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1

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2011 CFR

...25.237 Wind velocities. (a) For land planes and amphibians, the following applies: (1) A 90-degree cross...accretion defined in appendix C. (b) For seaplanes and amphibians, the following applies: (1) A 90-degree...

2011-01-01

2

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2012 CFR

...25.237 Wind velocities. (a) For land planes and amphibians, the following applies: (1) A 90-degree cross...accretion defined in appendix C. (b) For seaplanes and amphibians, the following applies: (1) A 90-degree...

2012-01-01

3

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2013 CFR

...25.237 Wind velocities. (a) For land planes and amphibians, the following applies: (1) A 90-degree cross...accretion defined in appendix C. (b) For seaplanes and amphibians, the following applies: (1) A 90-degree...

2013-01-01

4

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2010 CFR

...25.237 Wind velocities. (a) For land planes and amphibians, the following applies: (1) A 90-degree cross...accretion defined in appendix C. (b) For seaplanes and amphibians, the following applies: (1) A 90-degree...

2010-01-01

5

14 CFR 25.237 - Wind velocities.  

...25.237 Wind velocities. (a) For land planes and amphibians, the following applies: (1) A 90-degree cross...accretion defined in appendix C. (b) For seaplanes and amphibians, the following applies: (1) A 90-degree...

2014-01-01

6

Solar wind proton temperature-velocity relationship  

NASA Technical Reports Server (NTRS)

Helios 1 data are analyzed to find an experimental fit for the temperature-velocity relationship at 1 AU. It is shown that the proton temperature-velocity changes at a velocity of approximately 500 km/s. Interplanetary dynamic processes, i.e., stream interactions, are shown to affect the temperature-velocity relationships less than 22 percent; the functional form of these relationships appears to be preserved throughout the solar cycle. It is pointed out that any comprehensive model of the solar wind will have to address the difference in the temperature-velocity relationship between the low- and high-speed wind, since this is a product of the acceleration and subsequent heating process generating the solar wind.

Lopez, R. E.; Freeman, J. W.

1986-01-01

7

Characterization of ionic wind velocity  

Microsoft Academic Search

When a strong electric field is generated between a sharp object at high voltage and a grounded electrode in a gas medium, a corona is formed near the tip of the sharp object and, as a result, the gas medium is set in motion. The current study reports on the flow behavior of a single-stage ion wind generator with and

Matthew Rickard; Derek Dunn-Rankin; Felix Weinberg; Fred Carleton

2005-01-01

8

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

9

Design of wind farm layout for maximum wind energy capture Andrew Kusiak*, Zhe Song  

E-print Network

Accepted 24 August 2009 Available online 22 September 2009 Keywords: Wind farm Wind turbine Layout design based on wind turbine locations, and wind direction. Since the turbine layout design is a constrainedDesign of wind farm layout for maximum wind energy capture Andrew Kusiak*, Zhe Song Intelligent

Kusiak, Andrew

10

Design of a wind turbine-generator system considering the conformability to wind velocity fluctuations  

SciTech Connect

The conformability of the rated power output of the wind turbine-generator system and of the wind turbine type to wind velocity fluctuations are investigated with a simulation model. The authors examine three types of wind turbines: the Darrieus-Savonius hybrid, the Darrieus proper and the Propeller. These systems are mainly operated at a constant tip speed ratio, which refers to a maximum power coefficient points. As a computed result of the net extracting power, the Darrieus turbine proper has little conformability to wind velocity fluctuations because of its output characteristics. As for the other turbines, large-scale systems do not always have an advantage over small-scale systems as the effect of its dynamic characteristics. Furthermore, it is confirmed that the net extracting power of the Propeller turbine, under wind direction fluctuation, is much reduced when compared with the hybrid wind turbine. Thus, the authors conclude that the appropriate rated power output of the system exists with relation to the wind turbine type for each wind condition.

Wakui, Tetsuya; Hashizume, Takumi; Outa, Eisuke

1999-07-01

11

Maximum power tracking control scheme for wind generator systems  

E-print Network

The purpose of this work is to develop a maximum power tracking control strategy for variable speed wind turbine systems. Modern wind turbine control systems are slow, and they depend on the design parameters of the turbine and use wind and/or rotor...

Mena Lopez, Hugo Eduardo

2008-10-10

12

Maximum power tracking control scheme for wind generator systems  

E-print Network

The purpose of this work is to develop a maximum power tracking control strategy for variable speed wind turbine systems. Modern wind turbine control systems are slow, and they depend on the design parameters of the turbine and use wind and/or rotor...

Mena, Hugo Eduardo

2009-05-15

13

Maximum tunneling velocities in symmetric double well potentials  

NASA Astrophysics Data System (ADS)

We consider coherent tunneling of one-dimensional model systems in non-cyclic or cyclic symmetric double well potentials. Generic potentials are constructed which allow for analytical estimates of the quantum dynamics in the non-relativistic deep tunneling regime, in terms of the tunneling distance, barrier height and mass (or moment of inertia). For cyclic systems, the results may be scaled to agree well with periodic potentials for which semi-analytical results in terms of Mathieu functions exist. Starting from a wavepacket which is initially localized in one of the potential wells, the subsequent periodic tunneling is associated with tunneling velocities. These velocities (or angular velocities) are evaluated as the ratio of the flux densities versus the probability densities. The maximum velocities are found under the top of the barrier where they scale as the square root of the ratio of barrier height and mass (or moment of inertia), independent of the tunneling distance. They are applied exemplarily to several prototypical molecular models of non-cyclic and cyclic tunneling, including ammonia inversion, Cope rearrangement of semibullvalene, torsions of molecular fragments, and rotational tunneling in strong laser fields. Typical maximum velocities and angular velocities are in the order of a few km/s and from 10 to 100 THz for our non-cyclic and cyclic systems, respectively, much faster than time-averaged velocities. Even for the more extreme case of an electron tunneling through a barrier of height of one Hartree, the velocity is only about one percent of the speed of light. Estimates of the corresponding time scales for passing through the narrow domain just below the potential barrier are in the domain from 2 to 40 fs, much shorter than the tunneling times.

Manz, Jörn; Schild, Axel; Schmidt, Burkhard; Yang, Yonggang

2014-10-01

14

Velocity shear generation of solar wind turbulence  

NASA Technical Reports Server (NTRS)

A two-dimensional incompressible MHD spectral code is used to show that shear-driven turbulence is a possible means for producing many observed properties of the evolution of the magnetic and velocity fluctuations in the solar wind and, in particular, the evolution of the cross helicity ('Alfvenicity') at small scales. It is shown that large-scale shear can nonlinearly produce a cascade to smaller scale fluctuations even when the linear Kelvin-Helmholtz mode is stable, and that a roughly power law inertial range is established by this process. The evolution found is similar to that seen in some other simulations of MHD turbulence.

Roberts, D. A.; Goldstein, Melvyn L.; Matthaeus, William H.; Ghosh, Sanjoy

1992-01-01

15

Velocity Analysis of M13 by Maximum Likelyhood Method  

NASA Astrophysics Data System (ADS)

We present new approach to analysis of velocity data of globular clusters. Maximum likelihood method is applied to get model parameters such as central potential, anisotropy radius, and total mass fractions in each mass class. This method can avoid problems in conventional binning method of chi-square. We utilize three velocity components, one from line of sight radial velocity and two from proper motion data. In our simplified scheme we adopt 3 mass-component model with unseen high mass stars, intermediate visible stars, and low mass dark remnants. Likelihood values are obtained for 124 stars in M13 for various model parameters. Our preferred model shows central potential of W_o = 7 and anisotropy radius with 7 core radius. And it suggests non-negligible amount of unseen high mass stars and considerable amount of dark remnants in M13.

Oh, K. S.; Lin, D. N. C.

1992-06-01

16

Wind velocity measurements using a pulsed LIDAR system: first results  

E-print Network

the three-dimensinal wind vector, the beam is inclined by 30 from vertical direction and measurements azimuth angles. The three-dimensional wind velocity vector is then derived from four successive characteristics of the wind field, e.g., they determine fast load changes on wind turbines. To characterize

Peinke, Joachim

17

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

18

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

19

Modulation of the Solar Wind Velocity by Mercury  

E-print Network

To study the variations in the solar wind velocity during inferior conjunctions of Mercury and Earth, we analyzed 54 events in the period 1995 to 2012 by the superimposed epoch method. We have found a noticeable increase in the velocity both before and after the conjunctions as well as decrease in the velocity within 3-4 days after them, which seems to be associated with Mercury's "shadow". The results obtained might be used to improve a forecast of the solar wind velocity.

Nikulin, Igor F

2013-01-01

20

Modulation of the solar wind velocity and density by Mercury  

NASA Astrophysics Data System (ADS)

To study the variations in the solar wind velocity during inferior conjunctions of Mercury and Earth, we analyzed 54 events in the period 1995-2012 by the superimposed epoch method. We have found a noticeable increase in the velocity both before and after the conjunctions as well as decrease in the velocity within 3-4 days after them (Mercury's “shadow”). Variations of the solar wind density in 1997-2013 show a similar character, but their dispersion is substantially larger than for the velocity. The results obtained might be used to analyze variations and to improve a forecast of the solar wind velocity and density.

Nikulin, I. F.

2014-09-01

21

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

22

Designing an Adaptive Fuzzy Controller for Maximum Wind Energy Extraction  

Microsoft Academic Search

The wind power production spreading, also aided by the transition from constant to variable speed operation, involves the development of efficient control systems to improve the effectiveness of power production systems. This paper presents a data-driven design methodology able to generate a Takagi-Sugeno-Kang (TSK) fuzzy model for maximum energy extraction from variable speed wind turbines. In order to obtain the

Vincenzo Galdi; Antonio Piccolo; Pierluigi Siano

2008-01-01

23

Velocity porosity reduction in strength of wind lines Clumping in Hot Star Winds  

E-print Network

Velocity porosity reduction in strength of wind lines Clumping in Hot Star Winds W.-R. Hamann, A-opus-13981 Dynamical simulation of the "velocity-porosity" reduction in observed strength of stellar of wind absorption lines. Instead of the porosity length formalism used to model effects on continuum

Owocki, Stanley P.

24

Radionuclide counting technique for measuring wind velocity and direction  

NASA Technical Reports Server (NTRS)

An anemometer utilizing a radionuclide counting technique for measuring both the velocity and the direction of wind is described. A pendulum consisting of a wire and a ball with a source of radiation on the lower surface of the ball is positioned by the wind. Detectors and are located in a plane perpendicular to pendulum (no wind). The detectors are located on the circumferene of a circle and are equidistant from each other as well as the undisturbed (no wind) source ball position.

Singh, J. J. (inventor)

1984-01-01

25

A fast maximum power extraction algorithm for wind energy systems  

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

26

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

27

Analytical expressions for maximum wind turbine average power in a Rayleigh wind regime  

SciTech Connect

Average or expectation values for annual power of a wind turbine in a Rayleigh wind regime are calculated and plotted as a function of cut-out wind speed. This wind speed is expressed in multiples of the annual average wind speed at the turbine installation site. To provide a common basis for comparison of all real and imagined turbines, the Rayleigh-Betz wind machine is postulated. This machine is an ideal wind machine operating with the ideal Betz power coefficient of 0.593 in a Rayleigh probability wind regime. All other average annual powers are expressed in fractions of that power. Cases considered include: (1) an ideal machine with finite power and finite cutout speed, (2) real machines operating in variable speed mode at their maximum power coefficient, and (3) real machines operating at constant speed.

Carlin, P.W.

1996-12-01

28

Urban-rural wind velocity differences  

Microsoft Academic Search

Wind speeds along a streamflow line through New York City are found to be decreased below (increased above) those at sites outside of the city during periods with regional wind speeds above (below) about 4 m\\/s. The decrease is attributed to increased values of the surface roughness parameter in the city, as compared to values in nearby non-urban regions. The

ROBERT D. BORNSTEIN; DOUGLAS SCOTT JOHNSON

1977-01-01

29

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

30

Wind Velocity Fluctuations Time Series Analysis  

Microsoft Academic Search

The temporal structure of wind was investigated by means of temporal correlations of 10-min wind time series measured over a period of one year (2004). The Hurst exponent (H), one of a number of methods to identify the existence of long-range correlations in experimental data, has been applied to quantify self-similarity scaling and correlations in the mesoscale temporal range. The

A M TARQUIS; M. C. MORATÓ; M. T. CASTELLANOS; J. L. DE MIGUEL

2006-01-01

31

Lower limit for the velocity fluctuation level in wind tunnels  

Microsoft Academic Search

The origins of the velocity fluctuations in the test section of a wind tunnel are discussed. Vorticity (turbulence converted from upstream) can be reduced by a careful design of the settling chamber to almost any desired level. The amplitudes of pressure waves propagating round the tunnel circuit can also be reduced considerably. The lowest levels of the velocity fluctuations in

U. Michel; E. Froebel

1988-01-01

32

Velocity Distributions and Proton Beam Production in the Solar Wind  

SciTech Connect

Helios, Ulysses, and Wind spacecraft have observed the velocity distribution functions (VDFs) of solar wind particles deviating significantly from Maxwellians. We review recent models using different approximations and mechanisms that determine various observed characteristics of the VDFs for the electrons, protons and minor ions. A new generation mechanism is proposed for super-Alfvenic proton beams and tails that are often observed in the fast solar wind. The mechanism is based on the proton trapping and acceleration by kinetic Alfven waves (KAWs), which carry a field-aligned potential well propagating with super-Alfven velocities.

Pierrard, Viviane; Voitenko, Yuriy [Belgian Institute for Space Aeronomy, Ringlaan-3-Avenue Circulaire, B-1180 Brussels (Belgium)

2010-03-25

33

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

34

[The study of maximum entropy method used in wind profiler].  

PubMed

In order to know the feasibility that the modern spectrum analysis ways are applied in wind profiler, the fast Fourier transform (FFT) and maximum entropy method (MEM) are contrasted by using simulation data and radar measurement data respectively. The result shows: (1) When the radar echo is strong, the effect of two methods are equivalent. But when the echo is weak, the MEM spectra are better than others. The MEM can powerfully remove the ground clutter contaminant. (2) The MEM spectra are smooth, so it can be used to reduce white noise influence also. (3) The iterative steps in MEM have some influence on the spectrum. The step calculated by final prediction error (FPE) rule is less. Using 15 steps in MEM can get a better result. The wind profiler radar echo is weak usually, so the conclusions of this paper can help improve the effect of spectrum analysis. PMID:22715790

Hu, Ming-bao; Zheng, Guo-guang; Zhang, Pei-chang

2012-04-01

35

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

36

Comparison of VLF Wave Activity in the Solar Wind During Solar Maximum and Minimum  

E-print Network

Comparison of VLF Wave Activity in the Solar Wind During Solar Maximum and Minimum: Ulysses and intermediate speed solar wind. The maximum intensity of the electromagnetic waves for the two solar cycle are similar for the slow and intermediate solar wind in both solar maximum and minimum phases. It is also

California at Berkeley, University of

37

Terminal velocities of the winds from rapidly rotating OB stars  

NASA Technical Reports Server (NTRS)

This paper presents measurements of terminal velocities of OB stars which are rapid rotators, based on archival high-dispersion IUE spectra of the C IV resonance doublet. The terminal velocities of the most rapidly rotating stars appear to be systematically lower than those of the less rapidly rotating stars (at least for the cooler stars), although the number of very rapid rotators is only three. The modified line-radiation driven wind model of Friend and Abbott, which takes into account the finite size of the star as well as its rotation, predicts that the terminal velocity should drop with increasing rotational velocity. However, when a smaller but very homogeneous subset of the data is used (BO giants only), the correlation between terminal velocity and rotational velocity disappears.

Friend, David B.

1990-01-01

38

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

39

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

40

Velocity dependence of heavy-ion stopping below the maximum  

NASA Astrophysics Data System (ADS)

In the slowing-down of heavy ions in materials, the standard description by Lindhard and Scharff assumes the electronic stopping cross section to be proportional to the projectile speed v up to close to a stopping maximum, which is related to the Thomas-Fermi speed vTF . It is well known that strict proportionality with v is rarely observed, but little is known about the systematics of observed deviations. In this study we try to identify factors that determine positive or negative curvature of stopping cross sections on the basis of experimental data and of binary stopping theory. We estimate the influence of shell structure of the target and of the equilibrium charge of the ion and comment the role of dynamic screening.

Sigmund, P.; Schinner, A.

2015-01-01

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

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

43

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

44

Does the scatterometer see wind speed or friction velocity?  

NASA Technical Reports Server (NTRS)

Studies of radar backscatter from the sea surface are referred either to the wind speed, U, or friction velocity, u(sub *). Bragg scattering theory suggests that these variations in backscatter are directly related to the height of the capillary-gravity waves modulated by the larger waves in tilt and by straining of the short wave field. The question then arises as to what characteristic of the wind field is most probably correlated with the wave number spectrum of the capillary-gravity waves. The justification for selecting U as the appropriate meteorological parameter to be associated with backscatter from L-band to Ku-band are reviewed. Both theoretical reasons and experimental evidence are used to demonstrate that the dominant parameter is U/C(lambda) where U is the wind speed at a height of about lambda/2 for waves having a phase speed of C(lambda).

Donelan, M. A.; Pierson, W. J., Jr.

1984-01-01

45

The Enhanced-model Ladar Wind Sensor and Its Application in Planetary Wind Velocity Measurements  

NASA Technical Reports Server (NTRS)

For several years we have been developing an optical air-speed sensor that has a clear application as a meteorological wind-speed sensor for the Mars landers. This sensor has been developed for aircraft use to replace the familiar, pressure-based Pitot probe. Our approach utilizes a new concept in the laser-based optical measurement of air velocity (the Enhanced-Mode Ladar), which allows us to make velocity measurements with significantly lower laser power than conventional methods. The application of the Enhanced-Mode Ladar to measuring wind speeds in the martian atmosphere is discussed.

Soreide, D. C.; Mcgann, R. L.; Erwin, L. L.; Morris, D. J.

1993-01-01

46

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

47

Mean velocity, turbulence intensity and turbulence convection velocity measurements for a convergent nozzle in a free jet wind tunnel  

NASA Technical Reports Server (NTRS)

The effect of light on the mean flow and turbulence properties of a 0.056 m circular jet were determined in a free jet wind tunnel. The nozzle exit velocity was 122 m/sec, and the wind tunnel velocity was set at 0, 12, 37, and 61 m/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, and eddy convection velocity were carried out using two linearized hot wire anemometers. Normalization factors were determined for the mean velocity and turbulence convection velocity.

Mccolgan, C. J.; Larson, R. S.

1978-01-01

48

Characteristics of Wind Velocity and Temperature Change Near an Escarpment-Shaped Road Embankment  

PubMed Central

Artificial structures such as embankments built during the construction of highways influence the surrounding airflow. Various types of damage can occur due to changes in the wind velocity and temperature around highway embankments. However, no study has accurately measured micrometeorological changes (wind velocity and temperature) due to embankments. This study conducted a wind tunnel test and field measurement to identify changes in wind velocity and temperature before and after the construction of embankments around roads. Changes in wind velocity around an embankment after its construction were found to be influenced by the surrounding wind velocity, wind angle, and the level difference and distance from the embankment. When the level difference from the embankment was large and the distance was up to 3H, the degree of wind velocity declines was found to be large. In changes in reference wind velocities around the embankment, wind velocity increases were not proportional to the rate at which wind velocities declined. The construction of the embankment influenced surrounding temperatures. The degree of temperature change was large in locations with large level differences from the embankment at daybreak and during evening hours when wind velocity changes were small. PMID:25136681

Kim, Young-Moon; You, Ki-Pyo; You, Jang-Youl

2014-01-01

49

Characteristics of wind velocity and temperature change near an escarpment-shaped road embankment.  

PubMed

Artificial structures such as embankments built during the construction of highways influence the surrounding airflow. Various types of damage can occur due to changes in the wind velocity and temperature around highway embankments. However, no study has accurately measured micrometeorological changes (wind velocity and temperature) due to embankments. This study conducted a wind tunnel test and field measurement to identify changes in wind velocity and temperature before and after the construction of embankments around roads. Changes in wind velocity around an embankment after its construction were found to be influenced by the surrounding wind velocity, wind angle, and the level difference and distance from the embankment. When the level difference from the embankment was large and the distance was up to 3H, the degree of wind velocity declines was found to be large. In changes in reference wind velocities around the embankment, wind velocity increases were not proportional to the rate at which wind velocities declined. The construction of the embankment influenced surrounding temperatures. The degree of temperature change was large in locations with large level differences from the embankment at daybreak and during evening hours when wind velocity changes were small. PMID:25136681

Kim, Young-Moon; You, Ki-Pyo; You, Jang-Youl

2014-01-01

50

Collisionless transport equations derived from a kinetic exospheric solar wind model with kappa velocity distribution functions  

E-print Network

In this paper we discuss the collisionless transport equations, continuity, momentum and energy conservation, derived from a kinetic exospheric model of the solar wind based on a kappa velocity distribution function of the electrons. The model is stationary and is based on a non-monotonic potential energy for the protons. The present study is carried out for an exobase located at 1.5 solar radii and for two different values of the kappa index. The maximum radial distance considered is equal to one astronomical unit. The moments of the velocity distribution function computed with the kinetic exospheric model for both electrons and protons are introduced into the mass continuity equation, momentum conservation equation and energy conservation equation. The relative importance of various terms in the macroscopic transport equations for each component species are analyzed and discussed. The results obtained show that the kinetic description based on kappa velocity distribution functions satisfies rigorously the t...

Voitcu, Gabriel; Lamy, Herve; Lemaire, Joseph; Echim, Marius

2014-01-01

51

Low-level nocturnal wind maximum over the central Amazon basin  

Microsoft Academic Search

A low-level nocturnal wind maximum is shown to exist over extensive and nearly undisturbed rainforest near the central Amazon city of Manaus. Analysis of meteorological data collected during the 1985 and 1987 Amazon Boundary Layer Experiments (ABLE 2A and 2B) indicates the presence of this nocturnal wind maximum during both the wet and dry seasons of the Central Amazon Basin.

Steven Greco; Michael Garstang; Samuel Houston

1992-01-01

52

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

53

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

54

Errors in the estimation of wall shear stress by maximum Doppler velocity  

PubMed Central

Objective Wall shear stress (WSS) is an important parameter with links to vascular (dys)function. Difficult to measure directly, WSS is often inferred from maximum spectral Doppler velocity (Vmax) by assuming fully-developed flow, which is valid only if the vessel is long and straight. Motivated by evidence that even slight/local curvatures in the nominally straight common carotid artery (CCA) prevent flow from fully developing, we investigated the effects of velocity profile skewing on Vmax-derived WSS. Methods Velocity profiles, representing different degrees of skewing, were extracted from the CCA of image-based computational fluid dynamics (CFD) simulations carried out as part of the VALIDATE study. Maximum velocities were calculated from idealized sample volumes and used to estimate WSS via fully-developed (Poiseuille or Womersley) velocity profiles, for comparison with the actual (i.e. CFD-derived) WSS. Results For cycle-averaged WSS, mild velocity profile skewing caused ±25% errors by assuming Poiseuille or Womersley profiles, while severe skewing caused a median error of 30% (maximum 55%). Peak systolic WSS was underestimated by ~50% irrespective of skewing with Poiseuille; using a Womersley profile removed this bias, but ±30% errors remained. Errors were greatest in late systole, when skewing was most pronounced. Skewing also introduced large circumferential WSS variations: ±60%, and up to ±100%, of the circumferentially averaged value. Conclusion Vmax-derived WSS may be prone to substantial variable errors related to velocity profile skewing, and cannot detect possibly large circumferential WSS variations. Caution should be exercised when making assumptions about velocity profile shape to calculate WSS, even in vessels usually considered long and straight. PMID:23398945

Mynard, Jonathan P.; Wasserman, Bruce A.; Steinman, David A.

2015-01-01

55

The torque-velocity relationship in large human muscles: maximum voluntary versus electrically stimulated behaviour.  

PubMed

The in vivo maximum voluntary torque-velocity profile for large muscle groups differs from the in vitro tetanic profile with lower than expected eccentric torques. Using sub-maximal transcutaneous electrical stimulation has given torque-velocity profiles with an eccentric torque plateau ?1.4 times the isometric value. This is closer to, but still less than, the in vitro tetanic profiles with plateaus between 1.5 and 1.9 times isometric. This study investigated the maximum voluntary and sub-maximum transcutaneous electrical stimulated torque-angle-angular velocity profiles for the knee extensors and flexors in a group of healthy males. Fifteen male subjects performed maximum voluntary and sub-maximum electrically stimulated (?40% for extensors and ?20% for flexors) eccentric and concentric knee extension and flexions on an isovelocity dynamometer at velocities ranging from ±50°s(-1) to ±400°s(-1). The ratio of peak eccentric to peak isometric torque (T(ecc)/T(0)) was compared between the maximum voluntary and electrically stimulated conditions for both extensors and flexors, and between muscle groups. Under maximum voluntary conditions the peak torque ratio, T(ecc)/T(0), remained close to 1 (0.9-1.2) while for the electrically stimulated conditions it was significantly higher (1.4-1.7; p<0.001) and within the range of tetanic values reported from in vitro studies. In all but one case there was no significant difference in ratios between the extensors and flexors. The results showed that even the largest muscle groups have an intrinsic T(ecc)/T(0) comparable with in vitro muscle tests, and it can be ascertained from appropriate in vivo testing. PMID:23313275

Pain, Matthew T G; Young, Fraser; Kim, Jinwoo; Forrester, Stephanie E

2013-02-22

56

A role of the altitude gradient of the thermospheric wind velocity in ionospheric F-region dynamics  

NASA Astrophysics Data System (ADS)

By processing the data of vertical ionospheric sounding in Almaty for 2000-2009, we obtained the distributions of the heights of the maximum ( h m F) and bottom ( h bot F) of the F2-layer, incremental changes in its semi-thickness (? h), the characteristic time of losses (?), and the vertical displacement velocity of the node of the thermospheric wind ( V) during the transitional time of the day during nighttime increases in the electron concentration at the layer maximum. The comparison of the measured V and modeled V m velocities showed a certain discrepancy. The influence of the altitude gradient of the meridional thermospheric wind velocity on the behaviors of h m F, h bot F, ? h, and ? during nighttime increases in the electron concentration is studied.

Yakovets, A. F.; Vodyannikov, V. V.; Nurmukhanbetova, K. Zh.; Gordienko, G. I.; Litvinov, Yu. G.

2011-06-01

57

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

58

Low-level nocturnal wind maximum over the central Amazon basin  

NASA Astrophysics Data System (ADS)

A low-level nocturnal wind maximum is shown to exist over extensive and nearly undisturbed rainforest near the central Amazon city of Manaus. Analysis of meteorological data collected during the 1985 and 1987 Amazon Boundary Layer Experiments (ABLE 2A and 2B) indicates 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-1 between 300 and 1000 m increase to 10 15m s-1 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. The night-time inversion extends up to 300 m with strong vertical shear of the horizontal wind below the inversion top and uniformly strong horizontal winds above the inversion top. Frictional decoupling of the air above the inversion from the rough forest below, however, is responsible for only part of the observed increase. 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. We suspect that stronger low-level winds are 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

59

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

60

Maximum efficiency control for variable speed wind driven generators with speed and power limits  

Microsoft Academic Search

A control strategy for the maximization of energy capture in variable-speed wind driven turbines is presented. This strategy allows following an operating trajectory with three different parts: maximum efficiency (normal operation), power and speed limitations. These limitations are introduced when there is more available energy than the consumed one or when the wind speed exceeds a certain value. Simulation results

Roberto Leidhold; Guillenno Garcia; Maria Inks Valla

2002-01-01

61

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

62

Dependence of US hurricane economic loss on maximum wind speed and storm size  

NASA Astrophysics Data System (ADS)

Many empirical hurricane economic loss models consider only wind speed and neglect storm size. These models may be inadequate in accurately predicting the losses of super-sized storms, such as Hurricane Sandy in 2012. In this study, we examined the dependences of normalized US hurricane loss on both wind speed and storm size for 73 tropical cyclones that made landfall in the US from 1988 through 2012. A multi-variate least squares regression is used to construct a hurricane loss model using both wind speed and size as predictors. Using maximum wind speed and size together captures more variance of losses than using wind speed or size alone. It is found that normalized hurricane loss (L) approximately follows a power law relation with maximum wind speed (V max) and size (R), L = 10c V maxa R b , with c determining an overall scaling factor and the exponents a and b generally ranging between 4-12 and 2-4 respectively. Both a and b tend to increase with stronger wind speed. Hurricane Sandy’s size was about three times of the average size of all hurricanes analyzed. Based on the bi-variate regression model that explains the most variance for hurricanes, Hurricane Sandy’s loss would be approximately 20 times smaller if its size were of the average size with maximum wind speed unchanged. It is important to revise conventional empirical hurricane loss models that are only dependent on maximum wind speed to include both maximum wind speed and size as predictors.

Zhai, Alice R.; Jiang, Jonathan H.

2014-05-01

63

Fuzzy-logic-based maximum power point tracking strategy for Pmsg variable-speed wind turbine generation systems  

Microsoft Academic Search

In order to achieve maximum power point tracking (MPPT) for wind power generation systems, the rotating speed of wind turbines should be adjusted in the real time according to wind speeds. However, fast wind speed variations and heavy inertia compromise the MPPT control of a wind turbine. In this paper, a fuzzy-logic based MPPT strategy is proposed for PMSG variable

Qingrong Zeng; Liuchen Chang; Riming Shao

2008-01-01

64

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

65

Infering Wind Vector Velocities from GPS Reflections at 38 km Altitude  

Microsoft Academic Search

The purpose of this contribution is to show the process of infering wind vector velocity from data gathered using a balloon equipped with a GPS reflection (GPSR) instrument. While the extraction of wind velocities has been demonstrated using low flying platforms, we extend the analysis to the data gathered at higher altitudes, up to 38 km. The MEditerranean Balloon EXperiment

E. Cardellach; A. Komjathy; D. Pino; A. Rius; G. Ruffini; V. U. Zavorotny

2001-01-01

66

Effect of wind tunnel air velocity on VOC flux rates from CAFO manure and wastewater  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind tunnels and flux chambers are often used to estimate volatile organic compound (VOC) emissions 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 ...

67

On the terminal velocities of winds in central stars of planetary nebulae  

NASA Technical Reports Server (NTRS)

The theory of radiatively driven stellar winds is applied to the central stars of planetary nebulae, and the predicted relation between escape velocity and terminal velocity of the wind is assessed. Ultraviolet spectra obtained with IUE indicate that the terminal velocities of winds from planetary nuclei, which range from 600 to 3600 km/sec, are strongly correlated with stellar temperature. The theory of radiative winds predicts that the terminal velocity of the wind = T(1.2), the constant of proportionality being a function of stellar mass and line-force parameter, alpha. Given a mass of 0.60 solar mass for central stars with winds, the line-force parameter alpha = 0.70, a value higher than Abbott's predictions, alpha = 0.61 (1982).

Heap, Sara R.

1986-01-01

68

Nearfield acoustic holography in wind tunnel by means of velocity LDV measurements  

E-print Network

Nearfield acoustic holography in wind tunnel by means of velocity LDV measurements H. Parisot in wind tunnel are required to charac- terize the main sources during airplanes conception. For a long disturbances. That is why it is interesting to develop another method allowing wind tunnel aeroacoustic sources

Boyer, Edmond

69

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

70

Role of wind stress in causing maximum transport through the Korea Strait in autumn  

NASA Astrophysics Data System (ADS)

Observations show that the maximum transport for the Tsushima Current (TC) through the Korea Strait occurs in autumn. For the TC, variation in transport changes the physical properties of the water as well as the distribution of nutrients, plankton, and other materials in the Japan/East Sea. Despite the importance of the TC, research is yet to unravel the cause of the maximum transport for the TC in autumn. In this study, observational data and numerical modeling data were analyzed in an effort to explore this phenomenon. The maximum transport through the Korea Strait was determined to be the result of the maximum onshore transport crossing the shelf break in the East China Sea (ECS); this transport is driven by strong northeasterly wind stress. Ekman transport driven by wind in the ECS is the primary cause of the maximum transport for the TC through the Korea Strait in autumn.

Cho, Yang-Ki; Seo, Gwang-Ho; Kim, Chang-Sin; Choi, Byoung-Ju; Shaha, Dinesh Chandra

2013-04-01

71

Climatological mean and interannual variance of United States surface wind speed, direction and velocity  

NASA Astrophysics Data System (ADS)

Means and variances of monthly mean wind speed, direction and velocity (the mean resultant vector) are derived for the period 1961-1990 at 216 stations in the coterminous United States. Direction and velocity means and variances are calculated using a complex-arithmetic extension of the equations for scalar mean and variance. Variance is derived from the 30-year time series of monthly means. While analyses of monthly mean wind fields are common, accompanying analyses of speed, direction, and velocity variance do not generally accompany them.Mean monthly wind direction and velocity fields show a typical seasonal progression from westerly and northwesterly winds in winter, to southerly winds in summer. Scalar and vector wind speeds are highest in winter and spring, and lowest in the summer. Seasonal variation in the mean fields is related to seasonal changes in mean sea level pressure, particularly east of the Rocky Mountains. In the western United States, mean winds often reflect channeling by local topography. The interannual variance of mean monthly wind speed, direction and velocity are related to seasonal variability in synoptic-scale features, such as the frequency of cyclones and anticyclones. Low variance occurs at a number of stations in the west, where topography restricts the range of wind variability. High velocity variance appears when both speed and direction variability are high, but it can occur also when speed variance is high and direction variance is low (or vice versa). Low velocity variance can result from low speed and direction variance, or from low mean wind velocities. The mean and variance characteristics of surface winds provide additional information on the surface climatology of the coterminous United States, and serve as a useful adjunct to other extant land-surface climatologies.

