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1

Extreme Velocity Wind Sensor  

NASA Technical Reports Server (NTRS)

This presentation provides an overview of the development of new hurricane wind sensor (Extreme Velocity Wind Sensor) for the Kennedy Space Center (KSC) which is designed to withstand winds of up to three hundred miles an hour. The proposed Extreme Velocity Wind Sensor contains no moveable components that would be exposed to extreme wind conditions. Topics covered include: need for new hurricane wind sensor, conceptual design, software applications, computational fluid dynamic simulations of design concept, preliminary performance tests, and project status.

Perotti, Jose; Voska, Ned (Technical Monitor)

2002-01-01

2

Maximum terminal velocity of relativistic rocket  

Microsoft Academic Search

The maximum terminal velocity problem of the classical propulsion is extended to a relativistic rocket assumed broken down into active mass, inert mass and gross payload. A fraction of the active mass is converted into energy shared between inert mass and active mass residual. Significant effects are considered. State and co-state equations are carried out to find the exhaust speed

G. Vulpetti

1985-01-01

3

14 CFR 25.237 - Wind velocities.  

...2014-01-01 2014-01-01 false Wind velocities. 25.237 Section 25.237 Aeronautics...Handling Characteristics § 25.237 Wind velocities. (a) For land planes and amphibians...A 90-degree cross component of wind velocity, demonstrated to be safe for...

2014-01-01

4

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2012 CFR

...2012-01-01 2012-01-01 false Wind velocities. 25.237 Section 25.237 Aeronautics...Handling Characteristics § 25.237 Wind velocities. (a) For land planes and amphibians...A 90-degree cross component of wind velocity, demonstrated to be safe for...

2012-01-01

5

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Wind velocities. 25.237 Section 25.237 Aeronautics...Handling Characteristics § 25.237 Wind velocities. (a) For land planes and amphibians...A 90-degree cross component of wind velocity, demonstrated to be safe for...

2010-01-01

6

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 2013-01-01 false Wind velocities. 25.237 Section 25.237 Aeronautics...Handling Characteristics § 25.237 Wind velocities. (a) For land planes and amphibians...A 90-degree cross component of wind velocity, demonstrated to be safe for...

2013-01-01

7

14 CFR 25.237 - Wind velocities.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Wind velocities. 25.237 Section 25.237 Aeronautics...Handling Characteristics § 25.237 Wind velocities. (a) For land planes and amphibians...A 90-degree cross component of wind velocity, demonstrated to be safe for...

2011-01-01

8

Maximum wind energy extraction strategies using power electronic converters  

Microsoft Academic Search

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

Quincy Qing Wang

2003-01-01

9

A Novel Scheme for Rapid Tracking of Maximum Power Point in Wind Energy Generation Systems  

Microsoft Academic Search

This paper presents a novel maximum power point (MPP) tracking (MPPT) algorithm for grid-connected wind energy generation systems (WEGS). This is a rapid tracking algorithm that uses the fact that the value of ????,?? an intermediate variable, especially defined for the purpose, remains constant ( =??MPP ) for a given WEGS at the MPP irrespective of the wind velocity. The

Vivek Agarwal; Rakesh K. Aggarwal; Pravin Patidar; Chetan Patki

2010-01-01

10

Radionuclide Counting Technique Measures Wind Velocity  

NASA Technical Reports Server (NTRS)

Proposed technique for measuring wind velocity based on inverse-squarelaw variation of radioactive counting rates. In proposal, radioative source is deposited on bottom of light, hollow sphere and suspended by flexible wire over radiation counter, Anemometer based on this concept is self-contained, portable, yet not too fragile. Used for extended periods of time, even at remote, inhospitable and inaccessible sites.

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

1983-01-01

11

Lidar Measurement of Wind Velocity Profiles in the Boundary Layer  

Microsoft Academic Search

A lidar technique for measuring wind in the atmospheric boundary is presented. Inhomogeneities in ambient aerosol content are used as tracers of the wind. This technique yields both horizontal components of the wind and the wind velocity variance. These results are achieved using a model which assumes an isotropic Gaussian distribution of turbulent velocities. Experimental results comparing lidar wind measurements

Jeffery T. Sroga; Edwin W. Eloranta; Ted Barber

1980-01-01

12

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

13

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

E-print Network

Design of wind farm layout for maximum wind energy capture Andrew Kusiak*, Zhe Song Intelligent sources of alternative energy. The construction of wind farms is destined to grow in the U.S., possibly twenty-fold by the year 2030. To maximize the wind energy capture, this paper presents a model for wind

Kusiak, Andrew

14

Maximum wind energy extraction strategies using power electronic converters  

NASA Astrophysics Data System (ADS)

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

Wang, Quincy Qing

2003-10-01

15

Maximum power tracking control scheme for wind generator systems  

E-print Network

of the three-phase inverter. In this work, the aerodynamic characteristics of wind turbines and the power conversion system topology are explained. The maximum power tracking control algorithm with a variable step estimator is introduced and the modeling...

Mena Lopez, Hugo Eduardo

2008-10-10

16

Maximum power tracking control scheme for wind generator systems  

E-print Network

of the three-phase inverter. In this work, the aerodynamic characteristics of wind turbines and the power conversion system topology are explained. The maximum power tracking control algorithm with a variable step estimator is introduced and the modeling...

Mena, Hugo Eduardo

2009-05-15

17

Wind velocity measurements using a pulsed LIDAR system: first results  

E-print Network

Wind velocity measurements using a pulsed LIDAR system: first results M W¨achter1, A Rettenmeier2. Wind velocity measurements were taken using a Leosphere Windcube LIDAR system, which operates relevance for wind energy utilization. Different technologies are in use in this field, among them LIDAR

Peinke, Joachim

18

Maximum power extraction algorithm for a small wind turbine  

Microsoft Academic Search

Today, a characteristic of the operating regime of small wind turbines is that they do not obtain the maximum power efficiency. Taking into account that that the operability margin can, in general, be enhanced, this paper sets out to develop algorithms designed to extract the maximum power. First, an analysis is made of existing algorithms and as a result, a

I. Kortabarria; J. Andreu; I. Marti?nez de Alegri?a; E. Ibarra; E. Robles

2010-01-01

19

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

20

Instantaneous torque ripple control and maximum power extraction in a permanent magnet reluctance generator driven wind energy conversion system  

Microsoft Academic Search

A usual wind energy conversion system (WECS) suffers from significant amount of torque ripples even if the wind velocity remains constant. These torque ripples propagate mechanical stress in the turbine-generator drive train and may eventually lead to the failure of its various components. This research paper presents a unified control strategy which yields maximum power from WECS while minimizing the

Erkan Sunan; Kazmi Syed Muhammad Raza; Hiroki Goto; Hai-Jiao Guo; O. Ichinokur

2010-01-01

21

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

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

22

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

23

Calibration of Instruments for Measuring Wind Velocity and Direction  

NASA Technical Reports Server (NTRS)

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

Vogler, Raymond D.; Pilny, Miroslav J.

1950-01-01

24

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

25

Vertical velocity in cirrus case obtained from wind profiler  

NASA Technical Reports Server (NTRS)

Cirrus clouds play an important role in the climate and general circulation because they significantly modulate the radiation properties of the atmosphere. However understanding the processes that govern their presence is made difficult by their high altitude, variable thickness, complex microphysical structure, and relatively little knowledge of the vertical motion field. In the FIRE 2 (First International Satellite Cloud Climatology Regional Experiment) experiment, a 404 MHz wind profiler was set up to provide continuous measurements of clear air wind field at Parsons, Kansas. Simultaneously, the NOAA wind profiler network supplied a wider spacial scale observation. On 26 Nov. 1991, the most significant cirrus cloud phenomena during the experiment with a jet streak at 250 Mb occurred. Analyses of the vertical wind velocity are made by utilizing different methods based on wind profiler data, among them the direct measurements from CSU wind profiler and NOAA network wind profilers, VAD (Velocity Azimuth Display) technique and the kinematic method.

Song, Ran; Cox, Stephen K.

