices allowed for a comparison with results of former studies pertaining to WindStation's performance. The experiment demonstrated very subtle differences between results in using DTED or GLS DEM elevation data. Additionally, CLC 2006 roughness data provided more noticeable improvements in the model's performance, but only in the resolution corresponding to the original roughness data. The best input data configuration resulted in the following mean values of error measure: root mean squared error of velocity = 1.0 m/s and mean absolute error of direction = 30°. The author concludes that, within specific meteorological conditions (relatively strong and constant synoptic forcing) and using the aforementioned input data, the Canyon model provides fairly acceptable results. Similarly, the quality of the presented remote sensing data is suitable for wind velocity modelling in the proposed resolution. However, CLC 2006 land use data should be first verified with a higher-resolution satellite or aerial imagery.

Jancewicz, Kacper

2014-06-01

166

Horizontal forward-motion velocities of terrestrial dust devils, comparison with ambient winds, and application to Mars  

NASA Astrophysics Data System (ADS)

Dust devils are convective vortices made visible by the dust and debris they entrain. They are most common in arid environments and have been observed on Earth and Mars. Martian dust devils have been identified both in images taken at the surface and in remote sensing observations from orbiting spacecraft. Observations from orbiting instruments that can acquire multiple images in rapid succession (e.g. the ESA Mars Express High Resolution Stereo Camera) have allowed the translational forward motion of dust devils to be calculated: martian dust devils travel across the landscape at speeds of up to tens of metres per second. However, it is unclear how these velocities relate to the local ambient wind conditions, as on Earth only anecdotal evidence exists that ties dust devil forward motion with local wind speed. If dust devil translational velocity can be reliably correlated to local winds, observations of dust devils could provide a proxy for wind speed measurements on Mars, and hence provide an important tool for testing mesoscale climate models. Here we present results from a field study of terrestrial dust devils performed in the southwest USA that seeks to measure dust devil horizontal velocity as a function of wind speed. We acquired stereo images of several hundred active dust devils and hence produced multiple size and position measurements for each dust devil. We used these data to calculate dust devil translational velocity. The dust devils we measured were within a study area bounded by three 10m meteorology towers. Hence we were able to correlate dust devil speed and direction with the local ambient wind speed and direction. We found that instantaneous dust devil translational velocity correlated well with instantaneous local ambient wind velocity. Day-averaged dust devil translational velocity correlated very well with day-averaged (between 11am and 5pm) ambient wind velocity. We found that dust devil horizontal speed is about 1.2 times the ambient 10 m height wind speed. If a similar methodology and result can be applied on Mars then we suggest that dust devils can indeed be used there as proxy measurements for local wind speed.

Balme, M. R.; Pathare, A.; Metzger, S.; Renno, N. O.; Towner, M.; Spiga, A.; Fenton, L. K.; Michaels, T. I.; Saca, F.; Elliott, H. M.

2011-12-01

167

Solar Wind Speed and Expansion Rate of the Coronal Magnetic Field in Solar Maximum and Minimum Phases  

NASA Astrophysics Data System (ADS)

Relationships between solar wind speed and expansion rate of the coronal magnetic field have been studied mainly by in-ecliptic observations of artificial satellites and some off-ecliptic data by Ulysses. In this paper, we use the solar wind speed estimated by interplanetary scintillation (IPS) observations in the whole heliosphere. Two synoptic maps of SWS estimated by IPS observations are constructed for two Carrington rotations CR 1830 and 1901; CR 1830 starting on the 11th of June, 1990 is in the maximum phase of solar activity cycle and CR 1901 starting on the 29th of September, 1995 is in the minimum phase. Each of the maps consist of 64800 (360×180) data points. Similar synoptic maps of expansion rate of the coronal magnetic field (RBR) calculated by the so-called `potential model' are also constructed under a radial field assumption for CR 1830 and CR1901. Highly significant correlation (r=-0.66) is found between the SWS and the RBR during CR1901 in the solar minimum phase; that is, high-speed winds emanate from photospheric areas corresponding to low expansion rate of the coronal magnetic field and low speed winds emanate from photospheric areas of high expansion rate. A similar result is found during CR 1830 in solar maximum phase, though the correlation is relatively low (r=-0.29). The correlation is improved when both the data during CR 1830 and CR 1901 are used together; the correlation coefficient becomes -0.67 in this case. These results suggest that the correlation analysis between the SWS and the RBR can be applied to estimate the solar wind speed from the expansion rate of the coronal magnetic field, though the correlation between them may depend on the solar activity cycle. We need further study of correlation analysis for the entire solar cycle to get an accurate empirical equation for the estimation of solar wind speed. If the solar wind speed is estimated successfully by an empirical equation, it can be used as an initial condition of a solar wind model for space weather forecasts.

Hakamada, Kazuyuki; Kojima, Masayoshi; Tokumaru, Munetoshi; Ohmi, Tomoaki; Yokobe, Atsushi; Fujiki, Ken'ichi

2002-05-01

168

Measuring air-sea gas exchange velocities in a large scale annular wind-wave tank  

NASA Astrophysics Data System (ADS)

In this study we present gas exchange measurements conducted in a large scale wind-wave tank. Fourteen chemical species spanning a wide range of solubility (dimensionless solubility, ? = 0.4 to 5470) and diffusivity (Schmidt number in water, Scw = 594 to 1194) were examined under various turbulent (u10 = 0.8 to 15 m s-1 conditions. Additional experiments were performed under different surfactant modulated (two different concentration levels of Triton X-100) surface states. This paper details the complete methodology, experimental procedure and instrumentation used to derive the total transfer velocity for all examined tracers. The results presented here demonstrate the efficacy of the proposed method, and the derived gas exchange velocities are shown to be comparable to previous investigations. The gas transfer behaviour is exemplified by contrasting two species at the two solubility extremes, namely nitrous oxide (N2O) and methanol (CH3OH). Interestingly, a strong transfer velocity reduction (up to a factor of three) was observed for N2O under a surfactant covered water surface. In contrast, the surfactant affected CH3OH, the high solubility tracer only weakly.

Mesarchaki, E.; Kräuter, C.; Krall, K. E.; Bopp, M.; Helleis, F.; Williams, J.; Jähne, B.

2014-06-01

169

The microscopic state of the solar wind: Links between composition, velocity distributions, waves and turbulence  

NASA Technical Reports Server (NTRS)

An overview is given of the microscopic state of the solar wind with emphasis on recent Ulysses high-latitude observations and previous Helios in-ecliptic observations. The possible links between composition, ionization state. velocity distribution functions of electrons, protons and heavy ions. kinetic plasma waves and MHD-scale turbulence are elaborated. Emphasis is placed on a connection of interplanetary kinetic-scale phenomena with their generating microscopic processes in the corona. The fast streams seem to consist of mesoscale pressure-balanced plasma filaments and magnetic flux tubes, reminiscent of the supergranular-size structures building the open corona, from which copious Alfven waves emanate. The wind from the magnetically structured and active corona shows developed compressive turbulence and considerable abundance and ionization state variations. Some modelling attempts to explain the observed element fractionation are briefly reviewed. The causes of the nonthermal particle features. such as proton-ion differential streaming, ion beams. temperature anisotropies, and skewed distributions associated with collisionless heat conduction, are ultimately to be searched in the fact, that the corona is never quiescent but fundamentally variable in space and time. Consequently, the radial evolution of the internal state of the wind resembles at all latitudes a complicated relaxation process, in the course of which the free (in comparison with LTE conditions) particle kinetic energy is converted into plasma waves and MHD turbulence on a wide range of scales. This leads to intermittent wave-particle interactions and unsteady anomalous transport, mixed with the weak effects of the rare Coulomb collisions. Spherical expansion and large-scale inhomogeneity forces the wind to attain microscopically a complex internal state of dynamic statistical equilibrium.

Marsch, E.

1995-01-01

170

Calibration of the maximum carboxylation velocity (vcmax) for the Caatinga for use in dynamic global vegetation models (DGVMs)  

NASA Astrophysics Data System (ADS)

The Caatinga biome in the semi-arid region of northeastern Brazil is extremely important due to its biodiversity and endemism. This biome, which is under high anthropogenic influences, presents high levels of environmental degradation, land use being among the main causes of such degradation. The simulations of land cover and the vegetation dynamic under different climate scenarios are important features for prediction of environmental risks and determination of sustainable pathways for the planet in the future. Modeling of the vegetation can be performed by use of dynamic global vegetation models (DGVMs). The DGVMs simulate the surface processes (e.g. transfer of energy, water, CO2 and momentum); plant physiology (e.g. photosynthesis, stomatal conductance) phenology; gross and net primary productivity, respiration, plant species classified by functional traits; competition for light, water and nutrients, soil characteristics and processes (e.g. nutrients, heterotrophic respiration). Currently, most of the parameters used in DGVMs are static pre-defined values, and the lack of observational information to aid choosing the most adequate values for these parameters is particularly critical for the semi-arid regions in the world. Through historical meteorological data and measurements of carbon assimilation we aim to calibrate the maximum carboxylation velocity (Vcmax), for the native species Poincianella microphylla, abundant in the Caatinga region. The field data (collected at Lat: 90 2' S, Lon: 40019' W) displayed two contrasting meteorological conditions, with precipitations of 16 mm and 104 mm prior to the sampling campaigns (April 9-13, 2012 and February 4-8, 2013; respectively). Calibration (obtaining values of Vcmax more suitable for vegetation of Caatinga) has been performed through an algorithm of pattern recognition: Classification And Regression Tree (CART) and calculation of the vapor pressure deficit (VPD), which was used as attribute for discrimination of data. CART can be utilized for classification or regression, being used in the context of this work for non-linear regression. Our results show that CART algorithm correctly classified data according to the two contrasting periods (i.e. correctly distinguished assimilation data measured during drier or rainy periods), and suggest average Vcmax values of 14.2 ?mol CO2 m-2 s-1 for the drier period and of 102.5 ?mol CO2 m-2 s-1 for the rainy period. Comparing the values obtained in this work with values obtained through a traditional parameter optimization technique, it is possible to gauge pros and cons of such a combination of field measurements and machine learning technique.

Rezende, L. C.; Arenque, B.; von Randow, C.; Moura, M. S.; Aidar, S. D.; Buckeridge, M. S.; Menezes, R.; Souza, L. S.; Ometto, J. P.

2013-12-01

171

Maximum velocity of shortening in relation to myosin isoform composition in single fibres from human skeletal muscles.  

PubMed Central

1. Maximum velocity of shortening (Vmax) and compositions of myosin heavy chain (MHC) and myosin light chain (MLC) isoforms were determined in single fibres from the soleus or the lateral region of the quadriceps (vastus lateralis) muscles in man. Muscle samples were obtained by percutaneous biopsy, and membranes were permeabilized by glycerol treatment (chemical skinning) or by freeze-drying. 2. Types I, IIA and IIB MHCs were resolved from single fibre segments by 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and five different fibre types were identified: fibres containing type I MHC, types I and IIA MHCs, type IIA MHC, types IIA and IIB MHCs, and type IIB MHC. Only a few fibres co-expressed types I and IIA MHCs but 28% of all quadriceps fibres expressed both IIA and IIB MHCs in variable proportions. Fibres co-expressing types I and IIB MHCs were not found. 3. Alkali (MLC1 and MLC3) and dithio nitrobenzoic acid (DTNB) (MLC2) myosin light chains were observed in all type II fibres in variable proportions. MLC (MLC1s and MLC2s) isoforms from type I fibres had lower migration rates than the corresponding isoforms from type II fibres (MLC1f and MLC2f). More than half of type I fibres in both soleus (65%) and quadriceps (68%) muscles also expressed 'fast' MLC3 and 36% of the type II fibres from quadriceps muscle expressed the slow isoform of MLC2. 4. Differences were observed in some mechanical characteristics of freeze-dried versus chemically skinned fibres. Maximum tension (P0) and specific tension were lower in freeze-dried types I and IIA fibres than in chemically skinned, while no differences were observed in the IIA/B fibres. The numbers of types I/IIA and IIB fibres were too low to allow statistical comparisons. In chemically skinned fibres, mean specific tension (0.20 +/- 0.01 N/mm2) did not vary with fibre type. In freeze-dried fibres, on the other hand, specific tensions varied according to MHC type: higher (P < 0.01) specific tensions were observed in types IIB (0.19 +/- 0.01 N/mm2) and type IIA/B fibres (0.18 +/- 0.04 N/mm2) than in type I fibres (0.12 +/- 0.02 N/mm2). The specific tension of type IIA fibres (0.12 +/- 0.05 N/mm2) did not differ significantly from the other fibre types. Cross-sectional areas and mean Vmax did not differ between freeze-dried and chemically skinned fibres, either when all fibres were pooled or within respective fibre types. Vmax data from all fibres of a given type, irrespective of membrane permeabilization technique, have therefore been pooled.(ABSTRACT TRUNCATED AT 400 WORDS) Images Fig. 1 Fig. 2 Fig. 6

Larsson, L; Moss, R L

1993-01-01

172

Wind tunnel investigation of the effect of high relative velocities on the structural integrity of birds  

NASA Technical Reports Server (NTRS)

An experimental investigation was conducted in a supersonic wind tunnel to determine the effect a sudden high velocity headwind had on the physical deformation and structural breakup characteristics of birds. Several sizes of recently killed birds were dropped into the test section at free-stream Mach numbers ranging from 0.2 to 0.8 and photographed with high-speed motion-picture cameras. These conditions simulated flow conditions encountered when birds are ingested into the inlets of high speed aircraft, thereby constituting a safety hazard to the aircraft and its occupants. The investigation shows that, over the range of headwind conditions tested, the birds remained structurally intact and did not suffer any appreciable deformation or structural breakup.

Bresnahan, D. L.

1972-01-01

173

A New Forecasting Index for Solar Wind Velocity Based on EIT 284 Å Observations  

NASA Astrophysics Data System (ADS)

Various solar wind forecasting methods have been developed during the past decade, such as the Wang Sheeley model and the Hakamada Akasofu Fry Version 2 (HAFv2) model. Also, considerable correlation has been found between the solar wind speed v and the coronal hole (CH) area A M on the visible side of the Sun, showing quantitative improvement of forecasting accuracy in low CME activity periods ( e.g., Vršnak, Temmer, and Veronig, Solar Phys. 240, 315, 2007a). Properties of lower layers of the solar atmosphere are good indications of the subsequent interplanetary and geomagnetic activities. We analyze the SOHO/EIT 284 Å images and construct a new forecasting factor (Pch) from the brightness of the solar EUV emission, and a good correlation is found between the Pch factor and the 3-day-lag solar wind velocity ( v) probed by the ACE spacecraft. The main difference between the Pch and A M factor is that Pch does not depend on the CH-boundary estimate and can reflect both the area and brightness of CH. A simple method of forecasting the solar wind speed near Earth in low CME activity periods is presented. Between Pch and v from 21 November until 26 December 2003, the linear correlation coefficient is R=0.89. For comparison we also analyze the data in the same period (DOY 25 125, 2005) as Vršnak, Temmer, and Veronig ( Solar Phys. 240, 315, 2007a), who used the CH areas A M for predicting the solar wind parameters. In this period the correlation coefficient between Pch and v is R=0.70, whereas for A M and v the correlation coefficient is R=0.62. The average relative difference between the calculated and the observed values is overline{|?|}? 12.15% . Furthermore, for the ten peaks during the analysis period, Pch and v show a correlation coefficient of R=0.78, and the average relative difference between the calculated and the observed peak values is overline{|?|}? 5.83% . Moreover, the Pch factor can eliminate personal bias in the forecasting process, which existed in the method using CH area as input parameter, because CH area depends on the CH-boundary estimate but Pch does not. Until now the CH-boundary could not be easily determined since no quantitative criteria can be used to precisely locate CHs from observations, which led to differences in forecasting accuracy.

Luo, Bingxian; Zhong, Qiuzhen; Liu, Siqing; Gong, Jiancun

2008-07-01

174

Measurement of the horizontal velocity of wind perturbations in the middle atmosphere by spaced MF radar systems  

NASA Technical Reports Server (NTRS)

Two remote receiving sites have been set up at a distance of approx 40 km from the main MF radar system. This allows measurement of upper atmosphere winds from 60-120 km (3 km resolution) at the corners of an approximately equilateral triangle of side approx 20 km. Some preliminary data are compared through cross correlation and cross spectral analysis in an attempt to determine the horizontal velocity of wind perturbations and/or the horizontal wavelength and phase velocity of gravity waves.

Meek, C. E.; Manson, A. H.; Smith, M. J.

1983-01-01

175

AXAOTHER XL -- A spreadsheet for determining doses for incidents caused by tornadoes or high-velocity straight winds  

SciTech Connect

AXAOTHER XL is an Excel Spreadsheet used to determine dose to the maximally exposed offsite individual during high-velocity straight winds or tornado conditions. Both individual and population doses may be considered. Potential exposure pathways are inhalation and plume shine. For high-velocity straight winds the spreadsheet has the capability to determine the downwind relative air concentration, however for the tornado conditions, the user must enter the relative air concentration. Theoretical models are discussed and hand calculations are performed to ensure proper application of methodologies. A section has also been included that contains user instructions for the spreadsheet.

Simpkins, A.A.

1996-09-01

176

Application of ``POLIS'' PIV system for measurement of velocity fields in a supersonic flow of the wind tunnels  

NASA Astrophysics Data System (ADS)

Measurement results on the mean velocity fields and fields of velocity pulsations in the supersonic flows obtained by means of the PIV measurement set “POLIS” are presented. Experiments were carried out in the supersonic blow-down and stationary wind tunnels at the Mach numbers of 4.85 and 6. The method of flow velocity estimate in the test section of the blow-down wind tunnel was grounded by direct measurements of stagnation pressure in the setup settling chamber. The size of tracer particles introduced into the supersonic flow by a mist generator was determined; data on the structure of pulsating velocity in a track of an oblique-cut gas-dynamic whistle were obtained under the conditions of self-oscillations.

Akhmetbekov, Y. K.; Bilsky, A. V.; Markovich, D. M.; Maslov, A. A.; Polivanov, P. A.; Tsyryul'Nikov, I. S.; Yaroslavtsev, M. I.

2009-09-01

177

Swimming performance of delta smelt: maximum performance, and behavioral and kinematic limitations on swimming at submaximal velocities.  

PubMed

Swimming performance, measured as critical swimming velocity (Ucrit) and endurance, and swimming behavior and kinematics were measured in delta smelt Hypomesus transpacificus, a threatened estuarine planktivore. Most fish (58 % of the Ucrit test group) were capable of achieving and sustaining moderately high velocities: mean Ucrit was 27.6±5.1 cm s-1 (s.d.). Ucrit was not affected by either acclimation temperature (12­21 °C) or fish size (3.2­6.8 cm standard length) and was generally comparable with values measured for other similarly sized fishes. The remaining 42 % of the fish failed to swim at velocities above 10­15 cm s-1. Interestingly, of the fish that provided a Ucrit measurement, 62 % experienced at least one temporary swimming failure between 10 and 20 cm s-1. Endurance was highly variable and, for all velocities, not normally distributed; the only significant decrease, from 6 h to 64 min, occurred between 10 and 15 cm s-1. Kinematic analyses of stroke frequency, stroke amplitude, stride length, glide frequency, glide duration, proportion of time spent stroking and the number of strokes between successive glides showed that delta smelt employed three velocity-dependent swimming gaits: a discontinuous 'stroke-and-glide' swimming behavior below 10 cm s-1; a continuous swimming behavior above 15 cm s-1 and up to Ucrit; and a discontinuous 'burst-and-glide' swimming behavior at velocities above Ucrit. Swimming failure at velocities between 10 and 20 cm s-1 coincided with the transition from 'stroke-and-glide' swimming to continuous swimming; delta smelt were unable or unwilling to swim steadily in the flume within this transition velocity range. These results underscore the importance of monitoring and quantifying behavior in experiments intended as physiological performance tests of whole animals. PMID:9427668

Swanson; Young; j

1998-01-01

178

Mass-loss from dusty, low outflow-velocity AGB stars. I. Wind structure and mass-loss rates  

NASA Astrophysics Data System (ADS)

We present the first results of a CO(2-1), (1-0), and 86 GHz SiO maser survey of AGB stars, selected by their weak near-infrared excess. Among the 65 sources of the present sample we find 10 objects with low CO outflow velocities, vexp <~ 5 km s-1. Typically, these sources show (much) wider SiO maser features. Additionally, we get 5 sources with composite CO line profiles, i.e. a narrow feature is superimposed on a broader one, where both components are centered at the same stellar velocity. The gas mass-loss rates, outflow velocities and velocity structures suggested by these line profiles are compared with the results of hydrodynamical model calculations for dust forming molecular winds of pulsating AGB stars. The observations presented here give support to our recent low outflow-velocity models, in which only small amounts of dust are formed. Therefore, the wind generation in these models is dominated by stellar pulsation. We interpret the composite line profiles in terms of successive winds with different characteristics. Our hydrodynamical models, which show that the wind properties may be extremely sensitive to the stellar parameters, support such a scenario. Based on observations obtained at the European Southern Observatory, La Silla, Chile and at the IRAM, Pico Veleta, Spain.

Winters, J. M.; Le Bertre, T.; Jeong, K. S.; Nyman, L.-Å.; Epchtein, N.

2003-10-01

179

CO2 Doppler lidar measurement of wind velocity and relative backscatter associated with the nocturnal boundary layer  

Microsoft Academic Search

Heterodyne CO2 Doppler lidar measurements of horizontal wind velocity from the surface to 11,000 feet AGL using the Velocity Azimuth Display (VAD) method were made at Holloman AFB, NM from the end of July through mid-August 1998. These data were entered real-time into the space maneuver vehicle descent analysis program to make flight performance predictions needed for test decisions. Daily

John R. Roadcap; Patrick J. McNicholl; Mitchell H. Laird; Robert A. Swirbalus

1999-01-01

180

Effect of maximum torque according to the permanent magnet configuration of a brushless dc motor with concentrated winding  

NASA Astrophysics Data System (ADS)

A brushless dc (BLDC) motor, which has a permanent magnet (PM) component, is a potential candidate for hybrid or electric vehicle applications. Minimizing the BLDC motor size is an important requirement for application. This requirement is usually satisfied by adopting a high performance permanent magnet or improved winding methods. The PM configuration is also a critical point in design. This article presents the effect of the PM configuration on motor performance, especially the maximum torque. Four representative BLDC motor types are analytically investigated under the condition that the volume of the PM and magnetic material is constant. An embedded interior permanent magnet motor has the best torque performance the maximum torque of which is more than 1.5 times larger than that of the surface mounted permanent magnet motor. The performance of back electromotive force, instantaneous torques is also investigated.

Lee, Kab-Jae; Kim, Sol; Lee, Ju; Oh, Jae-Eung

2003-05-01

181

Investigation on the impact of the environment wind velocity on the indirect air-cooling tower performance  

NASA Astrophysics Data System (ADS)

The wind velocity plays a crucial role in the operation characteristic of indirect cooling tower. In this paper a 2×330MW vertical arrangement indirect air-cooled system was taken as research object, and numerical simulation method was used to analyze the relative influence of the wind speed, ranging from 4m/s to 18m/s, on the outlet water temperature of cooling tower, the outlet air temperature of radiator, the facing wind speed of the fan segment and on the outlet air speed of the cooling tower. The result shows that the impact of the natural wind speed on the cooling tower efficiency varies greatly and this impact increases as the wind speed increases.

Qin, Yongbo; Gu, Hongfang; Wang, Haijun; Chen, Guoyong

2013-07-01

182

Conditional Maximum Covariance Analysis and Its Application to the Tropical Indian Ocean SST and Surface Wind Stress Anomalies(.  

NASA Astrophysics Data System (ADS)

This study introduces the conditional maximum covariance analysis (CMCA). The normal maximum covariance analysis (MCA) is a method that isolates the most coherent pairs of spatial patterns and their associated time series by performing an eigenanalysis on the temporal covariance matrix between two geophysical fields. Different from the normal MCA, the CMCA not only isolates the most coherent patterns between two fields but also excludes the unwanted signal by subtracting the regressed value of each employed field that depends on the unwanted signal.To evaluate the usefulness of the CMCA, it is applied to the tropical Indian Ocean sea surface temperature and surface wind stress anomalies, from which the El Niño-Southern Oscillation (ENSO) signal is removed. Results show that the first mode of the CMCA represents an east-west contrast pattern in SST and a monopole pattern in the zonal wind stress centered at the equatorial central Indian Ocean. The corresponding expansion coefficients are completely uncorrelated with the ENSO index. On the other hand, in the normal MCA, the expansion coefficients are correlated with both the ENSO index and the Indian Ocean east-west contrast pattern index. Thus, the CMCA method effectively detected the coherent patterns induced by the local air-sea interaction without the ENSO signal considered as an external factor, whereas the normal MCA detected the coherent patterns, but the effects of local and external factors cannot be separated.

An, Soon-Il

2003-09-01

183

Maximum power point tracking control and voltage regulation of a DC grid-tied wind energy conversion system based on a novel permanent magnet reluctance generator  

Microsoft Academic Search

This research paper aims to employ a new permanent magnet reluctance generator in a variable speed wind energy conversion system (WECS) of a grid-tied distributed generation application. The grid integration of WECS is achieved through cascaded dc-dc converters ensuring maximum power extraction from the wind energy while maintaining a constant output voltage at the grid side. The surplus power is

Kazmi Syed Muhammad Raza; Hiroki Goto; Hai-Jiao Guo; Osamu Ichinokura

2007-01-01

184

A neural network study of the mapping from solar magnetic fields to the daily average solar wind velocity  

Microsoft Academic Search

Predictions of the daily solar wind velocity (V) at 1 AU from the flux tube expansion factor fs are examined with radial basis function neural networks. The flux tube expansion factor is calculated from the potential field model, using Wilcox Solar Observatory magnetograms, with the source surface placed at 2.5 solar radii. The time series extend over 20 years from

Peter Wintoft; Henrik Lundstedt

1999-01-01

185

On the temperature anisotropy of the core part of the proton velocity distribution function in the solar wind  

Microsoft Academic Search

In this paper we analyze the temperature anisotropy of velocity distribution functions (VDFs) of protons measured by the Helios spacecraft in fast solar wind. We concentrate on data obtained during the primary mission, including the first perihelion passage, of Helios 2 in a distance range between 0.98 and 0.29 AU for the days 23 through 114 of the year 1976.

E. Marsch; X.-Z. Ao; C.-Y. Tu

2004-01-01

186

An Estimate of Solar Wind Velocity Profiles in a Coronal Hole and Coronal Streamer Area (6-40R)  

NASA Technical Reports Server (NTRS)

Using the total electron content data obtained by the Ulysses Solar Corona Experiment during the first solar conjunction in summer 1991 (Bird et al., 1994), an estimate is presented of solar wind velocity profiles in a coronal hole and a coronal streamer area in the range between 6 and 40 solar radii.

Patzold, M.; Tsurutani, B. T.; Bird, M. K.

1995-01-01

187

Wavelength dependence of coherent and incoherent satellite-based lidar measurements of wind velocity and aerosol backscatter  

NASA Technical Reports Server (NTRS)

The results are presented of a capability study of Earth orbiting lidar systems, at various wavelengths from 1.06 to 10.6 microns, for the measurement of wind velocity and aerosol backscatter, and for the detection of clouds. Both coherent and incoherent lidar systems were modeled and compared for the aerosol backscatter and cloud detection applications.

Kavaya, M. J.; Huffaker, R. M.

1986-01-01

188

A Semiempirical Determination of the Wind Velocity Structure for the Hybrid-Chromosphere Star alpha Trianguli Australis  

NASA Astrophysics Data System (ADS)

We have used the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope to study the wind of the hybrid-chromosphere star ? TrA (K4 II). The stellar wind produces significant absorption at negative radial velocities in the chromospheric Mg II resonance lines (h and k). Spectra obtained with the GHRS echelle high-resolution grating (4A 85,000) on 1993 February 10 and 1994 May 1 reveal complex interstellar absorption in the Mg II emission lines and a high-velocity wind absorption feature centered near -95 km s-1. The 1993 February observation shows an asymmetry of the Mg II emission cores, corresponding to an apparent redshift of 6.0±1.5 km s-1. We construct a simple wind model that explains several of the key observational features. The scattering of the Mg II h and k photons in a geometrically extended region dominates the observed flux near line center, which supports the assignment of the low-velocity absorption components to interstellar absorption rather than to a chromospheric self-reversal. For the 1993 February observation, the parameters for our simple wind model are as follows: terminal velocity V(?) = 100 km s-1, turbulent velocity Vturb = 24 km s-1, M? ˜ 1.8 × 1010 Msun yr-1, for a fixed value of the velocity-law parameter ? = 1 and fixed stellar radius of R* = 97 Rsun, assuming Mg II is the dominant ionization state in the flow. Our analysis of the 1994 May observation resulted in similar values for these parameters, and the mass-loss rate could be as small as M? ˜ 1.6 × 10-10 Msun yr-1. The value of ? is uncertain (? 0.3) and if ? ˜ 3.5 as found from the recent analysis of the ? Aurigae systems, M? could be larger by a factor of 3-4. A comparison of our result with numerical solutions to the momentum and conservation equations reveals that the derived velocity distribution lies within a limited region of parameter space where there is a large nonthermal pressure on the plasma close to the base of the wind consistent with previous wind models for ? TrA. Our best model fit to the two interstellar absorption components indicates a total hydrogen column density toward ? TrA of NHI = 2 × 1019 cm-2.

Harper, Graham M.; Wood, Brian E.; Linsky, Jeffrey L.; Bennett, Philip D.; Ayres, Thomas R.; Brown, Alexander

1995-10-01

189

Field measurements of horizontal forward motion velocities of terrestrial dust devils: Towards a proxy for ambient winds on Mars and Earth  

NASA Astrophysics Data System (ADS)

Dust devils - convective vortices made visible by the dust and debris they entrain - are common in arid environments and have been observed on Earth and Mars. Martian dust devils have been identified both in images taken at the surface and in remote sensing observations from orbiting spacecraft. Observations from landing craft and orbiting instruments have allowed the dust devil translational forward motion (ground velocity) to be calculated, but it is unclear how these velocities relate to the local ambient wind conditions, for (i) only model wind speeds are generally available for Mars, and (ii) on Earth only anecdotal evidence exists that compares dust devil ground velocity with ambient wind velocity. If dust devil ground velocity can be reliably correlated to the ambient wind regime, observations of dust devils could provide a proxy for wind speed and direction measurements on Mars. Hence, dust devil ground velocities could be used to probe the circulation of the martian boundary layer and help constrain climate models or assess the safety of future landing sites. We present results from a field study of terrestrial dust devils performed in the southwest USA in which we measured dust devil horizontal velocity as a function of ambient wind velocity. We acquired stereo images of more than a 100 active dust devils and recorded multiple size and position measurements for each dust devil. We used these data to calculate dust devil translational velocity. The dust devils were within a study area bounded by 10 m high meteorology towers such that dust devil speed and direction could be correlated with the local ambient wind speed and direction measurements. Daily (10:00-16:00 local time) and 2-h averaged dust devil ground speeds correlate well with ambient wind speeds averaged over the same period. Unsurprisingly, individual measurements of dust devil ground speed match instantaneous measurements of ambient wind speed more poorly; a 20-min smoothing window applied to the ambient wind speed data improves the correlation. In general, dust devils travel 10-20% faster than ambient wind speed measured at 10 m height, suggesting that their ground speeds are representative of the boundary layer winds a few tens of meters above ground level. Dust devil ground motion direction closely matches the measured ambient wind direction. The link between ambient winds and dust devil ground velocity demonstrated here suggests that a similar one should apply on Mars. Determining the details of the martian relationship between dust devil ground velocity and ambient wind velocity might require new in situ or modelling studies but, if completed successfully, would provide a quantitative means of measuring wind velocities on Mars that would otherwise be impossible to obtain.