Klink, Katherine

1999-04-01

72

Excitation of velocity fluctuations and noise in a wind tunnel  

Microsoft Academic Search

The sources of noise generation in wind tunnels are examined in the light of recent research in this field. An analysis of the available data suggests that noise in wind tunnels is generated by large-scale structures, both in the free jet and in the internal flow within the diffuser. This conclusion is consistent with the fact that, in some wind

V. A. Vishniakov; A. G. Prozorov

1992-01-01

73

Probabilistic estimates of maximum acceleration and velocity in rock in the contiguous United States  

USGS Publications Warehouse

Maximum horizontal accelerations and velocities caused by earthquakes are mapped for exposure times of 10, 50 and 250 years at the 90-percent probability level of nonexceedance for the contiguous United States. In many areas these new maps differ significantly from the 1976 probabilistic acceleration map by Algermlssen and Perkins because of the increase in detail, resulting from greater emphasis on the geologic basis for seismic source zones. This new emphasis is possible because of extensive data recently acquired on Holocene and Quaternary faulting in the western United States and new interpretations of geologic structures controlling the seismicity pattern in the central and eastern United States.

Algermissen, Sylvester Theodore; Perkins, D.M.; Thenhaus, P.C.; Hanson, S.L.; Bender, B.L.

1982-01-01

74

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

75

Design of a maximum power tracking system for wind-energy-conversion applications  

Microsoft Academic Search

A wind-generator (WG) maximum-power-point-tracking (MPPT) system is presented, consisting of a high-efficiency buck-type dc\\/dc converter and a microcontroller-based control unit running the MPPT function. The advantages of the proposed MPPT method are that no knowledge of the WG optimal power characteristic or measurement of the wind speed is required and the WG operates at a variable speed. Thus, the system

Eftichios Koutroulis; Kostas Kalaitzakis

2006-01-01

76

Simulation of wind-blown sand movement and probability density function of liftoff velocities of sand particles  

Microsoft Academic Search

Accurately describing the probability density function (PDF) of liftoff or initial velocities of wind-blown sand ejecting from a sand bed is fundamental to understanding the mechanisms of wind-blown sand movement. Our objective was to investigate the efficacy of developing the PDF of liftoff velocities based on wind tunnel measurements of sand flux and wind speed profile. On the basis of

Ning Huang; Xiao Jing Zheng; You-He Zhou; R. Scott Van Pelt

2006-01-01

77

Wind Observations of Anomalous Cosmic Rays from Solar Minimum to Maximum  

NASA Technical Reports Server (NTRS)

We report the first observation near Earth of the time behavior of anomalous cosmic-ray N, O, and Ne ions through the period surrounding the maximum of the solar cycle. These observations were made by the Wind spacecraft during the 1995-2002 period spanning times from solar minimum through solar maximum. Comparison of anomalous and galactic cosmic rays provides a powerful tool for the study of the physics of solar modulation throughout the solar cycle.

Reames, D. V.; McDonald, F. B.

2003-01-01

78

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

79

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

80

A novel diagnosis algorithm of maximum frequency for longitudinal insulation fault of transformer winding  

Microsoft Academic Search

The transformer, as one of the most important equipment in the transmission and transformation systems, is directly related to the safety operations of the power grid. Because of the longitudinal insulation fault of transformer windings occupied the highest proportion in insulation faults, the research for the longitudinal insulation fault is has important significance for power grid. A maximum frequency algorithm

Yu-sheng Quan; Wei Li; Shan Jiang; Tie-ying Xu

2011-01-01

81

A Summary of Convective-Core Vertical Velocity Properties Using ARM UHF Wind Profilers in Oklahoma  

E-print Network

A Summary of Convective-Core Vertical Velocity Properties Using ARM UHF Wind Profilers in Oklahoma Sciences Division, Argonne National Laboratory, Argonne, Illinois # University of Oklahoma, Norman, Oklahoma @ Bureau of Meteorology, Melbourne, Victoria, Australia & Cooperative Institute for Research

Ohta, Shigemi

82

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

83

Excitation of velocity fluctuations and noise in a wind tunnel  

NASA Astrophysics Data System (ADS)

The sources of noise generation in wind tunnels are examined in the light of recent research in this field. An analysis of the available data suggests that noise in wind tunnels is generated by large-scale structures, both in the free jet and in the internal flow within the diffuser. This conclusion is consistent with the fact that, in some wind tunnels, a noticeable improvement has been achieved by moving perforation holes toward the end of the diffuser and increasing the distance between the perforations.

Vishniakov, V. A.; Prozorov, A. G.

1992-08-01

84

A simple method to estimate threshold friction velocity of wind erosion in the field  

Technology Transfer Automated Retrieval System (TEKTRAN)

Nearly all wind erosion models require the specification of threshold friction velocity (TFV). Yet determining TFV of wind erosion in field conditions is difficult as it depends on both soil characteristics and distribution of vegetation or other roughness elements. While several reliable methods ha...

85

MEASUREMENT OF MOTION CORRECTED WIND VELOCITY USING AN AEROSTAT LOFTED SONIC ANEMOMETER  

EPA Science Inventory

An aerostat-lofted, sonic anemometer was used to determine instantaneous 3 dimensional wind velocities at altitudes relevant to fire plume dispersion modeling. An integrated GPS, inertial measurement unit, and attitude heading and reference system corrected the wind data for th...

86

AMSU-A Tropical Cyclone Maximum Sustained Winds and Web Site  

NASA Technical Reports Server (NTRS)

The Advanced Microwave Sounding Unit (AMSU)-A instruments on the NOAA-15 and NOAA-16 satellites provide information on the warm cores of tropical cyclones from oxygen channel brightness temperature (Tb) measurements near 55 GHz. With appropriate assumptions, cyclone-scale Tb gradients can be directly related to middle-to-lower tropospheric height gradients. We have developed a method for diagnosis of maximum sustained winds (Vmax) from radially averaged Tb gradients in several of the AMSU channels. Calibration of the method with recon-based (or other in situ) winds results in better agreement than with Dvorak wind estimates. Gradient wind theory shows that the warm core Tb gradient signal increases non-linearly with wind speed, making microwave temperature sounders useful for diagnosing high wind speeds, but at the expense of a minimum useful detection limit of about 40 knots. It is found that accurate wind diagnoses depend upon (1) accounting for hydrometeor effects in the AMSU channels, and (2) maximizing signal-to-noise, since the 50 km resolution data cannot fully resolve the temperature gradients in the Vmax region, typically 10-20 km in scale. AMSU imagery and max diagnoses from specific hurricanes will be shown, including independent tests from the 2000 hurricane season.

Spencer, Roy; Goodman, H. Michael (Technical Monitor)

2001-01-01

87

Solar wind velocity and temperature in the outer heliosphere  

NASA Technical Reports Server (NTRS)

At the end of 1992, the Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were at heliocentric distances of 56.0, 37.3, and 39.0 AU and heliographic latitudes of 3.3 deg N, 17.4 deg N, and 8.6 deg S, respectively. Pioneer 11 and Voyager 2 are at similar celestial longitudes, while Pioneer 10 is on the opposite side of the Sun. All three spacecraft have working plasma analyzers, so intercomparison of data from these spacecraft provides important information about the global character of the solar wind in the outer heliosphere. The averaged solar wind speed continued to exhibit its well-known variation with solar cycle: Even at heliocentric distances greater than 50 AU, the average speed is highest during the declining phase of the solar cycle and lowest near solar minimum. There was a strong latitudinal gradient in solar wind speed between 3 deg and 17 deg N during the last solar minimum, but this gradient has since disappeared. The solar wind temperature declined with increasing heliocentric distance out to a heliocentric distance of at least 20 AU; this decline appeared to continue at larger heliocentric distances, but temperatures in the outer heliosphere were suprisingly high. While Pioneer 10 and Voyager 2 observed comparable solar wind temperatures, the temperature at Pioneer 11 was significantly higher, which suggests the existence of a large-scale variation of temperature with heliographic longitude. There was also some suggestion that solar wind temperatures were higher near solar minimum.

Gazis, P. R.; Barnes, A.; Mihalov, J. D.; Lazarus, A. J.

1994-01-01

88

Density, Velocity and Ionization Structure in Accretion-disc Winds  

NASA Astrophysics Data System (ADS)

We propose to exploit the unique capabilities of it FUSE to monitor variations in the wind-formed spectral lines of 3 luminous, low-inclination, cataclysmic variables (CVs). Our principal goal is to improve our understanding of the dynamics of accretion-disc winds. We have previously used HST to investigate substantial and rapid (sim hours to minutes) variability in our target stars, BZ Cam, RW Sex and V603 Aql, and have demonstrated that their disc-outflows are highly structured. We aim here to follow up our discoveries by securing FUSE time-series data. These observations will 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 will track the changing physical conditions in the outflow. A new sophisticated Monte Carlo code will be used to calculate the ionization structure of and radiative transfer through CV winds. This will allow us to establish the wind geometry, kinematics and ionization state, both in a time-averaged sense and as a function of time. Our FUSE observations will provide a legacy that will be fundamental to the development of dynamical models of accretion-disc-driven winds, permitting critical tests of recent hydrodynamic simulations of unstable, line-driven disc winds.

Long, Knox

89

Determination of maximum leaf velocity and acceleration of a dynamic multileaf collimator: Implications for 4D radiotherapy  

SciTech Connect

The dynamic multileaf collimator (MLC) can be used for four-dimensional (4D), or tumor tracking radiotherapy. However, the leaf velocity and acceleration limitations become a crucial factor as the MLC leaves need to respond in near real time to the incoming respiration signal. The aims of this paper are to measure maximum leaf velocity, acceleration, and deceleration to obtain the mechanical response times for the MLC, and determine whether the MLC is suitable for 4D radiotherapy. MLC leaf sequence files, requiring the leaves to reach maximum acceleration and velocity during motion, were written. The leaf positions were recorded every 50 ms, from which the maximum leaf velocity, acceleration, and deceleration were derived. The dependence on the velocity and acceleration of the following variables were studied: leaf banks, inner and outer leaves, MLC-MLC variations, gravity, friction, and the stability of measurements over time. Measurement results show that the two leaf banks of a MLC behave similarly, while the inner and outer leaves have significantly different maximum leaf velocities. The MLC-MLC variations and the dependence of gravity on maximum leaf velocity are statistically significant. The average maximum leaf velocity at the isocenter plane of the MLC ranged from 3.3 to 3.9 cm/s. The acceleration and deceleration at the isocenter plane of the MLC ranged from 50 to 69 cm/s{sup 2} and 46 to 52 cm/s{sup 2}, respectively. Interleaf friction had a negligible effect on the results, and the MLC parameters remained stable with time. Equations of motion were derived to determine the ability of the MLC response to fluoroscopy-measured diaphragm motion. Given the present MLC mechanical characteristics, 4D radiotherapy is feasible for up to 97% of respiratory motion. For the largest respiratory motion velocities observed, beam delivery should be temporarily stopped (beam hold)

Wijesooriya, K.; Bartee, C.; Siebers, J.V.; Vedam, S.S.; Keall, P.J. [Department of Radiation Oncology, Virginia Commonwealth University, Richmond, Virginia 23298 (United States)

2005-04-01

90

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

91

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

92

Influence of wind velocity on pollen concentration in urban canopy layer  

NASA Astrophysics Data System (ADS)

POLLEN RELEASE Temperature is the basic parameter for prediction of the beginning of the pollen season and identification days with good potential for pollen release. Different approaches are used for determination of the start of the pollen season: i) the sum of daily pollen counts = ?x criterion (Arnold 2002), ii) the mean temperature method during pre-defined period (Sparks, 2000), iii) the temperature sum method (Jones 1992). Another parameters influencing pollen release are: day light length, morning temperature gradient, relative humidity. The mentioned parameters enable to create the "statistical” model for determination of timing of pollen potential release. But, the correct determination of pollen release timing is only the first step to correct prediction of pollen concentration in air. The above mentioned collection of parameters isn't complete for correct pollen production prediction without inclusion of the actual wind velocity. The wind velocity directly influences the pollen release rate from mother plant and subsequently transport of pollen grains. From this reason, influence of wind conditions has to be considered as exactly as possible in complex prediction models. WIND VELOCITY AND POLLEN CONCENTRATION Results of in-situ measurements were used for carried out analysis of the relation between wind velocity and pollen concentration in an urban canopy layer. The mean daily wind velocities and the mean daily pollen concentrations were used as the input data describing the pollen season 2005 in an inner part of the city of Brno (pop. 400 000). The mean daily pollen concentrations were matched to corresponding mean daily wind velocity and depicted in graphs. This procedure was done for all locally monitored aeroallergens, namely Alnus, Ambrosia, Betula, Artemis, Corylus, Fraxinus, Poaceae and Quercus. Only days with significant pollen concentration (above 10% of maximal pollen season concentration) were considered for detail analysis. Clear evidence of the wind threshold velocity of pollination appears in the carried out graphical expression of in-situ measurement. The threshold velocity of pollination is the lowest wind velocity with significant concentration of pollen grains in the air. Wind velocity increase above the wind threshold velocity of pollination causes another increase in pollen maximal concentration until reaching the highest concentration of the pollen season. This trend reflects increase in the total pollen release rate due to increase of the air velocity in deeper layers of vegetation and branch bundles. Another increase of wind velocity causes decrease of the maximal air pollen concentration due to "dilution” of the canopy layer by vast quantity of fresh air. The described "triangle" trend was confirmed for majority of considered species. The particularly determined values of the wind threshold velocity of pollination in urban area are: Alnus 0,66 m/s, Ambrosia 0,4 m/s, Betula 0,59 m/s, Artemis 0,62 m/s, Corylus 0,75 m/s, Fraxinus 0,5 m/s, Poaceae 0,45 m/s and Quercus 0,66 m/s. The wind velocities corresponding to the highest pollen concentration values are: Alnus 0,95 m/s, Ambrosia 1,01 m/s, Betula 1,1 m/s, Artemis 0,8 m/s, Corylus 0,95 m/s, Fraxinus 1,1 m/s, Poaceae 1,29 m/s and Quercus 0,96 m/s.

Pospisil, J.; Jícha, M.

2009-09-01

93

A large enhancement of the maximum drift velocity of electrons in the channel of a field-effect heterotransistor  

SciTech Connect

It is shown that the optical-phonon momentum quantization in a GaAs quantum well resulting from the introduction of an InAs quantum-dot barrier layer provides for the elimination of inelastic scattering of electrons by optical phonons and, thus, makes the acceleration of electrons above the saturation drift velocity possible. It is shown experimentally that the maximum drift velocity of electrons in high electric fields in AlGaAs/GaAs heterostructure with InAs quantum-dot barriers introduced into the GaAs quantum well exceeds the saturation drift velocity in bulk GaAs by as much as a factor of 10. Such a rise in the maximum drift velocity of electrons ensures increased maximum current density, transconductance, and cutoff frequency of the heterostructure field-effect transistor with quantum dots.

Pozela, J. K. [Semiconductor Physics Institute (Lithuania)], E-mail: pozela@spi.pfi.lt; Mokerov, V. G. [Russian Academy of Sciences, Institute of the Microwave Semiconductor Electronics (Russian Federation)

2006-03-15

94

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

95

Combined vertical-velocity observations with Doppler lidar, cloud radar and wind profiler  

NASA Astrophysics Data System (ADS)

Case studies of combined vertical-velocity measurements of Doppler lidar, cloud radar and wind profiler are presented. The measurements were taken at the Meteorological Observatory Lindenberg, Germany. Synergistic products are presented that are derived from the vertical-velocity measurements of the three instruments: A comprehensive classification mask of vertically moving atmospheric targets and the terminal fall velocity of water droplets and ice crystals corrected for vertical air motion. It is shown that the measurements of the Doppler lidar can extent the view of the cloud radar and the wind profiler, especially when observing clouds.

Bühl, J.; Leinweber, R.; Görsdorf, U.; Radenz, M.; Ansmann, A.; Lehmann, V.

2015-01-01

96

Solar and solar wind sources of geomagnetic activity during grand solar maximum  

NASA Astrophysics Data System (ADS)

We have studied solar activity for over entire grand solar maximum from solar cycle 12 to 23. We have analyzed different solar activity proxies in detail and furthermore the solar originated disturbances and their geomagnetic effects. We compared the occurrence rate of the coronal mass ejections, high-speed streams and co-rotating interaction regions and the occurrence of geomagnetic storms and substorms. We identified and analyzed solar wind ULF waves in details. ULF fluctuations were identified from the solar wind using the Fourier method developed in this work. The solar wind ULFs were identified from ACE and Wind data and ground-based ULFs from Oulujärvi, Kilpisjärvi and Kevo magnetic observations. We found out that solar wind ULF occurrence peaks during the declining solar cycle phase in a same solar cycle phase where high-speed streams and substorms are found to peak. Our analysis furthermore shows that the trend of ULF waves detected from ground-based instruments is similar to the trend of solar wind ULFs.

Hynönen, Reko; Tanskanen, Eija

2014-05-01

97

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

Microsoft Academic Search

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

Daniel Y. Graybeal

2006-01-01

98

Accurate stellar rotational velocities using the Fourier transform of the cross correlation maximum  

NASA Astrophysics Data System (ADS)

Aims: We propose a method for measuring the projected rotational velocity vsini with high precision even in spectra with blended lines. Though not automatic, our method is designed to be applied systematically to large numbers of objects without excessive computational requirement. Methods: We calculated the cross correlation function (CCF) of the object spectrum against a zero-rotation template and used the Fourier transform (FT) of the CCF central maximum to measure the parameter vsini taking the limb darkening effect and its wavelength dependence into account. The procedure also improves the definition of the CCF base line, resulting in errors related to the continuum position under 1% even for vsini = 280 km s-1. Tests with high-resolution spectra of F-type stars indicate that an accuracy well below 1% can be attained even for spectra where most lines are blended. Results: We have applied the method to measuring vsini in 251 A-type stars. For stars with vsini over 30 km s-1 (2-3 times our spectra resolution), our measurement errors are below 2.5% with a typical value of 1%. We compare our results with Royer et al. (2002a) using 155 stars in common, finding systematic differences of about 5% for rapidly rotating stars.

Díaz, C. G.; González, J. F.; Levato, H.; Grosso, M.

2011-07-01

99

Passive A-band Wind Sounder (PAWS) for measuring tropospheric wind velocity profile  

Microsoft Academic Search

The Passive A-Band Wind Sounder (PAWS) was funded through NASA's Instrument Incubator Program (IIP) to determine the feasibility of measuring tropospheric wind speed profiles from Doppler shifts in absorption O2 A-band. It is being pursued as a low-cost and low-risk alternative capable of providing better wind data than is currently available. The instrument concept is adapted from the Wind Imaging

Grzegorz Miecznik; Robert Pierce; Pei Huang; Philip A. Slaymaker; Paul Kaptchen; Shane Roark; Brian R. Johnson; Donald F. Heath

2007-01-01

100

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

101

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 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 thus the measurement uncertainties are reduced. The method is used in the wind-tunnel experiment to measure dust deposition velocities for different particle sizes, wind speeds and surface conditions. For sticky-smooth wood and water surfaces, the observed dust deposition velocities are compared with the predictions using a dust deposition scheme, and the entire data set is compared with the data found in the literature. From the wind-tunnel experiments, a relatively reliable data set of dust deposition velocities is obtained, which is valuable for the development and validation of dust deposition schemes.

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

2014-09-01

102

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

103

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

104

Comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over Brazil  

NASA Astrophysics Data System (ADS)

We present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble (EPB) zonal drift velocities over northeastern Brazil during the October to December months of 2009 and 2010. The EPB zonal drift velocities are estimated utilizing images of the O I 630.0 nm emissions recorded by a wide-angle imaging system at Cajazeiras. Thermospheric neutral wind estimates are based upon common volume observations made by a bistatic Fabry-Perot interferometer (FPI) experiment using FPIs located at Cajazeiras and Cariri in Brazil observing the Doppler shift of the O I 630.0 nm emission. The results illustrate a similar pattern of nighttime and night-to-night variations in the zonal neutral winds and EPB zonal drift velocities. In general, the geomagnetic zonal neutral winds and the EPB velocities show an excellent agreement illustrating that the F region dynamo is fully developed. However, in the early evening hours the EPB zonal speed is slower than that of the background winds on several occasions. We conclude that this indicates that during the bubble evolution period in the early evening the F region dynamo is not fully activated.

Chapagain, Narayan P.; Makela, Jonathan J.; Meriwether, John W.; Fisher, Daniel J.; Buriti, Ricardo A.; Medeiros, Amauri F.

2012-06-01

105

Effective transport velocity and plume elongation in nocturnal valley wind fields  

SciTech Connect

Using three atmospheric tracers the effective transport velocity and plume elongation produced by nocturnal drainage wind in three different valleys were investigated. Tracer was released in each valley in a well defined drainage wind field and sequentially sampled at downvalley locations. The effective transport velocity (V-eff) was determined from the elapsed time from the start of the release to the time when the plume concentration reached 10% of its peak value and the distance from the release site. The plume elongation factor was determined from the ratio of the width (time) of the plume at 10% of its peak value to the duration of the release. This method was chosen as an objective analysis scheme. Mean measured winds (V) were computed from surface wind instruments along the drainage flow path with values weighted by the estimated time the plume was in the wind field best represented by a measurement. The values used were from the start of release to the time of arrival at the sampler in question. V is compred to V-eff to see how reasonable an estimate of plume transport in valleys can be made from a few surface measurements in the valley. The simple tracer technique used in the studies has proven to be a good one in accomplishing the stated objective of investigating effective transport velocity and plume elongation in nocturnal valley drainage winds.

Clements, W.E.; Barr, S.; Fowler, M.M.

1980-01-01

106

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

107

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

108

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

109

Large and small-scale structures of the local Galactic disc. A maximum entropy approach to the stellar velocity distribution  

NASA Astrophysics Data System (ADS)

An analytical model based on the maximum entropy approach is proposed to describe the eventual asymmetries of the velocity distribution, which are collected through its sample moments. If an extended set of moments is available, the current method provides a linear algorithm, associated with a Gramian system of equations, that leads to a fast and suitable estimation of the velocity distribution. In particular, it could be used to model multimodal distributions that cannot be described through Gaussian mixtures. The method is used with several samples from the HIPPARCOS and Geneva-Copenhagen survey catalogues. For the large-scale distribution, the phase density function may be obtained by fitting moments up to sixth order as a product of two exponential functions, one giving a background ellipsoidal shape of the distribution and the other accounting for the skewness and for the slight shift in the ellipsoidal isocontours in terms of the rotation velocity. The small-scale distribution can be deduced from truncated distributions, such as velocity-bounded samples with |V| ? 51 km s-1, which contain a complex mixture of early-type and young disc stars. By fitting up to ten-order moments, the maximum entropy approach gives a realistic portrait of actual asymmetries, showing a clear bimodal pattern: (i) around the Hyades-Pleiades stream, with negative radial mean velocity and (ii) around the Sirius-UMa stream, with slightly positive radial mean velocity. Among metallicity, colour, and other star properties, the eccentricity of the star's orbit behaves as a very good sampling parameter to find a more detailed structure for the disc velocity distribution, allowing distinctions between different eccentricity layers. For subsamples with eccentricities e<0.15, star velocities are approximately symmetrically distributed around the LSR in the radial direction, with a dearth of stars at the LSR. For e=0.15, the core distribution of the thin disc is supported by two major stellar groups with opposite radial velocities. Several simulations confirm that such a double-peaked distribution comes from the lognormal distribution of the velocity amplitudes. For maximum eccentricity 0.3 and maximum distance to the Galactic plane 0.5 kpc a representative thin disc sample is obtained. The “U-anomaly” along the radial direction is estimated straightforwardly 30-35 km s-1 from the contour plots. An explanation of the apparent vertex deviation of the disc from the swinging of those major kinematic groups around the LSR is then possible, which predicts a continuously changing orientation of the disc's pseudo ellipsoid.

Cubarsi, R.

2010-02-01

110

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

111

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

112

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

113

Latitudinal dependence of density and outflow velocity in the stellar wind of eta Carinae  

NASA Astrophysics Data System (ADS)

The Homunculus reflection nebula around the massive star ? Carinae provides the rare opportunity to observe the spectrum of a star from multiple directions. Doppler velocities of emission lines can be used to estimate the nebula's geometry accurately enough to infer how reflected stellar-wind profiles vary with latitude. HST/STIS spectra of hydrogen and helium lines seen in the Homunculus reveal a non-spherical stellar wind, with bipolar symmetry. P Cygni absorption in Balmer lines depends on latitude, with relatively high velocities and strong absorption near the poles. Higher velocities there are expected due to higher escape velocity if the star is rotating. However, the stronger hydrogen P Cygni absorption at high latitudes is surprising. It suggests higher mass flux toward the poles, perhaps resulting from equatorial gravity darkening on a rotating star. Reflected profiles of He I lines are more puzzling, and offer clues to ? Car's wind geometry and circumstellar ionization structure. In March 2000, during ? Car's normal state between periodic ‘spectroscopic events’ that repeat every 5.5 years, the wind appears to have had a fast, high-density polar wind, with higher ionization at low/mid latitudes. In spite of the lower densities at low/mid latitudes, a thin equatorial disk-wind may also be present. The bipolar wind geometry may imply that intrinsically asymmetric ejection helped form the Homunculus, rather than an externally constrained outflow, and it has interesting implications for the long-term variability of ? Carinae and excitation of its ejecta. Older STIS data obtained since 1998 reveal that this global stellar-wind geometry changes during ? Car's 5.5 year cycle, suggesting that the star's periodic spectroscopic events are shell ejections. Whether or not a companion star triggers these outbursts remains ambiguous. Dramatic changes in the wind occur at low latitudes, while the dense polar wind remains relatively stable during an event. The observed wind geometry and its variability have critical implications for the 5.5 year cycle, but do not provide a clear alternative to an eccentric binary system for generating ? Car's variable X-ray emission.

Smith, Nathan I.

2002-12-01

114

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

115

Nanogenerator as an active sensor for vortex capture and ambient wind-velocity detection  

E-print Network

sensitivity and good environment-friendly properties, the NG as an active sensor should play an important role as active sensors for heart-pulse,10 tire pressure12 and cantilever vibration13 measurements have beenNanogenerator as an active sensor for vortex capture and ambient wind-velocity detection Rui Zhang

Wang, Zhong L.

116

Estimating attitude and wind velocity using biomimetic sensors on a microrobotic bee  

E-print Network

Estimating attitude and wind velocity using biomimetic sensors on a microrobotic bee Sawyer B discusses recent developments in sen- sors for the Harvard RoboBee. The RoboBee is a sub-100 mg flapping the ocelli on a wire-mounted RoboBee that is free to rotate about its pitch axis. These flight-weight sensors

Fuller, Sawyer Buckminster

117

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

118

Mean Velocity, Turbulence Intensity and Turbulence Convection Velocity Measurements for a Convergent Nozzle in a Free Jet Wind Tunnel. Comprehensive Data Report  

NASA Technical Reports Server (NTRS)

The effect of flight on the mean flow and turbulence properties of a 0.056m circular jet were determined in a free jet wind tunnel. The nozzle exit velocity was 122 m/sec, and the wind tunnel velocity was set at 0, 12, 37, and 61 m/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, and eddy convection velocity were carried out using two linearized hot wire anemometers. This report contains the raw data and graphical presentations. The final technical report includes a description of the test facilities, test hardware, along with significant test results and conclusions.

Mccolgan, C. J.; Larson, R. S.

1977-01-01

119

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

120

LDA system for long-range cross-wind velocity measurements using pulsed laser radiation  

NASA Astrophysics Data System (ADS)

A mobile long-range LDA system, using frequency-doubled Nd:YAG lasers to deliver long-duration, nearly rectangular pulses with low electrical input, for the measurement of the atmospheric crosswind velocity is described. A microcomputer controls the correlator and contains new software to extract the wind velocity information from the LDA signals, taking into acount the particular shape of the signals and the occasionally poor SNR. Field measurements carried out over a distance of 100 m show that though the SNR is high enough under certain weather conditions to obtain accurate cross-wind velocity components, signals of good quality cannot be obtained either if the atmospheric optical scintillation is too high, or if the particle size distribution is biased towards particles with diameters of less than 5 microns.

Sommer, E.; Pfeifer, H. J.

1986-07-01

121

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

122

THE SIMULATION OF WIND-BLOWN SAND MOVEMENT AND PROBABILITY DENSITY FUNCTION OF LIFT-OFF VELOCITIES OF SAND GRAINS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Accurately describing the probability density function (PDF) of lift-off or initial velocities of wind-blown sand ejecting from a sand bed is fundamental to understanding the mechanisms of wind-blown sand movement. Our objective was to investigate the efficacy of developing the PDF of lift-off veloc...

123

Kinematical Structure of Wolf-Rayet Winds. II. Internal Velocity Scatter in WN Stars  

NASA Astrophysics Data System (ADS)

The shortward edge of the absorption core velocities - v_black as determined from low resolution archived IUE spectra from the INES database are presented for three P Cyg profiles of NV 1240, HeII 1640 and NIV 1720 for 51 Galactic and 64 LMC Wolf-Rayet stars of the WN subtype. These data, together with v_black of CIV 1550 line presented in Niedzielski and Skorzynski (2002) are discussed. Evidences are presented that v_black of CIV 1550 rarely displays the largest wind velocity among the four lines studied in detail and therefore its application as an estimator of the terminal wind velocity in WN stars is questioned. An average v_black of several lines is suggested instead but it is pointed out that v_black of HeII 1640 usually reveals the highest observable wind velocity in Galactic and LMC WN stars. It is shown that the stratification strength decreases from WNL to WNE stars and that for WNL stars there exists a positive relation between v_black and the Ionization Potential. The velocity scatter between v_black obtained from different UV lines is found to correlate well with the X-ray luminosity of single WN stars (correlation coefficient R=0.82 for the data obtained from the high resolution IUE spectra) and therefore two clumpy wind models of single WN stars are presented that allow the velocity scatter to persist up to very large distances from the stellar surface (r approx 500-1000 R_*). These models are used to explain the specific features of single WN stars like broad absorption troughs of strong lines having different v_black, X-ray fluxes, IR/radio continua and stratification relations.

Niedzielski, A.; Nugis, T.; Skorzynski, W.

2004-12-01

124

Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds  

NASA Technical Reports Server (NTRS)

The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle- and upper-tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. The gradient wind equation is recast to include AMSU-A-derived variables, Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V(sub max)). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1-10 T(sub b) data (delta(sub r)T(sub B)), the squares of these gradients, a channel-15-based scattering index (SI(sub 89)), and area-averaged T(sub B). Calculations of T(sub B) and delta(sub r)T(sub B) from mesoscale model simulations of Andrew reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center V(sub max) estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V(sub max), the average error standard deviation was 4.7 m/s. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m/s Operational considerations, including the detection of weak cyclones and false alarm reduction, are also discussed.

Spencer, Roy W.; Braswell, William D.

2001-01-01

125

Atlantic Tropical Cyclone Monitoring with AMSU-A: Estimation of Maximum Sustained Wind Speeds  

NASA Technical Reports Server (NTRS)

The first Advanced Microwave Sounding Unit temperature sounder (AMSU-A) was launched on the NOAA-15 satellite on 13 May 1998. The AMSU-A's higher spatial and radiometric resolutions provide more useful information on the strength of the middle and upper tropospheric warm cores associated with tropical cyclones than have previous microwave temperature sounders. The gradient wind relationship suggests that the temperature gradient near the core of tropical cyclones increases nonlinearly with wind speed. We recast the gradient wind equation to include AMSU-A derived variables. Stepwise regression is used to determine which of these variables is most closely related to maximum sustained winds (V(sub max)). The satellite variables investigated include the radially averaged gradients at two spatial resolutions of AMSU-A channels 1 through 10 T(sub b) data (delta(sub r)T(sub b)), the squares of these gradients, a channel 15 based scattering index (SI-89), and area averaged T(sub b). Calculations of Tb and delta(sub r)T(sub b) from mesoscale model simulations of Andrew reveal the effects of the AMSU spatial sampling on the cyclone warm core presentation. Stepwise regression of 66 AMSU-A terms against National Hurricane Center (NHC) V(sub max) estimates from the 1998 and 1999 Atlantic hurricane season confirms the existence of a nonlinear relationship between wind speed and radially averaged temperature gradients near the cyclone warm core. Of six regression terms, four are dominated by temperature information, and two are interpreted as correcting for hydrometeor contamination. Jackknifed regressions were performed to estimate the algorithm performance on independent data. For the 82 cases that had in situ measurements of V(sub max), the average error standard deviation was 4.7 m/s. For 108 cases without in situ wind data, the average error standard deviation was 7.5 m/s. Operational considerations, including the detection of weak cyclones and false alarm reduction are also discussed.

Spencer, Roy; Braswell, William D.; Goodman, H. Michael (Technical Monitor)

2001-01-01

126

Wind energy potential in Turkey  

Microsoft Academic Search

Lewis's methods are employed to evaluate the wind energy potentials of four selected locations, which have experienced relatively high wind velocities. In addition to Lewis's methods, the relations connecting the instantaneous and average wind powers, total and maximum wind energies for a given period of time are derived. Characteristics of wind energy, including rotor radius and tower height, are estimated

H. Külünk

1993-01-01

127

CO-RELATIVE STUDY OF SOLAR WIND STREAMS VELOCITY & COSMIC RAY INTENSITY VARIATIONS DURING 2002-2007  

E-print Network

Abstract: A correlative study of solar wind streams velocity & cosmic ray intensity variations during 2002-2007, using the hourly neutron monitor data of Moscow (R e = 2.39 GV) station. High speed plasma streams identified in the solar wind measurement, which can be separated into two categories: Coronal hole associated streams & flare generated solar streams. It is investigated that; the solar wind streams velocity is inversely related with cosmic ray intensity variation on long-term basis.

S. G. Singh; A. K. Saxena; R. P. Singh; Y. K. Singh

128

Dynamic aeroelastic stability of vertical-axis wind turbines under constant wind velocity  

NASA Astrophysics Data System (ADS)

The flutter problem associated with the blades of a class of vertical-axis wind turbines called Darrieus is studied in detail. The spinning blade is supposed to be initially curved in a particular shape characterized by a state of pure tension at the blade cross section. From this equilibrium position a three-dimensional linear perturbation pattern is superimposed to determine the dynamic aeroelastic stability of the blade in the presence of free wind speed by means of the Floquet-Lyapunov theory for periodic systems.