1993-01-01

26

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

Microsoft Academic Search

This paper reports a CFD wind tunnel study of wind patterns on a square-plan building with a refuge floor at its mid-height level. In this study, a technique of using calibrated power law equations of velocity and turbulent intensity applied as the boundary conditions in CFD wind tunnel test is being evaluated by the physical wind tunnel data obtained by

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

2005-01-01

27

Exploratory Meeting on Airborne Doppler Lidar Wind Velocity Measurements  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

28

A new maximum power point tracking control scheme for wind generation  

Microsoft Academic Search

According to the aerodynamical characteristic of the wind turbine, a maximum power point tracking (MPPT) is necessary to get high efficiency for wind power conversion, which means that the rotating speed of wind turbine should be adjusted in the real time to capture maximum wind power. Because of the fast variation of wind speed and the heavy inertia of generator,

Jia Yaoqin; Yang Zhongqing; Cao Binggang

2002-01-01

29

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

30

Azimuthal structure of the solar wind velocity and K-corona brightness in the heliospheric current sheet  

NASA Astrophysics Data System (ADS)

Solar wind velocity measurements at IMF sector boundary crossings at 1 AU during 1972-1977 are used to infer the azimuthal structure of the solar wind velocity in the heliospheric current sheet (HCS). The solar wind velocity in the in-ecliptic portion of the current sheet is found to vary from longitude to longitude, where it originates from the corona. The yearly average value of solar wind velocity in the HCS is found to vary with the phase of the solar cycle, with a maximum value around 1974. The K-corona brightness on the source surface corresponding to the IMF sector boundary crossings during the period under consideration also exhibits a similar but opposite pattern of variation when the data are averaged over a long period. It is concluded that there exists a longitudinal variation of solar wind velocity in the HCS.

Bala, B.; Prabhakaran Nayar, S. R.

1993-05-01

31

A proposed method for wind velocity measurement from space  

NASA Technical Reports Server (NTRS)

An investigation was made of the feasibility of making wind velocity measurements from space by monitoring the apparent change in the refractive index of the atmosphere induced by motion of the air. The physical principle is the same as that resulting in the phase changes measured in the Fizeau experiment. It is proposed that this phase change could be measured using a three cornered arrangement of satellite borne source and reflectors, around which two laser beams propagate in opposite directions. It is shown that even though the velocity of the satellites is much larger than the wind velocity, factors such as change in satellite position and Doppler shifts can be taken into account in a reasonable manner and the Fizeau phase measured. This phase measurement yields an average wind velocity along the ray path through the atmosphere. The method requires neither high accuracy for satellite position or velocity, nor precise knowledge of the refractive index or its gradient in the atmosphere. However, the method intrinsically yields wind velocity integrated along the ray path; hence to obtain higher spatial resolution, inversion techniques are required.

Censor, D.; Levine, D. M.

1980-01-01

32

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

Microsoft Academic Search

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

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

2009-01-01

33

Velocity shear layers in solar winds affect Earth's magnetosphere  

NASA Astrophysics Data System (ADS)

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

Bhattacharya, Atreyee

2012-09-01

34

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

35

ALADIN: an atmosphere laser doppler wind lidar instrument for wind velocity measurements from space  

Microsoft Academic Search

AEROSPATIALE, leading a European team, has just conducted a successful study, under ESA contract, to demonstrate the feasibility of a spaceborne Doppler wind lidar instrument meeting the scientific requirements of wind velocity measurements from space with high spatial resolution. A first parametric investigation, based upon the initial set of mission requirements, and supported by dedicated models and detailed trade-off studies,

Rodolphe Krawczyk; Jean-Bernard Ghibaudo; Jean-Yves Labandibar; David V. Willetts; M. Vaughan; G. Pearson; M. R. Harris; Pierre H. Flamant; P. Salamitou; Alain Dabas; R. Charasse; Thierri Midavaine; Michel Royer; H. Heimel

1995-01-01

36

Electronic frequency modulation for the increase of maximum measurable velocity in a heterodyne laser interferometer  

SciTech Connect

A Zeeman-type He-Ne laser is frequently used as a heterodyne laser due to the simple construction and the small loss of a light. However, the low beat frequency of the Zeeman-type laser limits the maximum measurable velocity. In this article, an electronic frequency modulation algorithm is proposed to overcome the drawback of the low velocity measurement capability by increasing the beat frequency electronically. The brief analysis, the measurement scheme of the proposed algorithm, and the experimental results are presented. It is demonstrated that the proposed algorithm is proven to enhance the maximum measurable velocity.

Choi, Hyunseung; La, Jongpil; Park, Kyihwan [Intelligent Manufacturing Group, LG Production Engineering Research Institute, 19-1 Cheongho-Ri, Jinwuy-myun, Pyungtaik, Kyunggi-Do 451-713 (Korea, Republic of); Compressor Development Group, Samsung Gwangju Electronic Company, 1119 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of); Department of Mechatronics, Gwangju Institute of Science and Technology, 1 Oryong-dong, Buk-gu, Gwangju 500-712 (Korea, Republic of)

2006-10-15

37

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

PubMed

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

Guan, D; Zhu, T

2000-04-01

38

Doppler CO2 lidar for wind velocity measurements  

Microsoft Academic Search

A monostatic biaxial Doppler lidar based on a hybrid CO2 laser with an intracavity telescopic beam expander is reported. The lidar is characterized by a laser pulse energy of 100 mJ, a pulse duration of 3-5 microsec, and a pulse repetition frequency of up to 10 Hz. The lidar is designed to measure the radial wind velocity component in the

V. Iu. Baranov; V. P. Kozolupenko; V. S. Mezhevov; Iu. E. Sizov; A. A. Khakhlev

1992-01-01

39

Analysis of the velocity law in the wind of the Be star Lambda Pavonis  

NASA Technical Reports Server (NTRS)

This paper reanalyzes the IUE spectra of Lambda Pavonis secured in 1982 (Sahade et al.). It is found that the profiles of the broad UV lines are either rotationally broadened or nonrotationally broadened and that the rotationally broadened profiles can be sorted out in two groups characterized by rotational velocity values of 170 km/s and of 210 km/s, respectively. From the analysis of the rotational and of the radial velocities it is possible to distinguish two regions in the extended atmosphere of the star, namely, a region which is rotating and a region which is expanding. In the rotating region, the radial velocities are about zero, and the rotational velocity increases from 170 km/s to 250 km/s. In the expanding region, the rotational energy dissipates, the wind is accelerated to a maximum of -155 km/s, and farther out it decelerates.

Chen, Haiqi; Ringuelet, Adela; Sahade, Jorge; Kondo, Yoji

1989-01-01

40

Velocity-Space Proton Diffusion in the Solar Wind Turbulence  

E-print Network

We study a velocity-space quasilinear diffusion of the solar wind protons driven by oblique Alfven turbulence at proton kinetic scales. Turbulent fluctuations at these scales possess properties of kinetic Alfven waves (KAWs) that are efficient in Cherenkov resonant interactions. The proton diffusion proceeds via Cherenkov kicks and forms a quasilinear plateau - nonthermal proton tail in the velocity distribution function (VDF). The tails extend in velocity space along the mean magnetic field from 1 to (1.5-3) VA, depending on the spectral break position, turbulence amplitude at the spectral break, and spectral slope after the break. The most favorable conditions for the tail generation occur in the regions where the proton thermal and Alfven velocities are about the same, VTp/VA = 1. The estimated formation times are within 1-2 h for typical tails at 1 AU, which is much shorter than the solar wind expansion time. Our results suggest that the nonthermal proton tails, observed in-situ at all heliocentric distan...

Voitenko, Yuriy

2013-01-01

41

A method for measuring mean wind velocities in a canyon with tracer balloons  

Microsoft Academic Search

A method using balloons as tracers for measuring mean wind velocity in street canyons or mountain valleys has been developed. Tests of the method with numerical experiments showed that the method reproduced an assumed wind field quite well provided that the buoyancy component of the balloon velocity was larger than the downward velocity component of the wind. Tests of the

C. M. Sheih; B. J. Billman; F. T. Depaul

1985-01-01

42

Slow and fast solar wind acceleration near solar maximum  

Microsoft Academic Search

2-site measurements of interplanetary scintillation (IPS) provide measurements of solar wind speed in regions of the heliosphere which are otherwise inaccessible. We present results from co-ordinated observations made with the EISCAT and MERLIN facilities during 1999 and 2000, covering heliocentric distances from 7 to 80 solar radii (R) predominantly in the slow solar wind. The 1999 results are compared with

A. R. Breen; P. Thomasson; C. A. Jordan; S. J. Tappin; R. A. Fallows; A. Canals; P. J. Moran

2002-01-01

43

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

44

A sensorless control method for maximum power point tracking of wind turbine generators  

Microsoft Academic Search

Wind energy has been regarded as an environmentally friendly, logistically feasible and economically responsible alternative energy resource. In order to produce as much power as possible in variable speed wind turbine generators, the maximum power point tracking (MPPT) becomes a hotspot of research in this field. In this paper, a simple control method for maximum power point tracking (MPPT) in

Zhenyu Ma

2011-01-01

45

Relationship between the IMF azimuthal angle and solar wind velocity  

NASA Astrophysics Data System (ADS)

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

Erofeev, D. V.