Balme, M. R.; Pathare, A.; Metzger, S. M.; Towner, M. C.; Lewis, S. R.; Spiga, A.; Fenton, L. K.; Renno, N. O.; Elliott, H. M.; Saca, F. A.; Michaels, T. I.; Russell, P.; Verdasca, J.

2012-11-01

190

Theoretical relationship between maximum value of the post-sunset drift velocity and peak-to-valley ratio of anomaly TEC  

Microsoft Academic Search

Theoretical study of electron density distribution in the nighttime equatorial ionosphere shows that linear relationships with statistically significant correlation coefficients exist between the maximum value of the post-sunset plasma drift velocity and the peak-to-valley ratio of anomaly TEC. The study is based on the low-latitude density model of Air Force Research Laboratory (AFRL) and the obtained relationships are valid for

B. Basu; J. M. Retterer; O. de La Beaujardière; C. E. Valladares; E. Kudeki

2004-01-01

191

Covariance statistics of turbulence velocity components for wind-energy-conversion system design-homogeneous, isotropic case  

SciTech Connect

When designing a wind energy converison system (WECS), it may be necessary to take into account the distribution of wind across the disc of rotation. The specific engineering applications include structural strength, fatigue, and control. This wind distribution consists of two parts, namely that associated with the mean wind profile and that associated with the turbulence velocity fluctuation field. The work reported herein is aimed at the latter, namely the distribution of turbulence velocity fluctuations across the WECS disk of rotation. A theory is developed for the two-time covariance matrix for turbulence velocity vector components for wind energy conversion system (WECS) design. The theory is developed for homogeneous and iotropic turbulance with the assumption that Taylor's hypothesis is valid. The Eulerian turbulence velocity vector field is expanded about the hub of the WECS. Formulae are developed for the turbulence velocity vector component covariance matrix following the WECS blade elements. It is shown that upon specification of the turbulence energy spectrum function and the WECS rotation rate, the two-point, two-time covariance matrix of the turbulent flow relative to the WECS bladed elements is determined. This covariance matrix is represented as the sum of nonstationary and stationary contributions. Generalized power spectral methods are used to obtain two-point, double frequency power spectral density functions for the turbulent flow following the blade elements. The Dryden turbulence model is used to demonstrate the theory. A discussion of linear system response analysis is provided to show how the double frequency turbulence spectra might be used to calculate response spectra of a WECS to turbulent flow. Finally the spectrum of the component of turbulence normal to the WECS disc of rotation, following the blade elements, is compared with experimental results.

Fichtl, G.H.

1983-09-01

192

The Evolution of the Spectrum of Solar Wind Velocity Fluctuations from 0.3 to 5 AU  

NASA Technical Reports Server (NTRS)

Recent work has shown that at 1 AU from the Sun the power spectrum of the solar wind magnetic field has the -5/3 spectral slope expected for Kolmogorov turbulence, but that the velocity has closer to a -3/2 spectrum. This paper traces the changes in solar wind velocity spectra from 0.3 to 5 AU using data from the Helios and Ulysses spacecraft to show that this is a transient stage in solar-wind evolution. The spectrum of the velocity is found to be flatter than that of the magnetic field for the higher frequencies examined for all cases until the slopes become equal (at -5/3) well past 1 AU when the wind is relatively nonAlfvenic. In some respects, in particular in the evolution of the frequency at which the spectrum changes from flatter at larger scales to a "turbulent" spectrum at smaller scales, the velocity field evolves more rapidly than the magnetic, and this is associated with the dominance of the magnetic energy over the kinetic at "inertial range" scales. The speed of the flow is argued to be largely unrelated to the spectral slopes, consistent with previous work, whereas high Alfvenicity appears to slow the spectral evolution, as expected from theory. This study shows that, for the solar wind, the idea of a simple "inertial range" with uniform spectral properties is not realistic, and new phenomenologies will be needed to capture the true situation. It is also noted that a flattening of the velocity spectrum often occurs at small scales.

Roberts, D. Aaron

2011-01-01

193

Effect of Solar-Wind Velocity, Magnetic Field and Density on Solar Energetic Particle Transport  

NASA Astrophysics Data System (ADS)

In large gradual solar energetic particle (SEP) events, energetic protons greatly amplify ambient upstream Alfvén waves near coronal-mass-ejection (CME) driven shocks. The waves grow until they are swept downstream of the shock. The amplified waves scatter the particles and “flatten” the SEP intensity energy spectrum at low energy at 1 AU, causing the streaming limit phenomenon. Both the wave and SEP intensities maximize near the shock and fall steeply with distance upstream. The SEPs are focused by the longitudinal gradient of the magnetic field B. The wave growth rate increases with energetic proton streaming and varies as f/?(np), with f the energetic proton phase-space density and np the plasma proton number density. Thus, in addition to the SEP release rate at the shock, the environmental quantities: np(r), B(r), the solar-wind velocity Vsw(r), and the Alfvén speed VA(r) also influence SEP transport. At heliocentric distance r? 8r?, np as well as B deviate significantly from ˜ r–2, Vsw rises slowly from near zero on the photosphere, and VA peaks near 4 r?. We have generalized our SEP transport model to take account of realistic radial dependences of the above solar-wind properties down to ˜2 r? in addition to the usual processes of wave and particle transport and Alfvén wave growth. The model has been applied to STEREO A observation of the 2011 March 21 SEP event with the preliminary conclusion that wave-damping processes rather than the environmental quantities are more likely to raise the predicted proton intensity at < 5 MeV to the higher observed values.

Ng, C. K.

2014-05-01

194

Real-time approaches to the estimation of local wind velocity for a fixed-wing unmanned air vehicle  

NASA Astrophysics Data System (ADS)

Three real-time approaches to estimating local wind velocity for a fixed-wing unmanned air vehicle are presented in this study. All three methods work around the navigation equations with added wind components. The first approach calculates the local wind speed by substituting the ground speed and ascent rate data given by the Global Positioning System (GPS) into the navigation equations. The second and third approaches utilize the extended Kalman filter (EKF) and the unscented Kalman filter (UKF), respectively. The results show that, despite the nonlinearity of the navigation equations, the EKF performance is proven to be on a par with the UKF. A time-varying noise estimation method based on the Wiener filter is also discussed. Results are compared with the average wind speed measured on the ground. All three approaches are proven to be reliable with stated advantages and disadvantages.

Chan, W. L.; Lee, C. S.; Hsiao, F. B.

2011-10-01

195

Simultaneous measurements of air-sea gas transfer velocity and near surface turbulence at low to moderate winds (Invited)  

NASA Astrophysics Data System (ADS)

Parameterization of air-sea gas transfer velocity was routinely made with wind speed. Near surface turbulent dissipation rate has been shown to have better correlation with the gas transfer velocity in a variety of aquatic environments (i.e., the small eddy model) while wind speed is low to moderate. Wind speed model may underestimate gas transfer velocity at low to moderate winds when the near surface turbulence is produced by other environmental forcing. We performed a series of field experiments to measure the CO2 transfer velocity, and the statistics of turbulence immediately below the air-water interface using a novel floating PIV and chamber system. The small eddy model was evaluated and the model coefficient was found to be a non-constant, and it varies with the local turbulent level (figure 1). Measure results also suggested an appropriate scaling of the vertical dissipation profile immediately below the interface under non-breaking conditions, which can be parameterized by the wind shear, wave height and wave age (figure 2). Figure 1. Relation between the coefficient of the small eddy model and dissipation rate. The data also include Chu & Jirka (2003) and Vachon et al. (2010). The solid regression line: ? = 0.188log(?)+1.158 Figure 2. Non-dimensional dissipation profiles. Symbols: measured data with the floating PIV. Solid line: regression of measured data with a -0.79 decaying rate. Dash line with -2 slope: Terray et al. (1996) relation. Dash line with two layer structure: Siddiqui & Loewen (2007) relation.

Wang, B.; Liao, Q.; Fillingham, J. H.; Bootsma, H. A.

2013-12-01

196

Infrared recombination line profiles - A diagnostic probe of the velocity field in the S106 stellar wind  

NASA Astrophysics Data System (ADS)

The velocity profiles of the Brackett-alpha and Pfund-gamma hydrogen recombination lines towards the young exciting star of the S106 bipolar H II region are presented. Both profiles show the presence of velocities on the order of 200 km/s within the ionized circumstellar envelope. However, the respective profiles are distinctly different in shape; the Pf-gamma profile is asymmetric and possesses a strong blue wing, whereas the Br-alpha profile exhibits mirror-image symmetry with respect to the line center. It is inferred that at the higher velocities both lines are at least partially optically thick. The asymmetry in the Pf-gamma profile may arise as a result of either obscuration by the stellar photosphere or the presence of a bipolar wind geometry close to the star. It appears that a decelerating velocity law is appropriate at distances from the star where the optically thick lines originate.

Garden, R. P.; Geballe, T. R.

1986-06-01

197

REINTERPRETATION OF SLOWDOWN OF SOLAR WIND MEAN VELOCITY IN NONLINEAR STRUCTURES OBSERVED UPSTREAM OF EARTH'S BOW SHOCK  

SciTech Connect

Two of the many features associated with nonlinear upstream structures are (1) the solar wind (SW) mean flow slows down and deviates substantially and (2) the temperature of the plasma increases in the structure. In this Letter, we show that the SW beam can be present throughout the entire upstream event maintaining a nearly constant beam velocity and temperature. The decrease of the velocity is due to the appearance of new particles moving in the opposite direction that act against the SW beam and reduce the mean velocity as computed via moments. The new population, which occupies a larger velocity space, also contributes to the second moment, increasing the temperature. The new particles include the reflected SW beam at the bow shock and another population of lower energies, accelerated nearby at the shock or at the boundary of the nonlinear structures.

Parks, G. K.; Lin, N. [Space Sciences Laboratory, University of California, Berkeley, CA (United States); Lee, E.; Hong, J. [School of Space Research, Kyung Hee University, Yongin, Gyeonggi (Korea, Republic of); Fu, S. Y. [School of Earth and Space Sciences, Peking University, Beijing (China); McCarthy, M. [Earth and Space Sciences, University of Washington, Seattle, WA (United States); Cao, J. B. [Beijing University of Aeronautics and Astronautics, 100190, Beijing (China); Liu, Y.; Shi, J. K. [Space Weather, National Space Science Center, Beijing (China); Goldstein, M. L. [NASA, Goddard Space Flight Center, Greenbelt, MD (United States); Canu, P. [Laboratory for Plasma Physics, Ecole Polytechnique, Paris (France); Dandouras, I. [CNRS, IRAP, 9 Ave. Colonel Roche, Toulouse (France); Reme, H., E-mail: parks@ssl.berkeley.edu [CNRS, IRAP, University of Toulouse, UPS-OMP, Toulouse (France)

2013-07-10

198

Effects of errors in velocity tilt on maximum longitudinal compression during neutralized drift compression of intense beam pulses: I. general description  

NASA Astrophysics Data System (ADS)

Neutralized drift compression offers an effective means for particle beam pulse compression and current amplification. In neutralized drift compression, a linear longitudinal velocity tilt (head-to-tail gradient) is applied to the non-relativistic beam pulse, so that the beam pulse compresses as it drifts in the focusing section. The beam current can increase by more than a factor of 100 in the longitudinal direction. We have performed an analytical study of how errors in the velocity tilt acquired by the beam in the induction bunching module limit the maximum longitudinal compression. It is found that the compression ratio is determined by the relative errors in the velocity tilt. That is, one-percent errors may limit the compression to a factor of one hundred. However, a part of the beam pulse where the errors are small may compress to much higher values, which are determined by the initial thermal spread of the beam pulse. It is also shown that sharp jumps in the compressed current density profile can be produced due to overlaying of different parts of the pulse near the focal plane. Examples of slowly varying and rapidly varying errors compared to the beam pulse duration are studied. For beam velocity errors given by a cubic function, the compression ratio can be described analytically. In this limit, a significant portion of the beam pulse is located in the broad wings of the pulse and is poorly compressed. The central part of the compressed pulse is determined by the thermal spread. The scaling law for maximum compression ratio is derived. In addition to a smooth variation in the velocity tilt, fast-changing errors during the pulse may appear in the induction bunching module if the voltage pulse is formed by several pulsed elements. Different parts of the pulse compress nearly simultaneously at the target and the compressed profile may have many peaks. The maximum compression is a function of both thermal spread and the velocity errors. The effects of the finite gap width of the bunching module on compression are analyzed analytically.

Kaganovich, Igor D.; Massidda, Scott; Startsev, Edward A.; Davidson, Ronald C.; Vay, Jean-Luc; Friedman, Alex

2012-06-01

199

Maximum drift velocity of electrons in selectively doped InAlAs/InGaAs/InAlAs heterostructures with InAs inserts  

SciTech Connect

The dependence of the electron mobility and drift velocity on the growth conditions, thickness, and doping of an InAs insert placed at the center of the quantum well in a selectively doped InAlAs/InGaAs/InAlAs heterostructure has been investigated. Record enhancement of the maximum drift velocity to (2-4) Multiplication-Sign 10{sup 7} cm/s in an electric field of 5 Multiplication-Sign 10{sup 3} V/cm has been obtained in a 17-nm-wide quantum well with an undoped 4-nm-thick InAs insert. In the structures with additional doping of the InAs insert, which facilitates an increase in the density of electrons in the quantum well to 4.0 Multiplication-Sign 10{sup 12} cm{sup -2}, the maximum drift velocity is as high as 2 Multiplication-Sign 10{sup 7} cm/s in an electric field of 7 Multiplication-Sign 10{sup 3} V/cm.

Silenas, A.; Pozela, Yu., E-mail: pozela@pfi.lt; Pozela, K.; Juciene, V. [Center for Physical Sciences and Technology, Semiconductor Physics Institute (Lithuania); Vasil'evskii, I. S.; Galiev, G. B.; Pushkarev, S. S.; Klimov, E. A. [Russian Academy of Sciences, Institute of Microwave Semiconductor Electronics (Russian Federation)

2013-03-15

200

Vegetation as an Indicator of High Wind Velocity: Phase I. Final Report.  

National Technical Information Service (NTIS)

The objective of this study is to develop methods of using wind deformed vegetation for the selection of optimum sites for utilization of wind energy. Five different indices of wind effects on trees have been developed and are presently being calibrated i...

E. W. Hewson J. E. Wade R. W. Baker

1977-01-01

201

A wind tunnel study of turbulent flow around single and multiple windbreaks, part I: Velocity fields  

Microsoft Academic Search

This paper describes wind-tunnel experiments on the flow around single and multiple porous windbreaks (height H), sheltering a model plant canopy (height H\\/3). The mean wind is normal to the windbreaks, which span the width of the wind tunnel. The incident turbulent flow simulates the adiabatic atmospheric surface layer. Five configurations are examined: single breaks of three solidities (low, medium,

M. J. Judd; M. R. Raupach; J. J. Finnigan

1996-01-01

202

The effect of wind velocity on transpiration in a mixed broadleaved deciduous forest  

NASA Astrophysics Data System (ADS)

Wind velocity (U) within and above forest canopies can alter the coupling between the vapor-saturated sub-stomatal airspace and the drier atmosphere aloft, thereby influencing transpiration rates. In practice, however, the actual increase in transpiration with increasing U depends on the aerodynamic resistance (RA) to vapor transfer compared to canopy resistance to water vapor flux out of leaves (RC, dominated by stomatal resistance, Rstom), and the rate at which RA decreases with increasing U. We investigated the effect of U on transpiration at the canopy scale using filtered meteorological data and sap flux measurements gathered from six diverse species of a mature broadleaved deciduous forest. Only under high light conditions, stand transpiration (EC) increased slightly (6.5%) with increasing U ranging from ~0.7 to ~4.7 m s-1. Under other conditions, sap flux density (Js) and EC responded weakly or did not change with U. RA, estimated from Monin-Obukhov similarity theory, decreased with increasing U, but this decline was offset by increasing RC, estimated from a rearranged Penman-Monteith equation, due to a concurrent increase in vapor pressure deficit (D). The increase of RC with D over the observed range of U was consistent with increased Rstom by ~40% based on hydraulic theory. Except for very rare half-hourly values, the proportion of RA to total resistance (RT) remained < 15% over the observed range of conditions. These results suggest that in similar forests and conditions, accounting for the effects of U-D relationship on Rstom would reduce the uncertainty of modeling canopy gas exchange more than accounting for the direct effect of U on RA.

Kim, D.; Oren, R.; Oishi, A. C.; Hsieh, C.; Phillips, N. G.; Novick, K. A.; Stoy, P. C.

2013-12-01

203

A Wind Tunnel Investigation of the Rate of Evaporation of Small Water Drops Falling at Terminal Velocity in Air  

Microsoft Academic Search

An experimental study of the effect of ventilation on the rate of evaporation of small water drops falling at terminal velocity in air has been carried out in a wind tunnel where water drops could he suspended freely in the tunnel airstream. For Reynolds numbers NRe2 it was found that the Sherwood number NSh was linearly related to NRe1\\/2NI, in

K. V. Beard; H. R. Pruppacher

1971-01-01

204

A Determination of the Terminal Velocity and Drag of Small Water Drops by Means of a Wind Tunnel  

Microsoft Academic Search

Measurements of the drag on small water drops falling in water-saturated air at terminal velocity were carried out in a wind tunnel for Reynolds numbers R between 0.2 and 200. The fractional deviation (D\\/Ds) 1 of the actual drag D from the Stokes drag Ds was determined as a function of R and empirical formulae for (D\\/Ds) 1 were derived

K. V. Beard; H. R. Pruppacher

1969-01-01

205

Critical wind velocity for arresting upwind gas and smoke dispersion induced by near-wall fire in a road tunnel.  

PubMed

In case of a tunnel fire, toxic gas and smoke particles released are the most fatal contaminations. It is important to supply fresh air from the upwind side to provide a clean and safe environment upstream from the fire source for people evacuation. Thus, the critical longitudinal wind velocity for arresting fire induced upwind gas and smoke dispersion is a key criteria for tunnel safety design. Former studies and thus, the models built for estimating the critical wind velocity are all arbitrarily assuming that the fire takes place at the centre of the tunnel. However, in many real cases in road tunnels, the fire originates near the sidewall. The critical velocity of a near-wall fire should be different with that of a free-standing central fire due to their different plume entrainment process. Theoretical analysis and CFD simulation were performed in this paper to estimate the critical velocity for the fire near the sidewall. Results showed that when fire originates near the sidewall, it needs larger critical velocity to arrest the upwind gas and smoke dispersion than when fire at the centre. The ratio of critical velocity of a near-wall fire to that of a central fire was ideally estimated to be 1.26 by theoretical analysis. Results by CFD modelling showed that the ratio decreased with the increase of the fire size till near to unity. The ratio by CFD modelling was about 1.18 for a 500kW small fire, being near to and a bit lower than the theoretically estimated value of 1.26. However, the former models, including those of Thomas (1958, 1968), Dangizer and Kenndey (1982), Oka and Atkinson (1995), Wu and Barker (2000) and Kunsch (1999, 2002), underestimated the critical velocity needed for a fire near the tunnel sidewall. PMID:17544576

Hu, L H; Peng, W; Huo, R

2008-01-15

206

Evaluation of wind environment around a residential complex using a PIV velocity field measurement technique  

Microsoft Academic Search

Wind-tunnel simulations were employed to evaluate the wind environment around a tested residential area located near industrial\\u000a complexes. The scaled-down geomorphological model of the test area was placed in the test section of a boundary layer wind\\u000a tunnel. Particle image velocimetry (PIV) measurements were made in five vertical planes and one horizontal plane around the\\u000a test area for two prevailing

Sang-Joon Lee; Cheol-Woo Park; Jong-Hoon Kang; Daichin

2009-01-01

207

On the stellar gravity and effective temperature dependence of the ratio of terminal to escape velocities in stellar winds  

NASA Astrophysics Data System (ADS)

The ratio of terminal to escape velocities, called R, observed for the winds in early-type stars is found to be linearly correlated with log Gamma. Gamma denotes the ratio of stellar to Eddington's luminosities. From the grid of profiles considered by Castor and Lamers (1979), it is estimated that at most an error of 10 percent is introduced by adopting the edge velocities as representative values of the terminal velocities of main sequence O-type stars. The parameter Delta is introduced. Delta is for observational studies a more reliable parameter than Gamma, since it is independent of both the masses and absolute luminosities adopted for the stars. It is found that O-type stars of different luminosity classes, including the B-type stars of luminosity classes III and higher, have values of R which are dependent on the position of the stars in the H-R diagram.

Carrasco, L.

208

The Rule Of Maximum Gross Bedform-Normal Transport: Constraining Aeolian Bedform Morphology And Formative Wind Regime Using Solely Orbital Imagery  

NASA Astrophysics Data System (ADS)

Although the formative wind regime and bedform morphology of several dune fields have been determined through extensive field work, nearly all planetary and many terrestrial dune fields are located in remote regions for which the only existing morphological data are spacecraft images. In the absence of other forms of data (e.g., anemometry, migration patterns), what can be determined about the sand-transporting winds that built these dune fields? We demonstrate that the rule of maximum gross bedform-normal transport (MGBNT) of Rubin and Hunter (1987) and Rubin and Ikeda (1990) can be applied in many remote situations to constrain both the potential wind regime and bedform type. By determining two formative wind directions from nearby unidirectional features (e.g., yardangs, wind streaks), the relative strengths of dune-building winds can be constrained by comparison of MGBNT to bedform orientation. In cases where only one formative wind direction can be identified, a second wind may be partially determined by "inverse-MGBNT" analysis. In these instances, a second wind may be identified from those that combine with a known (or assumed) sand-transporting wind to produce observed dune crestline orientations. We first demonstrate this method in a terrestrial setting where the bedform type and wind regime is well constrained, following with an example in Ganges Chasma on Mars. If the initial assumptions regarding likely sand-transporting wind directions are robust, then this technique proves to be reliable; in many locations on Mars and Titan it can be used as a constraint for atmospheric modeling. a) Linear or oblique dunes in a portion of the largest dune field in Ganges Chasma on Mars. b) Histogram of dune crestline orientations from a). c) Maximum gross bedform-normal transport analysis constraining the transport ratio of two likely sand-transporting winds. A southwesterly wind (black) combines with an east-southeasterly wind (black) with a transport ratio between 1:8 and1:1 to produce the crestlines observed in a) and b).

Fenton, L. K.

2012-12-01

209

Vegetation as an Indicator of High Wind Velocity. Final Report, June 15, 1978-June 14, 1979.  

National Technical Information Service (NTIS)

To use wind energy the resource must first be identified. This report describes techniques for using two widely distributed species of coniferous trees - Douglas-fir and Ponderosa Pine - as aids in wind-power prospecting. The report describes the need for...

E. W. Hewson J. E. Wade R. W. Baker

1979-01-01

210

On the relationship between relativistic electron flux and solar wind velocity: Paulikas and Blake revisited  

Microsoft Academic Search

Thirty years ago Paulikas and Blake (1979) showed a remarkable correlation between geosynchronous relativistic electron fluxes and solar wind speed (Vsw). This seminal result has been a foundation of radiation belt studies, space weather forecasting, and current understanding of solar wind radiation belt coupling. We have repeated their analysis with a considerably longer-running data set (1989–2010) from the Los Alamos

Geoffrey D. Reeves; Steven K. Morley; Reiner H. W. Friedel; Michael G. Henderson; Thomas E. Cayton; Gregory Cunningham; J. Bernard Blake; Rod A. Christensen; Davis Thomsen

2011-01-01

211

IMF orientation, solar wind velocity, and Pc 3--4 signals: A joint distribution  

Microsoft Academic Search

Separate studies using the same micropulsation data base in the period range 10--150 s have shown earlier that signal levels recorded during September, October, and November 1969 at Calgary correlated positively with both solar wind alignment of the IMF and solar wind speed, but each correlation contained enough scatter to allow for influence of the other factor. In this report,

Eugene W. Greenstadt; Howard J. Singer; Christopher T. Russell; John V. Olson

1979-01-01

212

Estimation of wind velocity and backscatter signal intensity from Doppler lidar returns  

Microsoft Academic Search

Doppler lidar offers a method of remotely measuring wind speeds in optically clear air. A laser source directs a pulse of narrowband optical radiation into the atmosphere. As the pulse propagates, it irradiates small aerosol particles, which scatter radiation back toward the lidar system. Because the aerosol particles are small enough to be borne by the wind, the frequency of

R. Michael Hardesty; W. Alan Brewer; B. J. Rye

1997-01-01

213

On the Maximum Luminosity of Galaxies and Their Central Black Holes: Feedback from Momentum-driven Winds  

NASA Astrophysics Data System (ADS)

We investigate large-scale galactic winds driven by momentum deposition. Momentum injection is provided by (1) radiation pressure produced by the continuum absorption and scattering of photons on dust grains and (2) supernovae (momentum injection by supernovae is important even if the supernova energy is radiated away). Radiation can be produced by a starburst or active galactic nucleus (AGN) activity. We argue that momentum-driven winds are an efficient mechanism for feedback during the formation of galaxies. We show that above a limiting luminosity, momentum deposition from star formation can expel a significant fraction of the gas in a galaxy. The limiting, Eddington-like luminosity is LM~=(4fgc/G)?4, where ? is the galaxy velocity dispersion and fg is the gas fraction; the subscript M refers to momentum driving. A starburst that attains LM moderates its star formation rate and its luminosity does not increase significantly further. We argue that elliptical galaxies attain this limit during their growth at z>~1 and that this is the origin of the Faber-Jackson relation. We show that Lyman break galaxies and ultraluminous infrared galaxies have luminosities near LM. Since these starbursting galaxies account for a significant fraction of the star formation at z>~1, this supports our hypothesis that much of the observed stellar mass in early-type galaxies was formed during Eddington-limited star formation. Star formation is unlikely to efficiently remove gas from very small scales in galactic nuclei, i.e., scales much smaller than that of a nuclear starburst. This gas is available to fuel a central black hole (BH). We argue that a BH clears gas out of its galactic nucleus when the luminosity of the BH itself reaches ~LM. This shuts off the fuel supply to the BH and may also terminate star formation in the surrounding galaxy. As a result, the BH mass is fixed to be MBH~=(fg?es/?G2)?4, where ?es is the electron scattering opacity. This limit is in accord with the observed MBH-? relation.

Murray, Norman; Quataert, Eliot; Thompson, Todd A.

2005-01-01

214

Influence of Wind Velocity Fluctuation on Air Temperature Difference between the Fan and Ground Levels and the Effect of Frost Protective Fan Operation  

NASA Astrophysics Data System (ADS)

We invested the influence of wind velocity fluctuation on air temperature difference between the fan (4.8 m) and ground levels (0.5 m) and the effect of frost protective fan operation in order to develop a new method to reduce electricity consumption due to frost protective fan operation. The results of the investigations are summarized as follows: (1) Air temperature difference between the fan (4.8 m) and ground levels (0.5 m) was decreased following an increase in wind velocity, and the difference was less than 1°C for a wind velocity more than 3.0 m/s at a height of 6.5 m. (2) When the wind velocity was more than 2-3 m/s, there was hardly any increase in the temperature of the leaves. In contrast, when the wind velocity was less than 2-3 m/s, an increase in the temperature of the leaves was observed. Based on these results, it is possible that when the wind velocity is greater than 2-3 m, it prevents thermal inversion. Therefore, there would be no warmer air for the frost protective fan to return to the tea plants and the air turbulence produced by the frost protective fan would not reach the plants under the windy condition.

Araki, Takuya; Matsuo, Kiyoshi; Miyama, Daisuke; Sumikawa, Osamu; Araki, Shinsuke

215

Third moments and the role of anisotropy from velocity shear in the solar wind  

NASA Astrophysics Data System (ADS)

In the interplanetary medium, fluctuations in velocity and magnetic field show evidence of turbulent energy cascades. Near 1 AU, Advanced Compositional Explorer (ACE) plasma and magnetic field data have been used by us to compute third-order moments. The cascade rate can be directly evaluated from these moments, and the results are in agreement with rate needed to account for proton heating. Assuming homogeneous shear flow, the total velocity can be split into the sum of a fluctuation and shear part. This approach can be taken to examine the role of velocity shear which at large scales is an important driver of the turbulence at 1 AU. We present results from a linear detrending of velocity for 12 hour samples and provide estimates of the various contributing third-order moments for the fluctuating and shear components. We find that the cascade rate can be recovered with an inferred anisotropy of the fluctuations due to velocity shear.

Smith, C. W.; Stawarz, J. E.; Vasquez, B. J.; Forman, M. A.

2010-12-01

216

HSTUV measurements of wind structure and velocities in Local Group OB stars  

Microsoft Academic Search

Archival HST FOS and GHRS data sets have been used to collect ultraviolet evidence for large- and small-scale stellar wind structure in extragalactic Local Group OB stars (i.e. SMC, LMC including R136, M31, M33 and NGC 6822). By comparison with previous studies of Galactic OB stars, wind activity is principally diagnosed in individual spectrograms via the presence of `narrow absorption

Raman K. Prinja; Paul A. Crowther

1998-01-01

217

Equilibrium points and zero velocity surfaces in the restricted four-body problem with solar wind drag  

NASA Astrophysics Data System (ADS)

We have analyzed the motion of an infinitesimal mass in the restricted four-body problem with solar wind drag. It is assumed that the forces which govern the motion are mutual gravitational attractions of the primaries, radiation pressure force and solar wind drag. We have derived the equations of motion and found the Jacobi integral, zero velocity surfaces, and particular solutions of the system. It is found that three collinear points are real when the radiation factor 0< ?<0.1 whereas only one real point is obtained when 0.125< ?<0.2. The stability property of the system is examined with the help of Poincaré surface of section (PSS) and Lyapunov characteristic exponents (LCEs). It is found that in presence of drag forces LCE is negative for a specific initial condition, hence the corresponding trajectory is regular whereas regular islands in the PSS are expanded.