Nitzsche, Fred

1994-05-01

129

Understanding the Benefits and Limitations of Increasing Maximum Rotor Tip Speed for Utility-Scale Wind Turbines  

NASA Astrophysics Data System (ADS)

For utility-scale wind turbines, the maximum rotor rotation speed is generally constrained by noise considerations. Innovations in acoustics and/or siting in remote locations may enable future wind turbine designs to operate with higher tip speeds. Wind turbines designed to take advantage of higher tip speeds are expected to be able to capture more energy and utilize lighter drivetrains because of their decreased maximum torque loads. However, the magnitude of the potential cost savings is unclear, and the potential trade-offs with rotor and tower sizing are not well understood. A multidisciplinary, system-level framework was developed to facilitate wind turbine and wind plant analysis and optimization. The rotors, nacelles, and towers of wind turbines are optimized for minimum cost of energy subject to a large number of structural, manufacturing, and transportation constraints. These optimization studies suggest that allowing for higher maximum tip speeds could result in a decrease in the cost of energy of up to 5% for land-based sites and 2% for offshore sites when using current technology. Almost all of the cost savings are attributed to the decrease in gearbox mass as a consequence of the reduced maximum rotor torque. Although there is some increased energy capture, it is very minimal (less than 0.5%). Extreme increases in tip speed are unnecessary; benefits for maximum tip speeds greater than 100-110 m/s are small to nonexistent.

Ning, A.; Dykes, K.

2014-06-01

130

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

131

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

132

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

133

Structure of Turbulence in Katabatic Flows below and above the Wind-Speed Maximum  

E-print Network

Measurements of small-scale turbulence made over the complex-terrain atmospheric boundary layer during the MATERHORN Program are used to describe the structure of turbulence in katabatic flows. Turbulent and mean meteorological data were continuously measured at multiple levels at four towers deployed along the East lower slope (2-4 deg) of Granite Mountain. The multi-level observations made during a 30-day long MATERHORN-Fall field campaign in September-October 2012 allowed studying of temporal and spatial structure of katabatic flows in detail, and herein we report turbulence and their variations in katabatic winds. Observed vertical profiles show steep gradients near the surface, but in the layer above the slope jet the vertical variability is smaller. It is found that the vertical (normal to the slope) momentum flux and horizontal (along the slope) heat flux in a slope-following coordinate system change their sign below and above the wind maximum of a katabatic flow. The vertical momentum flux is directed...

Grachev, Andrey A; Di Sabatino, Silvana; Fernando, Harindra J S; Pardyjak, Eric R; Fairall, Christopher W

2015-01-01

134

Occurrence of high-speed solar wind streams over the Grand Modern Maximum  

E-print Network

In the declining phase of the solar cycle, when the new-polarity fields of the solar poles are strengthened by the transport of same-signed magnetic flux from lower latitudes, the polar coronal holes expand and form non-axisymmetric extensions toward the solar equator. These extensions enhance the occurrence of high-speed solar wind streams (HSS) and related co-rotating interaction regions in the low-latitude heliosphere, and cause moderate, recurrent geomagnetic activity in the near-Earth space. Here, using a novel definition of geomagnetic activity at high (polar cap) latitudes and the longest record of magnetic observations at a polar cap station, we calculate the annually averaged solar wind speeds as proxies for the effective annual occurrence of HSS over the whole Grand Modern Maximum (GMM) from 1920s onwards. We find that a period of high annual speeds (frequent occurrence of HSS) occurs in the declining phase of each solar cycle 16-23. For most cycles the HSS activity clearly maximizes during one year...

Mursula, Kalevi; Holappa, Lauri

2015-01-01

135

Diffusion in velocity space of solar wind protons exposed to parallel and oblique plasma waves  

NASA Astrophysics Data System (ADS)

The solar wind plasma is permeated by all kinds of waves with a broad range of wavelengths and frequencies. Kinetic plasma waves in particular can resonantly interact with the ions, a process that is described within quasilinear theory as diffusion. The resulting effects on the proton velocity distribution function (VDF) are discussed. Theoretical predictions are compared with detailed measurements made in-situ by Helios, and found to comply favourably with resonant diffusion of the protons in the wave field. The shape of the proton VDF, showing an anisotropic core and a beam at positive velocities in the solar wind frame, can well be explained by scattering of the protons in weakly compressive and obliquely propagating Alfvén/ion-cyclotron and fast/slow-magnetoacoustic waves.

Marsch, Eckart; Tu, Chuanyi

2013-06-01

136

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

137

Development of tunable high pressure CO2 laser for lidar measurements of pollutants and wind velocities  

NASA Technical Reports Server (NTRS)

The problem of laser energy extraction at a tunable monochromatic frequency from an energetic high pressure CO2 pulsed laser plasma, for application to remote sensing of atmospheric pollutants by Differential Absorption Lidar (DIAL) and of wind velocities by Doppler Lidar, was investigated. The energy extraction principle analyzed is based on transient injection locking (TIL) at a tunable frequency. Several critical experiments for high gain power amplification by TIL are presented.

Levine, J. S.; Guerra, M.; Javan, A.

1980-01-01

138

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

139

A radionuclide counting technique for measuring wind velocity. [drag force anemometers  

NASA Technical Reports Server (NTRS)

A technique for measuring wind velocities of meteorological interest is described. It is based on inverse-square-law variation of the counting rates as the radioactive source-to-counter distance is changed by wind drag on the source ball. Results of a feasibility study using a weak bismuth 207 radiation source and three Geiger-Muller radiation counters are reported. The use of the technique is not restricted to Martian or Mars-like environments. A description of the apparatus, typical results, and frequency response characteristics are included. A discussion of a double-pendulum arrangement is presented. Measurements reported herein indicate that the proposed technique may be suitable for measuring wind speeds up to 100 m/sec, which are either steady or whose rates of fluctuation are less than 1 kHz.

Singh, J. J.; Khandelwal, G. S.; Mall, G. H.

1981-01-01

140

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

141

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

142

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

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

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

145

Responses of giant interneurons of the cockroach Periplaneta americana to wind puffs of different directions and velocities  

Microsoft Academic Search

1.Controlled wind puffs of different directions and velocities were delivered to the cerci of cockroaches (Periplaneta americana), while the responses of individually identifiable giant interneurons (GI's) were recorded intracellularly.2.All fourteen histologically identified GI's (seven bilateral pairs) respond with a burst of action potentials to wind from some or all directions. The directional sensitivity of a given GI is consistent from

Joanne Westin; Jonathan J. Langberg; Jeffrey M. Camhi

1977-01-01

146

Anorthite sputtering by H+ and Arq+ (q = 1-9) at solar wind velocities  

NASA Astrophysics Data System (ADS)

report sputtering measurements of anorthite-like material, taken to be representative of soils found in the lunar highlands, impacted by singly and multicharged ions representative of the solar wind. The ions investigated include protons, as well as singly and multicharged Ar ions (as proxies for the nonreactive heavy solar wind constituents), in the charge state range +1 to +9, at fixed solar wind-relevant impact velocities of 165 and 310 km/s (0.25 keV/amu and 0.5 keV/amu). A quartz microbalance approach (QCM) for determination of total sputtering yields was used. The goal of the measurements was to determine the sputtering contribution of the heavy, multicharged minority solar wind constituents in comparison to that due to the dominant H+ fraction. The QCM results show a yield increase of a factor of about 80 for Ar+ versus H+ sputtering and an enhancement by a factor of 1.67 between Ar9+ and Ar+, which is a clear indication of a potential sputtering effect.

Hijazi, H.; Bannister, M. E.; Meyer, H. M.; Rouleau, C. M.; Barghouty, A. F.; Rickman, D. L.; Meyer, F. W.

2014-10-01

147

Wind velocity measurements in the neutral boundary layer above hilly prairie  

NASA Technical Reports Server (NTRS)

The Flint Hills region in eastern Kansas is characterized by a strongly dissected rolling to hilly terrain with an average about 25 m of relief between steep ridges and valleys, and with ridges typically separated by distances of the order of 600 m. Intensive radiosonde observations during summer and fall of 1987 allowed the determination of some aspects of the wind regime in the region. For an assumed ground-surface reference of 330 m above sea level (asl), analysis of neutral profiles yielded a value z(0) of about 1.05 m, approximately. Good agreement was obtained between the values of friction velocity derived from wind profiles and values determined independently from the corresponding humidity profiles.

Sugita, Michiaki; Brutsaert, Wilfried

1990-01-01

148

Cluster/Peace Electrons Velocity Distribution Function: Modeling the Strahl in the Solar Wind  

NASA Technical Reports Server (NTRS)

We present a study of kinetic properties of the strahl electron velocity distribution functions (VDF's) in the solar wind. These are used to investigate the pitch-angle scattering and stability of the population to interactions with electromagnetic (whistler) fluctuations. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focuses on the mechanisms that control and regulate the pitch-angle and stability of strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the electron heat-flux and temperature anisotropy. The goal is to check whether the strahl electrons are constrained by some instability (e.g., the whistler instability), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by fitting the VDF's to a spectral spherical harmonic model from which the moments are derived directly from the model coefficients.

Figueroa-Vinas, Adolfo; Gurgiolo, Chris; Goldstein, Melvyn L.

2008-01-01

149

Lidar determination of winds by aerosol inhomogeneities: motion velocity in the planetary boundary layer.  

PubMed

The paper presents results from lidar measurements of wind velocity in the planetary boundary layer using correlation data processing. Two lidars are used in our experiments: a ruby lidar operating along slant paths and a YAG:Nd lidar operating for near vertical sounding used by us for the first time. On the basis of our experience the optimal sizes of aerosol inhomogeneities (30-300 m), the duration of the experiments (2-10 min), and the repetition rate of laser shots (fractions of hertz to several hertz) are determined. The results are compared to independent data obtained from anemometer measurements, theodolite- and radar-tracked pilot balloons. The range of differences is ~1-2 m/s in speed and 10-15 degrees in direction. Preliminary results from the use of lidar data to remotely sound the wind speed for various atmospheric stratifications and synoptic situations are described as well. PMID:20531786

Kolev, I; Parvanov, O; Kaprielov, B

1988-06-15

150

Flying Drosophila stabilize their vision-based velocity controller by sensing wind with their antennae.  

PubMed

Flies and other insects use vision to regulate their groundspeed in flight, enabling them to fly in varying wind conditions. Compared with mechanosensory modalities, however, vision requires a long processing delay (~100 ms) that might introduce instability if operated at high gain. Flies also sense air motion with their antennae, but how this is used in flight control is unknown. We manipulated the antennal function of fruit flies by ablating their aristae, forcing them to rely on vision alone to regulate groundspeed. Arista-ablated flies in flight exhibited significantly greater groundspeed variability than intact flies. We then subjected them to a series of controlled impulsive wind gusts delivered by an air piston and experimentally manipulated antennae and visual feedback. The results show that an antenna-mediated response alters wing motion to cause flies to accelerate in the same direction as the gust. This response opposes flying into a headwind, but flies regularly fly upwind. To resolve this discrepancy, we obtained a dynamic model of the fly's velocity regulator by fitting parameters of candidate models to our experimental data. The model suggests that the groundspeed variability of arista-ablated flies is the result of unstable feedback oscillations caused by the delay and high gain of visual feedback. The antenna response drives active damping with a shorter delay (~20 ms) to stabilize this regulator, in exchange for increasing the effect of rapid wind disturbances. This provides insight into flies' multimodal sensory feedback architecture and constitutes a previously unknown role for the antennae. PMID:24639532

Fuller, Sawyer Buckminster; Straw, Andrew D; Peek, Martin Y; Murray, Richard M; Dickinson, Michael H

2014-04-01

151

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

152

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

153

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

154

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

155

Design of a near-IR coherent lidar for high spatial and velocity resolution wind measurement  

NASA Technical Reports Server (NTRS)

A coherent Doppler lidar based on a CW diode-pumped, injection seeded, Th:YAG laser operating at approx. 2.02 microns is currently under development. This system is optimized for measurements of boundary layer winds with high spatial, temporal, and velocity resolution. Initially, the system will run alongside a new high repetition rate (5-10 kHz) CO2 mini-Master Oscillator Power Amplifier (mini-MOPA) Doppler lidar, which will provide simultaneous range-resolved Differential Absorption Lidar (DIAL) water vapor measurements. Water vapor DIAL operation of the 2 micron system is being considered as a future option. The anticipated specifications and the preliminary design are discussed.

Grund, Christian J.; Post, Madison J.

1992-01-01

156

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

157

Spectral Types and Wind Velocities for Massive Stars in R136  

NASA Astrophysics Data System (ADS)

We analyze spatially resolved, long-slit ultraviolet (UV) and optical stellar spectra of the compact starburst cluster R136 at the core of 30 Doradus. R136 is young and massive, making it an ideal place to study the upper end of the initial mass function. These spectra, taken with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, cover over 100 stars in the inner 4 arcseconds (1 parsec) of R136, a region which cannot be resolved with ground-based spectroscopy. In this poster we present both the UV and optical of over 20 of the brightest stars in R136, extracted with MULTISPEC, a tool written specifically for multiple objects in crowded fields. For each star we present an optical spectral type and a terminal wind velocity derived from the UV data

Bostroem, K. A.; Maíz Apellániz, J.; Caballero-Nieves, S. M.; Walborn, N. R.; Crowther, P. A.

2014-01-01

158

Intensity of the Fe XV emission line corona, the level of geomagnetic activity, and the velocity of the solar wind  

NASA Technical Reports Server (NTRS)

The method of superposed epochs is used to determine the average solar wind velocity and the Kp index following central meridian passage of coronal weak and bright features identified from OSO 7 isophotograms of the Fe XV (284 A) emission line. It is found that bright coronal regions possess magnetic fields of closed configuration, thus reducing particle escape, while coronal holes possess open magnetic field lines favorable to particle escape or enhanced outflow of the solar wind.

Bell, B.; Noci, G.

1976-01-01

159

Maximum tension and force-velocity properties of fatigued, single Xenopus muscle fibres studied by caffeine and high K+.  

PubMed Central

1. The importance of reduced maximum force-generating capacity in the development of skeletal muscle fatigue has been studied using potassium and caffeine contractures as tools. 2. Single, intact fibres isolated from the lumbrical and iliofibularis muscles of Xenopus were fatigued by repeated tetanic stimulations until they produced close to 40% of the original tetanic tension (P0). Using this stimulation scheme three major types of fibres can be distinguished: easily fatigued (type 1), fatigue resistant (type 2), and very fatigue-resistant (type 3) fibres (Westerblad & Lännergren, 1986). 3. When activated by 8-15 mM-caffeine-Ringer solutions fatigued fibres of all three types developed tensions similar to those of controls (81.0 +/- 6.6 vs. 83.9 +/- 4.2% of P0, respectively; means +/- S.D.). 4. Tension output also increased markedly when fatigued fibres were depolarized by 190 mM-K+ solution. The tension produced was in this case fibre type dependent: 71.4 +/- 6.6, 81.3 +/- 2.5 and 95.0 +/- 4.4% of P0 in fibre types 1, 2 and 3, respectively. 5. Force-velocity measurements were performed during caffeine contractures in fatigued iliofibularis fibres (types 1 and 2) to obtain more information about the functional state of cross-bridges. 6. In fatigued type 1 fibres the shortening velocity was reduced to about 25% of that in controls, while it was not significantly depressed in type 2 fibres. 7. It is concluded that cross-bridges of fatigued fibres can produce nearly full tension, but they may work at a much slower rate in this state. 8. Fibre types 1 and 2 mostly display a long-lasting, reversible state of severely depressed tension production during the recovery period, which has been named post-contractile depression, PCD (Westerblad & Lännergren, 1986). Fibres tested in this state generated full caffeine-activated tension and the shortening velocity was not significantly reduced. The tension output during K+ contractures was, however, markedly depressed (12.4 +/- 4.1% of P0). 9. In conclusion, cross-bridges are able to produce close to full tension during PCD as well as in the fatigued state if they are fully activated. The form of functional impairment seems, however, not to be the same in the two cases. PMID:2585298

Lännergren, J; Westerblad, H

1989-01-01

160

Determination of the mass loss rate and the terminal velocity of stellar winds. I Genetic algorithm for automatic line profile fitting  

E-print Network

Terminal wind velocity and mass loss rate are the most fundamental parameters of stellar winds. Unfortunately, their determination calls for high resolution spectroscopy in a range of wavelengths spanning from the ultraviolet to the infrared. For weak and/or distant objects, this becomes unfeasible. Nevertheless, it is possible to obtain an accurate estimate of these parameters through a simplified study of the formation processes of resonant lines which show P Cyg profiles. In this case, the line profile is a complex function of 6 parameters, with the radiative transport treatment becoming relatively inexpensive. However, preforming a 6 dimensional parameter fit raises a number of problems if one seeks an objective and automatic procedure to yield the optimal values, from which wind velocities and mass loss rates can be estimated. Useing a Likelihood function to construct a well defined statistical estimator of the goodness of fit which corresponds to a given model, we turn to a genetic algorithm through which we find the global maximum of the 6 dimensional Likelihood hyper-surface. We here present the implementation of the method, its successful testing with synthetic line profiles, where the answer is known in advance, together with first results of its application to real data

L. Georgiev; X. Hernandez

2005-01-28

161

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

162

Warm high velocity CO in the wind of Sakurai's Object (= V4334 Sgr)  

E-print Network

We present UKIRT UIST spectra of Sakurai's Object (=V4334 Sgr) showing CO fundamental band absorption features around 4.7 microns. The line-centres are at heliocentric radial velocity of -170+/-30 km/s. The number and relative strengths of the lines indicate a CO gas temperature of 400+/-100 K and CO column density of 7(+3/-2)x10^17 per square cm. The gas was moving away from the central star at an average speed of 290+/-30 km/s in 2003 September. The lines appeared sometime between mid 1999 (well after the opaque dust shell formed) and mid 2000 and may have been somewhat more blue--shifted initially than they are now. The observed CO velocity and temperature indicate the continued presence of a fast wind in the object, previously seen in the He I 1.083 micron line beginning just prior to massive dust formation, and more recently in atomic and ionized lines. The dust continuum is consistent with a temperature of 350+/-30 K, indicating continued cooling of the shell. The similar CO temperature suggests that the bulk of the CO absorption occurs just outside of the dust continuum surface.

S. P. S. Eyres; T. R. Geballe; V. H. Tyne; A. Evans; B. Smalley; H. L. Worters

2004-03-18

163

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

164

Maximum wind speeds and US hurricane losses R. J. Murnane1  

E-print Network

; revised 16 July 2012; accepted 17 July 2012; published 28 August 2012. [1] There is academic, commercial and loss is exponential and that loss increases with wind speed at a rate of 5% per m sÃ?1, 2009]. Studies tha

Elsner, James B.

165

Power strategies for maximum control structure of a wind energy conversion system with a synchronous machine  

Microsoft Academic Search

The control of a wind energy conversion system can be decomposed into two parts: a local control depending on the power structure and a global control (strategy) deduced from global considerations. The local part ensures an efficient energy management of each component of the system. The local control structure can be deduced from the Energetic Macroscopic Representation, which is a

A. Bouscayrol; Ph. Delarue; X. Guillaud

2005-01-01

166

Two-dimensional Cascade Investigation of the Maximum Exit Tangential Velocity Component and Other Flow Conditions at the Exit of Several Turbine Blade Designs at Supercritical Pressure Ratios  

NASA Technical Reports Server (NTRS)

The nature of the flow at the exit of a row of turbine blades for the range of conditions represented by four different blade configurations was evaluated by the conservation-of-momentum principle using static-pressure surveys and by analysis of Schlieren photographs of the flow. It was found that for blades of the type investigated, the maximum exit tangential-velocity component is a function of the blade geometry only and can be accurately predicted by the method of characteristics. A maximum value of exit velocity coefficient is obtained at a pressure ratio immediately below that required for maximum blade loading followed by a sharp drop after maximum blade loading occurs.

Hauser, Cavour H; Plohr, Henry W

1951-01-01

167

Measurement of wind velocity on the surface of Venus during operation of the Venera 9 and Venera 10 space probes  

Microsoft Academic Search

The paper reports on the first measurements of the wind velocity on the surface of Venus recorded during final phase of descent of Venera 9 and 10 and while on the surface. The cup anemometer system and some tests on earth for determining best placement of the equipment in order to eliminate any effect of the spacecraft are described. Venera-9

V. S. Avduevskii; S. L. Vishnevetskii; I. A. Golov; Iu. Ia. Karpeiskii; A. D. Lavrov; V. Ia. Likhushin; M. Ia. Marov; D. A. Melnikov; N. I. Pomogin; N. N. Pronina

1976-01-01

168

Effect of Wind Tunnel Air Velocity on VOC Flux from Standard Solutions and CAFO Manure/Wastewater  

Technology Transfer Automated Retrieval System (TEKTRAN)

Researchers and practitioners have used wind tunnels and flux chambers to quantify the flux of volatile organic compounds (VOCs), ammonia, and hydrogen sulfide and estimate emission factors from animal feeding operations (AFOs) without accounting for effects of air velocity or sweep air flow rate. L...

169

A Wind Tunnel Investigation of the Rate of Evaporation of Large 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 millimeter sized water drops failing at terminal velocity in air has been carried out in a wind tunnel where drops were suspended freely in the tunnel air stream. It was found that for drops in the size range 1150 µma02500 µm, the mean ventilation coefficient vh

H. R. Pruppacher; R. Rasmussen

1979-01-01

170

Comparison of drift velocities of nighttime equatorial plasma depletions with the ambient plasma drifts and the thermospheric neutral winds  

NASA Astrophysics Data System (ADS)

This study is for the first time to analyze satellite observations and compare the plasma depletion drifts with the ambient plasma drifts and the neutral winds in the post-sunset equatorial ionosphere. The local time and latitude variations of the drift velocities of O+ plasma depletions at 350--400 km altitude are derived from the observations of the Far Ultraviolet Imager (FUV) operated on the IMAGE satellite during March 10-June 7, 2002. The variations are compared with the simultaneous measurements of the ion drift velocities and the neutral winds by the ROCSAT-1 and the CHAMP satellites for a similar time period. The analysis shows that the zonal drift velocity of plasma depletions is smaller than both the ambient ion zonal drift velocity and the neutral zonal wind at 18-20 hour magnetic local time and after 21 hour the variations of these velocities are similar. The analysis also shows that the difference of the plasma depletion drift with the background is small at low latitudes. This is the first-ever satellite comparison of the plasma depletion drift with the ambient plasma drift as well as the neutral wind for a global scale, explaining many previous observations at single locations. Furthermore, the zonal drift velocity of the depletion is found in this study to have a large latitudinal gradient specifically at 12°-18° magnetic latitude, which again does not match the ambient ion drift and the neutral wind. This latitudinal difference has been reported by previous studies, but these studies use models and they only compare the depletion drifts with the modeled neutral winds. This study compares the satellite observations, and compares with both the neutral winds and the plasma drifts. The study provides a measure of the difference that has never been provided before by any study using global observations. It has been suggested that vertical polarization electric fields inside the plasma depletions are responsible for the eastward drift of the depletion structures. The difference in the latitudinal gradients seen here in this study could also be explained by the polarization electric fields. For the C-shaped depletion, the polarization electric fields drive a westward drift of plasma particles inside the depletion and this drift velocity changes with increasing latitude. Consequently, the depletion drifts eastward and the depletion drift has a larger latitudinal gradient than the ambient plasma drift.

Liu, G.; England, S.; Frey, H. U.; Immel, T. J.; Lin, C. S.; Pacheco, E.; Haeusler, K.; Doornbos, E.

2013-12-01

171

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

172

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

173

Derivation of wind velocity standard deviation values in the urban inertial sublayer from observations in the roughness sublayer  

NASA Astrophysics Data System (ADS)

The atmospheric turbulence in the surface layer over urban and suburban areas is affected by the presence of roughness elements. The roughness sublayer (RSL) extends from the ground up to about two to five times the mean building height of the area. Within RSL, turbulence is inhomogeneous and heat and momentum turbulent fluxes are not constant with height, therefore the Monin-Obukhov Similarity Theory (MOST) is not suitable and the surface-layer parameters (friction velocity, stability parameter) are not well defined. Instead, in the inertial sublayer (ISL) above the RSL, the turbulent fluxes are constant and the MOST is still considered valid. In air pollution models, observed surface-layer parameters available from data collected at urban or suburban stations might be used as inputs. Therefore, often RSL values are used in the parameterizations of the turbulence variables, such as the wind velocity standard deviations, as they were representative of the ISL, possibly leading to a not appropriate application of the MOST. We investigate whether it is possible to derive suitable values of the wind velocity standard deviations in the ISL using RLS observed parameters, through the analysis of a sonic anemometer dataset collected in a suburban site at three levels, two in the RSL and one in the ISL. The ISL wind velocity standard deviation are evaluated as similarity-like analytical functions of the RSL friction velocity and stability parameter. The RSL surface parameters are found to be satisfying scaling parameters and the empirical coefficients in the analytical formulation are estimated from the experimental data. Then the new analytical functions for wind velocity standard deviation are tested and verified against data collected during experiments in both homogeneous and heterogeneous conditions. Such approach could be useful in air pollution modeling over urban/suburban areas when ISL data are not available.

Falabino, Simona; Trini Castelli, Silvia

2014-05-01

174

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

175

Wind Velocity and Convergence Measurements at the Boulder Atmospheric Observatory Using Path-Averaged Optical Wind Sensors  

Microsoft Academic Search

In a cooperative field study of the planetary boundary layer, three optical wind sensors were placed around a 300 m meteorological tower in a 450 m equilateral triangle 3-4 m above the terrain. It was found that the convergence measured by the three-sensor system correlates well with in situ measurements of vertical wind by anemometers located on the tower at

Mu-King Tsay; Ting-I. Wang; R. S. Lawrence; G. R. Ochs; R. B. Fritz

1980-01-01

176

Parametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil moisture for arid and semi-arid areas  

E-print Network

partition scheme (in which the wind energy is transfered to the erodible surface as a functionParametrization of the increase of the aeolian erosion threshold wind friction velocity due to soil-derived dust emission in semi-arid regions needs to account for the in¯uence of the soil moisture on the wind

Boyer, Edmond

177

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

178

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

179

A New Technique using Electron Velocity Data from the Four Cluster Spacecraft to Explore Magnetofluid Turbulence in the Solar Wind  

NASA Technical Reports Server (NTRS)

It is now possible in certain circumstances to use velocity moments computed from the Plasma Electron and Current Experiment (PEACE) on the four Cluster spacecraft to determine a number of turbulence properties of the solar wind, including direct measurements of the vorticity and compressibility. Assuming that the four spacecraft are not co-planar and that there is only a linear variation of the plasma variables across the volume defined by the four satellites, one can estimate the curl of the fluid velocity, i.e., the vorticity. From the vorticity it is possible to explore directly intermittent regions in the solar wind where dissipation is likely to be enhanced. In addition, one can estimate directly the Taylor microscale.

Goldstein, Melvyn L.; Gurgiolo, C.; Fazakerley, A.; Lahiff, A.

2008-01-01

180

Some techniques for reducing the tower shadow of the DOE/NASA mod-0 wind turbine tower. [wind tunnel tests to measure effects of tower structure on wind velocity  

NASA Technical Reports Server (NTRS)

Wind speed profile measurements to measure the effect of a wind turbine tower on the wind velocity are presented. Measurements were made in the wake of scale models of the tower and in the wake of certain full scale components to determine the magnitude of the speed reduction (tower shadow). Shadow abatement techniques tested on the towers included the removal of diagonals, replacement of diagonals and horizontals with round cross section members, installation of elliptical shapes on horizontal members, installation of airfoils on vertical members, and application of surface roughness to vertical members.

Burley, R. R.; Savino, J. M.; Wagner, L. H.; Diedrich, J. H.

1979-01-01

181

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

182

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

183

Wind tunnel measurements of adobe abrasion by blown sand: profile characteristics in relation to wind velocity and sand flux  

Microsoft Academic Search

Blown sand causes various damages, such as extensive abrasion to crops, structural wear of facilities and buildings, and abrasion of soil clods and clayey materials generating fine particulate matter. In this study, experiments conducted in a straight-line blowing wind tunnel confirmed field observations and provided useful information for understanding abrasion profiles created by sand drift. Abrasion rates of 20 adobe

Liu Lian-You; Gao Shang-Yu; Shi Pei-Jun; Li Xiao-Yan; Dong Zhi-Bao

2003-01-01

184

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

185

THE WET BONDING FORCES IN SOILS AND THEIR EFFECT ON THRESHOLD FRICTION VELOCITY OF WIND EROSION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind erosion is a widespread process in the arid and semi arid regions of the world with implications on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. Arid ...

186

THE WET BONDING FORCES IN SOILS AND THEIR EFFECT THRESHOLD FRICTION VELOCITY OF WIND EROSION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind erosion is a widespread process in the arid and semi arid regions of the world with implications on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. Arid ...

187

Threshold wind velocities for sand movement in the Mescalero Sands of southeastern New Mexico  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind erosion activity was studied at two Chihuahuan Desert sites, the Gnome site which was contaminated with radioactivity from a nuclear device in 1961 and Near Field, a reference site. Saltation activity was measured with piezoelectric sensors, and those data were used to calculate threshold wind...

188

Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage  

NASA Astrophysics Data System (ADS)

We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using the CRIRES spectrograph mounted on the 8 m UT 1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in He i ?10833 extending up to -1900 km s-1 across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s-1) in the ultraviolet resonance lines of Si iv ??1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si ii ??1527, 1533 and C ii ??1334, 1335, show absorption only up to -1200 km s-1, indicating that the absorption with velocities -1200 to -2100 km s-1 originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6 m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989-2009) also show high-velocity absorption in He i ?10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s-1 is present in the phase range 0.976 ? ? ? 1.023 of the spectroscopic cycle, but absent in spectra taken at ? ? 0.94 and ? ? 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of ? ~ 240°-270°. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40°-60°. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 381.D-0262, 282.D-5043, and 383.D-0240; with the Hubble Space Telescope Imaging Spectrograph (HST/STIS) under programs 9420 and 9973; and with the 1.6 m telescope of the OPD/LNA (Brazil).

Groh, J. H.; Nielsen, K. E.; Damineli, A.; Gull, T. R.; Madura, T. I.; Hillier, D. J.; Teodoro, M.; Driebe, T.; Weigelt, G.; Hartman, H.; Kerber, F.; Okazaki, A. T.; Owocki, S. P.; Millour, F.; Murakawa, K.; Kraus, S.; Hofmann, K.-H.; Schertl, D.

2010-07-01

189

Simplified equations for the rotational speed response to inflow velocity variation in fixed-pitch small wind turbines  

NASA Astrophysics Data System (ADS)

We propose simplified equations for the rotational speed response to inflow velocity variation in fixed-pitch small wind turbines. The present formulation is derived by introducing a series expansion for the torque coefficient at the constant tip-speed ratio. By focusing on the first- and second-order differential coefficients of the torque coefficient, we simplify the original differential equation. The governing equation based only on the first-order differential coefficient is found to be linear, whereas the second-order differential coefficient introduces nonlinearity. We compare the numerical solutions of the three governing equations for rotational speed in response to sinusoidal and normal-random variations of inflow velocity. The linear equation gives accurate solutions of amplitude and phase lag. Nonlinearity occurs in the mean value of rotational speed variation. We also simulate the rotational speed in response to a step input of inflow velocity using the conditions of two previous studies, and note that the form of this rotational speed response is a system of first-order time lag. We formulate the gain and time constant for this rotational speed response. The magnitude of the gain is approximately three when the wind turbine is operated at optimal tip-speed ratio. We discuss the physical meaning of the derived time constant.

Suzuki, H.; Hasegawa, Y.

2015-02-01

190

The Origin of Non-Maxwellian Solar Wind Electron Velocity Distribution Function: Connection to Nanoflares in the Solar Corona  

E-print Network

The formation of the observed core-halo feature in the solar wind electron velocity distribution function is a long-time puzzle. In this letter based on the current knowledge of nanoflares we show that the nanoflare-accelerated electron beams are likely to trigger a strong electron two-stream instability that generates kinetic Alfv\\'en wave and whistler wave turbulence, as we demonstrated in a previous paper. We further show that the core-halo feature produced during the origin of kinetic turbulence is likely to originate in the inner corona and can be preserved as the solar wind escapes to space along open field lines. We formulate a set of equations to describe the heating processes observed in the simulation and show that the core-halo temperature ratio of the solar wind is insensitive to the initial conditions in the corona and is related to the core-halo density ratio of the solar wind and to the quasi-saturation property of the two-stream instability at the time when the exponential decay ends. This rel...

Che, H

2014-01-01

191

High-velocity, multistage, nozzled, ion driven wind generator and method of operation of the same adaptable to mesoscale realization  

NASA Technical Reports Server (NTRS)

Gas flows of modest velocities are generated when an organized ion flux in an electric field initiates an ion-driven wind of neutral molecules. When a needle in ambient air is electrically charged to a potential sufficient to produce a corona discharge near its tip, such a gas flow can be utilized downstream of a ring-shaped or other permeable earthed electrode. In view of the potential practical applications of such devices, as they represent blowers with no moving parts, a methodology for increasing their flow velocities includes exploitation of the divergence of electric field lines, avoidance of regions of high curvature on the second electrode, control of atmospheric humidity, and the use of linear arrays of stages, terminating in a converging nozzle. The design becomes particularly advantageous when implemented in mesoscale domains.

Dunn-Rankin, Derek (Inventor); Rickard, Matthew J. A. (Inventor)

2011-01-01

192

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

193

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

194

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

195

Large-scale vertical motion calculations in the AVE IV Experiment. [of atmospheric wind velocity  

NASA Technical Reports Server (NTRS)

Using 3- and 6-h consecutive rawinsonde and surface data from NASA's AVE IV Experiment, synoptic-scale vertical motion calculations are made using an adiabatic technique and three variations of the kinematic technique. Both subjective and objective comparisons in space and time between the sign and magnitude of the computed vertical velocities and precipitation intensities are made. These comparisons are conducted to determine which method would consistently produce realistic magnitudes, patterns, and vertical profiles of vertical velocity essential to the diagnostic study of the relationship between severe convective storms and their environment in AVE IV. The kinematic method, adjusted to the adiabatic value at 100 mb, proved to produce the best overall vertical velocities.

Wilson, G. S.

1976-01-01

196

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

197

The microscopic state of the solar wind--links between composition, velocity distributions and waves  

SciTech Connect

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. Emphasis is placed on the connection of interplanetary kinetic-scale phenomena with their generating microscopic processes in the corona. The fast streams seem to consist of mesoscale pressure-balanced magnetic flux tubes, reminiscent of the supergranular or smaller structures building the open corona, from which copious Alfven waves emanate. The wind from the magnetically structured and active corona shows considerable abundance and ionization state variations. Some modelling attempts to explain the observed element fractionation are mentioned. The nonthermal particle features, such as proton-ion differential streaming, ion beams, temperature anisotropies, and skewed electron distributions associated with collisionless heat conduction, and the related wave-particle interactions are discussed.