2008-04-01

46

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

47

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

48

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

49

Linearity of DMS transfer coefficient with both friction velocity and wind speed in the moderate wind speed range  

Microsoft Academic Search

In many air-sea gas exchange parameterizations, wind speed is the sole environmental controlling factor for exchange velocity, k. Here we examine also the role of friction velocity (u*) in the mid-range of wind speeds, using data from the 2007 Deep Ocean Gas Exchange Experiment. We measured dimethyl sulfide (DMS) fluxes and divided these by the interfacial concentration difference, ?CDMS, to

B. J. Huebert; B. W. Blomquist; M. X. Yang; S. D. Archer; P. D. Nightingale; M. J. Yelland; J. Stephens; R. W. Pascal; B. I. Moat

2010-01-01

50

Multifractal two-scale Cantor set model for slow solar wind turbulence in the outer heliosphere during solar maximum  

NASA Astrophysics Data System (ADS)

To quantify solar wind turbulence, we consider a generalized two-scale weighted Cantor set with two different scales describing nonuniform distribution of the kinetic energy flux between cascading eddies of various sizes. We examine generalized dimensions and the corresponding multifractal singularity spectrum depending on one probability measure parameter and two rescaling parameters. In particular, we analyse time series of velocities of the slow speed streams of the solar wind measured in situ by Voyager 2 spacecraft in the outer heliosphere during solar maximum at various distances from the Sun: 10, 30, and 65 AU. This allows us to look at the evolution of multifractal intermittent scaling of the solar wind in the distant heliosphere. Namely, it appears that while the degree of multifractality for the solar wind during solar maximum is only weakly correlated with the heliospheric distance, but the multifractal spectrum could substantially be asymmetric in a very distant heliosphere beyond the planetary orbits. Therefore, one could expect that this scaling near the frontiers of the heliosphere should rather be asymmetric. It is worth noting that for the model with two different scaling parameters a better agreement with the solar wind data is obtained, especially for the negative index of the generalized dimensions. Therefore we argue that there is a need to use a two-scale cascade model. Hence we propose this model as a useful tool for analysis of intermittent turbulence in various environments and we hope that our general asymmetric multifractal model could shed more light on the nature of turbulence.

Macek, W. M.; Wawrzaszek, A.

2011-05-01

51

The maximum potential to generate wind power in the contiguous United States is more than three times  

E-print Network

The maximum potential to generate wind power in the contiguous United States is more than three, the installed U.S. wind power capacity is now about 35 GW. While most of the wind potential comes from the windy

52

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

USGS Publications Warehouse

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

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

2007-01-01

53

Solar wind driving of magnetospheric ULF waves: Pulsations driven by velocity shear at the magnetopause  

NASA Astrophysics Data System (ADS)

We present results from global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind/magnetosphere interaction. These MHD simulations are used to study ultra low frequency (ULF) pulsations in the Earth's magnetosphere driven by shear instabilities at the flanks of the magnetopause. We drive the simulations with idealized, constant solar wind input parameters, ensuring that any discrete ULF pulsations generated in the simulation magnetosphere are not due to fluctuations in the solar wind. The simulations presented in this study are driven by purely southward interplanetary magnetic field (IMF) conditions, changing only the solar wind driving velocity while holding all of the other solar wind input parameters constant. We find surface waves near the dawn and dusk flank magnetopause and show that these waves are generated by the Kelvin-Helmholtz (KH) instability. We also find that two KH modes are generated near the magnetopause boundary. One mode, the magnetopause KH mode, propagates tailward along the magnetopause boundary. The other mode, the inner KH mode, propagates tailward along the inner edge of the boundary layer (IEBL). We find large vortical structures associated with the inner KH mode that are centered on the IEBL. The phase velocities, wavelengths, and frequencies of the two KH modes are computed. The KH waves are found to be fairly monochromatic with well-defined wavelengths. In addition, the inner and magnetopause KH modes are coupled and lead to a coupled oscillation of the low-latitude boundary layer. The boundary layer thickness, d, is computed and we find maximum wave growth for kd = 0.5-1.0, where k is the wave number, consistent with the linear theory of the KH instability. We comment briefly on the effectiveness of these KH waves in the energization and transport of radiation belt electrons.

Claudepierre, S. G.; Elkington, S. R.; Wiltberger, M.

2008-05-01

54

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

55

Remote Sensing Of Three-Dimensional Winds With Elastic Lidar: Explanation Of Maximum Cross-Correlation Method  

Microsoft Academic Search

Maximum cross-correlation provides a method to remotely determine highly resolved three-dimensional fields of horizontal winds with elastic lidar throughout large volumes of the planetary boundary layer (PBL). This paper details the technique and shows comparisons between elastic lidar winds, remotely sensed laser Doppler velocimeter (LDV) wind profiles, and radiosonde winds. Radiosonde wind data were acquired at Barcelona, Spain, during the

William T. Buttler; Cecilia Soriano; Jose M. Baldasano; George H. Nickel

2002-01-01

56

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

57

Scaling of maximum probability density functions of velocity and temperature increments in turbulent systems  

E-print Network

In this paper, we introduce a new way to estimate the scaling parameter of a self-similar process by considering the maximum probability density function (pdf) of tis increments. We prove this for $H$-self-similar processes in general and experimentally investigate it for turbulent velocity and temperature increments. We consider turbulent velocity database from an experimental homogeneous and nearly isotropic turbulent channel flow, and temperature data set obtained near the sidewall of a Rayleigh-B\\'{e}nard convection cell, where the turbulent flow is driven by buoyancy. For the former database, it is found that the maximum value of increment pdf $p_{\\max}(\\tau)$ is in a good agreement with lognormal distribution. We also obtain a scaling exponent $\\alpha\\simeq 0.37$, which is consistent with the scaling exponent for the first-order structure function reported in other studies. For the latter one, we obtain a scaling exponent $\\alpha_{\\theta}\\simeq0.33$. This index value is consistent with the Kolmogorov-Ob...

Huang, Y X; Zhou, Q; Qiu, X; Shang, X D; Lu, Z M; Liu, and Y L

2014-01-01

58

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

59

Linearity of DMS transfer coefficient with both friction velocity and wind speed in the moderate wind speed range  

Microsoft Academic Search

In many air-sea gas exchange parameterizations, wind speed is the sole environmental controlling factor for exchange velocity, k. Here we examine also the role of friction velocity (u*) in the mid-range of wind speeds, using data from the 2007 Deep Ocean Gas Exchange Experiment. We measured dimethyl sulfide (DMS) fluxes and divided these by the interfacial concentration difference, DeltaCDMS, to

B. J. Huebert; B. W. Blomquist; M. X. Yang; S. D. Archer; P. D. Nightingale; M. J. Yelland; J. Stephens; R. W. Pascal; B. I. Moat

2010-01-01

60

A quantum-dot heterostructure transistor with enhanced maximum drift velocity of electrons  

SciTech Connect

A new type of heterotransistor based on an AlGaAs/GaAs/InAs/GaAs/InAs structure with a layer of InAs quantum dots embedded directly into the GaAs channel is fabricated. High values of the maximum saturation current (up to 35 A/cm) and transconductance (up to 1300 mS/mm) are attained. The specific features of the current-voltage characteristics of the new device are explained in the context of a model that takes into account the ionization of quantum dots in high electric fields and tenfold enhancement of the electron drift velocity in a structure with an InAs quantum-dot layer in the vicinity of an AlGaAs/GaAs heterojunction.