Kumari, Reena; Kushvah, Badam Singh

2013-04-01

218

Development of pitch angle anisotropy and velocity diffusion of pickup ion shell distribution by solar wind turbulence  

NASA Technical Reports Server (NTRS)

The evolution of pitch angle anisotropy in initially isotropic spherical shell distribution of pickup ions subjected to a continuous influence of weak or moderate intrinsic solar wind turbulence is investigated using a physical model which assumes that the wave of the solar wind turbulence is propagating mainly in the direction parallel to the ambient magnetic field. It is shown that, because of the pitch angle dependence of the velocity diffusion process, a significant pitch angle anisotropy of pickup ion shell distribution develops in the early stage of the diffusion process. Although it is smeared out later on, the result can be of significant importance, especially if the pickup ion density is large, because the pitch angle anisotropy can excite collective instabilities and increase the wave level, thus accelerating the diffusion process.

Yoon, Peter H.; Ziebell, L. F.

1990-01-01

219

Survey of the spectral properties of turbulence in the solar wind, the magnetospheres of Venus and Earth, at solar minimum and maximum  

NASA Astrophysics Data System (ADS)

In the framework of the European FP7 project STORM ("Solar system plasma Turbulence: Observations, inteRmittency and Multifractals") we analyze the properties of turbulence in various regions of the solar system, for the minimum and respectively maximum of the solar activity. The main scientific objective of STORM is to advance the understanding of the turbulent energy transfer, intermittency and multifractals in space plasmas. Specific analysis methods are applied on magnetic field and plasma data provided by Ulysses, Venus Express and Cluster, as well as other solar system missions (e.g. Giotto, Cassini). In this paper we provide an overview of the spectral properties of turbulence derived from Power Spectral Densities (PSD) computed in the solar wind (from Ulysses, Cluster, Venus Express) and at the interface of planetary magnetospheres with the solar wind (from Venus Express, Cluster). Ulysses provides data in the solar wind between 1992 and 2008, out of the ecliptic, at radial distances ranging between 1.3 and 5.4 AU. We selected only those Ulysses data that satisfy a consolidated set of selection criteria able to identify "pure" fast and slow wind. We analyzed Venus Express data close to the orbital apogee, in the solar wind, at 0.72 AU, and in the Venus magnetosheath. We investigated Cluster data in the solar wind (for time intervals not affected by planetary ions effects), the magnetosheath and few crossings of other key magnetospheric regions (cusp, plasma sheet). We organize our PSD results in three solar wind data bases (one for the solar maximum, 1999-2001, two for the solar minimum, 1997-1998 and respectively, 2007-2008), and two planetary databases (one for the solar maximum, 2000-2001, that includes PSD obtained in the terrestrial magnetosphere, and one for the solar minimum, 2007-2008, that includes PSD obtained in the terrestrial and Venus magnetospheres and magnetosheaths). In addition to investigating the properties of turbulence for the minimum and maximum of the solar cycle we also analyze the spectral similarities and differences between fast and slow wind turbulence. We emphasize the importance of our data survey and analysis in the context of understanding the solar wind turbulence, the exploitation of data bases and as a first step towards developing a (virtual) laboratory for studying solar system plasma turbulence. Research supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement no 313038/STORM, and a grant of the Romanian Ministry of National Education, CNCS - UEFISCDI, project number PN-II-ID-PCE-2012-4-0418.

Echim, Marius M.

2014-05-01

220

Competing mechanisms of plasma transport in inhomogeneous configurations with velocity shear: the solar-wind interaction with earth's magnetosphere.  

PubMed

Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma. PMID:18232777

Faganello, M; Califano, F; Pegoraro, F

2008-01-11

221

Competing Mechanisms of Plasma Transport in Inhomogeneous Configurations with Velocity Shear: The Solar-Wind Interaction with Earth's Magnetosphere  

SciTech Connect

Two-dimensional simulations of the Kelvin-Helmholtz instability in an inhomogeneous compressible plasma with a density gradient show that, in a transverse magnetic field configuration, the vortex pairing process and the Rayleigh-Taylor secondary instability compete during the nonlinear evolution of the vortices. Two different regimes exist depending on the value of the density jump across the velocity shear layer. These regimes have different physical signatures that can be crucial for the interpretation of satellite data of the interaction of the solar wind with the magnetospheric plasma.

Faganello, M.; Califano, F.; Pegoraro, F. [Physics Department, University of Pisa, Pisa (Italy)

2008-01-11

222

A New Atmospheric Neutral Analyzer Instrument for Thermospheric Composition, Density and Wind Velocity Measurements on the ISWEAT Micro-Satellite  

NASA Astrophysics Data System (ADS)

We present the concept of a new atmospheric neutral analyzer (ANA) instrument and its unique capability to measure thermospheric composition, density and wind velocity, and the proposed Ionospheric Space Weather Effects in the Auroral Thermosphere (ISWEAT) micro-satellite. Using the 'Quicksat' micro-satellite bus, the ISWEAT will carry ANA as well as a dual-frequency GPS receiver (DGR) and a fluxgate magnetometer (FMG) to study the effects of magnetic storms and substorms on the thermosphere. ANA will combine the techniques of radio-frequency ion mass spectrometry and CCD-based low-energy ion velocity imaging, respectively, to measure mass- resolved 2-dimensional velocity distribution functions of atmospheric neutral species, including their 'non-thermal' components ('high-energy tails'). The DGR will measure the satellite position and velocity to cm and cm/s precision, respectively, as well as the large-scale ionospheric total electron contents (TEC), while FMG will measure magnetic field perturbations due to field-aligned current structures. The primary objective of ISWEAT is to use these measurements to study the effects of thermospheric expansion and associated ionospheric changes on 'anomalous' satellite drags at auroral latitudes during magnetic storms and substorms. Results of our mission concept study will be presented.

Yau, A. W.; Langley, R. B.; Noel, J.; Wallis, D. D.; Harrison, P.; Lunscher, W.

2008-12-01

223

Blowing in the Wind: I. Velocities of Chondrule-sized Particles in a Turbulent Protoplanetary Nebula  

NASA Technical Reports Server (NTRS)

Small but macroscopic particles - chondrules, higher temperature mineral inclusions, metal grains, and their like - dominate the fabric of primitive meteorites. The properties of these constituents, and their relationship to the fine dust grains which surround them, suggest that they led an extended existence in a gaseous protoplanetary nebula prior to their incorporation into their parent primitive bodies. In this paper we explore in some detail the velocities acquired by such particles in a turbulent nebula. We treat velocities in inertial space (relevant to diffusion), velocities relative to the gas and entrained microscopic dust (relevant to accretion of dust rims), and velocities relative to each other (relevant to collisions). We extend previous work by presenting explicit, closed-form solutions for the magnitude and size dependence of these velocities in this important particle size regime, and compare these expressions with new numerical calculations. The magnitude and size dependence of these velocities have immediate applications to chondrule and CAI rimming by fine dust, and to their diffusion in the nebula, which we explore separately.

Cuzzi, Jeffrey N.; Hogan, Robert C.; Fonda, Mark (Technical Monitor)

2003-01-01

224

THIRD MOMENTS AND THE ROLE OF ANISOTROPY FROM VELOCITY SHEAR IN THE SOLAR WIND  

SciTech Connect

We have extended the recent analyses of magnetohydrodynamic third moments as they relate to the turbulent energy cascade in the solar wind to consider the effects of large-scale shear flows. Moments from a large set of Advanced Composition Explorer data have been taken, and chosen data intervals are characterized by the rate of change in the solar wind speed. Mean dissipation rates are obtained in accordance with the predictions of homogeneous shear-driven turbulence. Agreement with predictions is best made for rarefaction intervals where the solar wind speed is decreasing with time. For decreasing speed intervals, we find that the dissipation rates increase with increasing shear magnitude and that the shear-induced fluctuation anisotropy is consistent with a relatively small amount.

Stawarz, Joshua E.; Vasquez, Bernard J.; Smith, Charles W. [Physics Department, Space Science Center, University of New Hampshire, Durham, NH 03824 (United States); Forman, Miriam A. [Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY 11794-3800 (United States); Klewicki, Joseph, E-mail: jek32@cisunix.unh.edu, E-mail: Bernie.Vasquez@unh.edu, E-mail: Charles.Smith@unh.edu, E-mail: Miriam.Forman@sunysb.edu, E-mail: Joe.Klewicki@unh.edu [Mechanical Engineering Department, University of New Hampshire, Durham, NH 03824 (United States)

2011-07-20

225

New measurements of vertical thermal structure and wind velocities in the Venusian mesosphere  

NASA Astrophysics Data System (ADS)

The Venus mesosphere is a highly variable transition region, in latitude, local time and over short time scales, between the zonal circulation of the lower atmosphere and the diurnal, sub-solar to anti-solar circulation in the upper atmosphere. In the framework of European Space Agency's second campaign of ground-based observations (Feb 8-22, 2009) in support of the Venus-Express mission, we coordinated new observations sampling a large range of altitudes in the Venus mesosphere on Feb. 7-8 and Feb. 14-15 : (1) James Clerk Maxwell Submillimeter Telescope (JCMT) submillimeter lines observations of mesospheric CO spectral lines measurements of temperature, CO mixing ratio and winds over the 95-115 km altitude range (Clancy et al., 2008), while SO2, SO and HDO observations were also probed in the 70-100 km range ; (2) Canada-France-Hawaii Telescope (CFHT) optical spectropolarimeter ESPaDOnS observations of visible Solar Fraunhofer lines measuring the winds at cloud tops near 70 km and visible CO2 lines 1-2 scale heights above (Widemann et al., 2007, 2008). Synchronization of wind measurements helps characterize possible correlation patterns between wind variations in the lower and middle mesosphere over a day time scale. Preliminary results will be presented at the meeting. Clancy, R.T., Sandor, B.J., and Moriarty-Schieven, G.H. 2008, Planet. Space Sci. 56, 1320-1334. Widemann, T., Lellouch, E., and Campargue, A. 2007, New Wind Measurements in Venus' Lower Mesosphere From Visible Spectroscopy, Planet. Space Sci. 55, 1741-1756 Widemann, T., Lellouch, E., Donati, J.-F., 2008, Venus Doppler winds at Cloud Tops Observed with ESPaDOnS at CFHT, Planet. Space Sci. 56, 1320-133 --

Widemann, T.; Sandor, B. J.; Clancy, R. T.; Lellouch, E.

2009-04-01

226

The velocity distribution function of the neutral lithium cloud produced by an AMPTE solar wind release  

Microsoft Academic Search

On Sept. 20, 1984 a release of photoionizing lithium neutrals was made in the quiet solar wind by the AMPTE-IRM spacecraft. The MSSL ion instrument on board the UKS spacecraft that was positioned about 30 km from the release center enabled measurement of significant fluxes of lithium ions to be made for about 3 min after the release; that is,

S. C. Chapman; A. D. Johnstone; A. J. Coates

1987-01-01

227

Wind tunnel velocity profiles generated by differentially-spaced flat plates  

Microsoft Academic Search

Production of linear shear with low turbulence level in a wind tunnel provides a convenient environment for testing the results of computational fluid dynamics simulations and equipment calibration. Boundary layer flow over a flat plate at zero incidence provides controlled deceleration of the approach flow according to plate length, with interacting boundary layers between adjoining flat plates merging to provide

J. C. Phillips; N. H. Thomas; R. J. Perkins; P. C. H. Miller

1999-01-01

228

The distribution of velocity and energy of saltating sand grains in a wind tunnel  

Microsoft Academic Search

Sand transport by wind is a special case of two-phase flow of gas and solids, with saltating grains accounting for about 75% of the transport rate. This form of flow is not only the main external agent moulding aeolian landforms but also the motive force responsible for transport, sorting and deposition of aeolian sediments. High-speed multiflash photography is an effective

Xue-Yong Zou; Zhou-Long Wang; Qing-Zhen Hao; Chun-Lai Zhang; Yu-Zhang Liu; Guang-Rong Dong

2001-01-01

229

Differential Velocity between Solar Wind Protons and Alpha Particles in Pressure Balance Structures  

NASA Technical Reports Server (NTRS)

Pressure balance structures (PBSs) are a common high-plasma beta feature in high-latitude, high-speed solar wind. They have been proposed as remnants of coronal plumes. If true, they should reflect the observation that plumes are rooted in unipolar magnetic flux concentrations in the photosphere and are heated as oppositely directed flux is advected into and reconnects with the flux concentration. A minimum variance analysis (MVA) of magnetic discontinuities in PBSs showed there is a larger proportion of tangential discontinuities than in the surrounding high-speed wind, supporting the hypothesis that plasmoids or extended current sheets are formed during reconnection at the base of plumes. To further evaluate the character of magnetic field discontinuities in PBSs, differential streaming between alpha particles and protons is analyzed here for the same sample of PBSs used in the MVA. Alpha particles in high-speed wind generally have a higher radial flow speed than protons. However, if the magnetic field is folded back on itself, as in a large-amplitude Alfven wave, alpha particles will locally have a radial flow speed less than protons. This characteristic is used here to distinguish between folded back magnetic fields (which would contain rotational discontinuities) and tangential discontinuities using Ulysses high-latitude, high-speed solar wind data. The analysis indicates that almost all reversals in the radial magnetic field in PBSs are folded back field lines. This is found to also be true outside PBSs, supporting existing results for typical high-speed, high-latitude wind. There remains a small number of cases that appear not to be folds in the magnetic field and which may be flux tubes with both ends rooted in the Sun. The distinct difference in MVA results inside and outside PBSs remains unexplained.

Yamauchi, Yohei; Suess, Steven T.; Steinberg, John T.; Sakurai, Takashi

2004-01-01

230

Differential Velocity Between Solar Wind Protons and Alpha Particles in Pressure Balance Structures  

NASA Technical Reports Server (NTRS)

Pressure balance structures (PBSs) are a common high plasma beta feature in high latitude, high speed solar wind. They have been proposed as remnants of coronal plumes. If true, they should reflect the observation that plumes are rooted in unipolar magnetic flux concentrations in the photosphere and are heated as oppositely directed flux is advected into and reconnects with the flux concentration. A minimum variance analysis (MVA) of magnetic discontinuities in PBSs showed there is a larger proportion of tangential discontinuities than in the surrounding high speed wind, supporting the hypothesis that plasmoids or extended current sheets are formed during reconnection at the base of plumes. To further evaluate the character of magnetic field discontinuities in PBSs, differential streaming between alpha particles and protons is analyzed here for the same sample of PBSs used in the MVA. Alpha particles in high speed wind generally have a higher radial flow speed than protons. However, if the magnetic field is folded back on itself, as in a large amplitude Alfven wave, alpha particles will locally have a radial flow speed less than protons. This characteristic is used here to distinguish between folded back magnetic fields (which would contain rotational discontinuities) and tangential discontinuities using Ulysses high latitude, high speed solar wind data. The analysis indicates that almost all reversals in the radial magnetic field in PBSs are folded back field lines. This is found to also be true outside PBSs, supporting existing results for typical high speed, high latitude wind. There remains a small number of cases that appear not to be folds in the magnetic field and which may be flux tubes with both ends rooted in the Sun. The distinct difference in MVA results inside and outside PBSs remains unexplained.

Yamauchi, Y.; Suess, S. T.; Steinberg, J. T.; Sakurai, T.

2003-01-01

231

Evolution of the Proton Velocity Distribution and Wave Spectrum in the Solar Wind Turbulence Cascade Transition to Kinetic Scales  

NASA Astrophysics Data System (ADS)

There are still a number of unanswered questions regarding the transition of the solar wind turbulent cascade to kinetic scales. Due to the large-scale structure and evolution of the solar wind, observed proton distributions typically are not isotropic, but instead cover the entire range between marginally unstable conditions of parallel and perpendicular temperature anisotropy. Furthermore, the proton distributions invariably possess an energetic tail. In both cases, it is not clear what the interplay is between the cascade, the temperature anisotropy, and the energetic tails. After briefly reviewing different approaches to investigating the kinetic regime, we report here on using hybrid simulations (kinetic ions, electron fluid) to quantify the resulting spectrum and evolution of the proton velocity distribution. We analyze the simulation wave spectra to determine the characteristic dependence on anisotropy and address the question of linear mode identification, using a number of different approaches. We calculate the derived observable spectrum as seen by a spacecraft in the solar wind as a function of magnetic field orientation and compare to observational results and theoretical expectations.

Krauss-Varban, D.; Salem, C. S.

2013-12-01

232

Influence of stator winding structure on the relation between PD value and maximum discharge quantity in deterioration diagnosis of hydro-generators  

Microsoft Academic Search

In this study, the authors investigated on-line deterioration diagnosis of hydro-generators. Simultaneous measurement was done under off-line condition by using an on-line PD monitor and an off-line PD measuring system. When a stator had wave-winding structure, a good correlation between the maximum electric discharges of the offline PD measuring system and PD values of the online PD monitor was seen.

Osamu Hattori; Takahiko Yamashita

2010-01-01

233

Lidar measurement of wind velocity turbulence spectra encountered by a rotating turbine blade  

SciTech Connect

A homodyne CO/sub 2/ lidar system beam was conically scanned around a horizontal axis to measure the wind speed and turbulence characteristics encountered by a rotating turbine blade. Turbulence spectra obtained from the scanning lidar differed considerably from those calculated from fixed-point anemometer measurements, showing a redistribution of energy from lower to higher frequencies. The differences appeared more pronounced during periods when the atmosphere was stable.

Hardesty, R.M.; Korrell, J.A.; Hall, F.F. Jr.

1982-01-01

234

The statistical relationship between solar wind parameters and geomagnetic activities during the maximum phase of the solar cycle 23(1999~2003)  

NASA Astrophysics Data System (ADS)

Title: The statistical relationship between solar wind parameters and geomagnetic activities during the maximum phase of the solar cycle 23(1999~2003) It is generally believed that the occurrence of magnetic storm depends upon the solar conditions, especially southward IMF component. To understand the solar wind-magnetosphere coupling, the influence of the solar wind parameters on the development of magnetic storms is examined during the maximum phase of the solar cycle 23(1999~2003). For this purpose the time-integrated solar wind parameters is compared with the time-integrated Dst during the main phase of each magnetic storm. Also examined is how the direction change of IMF By and Bz components(in GSM coordinate) during the main phase is related with the development of storm. Some results are worth noting: First, it is found that the correlation is high between the integrated IMF Bz and integrated Dst index during the main phase of magnetic storms. The high correlation between integrated AL index and integrated Dst index is also noted. Second, the direction of Bz plays a more important role in developing magnetic storms than that of By. Regardless of the By direction, over 60% of storms occurred when Bz component showed negative value. Third, the fluctuations of IMF By and Bz components seem to be one of the main sources leading to the development of magnetic storm.

Moon, G.

2010-12-01

235

Non-gyrotropic Velocity Distributions of Solar Wind Protons Observed by WIND/3DP --A Possible Evidence for Perpendicular Heating by Lower Hybrid Waves  

NASA Astrophysics Data System (ADS)

The velocity distribution function (VDF) of fast solar wind protons usually shows following features: (1) an anisotropic bi-shell-like core with T_perp>T_para; (2) a minor beam component aligned mainly along the local background magnetic field vector. The anisotropic core is theoretically characterized as a heating result by Alfven-cyclotron waves, while the field-aligned beam is attributed to be accelerated probably by kinetic Alfven waves or ion-acoustic waves. Here, we report a third part of the distribution, 'non-gyrotropic patch', based on observations from the 3DP plasma instrument onboard WIND. With the non-gyrotropic patch sticking out from the normal core part, the VDF is no longer axis-symmetric around local background magnetic field. This extra non-gyrotropic part may be a result of unidirectional perpendicular heating by some kind of high-frequency quasi-perpendicular electrostatic wave, which has yet to be observationally identified. As a speculation, we study the modification of protons in the velocity phase space by lower hybrid waves. In our result of test-particle simulation, we find the protons can be perpendicularly heated along the wave propagation direction, and a non-gyrotropic patch is formed as a result of such heating. Moreover, although the perpendicular-heated protons then diffusively rotate around the magnetic field, the non-gyrotropic patch still remains more condensed as compared with the other part of the same shell. Therefore, the observed non-gyrotropic distribution is suggested to be a possible evidence of perpendicular heating by high-frequency quasi-perpendicular electrostatic waves, e.g., lower hybrid waves.

He, J.; Tu, C.; Wang, L.; Marsch, E.; Yang, L.; Yao, S.

2013-12-01

236

Mitigation of Low-velocity, Wind-induced Vibration of an Architectural Spire  

Microsoft Academic Search

\\u000a This paper presents the results of analytical and experimental studies conducted on an architectural spire, which experienced\\u000a wind-induced vibrations shortly after its construction. The circular spire is attached to the corner of a 30-story building\\u000a along the upper ten stories then cantilevers up for 21.44 m (70.33 ft) with a pipe cross-section of 0.508 m (20 in)-diameter\\u000a for the first

Omer F. Tigli; Luca Caracoglia

237

Tangential discontinuities in the solar wind - Correlated field and velocity changes and the Kelvin-Helmholtz instability  

NASA Technical Reports Server (NTRS)

Three-dimensional Helios plasma and field data are used to investigate the relative changes in direction of the velocity and magnetic field vectors across tangential discontinuities (TDs) in the solar wind at solar distances of 0.29-0.50 AU. It is found for TDs with large Delta-v and (Delta-B)/B that Delta-v and Delta-B are closely aligned with each other, in agreement with the unexpected results of previous studies of TDs observed at 1 AU and beyond. It is shown that this effect probably results from the destruction by the Kelvin-Helmholtz instability of TDs for which Delta-v and Delta-B are not aligned. The observed decrease in the number of interplanetary discontinuities with increasing solar distance may be associated with the growth of the Kelvin-Helmholtz instability with decreasing Alfven speed.

Neugebauer, M.; Alexander, C. J.; Schwenn, R.; Richter, A. K.

1986-01-01

238

Wind-velocity lidar measurements by use of a Mach-Zehnder interferometer, comparison with a Fabry-Perot interferometer.  

PubMed

We present the first wind-velocity profiles obtained with a direct-detection Doppler lidar that uses a Mach-Zehnder interferometer (MZI) as spectral discriminator. The measurements were performed in the lower stratosphere, between 10 and 40 km in altitude, at the Observatoire de Haute Provence (OHP), France, during nighttime. They are in excellent agreement with those obtained simultaneously and independently with the already validated double Fabry-Perot interferometer (FPI) of the OHP Doppler lidar (mean difference lower than the combined standard deviation). A statistical analysis shows that the random error obtained with this experimental MZI is 1.94 times the Cramer-Rao lower bound and is approximately half of that given by the FPI (both operating in photometric mode). Nevertheless, the present MZI measurements are sensitive to the presence of atmospheric particles and need an additional correction, whereas the OHP FPI is designed to be insensitive to particulate scattering. PMID:14714660

Bruneau, Didier; Garnier, Anne; Hertzog, Albert; Porteneuve, Jacques

2004-01-01

239

A study of the geographic coverage properties of a satellite borne Doppler lidar wind velocity measuring system  

NASA Technical Reports Server (NTRS)

Geographic coverage frequency and geographic shot density for a satellite borne Doppler lidar wind velocity measuring system are measured. The equations of motion of the light path on the ground were derived and a computer program devised to compute shot density and coverage frequency by latitude-longitude sections. The equations for the coverage boundaries were derived and a computer program developed to plot these boundaries, thus making it possible, after an application of a map coloring algorithm, to actually see the areas of multiple coverage. A theoretical cross-swath shot density function that gives close approximations in certain cases was also derived. This information should aid in the design of an efficient data-processing system for the Doppler lidar.

Pate, T. H.

1982-01-01

240

Investigations of the air flow velocity field structure above the wavy surface under severe wind conditions by particle image velosimetry technique.  

NASA Astrophysics Data System (ADS)

Preliminary experiments devoted to measuring characteristics of the air flow above the waved water surface for the wide range of wind speeds were performed with the application of modified Particle Image Velosimetry (PIV) technique. Experiments were carried out at the Wind - wave stratified flume of IAP RAS (length 10 °, cross section of air channel 0.4×0.4 m) for four different axial wind speeds: 8.7, 13.5, 19 and 24 m/s, corresponding to the equivalent 10-m wind speeds 15, 20, 30 40 m/s correspondingly. Intensive wave breaking with forming foam crest and droplets generations was occurred for two last wind conditions. The modified PIV-method based on the use of continuous-wave (CW) laser illumination of the airflow seeded by tiny particles and with highspeed video. Spherical 20 ?m polyamide particles with density 1.02 g/sm3 and inertial time 7•10-3 s were used for seeding airflow with special injecting device. Green (532 nm) CW laser with 4 Wt output power was used as a source for light sheet. High speed digital camera Videosprint was used for taking visualized air flow images with the frame rate 2000 Hz s and exposure time 10 ms Combination including iteration Canny method [1] for obtaining curvilinear surface from the images in the laser sheet view and contact measurements of surface elevation by wire wave gauge installed near the border of working area for the surface wave profile was used. Then velocity air flow field was retrieved by PIV images processing with adaptive cross-correlation method on the curvilinear grid following surface wave profile. The mean wind velocity profiles were retrieved by averaging over obtained ensembles of wind velocity field realizations and over a wave period even for the cases of intensive wave breaking and droplets generation. To verify the PIV method additional measurements of mean velocity profiles over were carried out by the contact method using the Pitot tube. In the area of overlap, wind velocity profiles measured by both method were in a good agreement. The application of PIV method enabled us measuring wind velocity profiles much closer to water surface than in the case of contact method. As a result there exists the logarithmic parts in velocity profiles, which yield turbulent momentum flux from the slope and also the equivalent 10-m wind speed and the surface drag coefficient. It was shown that similarly to [2] the surface drag coefficient tends to saturate at wind velocities exceeding 25 m/s. The decrease of the water surface drag coefficient with wind velocity increase was not observed. This work was supported by RFBR (project 11-05-12047-ofi-m, 13-05-00865-a, 12-05-33070 mol-a-ved, 12-05-31435 mol-a, 12-05-01064-a). References 1. Canny, J. A. Computational approach to edge detection/ J.A. Canny// IEEE Trans. Pattern Analysis and Machine Intelligence. - 1986. - V. 8(6). - P. 679-698.. 2. Troitskaya, Y. I., D. A. Sergeev, A. A. Kandaurov, G. A. Baidakov, M. A. Vdovin, and V. I. Kazakov Laboratory and theoretical modeling of air-sea momentum transfer under severe wind conditions J.Geophys. Res., 117, C00J21, doi:10.1029/2011JC007778.

Troitskaya, Yuliya; Kandaurov, Alexander; Sergeev, Daniil; Ermakova, Olga

2013-04-01

241

Forward Velocity Effects on Fan Noise and the Suppression Characteristics of Advanced Inlets as Measured in the NASA-Ames 40 by 80 Foot Wind Tunnel.  

National Technical Information Service (NTIS)

Forward velocity effects on the forward radiated fan noise and on the suppression characteristics of three advanced inlets relative to a baseline cylindrical inlet were measured in the NASA Ames Research Center 40 x 80 foot Wind Tunnel. A modified JT15D t...

M. T. Moore

1980-01-01

242

The effect of the wind speed velocity on the stack pressure in medium-rise buildings in cold region of China  

Microsoft Academic Search

This paper presents the numerical simulation results of the stack effect in medium-rise buildings in Harbin, a typical city in the severe cold region of China. The simulation was carried out using the multizone ventilation model COMIS. The effect of the wind speed velocity and the temperature of the stairwell on the pressure difference curves shape have been investigated. The

Maatouk Khoukhi; Hiroshi Yoshino; Jing Liu

2007-01-01

243

Comparing solar wind velocity measurements derived from Sun-grazing Comet Lovejoy (C/2011 W3) as observed from multiple locations  

NASA Astrophysics Data System (ADS)

Comets' plasma (type I) tails have been studied as natural probes of the solar wind since the mid-20th century. Local solar wind conditions directly control the morphology and dynamics of a comet's plasma tail. During ideal observing geometries, the orientation and structure of the plasma tail can reveal large-scale and small-scale variations in the local solar wind structure. These variations can be manifested as tail condensations, kinks, and disconnection events. The technique employed in this study was established by analysing geocentric amateur observations of comets C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz). These amateur images, obtained with modern equipment and sensors, are arguably better in quality than professional images obtained only 2-3 decades ago. Multiple solar wind velocity estimates were derived from each image and the results compared to observed and modelled near-Earth solar wind data. Our unique analysis technique allows us to determine the latitudinal variations of the solar wind, heliospheric current sheet sector boundaries and the boundaries of transient features as a comet with an observable plasma tail probes the inner heliosphere. We present solar wind velocity measurements derived from multiple observing locations of comet Lovejoy (C/2011 W3) from the 14th - 19th December 2011 using recent images from the SECCHI and LASCO heliospheric imagers and coronagraphs aboard STEREO A and B, and SOHO. Comet Lovejoy was a very bright sungrazer, which plunged into the solar corona and largely survived its perihelion (1.19 solar radii) on 16th December at 00:17 UT. Lovejoy, an exception amongst sungrazers, displayed a prominent plasma tail pre-perihelion and post-perihelion, as it probed the solar atmosphere. Overlapping observation sessions from the three spacecraft provided the perfect opportunity to use comet Lovejoy as a diagnostic tool to understand solar wind variability close to the Sun. We plan to compare our observations to results of suitable simulations of plasma conditions in the corona and inner heliosphere during the time of Lovejoy's perihelion passage. The correlation of the solar wind velocity distribution from different observing locations can provide clues towards the morphology and orientation of the plasma tail. We also attempt to determine the non-radial contributions to the measured solar wind velocities via this study.

Ramanjooloo, Yudish; Jones, Geraint H.; Coates, Andrew J.; Owens, Mathew J.; Battams, Karl

2013-04-01

244

SAHARAN WIND REGIMES TRACED BY THE Sr–Nd ISOTOPIC COMPOSITION OF SUBTROPICAL ATLANTIC SEDIMENTS: LAST GLACIAL MAXIMUM vs TODAY  

Microsoft Academic Search

New Nd–Sr isotopic data on the <30?m lithic particles of surface and Last Glacial Maximum sediments recovered along the African margin between the Equator and the Gibraltar Strait are presented in combination with grain-size measurements. This <30?m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions. In the eolian fraction, both Sr and

F. E. GROUSSET; M. PARRA; A. BORY; P. MARTINEZ; P. BERTRAND; G. SHIMMIELD; R. M. ELLAM

1998-01-01

245

Dynamics of the turbidity maximum in the Fly River estuary, Papua New Guinea  

Microsoft Academic Search

Field studies in the Fly River estuary, Papua New Guinea, show that the turbidity maximum exists only at spring tides. The wind is important in wave-driven fluidization of the bed. The erosion rate varies with the sixth power of the water velocity. The suspended sediment settling velocity varies nonlinearly with the concentration. At least three-quarters of the river sediment inflow

Eric Wolanski; Brian King; Duncan Galloway

1995-01-01

246

Tests in the variable-density wind tunnel of related airfoils having the maximum camber unusually far forward  

NASA Technical Reports Server (NTRS)

A family of related airfoils having the position of maximum camber unusually far forward was investigated in the variable-density tunnel as an extension of the study recently completed of a large number of related airfoils. The new airfoils gave improved characteristics over those previously investigated, especially in regard to the pitching moment. Some of the new sections are markedly superior to well-known and commonly used sections and should replace them in applications requiring a slightly cambered section of moderate thickness having a small pitching-moment coefficient.