Marsch, E. [Max-Planck-Institut fuer Aeronomie, D-37191 Katlenburg-Lindau (Germany)

1996-07-20

198

A Method for the Instantaneous Determination of the Velocity and Direction of the Wind  

NASA Technical Reports Server (NTRS)

The laboratory instruments, which we often constructed with makeshift means, gave encouraging results and showed that they could satisfactorily meet the required conditions. By limiting ourselves to the employment of hot wires of 0.05 mm (0.002 in.) diameter, we obtained instruments which faithfully followed all the wind fluctuations of over 0.1 second and even much more rapid variations without any very great error.

Huguenard, E; Magnan, A; Planiol, A

1924-01-01

199

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 = 0.73 to 13.2 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 3) was observed for the relatively insoluble N2O under a surfactant covered water surface. In contrast, the surfactant effect for CH3OH, the high solubility tracer, was significantly weaker.

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

2015-01-01

200

Estimations of the maximum tangential velocity V ?m in the vortex core region and also the mean rotational velocity V oi near the concave wall surface in the returned flow type cyclone dust collector  

NASA Astrophysics Data System (ADS)

There are many types of cyclone dust collectors for separating the fine solid and dust particles from gases in the various industries and also in the home used purposes. For estimating the power loss and the collection efficiency, one of the most important factors is the maximum tangential velocity V ?m in the vortex core region in the cyclone body. In order to determine V ?m by the simple method, it is useful to apply the mechanical balance of the angular momentum fluxes under the assumption of Ogawa combined vortex model which is composed of the quasi-forced vortex in the vortex core region and also the quasi-free vortex surrounded the vortex core region and also under the assumption of the introduction of equivalent length Heq corresponding to the cone spaces of the cyclone body and the dust bunker. On the other hand, the mean rotational velocity V oi near the concave wall surface is also estimated by the mechanical balance of angular momentum fluxes with the moment of viscous friction force. For confirming the general applications of the obtained equations, the returned flow types cyclones changed the throat diameter D3 are designed. The material of the cyclone is the transparent acrylic resin. Therefore the inner surface of the cyclone body can be regarded as smooth surface. The comparisons of the measured velocities V ?m and V oi by a cylindrical Pitot tube are shown in good agreement with those of the proposed equations. The above stated results are described in detail.

Ogawa, Akira

2010-12-01

201

(abstract) Interplanetary Lyman-alpha Observations with the Galileo Ultraviolet Spectrometer: Solar Wind Latitude Variations and Multiple Scattering at Solar Maximum  

NASA Technical Reports Server (NTRS)

The Galileo Ultraviolet Spectrometer obtained a Lyman-alpha celestrial sphere map on 13,14 December 1990 near the first Earth encounter, with spacecraft near the interstellar wind downwind axis. The data show solar flux longitudinal and latitudinal asymmetries which are modeled with He 10830 Ssolar images. The difference between the observed brightness and a single scattering model is attributed to multiple scattering effects, which we also calculate. The data constrain the solar wind flux latitude variation at solar maximum. Other 1990-1992 Galileo Lyman-alpha data will be discussed.

Ajello, J. M.; Prior, W. R.; Barth, C. A.; Hord, C. W.; Simmons, K. E.; Hall, D. T.; White, O. R.

1993-01-01

202

Laser-Doppler system for local velocity measurement in wind tunnels - System design and experimental verification  

Microsoft Academic Search

The present report describes a laser-Doppler system designed for flow investigations carried out at distances of several meters. The optics described are designed for a maximum distance of 4.5 m. The system is operated using light scattered back from the natural particles in the flow so no additional flow seeding is required. The achievable signal amplitudes are calculated and it

F. Durst; F. Ernst; J. Voelklein

1987-01-01

203

Selection of dune shapes and velocities Part 1: Dynamics of sand, wind and barchans  

Microsoft Academic Search

:   Almost fifty years of investigations of barchan dunes morphology and dynamics is reviewed, with emphasis on the physical understanding\\u000a of these objects. The characteristic quantities measured on the field (shape, size, velocity) and the physical problems they\\u000a rise are presented. Then, we review the dynamical mechanisms explaining the formation and the propagation of dunes. In particular\\u000a a complete and

Bruno Andreotti; Philippe Claudin; Stéphane Douady

2002-01-01

204

Velocity profile similarity for viscous flow development along a longitudinally slotted wind-tunnel wall  

NASA Technical Reports Server (NTRS)

A discussion of the flow field measurements on the slot centerline of two different longitudinally slotted wind-tunnel walls is presented. The longitudinal and transverse components of these data are then transformed using the concept of flow similarity to demonstrate the applicability of the technique to the development of the viscous shear flow along and through a slotted wall. Results are presented showing the performance of the similarity transformations with variations in tunnel station, Mach number, and airfoil-induced curvature of the tunnel free stream.

Everhart, Joel L.; Goradia, Suresh H.

1988-01-01

205

Autonomous BDFIG-wind generator with torque and pitch control for maximum efficiency in a water pumping system  

Microsoft Academic Search

This paper presents and analyzes the operation strategy for an autonomous wind energy conversion system oriented to water pumping. It consists of a wind turbine with a Brushless Doubly-Fed Induction Generator (BDFIG), electrically coupled with a squirrel cage induction machine moving a centrifugal type water pump. Because of no brushes and slip rings, the BDFIG is suitable for autonomous systems,

P. Camocardi; P. Battaiotto; R. Mantz

2010-01-01

206

An atlas of monthly mean distributions of SSMI surface wind speed, AVHRR/2 sea surface temperature, AMI surface wind velocity, TOPEX/POSEIDON sea surface height, and ECMWF surface wind velocity during 1993  

NASA Technical Reports Server (NTRS)

The following monthly mean global distributions for 1993 are presented with a common color scale and geographical map: 10-m height wind speed estimated from the Special Sensor Microwave Imager (SSMI) on a United States (U.S.) Air Force Defense Meteorological Satellite Program (DMSP) spacecraft; sea surface temperature estimated from the Advanced Very High Resolution Radiometer (AVHRR/2) on a U.S. National Oceanic and Atmospheric Administration (NOAA) satellite; 10-m height wind speed and direction estimated from the Active Microwave Instrument (AMI) on the European Space Agency (ESA) European Remote Sensing (ERS-1) satellite; sea surface height estimated from the joint U.S.-France Topography Experiment (TOPEX)/POSEIDON spacecraft; and 10-m height wind speed and direction produced by the European Center for Medium-Range Weather Forecasting (ECMWF). Charts of annual mean, monthly mean, and sampling distributions are displayed.

Halpern, D.; Fu, L.; Knauss, W.; Pihos, G.; Brown, O.; Freilich, M.; Wentz, F.

1995-01-01

207

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

208

Traveling solar-wind bulk-velocity fluctuations and their effects on electron heating in the inner heliosphere  

E-print Network

Ambient plasma electrons undergo strong heating in regions associated with compressive traveling interplanetary solar-wind bulk-velocity jumps due to their specific interactions with the jump-inherent electric fields. After thermalization of this energy gain per shock passage through the operation of the Buneman instability, strong electron heating occurs that substantially influences the radial electron temperature profile. We describe the reduction of the jump amplitude due to energy expended by the traveling jump structure. We consider three effects; namely energy loss due to heating of electrons, energy loss due to work done against the pick-up-ion pressure gradient, and an energy gain due to nonlinear jump steepening. Taking these effects into account, we show that the decrease in jump amplitude with solar distance is more pronounced when the initial jump amplitude is higher in the inner solar system. Independent of the initial jump amplitude, it eventually decreases with increasing distance to a value o...

Fahr, Hans J; Verscharen, Daniel

2014-01-01

209

Pitch angle and velocity diffusions of newborn ions by turbulence in the solar wind  

NASA Technical Reports Server (NTRS)

The temporal evolution of the distribution function of newborn ions under the influence of intrinsic low-frequency solar wind turbulences is studied. In particular, an initial ring-beam distribution of newborn ions under the influence of hydromagnetic waves is considered. A simplified treatment of the resonance broadening effect is given, and its role in the pickup process is discussed. Two different configurations of wave polarization amd direction of propagation are considered. The conditions that lead either to the formation of anisotropic shells as a long-duration transient state or to rapid isotropization of the ion pitch angle distribution are discussed, as are the conditions which lead to significant acceleration of the ions.

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

1990-01-01

210

Estimation of neutral wind velocity in the ionospheric heights by HF-Doppler technique  

NASA Technical Reports Server (NTRS)

Three net stations located about 100 kilometers apart were set up around the station of the standard frequency and time signals (JJY) in central Japan and measurements of atmospheric gravity waves in the ionospheric heights (F-region, 200 to 400 km) were made by means of the HF-Doppler technique during the period of February 1983 to December 1983. The frequencies of the signals received are 5.0, 8.0 and 10.0 MHz, but only the 8.0 MHz signals are used for the present study, because no ambiguities due to the interference among other stations such as BPM, BSF, etc. exist by the use of 8.0 MHz. Two main results concerning the horizontal phase velocity of the atmospheric gravity waves with periods of 40 to 70 min may be summarized as follows: (1) the value of the phase velocity ranges from 50 m/s to 300 m/s; (2) the direction of the gravity wave propagation shows a definite seasonal variation. The prevailing direction of the gravity waves in winter is from north to south, which is consistent with the results obtained from other investigations. On the other hand, the two directions, from northeast to southwest and from southeast to northeast, dominate in summer.

Kitamura, T.; Takefu, M.; Hiroshige, N.

1985-01-01

211

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

212

Constraining Variable High Velocity Winds from Broad Absorption Line Quasars with Multi-Epoch Spectroscopy  

NASA Astrophysics Data System (ADS)

Broad absorption line (BAL) quasars probe the high-velocity gas ejected by luminous accreting black holes. BAL variability timescales place constraints on the size, location, and dynamics of the emitting and absorbing gas near the supermassive black hole. We present multi-epoch spectroscopy of seventeen BAL QSOs from the Sloan Digital Sky Survey (SDSS) using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST Spectrograph. These objects were identified as BALs in SDSS, observed with Chandra, and then monitored with FAST at observed-frame cadences of 1, 3, 9, 27, and 81 days, as well as 1 and 2 years. We also monitor a set of non-BAL quasars with matched redshift and luminosity as controls. We identify significant variability in the BALs, particularly at the 1 and 2 year cadences, and use its magnitude and frequency to constrain the outflows impacting the broad absorption line region.

Haggard, D.; Arraki, K. S.; Green, P. J.; Aldcroft, T.; Anderson, S. F.

2012-08-01

213

Variable Speed Wind Power Generation System Using Direct Torque Control Suited for Maximum Power Control within Voltage and Current Limitations of Converter  

NASA Astrophysics Data System (ADS)

This paper proposes a variable speed wind generation system using a direct torque controlled interior permanent magnet synchronous generator. The proposed system has no wind speed and generator position sensors, and thus, it is considered that the proposed system has cost and reliability advantages. The proposed direct torque control (DTC) system in wind power generation has several advantages over conventional current control. First, DTC is well suited for the maximum power point tracking (MPPT) control that is implemented by controlling the generator torque. Second, the method of flux-weakening to maintain the terminal voltage at the limiting value of the converter is simple. Finally, a novel method is proposed for torque limiting, which makes it easy to maintain the armature current at the limiting value. The proposed method accomplishes current limiting using the reactive torque, which is calculated as the inner product of the flux and current. This does not require generator parameters such as magnet flux and inductances. Experimental results demonstrate the effectiveness of the proposed system using a wind turbine emulator instead of the actual wind turbine.

Inoue, Yukinori; Morimoto, Shigeo; Sanada, Masayuki

214

Traveling solar-wind bulk-velocity fluctuations and their effects on electron heating in the heliosphere  

NASA Astrophysics Data System (ADS)

Ambient plasma electrons undergo strong heating in regions associated with compressive bulk-velocity jumps ?U that travel through the interplanetary solar wind. The heating is generated by their specific interactions with the jump-inherent electric fields. After this energy gain is thermalized by the shock passage through the operation of the Buneman instability, strong electron heating occurs that substantially influences the radial electron temperature profile. We previously studied the resulting electron temperature assuming that the amplitude of the traveling velocity jump remains constant with increasing solar distance. Now we aim at a more consistent view, describing the change in jump amplitude with distance that is caused by the heated electrons. We describe the reduction of the jump amplitude as a result of the energy expended by the traveling jump structure. We consider three effects: energy loss due to heating of electrons, energy loss due to work done against the pressure gradient of the pick-up ions, and an energy gain due to nonlinear jump steepening. Taking these effects into account, we show that the decrease in jump amplitude with solar distance is more pronounced when the initial jump amplitude is higher in the inner solar system. Independent of the initial jump amplitude, it eventually decreases with increasing distance to a value of about ?U/U ? 0.1 at the position of the heliospheric termination shock, where ?U is the jump amplitude, and U is the average solar-wind bulk velocity.The electron temperature, on the other hand, is strongly correlated with the initial jump amplitude and leads to electron temperatures between 6000 K and 20 000 K at distances beyond 50 AU. We compare our results with in situ measurements of the electron-core temperature from the Ulysses spacecraft in the plane of the ecliptic for 1.5 AU ? r ? 5 AU, where r is the distance from the Sun. Our results agree very well with these observations, which corroborates our extrapolated predictions beyond r = 5 AU.

Fahr, Hans J.; Chashei, Igor V.; Verscharen, Daniel

2014-11-01

215

The effect of wind velocity, air temperature and humidity on NH 3 and SO 2 transfer into bean leaves ( phaseolus vulgaris L.)  

NASA Astrophysics Data System (ADS)

The influence of wind velocity, air temperature and vapour pressure deficit of the air (VPD) on NH 3 and SO 2 transfer into bean leaves ( Phaseolus vulgaris L.) was examined using a leaf chamber. The measurements suggested a transition in the properties of the leaf boundary layer at a wind velocity of 0.3-0.4 ms -1 which corresponds to a Recrit value of about 2000. At higher wind velocities the leaf boundary layer resistance ( rb) was 1.5-2 times lower than can be calculated from the theory. Nevertheless, the assessed relationships between rb and wind velocity appeared to be similar to the theoretical derived relationship for rb. The NH 3 flux and in particular the SO 2 flux into the leaf strongly increased at a VPD decline. The increase of the NH 3 flux could be attributed to an increase of the stomatal conductance ( gs). However, the increase of the SO 2 flux could only partly be explained by an increase of gs. An apparent additional uptake was also observed for the NH 3 uptake at a low temperature and VPD. The SO 2 flux was also influenced by air temperature which could be explained by a temperature effect on gs. The results suggest that calculation of the NH 3 and SO 2 flux using data of gs gives a serious understimation of the real flux of these gases into leaves at a low temperature and VPD.

van Hove, L. W. A.; Vredenberg, W. J.; Adema, E. H.

216

Simulation comparison of a decoupled longitudinal control system and a velocity vector control wheel steering system during landings in wind shear  

NASA Technical Reports Server (NTRS)

A simulator comparison of the velocity vector control wheel steering (VCWS) system and a decoupled longitudinal control system is presented. The piloting task was to use the electronic attitude direction indicator (EADI) to capture and maintain a 3 degree glide slope in the presence of wind shear and to complete the landing using the perspective runway included on the EADI. The decoupled control system used constant prefilter and feedback gains to provide steady state decoupling of flight path angle, pitch angle, and forward velocity. The decoupled control system improved the pilots' ability to control airspeed and flight path angle during the final stages of an approach made in severe wind shear. The system also improved their ability to complete safe landings. The pilots preferred the decoupled control system in severe winds and, on a pilot rating scale, rated the approach and landing task with the decoupled control system as much as 3 to 4 increments better than use of the VCWS system.

Kimball, G., Jr.

1980-01-01

217

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

218

Monte Carlo studies of ocean wind vector measurements by SCATT: Objective criteria and maximum likelihood estimates for removal of aliases, and effects of cell size on accuracy of vector winds  

NASA Technical Reports Server (NTRS)

The scatterometer on the National Oceanic Satellite System (NOSS) is studied by means of Monte Carlo techniques so as to determine the effect of two additional antennas for alias (or ambiguity) removal by means of an objective criteria technique and a normalized maximum likelihood estimator. Cells nominally 10 km by 10 km, 10 km by 50 km, and 50 km by 50 km are simulated for winds of 4, 8, 12 and 24 m/s and incidence angles of 29, 39, 47, and 53.5 deg for 15 deg changes in direction. The normalized maximum likelihood estimate (MLE) is correct a large part of the time, but the objective criterion technique is recommended as a reserve, and more quickly computed, procedure. Both methods for alias removal depend on the differences in the present model function at upwind and downwind. For 10 km by 10 km cells, it is found that the MLE method introduces a correlation between wind speed errors and aspect angle (wind direction) errors that can be as high as 0.8 or 0.9 and that the wind direction errors are unacceptably large, compared to those obtained for the SASS for similar assumptions.

Pierson, W. J.

1982-01-01

219

The record of temperature, wind velocity and air humidity in the ? D and ? 18O of water inclusions in synthetic and Messinian halites  

NASA Astrophysics Data System (ADS)

Deuterium and oxygen isotope fractionations between liquid and vapor water were experimentally-determined during evaporation of a NaCl solution (35 g L -1) as a function of water temperature and wind velocity. In the case of a null wind velocity, slopes of ? D-? 18O trajectories of residual waters hyperbolically decrease with increasing water temperatures in the range 23-47 °C. For wind velocities ranging from 0.8 to 2.2 m s -1, slopes of the ? D-? 18O trajectories linearly increase with increasing wind velocity at a given water temperature. These experimental results can be modeled by using Rayleigh distillation equations taking into account wind-related kinetics effects. Deuterium and oxygen isotope compositions of water inclusions trapped by the precipitated halite crystals were determined by micro-equilibration techniques. These isotopic compositions accurately reflect those of the surrounding residual waters during halite growth. Isotopic compositions of water inclusions in twenty natural halites from the Messinian Realmonte mine in Sicily suggest precipitation temperatures of 34-4+10°C that match the homogenization temperatures obtained by microthermometry (median = 34 ± 5 °C). The similarity between the measured and experimental slopes of the ? D-? 18O evaporation trajectories suggests that the effect of wind was negligible during the genesis of these halite deposits. Hydrogen and oxygen isotope compositions of water inclusions from Realmonte halite also define a linear trend whose extrapolation until intersection with the Mediterranean Meteoric Water Line allows the characterization of the water source with ? D and ? 18O values of -70 ± 10‰ and -11.5 ± 1.5‰, respectively. These results reveal that the huge amounts of salts deposited in Sicily result from the evaporation of seawater mixed with a dominant fraction (?50%) of meteoric waters most likely deriving from alpine fluvial discharge.

Rigaudier, Thomas; Lécuyer, Christophe; Gardien, Véronique; Suc, Jean-Pierre; Martineau, François

2011-08-01

220

A Study of the Coronal Non-thermal Velocity in Polar Regions During the Rise from Solar Minimum to Solar Maximum in Cycle 24  

NASA Astrophysics Data System (ADS)

We explore the changes in coronal non-thermal velocity (V nt) measurements at the poles from solar minimum to solar maximum using Hinode EUV Imaging Spectrometer data. We find that although the intensity in the corona at the poles does tend to increase with the cycle, there are no significant changes in the V nt values. The locations of enhanced V nt values measured do not always have a counterpart in intensity, and they are sometimes located in weak emission regions. Unipolar magnetic streams, created through diffusion of the following polarity of the decaying active regions, slowly progress towards the poles. These streams are expected to be related to magnetic nulls as locations that indicate an increased likelihood for magnetic reconnection to occur. Through global potential field source-surface modelling, we determine how the number of nulls varied during the cycle and find that those that lie at < 1.1 solar radii vary significantly. We search for a correlation between the variation of the magnetic nulls and the V nt values, as it may be expected that with an increasing number of nulls, the V nt values in the corona increase as well. There is no correlation with the V nt values, however. This indicates that the magnetic structures that create the enhanced V nt behaviour are small-scale features and hence not easily measurable at the poles. Because they do not change during the solar cycle, they are likely to be created by a local dynamo. The variation of the upper range of V nt is reduced, which highlights that strongly dynamic behaviour is reduced as the solar maximum approaches. This is likely to be due to the reduced area of the polar coronal hole, which allows fewer opportunities for reconnection to occur between open and closed magnetic fields.

Harra, L.; Baker, D.; Edwards, S. J.; Hara, H.; Howe, R.; van Driel-Gesztelyi, L.

2015-01-01

221

Crustal seismicity and the earthquake catalog maximum moment magnitudes (Mcmax) in stable continental regions (SCRs): correlation with the seismic velocity of the lithosphere  

USGS Publications Warehouse

A joint analysis of global seismicity and seismic tomography indicates that the seismic potential of continental intraplate regions is correlated with the seismic properties of the lithosphere. Archean and Early Proterozoic cratons with cold, stable continental lithospheric roots have fewer crustal earthquakes and a lower maximum earthquake catalog moment magnitude (Mcmax). The geographic distribution of thick lithospheric roots is inferred from the global seismic model S40RTS that displays shear-velocity perturbations (?VS) relative to the Preliminary Reference Earth Model (PREM). We compare ?VS at a depth of 175 km with the locations and moment magnitudes (Mw) of intraplate earthquakes in the crust (Schulte and Mooney, 2005). Many intraplate earthquakes concentrate around the pronounced lateral gradients in lithospheric thickness that surround the cratons and few earthquakes occur within cratonic interiors. Globally, 27% of stable continental lithosphere is underlain by ?VS?3.0%, yet only 6.5% of crustal earthquakes with Mw>4.5 occur above these regions with thick lithosphere. No earthquakes in our catalog with Mw>6 have occurred above mantle lithosphere with ?VS>3.5%, although such lithosphere comprises 19% of stable continental regions. Thus, for cratonic interiors with seismically determined thick lithosphere (1) there is a significant decrease in the number of crustal earthquakes, and (2) the maximum moment magnitude found in the earthquake catalog is Mcmax=6.0. We attribute these observations to higher lithospheric strength beneath cratonic interiors due to lower temperatures and dehydration in both the lower crust and the highly depleted lithospheric root.

Mooney, Walter D.; Ritsema, Jeroen; Hwang, Yong Keun

2012-01-01

222

Wind  

NSDL National Science Digital Library

What part does the wind play in satisfying energy demands? This informational piece, part of a series about the future of energy, introduces students to wind as an energy source. Here students read about the history, uses, and efficiency of wind power. Information is also provided about benefits, limitations, and geographical considerations of wind power in the United States. Thought-provoking questions afford students chances to reflect on what they've read about the uses of wind power. Supplemental articles and information are available from a sidebar. Three energy-related web links are also provided. Copyright 2005 Eisenhower National Clearinghouse

Iowa Public Television. Explore More Project

2004-01-01

223

Solar-wind velocity measurements from near-Sun comets C/2011 W3 (Lovejoy), C/2011 L4 (Pan-STARRS), and C/2012 S1 (ISON)  

NASA Astrophysics Data System (ADS)

Since the mid-20th century, comets' plasma (type I) tails have been studied as natural probes of the solar wind [1]. Comets have induced magnetotails, formed through the draping of the heliospheric magnetic field by the velocity shear in the mass-loaded solar wind. These can be easily observed remotely as the comets' plasma tails, which generally point away from the Sun. Local solar-wind conditions directly influence 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. Over 50 % of observed catalogued comets are sungrazing comets [2], fragments of three different parent comets. Since 2011, two bright new comets, C/2011 W3 [3] (from hereon comet Lovejoy) and C/2012 S1 [4] (hereon comet ISON) have experienced extreme solar-wind conditions and insolation of their nucleus during their perihelion passages, approaching to within 8.3×10^5 km (1.19 solar radii) and 1.9×10^6 km (2.79 solar radii) of the solar centre. They each displayed a prominent plasma tail, proving to be exceptions amongst the observed group of sungrazing comets. These bright sungrazers provide unprecedented access to study the solar wind in the heretofore unprobed innermost region of the solar corona. The closest spacecraft in-situ sampling of the solar wind by the Helios probes reached 0.29 au. For this study, we define a sungrazing comet as one with its perihelion within the solar Roche limit (3.70 solar radii). We also extend this study to include C/2011 L4 [5] (comet Pan-STARRS), a comet with a much further perihelion distance of 0.302 au. The technique employed in this study was first established by analysing geocentric amateur observations of comets C/2001 Q4 (NEAT) and C/2004 Q2 (Machholz) [7]. These amateur images, obtained with modern equipment and sensors, rival and sometimes arguably exceed the quality of 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 [Ramanjooloo et al., in preparation] 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 comets Lovejoy from the 14th -- 19th December 2011, comet Pan-STARRS during 11th -- 16th March 2013 and comet ISON from 12th -- 29th November 2013. Observations were gathered from multiple resources, from the SECCHI heliospheric imagers aboard STEREO A and B [8], the LASCO coronagraphs aboard SOHO [9], as well as ground-based amateur and professional observations coordinated by the CIOC. Overlapping observation sessions from the three spacecraft and ground-based efforts provided the perfect opportunity to use these comets as a diagnostic tool to understand solar-wind variability close to the Sun. We plan to compare our observations to results of suitable simulations [10] of plasma conditions in the corona and inner heliosphere during each of the comets' 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 difficult-to-determine non-radial components of the measured solar-wind velocities.

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

2014-07-01

224

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

225

Comparison of wind velocity in thunderstorms determined from measurements by a ground-based Doppler radar and an F-106B airplane  

NASA Technical Reports Server (NTRS)

As a part of the NASA Storm Hazards Program, the wind velocity in several thunderstorms was measured by an F-106B instrumented airplane and a ground-based Doppler radar. The results of five airplane penetrations of two storms in 1980 and six penetrations of one storm in 1981 are given. Comparisons were made between the radial wind velocity components measured by the radar and the airplane. The correlation coefficients for the 1980 data and part of the 1981 data were 0.88 and 0.78, respectively. It is suggested that larger values for these coefficients may be obtained by improving the experimental technique and in particular by slaving the radar to track the airplane during such tests.

Usry, J. W.; Dunham, R. E., Jr.; Lee, J. T.

1985-01-01

226

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

227

Solar Wind Halo Formation by the Scattering of the Strahl via Direct Cluster/PEACE Observations of the 3D Velocity Distribution Function  

NASA Technical Reports Server (NTRS)

It has been suggested by a number of authors that the solar wind electron halo can be formed by the scattering of the strahl. On frequent occasions we have observed in electron angular skymaps (Phi/Theta-plots) of the electron 3D velocity distribution functions) a bursty-filament of particles connecting the strahl to the solar wind core-halo. These are seen over a very limited energy range. When the magnetic field is well off the nominal solar wind flow direction such filaments are inconsistent with any local forces and are probably the result of strong scattering. Furthermore, observations indicates that the strahl component is frequently and significantly anisotropic (Tper/Tpal approx.2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism. The empirical observational evidence between the halo and the strahl suggests that the strahl population may be, at least in part, the source of the halo component.

Figueroa-Vinas, Adolfo; Gurgiolo, Chris A.; Nieves-Chinchilla, Teresa; Goldstein, Melvyn L.

2010-01-01

228

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

229

RETRACTED: The influence of sand diameter and wind velocity on sand particle lift-off and incident angles in the windblown sand flux  

NASA Astrophysics Data System (ADS)

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy) This article has been retracted at the request of This article has been retracted at the request of the Editors-in-Chief. This article also contains significant similarity with parts of text, written by the same author(s), that have appeared in Tian-Li Bo, Xiao-Jing Zheng, Shao-Zhen Duan, Yi-Rui Liang, The influence of wind velocity and sand grain diameter on the falling velocities of sand particles, Powder Technology, Volume 241, June 2013, Pages 158-165. Tian-Li Bo, Xiao-Jing Zheng, Shao-Zhen Duan, Yi-Rui Liang, Analysis of sand particles' lift-off and incident velocities in wind-blown sand flux, Acta Mechanica Sinica, April 2013, Volume 29, Issue 2, pp 158-165. Tian-Li Bo, Xiao-Jing Zheng, Shao-Zhen Duan, Yi-Rui Liang, Influence of sand grain diameter and wind velocity on lift-off velocities of sand particles, The European Physical Journal E, May 2013, 36:50. Tian-Li Bo, Shao-Zhen Duan, Xiao-Jing Zheng, Yi-Rui Liang, The influence of sand bed temperature on lift-off and falling parameters in windblown sand flux, Geomorphology, Volume 204, 1 January 2014, Pages 477-484. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Bo, Tian-Li; Zheng, Xiao-Jing; Duan, Shao-Zhen; Liang, Yi-Rui

2013-05-01

230

ON THE EFFECT OF MOISTURE BONDING FORCES IN AIR-DRY SOILS ON THRESHOLD FRICTION VELOCITY OF WIND EROSION  

Technology Transfer Automated Retrieval System (TEKTRAN)

Wind erosion is a dominant geomorphological process in arid and semi-arid regions with major impacts on regional climate and desertification. The erosion process occurs when the wind speed exceeds a certain threshold value, which depends on a number of factors including surface soil moisture. The un...

231

Orientation cues for high-flying nocturnal insect migrants: do turbulence-induced temperature and velocity fluctuations indicate the mean wind flow?  

PubMed

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 given time. There are increasing indications that high-altitude orientation may be maintained by some intrinsic property of the wind rather than by visual perception of relative ground movement. Therefore, we first examined whether migrating insects could deduce the mean wind direction from the turbulent fluctuations in temperature. Within the atmospheric boundary-layer, temperature records show characteristic ramp-cliff structures, and insects flying downwind would move through these ramps whilst those flying crosswind would not. However, analysis of vertical-looking radar data on the common orientations of nocturnally migrating insects in the UK produced no evidence that the migrants actually use temperature ramps as orientation cues. This suggests that insects rely on turbulent velocity and acceleration cues, and refocuses attention on how these can be detected, especially as small-scale turbulence is usually held to be directionally invariant (isotropic). In the second part of the paper we present a theoretical analysis and simulations showing that velocity fluctuations and accelerations felt by an insect are predicted to be anisotropic even when the small-scale turbulence (measured at a fixed point or along the trajectory of a fluid-particle) is isotropic. Our results thus provide further evidence that insects do indeed use turbulent velocity and acceleration cues as indicators of the mean wind direction. PMID:21209956

Reynolds, Andy M; Reynolds, Don R; Smith, Alan D; Chapman, Jason W

2010-01-01

232

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

233

Inverse maximum gross bedform-normal transport 1: How to determine a dune-constructing wind regime using only imagery  

NASA Astrophysics Data System (ADS)

It has been a goal of aeolian science to use bedforms as indicators of local and regional sediment transport and atmospheric circulation, but even with the application of the rule of maximum gross-bedform normal transport (MGBNT), the underdetermined nature of the problem has precluded its application in all but the most simple cases. We present a method to apply the rule of MGBNT and its inverse (IMGBNT) from analysis of aeolian dune crestlines derived from aerial imagery. Although the solutions to IMGBNT analysis are non-unique, the possible transport vectors influencing bedform morphology can often be constrained by making inferences regarding bedform type (e.g., transverse, oblique, or longitudinal), resultant drift direction, and the ratio of transport vector magnitudes. The technique is demonstrated on the Great Sand Dunes, located in Colorado, USA. This dune field has a wide array of dune morphologies; eight crestline sets were identified and mapped. IMGBNT analysis and the subsequent constraint of possible solutions suggests that transport vectors from the southeast and southwest, with a SE:SW transport ratio of ˜1:2, produce oblique north-south oriented dunes that dominate the main dune field. These results compare favorably with MGBNT analysis of meteorologic measurements from three stations located adjacent to the Great Sand Dunes, which predict dune types and orientations similar to those observed in their vicinity.

Fenton, Lori K.; Michaels, Timothy I.; Beyer, Ross A.

2014-02-01

234

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. ...

235

Rocket-based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere  

NASA Astrophysics Data System (ADS)

The JOULE-II sounding rocket salvo was launched from Poker Flat Rocket Range into weak pulsating aurora following a moderate substorm at 0345 LT on 19 January 2007. We present in situ measurements of ion flow velocity and electric and magnetic fields combined with neutral wind observations derived from ground observations of in situ chemical tracers. Measured ion drifts in the 150-198 km and 92-105 km altitude ranges are consistent with ${\\vec{E} × ${\\vec{B} motion to within 16 m s-1 rms and with neutral wind velocity to within 20 m s-1, respectively. From these measurements we have calculated the ratio $\\kappa$ of the ion cyclotron and ion collision frequencies, finding $\\kappa$ = 1 at an altitude of 118 ± 0.3 km. Using direct measurements of ion current, we calculate the Joule heating rate and Pedersen and Hall conductivity profiles for this moderately active event and find height-integrated values of 390 W km-2 and 0.59 and 2.22 S, respectively. We also find that these values would have errors of up to tens of percent without coincident neutral wind measurements, and presumably more so during more active conditions. Ion flow vectors were measured at a rate of 125 s-1 however, no significant fluctuations were observed at spatial/temporal scales below ˜350 m and 0.5 s. Observational limits were 5.5 m and 0.016 s.

Sangalli, L.; Knudsen, D. J.; Larsen, M. F.; Zhan, T.; Pfaff, R. F.; Rowland, D.

2009-04-01

236

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

237

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

NASA Technical Reports Server (NTRS)

In Cram's theory for the formation of the K-coronal spectrum he observed the existence of temperature sensitive anti-nodes, which were separated by temperature insensitive nodes, at certain wave-lengths in the K-coronal spectrum. Cram also showed these properties were remarkably independent of altitude above the solar limb. 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 measurements 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 August 1999 in Elazig, Turkey. Here twenty fiber optic tips were positioned in the focal plane of the telescope to observe simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends were vertically stacked and placed at the primary focus of the spectrograph. By isolating the K-coronal spectrum from each fiber the temperature and the wind sensitive intensity ratios were calculated.

Reginald, Nelson L.

2000-01-01

238

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

239

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.