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

2006-03-15

61

Dependency of U.S. Hurricane Economic Loss on Maximum Wind Speed and Storm Size  

E-print Network

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 dependencies of normalized U.S. hurricane loss on both wind speed and storm size for 73 tropical cyclones that made landfall in the U.S. from 1988 to 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 (Vmax) and size (R). Assuming L=10^c Vmax^a R^b, c being a scaling factor, the coefficients, a and b, generally range between 4-12 and 2-4, respectively. Both a and b tend to increase with stronger wind speed. For large losses, a weighted regression model, with...

Zhai, Alice R

2014-01-01

62

Remote Sensing of Solar Wind Velocity Applying IPS Technique using MEXART  

NASA Astrophysics Data System (ADS)

Radio waves coming from compact cosmic radio sources are scattered by electron density fluctuations in the solar wind plasma, producing a diffraction pattern at Earth which moves along with the solar wind. This phenomenon results into flux density fluctuations observed by a radio telescope and it is known as Interplanetary Scintillation (IPS). By employing IPS observations, it is possible to track solar wind velocities in the inner heliosphere. The Mexican Array Radio Telescope (MEXART) is an new instrument devoted to IPS observations at 140 MHz. We present preliminar estimates of solar wind velocities by using IPS observations of the MEXART.

Mejia-Ambriz, J. C.; Gonzalez-Esparza, A.; Romero Hernandez, E.

2012-12-01

63

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

Microsoft Academic Search

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

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

2009-01-01

64

Design of Small Wind Turbine with Maximum Power Point Tracking Algorithm  

Microsoft Academic Search

This paper presents a complex design of Turbine with AC\\/DC converter containing Point Tracking Algorithm. The paper describes phenomenon and problems connected with designing particular parts for small wind turbine, such a generator addition, it shows short discussion between two different Maximum Power Point Tracking approaches experimental results.

M. Rolak; R. Kot; M. Malinowski; Z. Goryca; J. T. Szuster

2011-01-01

65

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

66

IPS measurements and azimuthal variation of solar-wind velocity on the heliospheric current sheet  

NASA Astrophysics Data System (ADS)

The solar-wind velocity tends to be a minimum along the heliospheric current sheet and increases with heliomagnetic latitude. In addition, an azimuthal variation of solar-wind velocity is found to exist on the current sheet. In this study of the solar-wind velocity variations on the current sheet, we have made use of interplanetary scintillation (IPS) measurements. This method provides solar-wind data over a larger range of heliolatitudes: +/- 80 deg or greater. We found that there exists a clear longitudinal variation of solar-wind velocity on the current sheet during 1973-1985. It is also noticeable that the pattern of variation changes with the phase of the solar cycle. On average, the solar-wind velocity varied from 300 to 550 km/s 1 on the current sheet during the period of study. It is also found that the longitudinal variation of the solar-wind velocity on the current sheet obtained using near-earth satellite data agrees well with that obtained using IPS data.

Bala, B.; Prabhakaran Nayar, S. R.

1993-02-01

67

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

68

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

69

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

70

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

71

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

72

Correlation lidar methods of wind-velocity measurement  

Microsoft Academic Search

The work presents the basic principles for the design of correlation lidar instruments for wind measurement. The space-time structure of aerosol inhomogeneities is studied theoretically and experimentally, and requirements on the parameters of correlation lidars are given. The appropriate signal-processing algorithms are examined, and different types of measurement errors are analyzed. Attention is given to examples of the application of

G. G. Matvienko; G. O. Zadde; E. S. Ferdinandov; I. N. Kolev; R. P. Avramova

1985-01-01

73

[Measurement of path transverse wind velocity profile using light forward scattering scintillation correlation method].  

PubMed

A new method for path transverse wind velocity survey was introduced by analyzing time lagged covariance function of different separation sub-apertures of Hartmann wavefront sensor. A theoretical formula was logically deduced for the light propagation path transverse wind velocity profile. According to the difference of path weighting function for different sub apertures spacing, how to select reasonable path weighting functions was analyzed. Using a Hartmann wavefront sensor, the experiment for measuring path transverse velocity profile along 1 000 m horizontal propagating path was carried out for the first time to our knowledge. The experiment results were as follows. Path transverse averaged velocity from sensor had a good consistency with transverse velocity from the wind anemometer sited near the path receiving end. As the path was divided into two sections, the path transverse velocity of the first section had also a good consistency with that of the second one. Because of different specific underlaying surface of light path, the former was greater than the later over all experiment period. The averaged values were 1.273 and 0.952 m x s(-1) respectively. The path transverse velocity of second section and path transverse averaged velocity had the same trend of decrease and increase with time. The correlation coefficients reached 0.86. PMID:25269279

Yuan, Ke-E; Lü, Wei-Yu; Zheng, Li-Nan; Hu, Shun-Xing; Huang, Jian; Cao, Kai-Fa; Xu, Zhi-Hai

2014-07-01

74

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

75

Evaluation of the maximum cross-correlation method of estimating sea surface velocities from sequential satellite images  

NASA Technical Reports Server (NTRS)

The maximum cross correlation (MCC) method of Leese et al. (1971) for estimating sea surface velocities from sequences of satellite images is evaluated by comparing the MCC fields obtained from sequences of AVHRR and CZCS with in situ data and velocity fields calculated with a high-resolution quasi-geostrophic model. The rms differences and vector correlations between the velocity field produced by the MCC method and the model's field are presented. It is shown that much of the difference between the MCC fields and either the in situ data or the model velocity fields can be accounted for by considering physical and biological processes not included in the MCC method. The conditions under which the method is likely to be most successful are discussed.

Tokmakian, Robin; Strub, P. Ted; Mcclean-Padman, Julie

1990-01-01

76

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

Microsoft Academic Search

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

Fichtl

1983-01-01

77

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

78

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

79

Comparison of CO2 Doppler lidar and GPS rawinsonde wind velocity measurements  

NASA Astrophysics Data System (ADS)

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

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

2001-09-01

80

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

81

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

82

FIS/ANFIS Based Optimal Control for Maximum Power Extraction in Variable-speed Wind Energy Conversion System  

NASA Astrophysics Data System (ADS)

An optimal control for maximizing extraction of power in variable-speed wind energy conversion system is presented. Intelligent gradient detection by fuzzy inference system (FIS) in maximum power point tracking control is proposed to achieve power curve operating near optimal point. Speed rotor reference can be adjusted by maximum power point tracking fuzzy controller (MPPTFC) such that the turbine operates around maximum power. Power curve model can be modelled by using adaptive neuro fuzzy inference system (ANFIS). It is required to simply well estimate just a few number of maximum power points corresponding to optimum generator rotor speed under varying wind speed, implying its training can be done with less effort. Using the trained fuzzy model, some estimated maximum power points as well as their corresponding generator rotor speed and wind speed are determined, from which a linear wind speed feedback controller (LWSFC) capable of producing optimum generator speed can be obtained. Applied to a squirrel-cage induction generator based wind energy conversion system, MPPTFC and LWSFC could maximize extraction of the wind energy, verified by a power coefficient stay at its maximum almost all the time and an actual power line close to a maximum power efficiency line reference.

Nadhir, Ahmad; Naba, Agus; Hiyama, Takashi

83

Variable High Velocity Winds from Broad Absorption Line Quasars  

NASA Astrophysics Data System (ADS)

We study broad absorption line quasars (BALQSOs) because these objects, in particular, probe the high velocity gas ejected by luminous accreting black holes. The variability timescales of BALs can help constrain the size, location, and dynamics of the emitting and absorbing gas near the supermassive black hole. We have obtained multi-epoch spectroscopy of seventeen BALQSOs from the Sloan Digital Sky Survey (SDSS) using the Fred Lawrence Whipple Observatory's 1.5m telescope's FAST Spectrograph. These objects were first identified as BALQSOs in SDSS, observed with Chandra, and then with FAST at 1, 3, 9, 27, and 81 day timescales. Additional observations are acquired for 1 and 2 year cadences. We also obtain a set of non-BAL quasar spectra of similar redshift and luminosity as controls. We identify significant variability and assess its magnitude and frequency in the observed spectra of our BAL QSOs and determine which constraints our investigations can put on the outflows impacting the BAL region.

Arraki, Kenza S.; Haggard, D.; Anderson, S.; Green, P.; Aldcroft, T.