Jacobs, Eastman N; Pinkerton, Robert M

1936-01-01

247

A Comparison of C/NOFS Neutral Wind Meter Thermospheric Measurements near 400 km under Solar Minimum Conditions and Those Approaching Solar Maximum  

NASA Astrophysics Data System (ADS)

Since the beginning of 2011, solar activity has increased leading to a recovery from the unusual thermospheric conditions of the recent solar minimum of 2008 and 2009. Examples of those unusual conditions were an unusually low neutral density and the periodic dominance of neutral helium at topside F-region altitudes measured by CINDI instruments aboard the Communication/ Navigation Outage Forecast System (C/NOFS). The CINDI Neutral Wind Meter (NWM) aboard C/NOFS contains two instruments, the Ram Wind Sensor (RWS) and Cross Track Sensor (CTS) which can obtain velocity, temperature, composition and relative pressure information about neutral particles within the limits of the C/NOFS orbit altitudes, currently 395km - 760km. Due to increased thermospheric densities and more monatomic oxygen present at orbit altitudes the instruments are no longer always working at the edge of their pressure tolerances. We will show current thermospheric conditions at these altitudes, as measured by the instruments, compared to the previous measurements during the deep solar minimum.

Haaser, R. A.

2012-12-01

248

Sedimentation modified by wind induced resuspension in a shallow tropical lagoon (Cote d'Ivoire)  

Microsoft Academic Search

In shallow environments, under certain conditions of fetch, wind velocity, bathymetry and bottom characteristics, resuspension\\u000a can be generated by wind induced waves. In the tropical Ebri lagoon, austral trade winds are dominant almost all year long,\\u000a and their velocity shows a marked diel pattern with maximum speed between noon and midnight. Only austral trade winds with\\u000a a speed >3 m

Robert Arfi; Daniel Guiral; Marc Bouvy

1994-01-01

249

Radial density, velocity and temperature profiles in a multi-species solar wind close to the coronal base: A self-consistent four-species model  

Microsoft Academic Search

We present a multi-species model of the solar wind close to the coronal base. Employing a five-moment approximation, the steady state profiles of densities, velocities as well as temperatures of electrons and three ion species, namely protons, alpha particles and a minor ion population such as oxygen, are obtained self-consistently for a region close to the base of the corona.

H. Fichtner; N. Vormbrock; S. R. Sreenivasan

2000-01-01

250

EnKF OSSE Experiments Assessing the Impact of HIRAD Wind Speed and HIWRAP Radial Velocity Data on Analysis of Hurricane Karl (2010)  

NASA Technical Reports Server (NTRS)

Previous studies (e.g., Zhang et al. 2009, Weng et al. 2011) have shown that radial velocity data from airborne and ground-based radars can be assimilated into ensemble Kalman filter (EnKF) systems to produce accurate analyses of tropical cyclone vortices, which can reduce forecast intensity error. Recently, wind speed data from SFMR technology has also been assimilated into the same types of systems and has been shown to improve the forecast intensity of mature tropical cyclones. Two instruments that measure these properties were present during the NASA Genesis and Rapid Intensification Processes (GRIP) field experiment in 2010 which sampled Hurricane Karl, and will next be co-located on the same aircraft for the subsequent NASA HS3 experiment. The High Altitude Wind and Rain Profiling Radar (HIWRAP) is a conically scanning Doppler radar mounted upon NASAs Global Hawk unmanned aerial vehicle, and the usefulness of its radial velocity data for assimilation has not been previously examined. Since the radar scans from above with a fairly large fixed elevation angle, it observes a large component of the vertical wind, which could degrade EnKF analyses compared to analyses with data taken from lesser elevation angles. The NASA Hurricane Imaging Radiometer (HIRAD) is a passive microwave radiometer similar to SFMR, and measures emissivity and retrieves hurricane surface wind speeds and rain rates over a much wider swath. Thus, this study examines the impact of assimilating simulated HIWRAP radial velocity data into an EnKF system, simulated HIRAD wind speed, and HIWRAP+HIRAD with the Weather Research and Forecasting (WRF) model and compares the results to no data assimilation and also to the Truth from which the data was simulated for both instruments.

Albers, Cerese; Sippel, Jason A.; Braun, Scott A.; Miller, Timothy

2012-01-01

251

Hot-Wire Anemometer Investigation of Surface Wind Velocity and Temperature Fluctuations at Two Southern California Sites.  

National Technical Information Service (NTIS)

An experimental investigation of the atmospheric turbulence velocity and temperature fields was performed at The Aerospace Corp. San Fernando Observatory on Van Norman Lake and at The Aerospace Corp. parking lot, El Segundo, Calif. The velocity fluctuatio...

D. H. Ross

1970-01-01

252

Toward a universal relationship between wind speed and gas exchange: Gas transfer velocities measured with 3He/SF6 during the Southern Ocean Gas Exchange Experiment  

NASA Astrophysics Data System (ADS)

Two 3He/SF6 dual-gas tracer injections were conducted during the Southern Ocean Gas Exchange Experiment (SO GasEx) to determine gas transfer velocities. During the experiment, wind speeds of up to 16.4 m s-1 were encountered. A total of 360 3He and 598 SF6 samples were collected at 40 conductivity-temperature-depth (CTD) rosette casts and two pumped stations. The gas transfer velocity k was calculated from the decrease in the observed 3He/SF6 ratio using three different approaches. Discrete points of wind speed and corresponding k were obtained from the change in 3He/SF6 ratio over three time intervals. The results were also evaluated using an analytical model and a 1-D numerical model. The results from the three approaches agreed within the error of the estimates of about ±13%-15% for Patch 1 and ±4% for Patch 2. Moreover, 3He/SF6 dual-tracer results from SO GasEx are similar to those from other areas in both the coastal and open ocean and are in agreement with existing parameterizations between wind speed and gas exchange. This suggests that wind forcing is the major driver of gas exchange for slightly soluble gases in the ocean and that other known impacts are either intrinsically related to wind or have a small effect (<20% on average) on time scales of the order of days to weeks. The functionality of the wind speed dependence (quadratic or cubic) cannot be unequivocally determined from SO GasEx results.

Ho, David T.; Wanninkhof, Rik; Schlosser, Peter; Ullman, David S.; Hebert, David; Sullivan, Kevin F.

2011-04-01

253

Coronal holes as sources of solar wind  

Microsoft Academic Search

We investigate the association of high-speed solar wind with coronal holes during the Skylab mission by: (1) direct comparison of solar wind and coronal X-ray data; (2) comparison of near-equatorial coronal hole area with maximum solar wind velocity in the associated streams; and (3) examination of the correlation between solar and interplanetary magnetic polarities. We find that all large near-equatorial

J. T. Nolte; A. S. Krieger; A. F. Timothy; R. E. Gold; E. C. Roelof; G. Vaiana; A. J. Lazarus; J. D. Sullivan; P. S. McIntosh

1976-01-01

254

Results from 1984 airborne Doppler lidar wind measurement program. Flight 6: Analysis of line-of-sight elevation angle errors and apparent Doppler velocities  

NASA Technical Reports Server (NTRS)

During the summer of 1984 the Marshall Space Flight Center's Airborne Doppler Lidar System (ADLS) made a series of wind measurements in the California Central Valley. This study quantifies the lidar beam angle errors and velocity errors through analysis of ground return signals. Line-of-sight elevation (LOSE) angle errors are under 1 deg. Apparent Doppler ground velocities, as large as 2m/s, are considerably less than in a previous flight experiment in 1981. No evidence was found of a Schuler resonance phenomenon common to inertial navigation systems (INS), however the aperiodic nature of the apparent velocities implies an error in the INS-derived ground speeds. Certain features and subtleties in the ground returns are explained in terms of atmospheric structure and characteristics of the ADLS hardware and software. Finally, least squares and low-pass filtering techniques are suggested for eliminating errors during post-processing.

Rothermel, Jeffry

1987-01-01

255

Scatterometer azimuthal response and wind wave directionality  

NASA Technical Reports Server (NTRS)

Azimuthal response of a scatterometer to radiation scattered by the sea surface was studied in a wind-wave tank. The variation of the normalized radar cross section with the azimuth angle is fitted by a three-term series. Results show that the upwind-downwind asymmetry decreases as the wind speed increases. The crosswind modulation depends on the wind velocity. The results show that the evolution of the long-wind-crosswind ratio evolves with wind speed in a manner similar to the evolution of the isotropy of short capillary-gravity waves. The maximum of the isotropy of the short wind waves is obtained for wind velocities close to 4 m/s. For the same value of the velocity, the variations of radar response between long-wind and crosswind directions is minimum. For lower or higher values of wind velocities the directional accuracy of the radar increases, since the wind-wave field tends to align in the wind direction.

Giovanangeli, J. P.; Le Calve, O.; Bliven, L.

1989-01-01

256

Evolution of the solar wind structure over a solar cycle: Interplanetary scintillation velocity measurements compared with coronal observations  

Microsoft Academic Search

Sixteen years of solar wind observations via the technique of interplanetary scintillation (IPS) are presented. By an ecliptic comparison with in situ spacecraft observations, these data are shown to be valuable estimates of the large-scale slowly evolving structures in the solar wind speed, but to underestimate the speed in small-scale or rapidly evolving structures. These IPS observations allow the large

B. J. Rickett; W. A. Coles

1991-01-01

257

Simultaneous measurements of particle backscattering and extinction coefficients and wind velocity by lidar with a Mach-Zehnder interferometer: principle of operation and performance assessment.  

PubMed

The development of remote-sensing instruments that can be used to monitor several parameters at the same time is important for the study of complex processes such as those that control climate and environment. In this paper the performance of a new concept of lidar receiver that allows for the direct measurement of aerosol and cloud optical properties simultaneously with wind velocity is investigated. This receiver uses a Mach-Zehnder interferometer. Two different configurations, either with four photometric output channels or with fringe imaging on a multichannel detector, are studied. Analytical expressions of the statistical errors are given under the assumption of Gaussian signal spectra. It is shown that similar accuracies can be achieved for both configurations. Performance modeling of the retrieval of semitransparent cloud optical scattering properties and wind velocity was done at different operation wavelengths for a Nd:YAG laser source. Results for such a lidar system onboard an aircraft flying at an altitude of 12 km show that for semitransparent clouds the best results were obtained at 355 nm, with relative standard deviations of 0.5% and 5% for the backscatter and extinction coefficients, respectively, together with a velocity accuracy of 0.2 ms(-1). The accuracy of optical properties retrieved for boundary layer aerosols are comparable, whereas the velocity accuracy is decreased to 1 ms(-1). Finally, an extrapolation to a large 355-nm spaceborne lidar shows accuracies in the range from 2.5% to 5% for the backscatter coefficient and from 10% to 15% for the extinction coefficient together with a vertical wind speed accuracy of better than 0.5 ms(-1) for semitransparent clouds and boundary layer, with a vertical resolution of 500 m and a 100 shot averaging. PMID:12617228

Bruneau, Didier; Pelon, Jacques

2003-02-20

258

WIND VELOCITIES AND SAND FLUXES IN MESQUITE DUNE-LANDS IN THE NORTHERN CHIHUAHUAN DESERT: A COMPARISON BETWEEN FIELD MEASUREMENTS AND THE QUIC (QUICK URBAN AND INDUSTRIAL COMPLEX) MODEL  

EPA Science Inventory

The poster shows comparisons of wind velocities and sand fluxes between field measurements and a computer model, called QUIC (Quick Urban & Industrial Complex). The comparisons were made for a small desert region in New Mexico. ...

259

Distribuicoes probabilisticas de velocidades do vento para avaliacao do potencial energetico eolico. (Probabilistic distributions of wind velocity for the evaluation of the wind power potential).  

National Technical Information Service (NTIS)

The theoretical model of wind speed distributions allow valuable information about the probability of events relative to the variable in study eliminating the necessity of a new experiment. The most used distributions has been the Weibull and the Rayleigh...

E. Z. Vendramini

1986-01-01

260

A Novel Sensorless MPPT Controller for a High-Efficiency Microscale Wind Power Generation System  

Microsoft Academic Search

In this paper, a novel maximum power point tracking (MPPT) controller with an adaptive compensation control is first proposed for a microscale wind power generation system (WPGS). Based on the adaptive control, the dynamic response is improved and more wind energy can be captured during wind velocity variations. For cost and reliability consideration, no mechanical sensors are used in this

Ching-Tsai Pan; Yu-Ling Juan

2010-01-01

261

Interplanetary and solar surface properties of coronal holes observed during solar maximum  

NASA Astrophysics Data System (ADS)

Data from the Solar Wind Ion Composition Spectrometer (SWICS) on board the Ulysses spacecraft and synoptic maps from Kitt Peak are used to analyze the relatively short-lived coronal holes which exist during the maximum phase of the solar activity cycle 23. They are compared with the persistent polar coronal holes which prevail around solar minimum. A solar wind velocity increase coinciding with a shift of the ionic charge composition toward lower charge states serves as a robust criterion for identifying solar wind streams emanating from solar maximum holes. This allows an unambiguous association of every stream identified in interplanetary space with a coronal hole on the solar surface with consistent magnetic polarity. Solar wind streams emanating from the solar maximum holes generally show lower velocities of 400 to 600 km/s compared to the polar hole stream velocities of 700 to 800 km/s. However, the SWICS O7+/O6+ charge-state ratios, which are a proxy for coronal temperatures, do not reveal a consistent difference. Though a number of solar maximum holes have a significantly, up to three times, higher temperature compared to the polar coronal holes, the majority of the investigated holes and specifically those with new cycle polarity have a coronal temperature within the range of polar hole temperatures. Likewise, the magnetic flux density in the solar maximum holes and in the polar coronal holes, as derived from the synoptic maps, is not strikingly different. Therefore any intrinsic difference between solar maximum holes and polar coronal holes is small. The striking discrepancy in their kinetic properties, namely the slower velocity of the solar wind streams emanating from solar maximum holes, may partly be attributed to deceleration of the solar wind during propagation to the spacecraft. The discrepancy may also be influenced by active regions in close proximity to the coronal holes, which presumably is more likely for smaller holes. There may, however, be a tendency for the faster wind streams to emanate from cooler holes.

Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.; Forsyth, R.

2003-04-01

262

The velocity and the density spectrum of the solar wind from simultaneous three-frequency IPS observations  

NASA Technical Reports Server (NTRS)

Density inhomogeneities in the solar wind cause fluctuations regarding the emission of small diameter radio sources. Such fluctuations are called interplanetary scintillation (IPS). IPS has been studied to obtain information on both the solar wind and on the radio sources. In the present investigation it is attempted to extract information about the solar wind from simultaneous IPS observations at three radio frequencies and a single antenna. Data were recorded at frequencies of 270 MHz, 340 MHz, and 470 MHz on a 91 m telescope. Five different radio sources were observed. The observations are compared with theoretical predictions for spectra, cross-spectra, and cross-correlations using weak scattering theory and various models for the wavenumber spectrum of density inhomogeneities in the solar wind. Good fits are obtained over the observed wavenumbers to a spectrum modeled as a power law.

Scott, S. L.; Rickett, B. J.; Armstrong, J. W.

1983-01-01

263

Discovery of very high velocity outflow in V Hydra - Wind from an accretion disk in a binary?  

NASA Technical Reports Server (NTRS)

High-resolution observations of lines from the CO v = 1-0 vibration-rotation band at 4.6 microns, taken with the FTS/KPNO 4-m telescope, are reported for the carbon-rich red giant V Hydra, which is surrounded by an extended expanding molecular envelope resulting from extensive mass loss. The spectrum shows, in addition to the expected absorption at the outflow velocity of the envelope, absorption extending up to 120 km/s bluewards of the stellar velocity. A comparison of the spectrum observed at two epochs shows that the high-velocity absorption features change with time. It is suggested that the observed high-velocity features in V Hydra arise in a high-velocity polar outflow from an accretion disk in a binary system, as proposed in the mass-loss model for bipolar envelopes by Morris (1988).

Sahai, R.; Wannier, P. G.

1988-01-01

264

Velocity Field of the Stellar Wind of the Wolf-Rayet Star in the V 444 Cyg Binary System: A Parametric Model  

NASA Astrophysics Data System (ADS)

An analysis of the ?4244 Å continuum light curve of the eclipsing variable V444 Cyg is used to reconstruct the velocity law v(r) of the stellar wind of the WR star in terms of Lamers parametric and powerlaw models. Both models are inconsistent with the observed light curve, and can be rejected at the <2% significance level. Departures of the Lamers parametric relation from the empirical v(r) law reconstructed in previous papers from the same ? 4244 Å light curve on sets of concave and convexo-concave functions are statistically significant. The stellar wind of the WN5 star continues to accelerate at a considerable distance from the star’s center. This corresponds to an acceleration parameter ?>1 in terms of a coarse Lamers-law approximation for the empirical v(r) field.

Antokhin, I. I.; Cherepashchuk, A. M.

2001-04-01

265

A theory of local and global processes which affect solar wind electrons. 1: The origin of typical 1 AU velocity distribution functions: Steady state theory  

NASA Technical Reports Server (NTRS)

A detailed first principle kinetic theory for electrons which is neither a classical fluid treatment nor an exospheric calculation is presented. This theory illustrates the global and local properties of the solar wind expansion that shape the observed features of the electron distribution function, such as its bifurcation, its skewness and the differential temperatures of the thermal and suprathermal subpopulations. Coulomb collisions are substantial mediators of the interplanetary electron velocity distribution function and they place a zone for a bifurcation of the electron distribution function deep in the corona. The local cause and effect precept which permeates the physics of denser media is modified for electrons in the solar wind. The local form of transport laws and equations of state which apply to collision dominated plasmas are replaced with global relations that explicitly depend on the relative position of the observer to the boundaries of the system.

Scudder, J. D.

1978-01-01

266

MACS, An Instrument, and a Methodology for Simulations and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona  

NASA Technical Reports Server (NTRS)

The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of great importance in understanding the coronal heating mechanism and the dynamics of coronal expansion. Cram presented the theory for the formation of the K-coronal spectrum and identified two important observations. He observed the existence of temperature sensitive anti-nodes at certain wavelengths in the theoretical K-coronal spectra. The anti-nodes are separated by temperature-insensitive nodes. Remarkably, Cram showed that the wavelengths of the nodes and anti-nodes are almost independent of altitude above the solar limb. Because of these features, Cram suggested that the intensity ratios at two anti-nodes could be used as a diagnostic of the electron temperature in the K-corona. Based on this temperature diagnostic technique prescribed by Cram a slit-based spectroscopic study was performed by Ichimoto et al. on the solar corona in conjunction with the total solar eclipse of 3 Nov 1994 in Putre, Chile to determine the temperature profile of the solar corona. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurement of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 Aug 1999 in Elazig, Turkey. In this instrument one end of each of twenty fiber optic tips were positioned in the focal plane of the telescope in such a way that we could observe conditions simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends of the fibers were vertically aligned and placed at the primary focus of the collimating lens of the spectrograph to obtain simultaneous and global spectra on the solar corona. By isolating the K-coronal spectrum from the spectrum recorded by each fiber the temperature and the wind sensitive intensity ratios were calculated to obtain simultaneous and global measurements of the thermal electron temperature and the solar wind velocity. We were successful in obtaining reliable estimates of the coronal temperature at many positions in the corona. This is the first time that simultaneous measurements of coronal temperatures have been obtained at so many points. However due to instrumental scattering encountered during observations, reliable estimates of the wind velocity turned out to be impossible to obtain. Although remedial measures were taken prior to observation, this task proved to be difficult owing to the inability to replicate the conditions expected during an eclipse in the laboratory. The full extent of the instrumental scattering was apparent only when we analyzed the observational sequence. Nevertheless the experience obtained from this very first attempt to simultaneously and globally measure both the wind velocity and the temperature on the solar corona have provided valuable information to conduct any future observations successfully.

Reginald, Nelson L.; Fisher, Richard R. (Technical Monitor)

2000-01-01

267

Linear dependence of the postsunset equatorial anomaly electron density on solar flux and its relation to the maximum prereversal E × B drift velocity through its dependence on solar flux  

NASA Astrophysics Data System (ADS)

The postsunset equatorial ionization anomaly, with maximum F layer electron density, Nemax, occurring near 2100 LT, has been found during solar maximum to be a linear function of the maximum prereversal E × B drift velocity (E × B drift). In order to examine this relation at all levels of solar flux, Nemax is measured during 13 years of an entire solar cycle by eight ionospheric sounders located in the anomaly in both north and south dip latitudes and in eastern Asia, the Pacific, and South America. At each location the monthly median Nemax increases linearly with the monthly average solar flux, Sa, over the range from 70 to 285 sfu. The linear function varies markedly with location and by month at each location. The relation to E × B drift, which is also a linear function of Sa, is determined using measurements of Nemax versus Sa measured at Bogota in the anomaly plotted as a function of E × B versus Sa measured at Jicamarca at the dip equator. The result is that Nemax is a linear function of E × B, which is in agreement with that found previously during solar maximum. Accordingly, the Nemax versus E × B relation is independent of Sa. The fact that Nemax is linear in Sa at each site implies Nemax is linear in E × B at each but with a functional dependence that varies with latitude and longitude.

Whalen, James A.

2004-07-01

268

Development of a simple wind speedometer for application in countries of the developing world  

NASA Astrophysics Data System (ADS)

The development of a wind measuring apparatus (WMA), which will record wind energy respectively wind power over longer periods is outlined. On the basis of the measurement data a decision can be made for the location of a wind mill generator. A favorably priced WMA was developed which will yield the following data: (1) device specific wind energy; (2) equivalent average wind velocity; and (3) equivalent average wind power. The device uses a constant breaking torque which can be adjusted so that measurements will only start at a predetermined minimum wind velocity. A mechanically operating switch can be installed which will interrupt the recording at a present maximum wind velocity. The apparatus has favorable manufacturing costs and the mechanically operating device is independent of an external energy source.

Grundmann, R.; Hallmann, W.; Schaefer, H.

1983-12-01

269

The polar wind: Recent observations  

NASA Astrophysics Data System (ADS)

The polar wind is an ambipolar outflow of thermal plasma from the high-latitude ionosphere to the magnetosphere, and it primarily consists of H+, He+ and O+ ions and electrons. Statistical and episodic studies based primarily on ion composition observations on the ISIS-2, DE-1, Akebono and Polar satellites over the past four decades have confirmed the existence of the polar wind. These observations spanned the altitude range from 1000 to ˜50,500 km, and revealed several important features in the polar wind that are unexpected from “classical” polar wind theories. These include the day night asymmetry in polar wind velocity, which is 1.5 2.0 times larger on the dayside; appreciable O+ flow at high altitudes, where the velocity at 5000 10,000 km is of 1 4 km/s; and significant electron temperature anisotropy in the sunlit polar wind, in which the upward-to-downward electron temperature ratio is 1.5 2. These features are attributable to a number of “non-classical” polar wind ion acceleration mechanisms resulting from strong ionospheric convection, enhanced electron and ion temperatures, and escaping atmospheric photoelectrons. The observed polar wind has an averaged ion temperature of ˜0.2 0.3 eV, and a rate of ion velocity increase with altitude that correlates strongly with electron temperature and is greatest at low altitudes (<4000 km for H+). The rate of velocity increase below 4000 km is larger at solar minimum than at solar maximum. Above 4000 km, the reverse is the case. This suggests that the dominant polar wind ion acceleration process may be different at low and high altitudes, respectively. At a given altitude, the polar wind velocity is highly variable, and is on average largest for H+ and smallest for O+. Near solar maximum, H+, He+, and O+ ions typically reach a velocity of 1 km/s near 2000, 3000, and 6000 km, respectively, and velocities of 12, 7, and 4 km/s, respectively, at 10,000 km altitude. Near solar minimum, the velocity of all three species is smaller at high altitudes. Observationally it is not always possible to unambiguously separate an energized “non-polar-wind” ion such as a low-energy “cleft ion fountain” ion that has convected into a polar wind flux tube from an energized “polar-wind” ion that is accelerated locally by “non-classical” polar-wind ion acceleration mechanisms. Significant questions remain on the relative contribution between the cleft ion fountain, auroral bulk upflow, and the topside polar-cap ionosphere to the O+ polar wind population at high altitudes, the effect of positive spacecraft charging on the lowest-energy component of the H+ polar wind population, and the relative importance of the various classical and non-classical ion acceleration mechanisms. These questions pose several challenges in future polar wind observations: These include measurement of the lowest-energy component in the presence of positive spacecraft potential, definitive determination and if possible active control of the spacecraft potential, definitive discrimination between polar wind and other inter-mixed thermal ion populations, measurement of the three-dimensional ion drift velocity vector and the parallel and perpendicular ion temperatures or the detailed three-dimensional velocity distribution function, and resolution of He+ and other minor ion species in the polar wind population.

Yau, Andrew W.; Abe, Takumi; Peterson, W. K.

2007-11-01

270

Radar Interferometer Investigations of the Horizontal Winds, Vertical Velocities, Vorticity, and Divergence Around Frontal Zones and in Mesoscale Waves.  

National Technical Information Service (NTIS)

The goal of the research has been to use the state-of-the-art, phased-array MU radar facility in Kyoto, Japan, to study the perturbation winds and turbulence associated with frontal zones and mesoscale waves. There are four critical parameters in the dyna...

M. F. Larsen

1992-01-01

271

Wind velocity, water vapor, and temperature measurements from space using 2 um Tm:Ho;YAG laser  

NASA Astrophysics Data System (ADS)

In meteorological and climatological fields, the scientific community will increasingly need global measurements of key atmospheric parameters with high spatial resolution (horizontal as well as vertical): the spaceborne lidars are the most suitable instruments for those missions. While backscatter lidar (ATLID, currently studied as ESA) is presently first candidate for space deployment, the next generation of lidars will be DIAL and Doppler wind lidars, presenting a higher level of complexity, mainly due to the large power and complex signal processing required. The present considered wind lidars are based on CO(subscript 2) lasers, whose space compliance still needs confirmation, while alexandrite lasers are considered for water vapor and temperature measurements, but they need flashlamp pumping which poses a lot of several thermal constraints and lifetime problems: on the other side, the recent developments achieved in solid-state technology allow to envisage diode pumping as most promising possibility for both previous applications.

Ghibaudo, Jean-Bernard; Krawczyk, Rodolphe; Armandillo, Errico; Faucheux, Marc A.; Benedetti-Michelangeli, G.; Hettlage, E.; Flamant, Pierre H.; Pelon, Jacques R.; Fantoni, Roberta; Salvetti, G.; Fiocco, G.; Luthy, Willy

1994-09-01

272

Micro-grid Dynamic Response Enhancement Using New Proportional Integral Wind Turbine Pitch Controller and Neuro-fuzzy Photovoltaic Maximum Power Point Tracking Controller  

Microsoft Academic Search

Power deregulation and shortage of transmission capacities have led to increased interest in distributed generators, especially renewable sources. In this study, a complete model is developed that can simulate in detail the transient dynamic performance of the micro-grid during and subsequent to the islanding process. Wind speed fluctuations cause high fluctuations in output power of a wind turbine, resulting in

Rashad M. Kamel; Aymen Chaouachi; Ken Nagasaka

2009-01-01

273

The velocity and magnetic field fluctuations of the solar wind at 1 AU: Statistical analysis of Fourier spectra and correlations with plasma properties  

NASA Astrophysics Data System (ADS)

Ten years of ACE plasma and magnetic field measurements are divided into 20,076 subintervals that are 4.55 h long. Each subinterval is Fourier analyzed resulting in a statistical ensemble of 20,076 realizations of the solar wind and its “turbulence.” Oxygen charge-state ratios are used to categorize each subinterval as coronal-hole-origin plasma, non-coronal-hole-origin plasma, or ejecta. A number of known properties of the solar wind v and B fluctuations are statistically confirmed and new informatin as functions of the type of plasma is obtained. For the fluctuations it is found that the coronal-hole-origin versus non-coronal-hole-origin classification is more fundamental than a fast-wind versus slow-wind classification. In the frequency range 4.3 × 10-4-1.9 × 10-3 Hz, the ensemble the mean spectral indices of the magnetic field, velocity, and total energy are -1.62, -1.41, and -1.52, however the spectral indices vary with changes in the type of plasma. The number of strong current sheets in each subinterval is recorded. The fluctuation amplitudes, Alfvén ratios, and outward-inward Elsasser ratios are all strongly correlated with the properties of the plasma and the density of current sheets. Regions wherein the fluctuation spectra are shallowest correspond to coronal-hole plasma; regions wherein the spectra are steepest correspond to non-coronal-hole plasma and ejecta. The autocorrelation times for the spectral indices and amplitudes are 20-30 h, similar to the autocorrelation times for the proton specific entropy, the carbon charge-state ratio, the density of strong current sheets, and the classification of plasma. Analysis is performed to interpret ensembles of spectra with variance error.

Borovsky, Joseph E.

2012-05-01

274

Further Experiments on the Velocity Field and Passive Scalar Structure in High Reynolds Number Grid-Generated Wind Tunnel Turbulence  

Microsoft Academic Search

Results of homogeneous, shearless turbulence up to R_lambda ~ 800, generated by an active grid consisting of randomly rotated flapping wings(Makita, H., Fluid Dyn. Res., 8), 53-64, 1991., are presented. The measurements were conducted in a 91 x 91 cm^2 x 10 m suction tunnel. The evolution of the velocity field is consistent with our earlier experiment(Mydlarski, L. and Warhaft,

L. Mydlarski; Z. Warhaft

1996-01-01

275

Forward velocity effects on fan noise and the suppression characteristics of advanced inlets as measured in the NASA Ames 40 by 80 foot wind tunnel: Acoustic data report  

NASA Astrophysics Data System (ADS)

Forward velocity effects on the forward radiated fan noise and on the suppression characteristics of three advanced inlets relative to a baseline cylindrical inlet were measured in a wind tunnel. A modified JT15D turbofan engine in a quiet nacelle was the source of fan noise; the advanced inlets were a CTOL hybrid inlet, an STOL hybrid inlet, and a treated deflector inlet. Also measured were the static to flight effects on the baseline inlet noise and the effects on the fan noise of canting the baseline inlet 4 deg downward to simulate typical wing mounted turbofan engines. The 1/3 octave band noise data from these tests are given along with selected plots of 1/3 octave band spectra and directivity and full scale PNL directivities. The test facilities and data reduction techniques used are also described.

Moore, M. T.

1981-01-01

276

Winds  

NSDL National Science Digital Library

In this problem-based learning (PBL) scenario, students prepare a presentation for investors showing how their fishing company has a significant advantage because it locates upwelling zones and fishing areas using TRMM (Tropical Rainfall Measuring Mission) and other satellite data. Prior to launching the PBL, students learn about wind: the topics of air pressure, coriolis effect, upwelling and the role of differential heating on the atmosphere are explored in classroom demonstrations. Materials required include a beaker, coffee grounds, drinking straw, balloon, flashlight, and turntable. The resource includes teacher background information, glossary, assessment rubric, and an appendix introducing problem-based learning.