240

CHANGES IN RECORDED MAXIMUM WIND SPEED FREQUENCY AND DIRECTION RELATING TO THE 1980 CHANGE IN PITOT EXPOSURE AND THE MOVE TO THE NEW OBSERVATORY  

Microsoft Academic Search

Dave Glidden is a Field Specialist in Wind and Mountain Climatology, and has conducted wind studies for the National Park Service in Rocky Mountain National Park in Colorado. More recently, he has pursued field work on the variability of mountain winds and gust factors in Denali National Park in Alaska. A strong advocate of women in the sciences, he has

D. E. GLIDDEN

241

Empirical relation between induced velocity, thrust, and rate of descent of a helicopter rotor as determined by wind-tunnel tests on four model rotors  

NASA Technical Reports Server (NTRS)

The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests.

Castles, Walter, Jr.; Gray, Robin B.

1951-01-01

242

Empirical Relation Between Induced Velocity, Thrust, and Rate of Descent of a Helicopter Rotor as Determined by Wind-tunnel Tests on Four Model Rotors  

NASA Technical Reports Server (NTRS)

The empirical relation between the induced velocity, thrust, and rate of vertical descent of a helicopter rotor was calculated from wind tunnel force tests on four model rotors by the application of blade-element theory to the measured values of the thrust, torque, blade angle, and equivalent free-stream rate of descent. The model tests covered the useful range of C(sub t)/sigma(sub e) (where C(sub t) is the thrust coefficient and sigma(sub e) is the effective solidity) and the range of vertical descent from hovering to descent velocities slightly greater than those for autorotation. The three bladed models, each of which had an effective solidity of 0.05 and NACA 0015 blade airfoil sections, were as follows: (1) constant-chord, untwisted blades of 3-ft radius; (2) untwisted blades of 3-ft radius having a 3/1 taper; (3) constant-chord blades of 3-ft radius having a linear twist of 12 degrees (washout) from axis of rotation to tip; and (4) constant-chord, untwisted blades of 2-ft radius. Because of the incorporation of a correction for blade dynamic twist and the use of a method of measuring the approximate equivalent free-stream velocity, it is believed that the data obtained from this program are more applicable to free-flight calculations than the data from previous model tests.

Castles, Walter, Jr; Gray, Robin B

1951-01-01

243

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 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 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

244

Non-gyrotropic proton and alpha-particle velocity distributions in the solar wind: TAUS observations and stability analysis  

NASA Technical Reports Server (NTRS)

Ion velocity distribution functions have been measured with high time resolution by the TAUS plasma instrument on the PHOBOS mission to Mars in 1989. The unambiguous separation of protons and alpha-particles by TAUS enabled us to study the nonthermal features of their distributions separately and to analyze the stability of the distributions against excitation of waves in the cyclotron-frequency domain. Typical nonthermal features include temperature anisotropies, with T(sub perpendicular) larger than T(sub parallel), and ion beam populations drifting along the local magnetic field direction. Also, distinctly non-gyrotropic alpha-particle velocity distributions were sometimes found. Non-gyrotropy strongly changes the wave dispersion and gives rise to new growing modes, related to the coupling of the standard wave modes existing in gyrotropic plasma. It is found that for the measured non-gyrotropic ion distributions the right-hand polarized wave can also be excited by a temperature anistropy instead of the usual beam drift.

Astudillo, H. F.; Marsch, E.; Livi, S.; Rosenbauer, H.

1995-01-01

245

Non-axisymmetric wind-accretion simulations. I. Velocity gradients of 3% and 20% over one accretion radius.  

NASA Astrophysics Data System (ADS)

We investigate the hydrodynamics of a variant of classical Bondi-Hoyle-Lyttleton accretion: a totally absorbing sphere moves at various Mach numbers (3 and 10) relative to a medium, which is taken to be an ideal gas having a velocity gradient (of 3% or 20% over one accretion radius) perpendicular to the relative motion. We examine the influence of the Mach number of the flow and the strength of the gradient upon the physical behaviour of the flow and the accretion rates of the angular momentum in particular. The hydrodynamics is modeled by the "Piecewise Parabolic Method" (PPM). The resolution in the vicinity of the accretor is increased by multiply nesting several grids around the sphere. Similarly to the 3D models without gradients published previously, models exhibit non-stationary flow patterns, although the Mach cone remains fairly stable. The accretion rates of mass, linear and angular momenta do not fluctuate as strongly as published previously for 2D models, but similarly to the 2D models, transient disks form around the accretor that alternate their direction of rotation with time. The average specific angular momentum accreted is roughly between 7% and 70% of the total angular momentum available in the accretion cylinder and is always smaller than the value of a vortex with Kepler velocity around the surface of the accretor. The fluctuations of the mass accretion rate in the models with small gradients (2%) are similar to the values of the models without gradients, while the models with large gradients (20%) exhibit larger fluctuations. The mass accretion rate is maximal when the specific angular momentum is zero, while the specific entropy tends to be smaller when the disks are prograde.

Ruffert, M.

1997-02-01

246

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

247

The interaction effect of fast and slow solar wind streams in interplanetary space on wind characteristics at the earth's orbit  

NASA Astrophysics Data System (ADS)

Quantitative relationships that represent the role of the interaction of fast and slow solar wind (SW) streams in the formation of characteristic SW properties at the earth's orbit are determined from observational data. It is shown that maximum values of the magnetic field and density peaks in the neighborhood of the sector boundary (SB) at the base of the high-speed stream front are associated with solar wind characteristics such as the SW minimum velocity near the SB, the maximum velocity in the central part of the fast stream, and the slope of the magnetic field neutral line to the solar plane at 2.5 solar radii.

Fainshtein, V. G.

1991-11-01

248

Field evidence for the upwind velocity shift at the crest of low dunes  

E-print Network

Wind topographically forced by hills and sand dunes accelerates on the upwind (stoss) slopes and reduces on the downwind (lee) sides. This secondary wind regime, however, possesses a subtle effect, reported here for the first time from field measurements of near-surface wind velocity over a low dune: the wind velocity close to the surface reaches its maximum upwind of the crest. Our field-measured data show that this upwind phase shift of velocity with respect to topography is found to be in quantitative agreement with the prediction of hydrodynamical linear analysis for turbulent flows with first order closures. This effect, together with sand transport spatial relaxation, is at the origin of the dune instability mechanism.

Claudin, P; Andreotti, B

2012-01-01

249

Field evidence for the upwind velocity shift at the crest of low dunes  

E-print Network

Wind topographically forced by hills and sand dunes accelerates on the upwind (stoss) slopes and reduces on the downwind (lee) slopes. This secondary wind regime, however, possesses a subtle effect, reported here for the first time from field measurements of near-surface wind velocity over a low dune: the wind velocity close to the surface reaches its maximum upwind of the crest. Our field-measured data show that this upwind phase shift of velocity with respect to topography is found to be in quantitative agreement with the prediction of hydrodynamical linear analysis for turbulent flows with first order closures. This effect, together with sand transport spatial relaxation, is at the origin of the mechanisms of dune initiation, instability and growth.

P. Claudin; G. F. S. Wiggs; B. Andreotti

2012-05-20

250

Predicting species' maximum dispersal distances from simple plant traits.  

PubMed

Many studies have shown plant species' dispersal distances to be strongly related to life-history traits, but how well different traits can predict dispersal distances is not yet known. We used cross-validation techniques and a global data set (576 plant species) to measure the predictive power of simple plant traits to estimate species' maximum dispersal distances. Including dispersal syndrome (wind, animal, ant, ballistic, and no special syndrome), growth form (tree, shrub, herb), seed mass, seed release height, and terminal velocity in different combinations as explanatory variables we constructed models to explain variation in measured maximum dispersal distances and evaluated their power to predict maximum dispersal distances. Predictions are more accurate, but also limited to a particular set of species, if data on more specific traits, such as terminal velocity, are available. The best model (R2 = 0.60) included dispersal syndrome, growth form, and terminal velocity as fixed effects. Reasonable predictions of maximum dispersal distance (R2 = 0.53) are also possible when using only the simplest and most commonly measured traits; dispersal syndrome and growth form together with species taxonomy data. We provide a function (dispeRsal) to be run in the software package R. This enables researchers to estimate maximum dispersal distances with confidence intervals for plant species using measured traits as predictors. Easily obtainable trait data, such as dispersal syndrome (inferred from seed morphology) and growth form, enable predictions to be made for a large number of species. PMID:24669743

Tamme, Riin; Götzenberger, Lars; Zobel, Martin; Bullock, James M; Hooftman, Danny A P; Kaasik, Ants; Pärtel, Meelis

2014-02-01

251

Wind loads on flat plate photovoltaic array fields. Phase III, final report  

SciTech Connect

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.

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

1981-04-01

252

Extraordinarily High Electron Densities Observed in the Crest of the Post-sunset Equatorial Anomaly, Their Persistence with Solar Rotation and the Evidence of an Enhancement of Maximum Pre-reversal ExB Drift Velocity  

NASA Astrophysics Data System (ADS)

Extremely high F layer electron densities, possibly the highest ever recorded, were observed in the crests of latitudinal profiles of maximum electron density in the post sunset equatorial anomaly. A chain of ionospheric sounders located in western America recorded values of NmF2 of 6.9, 6.5 and >6.5 x106 el/cm3 on the 3 days, Feb 14, Mar 13 and Apr 11, 1958. These days were 27 and 29 days apart, so were nearly the same day in 3 successive Carrington solar rotations. The levels indicate extremely high levels of maximum pre-reversal ExB drift velocity (ExBmax) as does the fact that equatorial bubbles were observed on 2 of the days and a bubble was likely to have occurred on the third. However, conditions which are associated with high ExBmax, low Kp and high F10.7, were present, but not at levels that were unusual in relation to the other days in the period. Dst and daytime NmE are also ordinary on these days. Each of the 3 days lies in a period of IMF "away" and possibly near a sector boundary as indicated by high latitude magnetograms. Proximity to a boundary is also not unique to these 3 days, but the recurrence with solar rotation suggests that sector structure may play a role. In addition to the remarkable recurrence in solar rotation, the significance of these observations is that they indicate the presence of some not yet understood mechanism that enhances the eastward electric field, hence ExBmax. Its presence at other times could contribute to the largely unexplained variability of ExBmax, of equatorial bubbles and of the resulting scintillation, so that its understanding could lead to much improved forecasts.

Whalen, J. A.

2004-12-01

253

Calculation of wind speeds required to damage or destroy buildings  

NASA Astrophysics Data System (ADS)

Determination of wind speeds required to damage or destroy a building is important not only for the improvement of building design and construction but also for the estimation of wind speeds in tornadoes and other damaging storms. For instance, since 1973 the U.S. National Weather Service has been using the well-known Fujita scale (F scale) to estimate the maximum wind speeds of tornadoes [Fujita, 1981]. The F scale classifies tornadoes into 13 numbers, F-0 through F-12. The wind speed (maximum gust speed) associated with each F number is given in Table 1. Note that F-6 through F-12 are for wind speeds between 319 mi/hr (mph) and the sonic velocity (approximately 760 mph; 1 mph = 1.6 km/kr). However, since no tornadoes have been classified to exceed F-5, the F-6 through F-12 categories have no practical meaning [Fujita, 1981].

Liu, Henry

254

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

255

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

256

Wind-tunnel studies of wing wake turbulence.  

NASA Technical Reports Server (NTRS)

Description of velocity measurements made in the wake of wings in the Ames 7 x 10 ft wind tunnel. Distributions of velocity components were measured with a three-wire anemometer up to 12 chord lengths downstream of a CV-990 aircraft model and a rectangular wing. Results show that increasing the drag increases the vortex core radius, reduces the maximum tangential velocities, and increases the magnitude of axial velocity defects. For the rectangular wing, axial velocity changes from a defect (wake flow) for angles of attack less than 9 deg to an excess (jet flow) for angles of attack greater than 9 deg. Wind-tunnel measurements of the near flowfield are compared with flight measurements of the far flowfield.

Chigier, N. A.; Corsiglia, V. R.

1972-01-01

257

PULSED ALFVEN WAVES IN THE SOLAR WIND  

SciTech Connect

Using 3 s plasma and magnetic field data from the Wind spacecraft located in the solar wind well upstream from Earth, we report observations of isolated, pulse-like Alfvenic disturbances in the solar wind. These isolated events are characterized by roughly plane-polarized rotations in the solar wind magnetic field and velocity vectors away from the directions of the underlying field and velocity and then back again. They pass over Wind on timescales ranging from seconds to several minutes. These isolated, pulsed Alfven waves are pervasive; we have identified 175 such events over the full range of solar wind speeds (320-550 km s{sup -1}) observed in a randomly chosen 10 day interval. The large majority of these events are propagating away from the Sun in the solar wind rest frame. Maximum field rotations in the interval studied ranged from 6 Degree-Sign to 109 Degree-Sign . Similar to most Alfvenic fluctuations in the solar wind at 1 AU, the observed changes in velocity are typically less than that predicted for pure Alfven waves (Alfvenicity ranged from 0.28 to 0.93). Most of the events are associated with small enhancements or depressions in magnetic field strength and small changes in proton number density and/or temperature. The pulse-like and roughly symmetric nature of the magnetic field and velocity rotations in these events suggests that these Alfvenic disturbances are not evolving when observed. They thus appear to be, and probably are, solitary waves. It is presently uncertain how these waves originate, although they may evolve out of Alfvenic turbulence.

Gosling, J. T. [Laboratory for Atmospheric and Space Physics, University of Colorado, 1234 Innovation Drive, Boulder, CO 80303 (United States); Tian, H. [High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307 (United States); Phan, T. D., E-mail: jack.gosling@lasp.colorado.edu [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

2011-08-20

258

Observations of wind turbine wakes and surface roughness effects on wind flow variability  

SciTech Connect

Wind data collected at nine meteorological towers at the Goodnoe Hills MOD-2 wind turbine site were analyzed to characterize the wind flow over the site both in the absence and presence of wind turbine wakes. Free-flow characteristics examined were the variability of wind speed and turbulence intensity across the site as a function of wind direction and surface roughness. The nine towers' data revealed that scattered areas of trees upwind of the site caused pronounced variations in the wind flow over the site. Wind turbine wake characteristics analyzed included the average velocity deficits, wake turbulence, wake width, wake trajectory, vertical profile of the wake, and the stratification of wake properties as a function of the ambient wind speed and turbulence intensity. The wind turbine rotor disk spanned a height of 15 m to 107 m. The nine towers' data permitted a detailed analysis of the wake behavior at a height of 32 m at various downwind distances from 2 to 10 rotor diameters (D). The relationship between velocity deficit and downwind distance was surprisingly linear, with average maximum deficits ranging from 34% at 2 D to 7% at 10 D. Largest deficits were at low wind speeds and low turbulence intensities. Average wake widths were 2.8 D at a downwind distance of 10 D. Implications for turbine spacing are that, for a wind farm with a 10-D row separation, array losses would be significantly greater for a 2-D than a 3-D spacing because of incremental effects caused by overlapping wakes. Other interesting wake properties observed were the wake turbulence, the vertical variation of deficits, and the trajectory of the wake.

Elliott, D.L.; Barnard, J.C. (Pacific Northwest Lab., Richland, WA (USA))

1990-01-01

259

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

260

Fuzzy regulator design for wind turbine yaw control.  

PubMed

This paper proposes the development of an advanced fuzzy logic controller which aims to perform intelligent automatic control of the yaw movement of wind turbines. The specific fuzzy controller takes into account both the wind velocity and the acceptable yaw error correlation in order to achieve maximum performance efficacy. In this way, the proposed yaw control system is remarkably adaptive to the existing conditions. In this way, the wind turbine is enabled to retain its power output close to its nominal value and at the same time preserve its yaw system from pointless movement. Thorough simulation tests evaluate the proposed system effectiveness. PMID:24693237

Theodoropoulos, Stefanos; Kandris, Dionisis; Samarakou, Maria; Koulouras, Grigorios

2014-01-01

261

Dynamic Analysis of Wind Generators  

Microsoft Academic Search

Wind power does not make any pollution and it also create a recyclable energy. The wind blade speeds significantly affect the measured output power. It is necessary to keep the wind blade tip speed to obtain maximum power. The wind blade speeds significantly affect the energy losses and the power coefficients. It is required to keep the wind blade tip

Ming-Hung Hsu

2007-01-01

262

MAXIMUM OXYGEN CONSUMPTION DURING EXERCISE AND COLD EXPOSURE IN DEER MICE, PEROMYSCUS MANICULATUS  

Microsoft Academic Search

Convenient methods were developed for measuring maximum oxygen consumption(Vo2max ) in untrained small mammals during treadmill exercise and cold exposure. Deer mice (Peromyscus maniculatus) were run once, for 6-rain periods at velocities exceeding maximal aerobic running speed, while instantaneous oxygen consumption was measured. The ~'o2max during cold exposure was deter- mined using high wind speeds to increase heat loss rates.

MARK A. CHAPPELL

1984-01-01

263

Exteremely High Velocity Outflows  

E-print Network

Extremely high velocity (EHV) wings, with full widths of 72 to 140 km/s, are seen on the CO J=3-2 lines toward W3 IRS 5, GL 490, NGC 2071, W28 A2, GL 2591, S140, and Cepheus A. The results of our survey suggest that EHV wings are common around infrared sources of moderate to high luminosity (500 to 4x10^5 Lsun) in dense regions. Line ratios imply that the EHV gas is usually optically thin and warm. Characteristic velocities range from 20 to 40 km/s, yielding timescales of 1600-4200 yr. Since most sources in this study are producing some ionizing photons, these short timescales suggest that neutral winds coexist with ionizing photons. We examined two possible sources for the EHV CO emission: a neutral stellar wind; and swept-up or entrained molecular gas. Neither can be ruled out. If the high-velocity (HV) gas is swept up by a momentum-conserving stellar wind traced by the extremely high velocity CO emission, most of the C in the winds from luminous objects cannot be in CO. If the EHV and HV forces are equal, the fraction of C in a form other than CO increases with source luminosity and with the production rate of ionizing photons.

Minho Choi; Neal J. Evans II; Daniel T. Jaffe

1993-07-05

264

Wind speeds in two tornadic storms and a tornado, deduced from Doppler Spectra  

SciTech Connect

Doppler spectra of a tornado were collected with a radar having a large unambiguous velocity range, +- 91 m s/sup -1/. Thus for the first time a presentation of nonaliased spectra was possible, showing direct measurement of radial velocities. By fitting the tornado model spectrum to data, the radius of maximum winds and tornado center location are deduced. Tornado spectral signature is defined as a double peak, symmetric with respect to the mean wind spectrum. Histograms of maximum measured wind speeds (from spectrum skirts) for two tornadic storms are obtained, and the histograms of velocity difference (between the left and right spectrum skirt) suggest that smaller scale turbulence (<500 m) is principally responsible for spectrum broadness.

Zrnic, D.; Istok, M.

1980-12-01

265

Maximum Likelihood  

NSDL National Science Digital Library

This material introduces the basic theory of maximum likelihood estimation by discussing the likelihood function, the log likelihood function, and maximizing these functions using calculus. Several exercises ask students to derive certain estimators, while others have students compare the behavior of those estimators with other possibilities through the use of various JAVA applets. The applets use the same control features: the sliders set the parameter values, the Â?Stop #Â? drop down menu sets the number of samples taken, the Â?Update #Â? drop down menu sets how often the graph and tables update during the experiment, the single arrow takes one sample, the double arrow runs the full experiment, the square stops the experiment, and the back arrow resets the applet. This page is one lesson from the Virtual Laboratories in Statistics.

Siegrist, Kyle

266

Meridional Winds Derived from COSMIC Radio Occultation Measurements  

NASA Astrophysics Data System (ADS)

Meridional winds derived from F2 layer peak parameters (NmF2 and hmF2) measured by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) using the servo method, are compared at multiple locations with winds derived from incoherent scatter radar (ISR) and Fabry-Perot interferometer (FPI) measurements. The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (NCAR-TIEGCM) is then employed to simulate the longitudinal variations of meridional winds. Comparisons show that there is generally good agreement between COSMIC winds and ISR, FPI and TIEGCM winds, although COSMIC winds are more equatorward near sunset hours. The COSMIC winds show significant longitudinal variations at latitude 40N (local winter) and 40S (local summer). At 40N, the COSMIC winds exhibit distinct and long duration higher velocity near the midnight hours and during late morning hours within the longitude range 110W to 20W, near the negative declination sector. Similarly, at 40S, the winds are characterized by distinct larger velocity for poleward winds from sunrise to afternoon hours within the longitude range of 120°E to 110°W, near the positive declination sector. At 40°S, another notable feature for the nighttime maximum equatorward winds is seen: there is a local time shift by about 2h from longitude range of 60W to 90E within the negative declination sector to other longitudes within positive declination sector. The NCAR TIEGCM reproduces these longitudinal configurations well, except during the daytime at 40N, and there are some discrepancies in wind magnitude. Analysis of NCAR TIEGCM simulations suggests that the longitudinal variation of meridional winds is mainly controlled by the magnetic declination.

Luan, X.; Solomon, S. C.

2007-12-01

267

Maximum gravitational recoil.  

PubMed

Recent calculations of gravitational radiation recoil generated during black-hole binary mergers have reopened the possibility that a merged binary can be ejected even from the nucleus of a massive host galaxy. Here we report the first systematic study of gravitational recoil of equal-mass binaries with equal, but counteraligned, spins parallel to the orbital plane. Such an orientation of the spins is expected to maximize the recoil. We find that recoil velocity (which is perpendicular to the orbital plane) varies sinusoidally with the angle that the initial spin directions make with the initial linear momenta of each hole and scales up to a maximum of approximately 4000 km s-1 for maximally rotating holes. Our results show that the amplitude of the recoil velocity can depend sensitively on spin orientations of the black holes prior to merger. PMID:17677894

Campanelli, Manuela; Lousto, Carlos O; Zlochower, Yosef; Merritt, David

2007-06-01

268

Acoustic particle velocity horns.  

PubMed

The paper considers receiving acoustic horns designed for particle velocity amplification and suitable for use in vector sensing applications. Unlike conventional horns, designed for acoustic pressure amplification, acoustic velocity horns (AVHs) deliver significant velocity amplification even when the overall size of the horn is much less than an acoustic wavelength. An AVH requires an open-ended configuration, as compared to pressure horns which are terminated at the throat. The appropriate formulation, based on Webster's one-dimensional horn equation, is derived and analyzed for single conical and exponential horns as well as for double-horn configurations. Predicted horn amplification factors (ratio of mouth-to-throat radii) were verified using numerical modeling. It is shown that three independent geometrical parameters principally control a horn's performance: length l, throat radius R(1), and flare rate. Below a predicted resonance region, velocity amplification is practically independent of frequency. Acoustic velocity horns are naturally directional, providing maximum velocity amplification along the boresight. PMID:22559364

Donskoy, Dimitri M; Cray, Benjamin A

2012-05-01

269

Wind energy utilization prospects  

Microsoft Academic Search

The chief technical, economic, and environmental aspects of wind energy utilization are considered. One approach being studied is to allow the aeroturbine RPM to vary with wind velocity and employ variable-speed, constant-frequency generating systems to obtain constant-frequency power to be pumped into existing utility mains. Study of generation costs for wind energy systems indicates that wind energy has the potential

R. Ramakumar; W. L. Hughes; H. J. Allison

1975-01-01

270

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

271

On extraction of time-varying mean wind speed from wind record based on stationarity index  

NASA Astrophysics Data System (ADS)

We have proposed in a previous study a non-stationary wind model to represent the typhoon record as a summation of a time-varying mean wind speed (TVM) and a stationary turbulence. This note further suggests a quantitative scheme, rather than the previous qualitative method, to find the best TVM for any given wind record. Trial TVMs are first extracted from the wind record by a data-processing technique named empirical mode decomposition. For each TVM, its corresponding turbulent component is computed by removing the TVM from the original wind record, and the degree of stationarity of the turbulence component is checked. The best TVM is taken as the one that leads to the maximum degree of stationarity. The degree of stationarity of turbulence is quantified by two indicators: ? the ratio of horizontal wind variability and wind speed; and ? the ratio of friction velocity at different Reynolds averaging periods. The applicability of the suggested scheme is validated with 550 typhoon and 3300 monsoon records of 10 minute duration and at different measurement heights. Threshold values for the two stationary indicators ? and ? are determined using field measurements and their sensitivities to the Reynolds averaging periods are discussed. Observations in this study demonstrate that the suggested scheme is proper for finding the TVM of a wind record. For a stationarity quantification of 10 minute duration record, the ? indicator with 30 second Reynolds averaging period is recommended.

Chen, Jun; Wu, Min

2012-08-01

272

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

273

Characteristics of the disastrous wind-sand environment along railways in the Gobi area of Xinjiang, China  

NASA Astrophysics Data System (ADS)

Based on detailed long-term data of wind regimes collected from typical ventilation sites along the railways in the Gobi area of Xinjiang, this study systematically analyzes the characteristics of the disastrous wind-sand environment along the railways by combining gradient sand sampling data collected by a wind-drift sand monitoring system and site survey data. Wind direction and speed rose diagrams revealed the prevailing wind direction in each wind area along the railways, and this is the wind direction from which the maximum frequency of sandstorms occurred. Drift potential characteristic parameters (RDP, RDD) and the direction variability (RDP/DP) showed that each wind area along the Gobi railway featured a long wind period, with strong power in a single wind direction. The special geological environment of the Gobi determines the wind-drift sand that features gravel of large grain size and unsaturation, which are different from the wind-drift sand in deserts. With increasing wind velocity, the density of the wind-drift sand increased steadily; however, at a certain critical value, the density surged. This study on the wind-sand environment of the Gobi has significance for railway safety. The critical value of wind velocity corresponded to an abrupt increase in the wind-drift sand density and should be taken into account during the planning process of railway safety passage, since this will lead to a decrease in frontal visual distance, and an associated decrease in safety. Additionally, the specific features of wind-drift sand activities, such as the abruptness and higher than usual sand height, should be considered during the process of designing sand-damage-control engineering measures.

Cheng, Jian-jun; Jiang, Fu-qiang; Xue, Chun-xiao; Xin, Guo-wei; Li, Kai-chong; Yang, Yin-hai

2015-02-01

274

Wind tunnel simulation of a wind turbine wake in neutral, stable and unstable wind flow  

NASA Astrophysics Data System (ADS)

Measurements of mean velocity, Reynolds stresses, temperature and heat flux have been made in the wake of a model wind turbine in the EnFlo meteorology wind tunnel, for three atmospheric boundary layer states: the base-line neutral case, stable and unstable. The full-to-model scale is approximately 300:1. Primary instrumentation is two-component LDA combine with cold-wire thermometry to measure heat flux. In terms of surface conditions, the stratified cases are weak, but there is a strong 'imposed' condition in the stable case. The measurements were made between 0.5D and 10D, where D is the turbine disk diameter. In the stable case the velocity deficit decreases more slowly; more quickly in the unstable case. Heights at which quantities are maximum or minimum are greater in the unstable case and smaller in the stable case. In the stable case the wake height is suppressed but the width is increased, while in the unstable case the height is increased and the width (at hub height) reaches a maximum and then decreases. The turbulence in the wake behaves in a complex way. Further work needs to be done, to cover stronger levels of surface condition, requiring more extensive measurements to properly capture the wake development.

Hancock, P. E.; Zhang, S.; Pascheke, F.; Hayden, P.

2014-12-01

275

High-velocity blueshifted Fe II absorption in the dwarf star-forming galaxy PHL 293B: evidence for a wind driven supershell?  

NASA Astrophysics Data System (ADS)

X-shooter and WHT-ISIS spectra of the star-forming galaxy PHL 293B also known as A2228-00 and SDSS J223036.79-000636.9 are presented in this paper. We find broad (FWHM = 1000 km s-1) and very broad (FWZI = 4000 km s-1) components in the Balmer lines, narrow absorption components in the Balmer series blueshifted by 800 km s-1, previously undetected Fe II multiplet (42) absorptions also blueshifted by 800 km s-1, IR Ca II triplet stellar absorptions consistent with [Fe/H] < -2.0 and no broad components or blueshifted absorptions in the He I lines. Based on historical records, we found no optical variability at the 5? level of 0.02 mag between 2005 and 2013 and no optical variability at the level of 0.1 mag for the past 24 yr. The lack of variability rules out transient phenomena like luminous blue variables or Type IIn supernovae as the origin of the blueshifted absorptions of H I and Fe II. The evidence points to either a young and dense expanding supershell or a stationary cooling wind, in both cases driven by the young cluster wind.

Terlevich, Roberto; Terlevich, Elena; Bosch, Guillermo; Díaz, Ángeles; Hägele, Guillermo; Cardaci, Mónica; Firpo, Verónica

2014-12-01

276

Wind-forcing of volume transport through Lancaster Sound  

NASA Astrophysics Data System (ADS)

Volume and freshwater transport through Lancaster Sound are estimated from mooring measurements collected in eastern Barrow Strait for 13 years between 1998 and 2011. Estimates from 2006 to 2011 confirm the relationship between surface wind and volume transport derived from data collected between 1998 and 2006. Volume transport through Barrow Strait along the Northwest Passage is significantly correlated with northeastward winds in the Beaufort Sea, parallel to the western coasts of the Canadian Arctic Archipelago, at monthly to interannual time scales. The location and wind direction for which there is maximum correlation are consistent with the flow being driven by a sea level difference between opposite ends of the Passage, and the difference being determined by setup caused by alongshore winds in the Beaufort Sea. Monthly alongshore wind anomalies account for 43% of the variance of the transport anomalies (p < 0.01). Examination of the residuals, after subtracting the volume transport driven by the Beaufort Sea winds from the total transport, showed that they are not significantly correlated with winds in Baffin Bay (p > 0.05). The annual cycles of the total volume transport and its part attributed to the Beaufort Sea wind both have peaks in the summer and are lowest in the autumn. Correlations of the volume transport anomaly with ice velocity anomalies are lower than with surface wind anomalies.

Peterson, Ingrid; Hamilton, James; Prinsenberg, Simon; Pettipas, Roger

2012-11-01

277

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

278

Doppler Radar Wind Profiles Iwan Holleman  

E-print Network

). The potential impact of a network of boundary layer wind profilers and sodars for mesoscale wind analysisDoppler Radar Wind Profiles Iwan Holleman Scientific Report, KNMI WR-2003-02, 2003 #12;2 #12 Strategy 18 3 Methods for Wind Profile Retrieval 25 3.1 Radial Velocity from Local Wind Model 25 3

Stoffelen, Ad

279

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

280

Meridional winds derived from COSMIC radio occultation measurements  

NASA Astrophysics Data System (ADS)

Meridional winds at the magnetic meridian in the upper thermosphere are derived from the peak height and density of the ionospheric F2 layer as retrieved by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites for 4 months from November 2006 to February 2007. These winds (referred to as COSMIC winds) are first validated by comparison at multiple locations with winds obtained from ground-based incoherent scatter radar (ISR) and Fabry-Perot interferometer (FPI) measurements. Then longitudinal variations of these winds are investigated and compared with simulations by the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (NCAR TIE-GCM). The results show generally good agreement between COSMIC winds, ground-based measurements, and the simulations. Significant longitudinal variations are presented in the COSMIC winds. At 40°N (local winter), around midnight the COSMIC winds exhibit stronger and longer-duration equatorward velocities within 110°W-20°W (large negative magnetic declination sector) than those in other longitudes; during late morning hours the poleward winds show similar longitudinal variations. At 40°S (local summer), during the daytime the poleward winds are stronger within 120°E-110°W (large positive magnetic declination sector) than in 60°W-90°E (large negative magnetic declination sector), while during the nighttime the maximum equatorward winds shifts about 2 h later in 60°W-90°E than in 120°E-110°W. Analysis of the TIE-GCM simulations suggests that the longitudinal variation of meridional winds is mainly induced by magnetic declination due to the contribution of geographic zonal wind.

Luan, Xiaoli; Solomon, Stanley C.

2008-08-01

281

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

282

From Dust Devil to Sustainable Swirling Wind Energy  

PubMed Central

Dust devils are common but meteorologically unique phenomena on Earth and on Mars. The phenomenon produces a vertical vortex motion in the atmosphere boundary layer and often occurs in hot desert regions, especially in the afternoons from late spring to early summer. Dust devils usually contain abundant wind energy, for example, a maximum swirling wind velocity of up to 25?m/s, with a 15?m/s maximum vertical velocity and 5?m/s maximum near-surface horizontal velocity can be formed. The occurrences of dust devils cannot be used for energy generation because these are generally random and short-lived. Here, a concept of sustained dust-devil-like whirlwind is proposed for the energy generation. A prototype of a circular shed with pre-rotation vanes has been devised to generate the whirlwind flow by heating the air inflow into the circular shed. The pre-rotation vanes can provide the air inflow with angular momentum. The results of numerical simulations and experiment illustrate a promising potential of the circular shed for generating swirling wind energy via the collection of low-temperature solar energy. PMID:25662574

Zhang, Mingxu; Luo, Xilian; Li, Tianyu; Zhang, Liyuan; Meng, Xiangzhao; Kase, Kiwamu; Wada, Satoshi; Yu, Chuck Wah; Gu, Zhaolin

2015-01-01

283

From dust devil to sustainable swirling wind energy.  

PubMed

Dust devils are common but meteorologically unique phenomena on Earth and on Mars. The phenomenon produces a vertical vortex motion in the atmosphere boundary layer and often occurs in hot desert regions, especially in the afternoons from late spring to early summer. Dust devils usually contain abundant wind energy, for example, a maximum swirling wind velocity of up to 25?m/s, with a 15?m/s maximum vertical velocity and 5?m/s maximum near-surface horizontal velocity can be formed. The occurrences of dust devils cannot be used for energy generation because these are generally random and short-lived. Here, a concept of sustained dust-devil-like whirlwind is proposed for the energy generation. A prototype of a circular shed with pre-rotation vanes has been devised to generate the whirlwind flow by heating the air inflow into the circular shed. The pre-rotation vanes can provide the air inflow with angular momentum. The results of numerical simulations and experiment illustrate a promising potential of the circular shed for generating swirling wind energy via the collection of low-temperature solar energy. PMID:25662574

Zhang, Mingxu; Luo, Xilian; Li, Tianyu; Zhang, Liyuan; Meng, Xiangzhao; Kase, Kiwamu; Wada, Satoshi; Yu, Chuck Wah; Gu, Zhaolin

2015-01-01

284

The effects of solar wind velocity distributions on the refilling of the lunar wake: ARTEMIS observations and comparisons to one-dimensional theory  

NASA Astrophysics Data System (ADS)

lunar plasma wake refills from all directions, with processes operating both parallel and perpendicular to the magnetic field. The resulting wake structure depends sensitively on the properties of the flowing plasma, including the form of the ion and electron velocity distributions. In this manuscript, we discuss theoretical approximations for the refilling of the lunar wake along the magnetic field. While an often-used treatment for the parallel refilling assumes cold ions, one can derive solutions for arbitrary ion velocity distributions. Similarly, though the most tractable theory utilizes Maxwellian electrons, one can derive solutions for other types of distributions. We discuss the theoretical framework for various one-dimensional solutions, spanning the full range from cold-ion theories to gas-dynamic solutions, and utilizing both Maxwellian and kappa electron distributions. We compare these solutions to ARTEMIS observations of the lunar wake, for time periods with appropriate plasma parameters. We also present cases that reveal the inherent limitations of one-dimensional approximations, including those related to electron anisotropies and those related to perpendicular processes associated with both fluid flow and ion gyro-motion.