2011-01-01

84

A Stand-Alone Hybrid Generation System Combining Solar Photovoltaic and Wind Turbine with Simple Maximum Power Point Tracking Control  

Microsoft Academic Search

This paper proposes a hybrid energy system combing solar photovoltaic and wind turbine as a small-scale alternative source of electrical energy where conventional generation is not practical. A simple and cost effective control technique has been proposed for maximum power point tracking from the photovoltaic array and wind turbine under varying climatic conditions without measuring the irradiance of the photovoltaic

Nabil A. Ahmed; Masafumi Miyatake

2006-01-01

85

Growing Neural Gas (GNG)Based Maximum Power Point Tracking for High-Performance Wind Generator With an Induction Machine  

Microsoft Academic Search

This paper presents a maximum power point track- ing (MPPT) technique for a high-performance wind generator with induction machine based on the growing neural gas (GNG) network. Here, a GNG network has been trained offline to learn the turbine characteristic surface torque versus wind speed and machine speed. It has been implemented online to perform the inversion of this function,

Maurizio Cirrincione; Marcello Pucci; Gianpaolo Vitale

2011-01-01

86

Hybrid Solar Photovoltaic\\/Wind Turbine Energy Generation System with Voltage-based Maximum Power Point Tracking  

Microsoft Academic Search

This article proposes a hybrid energy system combining solar photovoltaic and wind turbine as a small-scale alternative source of electrical energy where conventional generation is not practical. A simple and cost-effective control technique has been proposed for maximum power point tracking from the photovoltaic array and wind turbine under varying climatic conditions without measuring the irradiance of the photovoltaic or

Nabil A. Ahmed; Masafumi Miyatake; A. K. Al-Othman

2008-01-01

87

Design of a control scheme for a maximum power extraction in low power wind turbine-generator system  

Microsoft Academic Search

This document presents the modeling of a wind turbine-generator system and developing a control scheme for maximum power extraction. The system comprises a low-power variable speed wind rotor coupled to a squirrel cage induction generator through gearbox. The generator delivers electrical energy to a DC load through a PWM three phase rectifier which control variables are duty cycle and the

Elkin Edilberto Henao Bravo

2010-01-01

88

The use of wind probability distributions derived from the maximum entropy principle in the analysis of wind energy. A case study  

Microsoft Academic Search

This paper analyses the use of a general probability distribution obtained through application of the maximum entropy principle (MEP), constrained by the low-order statistical moments of a given set of wind speed data, in the estimation of wind energy. For this purpose, a comparison is made between the two parameter Weibull distribution and the distributions obtained through the MEP. This

Penélope Ramírez; José Antonio Carta

2006-01-01

89

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

90

Power spectrum of small-scale turbulent velocity fluctuations in the solar wind  

Microsoft Academic Search

It is well known that the power spectrum of magnetic field fluctuations in the solar wind exhibits a Kolmogorov spectrum f-alpha in the inertial range of the turbulence with a power law exponent alpha near 5\\/3. The power spectrum of velocity fluctuations has not been as well studied, partly because of the lack of high time resolution measurements needed to

J. J. Podesta; D. A. Roberts; M. L. Goldstein

2006-01-01

91

Power spectrum of small-scale turbulent velocity fluctuations in the solar wind  

Microsoft Academic Search

It is well known that the power spectrum of magnetic field fluctuations in the solar wind exhibits a Kolmogorov spectrum f?? in the inertial range of the turbulence with a power law exponent ? near 5\\/3. The power spectrum of velocity fluctuations has not been as well studied, partly because of the lack of high time resolution measurements needed to

J. J. Podesta; D. A. Roberts; M. L. Goldstein

2006-01-01

92

The change in Cosmic rays intensity variation with the Solar wind velocity variation  

Microsoft Academic Search

GRAPES-3 experiment is situated at Ooty in South India 76.7 East 11.4 North. Effective ob- servation area of our muon telescopes is 560 m 2 . They are the largest detector in the world of its kind. There were several reports that increase of the solar wind velocity suppresses the intensity of cosmic rays. But there are few which studied

Y. HAYASHI; K. HAYASHI; S. KAWAKAMI; T. MATSUYAMA; M. MINAMINO; T. OKUDA; S. OGIO; A. OSHIMA; N. SHIMIZU; S. K GUPTA; A. IYER; P. JANGADEESAN; S. KARTHIKEYAN; P. K MOHANTY; S. D MORRIS; P. K NAYAK; B. S RAO; K. C RAVINDRAN; H. TANAKA; S. C TONWAR; S. SHIBATA; I. MORISHITA

93

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

94

MICROCANTILEVER-BASED WEATHER STATION FOR TEMPERATURE, HUMIDITY AND WIND VELOCITY MEASUREMENT  

Microsoft Academic Search

The current study develops a new process for the fabrication of Pt resistor temperature detectors (RTD), cantilevers covered with a water-absorbent polyimide layer for humidity measurement and bending-up cantilevers to determining the wind velocity. Pt RTD's are fabricated on the silicon substrate. The temperature measurement is based on the linear resistance variations when temperature changes. The polyimide layer is spun

Chia-Yen Lee; Rong-Hua Ma; Yu-Hsiang Wang; Po-Cheng Chou; Lung-Ming Fu

95

Efficiency of lidar measurements of wind velocity using a correlation lidar  

Microsoft Academic Search

Suboptimal estimates of wind velocity were obtained using spectral processing of lidar signals. An error was found in these estimates, and the dependence of estimates on the atmospheric conditions and on the lidar parameters is assessed for experimentally validated models of correlation functions for lidar signals. Recommendations are offered regarding the choice of parameters for a two-path sounding scheme, taking

V. G. Astafurov; E. Iu. Ignatova; G. G. Matvienko

1992-01-01

96

Coherent CO2 lidars for measuring wind velocity and atmospheric turbulence  

Microsoft Academic Search

We have developed two coherent lidar systems based on cw and TEA CO2 lasers. The lidars have been tested and applied for the atmospheric wind velocity measurements. We have elaborated and experimentally verified a new method of nondestructive long-range measurement of the parameters of the atmospheric turbulence with a cw Doppler lidar (DL). The method is based on certain processing

Vyacheslav M. Gordienko; Anatoly A. Kormakov; Leonid A. Kosovsky; Nikolay N. Kurochkin; Grigory A. Pogosov; Alexander V. Priezzhev; Yurii Y. Putivskii

1994-01-01

97

Lidar determination of winds by aerosol inhomogeneities - Motion velocity in the planetary boundary layer  

Microsoft Academic Search

The paper presents results from lidar measurements of wind velocity in the planetary boundary layer using correlation data processing. Two lidars are used in the experiments: a ruby lidar operating along slant paths and a YAG:Nd lidar operating for near vertical sounding. On the basis of prior experience the optimal sizes of aerosol inhomogeneities (30-300 m), the duration of the

Ivan Kolev; Orlin Parvanov; Boiko Kaprielov

1988-01-01

98

Large-scale Solar Wind Evolution From Minimum To Maximum: Swan Observations  

NASA Astrophysics Data System (ADS)

Based on extensive modelling we conclude that the latitudinal distribution of helio- spheric Lyman- glow is sensitive to the latitudinal distribution of the slow/fast solar wind, averaged over heliographic longitude. In a plane perpendicular to the interstel- lar gas flow axis, an enhancement of the ionization rate about the solar equator, as observed by Ulysses in 1995, results in a decrease of the glow intensity at equato- rial latitudes ("the groove"). The FWHM of the groove is related to FWHM of the ionization rate enhancement by a linear formula, which makes it quite easy to infer the latitudinal extent of the slow solar wind (averaged over heliographic longitude) from appropriate observations of the heliospheric Lyman- glow. The depth of the groove depends on width of the ionization bulge width and for the assumed height of the ionization bulge it has maximum for the width of about 60 degrees. According to these results, we interpret the long-term changes of the pattern in time as a result of changes of the latitudinal extent of the slow solar wind, averaged over heliographic longitude. From early June, 1996 (the start of relevant SWAN observations) till early December, 1998, the slow solar wind was concentrated practically symmetrically at equatorial latitudes. Then it begun to migrate to higher latitudes, first in the south- ern hemisphere (June 1999), then in the northern (December 1999). In June 2000 it engulfed the whole Sun and continued doing so at least till the most recent SOHO pas- sage through the downwind axis in December 2001, with some transient north-south asymmetries in June 2001.