277

Velocity Distributions, Charge States and Abundances of Inner Source Pickup Ions as Obtained from the Solar Wind Charge Exchange Model  

NASA Astrophysics Data System (ADS)

Generally the origin of inner-source pickup ions is attributed to the interaction of solar wind ions with dust particles in the inner heliosphere. We have further developed the charge-exchange model of Wimmer- Schweingruber and Bochsler (2003) and quantified some results using the constraints provided by observations of dust size distributions, dust density distributions, and fluxes and abundances of pickup ions. Specifically, we have investigated the production of sputtered particles from small grains and find, that they could easily supply the observed amount of inner-source pickup ions. However, the apparent overabundance of neon among inner source pickup ions continues to pose an enigma, which could possibly be solved by constraining the production process to the outskirts of the solar corona.

Bochsler, P.; Moebius, E.; Wimmer-Schweingruber, R. F.

2006-12-01

278

Forward velocity effects on fan noise and the suppression characteristics of advanced inlets as measured in the NASA-Ames 40 by 80 foot wind tunnel  

NASA Technical Reports Server (NTRS)

Forward velocity effects on the forward radiated fan noise and on the suppression characteristics of three advanced inlets relative to a baseline cylindrical inlet were measured in the NASA Ames Research Center 40 x 80 foot Wind Tunnel. A modified JT15D turbofan engine in a quiet nacelle was the source of fan noise; the advanced inlets were a Conventional Takeoff/Landing (CTOL) hybrid inlet, a Short Takeoff/Landing (STOL) hybrid inlet, and a treated deflector inlet. Also measured were the static to flight effects on the fan noise of canting the baseline inlet 4 deg downward to simulate typical wing mounted turbofan engines. The CTOL hybrid inlet suppressed the high tip speed fan noise as much as 18 PNdB on a 61 m (200 ft) sideline scaled to a CF6 size engine while the STOL hybrid inlet suppressed the low tip speed fan noise as much as 13 PNdB on a 61 m (200 ft) sideline scaled to a OCSEE size engine. The deflector inlet suppressed the high tip speed fan noise as much as 13 PNdB at 61 m (200 ft) overhead scaled to a CF6 size engine. No significant changes in fan noise suppression for the CTOL and STOL hybrid inlets occurred for forward velocity changes above 21 m/s (68 ft/s) or for angle of attack changes up to 15 deg. However, changes in both forward velocity and angle of attack changed the deflector inlet noise unpredictably due to the asymmetry of the inlet flow field into the fan.

Moore, M. T.

1980-01-01

279

Determination of the Mass Loss Rate and the Terminal Velocity of Stellar Winds. I. Genetic Algorithm for Automatic Line Profile Fitting  

NASA Astrophysics Data System (ADS)

A new method for automatic fitting of Pline profiles in UV spectra of stellar winds is presented. The line source function is calculated using Sobolev's approximation and the emergent flux is obtained by exact integration of the equation of the radiation transport (similar to the SEI method described by Lamers et al. (1987)). The quality of the fit is evaluated using the likelihood estimator. The maximization of the likelihood is done by a genetic algorithm. The advantages of our method with respect to other similar approaches are its robustness and its insensibility to the initial guess. In addition, the algorithm guarantees the localization of the global maximum of the likelihood hypersurface, which is not the case for classical minimization algorithms. Here we present an implementation of the genetic algorithm for line profile fitting, its tests on both synthetic and real data and an estimation of the confidence limits of the results.

Georgiev, L.; Hernández, X.

2005-04-01

280

VisibleWind: wind profile measurements at low altitude  

NASA Astrophysics Data System (ADS)

VisibleWindTM is developing an inexpensive rapid response system, for accurately characterizing wind shear and small scale wind phenomena in the boundary layer and for prospecting suitable locations for wind power turbines. The ValidWind system can also collect reliable "ground truth" for other remote wind sensors. The system employs small (0.25 m dia.) lightweight balloons and a tracker consisting of an Impulse 200 XL laser rangefinder coupled to a PC for automated data recording. Experiments on balloon trajectories demonstrate that the laser detection of range (+/- 0.5 m), together with measured azimuth and altitude, is an inexpensive, convenient, and capable alternative to other wind tracking methods. The maximum detection range has been increased to 2200 meters using micro-corner-cube retroreflector tape on balloons. Low power LEDs enable nighttime tracking. To avoid large balloon gyrations about the mean trajectory, we use balloons having low ascent rates and subcritical Reynolds numbers. Trajectory points are typically recorded every 4 - 7 seconds. Atmospheric features observed under conditions of inversions or "light and variable winds" include abrupt onsets of shear at altitudes of 100-250 m, velocity changes of order 1-3 m/s within layers of 10-20 m thickness, and veering of the wind direction by 180 degrees or more as altitude increases from 300 to 500 m. We have previously reported comparisons of balloon-based wind profiles with the output of a co-located sodar. Even with the Impulse rangefinder, our system still requires a "man in the loop" to track the balloon. A future system enhancement will automate balloon tracking, so that laser returns are obtained automatically at 1 Hz. While balloon measurements of large-scale, high altitude wind profiles are well known, this novel measurement system provides high-resolution, real-time characterization of the fluctuating local wind fields at the bottom of the boundary layer where wind power turbines and other remote wind sensors must operate.

Wilkerson, Tom; Bradford, Bill; Marchant, Alan; Apedaile, Tom; Wright, Cordell

2009-09-01

281

Rotorwash wind sensor evaluation  

NASA Astrophysics Data System (ADS)

This project's purpose was to assess and document the ability of the Qualimetrics, Inc. model 2132 wind sensor (a cup and vane type sensor) to measure a rotor wash flow field as compared to the TSI, Inc. model 204D ion beam deflection sensor. The tests concentrated on the sensor's ability to capture dynamic characteristics of a helicopter rotor wash flow field. The project was conducted from April to November 1992 and consisted of quantitative laboratory and field testing. The laboratory testing included 9.5 hours of wind tunnel test time, subjecting each sensor to three step input tests at velocities of 20 knots, 50 knots, and 80 knots. Field test data were collected during one hour of SH-60B helicopter hover time at heights of 15 and 25 feet above ground level at distances of 35 and 70 feet from the wind sensors. Aircraft gross weights ranged between 19,600 and 20,500 pounds. All field test data were obtained in ambient wind conditions of approximately 8 knots at 40 degrees relative to the aircraft nose, -40 feet pressure altitude in an ambient temperature of 85 F. Laboratory data analysis indicates the model 2132 cup and vane sensor's time constant values were significantly higher than those of the model 204D ion beam sensor and varied relative to wind tunnel velocity settings. This indicates the model 2132 sensor's ability to accurately capture oscillations in a dynamic flow field is significantly less than the model 204D sensor. The model 2132 sensor did detect periodic or pulsating velocity magnitudes, but failed to capture significant oscillations as compared to the model 204D sensor. Comparative analysis of all field test event data indicate the model 2132 sensor only detected frequencies below 1.5 Hz and only captured an average of 46 percent of the model 204D sensor's maximum amplitude pulse values that were below 1.5 Hz. The model 2132 sensor's inability to capture many of the maximum pulse amplitudes is evidence of the sensor's limited capability to capture velocity magnitude variations in a dynamic flow field. The model 2132 cup and vane sensor's average and minimum velocities for each test event were significantly higher than the model 204D ion beam sensor's values. This is additional evidence that the model 2132 sensor is slower to respond to rapid changes in a dynamic flow field. Compared to the TSI, Inc. model 204D ion beam sensor, the Qualimetrics, Inc. model 2132 cup and vane sensor failed to measure accurately a rotorwash flow field in terms of frequency, amplitude, frequency content, and velocity magnitude and thus is not recommended for helicopter rotorwash velocity data collection.

Meyerhoff, Curtis L.; Lake, Robert E.; Gordge, Dennis N.

1993-08-01

282

Long-term Variation of Temperatures and Wind Velocities from Earth based Doppler-wind and Temperature Measurements in Venus Upper Atmosphere between 1990 and 2013 using the Infrared Heterodyne Spectrometer THIS  

NASA Astrophysics Data System (ADS)

Dynamics of the Venusian atmospheric transition zone between the sub-solar to anti-solar (SS-AS) flow dominated region above 120km and the superrotation dominated region below 90 km is not yet fully understood. Temperatures in the same region are not very well constrained and we lack in a comprehensive understanding of this atmospheric region. Therefore direct measurements of these parameters on various time scales and on different locations on the planet are essential for validation of global circulation models and a comprehensive understanding of the atmosphere. Such observations can be provided by the infrared heterodyne spectrometers THIS (University of Cologne) and HIPWAC (NASA GSFC). Operating around 10?m both instruments fully resolve CO2 non-LTE emission lines for Doppler-wind and temperature retrievals at an pressure level of 1?bar (~110 km). In addition to this "one-altitude" information the broader CO2 absorption lines can be used to gain information about the temperature profile lower down in the atmosphere (~60-90 km). Long term variability in Doppler-wind velocities and temperature at ~110km from campaigns between 1990 to 2013 will be presented. A report about local wave activities will be included. In addition recently retrieved temperature profiles from 60 to 90 km will be shown.

Sornig, Manuela; Stangier, Tobias; Krause, Pia; Wischnewski, Caro; Kostiuk, Ted; Livengood, Tim

2014-05-01

283

Universality of velocity spectra  

Microsoft Academic Search

The purpose of this paper is to present unified spectral models for the three-component velocity fluctuations observed in wind-tunnel generated shear flows and in the atmospheric boundary layer. Presently, only empirical models exist whose coefficients are based on the matching of these models with observed spectra. A general spectral model is presented which can be closely matched to velocity spectra

H. W. Tieleman

1995-01-01

284

Path planning and control for multiple point surveillance by an unmanned aircraft in wind  

Microsoft Academic Search

In this paper, we explore the surveillance of multiple waypoints by a constant velocity aircraft in the presence of wind. It is assumed that the aircraft has a maximum turning rate and that the wind is equal to a known constant plus small possibly time varying components. The proposed strategy consists of separate path planning and control algorithms. The path

Timothy G. McGee; J. Karl Hedrick

2006-01-01

285

Microburst Wind Structure and Evaluation of Doppler Radar for Airport Wind Shear Detection  

Microsoft Academic Search

Doppler weather radar data from the Joint Airport Weather Studies (JAWS) Project are used to determine the horizontal and vertical structure of airflow within microbursts. Typically, the associated downdraft is about 1 km wide and begins to spread horizontally at a height below 1 km. The median time from initial divergence at the surface to maximum differential wind velocity across

James W. Wilson; Rita D. Roberts; Cathy Kessinger; John McCarthy

1984-01-01

286

A statistical study of the interdependence of solar wind parameters  

NASA Astrophysics Data System (ADS)

Correlation analysis of solar wind parameters, namely solar wind velocity, proton density, proton temperature and mean interplanetary magnetic field (IMF) from the ACE spacecraft data near Earth, was done. To our best knowledge, this study is a novel one since we consider here only the parameters inside the solar wind, including the mean IMF and, hence, the solar wind is a self consistent system. We have proposed a Multiple Linear Regression (MLR) model for the prediction of the response variable (solar wind velocity) using the parameters proton density, proton temperature and mean IMF measured as daily averages. About 60% of the observed value can be predicted using this model. It is shown that, in general, the correlation between solar wind parameters is significant. A deviation from the prediction at the solar maximum is interpreted. These results are verified by a graphical method.

John, Shollykutty; Kurian, P. J.

2009-04-01

287

Generation of temperature anisotropy for alpha particle velocity distributions in solar wind at 0.3 AU: Vlasov simulations and Helios observations  

NASA Astrophysics Data System (ADS)

Solar wind "in situ" measurements from the Helios spacecraft in regions of the Heliosphere close to the Sun (˜0.3 AU), at which typical values of the proton plasma beta are observed to be lower than unity, show that the alpha particle distribution functions depart from the equilibrium Maxwellian configuration, displaying significant elongations in the direction perpendicular to the background magnetic field. In the present work, we made use of multi-ion hybrid Vlasov-Maxwell simulations to provide theoretical support and interpretation to the empirical evidences above. Our numerical results show that, at variance with the case of ?p?1 discussed in Perrone et al. (2011), for ?p=0.1 the turbulent cascade in the direction parallel to the ambient magnetic field is not efficient in transferring energy toward scales shorter than the proton inertial length. Moreover, our numerical analysis provides new insights for the theoretical interpretation of the empirical evidences obtained from the Helios spacecraft, concerning the generation of temperature anisotropy in the particle velocity distributions.

Perrone, D.; Bourouaine, S.; Valentini, F.; Marsch, E.; Veltri, P.

2014-04-01

288

Satellite-tracked cumulus velocities  

NASA Technical Reports Server (NTRS)

Basic problems in the interpretation of satellite-tracked low-cloud velocities are reviewed. The METRACOM system of cloud velocity computation is outlined, and caution is urged in converting cloud velocities into wind velocities. The motion of various cumulus cells over Springfield, Mo., Barbados, and Tampa, Fla., is analyzed. It is shown that multiturret cells do not always move with the wind, that addition and deletion of turrets belonging to a specific cell may cause erratic motion in a tracer cell, and that cumulus turrets between 0.3 and 2 miles in size are the best targets for inferring the mean wind velocity within the subcloud layers. It is concluded that the accuracy of wind velocity estimates will be no better than 2 meters/sec unless the physical and dynamic characteristics of cumulus motion are further investigated.

Fujita, T. T.; Pearl, E. W.; Shenk, W. E.

1975-01-01

289

Wind Engineering  

NASA Technical Reports Server (NTRS)

Dr. Jack Cermak, Director of Fluid Dynamics and Diffusion Laboratory, developed the first wind tunnel to simulate the changing temperatures, directions and velocities of natural winds. In this work, Cermak benefited from NASA technology related to what is known as the atmospheric boundary layer (ABL).

1983-01-01

290

Some solar cycle phenomena related to the geomagnetic activity from 1868 to 1980. II - High velocity wind streams and cyclical behavior of poloidal field  

Microsoft Academic Search

Geomagnetic activity related to the distribution around the sun of the corotating sources of solar wind is discussed. The physical conditions at the solar wind sources, the cyclical behavior of the poloidal field, and the relationships between the indices aa of geomagnetic activity and the solar wind parameters are reviewed. It is shown that, at the peak of its expansion,

P. A. Simon; J.-P. Legrand

1986-01-01

291

49 CFR 193.2067 - Wind forces.  

Code of Federal Regulations, 2010 CFR

...An assumed sustained wind velocity of not less than 150 miles...Administrator finds a lower velocity is justified by adequate supportive...data; or (ii) The most critical combination of wind velocity and duration, with...

2010-10-01

292

49 CFR 193.2067 - Wind forces.  

Code of Federal Regulations, 2010 CFR

...An assumed sustained wind velocity of not less than 150 miles...Administrator finds a lower velocity is justified by adequate supportive...data; or (ii) The most critical combination of wind velocity and duration, with...

2009-10-01

293

Wind wave-forced fine sediment erosion during the slack water periods in Hangzhou Bay, China  

NASA Astrophysics Data System (ADS)

The shallow water wave simulation model-SWAN incorporated with a simple fine sediment erosion model is applied to Hangzhou Bay, China, to model the horizontal distribution of the maximum bottom orbital velocity and corresponding fine sediment erosion rates induced by: (1) southeasterly steady winds (5, 20 and 30 m/s), (2) southwesterly steady winds (5 and 20 m/s); (3) northwesterly steady winds (5 and 20 m/s); (4) east-southeasterly steady winds (5 and 20 m/s); (5) easterly steady winds (5 and 20 m/s) under closed and unclosed boundaries; and (6) unsteady winds during the slack water periods. Results suggest: (1) the steady wind wave-induced maximum bottom orbital velocities and corresponding fine sediment erosion rates generally increased with the increasing steady winds; (2) closed and unclosed boundary conditions had more significant influences on modeled fine sediment erosion rates under 5 m/s easterly steady winds than 20 m/s; and (3) steady and unsteady wind wave-induced maximum bottom currents could be significant in eroding fine sediment bed in Hangzhou Bay. The results show implications for geomorphology, sedimentology, coastal erosion, and environmental pollution mitigation in Hangzhou Bay.

Shi, John Z.; Gu, Wen-Jun; Wang, Dian-Zhi

2008-08-01

294

Power Maximization Control of Variable Speed Wind Generation System Using Permanent Magnet Synchronous Generator  

NASA Astrophysics Data System (ADS)

This paper proposes the sensorless output power maximization control of the wind generation system. A permanent magnet synchronous generator (PMSG) is used as a variable speed generator in the proposed system. The generator torque is suitably controlled according to the generator speed and thus the power from a wind turbine settles down on the maximum power point by the proposed MPPT control method, where the information of wind velocity is not required. Moreover, the maximum available generated power is obtained by the optimum current vector control. The current vector of PMSG is optimally controlled according to the generator speed and the required torque in order to minimize the losses of PMSG considering the voltage and current constraints. The proposed wind power generation system can be achieved without mechanical sensors such as a wind velocity detector and a position sensor. Several experimental results show the effectiveness of the proposed control method.

Morimoto, Shigeo; Nakamura, Tomohiko; Takeda, Yoji

295

The wave state and sea spray related parameterization of wind stress applicable from low to extreme winds  

NASA Astrophysics Data System (ADS)

Recent field and laboratory observations indicate that the variation of drag coefficient with wind speed at high winds is different from that under low-to-moderate winds. By taking the effects of wave development and sea spray into account, a parameterization of sea surface aerodynamic roughness applicable from low to extreme winds is proposed. The corresponding relationship between drag coefficient and sea surface wind speed agrees well with the existing field and laboratory observational data. It is shown that, under low-to-moderate wind conditions so that the sea spray effects could be neglected, the nondimensional aerodynamic roughness first increases and then decreases with the increasing wave age; whereas under high wind conditions, the drag coefficient decreases with the increasing wind speed due to the modification of the logarithmic wind profile by the effect of sea spray droplets produced by bursting bubbles or wind tearing breaking wave crests. The drag coefficients and sea surface aerodynamic roughnesses reach their maximum values when the 10 m wind speeds are between 25 and 33 m s-1 for different wave developments. Correspondingly, the reduction of drag coefficient under high winds reduces the increasing rate of friction velocity with increasing wind speed.

Liu, Bin; Guan, Changlong; Xie, Lian

2012-11-01

296

Wind tunnel investigation on wind turbine wakes and wind farms  

NASA Astrophysics Data System (ADS)

The interaction between atmospheric boundary layer and wind farms leads to flow modifications, which need to be deeply characterized in order to relate them to wind farm performance. The wake flow produced from a wind farm is the result of a strong interaction between multiple turbine wakes, so that the wind farm configuration turns out to be one of the dominant features to enhance power production. For the present work a wind tunnel investigation was carried out with hot-wire anemometry and velocity measurements performed with multi-hole pressure probes. The tested wind farms consist of miniature three-bladed wind turbine models. Preliminarily, the wake flow generated from a single wind turbine is surveyed, which is characterized by a strong velocity defect lying in proximity of the wind turbine hub height. The wake gradually recovers by moving downstream; the characteristics of the incoming boundary layer and wind turbulence intensity can strongly affect the wake recovery, and thus performance of following wind turbines. An increased turbulence level is typically detected downstream of each wind turbine for heights comparable to the wind turbine blade top-tip. These wake flow fluctuations produce increased fatigue loads on the following wind turbines within a wind farm, which could represent a significant hazard for real wind turbines. Dynamics of vorticity structures present in wind turbine wakes are also investigated; particular attention is paid to the downstream evolution of the tip helicoidal vortices and to oscillations of the hub vortex. The effect of wind farm layout on power production is deeply investigated. Particular emphasis is placed on studying how the flow adjusts as it moves inside the wind farm and can affect the power production. Aligned and staggered wind farm configurations are analysed, also with varying separation distances in the streamwise and spanwise directions. The present experimental results are being used to test and guide the development of improved parameterizations of wind turbines in high-resolution numerical models, such as large-eddy simulations (LES).

Iungo, G. V.; Coëffé, J.; Porté-Agel, F.

2012-04-01

297

Long and short term variations of the polar wind  

NASA Astrophysics Data System (ADS)

We present long-term and short-term variations of the polar wind in the mid-altitude (2000- 9000) km polar ionosphere from Akebono (EXOS-D) suprathermal ion mass spectrometer (SMS) observations. In particular, we will discuss a dominant process for the thermal ion acceleration to cause a variation of the ion outflow flux in such a time scale. The polar wind is a thermal ion outflow driven by the ambipolar electric field as a result of plasma pressure gradient along the geomagnetic field under typical ionospheric condition. Therefore, the polar wind velocity largely depends on a vertical density profile of thermal plasma in the high-latitude polar ionosphere. In general, the thermal plasma density profile is strongly influenced by the magnitude of EUV energy input from the Sun. The Akebono observations show a weak correlation between the H+ and O+ polar wind velocity profile and the solar F10.7 index in the time scale of several to ten days, and it is suggestive of such a causal relationship. It is also found in the Akebono observations that the polar wind velocity variation has a component corresponding to a daily variation of the geomagnetic activity. In the present analysis, the velocity profile is defined by two parameters; 1) the lowest altitude where the polar wind acceleration is identified, 2) velocity variation ratio with respect to the altitude. Our analysis indicates that the magnitude of F10.7 and the geomagnetic activity are influential in determining the polar wind velocity profile. The solar-activity dependence and seasonal variation of the polar wind velocity profiles are also investigated by the data from the Akebono. These observations spanned a solar cycle, and covered a wide range of altitudes and invariant latitudes and a variety of geomagnetic activity conditions. At low (high) altitudes below (above) 4000 km, the increase of the averaged H+ and O+ ion velocities with altitude was larger (smaller) at solar minimum than at solar maximum. For example, the averaged H+ velocity on the dayside at 4000 km altitude was approximately 8 km s-1 at low solar activity, but about 5 km s-1 at high activity. This suggests that the averaged polar wind velocity correlates differently with solar activity and the dominant acceleration process may be different at low and high altitudes, respectively. For both H+ and O+ , the observed ion velocity at high altitude was largest in the summer under essentially all magnetic and solar activity conditions. We consider geophysical processes that may contribute to the observed velocities and their solar activity and seasonal dependences.

Abe, Takumi

298

Wind loads on flat plate photovoltaic array fields  

NASA Technical Reports Server (NTRS)

The results of an experimental analysis (boundary layer wind tunnel test) of the aerodynamic forces resulting from winds acting on flat plate photovoltaic arrays are presented. Local pressure coefficient distributions and normal force coefficients on the arrays are shown and compared to theoretical results. Parameters that were varied when determining the aerodynamic forces included tilt angle, array separation, ground clearance, protective wind barriers, and the effect of the wind velocity profile. Recommended design wind forces and pressures are presented, which envelop the test results for winds perpendicular to the array's longitudinal axis. This wind direction produces the maximum wind loads on the arrays except at the array edge where oblique winds produce larger edge pressure loads. The arrays located at the outer boundary of an array field have a protective influence on the interior arrays of the field. A significant decrease of the array wind loads were recorded in the wind tunnel test on array panels located behind a fence and/or interior to the array field compared to the arrays on the boundary and unprotected from the wind. The magnitude of this decrease was the same whether caused by a fence or upwind arrays.

Miller, R. D.; Zimmerman, D. K.

1981-01-01

299

Describing Velocity  

NSDL National Science Digital Library

Learn to connect position-time and velocity-time graphs. Explore velocity using an animated car icon connected to either a position-time or a velocity-time graph, or both. Then investigate other motion graphs. Describing Velocity is the fourth of five SmartGraphs activities designed for a typical physical science unit of study on the motion of objects.

Consortium, The C.

2012-02-07

300

Singapore Wind Climate.  

National Technical Information Service (NTIS)

The report documents the results of a study of wind speeds in Singapore suitable for engineering design purposes. The main findings of the report are: Annual maximum wind speed data were obtained from four meteorological stations; Fullerton Building, Teng...

P. N. Georgiou

1990-01-01

301

Wind turbine wake properties from Doppler lidar measurements  

NASA Astrophysics Data System (ADS)

Wake properties were estimated from the High-Resolution Doppler Lidar (HRDL) measurements during the Turbine Wake and Inflow Characterization Study (TWICS) in the spring of 2011. Velocity deficit, wake downwind extent, and wake meandering were obtained by detailed analysis of both lidar vertical-slice scans, performed straddling along the lidar-turbine centerline, and lidar conical scans, performed in narrow, nearly horizontal sectors that include the wind turbine inflow, and its wake at four levels. Simultaneous measurements of inflow and turbine outflow were corrected by terrain and wind direction to obtain mean wake properties. It has been found out that an operating wind turbine generates a wake with the maximum velocity deficit varying from 20% to 70% extending up to 10 rotor diameters downstream of the turbine, depending on the wind strength and atmospheric turbulence. Details including images and animations of the wake behavior will be presented.

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

2012-12-01

302

Measurements of the wind turbine wake parameters with a pulsed coherent lidar under various atmospheric conditions  

NASA Astrophysics Data System (ADS)

The strategy of measurements with a pulsed coherent Doppler lidar (PCDL) and the method of raw data processing to estimate the parameters of the wake formed behind a wind turbine downwind are suggested. Measurements with a 2-?m PCDL demonstrate that depending on the atmospheric conditions, the operating wind turbine generates a wake with maximum deficit of the wind velocity from 27 to 75% and longitudinal wake sizes varying from 120 to 1180 m. It is demonstrated that doubling of the turbulent energy dissipation rate causes the longitudinal size of the wake generated by the wind turbine to halve.

Smalikho, I. N.; Pitchugina, Y. L.; Banakh, V. A.; Brewer, W. A.

2013-01-01

303

Effects of atmospheric stability on the evolution of wind turbine wakes: Volumetric LiDAR scans  

NASA Astrophysics Data System (ADS)

Aerodynamic optimization of wind farm layout is a fundamental task to reduce wake effects on downstream wind turbines, thus to maximize wind power harvesting. However, downstream evolution and recovery of wind turbine wakes are strongly affected by the characteristics of the incoming atmospheric boundary layer (ABL) flow, like the vertical profiles of the mean wind velocity and the turbulence intensity, which are in turn affected by the ABL stability regime. Therefore, the characterization of the variability of wind turbine wakes under different ABL stability regimes becomes fundamental to better predict wind power harvesting and improve wind farm efficiency. To this aim, wind velocity measurements of the wake produced by a 2 MW Enercon E-70 wind turbine were performed with three scanning Doppler wind Light Detection and Ranging (LiDAR) instruments. One LiDAR was typically devoted to the characterization of the incoming wind, in particular wind velocity, shear and turbulence intensity at the height of the rotor disc. The other two LiDARs performed scans in order to characterize the wake velocity field produced by the tested wind turbine. The main challenge in performing field measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between LiDAR measurement volume and wake location, different LiDAR measurement procedures were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. Furthermore, volumetric scans of the wind turbine wake were performed under different wind conditions via two simultaneous LiDARs. Through the evaluation of the minimum wake velocity deficit as a function of the downstream distance, it is shown that the stability regime of the ABL has a significant effect on the wake evolution; specifically the wake recovers faster under convective conditions. This result suggests that atmospheric inflow conditions, and particularly thermal stability, should be considered for improved wake models and predictions of wind power harvesting.

Valerio Iungo, Giacomo; Porté-Agel, Fernando

2014-05-01

304

Orientation Cues for High-Flying Nocturnal Insect Migrants: Do Turbulence-Induced Temperature and Velocity Fluctuations Indicate the Mean Wind Flow?  

Microsoft Academic Search

Migratory insects flying at high altitude at night often show a degree of common alignment, sometimes with quite small angular dispersions around the mean. The observed orientation directions are often close to the downwind direction and this would seemingly be adaptive in that large insects could add their self-propelled speed to the wind speed, thus maximising their displacement in a

Andy M. Reynolds; Don R. Reynolds; Alan D. Smith; Jason W. Chapman; Alexander Borst

2010-01-01

305

Velocity fluctuations in the wake behind wind breakers and at the edge of the shear layer, and their correlations with the free stream  

Microsoft Academic Search

Wind tunnel tests and field experiments have been performed in order to compare, for neutral conditions, aspects of the wake flow in the external mixing layer of the upper region of a porous wire mesh fence, with a porosity of 70%, a tree canopy (cypress macrocarpa) with a porosity of 80%, and a dense wheat field.

U. Boldes; J. Colman; V. Nadal Mora; A. Zumarraga

1995-01-01

306

Changes in wind regime around a nickel-copper smelter at Monchegorsk, northwestern Russia  

NASA Astrophysics Data System (ADS)

Wind stress may significantly change plant damage by aerial pollutants. However, almost no information exists on pollution-induced changes in wind regime around the strong emission sources. Wind speed, measured in industrial barrens adjacent to the nickel-copper smelter at Monchegorsk (Kola Peninsula, NW Russia), was two to three times as high as in the slightly polluted and nearly unpolluted forests. The ratio between the maximum wind velocity within 30 s and the average velocity of that time interval showed no temporal variation, thus characterising the wind regime. This ratio was highest in unpolluted forests, suggesting the predominance of gusty winds; in industrial barrens the maximum wind speed was only slightly higher than the average value. Since topography did not explain the spatial variation in wind regime, I conclude that my data represent the first direct evidence for distinct changes in wind regime caused by pollution-induced habitat deterioration. The results suggest that initial (partly pollution-induced) forest disturbance causes secondary effects (like increased snow evaporation, followed by soil freezing and plant damage) that may enhance further disturbance in a positive feedback fashion.

Kozlov, M. V.

2002-05-01

307

Sensitivity Analysis of Wind Strength  

NSDL National Science Digital Library

This problem set introduces univariate and bivariate sensitivity analysis using the horizontal velocity profile of the wind in Matlab. This can be easily adapted for river flow, wind chill temperature, etc.

King, James

308

Electronic Excitation and Charge Transfer Processes in Collisions of H+, H_2^+, and H_3^+ Ions with Carbon Monoxide at Typical Solar-wind Velocities  

NASA Astrophysics Data System (ADS)

Luminescence in the 200-580 nm spectral region was observed in the collisions of H+, H_2^+, and H_3^+ with CO in the 50-1000 eV projectile energy range. Using computer simulations, we have identified emission of the following products in the observed spectra: the CO+(A-X) comet-tail system, CO+(B-X) first negative system, CO+(B-A) Baldet-Johnson system, and CO(b-a) third positive system. Also, an emission from atomic hydrogen (H? line at 486nm) has been observed. From the analysis of the experimental spectra, we have determined the absolute emission cross-sections for the formation of the observed products. Computer simulations gave the excited-product population distributions over vibrational and rotational energy levels. The vibrational level distribution from the CO+(A-X) comet-tail system is compared with the data for CO excited by 100 eV electrons and extreme ultraviolet radiation (XUV) photons. We have used these data to analyze the excitation conditions in the comet Humason (1961e). From the vibrational population distributions observed in the comet, we found that this distribution can be reproduced if electrons produce 25%, protons 70%, and XUV photons produce 5% of the emitting molecules. We find that the ratio of the CO+(B-X) emission to the sum of two main emissions (CO+(A-X)+CO+(B-X)) is velocity dependent and does not depend on the projectile ion type. For small velocities (below 100 km s-1) the ratio is about 5%, while for higher velocities it increases to 30%. For these data, we have found an empirical formula that satisfactorily describes the experimental data: R = R max(1 - v th/v), (where R max = 33%, v th = 87 km s-1). This could be used to infer the velocity of ions producing the observed emission of CO+ products.