Halekas, J. S.; Poppe, A. R.; McFadden, J. P.

2014-07-01

285

Uncertainty analysis of wind energy potential assessment  

Microsoft Academic Search

This study presents a framework to assess the wind resource of a wind turbine using uncertainty analysis. Firstly, probability models are proposed for the natural variability of wind resources that include air density, mean wind velocity and associated Weibull parameters, surface roughness exponent, and error for prediction of long-term wind velocity based on the Measure–Correlate–Predict method. An empirical probability model

Soon-Duck Kwon

2010-01-01

286

Dynamic Analysis of Wind Generators  

NASA Astrophysics Data System (ADS)

Wind power does not make any pollution and it also create a recyclable energy. The wind blade speeds significantly affect the measured output power. It is necessary to keep the wind blade tip speed to obtain maximum power. The wind blade speeds significantly affect the energy losses and the power coefficients. It is required to keep the wind blade tip speed to obtain the maximum power coefficient and minimum energy loss. The dynamic problems of the wind turbine generators are formulated by employing the differential quadrature method. The Euler-Bernoulli beam model is used to characterize the wind turbine generator blade. The differential quadrature method is used to transform the partial differential equations that present the dynamic behavior of the wind turbine generator blades into a discrete eigenvalue problem. The results show that the rotation speed could affect the frequencies of the wind generators. The inclined angle could not affect the frequencies of the wind generators significantly.

Hsu, Ming-Hung

287

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

288

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

289

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

290

The divergent wind component in data sparse tropical wind fields  

E-print Network

. Poisson equation solver d. Evaluation of stresmfunction/velocity potential algorithms e. Computing divergent and nondivergent winds. . . . f. Analydcal studies of the divergent wind component g. Aliasing of divergence estimates CHAPTER VI RESULTS... AND DISCUSSION a. Methods of computing stresmfunction and velocity potential 14 30 33 36 36 Table of Contents (Continued) Page b. Analysis of Sangster's method c. Manipulation of divergent wind component fields d. Time continuity e. Vector error...

Snyder, Bruce Alan

2012-06-07

291

Analysis of change in the wind speed ratio according to apartment layout and solutions.  

PubMed

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. PMID:24688430

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

2014-01-01

292

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. PMID:24688430

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

2014-01-01

293

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

294

CAT LIDAR wind shear studies  

NASA Technical Reports Server (NTRS)

The studies considered the major meteorological factors producing wind shear, methods to define and classify wind shear in terms significant from an aircraft perturbation standpoint, the significance of sensor location and scan geometry on the detection and measurement of wind shear, and the tradeoffs involved in sensor performance such as range/velocity resolution, update frequency and data averaging interval.

Goff, R. W.

1978-01-01

295

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

296

On the varying slope of velocity spectra  

NASA Technical Reports Server (NTRS)

Spectra of zonal, meridional and vertical wind velocity, measured during a 24 hour period with the spaced-antenna technique indicate quite a variable slope as a function of height. It is found that the spectral slope (1h to 24h) of all three components correlates with the mean horizontal wind velocity. A possible conclusion is that the frequency dependence of power density of horizontal and vertical fluctuation component apparently depends on the mean wind velocity. However, the vertical spectra at periods larger than about 1 hour can also be influenced by spillover (due to finite radar antenna beam width) from the horizontal fluctuation component or by a Doppler shift.

Rottger, J.

1986-01-01

297

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

298

Noise measurements around the Nibe (Denmark) wind turbines and the Windane 31 wind turbine  

NASA Astrophysics Data System (ADS)

Noise around the two 640 kW wind turbines, and a 300 kW wind turbine at various distances and wind velocities was measured. The results are stated partly as the energy equivalent, A-weighted sound pressure level as a function of the wind velocity, partly as frequency analyses based on tape recordings of the A-weighted sound pressure level. A subjective evaluation of the noise emission from the wind turbines is given.

Kristensen, J.

299

Midnight reversal of ionospheric plasma bubble eastward velocity to westward velocity during geomagnetically quiettime: Climatology and its model validation  

NASA Astrophysics Data System (ADS)

In an effort to better understand the dynamics of westward velocities of the nocturnal F-region plasma, the climatology of the westward traveling plasma bubbles - WTB - occurring during quiettime is studied here. The climatology of the WTB is analyzed here based on airglow images obtained during 14 quiet days between 2001 and 2006 at the Brazilian station São João do Cariri (Geographic 7.45°S, 36.5°W, dip ˜20°S). The frequency of occurrence of the WTB maximizes in the descending phase of the solar cycle. The WTB velocities ranged between ˜20 and 40 ms-1. The frequency of occurrence had a peak value of only 3.65% at 2345 LT. The maximum occurrence of the WTB was in July-September. No WTB have been observed from November until April in all years 2001-2006. We show for the first time theoretically that the WTB dominant forcing mechanisms during geomagnetically quiet days are westward thermospheric winds.

Sobral, José H. A.; de Castilho, Vivian M.; Abdu, M. A.; Takahashi, Hisao; Paulino, I.; Gasparelo, Ulisses A. C.; Arruda, Daniela C. S.; Mascarenhas, Matheus; Zamlutti, C. J.; Denardini, C. M.; Koga, Daiki; de Medeiros, A. F.; Buriti, R. A.

2011-07-01

300

Signal analysis using the maximum entropy method  

NASA Astrophysics Data System (ADS)

The analysis of discrete series is explained using the maximum entropy method in order to solve data processing problems in the aeroelastic study of wind turbines. Discrete Fourier spectrum and maximum entropy spectrum are compared. This method searches for an autoregressive model for a series containing a maximum of information about entropy. The autoregressive model is outlined and the notions 'information' and 'entropy' in signal analysis are defined. Energy and phase spectrum construction, starting from an autoregressive model, is described, with examples. The maximum entropy method is valuable where Fourier transformation techniques hardly work or fail.

Kuik, W.

1981-03-01

301

a Diagnostic Approach to Obtaining Planetary Boundary Layer Winds Using Satellite-Derived Thermal Data  

NASA Astrophysics Data System (ADS)

The feasibility of using satellite-derived thermal data to generate realistic synoptic-scale winds within the planetary boundary layer (PBL) is examined. Diagnostic "modified Ekman" wind equations from the Air Force Global Weather Central (AFGWC) Boundary Layer Model are used to compute winds at seven levels within the PBL transition layer (50 m to 1600 m AGL). Satellite-derived winds based on 62 predawn (0921 GMT 19 April 1979) TIROS-N soundings are compared to similarly-derived wind fields based on 39 AVE-SESAME II rawinsonde (RAOB) soundings taken 2 h later. Actual wind fields are also used as a basis for comparison. Qualitative and statistical comparisons show that the Ekman winds from both sources are in very close agreement, with an average vector correlation coefficient of 0.815. Best results are obtained at 300 m AGL. Satellite winds tend to be slightly weaker than their RAOB counterparts and exhibit a greater degree of cross-isobaric flow. The modified Ekman winds show a significant improvement over geostrophic values at levels nearest the surface. Horizontal moisture divergence, moisture advection, velocity divergence and relative vorticity are computed at 300 m AGL using satellite-derived winds and moisture data. Results show excellent agreement with corresponding RAOB-derived values. Areas of horizontal moisture convergence, velocity convergence, and positive vorticity are nearly coincident and align in regions which later develop intense convection. Vertical motion at 1600 m AGL is computed using stepwise integration of the satellite winds through the PBL. Values and patterns are similar to those obtained using the RAOB-derived winds. Regions of maximum upward motion correspond with areas of greatest moisture convergence and the convection that later develops.

Belt, Carol Lynn

302

The sun and heliosphere at solar maximum.  

PubMed

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's 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. PMID:14615526

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

2003-11-14

303

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

304

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. [Univ. of Colorado, Boulder, CO (United States). Dept. of Aerospace Engineering Sciences

1995-09-01

305

Biological Soil Crusts and Wind Erosion  

Microsoft Academic Search

\\u000a Wind is an important erosive force in deserts, where limited cover of vascular plant material offers little soil-surface protection.\\u000a Dust deposition by wind often exceeds that of fluvial deposition in these drier regions (Goudie 1978; Williams et al. 1995). Sediment production from soil surfaces occurs when wind forces exceed soil threshold friction velocities (TFV: the wind\\u000a velocity needed to detach

J. Belnap

306

Magnetically driven jets and winds: Exact solutions  

NASA Technical Reports Server (NTRS)

We present a general class of self-similar solutions of the full set of MHD equations that include matter flow, electromagnetic fields, pressure, and gravity. The solutions represent axisymmetric, time-independent, nonrelativistic, ideal, magnetohydrodynamic, collimated outflows (jet and winds) from magnetized accretion disks around compact objects. The magnetic field extracts angular momentum from the disk, accelerates the outflows perpedicular to the disk, and provides collimation at large distances. The terminal outflow velocities are of the order of or greater than the rotational velocity of the disk at the base of the flow. When a nonzero electric current flows along the jet, the outflow radius oscillates with axial distance, whereas when the total electric current is zero (with the return current flowing across the jet's cross section), the outflow radius increase to a maximum and then decreases. The method can also be applied to relativistic outflows.

Contopoulos, J.; Lovelace, R. V. E.

1994-01-01

307

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

308

Wind Tunnel Analysis of the Detachment Bubble on Bolund Island  

NASA Astrophysics Data System (ADS)

The flow topology on two scaled models (1:230 and 1:115) of the Bolund Island is analysed in two wind tunnels, focusing on the characteristics of the detachment pattern when the wind blows from 270° wind direction and the atmospheric condition is neutral. Since the experiments are designed as the simplest possible reference cases, no additional roughness is added neither to the models surface nor to the wind tunnel floor. Pressure measurements on the surface of the 1:230 scale model are used to estimate the horizontal extension of the intermittent recirculation region, by applying the diagnostic means based in exploring the pressure statistics, proposed in the literature for characterising bubbles on canonical obstacles. The analysis is done for a range of Reynolds numbers based on the mean undisturbed wind speed, U? and the maximum height of the island, h[5.1×104,8.5×104]. An isoheight mapping of the velocity field is obtained using 3D hotwire (3D HW). The velocity field in a vertical plane is determined using 3D HW and 2D particle image velocimetry (PIV) on the 1:115 scale model in order to reproduce and complete already existing results in the literature.

Yeow, T. S.; Cuerva, A.; Conan, B.; J, Pérez-Álvarez

2014-12-01

309

ACTIVE GALACTIC NUCLEUS OBSCURATION THROUGH DUSTY INFRARED-DOMINATED FLOWS. I. RADIATION-HYDRODYNAMICS SOLUTION FOR THE WIND  

SciTech Connect

We construct a radiation-hydrodynamics model for the obscuring toroidal structure in active galactic nuclei. In this model the obscuration is produced at parsec scales 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 two-dimensional radiation transfer problem in a flux-limited diffusion approximation. We iteratively couple the solution with calculations of stationary one-dimensional models for the wind and obtain the z-component of the velocity. Our results demonstrate that for active galactic nucleus (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.; Kallman, T. [Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center, Code 662, Greenbelt, MD 20771 (United States); Bisnovatyi-Kogan, G. S. [Space Research Institute, 84/32, Profsoyuznaya st., Moscow (Russian Federation)

2011-11-01

310

Turbulent Flow Properties Around a Staggered Wind Farm  

NASA Astrophysics Data System (ADS)

The fundamental properties of turbulent flow around a perfectly staggered wind farm are investigated in a wind tunnel. The wind farm consisted of a series of 10 rows by 2-3 columns of miniature wind turbines spaced 5 and 4 rotor diameters in the streamwise and spanwise directions respectively. It was placed in a boundary-layer flow developed over a smooth surface under thermally neutral conditions. Cross-wire anemometry was used to obtain high resolution measurements of streamwise and vertical velocity components at various locations within and above the wind farm. The results show that the staggered configuration is more efficient in terms of momentum transfer from the background flow to the turbines compared to the case of an aligned wind turbine array under similar turbine separations in the streamwise and spanwise directions. This leads to improved power output of the overall wind farm. A simplified analysis suggests that the difference in power output between the two configurations is on the order of 10%. The maximum levels of turbulence intensity in the staggered wind farm were found to be very similar to that observed in the wake of a single wind turbine, differing substantially with that observed in an aligned configuration with similar spacing. The dramatic changes in momentum and turbulence characteristics in the two configurations show the importance of turbine layout in engineering design. Lateral homogenization of the turbulence statistics above the wind farm allows for the development of simple parametrizations for the adjustment of flow properties, similar to the case of a surface roughness transition. The development of an internal boundary layer was observed at the upper edge of the wind farm within which the flow statistics are affected by the superposition of the ambient flow and the flow disturbance induced by the wind turbines. The adjustment of the flow in this layer is much slower in the staggered situation (with respect to its aligned counterpart), implying a change in the momentum/power available at turbine locations. Additionally, power spectra of the streamwise and vertical velocity components indicate that the signature of each turbine-tip vortex structure persists to locations deep within the wind farm.

Chamorro, Leonardo P.; Arndt, R. E. A.; Sotiropoulos, Fotis

2011-12-01

311

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

312

Performance of a 2-micrometer coherent Doppler lidar for wind measurements  

NASA Technical Reports Server (NTRS)

Measurements of boundary layer winds are presented using a 2-micrometer coherent Doppler lidar and the optimal performance of the maximum likelihood estimator. The systematic error for single-shot estimates was estimated as 3.6 cm/s using measurements from a stationary hard target. The estimation error for measurements of the radial component of the wind field was determined, as well as the fraction of the estimates that are randomly distributed over the velocity search space, when the signal power is low and speckle fading is important. The results from actual data are compared with the results from ideal simulations. The first direct estimation of the spatial structure function of the radial wind field and of the energy dissipation rate is presented for both horizontal and vertical directions of propagation. The rms estimation error of the velocity estimates is found to be within 30% of ideal performance based on simulation.

Frehlich, Rod; Hannon, Stephen M.; Henderson, Sammy W.

1994-01-01

313

Winds over saltcedar  

USGS Publications Warehouse

An analysis of hourly wind speeds above and within a stand of saltcedar near Buckeye, Arizona, reveals that in 90% of all observed cases, the wind profiles above the stand can be represented by the simple logarithmic equation: uz = u* k 1n ( z z0) where uz is the velocity at height z. The roughness length (z0), (disregarding zero displacement), varies with a stability ratio similar to Richardson's number. The friction velocity, u*, depends on the wind speeds above the vegetation. Von Karman's constant, k, equals 0.41. Within the thickets there is considerable turbulence, and irregular wind inversions occur during daylight hours. The results are important for estimating water losses by evapotranspiration by either the energy-budget or the mass-transfer formulae. ?? 1970.

Van Hylckama, T. E. A.

1970-01-01

314

Pickup Ion Velocity Distributions at Titan: Effects of Spatial Gradients  

NASA Technical Reports Server (NTRS)

The principle source of pickup ions at Titan is its neutral exosphere, extending well above the ionopause into the magnetosphere of Saturn or the solar wind, depending on the moon's orbital position. Thermal and nonthermal processes in the thermosphere generate the distribution of neutral atoms and molecules in the exosphere. The combination of these processes and the range of mass numbers, 1 to over 28, contribute to an exospheric source structure that produces pickup ions with gyroradii that are much larger or smaller than the corresponding scale heights of their neutral sources. The resulting phase space distributions are dependent on the spatial structure of the exosphere as well as that of the magnetic field and background plasma. When the pickup ion gyroradius is less than the source gas scale height, the pickup ion velocity distribution is characterized by a sharp cutoff near the maximum speed, which is twice that of the ambient plasma times the sine of the angle between the magnetic field and the flow velocity. This was the case for pickup H(sup +) ions identified during the Voyager 1 flyby. In contrast, as the gyroradius becomes much larger than the scale height, the peak of the velocity distribution in the source region recedes from the maximum speed. Iri addition, the amplitude of the distribution near the maximum speed decreases. These more beam like distributions of heavy ions were not observed from Voyager 1 , but should be observable by more sensitive instruments on future spacecraft, including Cassini. The finite gyroradius effects in the pickup ion velocity distributions are studied by including in the analysis the possible range of spatial structures in the neutral exosphere and background plasma.

Hartle, R. E.; Sittler, E. C.

2004-01-01

315

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

316

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

317

Wind resources and wind farm wake effects offshore observed from satellite  

E-print Network

Wind resources and wind farm wake effects offshore observed from satellite Charlotte Bay Hasager to quantify the wake effect at two large offshore wind farms in Denmark. It is found that the wake velocity than for near-neutral conditions. Keywords: satellite, offshore wind resource, wake. 1 Introduction

318

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

319

A numerical investigation of wind speed effects on lake-effect storms  

NASA Astrophysics Data System (ADS)

Observations of lake-effect storms that occur over the Great Lakes region during late autumn and winter indicate a high sensitivity to ambient wind speed and direction. In this paper, a two-dimensional version of the Penn State University/National Center for Atmospheric Research (PSU/NCAR) model is used to investigate the wind speed effects on lake-effect snowstorms that occur over the Great Lakes region. Theoretical initial conditions for stability, relative humidity, wind velocity, and lake/land temperature distribution are specified. Nine different experiments are performed using wind speeds of U=0, 2, 4,..., 16 m s-1. The perturbation wind, temperature, and moisture fields for each experiment after 36 h of simulation are compared. It is determined that moderate (4 6 m s-1) wind speeds result in maximum precipitation (snowfall) on the lee shore of the model lake. Weak wind speeds (0? U<4 m s-1) yield significantly higher snowfall amounts over the lake along with a spatially concentrated and intense response. Strong wind speeds (6< U?16 m s-1), yield very little, if any, significant snowfall, although significant increases in cloudiness, temperature, and perturbation wind speed occur hundreds of kilometers downwind from the lake.

Sousounis, Peter J.

1993-04-01

320

ACOUSTIC STUDY OF THE UD / GAMESA WIND TURBINE PROJECT  

E-print Network

/s). Maximum sound power is first produced by the wind turbine at the design wind speed. The study average sound levels are in the range of 34 to 56 dBA. · The maximum wind turbine sound level under design turbine sound level under design wind conditions at the closest university receivers (Class B noise zone

Firestone, Jeremy

321

The H_2O(+) Velocity Field in Comet Hale-Bopp, Observations and MHD Models  

NASA Astrophysics Data System (ADS)

The 3.5-meter WIYN Telescope and its Multi-Object Spectrograph (MOS)obtained simultaneous spectra at many points in the coma of Comet Hale-Bopp between 1996 October and 1997 April. The "Hydra" fiber positioner was used to sample a ring pattern of points about the nucleus with a minimum spacing of 40 arc seconds and a maximum radius of 22.5 arc minutes. A integral field device called "Densepak" was also used to sample a 7 x 13 rectangular pattern of 91, 3 arc second fibers on 4 arc second centers. The bench spectrograph was used in the echelle mode with an interference filter to isolate a single order and covered the wavelength range from 6100 Angstroms to 6400 Angstroms with resolution of approximately 15,000. This spectral region contains the emission features of H_2O(+) . From these data we have extracted the radial velocity of the H_2O(+) . We find the acceleration in the anit-sun direction to be of the order of 20 cm sec(-) (2) . The measured velocity fields have been compared to full 3D MAUS-MHD models. The models suggest that the degree ofconfinement of the coma and the velocities attained in the anti-sun direction depend sensitively upon the velocity of the ambient solar wind. The observed velocity fields are consistent with the confinement of the near coma by a relatively slow solar wind while the speeds attained at distances of the order of a million kilometers in the anti-sun direction are more like those produced by a fast solar wind. The observations were obtained at a time when Hale-Bopp was at intermediate heliocentric latitudes where the solar wind speed is known to change rapidly from slow to fast modes. This situation is under further investigation.

Anderson, C. M.; Combi, M. R.; Gombosi, T.; Hansen, K. C.

1998-09-01

322

Post-Main-Sequence Changes in Rotational Velocities  

NASA Astrophysics Data System (ADS)

For 1377 dwarfs and 381 giants of types B and A, we present mean observed projected rotational velocities for normal plus abnormal spectral types combined. For the dwarfs, Vsini is statistically constant at 127+/-15 km s-1 from B0 V to A5 V. Using the interior models of Bertelli et al., we predict the rotational velocities of the giants. We assume an age of 30×106 yr for the observed dwarfs. The predicted giant rotational velocities agree well with the observed values if angular momentum is conserved in rigid-body rotation; the observed minus the computed is -7+/-4 km s-1. Significant loss of angular momentum by mass loss (stellar winds) cannot occur because the observed rotational velocities of the giants are already at the maximum level allowed by either conservation mechanism. Comparison with three other studies indicates that angular momentum is conserved by rigid-body rotation if the expansion is less than a factor of 4, but conserved in shells if the expansion is more.

Abt, Helmut A.

2003-01-01

323

Wind characteristics of the troposphere and lower stratosphere during the passage of a tropical cyclone over India using VHF radar  

NASA Astrophysics Data System (ADS)

A tropical depression formed in the west central Bay of Bengal on 15th October 2001 intensified into a cyclonic storm and crossed over the Indian mesosphere stratosphere troposphere (MST) Radar site at Gadanki (13.5°N, 79.2°E), India on the next day morning. Three-dimensional wind characteristics of the troposphere and lower stratosphere have been studied based on the continuous observations using MST radar at Gadanki during 15 16 October 2001. Horizontal wind components in the upper troposphere and lower stratosphere showed an abrupt increase during the passage of the storm, whereas the wind changed its direction and became very weak in lower levels (4 8 km). The observed vertical velocity was very high in the level of maximum convective outflow (10 12 km). After the passage of the cyclonic storm upper and lower tropospheric wind speed reduced considerably, whereas the mid-tropospheric wind speed increased.

Mrudula, G.; Mohan Kumar, K.; Kishore Kumar, K.

2006-05-01

324

Variable Winds and Dust Formation in R Coronae Borealis Stars  

E-print Network

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I 10830 lines of twelve R Coronae Borealis (RCB) stars over short (1 month) and long (3 year) 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 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; Zhang, Wanshu

2013-01-01

325

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

326

VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS  

SciTech Connect

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I {lambda}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 {approx}400 km s{sup -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.; Zhang Wanshu [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Geballe, T. R., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: wzhan21@lsu.edu, E-mail: tgeballe@gemini.edu [Gemini Observatory, 670 N. A'ohoku Place, Hilo, HI 96720 (United States)

2013-08-01

327

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

328

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

329

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

330

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

331

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

332

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

333

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

334

New Measurements of the Winds of Uranus  

Microsoft Academic Search

Hubble Space Telescope imaging of Uranus in 1994, 1997, 1998, and 2000 revealed 13 cloud features, allowing the first measurements of wind velocities at northern latitudes not accessible to the Voyager cameras and new measurements of southern-latitude wind velocities determined during the 1986 Voyager encounter. Images acquired with the Keck 10-meter telescope adaptive optics system in June 2000 also showed

H. B. Hammel; K. Rages; G. W. Lockwood; E. Karkoschka; I. de Pater

2001-01-01

335

Wind energy in the built environment: concentrator effects of buildings  

Microsoft Academic Search

This thesis deals with wind energy conversion in the built environment. It gives a description of the wind resources in the built environment that can be converted into energy by a wind turbine. With a focus on maximum energy yield of the wind turbine, it especially deals with the integration of wind turbine and building in such a way that

Sander Mertens

2006-01-01

336

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

337

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

338

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

339

Wind-systems technical notes: 1981  

NASA Astrophysics Data System (ADS)

Specialized tests of small wind systems and other investigations were compiled. Subjects include: controlled velocity tests, dynamometer tests, failure analysis, design of a digital speed control circuit for induction wind turbine generators and collection of wind turbine generator rpm data via an FM wireless intercom system.

Shuler, S. A.; Stafford, J. V.

1982-03-01

340

Acceleration and Dissipation in Relativistic Winds  

E-print Network

I argue that ideal MHD relativistic winds are always limited in practice to asymptotic 4-velocity $\\gamma_\\infty \\approx \\sigma_0^{1/3}$ and asymptotic magnetization $\\sigma \\sim \\sigma_0^{2/3} \\gg 1$, where $\\sigma_0$ is the wind magnetization with respect to the rest energy density, evaluated at the light cylinder of the rotating, magnetized compact object that drives the flow. This suggests that the observed low value of he asymptotic $\\sigma$ in the equatorial sectors of the winds driving Pulsar Wind Nebulae and the associated high values of the asymptotic 4-velocity are a consequence of magentic dissipation in the wind zone.

Jonathan Arons

2003-10-17

341

Application of a method for the automatic detection and Ground-Based Velocity Track Display (GBVTD) analysis of a tornado crossing the Hong Kong International Airport  

NASA Astrophysics Data System (ADS)

A weak tornado with a maximum Doppler velocity shear of about 40 m s - 1 moved across the Hong Kong International Airport (HKIA) during the evening of 20 May 2002. The tornado caused damage equivalent to F0 on the Fujita Scale, based on a damage survey. The Doppler velocity data from the Hong Kong Terminal Doppler Weather Radar (TDWR) are studied using the Ground-Based Velocity Track Display (GBVTD) method of single Doppler analysis. The GBVTD analysis is able to clearly depict the development and decay of the tornado though it appears to underestimate its magnitude. In the pre-tornadic state, the wind field is characterized by inflow toward the center near the ground and upward motion near the center. When the tornado attains its maximum strength, an eye-like structure with a downdraft appears to form in the center. Several minutes later the tornado begins to decay and outflow dominates at low levels. Assuming cyclostrophic balance, the pressure drop 200 m from the center of the tornado at its maximum strength is calculated to be about 6 hPa. To estimate the maximum ground-relative wind speed of the tornado, the TDWR's Doppler velocities are adjusted for the ratio of the sample-volume size of the radar and the radius of the tornado, resulting in a peak wind speed of 28 m s - 1 , consistent with the readings from a nearby ground-based anemometers and the F0 damage observed. An automatic tornado detection algorithm based on Doppler velocity difference (delta-V) and temporal and spatial continuity is applied to this event. The locations and the core flow radii of the tornado as determined by the automatic method and by subjective analysis agree closely.

Chan, P. W.; Wurman, J.; Shun, C. M.; Robinson, P.; Kosiba, K.

2012-03-01

342

SNR-INDEPENDENT VELOCITY ESTIMATION FOR MOBILE CELLULAR COMMUNICATIONS SYSTEMS  

E-print Network

component of a mobile terminal's velocity has a linear relationship with the maximum Doppler frequency fm of a demodulated signal can also be used to estimate velocity, either directly 2], or using higher order statistics

Blostein, Steven D.

343

Development of a wind gust model to estimate gust speeds and their return periods  

NASA Astrophysics Data System (ADS)

Spatially dense observations of gust speeds are necessary for various applications, but their availability is limited in space and time. This work presents an approach to help to overcome this problem. The main objective is the generation of synthetic wind gust velocities. With this aim, theoretical wind and gust distributions are estimated from ten years of hourly observations collected at 123 synoptic weather stations provided by the German Weather Service. In a first step, an exposure correction is applied on measurements of the mean wind velocity to reduce the influence of local urban and topographic effects. In a second step, a transfer function is built between distribution parameters of wind and gust velocities. The aim of this step is to estimate the parameters of gusts at stations where only wind speed data is available. These parameters can be used in a third step to generate synthetic gusts, which can improve the accuracy of return periods at test sites with a lack of observations. The second objective is to determine return periods much longer than the nominal length of the original time series by considering extreme value statistics. Estimates for both local maximum return periods and average return periods for single historical events are provided. The comparison of maximum and average return periods shows that even storms with short average return periods may lead to local wind gusts with return periods of several decades. Despite uncertainties caused by the short length of the observational records, the method leads to consistent results, enabling a wide range of possible applications.

Seregina, Larisa; Haas, Rabea; Born, Kai; Pinto, Joaquim G.

2014-05-01

344

The Solar Wind  

NASA Technical Reports Server (NTRS)

The first evidence of the solar wind was provided through observations of comet tail deflections by L. Biermann in 1951. A cometary ion tail is oriented along the difference between the cometary and solar wind velocities, whereas the dust tail is in the antisunward direction; the ion tail directions demonstrated the existence of an outflow of ionized gas from the Sun (the solar wind) and allowed estimates of solar wind speed. Spacecraft observations have now established that at 1 AU the solar wind has a typical ion number density of about 7 /cc and is composed by number of about 95% protons and 5% Helium, with other minor ions also present. The solar wind as observed at 1 AU in the ecliptic has speeds typically in the range 300-700 km/ s. At such speeds ions travel from the Sun to 1 AU in from 2.5 to 6 days. The impact of the solar wind on planets with magnetic fields (Earth, Jupiter, Saturn, Uranus, Neptune) causes phenomena such as magnetospheres, aurorae, and geomagnetic storms, whereas at objects lacking magnetospheres (Mars, Venus, comets), atmospheric neutrals undergo charge exchange and are picked up by the solar wind flow. The solar wind also shields the Earth from low energy cosmic rays, and is responsible for the existence of the anomalous component of the cosmic rays a low energy component that is created locally rather than in the galaxy. Presented here is a brief introduction to the solar wind and a description of some current topics of research. Solar wind properties vary a great deal due to the changing magnetic structure on the Sun.

Goldstein, B. E.

1998-01-01

345

Wind farm array wake losses  

SciTech Connect

A wind turbine wake study was conducted in the summer of 1987 at an Altamont Pass wind electric generating facility. The wind speed deficits, turbulence, and power deficits from an array consisting of several rows of wind turbines is discussed. A total of nine different test configurations were evaluated for a downwind spacing ranging from 7 rotor diameters (RD) to 34 RD and a cross wind spacing of 1.3 RD and 2.7 RD. Wake power deficits of 15% were measured at 16 RD and power losses of a few percent were even measurable at 27 RD for the closer cross wind spacing. For several rows of turbines separated by 7-9 RD the wake zones overlapped and formed compound wakes with higher velocity deficits. The wind speed and direction turbulence in the wake was much higher than the ambient turbulence. The results from this study are compared to the findings from other similar field measurements.

Baker, R.W. [Impact Weather, Washougal, WA (United States); McCarthy, E.F. [Wind Economics & Technology, Inc., Martinez, CA (United States)

1997-12-31

346

WIND ENERGY Wind Energ. (2014)  

E-print Network

the turbulent atmosphere and the wind turbine wake in order to optimize the design of the wind turbine as well.com). DOI: 10.1002/we.1792 RESEARCH ARTICLE Self-similarity and turbulence characteristics of wind turbine by a single wind turbine are studied in this paper with a new large eddy simulation (LES) code, the wind

347

Observations of sunspot umbral velocity oscillations.  

NASA Technical Reports Server (NTRS)

Review of sunspot umbral velocity measurements obtained free from any cross talk introduced by photospheric and penumbral scattered light by using lines formed only in the sunspot umbrae and showing no Zeeman effect. The maximum peak-to-peak amplitude of the umbral oscillatory velocity component is found to be of the order of 0.5 km per sec.

Bhatnagar, A.; Livingston, W. C.; Harvey, J. W.

1972-01-01

348

Meaningful wind chill indicators derived from heat transfer principles.  

PubMed

The wind chill index (WCI) and the more widely used wind chill equivalent temperature represent an attempt to combine several weather-related variables (temperature, wind velocity and solar radiation) into a single index which can indicate human comfort. Since its introduction in 1945, the WCI has been criticized mainly on the ground that the underlying model does not comply with modern heat transfer theory. In spite of that, the WCI, "calibrated" to human comfort, has proven to be successful in predicting discomfort and tolerance of man to the cold. Nevertheless, neither the WCI nor the wind chill equivalent temperature can be actually measured and, therefore, without the additional 'calibration' they are meaningless. In this study we have shown that the WCI represents the instantaneous rate of heat loss from bare skin at the moment of exposure to the cold, and as such, it correlates reasonably well with measurable variables that represent a feeling of cold. Two new wind chill indicators have been introduced: exposed skin temperature and maximum exposure time. These indicators yield more information than the WCI provides, are measurable, have physical meaning and are based on established heat transfer principles. PMID:7558408

Brauner, N; Shacham, M

1995-08-01

349

Long term variability of B supergiant winds  

NASA Technical Reports Server (NTRS)

The object of this observing proposal was to sample wind variability in B supergiants on a daily basis over a period of several days in order to determine the time scale with which density variability occurs in their winds. Three stars were selected for this project: 69 Cyg (B0 Ib), HD 164402 (B0 Ib), and HD 47240 (B1 Ib). Three grey scale representations of the Si IV lambda lambda 1400 doublet in each star are attached. In these figures, time (in days) increases upward, and the wavelength (in terms of velocity relative to the rest wavelength of the violet component of the doublet) is the abscissa. The spectra are normalized by a minimum absorption (maximum flux) template, so that all changes appear as absorptions. As a result of these observations, we can now state with some certainty that typical B supergiants develop significant wind inhomogeneities with recurrence times of a few days, and that some of these events show signs of strong temporal coherence.

Massa, Derck L.