Bzowski, M.; Mäkinen, T.; Summanen, T.; Kyrölä, E.; Quémerais, E.

99

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

100

Vertical velocities and momentum fluxes derived from wind measurements in the dusk auroral oval  

NASA Technical Reports Server (NTRS)

Results are presented on a chemical release experiment carried out on March 20, 1985 in connection with NASA's Cooperative Observations of Polar Electrodynamics I campaign. Simultaneous neutral wind measurements in E region were carried out at three separate locations over a triangular region with sides of about 150 km in the dusk auroral oval, and the three wind profiles were used to calculate values of divergence and vorticity over the area. The vertical velocity over the hight range was calculated using the mass continuity equation, and the instantaneous vertical momentum fluxes in the E region were derived using the combination of horizontal-wind measurements and calculated vertical velocities. Results show that there is strong coupling between layers in the E region and that the momentum-flux-induced accelerations are at least comparable in magnitude to the pressure gradient and Coriolis force accelerations.

Larsen, M. F.; Mikkelsen, I. S.

1990-01-01

101

Anisotropy and symmetry of fluctuations in the solar wind magnetic field and velocity  

NASA Astrophysics Data System (ADS)

The behavior of correlation tensors of fluctuations in the solar wind magnetic field and velocity is studied during different phases of a solar cycle on the basis of a 45-year measurement series of solar wind parameters. It is found that the orientation of fluctuations in the magnetic field and velocity is approximately axisymmetric relative to the direction of a local magnetic field during high solar activity. This symmetry is violated significantly during periods of low solar activity, and deviations from the symmetry are regular and oppositely directed during minima of even and odd 11-year cycles, which is probably connected with variations in the orientation of the Sun's magnetic field. The dependence of the power of fluctuations on the local magnetic field direction reveals significant deviations from local symmetry during all phases of a solar cycle, especially for velocity fluctuations.

Erofeev, D. V.

2012-12-01

102

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

103

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

104

Control of a wind-driven self-excited induction generator water-pumping system for maximum utilization efficiency  

SciTech Connect

This paper analyzes a stand-alone water-pumping system consisting of a motor-pump set supplied by a wind-driven self-excited induction generator. In order to achieve maximum utilization efficiency, the system designer is interested in optimally matching the system components together so that maximum energy available from the wind is absorbed and utilized all the time. Unfortunately, this optimal matching is speed-dependent and hence no single matching is valid for all wind speeds. Therefore the operating point of the system must vary with wind speed. In this paper, a control strategy is formulated which properly adjust the operating point of the system to coincide with the maximum power operating condition. The self-excited induction generator (SEIG) is basically an induction machine which is driven by a prime mover such as a wind turbine while a capacitor is connected across its stator terminals. The SEIG supplies an induction motor which is coupled to a water pump. The system need not operate continuously and water can be used directly for drinking and irrigation or it can be collected in a storage tank for later use. Due to the high cost of the wind turbine and equipment, the system designer is interested in maximizing the amount of pumped water per day. This can be achieved by proper selection and matching of the system components. However, proper matching of the system components together is not sufficient to guarantee maximum utilization since matching is dependent on wind speed. Therefore, certain system components must be controlled according to wind speed, such that matching is achieved all the time. This paper presents a control strategy to control the excitation capacitance of the induction generator such that its generated terminal voltage, which is applied to the induction motor, is kept constant as the rotor speed varies with wind speed.

Alghuwainem, S.M.

1998-07-01

105

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

106

Assessing the Evolution of the Solar Wind through the Spectrum of Velocity Fluctuations from 1 5 AU.  

E-print Network

. Measurements of the spectrum of velocity and magnetic field fluctuations agree well with predictions of the magnetic field fluctuations in the inertial range diverge from the power laws of velocity fluctuations. We1 Assessing the Evolution of the Solar Wind through the Spectrum of Velocity Fluctuations from 1

107

The efficiency of lidar measurements of wind velocity by a correlation lidar  

SciTech Connect

A suboptimal estimate of the wind velocity based on the spectral processing of lidar signals is constructed. The error of this estimate is calculated and its calculations are performed for different atmospheric conditions and instrumental parameters for the experimentally confirmed models of the correlation functions of lidar signals. Some recommendations are given on the choice of parameters of a two-path method of sounding with an account of evolution time of the aerosol inhomogeneities. 10 refs., 4 figs., 1 tab.

Astafurov, V.G.; Ignatova, E.Yu.; Matvienko, G.G. (Institute of Atmospheric Optics, Tomsk (Russian Federation))

1992-05-01

108

Evaporation under cavity flow: laser speckle correlation of the wind velocity above the liquid surface  

NASA Astrophysics Data System (ADS)

One of the major accident scenarios in industrial safety deals with liquid pool evaporation consequent to a tank rupture. Numerous previous studies have been performed and several correlations are available in the literature. It appears that all of the correlations are strongly dependent on wind velocity but have nevertheless been all created under a boundary layer flow above the pool. However, industrial safety bunds do not allow such a profile because of obstacles and so cavity flows may occur. For such a configuration, is it then possible to describe the evaporation phenomena thanks to correlations in the literature? Experiments involving evaporation under this configuration have thus been performed in this work. Particular care is devoted to the wind profile measurement as the wind velocity is one of the main parameters. Digital speckle correlation insures high accuracy and good spatial resolution. We used a double pulse YAG laser (200mJ, 15Hz at 532 nm) with a high resolution double frame camera (2048 pixel x 2048 pixels, 15Hz). The experiments involve 200 liters (200L) of liquid (acetone and water) in a 58 cm diameter pool. The pool is located in the wind tunnel facility. The study presents 2 different wind velocities (2m.s-1 and 4m.s-1) and four different dike step heights (0 cm, 3 cm, 6 cm and 10 cm). Displacement vector maps are obtained after adaptative correlation and related processing. The final results are also crossed with IR measurements and open new fields of investigation that will be discussed.

Forestier, Serge; Heymes, Frédéric; Slangen, Pierre; Munier, Laurent; Lapébie, Emmanuel; Dusserre, Gilles

109

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

110

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

111

A Comparison of Anemometer and Lidar-Sensed Wind Velocity Data  

Microsoft Academic Search

Comparisons between measurements of a wind component by a Doppler lidar and by a conventional anemometer are presented. The two measurement techniques provided thirteen 15 min data sets which agreed within 0.04 m s1 on the average. The maximum difference was 0.12 m s1, which constitutes less than 3% discrepancy, referred to the period average. The results conclusively demonstrate the

M. J. Post; R. L. Schwiesow; R. E. Cupp; D. A. Haugen; J. T. Newman

1978-01-01

112

Uncertainties in wind speed dependent CO 2 transfer velocities due to airflow distortion at anemometer sites on ships  

Microsoft Academic Search

Data from platforms, research vessels and mer- chant ships are used to estimate ocean CO2 uptake via param- eterisations of the gas transfer velocity (k) and measurements of the difference between the partial pressures of CO2 in the ocean (pCO2 sw) and atmosphere (pCO2 atm) and of wind speed. Gas transfer velocities estimated using wind speed dependent parameterisations may be

F. Griessbaum; B. I. Moat; Y. Narita; M. J. Yelland; O. Klemm; M. Uematsu

2010-01-01

113

Cluster/PEACE Electron Velocity Distribution Function Modeling in the Solar Wind  

NASA Astrophysics Data System (ADS)

We present a study of the kinetic properties of the electron velocity distribution functions in the solar wind to model the electron heat-flux and temperature anisotropy, to investigate the stability of electron to the excitation of whistler waves. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focused in the mechanisms that control and regulates whistler electron instabilities in the solar wind. These mechanisms are not well understood. We investigate the electron heat-flux and temperature anisotropy as a function of two important parameters, namely the electron parallel plasma ?e\\Vert and the electron collisional age Ae defined as the number of collisions suffered by an electron during the expansion of the solar wind. The goal is to check whether the electrons are constrained and regulated by some instability (e.g., the whistler instability), or are driven by collisions. The electron heat-flux and temperature anisotropy are determined by moments of the velocity distribution functions (VDF) and/or model fitting of the electron VDF using a superposition of a bi-Maxwellian core distribution, bi-Kappa halo and strahl distributions.