Werbowy, S.; Pranszke, B.

2014-01-01

309

Energy from the Wind  

ERIC Educational Resources Information Center

The large-scale generation of electrical power by wind turbine fields is discussed. It is shown that the maximum power that can be extracted by a wind turbine is 16/27 of the power available in the wind. (BB)

Pelka, David G.; And Others

1978-01-01

310

Efficient Low-Speed Flight in a Wind Field  

NASA Technical Reports Server (NTRS)

A new software tool was needed for flight planning of a high altitude, low speed unmanned aerial vehicle which would be flying in winds close to the actual airspeed of the vehicle. An energy modeled NLP (non-linear programming) formulation was used to obtain results for a variety of missions and wind profiles. The energy constraint derived included terms due to the wind field and the performance index was a weighted combination of the amount of fuel used and the final time. With no emphasis on time and with no winds the vehicle was found to fly at maximum lift to drag velocity, V(sub md). When flying in tail winds the velocity was less than V(sub md), while flying in head winds the velocity was higher than V(sub md). A family of solutions was found with varying times of flight and varying fuel amounts consumed which will aid the operator in choosing a flight plan depending on a desired landing time. At certain parts of the flight, the turning terms in the energy constraint equation were found to be significant. An analysis of a simpler vertical plane cruise optimal control problem was used to explain some of the characteristics of the vertical plane NLP results.

Feldman, Michael A.

1996-01-01

311

Active yaw control with sensorless wind speed and direction measurements for horizontal axis wind turbines  

Microsoft Academic Search

An active yaw control algorithm for wind turbines without wind intensity and direction measurement is presented. The algorithm is based on the maximum generated power as an indication to determine the maximum wind speed direction. Few program instructions are added to the controller program to implement the Hill Climbing Control for maximum power from either the load current and wind

F. A. Farret; L. L. Pfischer; D. P. Bernardon

2000-01-01

312

Wind velocity measurement accuracy with highly stable 12 mJ/pulse high repetition rate CO2 laser master oscillator power amplifier  

NASA Technical Reports Server (NTRS)

A coherent CO2 lidar operating in a master oscillator power amplifier configuration (MOPA) is described for both ground-based and airborne operation. Representative data taken from measurements against stationary targets in both the ground-based and airborne configurations are shown for the evaluation of the frequency stability of the system. Examples of data are also given which show the results of anomalous system operation. Overall results demonstrate that velocity measurements can be performed consistently to an accuracy of + or - 0.5 m/s and in some cases + or - 0.1 m/s.

Bilbro, James W.; Johnson, Steven C.; Rothermel, Jeffry

1987-01-01

313

Terminal velocity of wind, mass loss, and absorption lines of the central star of the planetary nebula 75 + 35.1 deg  

NASA Technical Reports Server (NTRS)

The high-galactic latitude planetary nebula 75 + 35.1 deg was observed in the high-dispersion mode of the International Ultraviolet Explorer (IUE) satellite in the wavelength range 1150-1950 A. The N V resonance doublet at 1240 A and O V subordinate line at 1371 A exhibit strong stellar P Cygni profiles with absorption extending to -2150 km/s and -1000 km/s, respectively. Application of the first moment method implies a mass-loss rate of M = (1-3) x 10 to the -8th solar mass/yr. The high ionization of the wind lines and the presence of strong Fe VI and Fe V lines in the stellar photosphere support that this object is quite hot. A Teff of 75,000 + or - 10,000 K was adopted, although Tc = 94,000 K was found previously from low-resolution IUE data.

Feibelman, Walter A.; Bruhweiler, Frederick C.

1989-01-01

314

Terminal velocity of wind, mass loss, and absorption lines of the central star of the planetary nebula 75 + 35. 1 deg  

SciTech Connect

The high-galactic latitude planetary nebula 75 + 35.1 deg was observed in the high-dispersion mode of the International Ultraviolet Explorer (IUE) satellite in the wavelength range 1150-1950 A. The N V resonance doublet at 1240 A and O V subordinate line at 1371 A exhibit strong stellar P Cygni profiles with absorption extending to -2150 km/s and -1000 km/s, respectively. Application of the first moment method implies a mass-loss rate of M = (1-3) x 10 to the -8th solar mass/yr. The high ionization of the wind lines and the presence of strong Fe VI and Fe V lines in the stellar photosphere support that this object is quite hot. A Teff of 75,000 + or - 10,000 K was adopted, although Tc = 94,000 K was found previously from low-resolution IUE data. 18 refs.

Feibelman, W.A.; Bruhweiler, F.C. (NASA, Goddard Space Flight Center, Greenbelt, MD (USA) Catholic Univ. of America, Washington, DC (USA))

1989-12-01

315

Integrative characteristic evaluation of DFIG maximum power extraction using lookup table approach  

Microsoft Academic Search

A DFIG wind turbine is a variable-speed wind turbine widely used in modern wind power industry. The maximum power extraction of the turbine is affected by (1) electrical characteristics of the generator, (2) aerodynamic characteristics of the turbine blades, and (3) maximum power extraction control strategies. This paper presents a DFIG maximum power extraction study through integrated steady-state characteristic and

Shuhui Li; Timothy A. Haskew; Eduard Muljadi

2010-01-01

316

Oblique, Stratified Winds about a Shelter Fence. Part I: Measurements.  

NASA Astrophysics Data System (ADS)

Wind statistics were measured using cup and sonic anemometers, placed upwind and downwind from a porous plastic windbreak fence (height h = 1.25 m, length Y = 114 m, resistance coefficient kr0 = 2.4, and porosity p = 0.45) standing on otherwise uniform land (short grass with roughness length z0 1.9 cm). Intercomparison with collocated two-dimensional sonic anemometers suggested that, except in strongly stratified winds, cup anemometers (distance constant 1.5 m), subjected to a uniform overspeeding correction (here 10%), provide a reasonably accurate transect of the mean wind across the disturbed flow region. The measurements, binned with respect to mean wind direction and stratification, establish that the resistance coefficient of a windbreak of this type implies the maximum (or “potential”) mean wind reduction, a potential that is realized in neutral, perpendicular flow and for which a semiempirical formula is derived. Obliquity of the approaching wind reduces actual shelter effectiveness below the potential value, as was already known. However, a systematic influence of stratification could only be discriminated in winds that were not too far (say, within about ±30°) from perpendicular, under which conditions both stable and unstable stratification reduced shelter effectiveness. The “quiet zone,” in which velocity standard deviations (?u, ?) are reduced relative to the approach flow, was found to extend farther downwind for the normal velocity component (u) than for the parallel component ().


Wilson, John D.

2004-08-01

317

Velocity distributions in glottal models.  

PubMed

Velocity distributions within three models of the human larynx, namely, a rigid plexiglas model, an excised canine larynx, and a computational model are investigated with experimental and theoretical analyses. A plexiglas wind tunnel with interchangeable glottal constrictions was used as a two-dimensional steady-flow model to measure velocity and pressure for various glottal shapes. A canine excised larynx was used as a prototype pulsatile flow model to study pressure and velocity variations during phonation. Results of the plexiglas modelling indicated a parabolic laminar velocity profiles upstream of the glottal constriction and turbulent and asymmetric velocity profile downstream of the glottal constriction. The time-averaged velocities of the excised larynx had similarities with the plexiglas model results, and instabilities and asymmetries were also demonstrated by the computational method. PMID:8653178

Alipour, F; Scherer, R; Knowles, J

1996-03-01

318

An estimate of solar wind velocity profiles in an coronal hole and a coronal streamer area (6-40 solar radius)  

NASA Technical Reports Server (NTRS)

Using the total electron content data obtained by the Ulysses Solar Corona Experiment during the superior solar conjunction in summer 1991, we selected two data sets, one associated with a coronal hole and the other one with coronal streamer crossings. By doing this data splitting, we find two entirely different density profiles varying as r(exp -2.7) and r(exp -2.3) for the coronal hole and coronal streamers, respectively. Assuming mass flux conservation from the inner corona to one AU, an estimate for the velocity profiles or acceleration in these two different regions can be determined. The more negative exponent of the coronal hole density profile indicates a more extended heating and acceleration region or more flaring, or both. Various possible explanations will be discussed.

Paetzold, M.; Tsurutani, B. T.; Bird, M. K.

1995-01-01

319

The sun and heliosphere at solar maximum  

NASA Technical Reports Server (NTRS)

Recent Ulysses observations from the Sun's equator to the poles reveal fundamental properties of the three-dimensional heliosphere at the maximum in solar activity. The heliospheric magnetic field originates from a magnetic dipole oriented nearly perpendicular to, instead of nearly parallel to, the Sun'rotation axis. Magnetic fields, solar wind, and energetic charged particles from low-latitude sources reach all latitudes, including the polar caps. The very fast high-latitude wind and polar coronal holes disappear and reappear together. Solar wind speed continues to be inversely correlated with coronal temperature. The cosmic ray flux is reduced symmetrically at all latitudes.

Smith, E. J.; Marsden, R. G.; Balogh, A.; Gloeckler, G.; Geiss, J.; McComas, D. J.; McKibben, R. B.; MacDowall, R. J.; Lanzerotti, L. J.; Krupp, N.; Krueger, H.; Landgraf, M.

2003-01-01

320

Maximum Urban Heat Island Intensity in Seoul.  

NASA Astrophysics Data System (ADS)

The maximum urban heat island (UHI) intensity in Seoul, Korea, is investigated using data measured at two meteorological observatories (an urban site and a rural site) during the period of 1973-96. The average maximum UHI is weakest in summer and is strong in autumn and winter. Similar to previous studies for other cities, the maximum UHI intensity is more frequently observed in the nighttime than in the daytime, decreases with increasing wind speed, and is pronounced for clear skies. A multiple linear regression analysis is performed to relate the maximum UHI to meteorological elements. Four predictors considered in this study are the maximum UHI intensity for the previous day, wind speed, cloudiness, and relative humidity. The previous-day maximum UHI intensity is positively correlated with the maximum UHI, and the wind speed, cloudiness, and relative humidity are negatively correlated with the maximum UHI intensity. Among the four predictors, the previous-day maximum UHI intensity is the most important. The relative importance among the predictors varies depending on time of day and season. A three-layer back-propagation neural network model with the four predictors as input units is constructed to predict the maximum UHI intensity in Seoul, and its performance is compared with that of a multiple linear regression model. For all test datasets, the neural network model improves upon the regression model in predicting the maximum UHI intensity. The improvement of the neural network model upon the regression model is 6.3% for the unstratified test data, is higher in the daytime (6.1%) than in the nighttime (3.3%), and ranges from 0.8% in spring to 6.5% in winter.

Kim, Yeon-Hee; Baik, Jong-Jin

2002-06-01

321

Measurement procedures for characterization of wind turbine wakes with scanning Doppler wind LiDARs  

NASA Astrophysics Data System (ADS)

The wake flow produced from an Enercon E-70 wind turbine is investigated through three scanning Doppler wind LiDARs. One LiDAR is deployed upwind to characterize the incoming wind, while the other two LiDARs are located downstream to carry out wake measurements. The main challenge in performing measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between the LiDAR measurement volume and wake location, different measuring techniques were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. The characterization of the wake recovery along the downwind direction is performed. Moreover, wake turbulence peaks are detected at turbine top-tip height, which can represent increased fatigue loads for downstream wind turbines within a wind farm.

Iungo, G. V.; Porté-Agel, F.

2013-05-01

322

Multiterminal LVDC system for optimal acquisition of power in wind-farm using induction generators  

Microsoft Academic Search

Optimal wind-power acquisition requires automatic tracking of the optimum wind-turbine speed for the prevailing wind velocity. As the wind velocity keeps changing with time so the wind-turbine must keep adjusting its speed. In a wind-farm, the wind velocities depend on the locations of the wind-turbines, each of which has its optimal turbine speed at any given time. With an eye

Weixing Lu; Boon Teck Ooi

2002-01-01

323

Wind turbine  

DOEpatents

A wind turbine of the type having an airfoil blade (15) mounted on a flexible beam (20) and a pitch governor (55) which selectively, torsionally twists the flexible beam in response to wind turbine speed thereby setting blade pitch, is provided with a limiter (85) which restricts unwanted pitch change at operating speeds due to torsional creep of the flexible beam. The limiter allows twisting of the beam by the governor under excessive wind velocity conditions to orient the blades in stall pitch positions, thereby preventing overspeed operation of the turbine. In the preferred embodiment, the pitch governor comprises a pendulum (65,70) which responds to changing rotor speed by pivotal movement, the limiter comprising a resilient member (90) which engages an end of the pendulum to restrict further movement thereof, and in turn restrict beam creep and unwanted blade pitch misadjustment.

Cheney, Jr., Marvin C. (Glastonbury, CT)

1982-01-01

324

Symbolic analysis of slow solar wind data using rank order statistics  

NASA Astrophysics Data System (ADS)

We analyze time series data of the fluctuations of slow solar wind velocity using rank order statistics. We selected a total of 18 data sets measured by the Helios spacecraft at a distance of 0.32 AU from the sun in the inner heliosphere. The data sets correspond to the years 1975-1982 and cover the end of the solar activity cycle 20 to the middle of the activity cycle 21. We first apply rank order statistics to time series from known nonlinear systems and then extend the analysis to the solar wind data. We find that the underlying dynamics governing the solar wind velocity remains almost unchanged during an activity cycle. However, during a solar activity cycle the fluctuations in the slow solar wind time series increase just before the maximum of the activity cycle.

Suyal, Vinita; Prasad, Awadhesh; Singh, Harinder P.

2012-03-01

325

Quantum Gravity and Maximum Attainable Velocities in the Standard Model  

SciTech Connect

A main difficulty in the quantization of the gravitational field is the lack of experiments that discriminate among the theories proposed to quantize gravity. Recently we showed that the Standard Model(SM) itself contains tiny Lorentz invariance violation(LIV) terms coming from QG. All terms depend on one arbitrary parameter {alpha} that set the scale of QG effects. In this talk we review the LIV for mesons nucleons and leptons and apply it to study several effects, including the GZK anomaly.

Alfaro, Jorge [Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)

2007-06-19

326

Wind-Turbine Wakes in a Convective Boundary Layer: A Wind-Tunnel Study  

NASA Astrophysics Data System (ADS)

Thermal stability changes the properties of the turbulent atmospheric boundary layer, and in turn affects the behaviour of wind-turbine wakes. To better understand the effects of thermal stability on the wind-turbine wake structure, wind-tunnel experiments were carried out with a simulated convective boundary layer (CBL) and a neutral boundary layer. The CBL was generated by cooling the airflow to 12-15 °C and heating up the test section floor to 73-75 °C. The freestream wind speed was set at about 2.5 m s-1, resulting in a bulk Richardson number of -0.13. The wake of a horizontal-axis 3-blade wind-turbine model, whose height was within the lowest one third of the boundary layer, was studied using stereoscopic particle image velocimetry (S-PIV) and triple-wire (x-wire/cold-wire) anemometry. Data acquired with the S-PIV were analyzed to characterize the highly three-dimensional turbulent flow in the near wake (0.2-3.2 rotor diameters) as well as to visualize the shedding of tip vortices. Profiles of the mean flow, turbulence intensity, and turbulent momentum and heat fluxes were measured with the triple-wire anemometer at downwind locations from 2-20 rotor diameters in the centre plane of the wake. In comparison with the wake of the same wind turbine in a neutral boundary layer, a smaller velocity deficit (about 15 % at the wake centre) is observed in the CBL, where an enhanced radial momentum transport leads to a more rapid momentum recovery, particularly in the lower part of the wake. The velocity deficit at the wake centre decays following a power law regardless of the thermal stability. While the peak turbulence intensity (and the maximum added turbulence) occurs at the top-tip height at a downwind distance of about three rotor diameters in both cases, the magnitude is about 20 % higher in the CBL than in the neutral boundary layer. Correspondingly, the turbulent heat flux is also enhanced by approximately 25 % in the lower part of the wake, compared to that in the undisturbed CBL inflow. This study represents the first controlled wind-tunnel experiment to study the effects of the CBL on wind-turbine wakes. The results on decreased velocity deficit and increased turbulence in wind-turbine wakes associated with atmospheric thermal stability are important to be taken into account in the design of wind farms, in order to reduce the impact of wakes on power output and fatigue loads on downwind wind turbines.

Zhang, Wei; Markfort, Corey D.; Porté-Agel, Fernando

2013-02-01

327

Wind shear radar simulation  

NASA Technical Reports Server (NTRS)

Viewgraphs used in a presentation on wind shear radar simulation are given. Information on a microburst model of radar reflectivity and wind velocity, radar pulse output, the calculation of radar return, microburst power spectrum, and simulation plans are given. A question and answer session is transcribed.

Britt, Charles L.

1988-01-01

328

Extreme winds in Denmark  

Microsoft Academic Search

Wind-speed data from four sites in Denmark have been analyzed in order to obtain estimates of the basic wind velocity, defined as the 50yr wind speed (10min averages) under standard conditions, i.e., 10 m over a homogeneous terrain with the roughness length 0.05 m. The sites are Skjern (15yr), Kegnæs (7yr), Sprogø (20yr), and Tystofte (16yr). The measured data are

L. Kristensen; O. Rathmann; S. O. Hansen

2000-01-01

329

An analysis of drag force and moment for upright porous wind fences  

NASA Astrophysics Data System (ADS)

Upright porous wind fences have been studied extensively because of their wide use. This paper analyzes the drag force and moment of fences to provide corroborating evidence for design of the optimal porosity that has been suggested in previous studies. The analysis of drag force and moment was based on the velocity measurements from scaled simulation tests in a wind tunnel. Particle image velocimetry was employed to provide detailed measurements of the instantaneous velocity fields around fences with different levels of porosity at different free-stream wind velocities. The data enabled us to calculate drag force and moment of fences using the integral form of momentum equation and the integral form of angular momentum equation. The drag force and moment were converted to dimensionless drag coefficient and moment coefficient. Drag force, moment, drag coefficient and moment coefficient revealed a critical fence porosity of around 0.3, which was consistent with the optimal porosity suggested in previous studies. At this critical porosity, the vertical drag force was zero, and the means of drag coefficients and moment coefficients for different wind velocities attained their maximum. The vertical drag force changed direction when the fence porosity became greater or less than the critical porosity. When the porosity was increased beyond the critical value the drag coefficient and moment coefficient decreased rapidly. Empirical equations were developed to relate drag force and moment to wind velocity, fence porosity and height.

Dong, Zhibao; Mu, Qingsong; Luo, Wanyin; Qinan, Guangqiang; Lu, Ping; Wang, Hongtao

2008-02-01

330

AGN Obscuration Through Dusty Infrared Dominated Flows. 1; Radiation-Hydrodynamics Solution for the Wind  

NASA Technical Reports Server (NTRS)

We construct a radiation-hydrodynamics model for the obscuring toroidal structure in active galactic nuclei. In this model the obscuration is produced at parsec scale by a dense, dusty wind which is supported by infrared radiation pressure on dust grains. To find the distribution of radiation pressure, we numerically solve the 2D radiation transfer problem in a flux limited diffusion approximation. We iteratively couple the solution with calculations of stationary 1D models for the wind, and obtain the z-component of the velocity. Our results demonstrate that for AGN luminosities greater than 0.1 L(sub edd) external illumination can support a geometrically thick obscuration via outflows driven by infrared radiation pressure. The terminal velocity of marginally Compton-thin models (0.2 < tau(sub T) < 0.6), is comparable to or greater than the escape velocity. In Compton thick models the maximum value of the vertical component of the velocity is lower than the escape velocity, suggesting that a significant part of our torus is in the form of failed wind. The results demonstrate that obscuration via normal or failed infrared-driven winds is a viable option for the AGN torus problem and AGN unification models. Such winds can also provide an important channel for AGN feedback.

Dorodnitsyn, A.; Bisnovatyi-Kogan. G. S.; Kallman, T.

2011-01-01

331

Analysis of Change in the Wind Speed Ratio according to Apartment Layout and Solutions  

PubMed Central

Apartment complexes in various forms are built in downtown areas. The arrangement of an apartment complex has great influence on the wind flow inside it. There are issues of residents' walking due to gust occurrence within apartment complexes, problems with pollutant emission due to airflow congestion, and heat island and cool island phenomena in apartment complexes. Currently, the forms of internal arrangements of apartment complexes are divided into the flat type and the tower type. In the present study, a wind tunnel experiment and computational fluid dynamics (CFD) simulation were performed with respect to internal wind flows in different apartment arrangement forms. Findings of the wind tunnel experiment showed that the internal form and arrangement of an apartment complex had significant influence on its internal airflow. The wind velocity of the buildings increased by 80% at maximum due to the proximity effects between the buildings. The CFD simulation for relaxing such wind flows indicated that the wind velocity reduced by 40% or more at maximum when the paths between the lateral sides of the buildings were extended.

Hyung, Won-gil; Kim, Young-Moon; You, Ki-Pyo

2014-01-01

332

Terminal Velocity  

NSDL National Science Digital Library

This lab is an inquiry activity in that students have not been exposed to the idea of terminal velocity, though they are using skills that they already have to analyze the balloon's motion. The lab is both a review of graphing and translating distance ver

Horton, Michael

2009-05-30

333

The Structure and Temporal Stability of Jupiter's Zonal Winds: A Study of the North Tropical Region  

NASA Astrophysics Data System (ADS)

This paper investigates possible long-term zonal wind variations using Voyager (1979), Hubble Space Telescope (HST; 1995, 1997, 1998), and Galileo Orbiter (1997) data that has all been processed and analyzed in the same manner for consistency. Previous attempts to measure the zonal wind profile in Voyager data had yielded inconsistent results for the maximum eastward jet near 23.7° N latitude from different studies (A. P. Ingersoll et al., 1979, Nature280, 773-775; ibid 1981, J. Geophys. Res.86, 8733-8743; T. Maxworthy 1984, Planet. Space Sci.32, 1053-1058; S. Limaye 1986, Icarus65, 335-352). This paper compares previous measurements and includes new independent analysis to conclude that the correct wind jet velocity at the time of Voyager is close to 182 m s -1, most consistent with the reported results of Maxworthy (1984). In the data sets from different epochs the overall shape of the wind profile and locations of the prograde and retrograde jets remain constant, but there are amplitude changes at a few latitudes. The largest velocity deviations between the Voyager and the 1995-1997 HST profiles occurred in the maximum eastward jet, near 23.7° N, and at 6° S and 20° S planetographic latitude. Possible causes for an apparent zonal wind decrease were explored using Galileo visible and HST near-infrared data, and the wind velocity change was determined to be real. A very definite change in cloud structure and brightness has also occurred at 23.7° N. Additionally, surface brightness changes seen at 6° S and 20° S also correlated with changes in wind speed. HST WFPC2 data obtained in 1998 showed the recovery of the 23.7° N region to a Voyager-like appearance and an increase in wind velocity to the Voyager value.

Simon, Amy A.

1999-09-01

334

On the extraordinary katabatic winds of Adélie Land  

NASA Astrophysics Data System (ADS)

The winds observed in Adélie Land, eastern Antarctica, are the strongest observed anywhere on Earth close to sea level, e.g., Cape Denison measured a mean annual wind speed of about 20ms-1. Some historic data from the area are available; however, such measurements were carried out at different places for different time periods. Hence in December 1992, we placed four automatic weather stations along the coast of Adélie Land, two in the maximum wind jet (Port Martin and Cape Denison) and one on each side of this jet (D 10 close to Dumont d'Urville and Penguin Point, respectively). We obtained about three months of good data, as on March 25, 1993, a strong storm destroyed three of the four wind sensors. Wind velocities are discussed as a function of other meteorological parameters. Further, the interrelationships between the stations are described. Some of the findings are (1) the very high wind speeds reported earlier this century are in agreement with our measurements; the wind directional constancy is high; (2) historic measurements reported Cape Denison to be the windiest station, not only for Antarctica, but also close to sea level for planet Earth; again our measurements are in agreement; (3) very strong wind speeds have a more down-slope direction than weaker ones; (4) the general atmospheric pressure gradient enhanced or inhibited the gravity flow; this is especially well pronounced in summer; and (5) in summer, above normal pressure is correlated with above normal temperatures; in fall the opposite holds true.

Wendler, Gerd; Stearns, Charles; Weidner, George; Dargaud, Guillaume; Parish, Thomas

335

Placement of wind turbines using genetic algorithms  

Microsoft Academic Search

A genetic algorithm approach is employed to obtain optimal placement of wind turbines for maximum production capacity while limiting the number of turbines installed and the acreage of land occupied by each wind farm. Specifically, three cases are considered—(a) unidirectional uniform wind, (b) uniform wind with variable direction, and (c) non-uniform wind with variable direction. In Case (a), 600 individuals

S. A. Grady; M. Y. Hussaini; M. M. Abdullah

2005-01-01

336

Design considerations for large wind mills  

Microsoft Academic Search

The paper discusses considerations for calculating power output and blade loadings of large wind turbines. Procedures are outlined for determining blade loadings under several operating conditions: constant wind velocity condition, varying velocity condition, gust condition, electrical disturbance condition, overspeed condition, and under idling and locked conditions, with or without ice. Failure of the Smith-Putnam wind turbine, constructed in 1939, is

C. J. Wilcox

1975-01-01

337

Discontinuities in the solar wind  

Microsoft Academic Search

The nonuniform emission of the solar wind from the sun means that conditions are established which favor the development of discontinuities in the plasma parameters. Since the solar wind is in rapid proper motion with respect to the sun and the earth, examination of these discontinuities requires that the wind velocity be transformed away. Then it is found that they

D. S. Colburn; C. P. Sonett

1966-01-01

338

Wind profiler signal detection improvements  

NASA Technical Reports Server (NTRS)

Research is described on potential improvements to the software used with the NASA 49.25 MHz wind profiler located at Kennedy Space Center. In particular, the analysis and results are provided of a study to (1) identify preferred mathematical techniques for the detection of atmospheric signals that provide wind velocities which are obscured by natural and man-made sources, and (2) to analyze one or more preferred techniques to demonstrate proof of the capability to improve the detection of wind velocities.

Hart, G. F.; Divis, Dale H.

1992-01-01

339

Wind tunnel study on wind and turbulence intensity profiles in wind turbine wake  

NASA Astrophysics Data System (ADS)

In recent years, there has been a rapid development of the wind farms in Japan. It becomes very important to investigate the wind turbine arrangement in wind farm, in order that the wake of one wind turbine does not to interfere with the flow in other wind turbines. In such a case, in order to achieve the highest possible efficiency from the wind, and to install as many as possible wind turbines within a limited area, it becomes a necessity to study the mutual interference of the wake developed by wind turbines. However, there is no report related to the effect of the turbulence intensity of the external flow on the wake behind a wind turbine generated in the wind tunnel. In this paper, the measurement results of the averaged wind profile and turbulence intensity profile in the wake in the wind tunnel are shown when the turbulence intensity of the external wind was changed. The wind tunnel experiment is performed with 500mm-diameter two-bladed horizontal axis wind turbine and the wind velocity in wake is measured by an I-type hot wire probe. As a result, it is clarified that high turbulence intensities enable to the entrainment of the main flow and the wake and to recover quickly the velocity in the wake.

Maeda, Takao; Kamada, Yasunari; Murata, Junsuke; Yonekura, Sayaka; Ito, Takafumi; Okawa, Atsushi; Kogaki, Tetsuya

2011-06-01

340

Optimization of Wind Turbine Airfoils/Blades and Wind Farm Layouts  

NASA Astrophysics Data System (ADS)

Shape optimization is widely used in the design of wind turbine blades. In this dissertation, a numerical optimization method called Genetic Algorithm (GA) is applied to address the shape optimization of wind turbine airfoils and blades. In recent years, the airfoil sections with blunt trailing edge (called flatback airfoils) have been proposed for the inboard regions of large wind-turbine blades because they provide several structural and aerodynamic performance advantages. The FX, DU and NACA 64 series airfoils are thick airfoils widely used for wind turbine blade application. They have several advantages in meeting the intrinsic requirements for wind turbines in terms of design point, off-design capabilities and structural properties. This research employ both single- and multi-objective genetic algorithms (SOGA and MOGA) for shape optimization of Flatback, FX, DU and NACA 64 series airfoils to achieve maximum lift and/or maximum lift to drag ratio. The commercially available software FLUENT is employed for calculation of the flow field using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a two-equation Shear Stress Transport (SST) turbulence model and a three equation k-kl-o turbulence model. The optimization methodology is validated by an optimization study of subsonic and transonic airfoils (NACA0012 and RAE 2822 airfoils). In this dissertation, we employ DU 91-W2-250, FX 66-S196-V1, NACA 64421, and Flat-back series of airfoils (FB-3500-0050, FB-3500-0875, and FB-3500-1750) and compare their performance with S809 airfoil used in NREL Phase II and III wind turbines; the lift and drag coefficient data for these airfoils sections are available. The output power of the turbine is calculated using these airfoil section blades for a given B and lambda and is compared with the original NREL Phase II and Phase III turbines using S809 airfoil section. It is shown that by a suitable choice of airfoil section of HAWT blade, the power generated by the turbine can be significantly increased. Parametric studies are also conducted by varying the turbine diameter. In addition, a simplified dynamic inflow model is integrated into the BEM theory. It is shown that the improved BEM theory has superior performance in capturing the instantaneous behavior of wind turbines due to the existence of wind turbine wake or temporal variations in wind velocity. The dissertation also considers the Wind Farm layout optimization problem using a genetic algorithm. Both the Horizontal --Axis Wind Turbines (HAWT) and Vertical-Axis Wind Turbines (VAWT) are considered. The goal of the optimization problem is to optimally position the turbines within the wind farm such that the wake effects are minimized and the power production is maximized. The reasonably accurate modeling of the turbine wake is critical in determination of the optimal layout of the turbines and the power generated. For HAWT, two wake models are considered; both are found to give similar answers. For VAWT, a very simple wake model is employed. Finally, some preliminary investigation of shape optimization of 3D wind turbine blades at low Reynolds numbers is conducted. The optimization employs a 3D straight untapered wind turbine blade with cross section of NACA 0012 airfoils as the geometry of baseline blade. The optimization objective is to achieve maximum Cl/Cd as well as maximum Cl. The multi-objective genetic algorithm is employed together with the commercially available software FLUENT for calculation of the flow field using the Reynolds-Averaged Navier-Stokes (RANS) equations in conjunction with a one-equation Sparlart-Allmaras turbulence model. The results show excellent performance of the optimized wind turbine blade and indicate the feasibility of optimization on real wind turbine blades with more complex shapes in the future. (Abstract shortened by UMI.)