1995-01-01

350

Application of Wind Fetch and Wave Models for Habitat Rehabilitation and Enhancement Projects  

USGS Publications Warehouse

Models based upon coastal engineering equations have been developed to quantify wind fetch length and several physical wave characteristics including significant height, length, peak period, maximum orbital velocity, and shear stress. These models, developed using Environmental Systems Research Institute's ArcGIS 9.2 Geographic Information System platform, were used to quantify differences in proposed island construction designs for three Habitat Rehabilitation and Enhancement Projects (HREPs) in the U.S. Army Corps of Engineers St. Paul District (Capoli Slough and Harpers Slough) and St. Louis District (Swan Lake). Weighted wind fetch was calculated using land cover data supplied by the Long Term Resource Monitoring Program (LTRMP) for each island design scenario for all three HREPs. Figures and graphs were created to depict the results of this analysis. The difference in weighted wind fetch from existing conditions to each potential future island design was calculated for Capoli and Harpers Slough HREPs. A simplistic method for calculating sediment suspension probability was also applied to the HREPs in the St. Paul District. This analysis involved determining the percentage of days that maximum orbital wave velocity calculated over the growing seasons of 2002-2007 exceeded a threshold value taken from the literature where fine unconsolidated sediments may become suspended. This analysis also evaluated the difference in sediment suspension probability from existing conditions to the potential island designs. Bathymetric data used in the analysis were collected from the LTRMP and wind direction and magnitude data were collected from the National Oceanic and Atmospheric Administration, National Climatic Data Center.

Rohweder, Jason; Rogala, James T.; Johnson, Barry L.; Anderson, Dennis; Clark, Steve; Chamberlin, Ferris; Runyon, Kip

2008-01-01

351

Optimum windings for linear induction machines.  

NASA Technical Reports Server (NTRS)

The matrix method of calculating linear induction machine performance as a function of winding current distribution was extended to determine the winding current distribution for maximum efficiency. Application of the method to typical magnetohydrodynamic generator geometries showed that electrical efficiencies of 0.5 to 0.6 are possible with fractional wavelength windings and without insulating vanes in the flow.

Elliott, D. G.

1973-01-01

352

Designing Drive Trains for the Next Generation of Wind Turbines (FloDesign Wind Turbine Corporation)  

Microsoft Academic Search

Today's wind turbines have nearly reached their maximum possible efficiency and are limited to sites with a narrow profile of wind patterns. The patent-pending Mixer Ejector Wind Turbine (MEWT) concept proposed by FloDesign promises to outperform existing wind turbines by a factor of three or more in a much wider range of wind resources. Olin College’s FloDesign SCOPE team was

Mateen Abdul; Kelcy Adamec; Gavin Boggs; Matthew Crawford; Kevin Sihlanick; Russell Torres

2009-01-01

353

Screening length and the direction of plasma winds  

E-print Network

We study the screening length of a heavy quark-antiquark pair in strongly coupled gauge theory plasmas flowing at velocity v following a proposal by Liu, Rajagopal, and Wiedemann. We analyze the screening length as the direction of the plasma winds vary. To leading order in v, this angle-dependence can be studied analytically for many theories by extending our previous formalism. We show that the screening length is locally a minimum (maximum) when the pair is perpendicular (parallel) to the plasma winds, which has been observed for the N=4 plasma. Also, we compare AdS/CFT results with weak coupling ones, and we discuss the subleading dependence on v for the Dp-brane.

Makoto Natsuume; Takashi Okamura

2007-06-01

354

Wild Wind  

NSDL National Science Digital Library

Students learn the difference between global, prevailing and local winds. They make wind vanes out of paper, straws and soda bottles and use them to measure wind direction over time. They analyze their data to draw conclusions about the local prevailing winds.

Integrated Teaching And Learning Program

355

A Simple Empirical Model for Predicting the Decay of Tropical Cyclone Winds after Landfall  

Microsoft Academic Search

An empirical model for predicting the maximum wind of landfalling tropical cyclones is developed. The model is based upon the observation that the wind speed decay rate after landfall is proportional to the wind speed. Observations also indicate that the wind speed decays to a small, but nonzero, background wind speed. With these assumptions, the wind speed is determined from

John Kaplan; Mark Demaria

1995-01-01

356

Heating by wind  

NASA Astrophysics Data System (ADS)

The economical design of a wind power plant combined with a heat accumulator is discussed. A gliding-museum to be built on the Wasserkuppe in the Rhoen mountain is used as an example to investigate which wind power plant and storage alternative can be considered based on meteorological basic data and the heat demand required. A system optimization regarding technical and economical points is used to study the wind power plant and to indicate the best accumulator. The maximum storage time established by an economic optimization is one to two days. In this regard no difference is made between sun energy and wind energy, and the storage size can span the day/night cycle.

Auer, F.

1982-01-01

357

Kinetic and Potential Sputtering of Lunar Regolith: Contribution of Solar-Wind Heavy Ions  

NASA Technical Reports Server (NTRS)

Sputtering of lunar regolith by protons as well as solar-wind heavy ions is considered. From preliminary measurements of H+, Ar+1, Ar+6 and Ar+9 ion sputtering of JSC-1A AGGL lunar regolith simulant at solar wind velocities, and TRIM simulations of kinetic sputtering yields, the relative contributions of kinetic and potential sputtering contributions are estimated. An 80-fold enhancement of oxygen sputtering by Ar+ over same-velocity H+, and an additional x2 increase for Ar+9 over same-velocity Ar+ was measured. This enhancement persisted to the maximum fluences investigated is approximately 1016/cm (exp2). Modeling studies including the enhanced oxygen ejection by potential sputtering due to the minority heavy ion multicharged ion solar wind component, and the kinetic sputtering contribution of all solar wind constituents, as determined from TRIM sputtering simulations, indicate an overall 35% reduction of near-surface oxygen abundance. XPS analyses of simulant samples exposed to singly and multicharged Ar ions show the characteristic signature of reduced (metallic) Fe, consistent with the preferential ejection of oxygen atoms that can occur in potential sputtering of some metal oxides.

Meyer, F. W.; Harris, P. R.; Meyer, H. M., III; Hijiazi, H.; Barghouty, A. F.

2013-01-01

358

Wind Variability in BZ Camelopardalis  

NASA Astrophysics Data System (ADS)

Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur frequently in this star. We confirm the results of Ringwald & Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We also commonly find blueshifted emission components in the H? line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald & Naylor reported common occurrences of redshifted H? emission components in their BZ Cam spectra. We have attributed these emission components in H? to occasions when gas concentrations in the bipolar wind (both front side and back side) become manifested as emission lines as they move beyond the disk's outer edge. We also suggest, based on changes in the P-Cygni profiles during an episode, that the progression from larger to smaller expansion velocities is due to the higher velocity portions of a wind concentration moving beyond the edge of the continuum light of the disk first, leaving a net redward shift of the remaining absorption profile. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the He I ?5876 line, finding P = 0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We argue that the radiation-driven wind in BZ Cam receives an initial boost by acting on gas that has been lifted above the disk by the interaction of the accretion stream with the disk, thereby imposing flickering timescales onto the wind events, as well as leading to an orbital modulation of the wind due to the non-axisymmetric nature of the stream/disk interaction. Simultaneous photometry and spectroscopy were acquired on three nights in order to test the possible connection between flickering continuum light and the strength of the front-side wind. We found strong agreement on one night, some agreement on another, and no agreement on the third. We suggest that some flickering events lead to only back-side winds which will not have associated P-Cygni profiles.

Honeycutt, R. K.; Kafka, S.; Robertson, J. W.

2013-02-01

359

Stationary Plasma Thruster Ion Velocity Distribution  

NASA Technical Reports Server (NTRS)

A nonintrusive velocity diagnostic based on laser induced fluorescence of the 5d4F(5/2)-6p4D(5/2) singly ionized xenon transition was used to interrogate the exhaust of a 1.5 kW Stationary Plasma Thruster (SPT). A detailed map of plume velocity vectors was obtained using a simplified, cost-effective, nonintrusive, semiconductor laser based scheme. Circumferential velocities on the order of 250 m/s were measured which implied induced momentum torques of approximately 5 x 10(exp -2) N-cm. Axial and radial velocities were evaluated one mm downstream of the cathode at several locations across the width of the annular acceleration channel. Radial velocities varied linearly with radial distance. A maximum radial velocity of 7500 m/s was measured 8 mm from the center of the channel. Axial velocities as large as 16,500 m/s were measured.

Manzella, David H.

1994-01-01

360

High-resolution optical spectroscopy of the R Coronae Borealis star V532 Ophiuchi at maximum light  

E-print Network

High-resolution optical spectra of the R Coronae Borealis (RCB) star V532 Oph at light maximum are discussed. The absolute visual magnitude M_V of the star is found to be -4.9 \\pm 0.5. The elemental abundances suggest the star belongs to the majority class of RCB stars but is among the most O-poor of this class with mild enhancements of heavy elements Y, Zr, Ba and La. The C_2 Swan bands are weak in V532 Oph relative to R CrB. Other aspects of the high-resolution spectrum confirm that V532 Oph is representative of majority RCBs, i.e., the radial velocity is variable, circumstellar material is present and the photosphere feeds a high-velocity stellar wind.

Rao, N Kameswara; Woolf, Vincent M; Hema, B P

2014-01-01

361

A modification of the method of Carey and Sparks (1986) to estimate eruption column height from maximum clast dispersal  

NASA Astrophysics Data System (ADS)

The method of Carey and Sparks (1986) has been widely applied to estimate the hight of eruptive columns from the dispersal of the maximum clast size. These authors presented curves of maximum downwind range versus crosswind range for different clast diameters and wind speeds obtained from the numerical solution of a column model developed by Sparks(1986). An improved model of eruptive column was later developed by Woods (1988). In this work we present the results of the simulation of clast dispersal following the procedure of Carey and Sparks (1986) and the eruption column of Woods (1988). The numerical calculations were carried out with a code that computes the height of the column and the vertical velocity, the density and the radius along the column. The code determines then the support envelopes for a given clast size and their fall, after leaving the column, are computed from the equations of motion with viscous friction. For the same downwind and crosswind ranges, this method yields column heights about 10% smaller than the method of Carey and Sparks and about 20% higher wind velocities. The height of the crater above sea level plays also a small role in the results. We present comparisons for the 1982 eruption columns from El Chichon volcano. References Carey S and RSJ Sparks (1986) Bull. Volcanol. 48: 109-125 Sparks RSJ (1986) Bull. Volcanol. 48: 3-15 Woods AW (1988) Bull. Volcanol. 50: 169-193

Espindola, J.

2010-12-01

362

Direct numerical simulation of a turbulent wind over a wavy water surface  

NASA Astrophysics Data System (ADS)

Parameterization of the wind-water-waves interaction is a key problem of the air-sea system modeling. Of most importance are water waves with sufficiently large steepness, when nonlinear effects related to the boundary layer separation and vortex generation in the wind flow are well pronounced. Known experimental techniques (contact methods and particle image velocimetry) are not yet able to provide a full, detailed understanding of the wind flow in the viscous sublayer and the buffer region. As an alternative, we consider direct numerical simulations (DNS). In the present paper we discuss numerical algorithm and results of DNS of a turbulent wind flow over a wavy water surface. Waves with maximum steepness of ka = 0.2, wave age 0 < c/u* < 10, and Reynolds number Re = 15,000 are considered. Full, 3-D Navier-Stokes equations are solved in curvilinear coordinates in a reference frame moving with the wave phase speed c. DNS results show that an instantaneous velocity field is characterized by the presence of well-pronounced separation zones in the vicinity of the wave crests whereas the average velocity field is nonseparating. We also perform a comparison of the DNS results with the predictions of a theoretical quasi-linear model of the wind-wave interaction.

Druzhinin, O. A.; Troitskaya, Y. I.; Zilitinkevich, S. S.

2012-11-01

363

Winds in R Coronae Borealis Stars  

E-print Network

We present new spectroscopic observations of the He I $\\lambda$10830 line in R Coronae Borealis (RCB) stars which provide the first strong evidence that most, if not all, RCB stars have winds. It has long been suggested that when dust forms around an RCB star, radiation pressure accelerates the dust away from the star, dragging the gas along with it. The new spectra show that nine of the ten stars observed have P-Cygni or asymmetric blue-shifted profiles in the He I $\\lambda$10830 line. In all cases, the He I line indicates a mass outflow - with a range of intensity and velocity. Around the RCB stars, it is likely that this state is populated by collisional excitation rather than photoionization/recombination. The line profiles have been modeled with an SEI code to derive the optical depth and the velocity field of the helium gas. The results show that the typical RCB wind has a steep acceleration with a terminal velocity of \\Vinf = 200-350 \\kms and a column density of N $\\sim10^{12}$ cm$^{-2}$ in the He I $\\lambda$10830 line. There is a possible relationship between the lightcurve of an RCB star and its He I $\\lambda$10830 profile. Stars which have gone hundreds of days with no dust-formation episodes tend to have weaker He I features. The unusual RCB star, V854 Cen, does not follow this trend, showing little or no He I absorption despite high mass-loss activity. The He I $\\lambda$10830 line in R CrB itself, which has been observed at four epochs between 1978 and 2001, seems to show a P-Cygni or asymmetric blue-shifted profile at all times whether it is in decline or at maximum light.

Geoffrey C. Clayton; T. R. Geballe; Luciana Bianchi

2003-06-04

364

Insights from coordinated observations of neutral winds and equatorial plasma bubbles  

NASA Astrophysics Data System (ADS)

Installed in northeastern Brazil in 2009, the Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) comprises a suite of instruments to study the low-latitude ionosphere/thermosphere system. Two Fabry-Perot interferometers (FPIs) provide estimates of vector horizontal neutral winds in addition to the neutral temperature at an altitude of approximately 250 km. A wide-angle imaging system provides two-dimensional images of ionospheric structure, specifically equatorial plasma bubbles (EPBs). Finally, several Global Positioning System (GPS) receivers provide estimates of the background total electron content and scintillation environment imposed by these bubbles. We present results from the first three years of this experiment detailing the climatology of the neutral winds and temperatures during the transition from the deep solar minimum of 2008 towards the impending solar maximum. Furthermore, we discuss the coupling between the thermosphere and ionosphere through a coordinated analysis of neutral winds and the drift velocity of EPBs.

Makela, Jonathan J.; Meriwether, John; Buriti, Ricardo; Chapagain, Narayan; Fisher, Daniel

2012-07-01

365

Wind profile perturbation analysis for STS  

NASA Technical Reports Server (NTRS)

Two case studies of the relationship between STS ascent structural loads and wind profile characteristics are described. In the first case study, a wind profile with relatively weak winds is used to demonstrate the importance of launch vehicle velocity relative to the air and its effect on loads. In the second study, a pair of wind profiles is used to show how the determination of load exceedances is strongly influenced by the wind load persistence allowances for the baseline and two day-of-launch (DOL) steering commands called I-LOADs. Characteristics of the wind profiles and associated trajectory variable and wind-sensitive load indicators are examined. Energy spectra of in-plane and out-of-plane wind component and a load indicator are presented. An analysis of load indicator sensitivity to wind perturbation energy in the 1600-6400 m wavelength band for baseline and DOL I-LOAD is described.

Adelfang, S. I.; Smith, O. E.; Whitehead, D. S.

1991-01-01

366

Maximum Power Point  

NSDL National Science Digital Library

Students learn how to find the maximum power point (MPP) of a photovoltaic (PV) panel in order to optimize its efficiency at creating solar power. They also learn about real-world applications and technologies that use this technique, as well as Ohm's law and the power equation, which govern a PV panel's ability to produce power.

Integrated Teaching And Learning Program

367

Maximum Tolerated Dose Studies  

Microsoft Academic Search

A three-stage maximum repeatable dose (MRD) protocol is described in which the MRD is established by dose incrementation, followed by administration of this dose for at least seven days, with the final stage being single dose administration of the doses anticipated for the one-month studies. The toxicokinetic measurements which are made in support of this protocol are illustrated with data

P. F. Carey; N. W. Spurling

1994-01-01

368

MF radar observations of meteors and meteor-derived winds at Syowa (69°S, 39°E), Antarctica: A comparison with simultaneous spaced antenna winds  

NASA Astrophysics Data System (ADS)

The first results of long-term meteor observations made with Syowa MF radar (69°S, 39°E), Antarctica, are presented. In winter, meteor wind measurements can be conducted throughout the day without being severely affected by group retardation or total reflection, while in summer the observations are confined within several hours around 0000 local time (LT). Daily meteor echo rates (roughly 300-1000) are clearly anticorrelated with local K indices, indicating that the observations mostly represent geomagnetically quiet conditions. Echoes are distributed from around 80 km to 120 km, with the peak altitude at around 100 km. The maximum height is set by the relatively slow sampling frequency employed (5 Hz) and is expected to be extended by using a higher frequency. Meteor and full correlation analysis (FCA) winds in winter months are compared. They agree well at around 90 km, while the FCA winds tend to underestimate the meteor winds at upper altitudes. A notable finding is that the directions of wind velocities can also be different. The FCA winds show less height variations above about 90 km and it appears as though the FCA heights are overestimated. A case study of angles of arrival estimated from MF echoes suggests a possibility that meteor echoes contaminate ionospheric echoes down to as low as 80 km. However, quantitative evaluation of meteor contamination effects, if any, on FCA wind velocities has not been done yet and remains a future topic to be studied. Other sources which cause the differences should also be sought. The remarkably wide height coverage of the present MF radar observations (from around 60 to nearly 120 km) using both FCA and meteor techniques simultaneously will greatly contribute to polar mesosphere and lower thermosphere study.

Tsutsumi, M.; Aso, T.

2005-12-01

369

Solar wind composition  

NASA Technical Reports Server (NTRS)

Advances in instrumentation have resulted in the determination of the average abundances of He, C, N, O, Ne, Mg, Si, S, and Fe in the solar wind to approximately 10%. Comparisons with solar energetic particle (SEP) abundances and galactic cosmic ray abundances have revealed many similarities, especially when compared with solar photospheric abundances. It is now well established that fractionation in the corona results in an overabundance (with respect to the photosphere) of elements with first ionization potentials less than 10 eV. These observations have in turn led to the development of fractionation models that are reasonably successful in reproducing the first ionization (FIP) effect. Under some circumstances it has been possible to relate solar wind observations to particular source regions in the corona. The magnetic topologies of the source regions appear to have a strong influence on the fractionation of elements. Comparisons with spectroscopic data are particularly useful in classifying the different topologies. Ions produced from interstellar neutral atoms are also found in the solar wind. These ions are picked up by the solar wind after ionization by solar radiation or charge exchange and can be identified by their velocity in the solar wind. The pick-up ions provide most of the pressure in the interplanetary medium at large distances. Interstellar abundances can be derived from the observed fluxes of solar wind pick-up ions.

Ogilvie, K. W.; Coplan, M. A.

1995-01-01

370

Observing Equatorial Thermospheric Winds and Temperatures with a New Mapping Technique  

NASA Astrophysics Data System (ADS)

Application of the Fabry-Perot interferometer (FPI) at Arequipa, Peru (16.4S, 71.4 W) to measure the Doppler shifts and Doppler broadenings in the equatorial O(1D) 630-nm nightglow has resulted in numerous detections of a large-scale thermospheric phenomenon called the Midnight Temperature Maximum (MTM). A recent detector upgrade with a CCD camera has improved the accuracy of these measurements by a factor of 5. Temperature increases of 50 to 150K have been measured during nights in April and July, 2005, with error bars less than 10K after averaging in all directions. Moreover, the meridional wind measurements show evidence for a flow reversal from equatorward to poleward near local midnight for such events. A new observing strategy based upon the pioneering work of Burnside et al.[1981] maps the equatorial wind and temperature fields by observing in eight equally-spaced azimuth directions, each with a zenith angle of 60 degrees. Analysis of the data obtained with this technique gives the mean wind velocities in the meridional and zonal directions as well as the horizontal gradients of the wind field for these directions. Significant horizontal wind gradients are found for the meridional direction but not for the zonal direction. The zonal wind blows eastward throughout the night with a maximum speed of ~150 m/s near the middle of the night and then decreases towards zero just before dawn. In general, the fastest poleward meridional wind is observed near mid-evening. By the end of the night, the meridional flow tends to be more equatorward at speeds of about 50 m/s. Using the assumption that local time and longitude are equivalent over a period of 30 minutes, a map of the horizontal wind field vector field is constructed over a range of 12 degrees latitude centered at 16.5 S. Comparison between MTM nights and quiet nights (no MTM) revealed significant differences in the horizontal wind fields. Using the method of Fourier decomposition of the line-of-sight winds, the vertical wind can be retrieved from the horizontal flow divergence with a much-improved sensitivity than that represented by direct zenith measurements. The value of the vertical wind speed ranges from -5 to 5 m/s. Some nights seem to present gravity wave activity with periodic fluctuations of 1-2 hours visible in the vertical winds as well as in the temperature series.

Faivre, M. W.; Meriwether, J. W.; Sherwood, P.; Veliz, O.

2005-12-01

371

Investigation of the maximum load alleviation potential using trailing edge flaps controlled by inflow data  

NASA Astrophysics Data System (ADS)

The maximum fatigue load reduction potential when using trailing edge flaps on mega-watt wind turbines was explored. For this purpose an ideal feed forward control algorithm using the relative velocity and angle of attack at the blade to control the loads was implemented. The algorithm was applied to time series from computations with the aeroelastic code HAWC2 and to measured time series. The fatigue loads could be reduced by 36% in the computations if the inflow sensor was at the same position as the blade load. The decrease of the load reduction potential when the sensor was at a distance from the blade load location was investigated. When the algorithm was applied to measured time series a load reduction of 23% was achieved which is still promissing, but significantly lower than the value achieved in computations.

Fischer, A.; Madsen, H. A.

2014-12-01

372

Solar Wind Electrons  

Microsoft Academic Search

Average characteristics of solar wind electron velocity distributions as well as the range and nature of their variations are presented. The measured distributions are generally symmetric about the heat flux direction and are adequately parameterized by the superposition of a nearly bi-Maxwellian function which characterizes the low-energy electrons and a bi-Maxwellian function which characterizes a distinct, ubiquitous component of higher-energy

W. C. Feldman; J. R. Asbridge; S. J. Bame; M. D. Montgomery; S. P. Gary

1975-01-01

373

Neural network based wind speed sensorless MPPT controller for variable speed wind energy conversion systems  

Microsoft Academic Search

A wind speed sensorless neural network (NN) based maximum power point tracking (MPPT) control algorithm for variable speed wind energy conversion system (WECS) is proposed. The proposed method is developed using Jordan type recurrent NN which is trained online using back-propagation. The algorithm, without requiring the knowledge of wind speed, air density or turbine parameters, generates at its output the

J. S. Thongam; P. Bouchard; R. Beguenane; I. Fofana

2010-01-01

374

Effects of wind direction and wind farm layout on turbine wakes and power losses in wind farms: An LES study  

NASA Astrophysics Data System (ADS)

A recently-developed large-eddy simulation (LES) framework is validated and used to investigate the effects of wind direction and wind farm layout on the turbine wakes and power losses in wind farms. The subgrid-scale (SGS) turbulent stress is parameterized using a tuning-free Lagrangian scale-dependent dynamic SGS model. The turbine-induced forces are computed using a dynamic actuator-disk model with rotation (ADM-R), which couples blade-element theory with a turbine-specific relation between the blade angular velocity and the shaft torque to compute simultaneously turbine angular velocity and power output. Here, we choose the Horns Rev offshore wind farm as a case study for model validation. A series of simulations are performed for a wide range of wind direction angles. Results from the simulations are in good agreement with observed power data from the Horns Rev wind farm, and show a strong impact of wind direction on the farm power production and the spatial distribution of turbine-wake characteristics (e.g., velocity deficit and turbulence intensity). This can be explained by the fact that changing the wind angle can be viewed as changing the wind farm layout relative to the incoming wind, while keeping the same wind turbine density. To further investigate the effect of wind farm layout on the flow and the power extracted by the farm, simulations of wind farms with different circular and elliptic layouts are performed to compare with the results of the Horns Rev wind farm simulations. The results show that the proposed layouts not only provide more stable power output with different wind directions, but also enhance the performance of the total farm power production.

Wu, Yu-Ting; Porté-Agel, Fernando

2014-05-01

375

A laboratory study of friction-velocity estimates from scatterometry - Low and high regimes  

NASA Technical Reports Server (NTRS)

Measurements from scatterometers pointing at wind-waves in three large wave tanks are examined to study fetch effects and the correlation with wind friction velocity. Time-series measurements were made at 13, 35, and 95 m with a Ka-band scatterometer aimed upwind at 30 deg incidence angle and vertical polarization. Average normalized radar cross-section (sigma-0) values from all fetches follow a common trend for sigma-0 as a function of wind friction velocity, so the fetch dependence is negligible. An empirical power-law model yields a high correlation between sigma-0 and wind friction velocity, but, because systematic anomalies arise, we reexamine a turbulence approach that delineates low and high regimes with a transition at a wind friction velocity of approximately 25 cm/s. Using this criteria, the data are well represented by a two-section power-law relationship between sigma-0 and wind friction velocity.

Bliven, L. F.; Giovanangeli, J.-P.; Wanninkhof, R. H.; Chapron, B.

1993-01-01

376

Question of the Day: Flow of Winds and Moisture  

NSDL National Science Digital Library

This activity addresses the flow of surface winds and moisture. On the figure below, draw a)direction of air flow (winds), b) locations with highest evaporation from the sea surface, and zone(s) of maximum ...

377

A wind energy analysis of Grenada: an estimation using the ‘Weibull’ density function  

Microsoft Academic Search

The Weibull density function has been used to estimate the wind energy potential in Grenada, West Indies. Based on historic recordings of mean hourly wind velocity this analysis shows the importance to incorporate the variation in wind energy potential during diurnal cycles. Wind energy assessments that are based on Weibull distribution using average daily\\/seasonal wind speeds fail to acknowledge that

D Weisser

2003-01-01

378

Wind power assessment  

NASA Astrophysics Data System (ADS)

A wind energy study of the East and Gulf coastal regions of the United States is being carried out at the University of Virginia under the direction of Michael Garstang and Roger A. Pielke. The Chesapeake Bay area, because of its complex coastline configuration, is one of three East and Gulf coastal areas which have been chosen for intensive study. A three-dimensional computer model and a field observational program have been executed for the Chesapeake Bay area.Baroclinic factors, the result of land-sea temperature differences and changes in aerodynamic roughness between land and sea, are known to generate local wind circulations over and near coastlines. The complexities of coastline configuration of the Chesapeake Bay and offshore islands result in an interaction between the large-scale wind fields and the locally induced circulations. These interactions produce regions of persistently high and low wind speeds near the surface, and these wind speeds can be reproduced numerically (see cover, EOS, December 11, 1979). A conspicuous and persistent feature of wintertime model predictions of the wind power distribution in the Chesapeake Bay area is the landward minimum-seaward maximum shown in Figure 1.

Snow, J. W.; Garstang, M.

379

Toasty Wind  

NSDL National Science Digital Library

In this quick activity, learners use a toaster to investigate the source for the Earth's wind. Learners hold a pinwheel above a toaster to discover that rising heat causes wind. Use this activity to introduce learners to the process of convection as a source for wind. This resource also explains how convection causes thunderstorms and lists important thunderstorm safety tips.

Service, National W.

2012-07-24

380

A correlative study of simultaneously measured He(++) fluxes in the solar wind and in the magnetosphere utilizing Imp-1 and 1971-089A satellite data  

NASA Technical Reports Server (NTRS)

Simultaneously measured He(++) fluxes in the solar wind and in the magnetosphere were studied using data from the plasma spectrometer on the Imp I satellite and the energetic ion mass spectrometer on the low altitude polar orbiting satellite 1971-89A. A detailed comparison of the He(++) energy spectra measured simultaneously in the solar wind and in the low altitude dayside polar cusp on March 7, 1972 was made. The energy-per-unit-charge range of the energetic ion mass spectrometer on board the polar orbiting satellite was 700 eV to 12 keV. Within this range there was a clear maximum in the He(++) energy spectrum at approximately 1.5 keV/nucleon. There was not a clearly defined maximum in the H(+) spectrum, but the data were consistent with a peak between 0.7 and 1.0 keV/nucleon. Both spectra could be reasonably well fit with a convecting Maxwellian plus a high energy tail; however, the mean velocity for He(++) distribution was significantly greater than that for the H(+) distribution. The simultaneous solar wind measurements showed the mean velocities for both ion species to be approximately 600 km/sec. The discrepancies between the relative velocity distributions in the low altitude cusp and those in the solar wind are consistent with a potential difference of approximately 1.4 kV along their flow direction between the two points of observation.

Shelley, E. G.

1975-01-01

381

Solar wind driving of dayside field-aligned currents  

NASA Astrophysics Data System (ADS)

Variations in the dayside field-aligned current (FAC) density (J//), field-aligned parallel potential drop (?$\\phi$//), peak precipitating electron energy (peak Ee), and precipitating electron energy flux ($\\varepsilon$) as functions of solar wind (SW) and interplanetary magnetic field (IMF) are investigated with Defense Meteorological Satellite Program observations and a quasi-stationary low-latitude boundary layer (LLBL)-FAC coupling model. Region 1 (R1) J// responses to variations in SW velocity (Vsw) and density (nsw) at 8-16 magnetic local time (MLT) suggest that R1 at these local times is frequently open while R1 at 6-08 and 17-18 MLT is frequently closed. R2 is located mostly on closed field lines. In the afternoon open R1 at 12-16 MLT, an increase in nsw increases J//, decreases maximum peak Ee (proxy for ?$\\phi$//), but has little effect on maximum $\\varepsilon$. In the same R1 region, an increase in Vsw increases J//, maximum peak Ee, and maximum $\\varepsilon$. The dependencies of J//, maximum peak Ee, and maximum $\\varepsilon$ are consistent with the Knight relation and the voltage generator at the magnetopause boundary in the afternoon open R1. In the midmorning and midafternoon, the response of J// to Vsw is higher for southward than for northward IMF. This can be attributed to the higher-velocity shear at the magnetopause boundary due to higher sunward convection in the LLBL inside the magnetopause. R1 in the closed-field lines near dawn and dusk appears to be more sensitive to merging rate (d?/dt = Vsw4/3 BT2/3 sin8/3($\\theta$c/2)) than to SW dynamic pressure.

Wing, Simon; Ohtani, Shin-ichi; Johnson, Jay R.; Echim, Marius; Newell, Patrick T.; Higuchi, Tomoyuki; Ueno, Genta; Wilson, Gordon R.

2011-08-01

382

RAWS: The spaceborne radar wind sounder  

NASA Astrophysics Data System (ADS)

The concept of the Radar Wind Sounder (RAWS) is discussed. The goals of the RAWS is to estimate the following three qualities: the echo power, to determine rain rate and surface wind velocity; the mean Doppler frequency, to determine the wind velocity in hydrometers; and the spread of the Doppler frequency, to determine the turbulent spread of the wind velocity. Researchers made significant progress during the first year. The feasibility of the concept seems certain. Studies indicate that a reasonably sized system can measure in the presence of ice clouds and dense water clouds. No sensitivity problems exist in rainy environments. More research is needed on the application of the radar to the measurement of rain rates and winds at the sea surface.

Moore, Richard K.

1991-09-01

383

RAWS: The spaceborne radar wind sounder  

NASA Technical Reports Server (NTRS)

The concept of the Radar Wind Sounder (RAWS) is discussed. The goals of the RAWS is to estimate the following three qualities: the echo power, to determine rain rate and surface wind velocity; the mean Doppler frequency, to determine the wind velocity in hydrometers; and the spread of the Doppler frequency, to determine the turbulent spread of the wind velocity. Researchers made significant progress during the first year. The feasibility of the concept seems certain. Studies indicate that a reasonably sized system can measure in the presence of ice clouds and dense water clouds. No sensitivity problems exist in rainy environments. More research is needed on the application of the radar to the measurement of rain rates and winds at the sea surface.

Moore, Richard K.

1991-01-01

384

The Stellar Wind of MWC 349A  

NASA Astrophysics Data System (ADS)

The radial velocities of radio recombination lines from 15 to 20,000 GHz facilitate a kinematic probe of the stellar wind (outflow) from MWC 349A. These data and an earlier fit to the free-free continuum emission determine the radial velocity of the stellar wind out to more than 100 AU. The derived gas flow fits a ``beta law'' with ?=6 and a terminal velocity of 32 km s-1. The derived mass loss via the wind is about 4×10-6Msolar yr-1 at a radius of 50 AU from the star, comparable to the value derived earlier by Cohen et al. by modeling an image of the 5 GHz emission observed with the Very Large Array. This outflow could also be the evaporation from the circumstellar disk rather than a conventional stellar wind. The stellar recession velocity appears to be about 12 km s-1.

Gordon, M. A.

2003-06-01

385

Oscillations of the thermospheric wind during passage of the Large Scale Traveling Ionospheric Disturbances  

NASA Astrophysics Data System (ADS)

Amplitudes of thermospheric meridional wind velocity oscillations related with the passage of large-scale traveling ionospheric disturbances (LSTIDs) were derived from data of observations of the night ionospheric F2-layer. Observations were carried out at the Institute of Ionosphere (Almaty, 76° 55' E, 43° 15' N) in 2000 - 2007 by a digital ionosonde 'Parus'. Data processing allowed to obtain time variations in the electron density (Nh(t)) for series of fixed altitudes and variations of the F2-layer peak height (hmF) and the F2- layer bottom height (hbotF). We developed a technique for estimation of amplitudes of thermospheric wind oscillations by using parameters of oscillations of the hmF and hbotF . The distributions of LSTIDs periods, amplitudes (?hmF and ?hbotF) of variations of altitudes of the F2- layer peak and its bottom are presented for the disturbed and quiet geomagnetic fields. Periods are distributed in the range of 40 to 200 min with a maximum occurrence probability in the range of 60 to 140 min for conditions of the disturbed magnetic field and in the range of 80 to 160 min for the quiet field. Maximum occurrence probability for ?hmF lies in the range of 20 to 80 km for the disturbed magnetic field and in the range of 20 to 60 km for the quiet one. Results of calculating the amplitudes of oscillations of the thermospheric wind velocity at the F2- layer peak and bottom showed that they were distributed in the range of about 10 to 130 m/s with most probable values ??lying in the range of about 40 to 70 m/s. It was found that the average amplitudes of velocity oscillations at the F2- layer peak exceeded the average amplitudes at the F2- layer bottom by the value of ? 9.0 m/s. This excess appears to be due to the diffusion term contributing in the ion velocity along the magnetic field lines. On the heights of the F2- layer bottom located below about 300 km, this contribution is small and the technique allows deriving the true value of the oscillation amplitudes of the neutral wind velocity. On the heights of the F2- layer peak located usually above 300 km, this contribution becomes significant, and evaluation of the oscillation amplitudes of the thermospheric wind velocity are overstated by the value of the diffusion term.