Chinchilla, T. N.; Viñas, A. F.; Goldstein, M. L.

2007-12-01

114

Comparative Flight and Full-Scale Wind-Tunnel Measurements of the Maximum Lift of an Airplane  

NASA Technical Reports Server (NTRS)

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

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

1938-01-01

115

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

116

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

NASA Astrophysics Data System (ADS)

This study provides a fast and easy-to-apply method to estimate threshold friction velocity (TFV) of wind erosion in the field. Wind tunnel experiments and a variety of ground measurements including air gun, pocket penetrometer, torvane, and roughness chain were conducted in Moab, Utah and cross-validated in the Mojave Desert, California. Patterns between TFV and ground measurements were examined to identify the optimum method for estimating TFV. The results show that TFVs were best predicted using the air gun and penetrometer measurements in the Moab sites. This empirical method, however, systematically underestimated TFVs in the Mojave Desert sites. Further analysis showed that TFVs in the Mojave sites can be satisfactorily estimated with a correction for rock cover, which is presumably the main cause of the underestimation of TFVs. The proposed method may be also applied to estimate TFVs in environments where other non-erodible elements such as postharvest residuals are found.

Li, Junran; Okin, Gregory S.; Herrick, Jeffrey E.; Belnap, Jayne; Munson, Seth M.; Miller, Mark E.

2010-05-01

117

Modification of Proton Velocity Distributions by Alfvenic Turbulence in the Solar Wind  

E-print Network

In the present paper, the proton velocity distribution function (VDF)in the solar wind is determined by solving numerically the kinetic evolution equation. We compare the results obtained when considering the effects of ex- ternal forces and Coulomb collisions with those obtained by adding effects of Alfven wave turbulence. We use Fokker-Planck diffusion terms due to Alfvenic turbulence, which take into account observed turbulence spectra and kinetic effects of finite proton gyroradius. Assuming a displaced Maxwellian for the proton VDF at the simulation boundary at 14 solar radii, we show that the turbulence leads to a fast (within several solar radii) development of the anti-sunward tail in the proton VDF. Our results provide a natural explanation for the nonthermal tails in the proton VDFs, which are often observed in-situ in the solar wind beyond 0.3 AU.

Pierrard, Viviane

2013-01-01

118

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

NASA Astrophysics Data System (ADS)

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.

Gurgiolo, C.; Viñas, A. F.; Nieves-Chinchilla, T.; Goldstein, M. L.

2008-12-01

119

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

120

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

121

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

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

122

Dynamics of Low-latitude Thermosphere-Ionosphere from Coincident Observations of Zonal Neutral Winds and EPB Velocity from Brazil and Peru  

NASA Astrophysics Data System (ADS)

The Remote Equatorial Nighttime Observatory of Ionospheric Regions (RENOIR) experiment comprises a suite of instruments operating in northeastern Brazil at Cajazeiras (6.86°S, 38.56°W) and Cariri (7.38°S, 36.53°W) since 2009. This experiment consists of a wide-angle imaging system at Cajazeiras and Fabry-Perot interferometers (FPI) at each site. As part of a separate experiment, two FPIs were deployed in western Peru at Merihill (11.96°S, 76.86°W) and Nazca (14.97°S, 74.89°W) in 2010. In this presentation, we discuss the results obtained from these experiments. When operating individually, each FPI provides measurements of the zonal or meridional neutral winds in the cardinal look directions. A second mode is available, the common volume mode, in which two FPIs (in either Brazil or Peru) make coordinated and collocated measurements of both the zonal and meridional winds. Using the resultant data, we present the climatology of thermospheric neutral winds during the transition from the deep solar minimum to the impending solar maximum conditions from both the east and west coasts of South America. Furthermore, we discuss the coupling between the thermosphere and ionosphere through an analysis of coincident observations of the zonal neutral winds and the drift velocities of Equatorial Plasma Bubbles (EPBs). The results show the neutral winds and EPB drift velocities agree well, illustrating that the F-region dynamo is, in general, fully developed. However, in the early evening hours, the EPB drift velocity is slower than that of the neutral winds on several occasions suggesting the F-region dynamo is not fully activated during the development phase of the EPBs.

Chapagain, N. P.; Makela, J. J.; Meriwether, J. W.; Fisher, D. J.; Chau, J. L.; Buriti, R.

2013-05-01

123

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

124

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

NASA Technical Reports Server (NTRS)

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

Smith, M. A. H.

1978-01-01

125

Nearly Dissipationless Evolution of Solar Wind Velocity Fluctuations Near the Sun  

NASA Astrophysics Data System (ADS)

Various observations have suggested that there is a need for a strong dissipation mechanism in the solar wind at Solar Probe distances in order to bring agreement between coronal and in situ observations of fluctuations in the plasma velocity. This paper will show that using the best data we have, from the SOHO SUMER and UVCS measurements in the corona and Helios measurements from 0.3 to 1 AU, that the observations match quite well a nearly dissipationless (WKB) evolution apart from the turbulent dissipation known to take place in the heliosphere. The evolution of the amplitudes, especially in unstructured slow or fast solar wind, is consistent with a model in which the turbulent dissipation begins to be important some distance out in the heliosphere (0.2 AU?), and does not play a strong role closer in. Fluctuations in more structured, less Alfvénic, wind may have undergone more dissipation, but are consistent with the same level of fluctuations near the Sun as the Alfvénic regions.

Roberts, D.

2012-12-01

126

Zonal wind velocity profiles in the equatorial electrojet derived from phase velocities of type II radar echoes  

NASA Astrophysics Data System (ADS)

Zonal wind profiles in the daytime equatorial electrojet are inferred from the Doppler shifts of type II radar echoes observed at the Jicamarca Radio Observatory (JRO) in Perú. The inference is based on a three-dimensional electrostatic potential model. The model includes anomalous effects and is constrained by radar and magnetometer data. The amplitude and phase of the calculated zonal wind profiles are in general agreement with representative wind profiles measured by the WINDII instrument on board the Upper Atmosphere Research Satellite (UARS). The calculated winds also have the same general characteristics as zonal wind profiles measured by rocket-borne chemical release experiments. However, the magnitude of the latter are larger than the former. The temporal behavior of the calculated zonal winds suggests a downward phase progression with a roughly semidiurnal period.

Shume, E. B.; Hysell, D. L.; Chau, J. L.

2005-12-01

127

Assessing Southern Hemisphere Westerly Wind Changes during the Last Glacial Maximum using Paleo-data Synthesis (Invited)  

NASA Astrophysics Data System (ADS)

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

Kohfeld, K. E.; Graham, R. M.; De Boer, A. M.; Wolff, E. W.; Sime, L. C.; Le Quere, C.; Bopp, L.

2013-12-01

128

Electron Velocity Distribution Function in Magnetic Clouds in the Solar Wind  

NASA Technical Reports Server (NTRS)

We present a study of the kinetic properties of the electron velocity distribution functions within magnetic clouds, since they are the dominant thermal component. The study is based on high time resolution data from the GSFC WIND/SWE electron spectrometer and the Berkeley 3DP electron plasma instruments. Recent studies on magnetic clouds have shown observational evidence of anti-correlation between the total electron density and electron temperature, which suggest a polytrope law P(sub e) = alpha(Nu(sub e) (sup gamma)) for electrons with the constant gamma approximates 0.5 < 1. This anti-correlation and small polytropic gamma-values is interpreted in the context of the presence of highly non-Maxwellian electron distributions (i.e. non-thermal) within magnetic clouds. These works suggested that the non-thermal electrons can contribute as much as 50% of the total electron pressure within magnetic clouds. We have revisited some of the magnetic cloud events previously studied and attempted to quantify the nature of the non-thermal electrons by modeling the electron velocity distribution function using a kappa distribution function to characterize the kinetic non-thermal effects. If non-thermal tail effects are the source for the anti-correlation between the moment electron temperature and density and if the kappa distribution is a reasonable representative model of non-thermal effects, then the electron velocity distribution within magnetic clouds should show indication for small K-values when gamma < 1.

Nieves-Chinchil, Teresa; Vinas, Adolfo F.; Bale, Stuart D.