Chen, Xiaomin

341

Maximizing wind penetration using voltage stability based methods for sizing and locating new wind farms in power system  

Microsoft Academic Search

Current methods in which maximum sizes of new wind farms are determined do not take into consideration their impact on future wind penetration levels. In this paper, two methods are proposed to determine maximum sizes of multiple new wind farms for maximizing wind penetration levels. In both methods, each new wind farm size is determined using an iterative process where

Ala A Tamimi; Anil Pahwa; Shelli Starrett; Noman Williams

2010-01-01

342

Helium, hydrogen, and oxygen velocities observed on ISEE-3  

NASA Technical Reports Server (NTRS)

The velocities of hydrogen, helium, and oxygen ions over a full range of solar wind conditions were recorded by the ion composition instrument and Los Alamos National Laboratory plasma instrument aboard the International Sun Earth Explorer. Interspecie velocity differences were observed frequently. For solar wind velocities between 300 and 400 km s(-1) the helium velocity exceeded the hydrogen velocity by 5 km s(-1) the average difference was 14 km s(-1), however no evidence was found for a nonzero average velocity difference between helium and oxygen ions even at the higher velocities. Velocity differences were examined in a number of streams and across a number of interplanetary shocks. Generally helium hydrogen velocity differences are bounded by the Alfven speed. Velocity differences show abrupt changes across interplanetary discontinuities, presumably tangential. The electrostatic potential change across a shock produces differences between the velocities of ions having different charges.

Ogilvie, K. W.; Coplan, M. A.; Zwicki, R. D.

1982-01-01

343

Maximum Score Type Estimators  

Microsoft Academic Search

This paper presents maximum score type estimators for linear, binomial, tobit and truncated regression models. These estimators estimate the normalized vector of slopes and do not provide the estimator of intercept, although it may appear in the model. Strong consistency is proved. In addition, in the case of truncated and tobit regression models, maximum score estimators allow restriction of the

Marcin Owczarczuk

2009-01-01

344

Turbulent velocity spectra in superfluid flows  

Microsoft Academic Search

We present velocity spectra measured in three cryogenic liquid 4He steady flows: grid and wake flows in a pressurized wind tunnel capable of achieving mean velocities up to 5 m\\/s at temperatures above and below the superfluid transition, down to 1.7 K, and a ``chunk'' turbulence flow at 1.55 K, capable of sustaining mean superfluid velocities up to 1.3 m\\/s.

J. Salort; C. Baudet; B. Castaing; B. Chabaud; F. Daviaud; T. Didelot; P. Diribarne; B. Dubrulle; Y. Gagne; F. Gauthier; A. Girard; B. Hébral; B. Rousset; P. Thibault; P.-E. Roche

2010-01-01

345

Pulsar Winds in Supernova Remnants: hydrodynamical simulations  

Microsoft Academic Search

I will consider the interaction of a pulsar wind with its associated supernova remnant by presenting results from (magneto-)hydrodynamical simulations. The pulsar wind blows a bubble (pulsar wind nebula) into the expanding supernova remnant. I will consider the scenario for which the pulsar gains a kick velocity at its birth event. This yields a pulsar wind nebula which is close

E. van der Swaluw

2002-01-01

346

Horizontal wind rotor. Final technical report  

Microsoft Academic Search

A vertical axis wind machine called, ''Horizontal Wind Rotor'' conceived in 1979 by the Grantee E.J. Guard was an effort to marry a new high tech carousel type wind rotor to a basic building design for the purpose of generating practical amounts of electricty. This was directed especially towards high performance power generation, relative to low average wind velocity fields,

Guard

1983-01-01

347

Magnetospheric feedback in solar wind energy transfer  

Microsoft Academic Search

The solar wind kinetic energy fueling all dynamical processes within the near-Earth space is extracted in a dynamo process at the magnetopause. This direct energy transfer from the solar wind into the magnetosphere depends on the orientation of the interplanetary magnetic field (IMF) as well as other solar wind parameters, such as the IMF magnitude and solar wind velocity. Using

M. Palmroth; H. E. J. Koskinen; T. I. Pulkkinen; P. K. Toivanen; P. Janhunen; S. E. Milan; M. Lester

2010-01-01

348

On the influence of solar wind conditions on the outer-electron radiation belt  

NASA Astrophysics Data System (ADS)

The dependence of outer-radiation belt electron fluxes upon solar wind velocity and density is investigated using the OMNI solar wind database and LANL-GEO geosynchronous satellites for a period spanning over 20 years. Two dimensional probability distribution functions (PDF) of the flux-solar wind velocity (Vsw) and flux-solar wind density are calculated for electron energies in the 10's of keV to MeV range. The PDF's are normalized by Vsw and density and reveal new distinct relationships. Triangle-shaped flux-Vsw distributions become non-linear PDF's, and the most probable flux increases with Vsw. The only significant saturation of fluxes observed with an increase in Vsw occurs for the lower energy electron fluxes (31.7 keV). The low energy fluxes exhibit a positive correlation with solar wind density, while mid-to-high energy electron fluxes are anti-correlated with density. The maximum probability in the PDF's depends upon both velocity and density, the probability is higher for larger Vsw, and the maximum probability is larger for a given Vsw than for density. The results indicate that Vsw may be more important for determination of fluxes than density, especially for periods of high Vsw if suitable mixed delay times are applied to each solar wind parameter. It is shown that the source population of relativistic electrons of tens of keV exhibit a 2-D normalized flux-Vsw PDF, which is strikingly similar to that of the relativistic electrons. The findings support a model whereby solar wind velocity drives convective transport of source and seed electrons, to the inner magnetosphere, where local acceleration and subsequent radial diffusion is responsible for the enhanced fluxes. The results of this study also indicate that, statistically, ULF waves driven by dynamic pressure variations may act as a significant cause of loss for electrons in the 100's of keV to MeV range.

Kellerman, A. C.; Shprits, Y. Y.

2012-05-01

349

Maximum Power Training and Plyometrics for Cross-Country Running.  

ERIC Educational Resources Information Center

Provides a rationale for maximum power training and plyometrics as conditioning strategies for cross-country runners, examining: an evaluation of training methods (strength training and maximum power training and plyometrics); biomechanic and velocity specificity (role in preventing injury); and practical application of maximum power training and…

Ebben, William P.

2001-01-01

350

Maximum thrust mode evaluation  

NASA Technical Reports Server (NTRS)

Measured reductions in acceleration times which resulted from the application of the F-15 performance seeking control (PSC) maximum thrust mode during the dual-engine test phase is presented as a function of power setting and flight condition. Data were collected at altitudes of 30,000 and 45,000 feet at military and maximum afterburning power settings. The time savings for the supersonic acceleration is less than at subsonic Mach numbers because of the increased modeling and control complexity. In addition, the propulsion system was designed to be optimized at the mid supersonic Mach number range. Recall that even though the engine is at maximum afterburner, PSC does not trim the afterburner for the maximum thrust mode. Subsonically at military power, time to accelerate from Mach 0.6 to 0.95 was cut by between 6 and 8 percent with a single engine application of PSC, and over 14 percent when both engines were optimized. At maximum afterburner, the level of thrust increases were similar in magnitude to the military power results, but because of higher thrust levels at maximum afterburner and higher aircraft drag at supersonic Mach numbers the percentage thrust increase and time to accelerate was less than for the supersonic accelerations. Savings in time to accelerate supersonically at maximum afterburner ranged from 4 to 7 percent. In general, the maximum thrust mode has performed well, demonstrating significant thrust increases at military and maximum afterburner power. Increases of up to 15 percent at typical combat-type flight conditions were identified. Thrust increases of this magnitude could be useful in a combat situation.

Orme, John S.; Nobbs, Steven G.

1995-01-01

351

Wind Characteristics Analyses and Determination of Appropriate Wind Turbine for Amasra—Black Sea Region, Turkey  

Microsoft Academic Search

In this study, wind characteristics of Amasra were analyzed with hourly wind data collected between 1997 and 2006. Wind characteristics such as monthly average mean speeds, power densities, turbulence intensities, maximum gust, and prevailing wind directions were identified. Weibull distribution model was used to determine energy output of thirty commercial wind turbines ranging from 335 to 3000 kW. Estimated mean

S. A. Akda?; Ö. Güler

2010-01-01

352

Wind Speed Estimation Based Sensorless Output Maximization Control for a Wind Turbine Driving a DFIG  

Microsoft Academic Search

This paper proposes a wind speed estimation based sensorless maximum wind power tracking control for variable-speed wind turbine generators (WTGs). A specific design of the proposed control algorithm for a wind turbine equipped with a doubly fed induction generator (DFIG) is presented. The aerodynamic characteristics of the wind turbine are approximated by a Gaussian radial basis function network based nonlinear

Wei Qiao; Wei Zhou; JosÉ M. Aller; Ronald G. Harley

2008-01-01

353

Dynamic stall occurrence on a horizontal axis wind turbine blade  

SciTech Connect

Surface pressure data from the National Renewable Energy Laboratory`s ``Combined Experiment`` were analyzed to provide a statistical representation of dynamic stall occurrence on a downwind horizontal axis wind turbine (HAWT). Over twenty thousand blade rotational cycles were each characterized at four span locations by the maximum leading edge suction pressure and by the azimuth, velocity, and yaw at which it occurred. Peak suction values at least twice that seen in static wind tunnel tests were taken to be indicative of dynamic stall. The occurrence of dynamic stall at all but the inboard station (30% span) shows good quantitative agreement with the theoretical limits on inflow velocity and yaw that should yield dynamic stall. Two hypotheses were developed to explain the discrepancy at 30% span. Estimates are also given for the frequency of dynamic stall occurrence on upwind turbines. Operational regimes were identified which minimize the occurrence of dynamic stall events.

Shipley, D.E.; Miller, M.S.; Robinson, M.C. [Colorado Univ., Boulder, CO (United States). Dept. of Aerospace Engineering Sciences

1995-07-01

354

Maxometers (peak wind speed anemometers)  

NASA Technical Reports Server (NTRS)

An instrument for measuring peak wind speeds under severe environmental conditions is described, comprising an elongated cylinder housed in an outer casing. The cylinder contains a piston attached to a longitudinally movable guided rod having a pressure disk mounted on one projecting end. Wind pressure against the pressure disk depresses the movable rod. When the wind reaches its maximum speed, the rod is locked by a ball clutch mechanism in the position of maximum inward movement. Thereafter maximum wind speed or pressure readings may be taken from calibrated indexing means.

Kaufman, J. W.; Camp, D. W.; Turner, R. E. (inventors)

1973-01-01

355

The maximum likelihood degree  

Microsoft Academic Search

Maximum likelihood estimation in statistics leads to the problem of\\u000amaximizing a product of powers of polynomials. We study the algebraic degree of\\u000athe critical equations of this optimization problem. This degree is related to\\u000athe number of bounded regions in the corresponding arrangement of\\u000ahypersurfaces, and to the Euler characteristic of the complexified complement.\\u000aUnder suitable hypotheses, the maximum

Serkan Hosten; Amit Khetan; Bernd Sturmfels

2006-01-01

356

Maximum ratio transmission  

Microsoft Academic Search

This paper presents the concept, principles, and analysis of maximum ratio transmission for wireless communications, where multiple antennas are used for both transmission and reception. The principles and analysis are applicable to general cases, including maximum-ratio combining. Simulation results agree with the analysis. The analysis shows that the average overall signal-to-mise ratio (SNR) is proportional to the cross correlation between

Titus K. Y. Lo

1999-01-01

357

Frequency spectra of vertical velocity from Flatland VHF radar data  

SciTech Connect

The vertical wind velocity over very flat terrain was observed every 153 s in the troposphere and lower stratosphere by the Flatland radar, near Champaign-Urbana, Illinois. By stratifying the spectra in various ways, the authors find the following: (1) the spectra were independent of altitude within the troposphere or lower stratosphere, but the spectra in the two regions differed in amplitude and frequency; (2) at a given altitude the spectra were independent of the wind shear d{bar u}/dz, the buoyancy frequency N, and the maximum wind speed below 16 km; (3) the change of spectral shape and amplitude with increasing background wind speed {bar u} was much less than at stations near mountains. The variance of the spectra, equal to twice the vertical kinetic energy per unit mass, roughly doubled as {bar u} increased by 10 m/s; (4) the spectra were consistent with being due to a spectrum of gravity waves, as indicated by the sharp drop in spectral amplitude near N at small {bar u} and by the fact that the observed change of shape with increasing {bar u} was quite consistent with the change of shape of model Doppler-shifted gravity wave spectra; (5) the results of comparison between the observed and model spectra are consistent with an intrinsic gravity wave spectrum that is invariant with {bar u}, d{bar u}/dz, etc., contrary to expectations from gravity wave theory; (6) the results are insensitive to the azimuthal distribution of gravity wave energy, as long as the distribution is roughly symmetrical relative to the mean flow; (7) the resulting characteristic horizontal phase velocity c{sub *} of the intrinsic frequency spectrum was about 6 m/s in both the troposphere and the stratosphere.

VanZandt, T.E.; Green, J.L. (National Oceanic and Atmospheric Administration, Boulder, CO (USA)); Nastrom G.D. (St. Cloud State Univ., MN (USA))

1991-02-20

358

Supplement Regarding Pressure-Velocity-Velocity Statistics.  

National Technical Information Service (NTIS)

The sensitivity to compressibility of a fluid of the relationship between pressure-velocity-velocity (PVV) statistics and velocity structure functions is quantified. For the first time, correct and complete incompressibility conditions on fourth-order vel...

R. J. Hill

1996-01-01

359

Effect of protection against wind according to the variation porosity of wind fence  

Microsoft Academic Search

This study examines shelter effect against the wind by using wind fence with various porosities and distance. The shelter\\u000a effect of wind fence was investigated by a wind tunnel test. Flow characteristics of velocities and turbulences behind wind\\u000a fence were measured using a hot-wire anemometer. This was done by varying the porosity by 0, 20, and 40% of the wind

Ki-Pyo You; Young-Moon Kim

2009-01-01

360

Boundary Layer Wind Profile measurements for Emission Assessments  

NASA Astrophysics Data System (ADS)

There is an ongoing effort to permanently equip NASA Langley Research Center (LaRC), Hampton, Virginia, USA as a super site for continuously monitoring weather and air quality in the atmospheric boundary layer. As a part of this effort, air quality campaign was carried out from August 1 to August 31, 2009 here at NASA LaRC. Various instruments for carrying out chemistry and physics measurements of the atmosphere as well as ground based in-situ experiments were assembled at this site. This suite of field instruments included atmospheric chemistry profiles using UV spectrometer, water vapor and temperature profiles using an IR Fourier Transform spectrometer, and wind lidar. The wind lidar was used to gather boundary layer wind velocity profiles. In this paper, wind field evolution measurements made using the Leosphere's WLS 70 windcubeTM lidar will be presented. The WindcubeTM is an active, compact, remote sensor that uses a pulsed laser source operating at 1.54 microns. The system operates based on heterodyne lidar techniques to measure Doppler shift of laser radiation backscattered by particles in the air. The output of lidar system provides minimum and maximum, direction, and standard deviation of horizontal and vertical wind speeds as well as SNR values. Wind profile measurements were made from August 10 to September 14, 2009. Wind speed and direction were gathered and analyzed. Boundary layer height up to 2 km with height resolution of 50 m has been obtained. The wind field evolution measurements includes strong wind veer and large updrafts. Plans are underway to expand this site with advanced wind lidar for air quality experiments.

Prasad, Narasimha

2010-05-01

361

A Theoretical Analysis of the Wind Power Generation System Using a Simulated Windmill  

NASA Astrophysics Data System (ADS)

The new constitution method of the wind power generation simulator considering output characteristics of the windmill is proposed. The rotational speed of the windmill changes by not only wind velocity but also condition of the load connected with the generator. Therefore, the technique which fed back the torque of the generator was verified for the estimation of the rotational speed in addition to wind velocity and characteristics of the windmill. Characteristics of the operation of the simulator resembled actual windmill, and the validity of the simulator was approximately confirmed. In addition, derivation technique of the maximum power point proposed in advance was applied to this equipment, and the operating characteristic was verified by the experiment.

Amei, Kenji; Iida, Tadashi; Ohji, Takahisa; Sakui, Masaaki

362

Prediction of solar energetic particle event histories using real-time particle and solar wind measurements  

NASA Technical Reports Server (NTRS)

The comparatively well-ordered magnetic structure in the solar corona during the decline of Solar Cycle 20 revealed a characteristic dependence of solar energetic particle injection upon heliographic longitude. When analyzed using solar wind mapping of the large scale interplanetary magnetic field line connection from the corona to the Earth, particle fluxes display an approximately exponential dependence on heliographic longitude. Since variations in the solar wind velocity (and hence the coronal connection longitude) can severely distort the simple coronal injection profile, the use of real-time solar wind velocity measurements can be of great aid in predicting the decay of solar particle events. Although such exponential injection profiles are commonplace during 1973-1975, they have also been identified earlier in Solar Cycle 20, and hence this structure may be present during the rise and maximum of the cycle, but somewhat obscured by greater temporal variations in particle injection.

Roelof, E. C.; Gold, R. E.

1978-01-01

363

Poleward expansion of the westward electrojet depending on the solar wind and IMF parameters  

NASA Astrophysics Data System (ADS)

The effect of the interplanetary parameters on the latitudinal position of the substorm westward electrojet is studied in the work. The data from the IMAGE chain of magnetic stations and POLAR and WIND satellites for the period close to the solar activity minimum (1995-1996) and for the period of the solar activity maximum (2000) have been used for this purpose. It has been indicated that the electrojet poleward edge reaches, on average, higher latitudes at a higher solar wind velocity and at a larger ( B s ) IMF southward component. It has been indicated that the average latitude of the westward electrojet center increases with increasing solar wind velocity and decreases with increasing IMF southward component, as a result of which the electrojet center is, specifically, not observed at high geomagnetic latitudes at large values of the IMF southward component.

Despirak, I. V.; Lubchich, A. A.; Biernat, H. K.; Yahnin, A. G.

2008-06-01

364

Aeroacoustic noise measurements in wind tunnel  

NASA Astrophysics Data System (ADS)

The paper describes the general characteristics of the lowspeed Acoustic Research Wind Tunnel constructed in the Aerodynamics Laboratory of E.N.S.M.A (poitiers/France) and presents the results of the preliminary experiments conducted in this wind tunnel. The wind tunnel is of open test section, open circuit and blower type. It has a test section of 30x30 sq cm and a mean velocity of 42 m/s. Aerodynamic measurements revealed a maximum turbulence intensity of less than 1%. The open test section is completely enclosed within a acoustically lined semi-anechoic chamber of dimensions 3.3x4/2.8 sq cm. Acoustic calibration of the wind tunnel is done by using both white noise and pure tone noise sources and it was observed that the tunnel can be considered to be anechoic above 100 Hz for white noise tests. Preliminary measurements of aerodynamic noise are performed by using both smooth and artificially roughened circular cylinders placed in the open test section of the wind tunnel. An aeroacoustic coherence function is deviced in order to classify the subsonic flow at moderate Reynolds numbers 5.05x10 to the 4th power Re sub d around a circular cylinder in its different flow regimes; subcritical, transcritical and supercritical. The method uses simultaneous measurements of the power spectra of the far field acoustic pressure and of the turbulent longitudinal velocity fluctuations in the wake of the cylinder as well as their cross spectra density functions CSD and especially the coherence function between the two signals. The values of the coherent function corresponding to the critical Strouhal frequencies are intense in the subcritical regime, decrease sharply in the transcritical domain and then increase and stabilize in the supercritical regime.

Alemdaroglu, H. N.

1984-02-01

365

The dynamics of buoyant jets in a linearly stratified ambient cross-flow: Implications for the interaction between volcanic plumes and wind  

NASA Astrophysics Data System (ADS)

Volcanic plumes produced by explosive eruptions commonly interact with atmospheric wind causing plume bending and a reduction of its maximum rise height. It is well known that the maximum height reached by a buoyant plume rising in a cross-flow with uniform velocity is controlled by the plume buoyancy flux at the source, the strength of the initial environmental density stratification, the wind velocity and the efficiency of turbulent entrainment. Although numerous studies have been carried out to understand the effects of variations of environmental and source conditions on the plume maximum height, turbulent entrainment has not been taken into account with the same level of detailed analysis. Here, we present new laboratory experiments aimed at better understanding the contribution of the turbulent entrainment to determining the plume maximum height. The experiments consist in injecting downward fresh water in a tank containing an aqueous NaCl solution with linear density stratification. The jet source is towed at a constant speed through the stationary fluid in order to produce a cross-flow. According to the range of source and environmental conditions, the buoyant jet is distorted or bent-over and its maximum rise height is reduced up to a factor of 2 when wind speed is high. We quantify the efficiency of turbulent entrainment due to wind in our experiments and we show that the dynamical regime strongly depends on the ratio of the horizontal wind speed and the vertical plume velocity, and on the Richardson number defined at the source. Our results provide a robust framework to characterize the entrainment coefficient due to wind in a 1D model of turbulent jet rising in a linearly stratified ambient cross-flow, and hence can be used for the assessment of the impact of atmospheric winds on the dynamics of explosive volcanic plumes.

Carazzo, Guillaume; Girault, Frédéric; Aubry, Thomas; Bouquerel, Hélène; Kaminski, Édouard

2014-05-01

366

Observation of the critical velocity peak in superfluid films  

NASA Technical Reports Server (NTRS)

Critical flow velocities measured by Doppler-shifted third sound in unsaturated helium II films are shown to exhibit a well-defined maximum as a function of film thickness and at this maximum to be considerably higher than those usually found in film flow. In addition the critical velocity is strongly temperature dependent below the maximum and relatively temperature independent above.

Telschow, K.; Rudnick, I.; Wang, T. G.

1974-01-01

367

An examination of wake effects and power production for a group of large wind turbines  

SciTech Connect

Data from a group of three MOD-2 wind turbines and two meteorological towers at Goodnoe Hills were analyzed to evaluate turbine power output and wake effects (losses in power production due to operation of upwind turbines), and atmospheric factors influencing them. The influences of variations in the ambient wind speed, wind direction, and turbulence intensity were the primary factors evaluated. Meteorological and turbine data collected at the Goodnoe Hills site from April 1 to October 17, 1985, were examined to select the data sets for these analyses. Wind data from the two meteorological towers were evaluated to estimate the effect of a wake from an upwind turbine on the wind flow measured at the downwind tower. Maximum velocity deficits were about 25% and 12% at downwind distances of 5.8 and 8.3 rotor diameters (D), respectively. However, the maximum deficits at 5.8 D were about 14/degree/ off the centerline orientation between the turbine and the tower, indicating significant wake curvature. Velocity deficits were found to depend on the ambient wind speed, ranging from 27% at lower speeds (15 to 25 mph) to 20% at higher speeds (30 to 35 mph). Turbulence intensity increases dramatically in the wake by factors of about 2.3 and 1.5 over ambient conditions at 5.8 D and 8.3 D, respectively. An analysis of the ambient (non-wake) power production for all three turbines showed that the MOD-2 power output depends, not only on wind speed, but also on the turbulence intensity. At wind speeds below rated, there was a dramatic difference in turbine power output between low and high turbulence intensities for the same wind speed. One of the turbines had vortex generators on the blades. This turbine produced from 10% to 13% more power than the other two turbines when speeds were from 24 to 31 mph. 11 refs., 21 figs., 2 tabs.

Elliott, D.L.; Buck, J.W.; Barnard, J.C.

1988-04-01

368

THREE-DIMENSIONAL NUMERICAL SIMULATIONS OF MAGNETIZED WINDS OF SOLAR-LIKE STARS  

SciTech Connect

By means of self-consistent three-dimensional magnetohydrodynamics (MHD) numerical simulations, we analyze magnetized solar-like stellar winds and their dependence on the plasma-{beta} parameter (the ratio between thermal and magnetic energy densities). This is the first study to perform such analysis solving the fully ideal three-dimensional MHD equations. We adopt in our simulations a heating parameter described by {gamma}, which is responsible for the thermal acceleration of the wind. We analyze winds with polar magnetic field intensities ranging from 1 to 20 G. We show that the wind structure presents characteristics that are similar to the solar coronal wind. The steady-state magnetic field topology for all cases is similar, presenting a configuration of helmet streamer-type, with zones of closed field lines and open field lines coexisting. Higher magnetic field intensities lead to faster and hotter winds. For the maximum magnetic intensity simulated of 20 G and solar coronal base density, the wind velocity reaches values of {approx}1000 km s{sup -1} at r {approx} 20r {sub 0} and a maximum temperature of {approx}6 x 10{sup 6} K at r {approx} 6r {sub 0}. The increase of the field intensity generates a larger 'dead zone' in the wind, i.e., the closed loops that inhibit matter to escape from latitudes lower than {approx}45 deg. extend farther away from the star. The Lorentz force leads naturally to a latitude-dependent wind. We show that by increasing the density and maintaining B {sub 0} = 20 G the system recover back to slower and cooler winds. For a fixed {gamma}, we show that the key parameter in determining the wind velocity profile is the {beta}-parameter at the coronal base. Therefore, there is a group of magnetized flows that would present the same terminal velocity despite its thermal and magnetic energy densities, as long as the plasma-{beta} parameter is the same. This degeneracy, however, can be removed if we compare other physical parameters of the wind, such as the mass-loss rate. We analyze the influence of {gamma} in our results and we show that it is also important in determining the wind structure.

Vidotto, A. A.; Jatenco-Pereira, V. [University of Sao Paulo, Rua do Matao 1226, Sao Paulo, SP 05508-090 (Brazil); Opher, M. [George Mason University, 4400 University Drive, Fairfax, VA 22030-4444 (United States); Gombosi, T. I. [University of Michigan, 1517 Space Research Building, Ann Arbor, MI 48109-2143 (United States)], E-mail: aline@astro.iag.usp.br

2009-07-01

369

A wind tunnel investigation of wind turbine wakes: Boundary-layer turbulence and surface roughness effects  

Microsoft Academic Search

Wind turbine wakes are known to have an important effect on power generation and fatigue loads in wind energy parks. Wake characteristics are expected to depend on the incoming atmospheric boundary layer flow statistics (mean velocity and turbulence levels). Here, results are presented from a wind tunnel experiment carried out at the St. Anthony Falls Laboratory atmospheric boundary layer wind

L. Chamorro; F. Porte-Agel

2008-01-01

370

Wind tunnel blockage corrections: Review and application to Savonius vertical-axis wind turbines  

Microsoft Academic Search

An investigation into wake and solid blockage effects of vertical axis wind turbines (VAWTs) in closed test-section wind tunnel testing is described. Static wall pressures have been used to derive velocity increments along wind tunnel test section which in turn are applied to provide evidence of wake interference characteristics of rotating bodies interacting within this spatially restricted domain. Vertical-axis wind

Ian Ross; Aaron Altman

2011-01-01

371

The Maximum Principle.  

National Technical Information Service (NTIS)

A relatively simple proof of the maximum principle is presented. The main objective was to obtain a proof, similar to that due to Halkin, but replacing the use of Brouwer's fixed point theorem by an easily proven contraction mapping theorem. The first use...

G. F. Bryant D. Q. Mayne

1973-01-01

372

Wind Speed Estimation and Wake model Re-calibration for Downregulated Offshore Wind Farms  

NASA Astrophysics Data System (ADS)

In recent years, the wind farm sizes have increased tremendously and with increasing installed capacity, the wind farms are requested to downregulate from their maximum possible power more frequently, especially in the offshore environment. Determination of the possible (or available) power is crucial not only because the reserve power has considerable market value but also for wind farm developers to be properly compensated for the loss during downregulation. While the available power calculation is straightforward for a single turbine, it gets rather complicated for the whole wind farm due to the change in the wake characteristics. In fact, the wake losses generated by the upstream turbine(s) decrease during downregulation and the downstream turbines therefore see more wind compared to the normal operation case. Currently, the Transmission System Operators (TSOs) have no real way to determine exactly the available power of a whole wind farm which is downregulated. Therefore, the PossPOW project aims to develop a verified and internationally accepted way to determine the possible power of a down-regulated offshore wind farm. The first phase of the project is to estimate the rotor effective wind speed. Since the nacelle anemometers are not readily available and are known to have reliability issues, the proposed method is to use power, pitch angle and rotational speed as inputs and combine it with a generic Cp model to estimate the wind speed. The performance of the model has been evaluated for both normal operation and downregulation periods using two different case studies: Horns Rev-I wind farm and NREL 5MW single turbine. During downregulation, the wake losses are not as severe and the velocity deficits at the downstream turbines are smaller as if also the wake is "downregulated". On the other hand, in order to calculate the available power, the wakes that would have been produced normally (if the turbines were not curtailed) are of importance, not the downregulated wake. For this reason, the proposed methodology is to use the clear wind without the wake (downregulated or not) as inputs to the wake model. Then a dynamic wake model can be directly applied to estimate the velocity deficit row by row inside the wind farm and calculate the possible power output on the wind farm scale. Most of the computationally affordable wake models have only been used to acquire long term, statistical information and verified using 10-min averaged data. However for smaller averaging bins or real-time modeling, the dynamics of the flow inside the wind farm such as wind direction variability and wake meandering is much more significant. Therefore GCLarsen wake model, which has been implemented in WindPro and shown to perform also well on offshore in Wake benchmark work package in EERA-DTOC, is re-calibrated and validated for single wake case in Horns Rev-I offshore wind farm.

Göçmen Bozkurt, Tuhfe; Giebel, Gregor; Kjølstad Poulsen, Niels; Réthoré, Pierre-Elouan; Mirzaei, Mahmood

2014-05-01

373

Evaluation of wind electric energy based on martian wind measurements  

NASA Astrophysics Data System (ADS)

Since Mars is characterized by strong surface wind, electric power generation by the wind activity has been proposed as a possible power source for martian base station as well as that for exploration module (George James et al., 1999, Vimal Kumar et al., 2010). George and Vimal estimated total power as 19kW and 500W, which they conclude is sufficient value as a power source of small exploration module. These values seem comparable to that used in MER( 900Wh per day ). But their estimate largely depends on the model of wind velocity and reevaluation is necessary based on plausible wind model as well as more realistic assumptions about power generation. This study evaluates plausible range of available power by using surface wind model estimated by Viking Lander measurements. Meteorological package of Viking Lander measured wind velocity and its direction at 1.6m hight at every 60 min. for 200 sols. We estimate wind statistics by using Weibull distribution function and elevation offset. We calculate the wind energy by wind turbines as the integrated value of power produced in a Martian day, and compare with solar panel and nuclear battery under various conditions (Mars ground roughness, blade length, shape of wind turbine and rotor height from the ground). As a result of the calculations, we obtain reasonable amount of wind electricity (1000 Wh per day ), which can be used if we select proper locations and suitable wind turbine.

Nishikawa, Y.; Kurita, K.