Yakovets, Artur; Vodyannikov, Victor; Gordienko, Galina; Litvinov, Yuri

2014-05-01

386

The Solar Wind in the Outer Heliosphere at Solar John D. Richardson and Chi Wang  

E-print Network

The Solar Wind in the Outer Heliosphere at Solar Maximum John D. Richardson and Chi Wang Center solar wind observations in the outer heliosphere, concentrating on the recent data near solar maximum-absence of a latitudinal speed gradient at solar maximum allows us to measure the speed decrease of the solar wind and nd

Richardson, John

387

On the correlation between interplanetary nano dust particles and solar wind properties from STEREO/SWAVES  

NASA Astrophysics Data System (ADS)

Dust particles provide an important fraction of the matter composing the interplanetary medium, their mass density at 1 AU being comparable to the one of the solar wind. Among them, dusts of nanometer size-scale can be detected using radio and plasma waves instruments because they move at roughly the solar wind speed. The high velocity impact of a dust particle generates a small crater on the spacecraft: the dust particle and the crater material are vaporized. This produces a plasma cloud whose associated electrical charge induces an electric pulse measured with radio and plasma instruments. Since their first detection in the interplanetary medium (Meyer-Vernet et al. 2009), nanodusts have been routinely measured using STEREO/WAVES instrument (Zaslavsky et al. 2012) We present the nanodust properties during the 2007-2012 period on STEREO. Since the maximum size of the plasma cloud is larger for smaller local solar wind density, we expect to observe an anticorrelation between the detected voltage amplitude and the ambient solar wind density, as suggested recently by Le Chat et al. (2012). Moreover, the variations in solar wind speed and magnetic field are expected to affect the nano dust dynamics. Using STEREO/WAVES/Low Frequency Receiver (LFR) data, we study correlations of in situ solar wind properties and detection of nanodust impacts as well as some possible effects of Coronal Mass Ejections (CME) on nanodusts acceleration.

Issautier, K.; LE CHAT, G.; Meyer-Vernet, N.; Belheouane, S.; Zaslavsky, A.; Zouganelis, I.; Mann, I.; Maksimovic, M.

2012-12-01

388

Saltation transport rate in unsteady wind variations.  

PubMed

Wind flow in the atmospheric boundary layer is usually turbulent. The gusty wind significantly influences the saltation transport which is treated as equilibrium saltation. This study performs one-dimension numerical simulations of unsteady sand saltation to discuss the effects of parameters of periodical wind variations on saltation response and sand transport rate prediction. The results show that unsteady transport rates are larger than steady rates of equivalent mean wind velocity. The ratio of unsteady/steady transport rates increases with the increase of amplitude and frequency. For the average wind velocities much larger than the threshold value, the errors of transport rates predicted by unsteady and steady model are about 10%, while for a wind velocity slightly larger than saltation threshold, the errors will be more than 200%. The sand transport rates are not zero even though the average wind velocity equals (is even smaller than) the threshold value, whereas Q must be zero in the steady model. Finally, an unsteady transport rate prediction formula is proposed which takes mean velocity, fluctuating intensity and period as independent variables. PMID:24853633

Wang, Ping; Zheng, Xiaojing

2014-05-01

389

Airfoils for wind turbine  

DOEpatents

Airfoils are disclosed for the blade of a wind turbine wherein each airfoil is characterized by a thickness in a range from 16%-24% and a maximum lift coefficient designed to be largely insensitive to roughness effects. The airfoils include a family of airfoils for a blade 15 to 25 meters in length, a family of airfoils for a blade 1 to 5 meters in length, and a family of airfoils for a blade 5 to 10 meters in length. 10 figs.

Tangler, J.L.; Somers, D.M.

1996-10-08

390

Airfoils for wind turbine  

DOEpatents

Airfoils for the blade of a wind turbine wherein each airfoil is characterized by a thickness in a range from 16%-24% and a maximum lift coefficient designed to be largely insensitive to roughness effects. The airfoils include a family of airfoils for a blade 15 to 25 meters in length, a family of airfoils for a blade 1 to 5 meters in length, and a family of airfoils for a blade 5 to 10 meters in length.

Tangler, James L. (Boulder, CO); Somers, Dan M. (State College, PA)

1996-01-01

391

Ris R 1068EN Extreme Winds  

E-print Network

of the basic wind velocity which is de ned as the 50-year wind speed under standard conditions, i.e. ten the total 50-year extreme load on a general structure without symmetry in an inhomogeneous terrain west, Skjern 15 years, Kegn s 7 years, Sprog 20 years, and Tystofte 15 years. The data are ten minute

392

Load attenuating passively adaptive wind turbine blade  

Microsoft Academic Search

A method and apparatus for improving wind turbine performance by alleviating loads and controlling the rotor. The invention employs the use of a passively adaptive blade that senses the wind velocity or rotational speed, and accordingly modifies its aerodynamic configuration. The invention exploits the load mitigation prospects of a blade that twists toward feather as it bends. The invention includes

Paul S. Veers; Donald W. Lobitz

2003-01-01

393

Ris National Laboratory Wind Energy Department  

E-print Network

Risø National Laboratory Postprint Wind Energy Department Year 2007 Paper: www. The friction velocity is taken to decrease linearly through the boundary layer. The wind profile length scale is composed of three component length scales. In the surface layer the first length scale is taken to increase

394

Shipment and storage effects on the terminal velocity of seeds  

Microsoft Academic Search

Mechanistic models of seed dispersal by wind include terminal velocity as the main seed characteristic that influences the\\u000a dispersal process and hence the resulting dispersal kernels and spread rates. Accurate measurement of the terminal velocity\\u000a of seeds is therefore pivotal. However, compression during shipment through the post or during storage between collection\\u000a in the field and terminal velocity measurements in

Katherine M. Marchetto; Eelke Jongejans; Matthew L. Jennis; Emily M. Haner; Caitlin T. Sullivan; Dave Kelly; Katriona Shea

2010-01-01

395

Sea surface velocities from visible and infrared multispectral atmospheric mapping sensor imagery  

NASA Technical Reports Server (NTRS)

High resolution (100 m), sequential Multispectral Atmospheric Mapping Sensor (MAMS) images were used in a study to calculate advective surface velocities using the Maximum Cross Correlation (MCC) technique. Radiance and brightness temperature gradient magnitude images were formed from visible (0.48 microns) and infrared (11.12 microns) image pairs, respectively, of Chandeleur Sound, which is a shallow body of water northeast of the Mississippi delta, at 145546 GMT and 170701 GMT on 30 Mar. 1989. The gradient magnitude images enhanced the surface water feature boundaries, and a lower cutoff on the gradient magnitudes calculated allowed the undesirable sunglare and backscatter gradients in the visible images, and the water vapor absorption gradients in the infrared images, to be reduced in strength. Requiring high (greater than 0.4) maximum cross correlation coefficients and spatial coherence of the vector field aided in the selection of an optimal template size of 10 x 10 pixels (first image) and search limit of 20 pixels (second image) to use in the MCC technique. Use of these optimum input parameters to the MCC algorithm, and high correlation and spatial coherence filtering of the resulting velocity field from the MCC calculation yielded a clustered velocity distribution over the visible and infrared gradient images. The velocity field calculated from the visible gradient image pair agreed well with a subjective analysis of the motion, but the velocity field from the infrared gradient image pair did not. This was attributed to the changing shapes of the gradient features, their nonuniqueness, and large displacements relative to the mean distance between them. These problems implied a lower repeat time for the imagery was needed in order to improve the velocity field derived from gradient imagery. Suggestions are given for optimizing the repeat time of sequential imagery when using the MCC method for motion studies. Applying the MCC method to the infrared brightness temperature imagery yielded a velocity field which did agree with the subjective analysis of the motion and that derived from the visible gradient imagery. Differences between the visible and infrared derived velocities were 14.9 cm/s in speed and 56.7 degrees in direction. Both of these velocity fields also agreed well with the motion expected from considerations of the ocean bottom topography and wind and tidal forcing in the study area during the 2.175 hour time interval.

Pope, P. A.; Emery, W. J.; Radebaugh, M.

1992-01-01

396

Calculations of the cosmic ray modulation in interplanetary space taking into account the possible dependence of the transport travel for the scattering of the particles and of the velocity of the solar winds on the angles they make with the helioequator plane: The case of isotropic diffusion  

NASA Technical Reports Server (NTRS)

The modulation of galactic cosmic rays is studied by the magnetic heterogeneities stream on the assumption that the diffusion coefficient is reduced whereas the solar wind velocity is increased with the growth of the angle between the sun's rotation axis and the direction of solar plasma motion. The stationary plane problem of isotropic diffusion is solved as it applies to two cases: (1) with due account of particle retardation by the antiphermium mechanism; and (2) without an account of the above mechanism. This problem is solved by the grid method in the polar coordinate system. The results of the calculations are followed by a discussion of the method of solution and of the errors.

Dorman, L. I.; Kobilinski, Z.

1975-01-01

397

Far Ultraviolet Spectroscopic Explorer Snapshot Survey of O VI Variability in the Winds of 66 OB-Type Stars  

NASA Astrophysics Data System (ADS)

We have used the Far Ultraviolet Spectroscopic Explorer to conduct a snapshot survey of O VI variability in the winds of 66 OB-type stars in the Galaxy and the Magellanic Clouds. These time series consist of two or three observations separated by intervals ranging from a few days to several months. Although these time series provide the bare minimum of information required to detect variations, this survey demonstrates that the O VI doublet in the winds of OB-type stars is variable on various scales in both time and velocity. For spectral types from O3 to B1, 64% vary in time. At spectral types later than B1, no wind variability is observed. In view of the limitations of this survey, this fraction represents a lower limit on the true incidence of variability in the O VI wind lines, which is very common and probably ubiquitous. In contrast, for S IV and P V, only a small percentage of the whole sample shows wind variations, although this may be principally due to selection effects. The observed variations extend over several hundreds of kilometers per second of the wind profile and can be strong. The width over which the wind O VI profile varies is only weakly correlated with the terminal velocity (v?), but a significant correlation (close to a 1:1 relationship) is derived between the maximum velocity of the variation and v?. High-velocity O VI wind absorption features (possibly related to the discrete absorption components seen in other wind lines) are also observed in 46% of the cases for spectral types from O3 to B0.5. These features are variable, but the nature of their propagation cannot be determined from this survey. If X-rays can produce sufficient O VI by Auger ionization of O IV and the X-rays originate from strong shocks in the wind, this study suggests that stronger shocks occur more frequently near v?, causing an enhancement of O VI near v?.

Lehner, N.; Fullerton, A. W.; Massa, D.; Sembach, K. R.; Zsargó, J.

2003-05-01

398

A simplified prediction of droplet velocity distributions in a spray  

NASA Astrophysics Data System (ADS)

The coupled droplet size and velocity distribution in a spray has been predicted using the maximum entropy formalism and fundamental conservation constraints. The shape of the droplet size distribution is in good agreement with the Rosin-Rammler distribution. The distribution of velocity at any particular droplet size is Gaussian in shape. A simple drag model is used to propagate the distribution downstream through a gas field having a constant and uniform velocity. It shows that in the absence of turbulence and other disturbances, the velocity distributions collapse toward their means long before those mean velocities reach the gas-phase velocity.

Sellens, R. W.; Brzustowski, T. A.

1986-09-01

399

Control policies for wind-energy conversion systems  

Microsoft Academic Search

Wind energy is usually converted into electrical energy through a wind rotor driving a generator. It is well known that maximum conversion efficiency occurs when the wind rotor is loaded in such a way that its rotational speed is allowed to fluctuate in sympathy with wind-speed variations. In the paper, the wind-rotor\\/generator dynamics are investigated for a number of control

I. K. Buehring; L. L. Freris

1981-01-01

400

Cluster observations on linear magnetic decreases in the solar wind at 1 AU  

NASA Astrophysics Data System (ADS)

Magnetic decreases (MDs) are structures observed in interplanetary space with significant decreases in the magnetic field magnitude, of which the events with no or little change in the field direction are linear magnetic decreases (LMDs). Xiao et al., (2010) have reported that the geometrical shape of LMDs observed in the solar wind at 1 AU was consistent with rotational ellipsoid, and the occurrence rate was about 3.7 LMDs/d. It was found that not only the occurrence rate but also the geometrical shape of LMDs had no significant change from 0.72 AU to 1 AU in comparison with Zhang et al., (2008)'s results, which may infer that most of LMDs observed at 1 AU were formed and fully developed before 0.72 AU. Recently, we have focused on the magnetic field and plasma (e.g. ion density and velocity) characteristics of those LMD structures observed during the period of 2001 to 2009. Compared with the average solar wind condition, it is shown that the LMDs prefer to be observed in the region with relatively lower magnetic field magnitude, higher ion density, larger plasma ? (ratio of the thermal pressure to the magnetic pressure) and slower solar wind velocity. We also investigated the LMDs which located in the interplanetary coronal mass ejections (ICME) or the sheath of the ICME. It is found that the events related to ICMEs could account for more than 20% of LMDs during solar maximum. Therefore, the ICME should be an important source of the LMDs during the solar maximum. However, other mechanisms during the solar minimum may be more important, because the occurrence rate of LMDs during the solar minimum is higher than that of the solar maximum. We also calculate the propagation speed of the structures in the solar wind frame to infer the generation mechanism of these structures.

Xiao, T.; Shi, Q.; Tian, A.; Fu, S.; Pu, Z.; Zong, Q.; Sun, W.; Lucek, E. A.; Reme, H.

2013-12-01

401

"Velocities" in Quantum Mechanics  

E-print Network

The present paper deals with some kind of quantum ``velocity'' which is introduced by the method of hydrodynamical analogy. It is found that this ``velocity'' is in general irrotational, namely, a vorticity vanishes, and then a velocity potential must exist in quantum mechanics. In some elementary examples of stable systems we will see what the ``velocities'' are. In particular, the two-dimensional flows of these examples can be expressed by complex velocity potentials whose real and imaginary parts are the velocity potentials and stream functions, respectively.

Shimbori, T; Shimbori, Toshiki; Kobayashi, Tsunehiro

2000-01-01

402

"Velocities" in Quantum Mechanics  

E-print Network

The present paper deals with some kind of quantum ``velocity'' which is introduced by the method of hydrodynamical analogy. It is found that this ``velocity'' is in general irrotational, namely, a vorticity vanishes, and then a velocity potential must exist in quantum mechanics. In some elementary examples of stable systems we will see what the ``velocities'' are. In particular, the two-dimensional flows of these examples can be expressed by complex velocity potentials whose real and imaginary parts are the velocity potentials and stream functions, respectively.

Toshiki Shimbori; Tsunehiro Kobayashi

2000-04-21

403

Flatback airfoil wind tunnel experiment.  

SciTech Connect

A computational fluid dynamics study of thick wind turbine section shapes in the test section of the UC Davis wind tunnel at a chord Reynolds number of one million is presented. The goals of this study are to validate standard wind tunnel wall corrections for high solid blockage conditions and to reaffirm the favorable effect of a blunt trailing edge or flatback on the performance characteristics of a representative thick airfoil shape prior to building the wind tunnel models and conducting the experiment. The numerical simulations prove the standard wind tunnel corrections to be largely valid for the proposed test of 40% maximum thickness to chord ratio airfoils at a solid blockage ratio of 10%. Comparison of the computed lift characteristics of a sharp trailing edge baseline airfoil and derived flatback airfoils reaffirms the earlier observed trend of reduced sensitivity to surface contamination with increasing trailing edge thickness.

Mayda, Edward A. (University of California, Davis, CA); van Dam, C.P. (University of California, Davis, CA); Chao, David D. (University of California, Davis, CA); Berg, Dale E.

2008-04-01

404

Three-Dimensional Venturi Sensor for Measuring Extreme Winds  

NASA Technical Reports Server (NTRS)

A three-dimensional (3D) Venturi sensor is being developed as a compact, rugged means of measuring wind vectors having magnitudes of as much as 300 mph (134 m/s). This sensor also incorporates auxiliary sensors for measuring temperature from -40 to +120 F (-40 to +49 C), relative humidity from 0 to 100 percent, and atmospheric pressure from 846 to 1,084 millibar (85 to 108 kPa). Conventional cup-and-vane anemometers are highly susceptible to damage by both high wind forces and debris, due to their moving parts and large profiles. In addition, they exhibit slow recovery times contributing to an inaccurately high average-speed reading. Ultrasonic and hot-wire anemometers overcome some of the disadvantages of the cup and-vane anemometers, but they have other disadvantageous features, including limited dynamic range and susceptibility to errors caused by external acoustic noise and rain. In contrast, the novel 3D Venturi sensor is less vulnerable to wind damage because of its smaller profile and ruggedness. Since the sensor has no moving parts, it provides increased reliability and lower maintenance costs. It has faster response and recovery times to changing wind conditions than traditional systems. In addition, it offers wide dynamic range and is expected to be relatively insensitive to rain and acoustic energy. The Venturi effect in this sensor is achieved by the mirrored double-inflection curve, which is then rotated 360 to create the desired detection surfaces. The curve is optimized to provide a good balance of pressure difference between sensor ports and overall maximum fluid velocity while in the shape. Four posts are used to separate the two shapes, and their size and location were chosen to minimize effects on the pressure measurements. The 3D Venturi sensor has smart software algorithms to map the wind pressure exerted on the surfaces of the design. Using Bernoulli's equation, the speed of the wind is calculated from the differences among the pressure readings at the various ports. The direction of the wind is calculated from the spatial distribution and magnitude of the pressure readings. All of the pressure port sizes and locations have been optimized to minimize measurement errors and to reside in areas demonstrating a stable pressure reading proportional to the velocity range.

Zysko, Jan A.; Perotti, Jose M.; Amis, Christopher; Randazzo, John; Blalock, Norman; Eckhoff, Anthony

2003-01-01

405

Wind Generator  

NSDL National Science Digital Library

Windmills have been used for hundreds of years to collect energy from the wind in order to pump water, grind grain, and more recently generate electricity. There are many possible designs for the blades of a wind generator and engineers are always trying new ones. Design and test your own wind generator, then try to improve it by running a small electric motor connected to a voltage sensor.

Consortium, The C.

2012-05-21

406

Power curve control in micro wind turbine design  

Microsoft Academic Search

In this work, a micro wind turbine will be designed and built for a series of wind tunnel tests (rotor dynamics and Wind Turbine (WT) start-up velocity). Its design stems from an original numerical code, developed by the authors, based on the Blade Element Momentum (BEM) Theory.From classic design criteria, having evaluated all the geometric characteristics, an innovative methodology will

R. Lanzafame; M. Messina

2010-01-01

407

Modeling and controller design of a wind energy conversion system including a matrix converter  

NASA Astrophysics Data System (ADS)

In this thesis, a grid-connected wind-energy converter system including a matrix converter is proposed. The matrix converter, as a power electronic converter, is used to interface the induction generator with the grid and control the wind turbine shaft speed. At a given wind velocity, the mechanical power available from a wind turbine is a function of its shaft speed. Through the matrix converter, the terminal voltage and frequency of the induction generator is controlled, based on a constant V/f strategy, to adjust the turbine shaft speed and accordingly, control the active power injected into the grid to track maximum power for all wind velocities. The power factor at the interface with the grid is also controlled by the matrix converter to either ensure purely active power injection into the grid for optimal utilization of the installed wind turbine capacity or assist in regulation of voltage at the point of connection. Furthermore, the reactive power requirements of the induction generator are satisfied by the matrix converter to avoid use of self-excitation capacitors. The thesis addresses two dynamic models: a comprehensive dynamic model for a matrix converter and an overall dynamical model for the proposed wind turbine system. The developed matrix converter dynamic model is valid for both steady-state and transient analyses, and includes all required functions, i.e., control of the output voltage, output frequency, and input displacement power factor. The model is in the qdo reference frame for the matrix converter input and output voltage and current fundamental components. The validity of this model is confirmed by comparing the results obtained from the developed model and a simplified fundamental-frequency equivalent circuit-based model. In developing the overall dynamic model of the proposed wind turbine system, individual models of the mechanical aerodynamic conversion, drive train, matrix converter, and squirrel-cage induction generator are developed and combined to enable steady-state and transient simulations of the overall system. In addition, the constraint constant V/f strategy is included in the final dynamic model. The model is intended to be useful for controller design purposes. The dynamic behavior of the model is investigated by simulating the response of the overall model to step changes in selected input variables. Moreover, a linearized model of the system is developed at a typical operating point, and stability, controllability, and observability of the system are investigated. Two control design methods are adopted for the design of the closed-loop controller: a state-feedback controller and an output feedback controller. The state-feedback controller is designed based on the Linear Quadratic method. An observer block is used to estimate the states in the state-feedback controller. Two other controllers based on transfer-function techniques and output feedback are developed for the wind turbine system. Finally, a maximum power point tracking method, referred to as mechanical speed-sensorless power signal feedback, is developed for the wind turbine system under study to control the matrix converter control variables in order to capture the maximum wind energy without measuring the wind velocity or the turbine shaft speed.

Barakati, S. Masoud

408

Wind measurements by electromagnetic probes  

NASA Technical Reports Server (NTRS)

The emerging technology of electromagnetic probing of the atmosphere to measure winds used in a space vehicle ascent winds load calculations is presented. The frequency range, altitude, and resolution for the following probes are presented: lidars, microwave radars, and clear-air Doppler radars (popularly known as wind profilers). The electromagnetic probing of the atmosphere by clear-air radars and lasers is the new technology to supplement balloon-borne wind sensors used to determine ascent wind loads of space vehicles. The electromagnetic probes measure the wind velocity using the Doppler effect. This is the radar technology used in MSFC's Radar Wind Profiler, and is similar to the technology used in conventional Doppler systems except that the frequency is generally lower, antenna is bigger, and dwell time much longer. Designed for unattended and automated instrumentation in providing measurements of the wind in the troposphere, the profiler employs Doppler radar technology and is currently being put in operation at NASA Kennedy Space Center, Florida.

Susko, Michael

1988-01-01

409

A Comparison of Solar Wind Parameters from tExperiments on the IMP 8 and Wind Spacecraf  

E-print Network

A Comparison of Solar Wind Parameters from tExperiments on the IMP 8 and Wind Spacecraf A. J- ent show a velocity dependence not seen in the comparison of densi- M ties from the two MIT) solar wind nstrument on the IMP 8 uses a Faraday Cup sensor which looks out in the equatorial plane

Richardson, John

410

Midnight Temperature Maximum Observations Over Millstone Hill  

NASA Astrophysics Data System (ADS)

The thermospheric Midnight Temperature Maximum (MTM) is a large-scale neutral temperature anomaly usually observed at low latitudes. The magnitude of temperature enhancements during low-latitude MTM events is about 50-150 K and its occurrence is linked to poleward surges in an otherwise "quiescent" equatorward meridional flow. The MTM is also associated with the post-midnight brightness of 630 nm (redline) emission and the downward descent of the F-region plasma (midnight collapse). Recent experimental and modeling studies have indicated that MTM anomalies extend into mid-latitudes, although observational evidence of the mid-latitude MTM in the literature is limited to a single site in the Southern Hemisphere. In this paper, we present observations of Northern Hemisphere mid-latitude MTM in Faby-Perot Interferometer (FPI) redline data from Millstone Hill Observatory (42.6° N, 71.49° W). The FPI at Millstone Hill has been operating since April, 2010 and providing F-region night-time neutral winds and temperatures. We present case studies of post-midnight red-line temperature enhancements and correlated poleward surges in the meridional neutral winds.; An example of Millstone Hill redline temperature and neutral wind measurements during an MTM event.

Azeem, S. I.; Crowley, G.; Noto, J.; Kerr, R. B.; Kapali, S.; Riccobono, J.; Migliozzi, M.

2012-12-01

411

High-velocity penetrators  

Microsoft Academic Search

This paper summarizes the results of studies, coupled with a series of tests, that investigated rigid-body projectiles (penetrators) at high (up to 5500 ft\\/sec) velocities. Before these studies, it had been hypothesized that a velocity limit would be reached at which increasing the velocity would not commensurately increase depth of penetration into a target. It was further inferred that a

Ronald G. Lundgren

1994-01-01

412

Initial drop size and velocity distributions for airblast coaxial atomizers  

NASA Technical Reports Server (NTRS)

Phase Doppler measurements were used to determine initial drop size and velocity distributions after a complete disintegration of coaxial liquid jets. The Sauter mean diameter (SMD) distribution was found to be strongly affected by the structure and behavior of the preceding liquid intact jet. The axial measurement stations were determined from the photographs of the coaxial liquid jet at very short distances (1-2 mm) downstream of the observed break-up locations. Minimum droplet mean velocities were found at the center, and maximum velocities were near the spray boundary. Size-velocity correlations show that the velocity of larger drops did not change with drop size. Drop rms velocity distributions have double peaks whose radial positions coincide with the maximum mean velocity gradients.

Eroglu, H.; Chigier, N.

1991-01-01

413

Constraints on Deep-seated Zonal Winds Inside Jupiter and Saturn  

E-print Network

The atmospheres of Jupiter and Saturn exhibit strong and stable zonal winds. How deep the winds penetrate unabated into each planet is unknown. Our investigation favors shallow winds. It consists of two parts. The first part makes use of an Ohmic constraint; Ohmic dissipation associated with the planet's magnetic field cannot exceed the planet's net luminosity. Application to Jupiter (J) and Saturn (S) shows that the observed zonal winds cannot penetrate below a depth at which the electrical conductivity is about six orders of magnitude smaller than its value at the molecular-metallic transition. Measured values of the electrical conductivity of molecular hydrogen yield radii of maximum penetration of 0.96R_J and 0.86R_S, with uncertainties of a few percent of R. At these radii, the magnetic Reynolds number based on the zonal wind velocity and the scale height of the magnetic diffusivity is of order unity. These limits are insensitive to difficulties in modeling turbulent convection. They permit complete penetration along cylinders of the equatorial jets observed in the atmospheres of Jupiter and Saturn. The second part investigates how deep the observed zonal winds actually do penetrate. Truncation of the winds in the planet's convective envelope would involve breaking the Taylor-Proudman constraint on cylindrical flow. This would require a suitable nonpotential acceleration which none of the obvious candidates appears able to provide. Accelerations arising from entropy gradients, magnetic stresses, and Reynolds stresses appear to be much too weak. These considerations suggest that strong zonal winds are confined to shallow, stably stratified layers, with equatorial jets being the possible exception.

Junjun Liu; Peter Goldreich; David Stevenson

2007-11-25

414

Forecastability as a Design Criterion in Wind Resource Assessment: Preprint  

SciTech Connect

This paper proposes a methodology to include the wind power forecasting ability, or 'forecastability,' of a site as a design criterion in wind resource assessment and wind power plant design stages. The Unrestricted Wind Farm Layout Optimization (UWFLO) methodology is adopted to maximize the capacity factor of a wind power plant. The 1-hour-ahead persistence wind power forecasting method is used to characterize the forecastability of a potential wind power plant, thereby partially quantifying the integration cost. A trade-off between the maximum capacity factor and the forecastability is investigated.

Zhang, J.; Hodge, B. M.

2014-04-01

415

Dust particle velocity measurement  

NASA Technical Reports Server (NTRS)

A laser Doppler velocimeter was used to measure the velocity distributions for particles entering a vacuum chamber from the atmosphere through calibrated leaks. The relative number of particles per velocity interval was obtained for particulates of three size distributions and two densities passing through six different leak geometries. The velocity range 15 to 320 meters per second was investigated. Peak particle velocities were found to occur in the 15 to 150 meters per second range depending upon type of particle and leak geometry. A small fraction of the particles were found to have velocities in the 150 to 320 meters per second range.

Thielman, L. O.

1976-01-01

416

Meteorology (Wind)  

... is in each range (0-2, 3-6, 7-10, 11-14, 15-18, 19-25 m/s).   Wind Speed at 50 m at 3-hourly intervals (m/s)   ... be adjusted to heights from 10 to 300 meters using the Gipe power law. Wind speeds may be adjusted for different terrain by selecting from ...

2014-09-25

417

Wind energy  

Microsoft Academic Search

General resources of wind energy are evaluated, and its main applications are considered, such as conversion into electricity and heat, hydrogen production, and irrigation, along with the associated problem of long-term energy storage. The basic principles of windmill system design and favorable location selection are outlined. The environmental impact of the windmill systems is discussed. It is noted that wind

B. Sorensen

1976-01-01

418

Sea surface wind stress in stratified atmospheric flow  

SciTech Connect

The paper presents the wind shear stress on the sea surface as well as the velocity profile in stably stratified atmospheric boundary layer flow over wind waves by using similarity theory. For a given geostrophic velocity, Coriolis parameter, spectral peak period and stratification parameter the sea surface shear stress is determined. Further, the direction of the sea surface shear stress and the velocity profile are given. Parameterizations of the results are also presented. Finally, the engineering relevance of the results is discussed.

Myrhaug, D. [Norwegian Univ. of Science and Technology, Trondheim (Norway). Dept. of Marine Hydrodynamics; Slaattelid, O.H. [Norwegian Marine Technology Research Inst., Trondheim (Norway)

1996-12-31

419

Splash of a waterdrop at terminal velocity.  

PubMed

High-speed movies of splash formation caused by waterdrop impact at terminal velocity in thin water layers show that splash size increases with drop size. For increasing water depth, splash size increases to a maximum at a depth of one-third drop diameter; splash size then decreases to a constant size for depths greater than three drop diameters. PMID:17772517

Mutchler, C K; Hansen, L M

1970-09-25

420

Discovery of Multiple High-Velocity Narrow Circumstellar NaI D Lines in Nova V1280 Sco  

NASA Astrophysics Data System (ADS)

We discovered multiple high-velocity (ranging from -900 to -650 km s-1) and narrow (FWHM ˜ 15 km s-1) absorption components corresponding to both the D2 and the D1 lines of NaI on a high-dispersion spectrum of V1280 Sco, observed on 2009 May 9 (UT), 814d after the V band maximum. Subsequent observations carried out on 2009 June and July confirmed at least 11 distinct absorption components in both systems. Some components had deepened during the two-month period while their HWHMs and wavelengths remained nearly constant. We suggest that these high-velocity components originated in cool clumpy gas clouds moving on the line-of-sight, produced during interactions between pre-existing cool circumstellar gas and high-velocity gas ejected in the nova explosion. The optical region spectrum of V1280 Sco in 2009 is dominated by the continuum radiation, and exhibits no forbidden line characterizing the nebular phase of typical novae. Permitted FeII lines show doubly peaked emission profiles, and some strong FeII lines are accompanied by a blue-shifted (˜-255 km s-1) absorption component. However, no high-velocity and narrow components corresponding to those of NaI could be detected in FeII lines nor in the Balmer lines. The 255km s-1 low-velocity absorption component most probably originates in the wind from the nova.

Sadakane, Kozo; Tajitsu, Akito; Mizoguchi, Sahori; Arai, Akira; Naito, Hiroyuki

2010-02-01

421

The prototype colliding-wind pinwheel WR 104  

E-print Network

Results from the most extensive study of the time-evolving dust structure around the prototype "Pinwheel" nebula WR 104 are presented. Encompassing 11 epochs in three near-infrared filter bandpasses, a homogeneous imaging data set spanning more than 6 years (or 10 orbits) is presented. Data were obtained from the highly successful Keck Aperture Masking Experiment, which can recover high fidelity images at extremely high angular resolutions, revealing the geometry of the plume with unprecedented precision. Inferred properties for the (unresolved) underlying binary and wind system are orbital period 241.5 +/- 0.5 days and angular outflow velocity of 0.28 +/- 0.02 mas/day. An optically thin cavity of angular size 13.3 +/- 1.4 mas was found to lie between the central binary and the onset of the spiral dust plume. Rotational motion of the wind system induced by the binary orbit is found to have important ramifications: entanglement of the winds results in strong shock activity far downstream from the nose of the bowshock. The far greater fraction of the winds participating in the collision may play a key role in gas compression and the nucleation of dust at large radii from the central binary and shock stagnation point. Investigation of the effects of radiative braking pointed towards significant modifications of the simple hydrostatic colliding wind geometry, extending the relevance of this phenomena to wider binary systems than previously considered. Limits placed on the maximum allowed orbital eccentricity of e < 0.06 argue strongly for a prehistory of tidal circularization in this system. Finally we discuss the implications of Earth's polar (i < 16 deg) vantage point onto a system likely to host supernova explosions at future epochs.

Peter Tuthill; John Monnier; Nicholas Lawrance; William Danchi; Stan Owocki; Kenneth Gayley

2007-12-13

422

Highly Alfvenic Slow Solar Wind  

NASA Technical Reports Server (NTRS)

It is commonly thought that fast solar wind tends to be highly Alfvenic, with strong correlations between velocity and magnetic fluctuations, but examples have been known for over 20 years in which slow wind is both Alfvenic and has many other properties more typically expected of fast solar wind. This paper will present a search for examples of such flows from more recent data, and will begin to characterize the general characteristics of them. A very preliminary search suggests that such intervals are more common in the rising phase of the solar cycle. These intervals are important for providing constraints on models of solar wind acceleration, and in particular the role waves might or might not play in that process.

Roberts, D. Aaron

2010-01-01

423

Slow and fast solar wind - data selection and statistical analysis  

NASA Astrophysics Data System (ADS)

In this work we consider the important problem of selection of slow and fast solar wind data measured in-situ by the Ulysses spacecraft during two solar minima (1995-1997, 2007-2008) and solar maximum (1999-2001). To recognise different types of solar wind we use a set of following parameters: radial velocity, proton density, proton temperature, the distribution of charge states of oxygen ions, and compressibility of magnetic field. We present how this idea of the data selection works on Ulysses data. In the next step we consider the chosen intervals for fast and slow solar wind and perform statistical analysis of the fluctuating magnetic field components. In particular, we check the possibility of identification of inertial range by considering the scale dependence of the third and fourth orders scaling exponents of structure function. We try to verify the size of inertial range depending on the heliographic latitudes, heliocentric distance and phase of the solar cycle. Research supported by the European Community's Seventh Framework Programme (FP7/2007 - 2013) under grant agreement no 313038/STORM.

Wawrzaszek, Anna; Macek, Wies?aw M.; Bruno, Roberto; Echim, Marius

2014-05-01

424

Spall velocity measurements from laboratory impact craters  

NASA Technical Reports Server (NTRS)

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 events and from estimates based on range measurements of the spall fragments. The maximum spall velocity<