2012-12-01

374

Doppler velocity dealiasing with millimeter wave radar RHI data  

Microsoft Academic Search

Millimeter wave radar has a unique advantage on detecting cloud microphysical structure. However, it is easy to cause the velocity aliasing due to its short wavelength. Velocity dealiasing is an effective means of detecting wind field information with Doppler radar. This paper reviews the cause of velocity folding and proposed a human-machine interaction method aimed at millimeter wave radar in

Lixue Song; Ming Wei

2010-01-01

375

Variable Winds and Dust Formation in R Coronae Borealis Stars  

NASA Astrophysics Data System (ADS)

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I ?10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities ~400 km s-1 appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the decline and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.

Clayton, Geoffrey C.; Geballe, T. R.; Zhang, Wanshu

2013-08-01

376

Causes of longitude-latitudinal variations in the ionospheric F2-layer maximum in summer nighttime conditions}\\  

NASA Astrophysics Data System (ADS)

[1] The causes of longitudinal and latitudinal variations in the F2-layer maximum in the summer nighttime ionosphere at middle, subauroral, and auroral latitudes are investigated. To do this the following problems are solved in sequence. The longitudinal variations in hmF2 are studied in the belt of invariant latitudes between 40° and 65° according to the Intercosmos 19 satellite data. It is shown that the longitudinal effect in the quiet ionosphere is rather stable but differs by its character in the Southern and Northern hemispheres. Considerable discrepancies between Intercosmos 19 data and International Reference Ionosphere (IRI) model are detected at high latitudes. On the basis of the longitudinal variations in hmF2 using the servo model of the ionosphere and the Mass Spectrometer Incoherent Scatter thermosphere model, variations in the vertical drift velocity, W, caused by neutral wind are calculated. In terms of the Tikhonov regularization method, the approach to a solution of the inverse problem on deriving meridional and zonal components of the neutral wind from the longitudinal variations in W is developed. A comparison with the Horizontal Wind Model (HWM) neutral wind model is performed and an attempt to correct this model for the considered conditions is made. Estimation of the contribution of the neutral wind, composition and temperature into longitudinal and latitudinal variations in hmF2 is performed. The causes of the asymmetry between the Northern and Southern hemispheres are discussed.

Karpachev, A. T.; Gasilov, N. A.

2006-02-01

377

Selected wind tunnel test results for the Darrieus wind turbine  

Microsoft Academic Search

Five blade configurations of a 2-m-diam Darrieus wind turbine have been tested in the Vought Corporation 4.6- x 6.1-m (15- x 20-ft) Low-Speed Wind Tunnel. Rotor solidity, Reynolds number, and freestream velocities tested were in the following ranges: solidity, 13 to 30%; Reynolds number, 1 to 3 x 10⁵; freestream velocity, 7 to 11 m\\/s. The airfoil selection for all

B. F. Blackwell; R. E. Sheldahl

1977-01-01

378

Selected wind tunnel test results for the Darrieus wind turbine  

Microsoft Academic Search

Five blade configurations of a 2-m-diam Darrieus wind turbine have been tested in a low-speed wind tunnel. Rotor solidity, Reynolds number, and free-stream velocities tested were in the following ranges: solidity, 13-30%; Reynolds number, 100,000-300,000; free-stream velocity, 7-11 m\\/s. The airfoil selection for all configurations was NACA 0012. The parameters measured were rotor torque, rotor rotational speed, and tunnel conditions.

B. F. Blackwell; R. E. Sheldahl

1977-01-01

379

Wind turbine wake characterization using long-range Doppler lidar  

NASA Astrophysics Data System (ADS)

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 techniques are developed to distinguish wakes from the background variability, and moreover, wakes are then classified by width, height, length, and velocity deficit based on atmospheric stability and inflow conditions. By integrating these advanced observational capabilities with innovative approaches to atmospheric modeling, this work will help to improve simulation tools used to quantify power loss and fatigue loading due to wake effects, thereby aiding the optimization of wind farm layouts.

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

2012-12-01

380

Longitudinal variation and waves in Jupiter's south equatorial wind jet  

NASA Astrophysics Data System (ADS)

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5°S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and increasing with distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of ˜140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7°N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75-100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 ± 0.7-day period. This oscillating motion has a wavelength of ˜20° and a speed of 101 ± 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of multiple wave modes, the difference in dominant cloud appearance between 7°N and 7.5°S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

Simon-Miller, Amy A.; Rogers, John H.; Gierasch, Peter J.; Choi, David; Allison, Michael D.; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-04-01

381

Longitudinal Variation and Waves in Jupiter's South Equatorial Wind Jet  

NASA Technical Reports Server (NTRS)

A detailed study of the chevron-shaped dark spots on the strong southern equatorial wind jet near 7.5 S planetographic latitude shows variations in velocity with longitude and time. The presence of the large anticyclonic South Equatorial Disturbance (SED) has a profound effect on the chevron velocity, causing slower velocities to its east and accelerations over distance from the disturbance. The chevrons move with velocities near the maximum wind jet velocity of approx 140 m/s, as deduced by the history of velocities at this latitude and the magnitude of the symmetric wind jet near 7 N latitude. Their repetitive nature is consistent with a gravity-inertia wave (n = 75 to 100) with phase speed up to 25 m/s, relative to the local flow, but the identity of this wave mode is not well constrained. However, for the first time, high spatial resolution movies from Cassini images show that the chevrons oscillate in latitude with a 6.7 +/- 0.7-day period. This oscillating motion has a wavelength of approx 20 and a speed of 101 +/- 3 m/s, following a pattern similar to that seen in the Rossby wave plumes of the North Equatorial Zone, and possibly reinforced by it. All dates show chevron latitude variability, but it is unclear if this larger wave is present during other epochs, as there are no other suitable time series movies that fully delineate it. In the presence of mUltiple wave modes, the difference in dominant cloud appearance between 7 deg N and 7.5 deg S is likely due to the presence of the Great Red Spot, either through changes in stratification and stability or by acting as a wave boundary.

Simon-Miller, Amy A.; Choi, David; Rogers, John H.; Gierasch, Peter J.; Allison, Michael D.; Adamoli, Gianluigi; Mettig, Hans-Joerg

2012-01-01

382

On the Effect of Offshore Wind Parks on Ocean Dynamics  

NASA Astrophysics Data System (ADS)

Nowadays renewable energy resources play a key role in the energy supply discussion and especially an increasingly interest in wind energy induces intensified installations of wind parks. At this offshore wind energy gains in popularity in the course of higher and more consistent energy availability than over land. For example Germany's government adopted a national interurban offshore wind energy program comprising the construction of hundreds of wind turbines within Germany's Exclusive Economic Zone to ensure up to 50% of Germany's renewable energy supply. The large number of installation in coastal regions asks for analyzing the impact of offshore wind parks (OWPs) on the atmosphere and the ocean. As known from literature such wind parks excite also-called wake-effect and such an influence on the wind field in turn affects ocean circulation. To cover OWP's impact on ocean dynamics we evaluate model simulations using the Hamburg Shelf-Ocean-Model (HAMSOM). All simulations were driven with a wind forcing produced by the Mesoscale Atmosphere Model of the Hamburg University (METRAS) which has implemented wind turbines. Wind forcing data were generated in collaboration with and by courtesy of the Meteorological Institute of the University of Hamburg, Department Technical Meteorology, Numeric Modeling-METRAS. To evaluate dynamical changes forced by the OWP's wind wake-effect we did a sensitivity study with a theoretical setup of a virtual ocean of 60m depth with a flat bottom and a temperature and salinity stratification according to common North Sea's conditions. Here our results show that already a small OWP of 12 wind turbines, placed in an area of 4 km^2, lead to a complex change in ocean dynamics. Due to the wake-effect zones of upwelling and downwelling are formed within a minute after turning-on wind turbines. The evolving vertical cells have a size of around 15x15 kilometers with a vertical velocity in order of 10^-2 mm/sec influencing the dynamic of an area being hundred times bigger than the wind park itself. The emerged vertical structure is generated due to a newly created geostrophic balance resulting in a redistribution of the ocean mass field. A number of additional upwelling and downwelling cells around the wind park support an intensified vertical dispersion through all layers and incline the thermocline which also influences the lower levels. The disturbances of mass show a dipole structure across the main wind direction with a maximum change in thermocline depth of some meters close to the OWP. Diffusion, mostly driven by direct wind induced surface shear is also modified by the wind turbines and supports a further modification of the vertical patterns. Considering that wind turbines operate only in a special window of wind speed, i.e. wind turbines will stop in case of too weak or too strong wind speeds as well as in case of technical issues, the averaged dimension and intensity of occurring vertical cells depend on the number of rotors and expected wind speeds. Finally we will focus on scenario runs for the North Sea under fully realistic conditions to estimate possible changes in ocean dynamics due to OWPs in future and these results will be further used for process analyzes of the ecosystem. If we assume a continuous operation of North Sea's OWPs in future we expect a fundamental constant change in ocean dynamics and moreover in the ecosystem in its vicinity.

Ludewig, E.; Pohlmann, T.

2012-12-01

383

Variability of atmospheric winds and waves in the Arctic polar mesosphere during a stratospheric sudden warming  

NASA Astrophysics Data System (ADS)

A ground-based wide angle Michelson Interferometer was used to monitor the temporal variation of winds and waves in the mesopause region at Resolute Bay, Canada (74.9°N, 94.9°W) during a stratospheric warming event of February 2001. Observed variability of zonal and meridional winds is compared to the daily mean temperature fields at 3.16 hPa from assimilated stratospheric data. Reversal of eastward zonal winds is seen to occur during maximum mean temperatures in the stratospheric polar cap. Spectral analysis of the wind-velocity time series shows the evolution of different periodicities and their amplitudes. A cool period between two warming events shows a decrease in the amplitude of the semi-diurnal tide and an increase in the power of waves shorter than 12 hours before peak stratospheric temperatures are reached.

Bhattacharya, Yajnavalkya; Shepherd, G. G.; Brown, S.

2004-12-01

384

Tropical F region winds from O I 1356-A and forbidden O I 6300-A emissions. II - Analysis of OGO 4 data  

NASA Technical Reports Server (NTRS)

The OGO 4 tropical nightglow data on the O I 1356-A and forbidden O I 6300-A emissions during several months in the fall of 1967 are analyzed in conjunction with theoretical models. From the latitudinal asymmetry present in the tropical emissions the neutral wind velocities in the magnetic meridian at the time of the observations are found to reach 150 m/s near 2000 LT in the Pacific sector and 110 m/s in the Indian sector. The longitudinal dependence of the emissions indicates a strong zonal component (referred to geographic coordinates) and allows the resolution of the inferred wind velocities into geographic zonal and meridional wind components. The geographic zonal component reaches a maximum velocity of 260 m/s near 2200 LT.

Bittencourt, J. A.; Tinsley, B. A.; Hicks, G. T.; Reed, E. I.

1976-01-01

385

A prediction model for simulating near-surface wind gusts.  

PubMed

According to an analysis on the characteristic of 1 Hz wind speed data continuously sampled in the region below 2 m, an empirical model of natural wind was proposed to predict streamwise fluctuating wind gusts in a field based on friction velocity, mean wind velocity and standard deviation at 2 m. The predicted results achieved a good agreement with the experimental data, and the prediction model has a potential value in simulating sand transport under natural wind conditions. PMID:23708838

Zhang, Jinghong; Wang, Ping; Zheng, Xiaojing

2013-05-01

386

Wind turbine aerodynamics and loads control in wind shear flow  

Microsoft Academic Search

Wind turbine is subjected to some asymmetrical effects like wind shear, which will lead to unsteady blade airloads and performance. Fatigue loads can lead to damage of turbine components and eventually to failures. It is evident that the variation of the velocity over the rotor disc has an influence on the blade and introduces both flap-wise and edge-wise fatigue damage

Xin Shen; Xiaocheng Zhu; Zhaohui Du

2011-01-01

387

Spall velocity measurements from laboratory impact craters  

Microsoft Academic Search

Spall velocities were measured for a series of impacts into San Marcos gabbro. Impact velocities ranged from 1 to 6.5 km\\/sec. Projectiles varied in material and size with a maximum mass of 4g for a lead bullet to a minimum of 0.04 g for an aluminum sphere. The spall velocities were calculated both from measurements taken from films of the

Carol A. Polanskey; Thomas J. Ahrens

1986-01-01

388

Observation of high-resolution wind fields and offshore wind turbine wakes using TerraSAR-X imagery  

NASA Astrophysics Data System (ADS)

1. Introduction Numerous large-scale offshore wind farms have been built in European waters and play an important role in providing renewable energy. Therefore, knowledge of behavior of wakes, induced by large wind turbines and their impact on wind power output is important. The spatial variation of offshore wind turbine wake is very complex, depending on wind speed, wind direction, ambient atmospheric turbulence and atmospheric stability. In this study we demonstrate the application of X-band TerraSAR-X (TS-X) data with high spatial resolution for studies on wind turbine wakes in the near and far field of the offshore wind farm Alpha Ventus, located in the North Sea. Two cases which different weather conditions and different wake pattern as observed in the TS-X image are presented. 2. Methods The space-borne synthetic aperture radar (SAR) is a unique sensor that provides two-dimensional information on the ocean surface. Due to their high resolution, daylight and weather independency and global coverage, SARs are particularly suitable for many ocean and coastal applications. SAR images reveal wind variations on small scales and thus represent a valuable means in detailed wind-field analysis. The general principle of imaging turbine wakes is that the reduced wind speed downstream of offshore wind farms modulates the sea surface roughness, which in turn changes the Normalized Radar Cross Section (NRCS, denoted by ?0) in the SAR image and makes the wake visible. In this study we present two cases at the offshore wind farm Alpha Ventus to investigate turbine-induced wakes and the retrieved sea surface wind field. Using the wind streaks, visible in the TS-X image and the shadow behind the offshore wind farm, induced by turbine wake, the sea surface wind direction is derived and subsequently the sea surface wind speed is calculated using the latest generation of wind field algorithm XMOD2. 3. Case study alpha ventus Alpha Ventus is located approximately 45 km from the coast of Borkum, Germany, and consists of twelve 5-Megawatt wind power turbines. The retrieved results are validated by comparing with QuikSCAT measurements, the results of the German Weather Service (DWD) atmospheric model and in-situ measurements of wind speed and wind direction, obtained from the research platform FiNO1, installed 400 m west of Alpha Ventus. 4. Conclusion In the presented case study we quantify the wake characteristics of wake length, wake width, maximum velocity de?cit, wake merging and wake meandering. We show that SAR has the capability to map the sea surface two-dimensionally in high spatial resolution which provides a unique opportunity to observe spatial characteristics of offshore wind turbine wakes. The SAR derived information can support offshore wind farming with respect to optimal siting and design and help to estimate their effects on the environment.

Gies, Tobias; Jacobsen, Sven; Lehner, Susanne; Pleskachevsky, Andrey

2014-05-01

389

Modern estimation of the parameters of the Weibull wind speed distribution for wind energy analysis  

Microsoft Academic Search

Three methods for calculating the parameters of the Weibull wind speed distribution for wind energy analysis are presented: the maximum likelihood method, the proposed modified maximum likelihood method, and the commonly used graphical method. The application of each method is demonstrated using a sample wind speed data set, and a comparison of the accuracy of each method is also performed.

J. V. Seguro; T. W. Lambert

2000-01-01

390

Harnessing Wind  

NSDL National Science Digital Library

Students are introduced to the ways that engineers study and harness the wind. They learn about the different kinds of winds and how to measure wind direction. In addition, they learn how air pressure creates winds and how engineers design and test wind turbines to harness renewable wind energy.

Integrated Teaching And Learning Program

391

Coronal temperatures, heating, and energy flow in a polar region of the sun at solar maximum  

NASA Technical Reports Server (NTRS)

The profiles of resonantly scattered Lyman-alpha coronal radiation have been used to determine the hydrogen kinetic temperature from 1.5 to 4 solar radius from the center of the polar region of the corona observed in 1980 at solar maximum. Hydrogen temperatures derived from the line profiles were found to decrease with height from 1.2 million K at r = 1.5 solar radii to 600,000 K at r = 4 solar radius. Comparison of the measured kinetic temperatures with predictions from a semiempirical two-fluid model showed evidence of a small amount of heating or a nonthermal contribution to the motions of coronal protons between 1.5 and 4 solar radius. The widths of the profiles confirmed an upper limit of 110 + or - 15 km/s on the rms magnitude of the line-of-sight component of velocities between 1.5 and 4 solar radius. Density measurements obtained in situ in the solar wind in the ecliptic were used to locate the sources of low speed and high-speed winds in the polar region. An eclipse photograph of the corona at solar maximum is provided.

Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Munro, R. H.

1985-01-01

392

Wind-speed measurements with a scanning elastic-backscatter lidar  

SciTech Connect

During the 1992 Summer Olympics, the Los Alamos National Laboratory (LANL) lidar team participated in the Barcelona Air Quality Initiative (BAQI). One of the main objectives of this experiment was the remote measurement of wind speeds around the city to verify wind speeds and directions predicted by the Nonhydrostatic Mesoscale Model (MEMO). Remote determination of wind velocities in the mixing layer is important for the verification and determination of critical input parameters of urban-pollution transport models. Most present elastic-backscatter-lidar wind-speed-measurement methods rely on data acquired over time periods between 5 to 10 minutes (Matsui, 1990) and 30 minutes to 1 hour (Schols, et al. 1992). Lidar can measure the spatial properties of the wind field over large volumes of space. This capability is an improvement over present methods, which rely on instruments attached to balloons that measure only those winds along the path the balloon travels. The material that follows describes the principles implicit in the measurement of winds with an elastic-backscatter lidar, as well as the maximum cross-correlation algorithm used to extract wind speeds from lidar data acquired during the Summer Olympics at Barcelona, Spain, in July 1992.

Buttler, W.T.; Eichinger, W.E.

1994-01-01

393

Exploration of Solar Wind Acceleration Region Using Interplanetary Scintillation of Water Vapor Maser Source and Quasars  

NASA Technical Reports Server (NTRS)

Single-station observations of interplanetary scintillation (IPS) at three microwave frequencies; 2 GHz, 8 GHz and 22 GHz have been carried out between 1989 and 1998 using a large (34 m farad) radio telescope at the Kashima Space Research Center of the Communications Research Laboratory. The aim of these observations is to explore the near-sun solar wind, which is the key region for the study of the solar wind acceleration mechanism. Strong quasars; 3C279 and 3C273B were used for Kashima IPS observations at 2 GHz and 8 GHz, and a water vapor maser source, IRC20431 was used for the IPS observations at 22 GHz. Solar wind velocities derived from Kashima IPS data suggest that the solar wind acceleration takes place at radial distances between 10 and 30 solar radii (R(sub s)) from the sun. Properties of the turbulence spectrum (e.g. anisotropy, spectral index, inner scale) inferred from Kashima data are found to change systematically in the solar wind acceleration region. While the solar wind in the maximum phase appears to be dominated by the slow wind, fast and rarefied winds associated with coronal holes are found to develop significantly at high latitudes as the solar activity declines. Nevertheless, Kashima data suggests that the location of the acceleration region is stable throughout the solar cycle.

Tokumaru, Munetoshi; Yamauchi, Yohei; Kondo, Tetsuro

2001-01-01

394

Solar wind proton deposition into the Martian atmosphere  

Microsoft Academic Search

The direct impact of solar wind H + with the planet Mars is calculated using a three- dimensional hybrid particle code. The simulation results show a strong dependence on solar wind velocity and interplanetary magnetic field angle with the solar wind velocity vector. The energy fluxes calculated approach the solar EUV heating rates fxom photoelectrons and are found to be

Stephen H. Brecht

1997-01-01

395

The F2 wind tunnel at Fauga-Mauzac  

NASA Technical Reports Server (NTRS)

Details on the French subsonic wind-tunnel F2 that becomes operational on July 1983 are presented. Some of the requirements were: (1) installation of models on any wall of the facility, (2) good observation points due to transparent walls, (3) smooth flow, (4) a laser velocimeter, and (5) easy access and handling. The characteristics include a nonpressurized return circuit, dimensions of 5 x 1.4 x 1.8 m, maximum velocity of 100 m/s and a variable speed fan of 683 kW.

Afchain, D.; Broussaud, P.; Frugier, M.; Rancarani, G.

1984-01-01

396

Stability Simulation of Wind Turbine Systems  

Microsoft Academic Search

A simulation and digital computer modeling effort is described in which a wind turbine-generator system is adapted for stability evaluation using a large scale transient stability computer program. Component models of the MOD-2 wind generator system are described and their digital model equations are provided. A versatile wind velocity model is described, which provides the capability of simulating a wide

P. M. Anderson; Anjan Bose

1983-01-01

397

WINDS AND CURRENT PATTERNS IN FALSE BAY  

Microsoft Academic Search

Wind records from six reporting stations in the vicinity of False Bay have been analysed, and the mean directional frequency and velocity combined to give relative ‘wind run’ for each station and season are shown in the form of wind roses.Methods of current measurements are briefly discussed, and the ‘dye-bomb’ technique using aircraft chosen to obtain a nearly synoptic pattern

G. R. Atkins

1970-01-01

398

Hanford Site peak gust wind speeds  

SciTech Connect

Peak gust wind data collected at the Hanford Site since 1945 are analyzed to estimate maximum wind speeds for use in structural design. The results are compared with design wind speeds proposed for the Hanford Site. These comparisons indicate that design wind speeds contained in a January 1998 advisory changing DOE-STD-1020-94 are excessive for the Hanford Site and that the design wind speeds in effect prior to the changes are still appropriate for the Hanford Site.

Ramsdell, J.V.

1998-09-29

399

Maximum windmill efficiency in finite time  

NASA Astrophysics Data System (ADS)

The fraction of the kinetic energy of the wind impinging on the rotor-swept area that a wind turbine can convert to useful power has been shown by Betz in an idealized laminar-flow model to have an upper limit of 16/27 or 59% approximately [I. H. Shames, Mechanics of Fluids, 2nd ed. (McGraw-Hill, New York, 1982), pp. A26-A31]. This figure is known as Betz number. Other studies [A. Rauh and W. Seelret, Appl. Energy 17, 15 (1984)] suggested that this figure should be considered as a guideline. In this paper, a new model is introduced and its efficiency at maximum power output is derived. The derived value is shown to be a function of the Betz number B and given by the formula ?mp=1-1-B. This value is 36.2%, which agrees well with those of actually operating wind turbines. As a guideline, the wind turbine efficiency can be considered to be within the range of the two numbers of merit, the Betz number and ?mp.

Huleihil, Mahmoud

2009-05-01

400

Introduction to maximum entropy  

SciTech Connect

The maximum entropy (MaxEnt) principle has been successfully used in image reconstruction in a wide variety of fields. We review the need for such methods in data analysis and show, by use of a very simple example, why MaxEnt is to be preferred over other regularizing functions. This leads to a more general interpretation of the MaxEnt method, and its use is illustrated with several different examples. Practical difficulties with non-linear problems still remain, this being highlighted by the notorious phase problem in crystallography. We conclude with an example from neutron scattering, using data from a filter difference spectrometer to contrast MaxEnt with a conventional deconvolution. 12 refs., 8 figs., 1 tab.

Sivia, D.S.

1988-01-01

401

Numerical Simulations of Laminar Air-Water Flow of a Non-linear Progressive Wave at Low Wind Speed  

NASA Astrophysics Data System (ADS)

A numerical simulation for two-dimensional laminar air-water flow of a non-linear progressive water wave with large steepness is performed when the background wind speed varies from zero to the wave phase speed. It is revealed that in the water the difference between the analytical solution of potential flow and numerical solution of viscous flow is very small, indicating that both solutions of the potential flow and viscous flow describe the water wave very accurately. In the air the solutions of potential and viscous flows are very different due to the effects of viscosity. The velocity distribution in the airflow is strongly influenced by the background wind speed and it is found that three wind speeds, , (the maximum orbital velocity of a water wave), and (the wave phase speed), are important in distinguishing different features of the flow patterns.

Wen, X.; Mobbs, S.

2014-03-01

402

Aeolian sand transport: a wind tunnel model  

NASA Astrophysics Data System (ADS)

Wind sand transport is an important geological process on earth and some other planets. Formulating the wind sand transport model has been of continuing significance. Majority of the existing models relate sand transport rate to the wind shear velocity based on dynamic analysis. However, the wind shear velocity readapted to blown sand is difficult to determine from the measured wind profiles when sand movement occurs, especially at high wind velocity. Moreover, the effect of grain size on sand transport is open to argument. Detailed wind tunnel tests were carried out with respect to the threshold velocity, threshold shear velocity, and transport rate of differently sized, loose dry sand at different wind velocities to reformulate the transport model. The results suggest that the relationship between threshold shear velocity and grain size basically follow the Bagnold-type equation for the grain size d>0.1 mm. However, the threshold coefficient A in the equation is not constant as suggested by Bagnold, but decreases with the particle Reynolds number. The threshold velocity at the centerline height of the wind tunnel proved to be directly proportional to the square root of grain diameter. Attempts have been made to relate sand transport rate to both the wind velocity and shear velocity readapted to the blown sand movement. The reformulated transport model for loose dry sand follows the modified O'Brien-Rindlaub-type equation: Q= f1( d)(1- Ru) 2( ?/ g) V3, or the modified Bagnold-type equation: Q= f2( d)(1- Rt) 0.25( ?/ g) U*3. Where Q is the sand transport rate, the sand flux per unit time and per unit width, in kg m -1 s -1; ? is the air density, 1.25 kg m -3; g is the acceleration due to gravity, 9.81 m s -2; Ru= Vt/ V; Rt= U*t/ U*; V is the wind velocity at the centerline of the wind tunnel, in m s -1; Vt is the threshold velocity measured at the same height as V, in m s -1; U* is the shear velocity with saltating flux, in m s -1; U*t is threshold shear velocity, in m s -1; f1( d)=1/(475.24+93.62 d/ D); f2( d)=1.41+4.98exp(-0.5(ln( d/1.55 D)/0.57) 2); d is the grain diameter, in mm; and D is the reference grain diameter, equals 0.25 mm. The Bagnold's equation that asserts for a given wind drag the rate of movement of a fine sand is less than that of a coarse sand is not supported by the reformulated models.

Dong, Zhibao; Liu, Xiaoping; Wang, Hongtao; Wang, Xunming

2003-09-01

403

Wind generator kite system  

SciTech Connect

This invention relates to a new system for generating electrical energy by wind power. The wind generator is suspended in the air like a kite by wind currents and is attached to the earth by a high strength cable to which are attached electric cables and a natural gas pipe. The numerous small wind generators are mounted in a box-like kite enclosure, which are raised to the desired elevation by rotary blade power with the assistance of a gas balloon. The wind generator kite is raised and lowered to the proper elevation for maximum electrical output. A complete system, including control methods, permits the production of electricity at a lower cost than conventional methods and provides means for generating large amounts of power with a high load factor.

Pugh, P. F.

1984-12-04

404

Carbon monoxide (CO) maximum over the Zagros mountains in the Middle East: Signature of mountain venting?  

NASA Astrophysics Data System (ADS)

We report an intriguing feature observed in daytime measurements of CO over the Middle East, in spring and summer, by the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument. Enhanced CO is observed over the Zagros mountains of Iran, following the local topography over this region (25-40N, 40-60E). The MOPITT averaging kernels do not seem to indicate any data artifacts in this area. We argue that this feature likely forms by the process of mountain venting by thermal winds caused by strong daytime differential heating. This is consistent with an analysis of vertical velocity in the NCEP reanalysis data in this region. The phenomenon was observed in all the years of available MOPITT measurements and may have implications for the pollution episodes in the region and the Middle East ozone maximum that has been observed earlier.

Kar, Jayanta; Drummond, James R.; Jones, Dylan B. A.; Liu, Jane; Nichitiu, Florian; Zou, Jason; Gille, John C.; Edwards, David P.; Deeter, Merritt N.

2006-08-01

405

Small scale wind perturbation analysis for vertically rising launch vehicles  

NASA Technical Reports Server (NTRS)

This paper discusses the determination of small-scale vertical wind spectra used with space flight and ballistic technology. In particular, Jimsphere, a precision balloon wind sensor with high radar reflectivity is considered. Gross wind velocity data is analyzed to subtract the steady-state wind and wind change-shear effects. A residue of small wind perturbations is left in the horizontal (scalar) along the vertical direction. An analysis leading to formulation of the covariance function with altitude is presented. The function is decoupled to yield an almost periodic representation of the vertical wind perturbations. Forcing functions are determined when the representation is coupled with the vehicle velocity characteristics.

Chenoweth, H. B.

1980-01-01

406

Low and high velocity clouds produced by young stellar clusters  

NASA Astrophysics Data System (ADS)

Context: Intermediate and high velocity HI clouds rain onto the plane of our Galaxy. They are observed at heights of between 500 and 1500 pc, falling onto the Galactic plane at velocities from 50 to 140 km s-1. Aims: To explain the origin of these clouds, we present a galactic fountain model, driven by the wind from a super stellar cluster (SSC). Methods: We solve the equations for a steady, radiative de Laval nozzle flow. We consider two effects not considered previously in astrophysical nozzle flow models: cooling functions for different metallicities, and the direct action of the galactic gravitational field on the gas flowing along the nozzle. Results: For an adiabatic nozzle flow, the gravity acting directly on the gas within the nozzle “stalls” the nozzle flow for initial wind velocities lower than the escape velocity from the Galaxy. For the same wind velocity, a radiative nozzle flow stalls at lower altitudes above the galactic plane. We find that SSC winds with velocities of vw = 500-800 km s-1 produce nozzles stall at heights of xm = 1-15 kpc. The stalled nozzle flow then rains back onto the galactic plane at velocities in the range observed in intermediate and high velocity HI clouds. Conclusions: We study a nozzle flow driven by a wind from a SSC close to the Galactic centre. We find that for velocities within the range expected for a SSC wind, we can produce nozzle flows that stall above the galactic plane. These stalled flows produce cool, infalling clouds with velocities similar to those of intermediate and high velocity HI clouds.

Rodríguez-González, A.; Raga, A. C.; Cantó, J.

2009-07-01

407

Mean winds in the MLT, the SQBO and MSAO over Ascension Island (8° S, 14° W)  

NASA Astrophysics Data System (ADS)

Mean winds in the mesosphere and lower thermosphere (MLT) over Ascension Island (8° S, 14° W) have been measured at heights of approximately 80-100 km by a meteor radar. The results presented in this study are from the interval October 2001 to December 2011. In all years, the monthly-mean meridional winds display a clear annual oscillation. Typically, these winds are found to be southward during April-October, when they reach velocities of up to about -23 m s-1, and northward throughout the rest of the year, when they reach velocities up to about 16 m s-1. The monthly-mean zonal winds are generally westward throughout most of the year and reach velocities of up to about -46 m s-1. However, eastward winds are observed in May-August and again in December at the lower heights observed. These eastward winds reach a maximum at heights of about 86 km with velocities of up to about 36 m s-1, but decay quickly at heights above and below that level. The mesospheric semi-annual oscillation (MSAO) is clearly apparent in the observed monthly-mean zonal winds. The winds in first westward phase of the MSAO are observed to be much stronger than in the second phase. The westward phase of the MSAO is found to maximise at heights of about 84 km with typical first-phase wind velocities