2006-01-01

129

Calculation of area-averaged vertical profiles of the horizontal wind velocity from volume-imaging lidar data  

NASA Astrophysics Data System (ADS)

Area-averaged horizontal wind measurements are derived from the motion of spatial inhomogeneities in aerosol backscattering observed with a volume-imaging lidar. Spatial averaging provides high precision, reducing sample variations of wind measurements well below the level of turbulent fluctuations, even under conditions of very light mean winds and strong convection or under the difficult conditions represented by roll convection. Wind velocities are measured using the two-dimensional spatial cross correlation computed between successive horizontal plane maps of aerosol backscattering, assembled from three-dimensional lidar scans. Prior to calculation of the correlation function, three crucial steps are performed: (1) the scans are corrected for image distortion by the wind during a finite scan time; (2) a temporal high pass median filtering is applied to eliminate structures that do not move with the wind; and (3) a histogram equalization is employed to reduce biases to the brightest features.

Schols, J. L.; Eloranta, E. W.

1992-11-01

130

Calculation of area-averaged vertical profiles of the horizontal wind velocity from volume-imaging lidar data  

NASA Technical Reports Server (NTRS)

Area-averaged horizontal wind measurements are derived from the motion of spatial inhomogeneities in aerosol backscattering observed with a volume-imaging lidar. Spatial averaging provides high precision, reducing sample variations of wind measurements well below the level of turbulent fluctuations, even under conditions of very light mean winds and strong convection or under the difficult conditions represented by roll convection. Wind velocities are measured using the two-dimensional spatial cross correlation computed between successive horizontal plane maps of aerosol backscattering, assembled from three-dimensional lidar scans. Prior to calculation of the correlation function, three crucial steps are performed: (1) the scans are corrected for image distortion by the wind during a finite scan time; (2) a temporal high pass median filtering is applied to eliminate structures that do not move with the wind; and (3) a histogram equalization is employed to reduce biases to the brightest features.

Schols, J. L.; Eloranta, E. W.

1992-01-01

131

THE LICK AGN MONITORING PROJECT: VELOCITY-DELAY MAPS FROM THE MAXIMUM-ENTROPY METHOD FOR Arp 151  

SciTech Connect

We present velocity-delay maps for optical H I, He I, and He II recombination lines in Arp 151, recovered by fitting a reverberation model to spectrophotometric monitoring data using the maximum-entropy method. H I response is detected over the range 0-15 days, with the response confined within the virial envelope. The Balmer-line maps have similar morphologies but exhibit radial stratification, with progressively longer delays for H{gamma} to H{beta} to H{alpha}. The He I and He II response is confined within 1-2 days. There is a deficit of prompt response in the Balmer-line cores but strong prompt response in the red wings. Comparison with simple models identifies two classes that reproduce these features: free-falling gas and a half-illuminated disk with a hot spot at small radius on the receding lune. Symmetrically illuminated models with gas orbiting in an inclined disk or an isotropic distribution of randomly inclined circular orbits can reproduce the virial structure but not the observed asymmetry. Radial outflows are also largely ruled out by the observed asymmetry. A warped-disk geometry provides a physically plausible mechanism for the asymmetric illumination and hot spot features. Simple estimates show that a disk in the broad-line region of Arp 151 could be unstable to warping induced by radiation pressure. Our results demonstrate the potential power of detailed modeling combined with monitoring campaigns at higher cadence to characterize the gas kinematics and physical processes that give rise to the broad emission lines in active galactic nuclei.

Bentz, Misty C.; Barth, Aaron J.; Walsh, Jonelle L. [Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States); Horne, Keith [SUPA Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Bennert, Vardha Nicola; Treu, Tommaso [Physics Department, University of California, Santa Barbara, CA 93106 (United States); Canalizo, Gabriela [Institute of Geophysics and Planetary Physics, University of California, Riverside, CA 92521 (United States); Filippenko, Alexei V. [Department of Astronomy, University of California, Berkeley, CA 94720-3411 (United States); Gates, Elinor L. [Lick Observatory, P.O. Box 85, Mount Hamilton, CA 95140 (United States); Malkan, Matthew A. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90024 (United States); Minezaki, Takeo [Institute of Astronomy, School of Science, University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan); Woo, Jong-Hak, E-mail: mbentz@uci.ed [Astronomy Program, Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 151-742 (Korea, Republic of)

2010-09-01

132

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

NASA Astrophysics Data System (ADS)

Heterodyne CO2 Doppler lidar measurements of horizontal wind velocity from the surface to 11,000 feet AGL using the Velocity Azimuth Display (VAD) method were made at Holloman AFB, NM from the end of July through mid-August 1998. These data were entered real-time into the space maneuver vehicle descent analysis program to make flight performance predictions needed for test decisions. Daily measurements encompassed the early morning time period associated with the stably-stratified nocturnal boundary layer (NBL). Measurement periods were characterized by growth the decay of wind maxima or jets at different altitudes. Strong vertical shears were often observed in conjunction with these wind maxima. Relative backscatter profiles at the lowest altitudes exhibited periodic oscillations on most mornings. Relative backscatter profiles at the lowest altitudes exhibited periodic oscillations on most mornings. The observed NBL wind profiles were poorly represented by the Ekman model.

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

1999-08-01

133

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

134

Determination of the Maximum Aerodynamic Efficiency of Wind Turbine Rotors with Winglets  

Microsoft Academic Search

The present work contains theoretical considerations and computational results on the nature of using winglets on wind turbines. The theoretical results presented show that the power augmentation obtainable with winglets is due to a reduction of tip-effects, and is not, as believed up to now, caused by the downwind vorticity shift due to downwind winglets. The numerical work includes optimization

Jeppe Johansen

2007-01-01

135

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

PubMed Central

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.

2014-01-01

136

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

Microsoft Academic Search

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

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

1999-01-01

137

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

138

Saharan Wind Regimes Traced by the Sr-Nd Isotopic Composition of Subtropical Atlantic Sediments: Last Glacial Maximum vs Today  

NASA Astrophysics Data System (ADS)

New Nd-Sr isotopic data on the <30 ?m lithic particles of surface and Last Glacial Maximum sediments recovered along the African margin between the Equator and the Gibraltar Strait are presented in combination with grain-size measurements. This <30 ?m size fraction allows us to eliminate any hemipelagic contribution that could occur in the coarser fractions. In the eolian fraction, both Sr and Nd isotopic tracers reveal the same major northwestern origin (Mauritania, Mali, southern Algeria and Morocco). The Archaean formations of the western Saharan shield could be the source of the very unradiogenic ratios observed here. The more southern regions (Senegal, Guinea) act only as secondary sources. A similar pattern is observed for the LGM. Lithic particles are mostly transported by both Trade and Saharan Air Layer (SAL) winds, along an approximate NE-SW axis; this main feature matches the 'southern plume', characterizing the dust transport observed during winter. No significant latitudinal shift of the belt winds is observed between the LGM and today. At the LGM, however, dust fluxes were 2-4 times higher than today, leading to a more 'Archaean-type' imprint in the deposits. We do not observe any clear relationship between the latitudinal variability of the upwelling systems identified in this region at the LGM and the location of the major wind systems. Both enhanced aridity on the continent and increased wind speed probably occurred together over western tropical Africa during the Last Glacial period.

Grousset, F. E.; Parra, M.; Bory, A.; Martinez, P.; Bertrand, P.; Shimmield, G.; Ellam, R. M.

139

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

140

Vertical velocity and turbulence aspects during Mistral events as observed by UHF wind profilers  

NASA Astrophysics Data System (ADS)

The general purpose of this paper is to experimentally study mesoscale dynamical aspects of the Mistral in the coastal area located at the exit of the Rhône-valley. The Mistral is a northerly low-level flow blowing in southern France along the Rhône-valley axis, located between the French Alps and the Massif Central, towards the Mediterranean Sea. The experimental data are obtained by UHF wind profilers deployed during two major field campaigns, MAP (Mesoscale Alpine Program) in autumn 1999, and ESCOMPTE (Expérience sur Site pour COntraindre les Modèles de Pollution atmosphériques et de Transports d'Emission) in summer 2001. Thanks to the use of the time evolution of the vertical profile of the horizontal wind vector, recent works have shown that the dynamics of the Mistral is highly dependent on the season because of the occurrence of specific synoptic patterns. In addition, during summer, thermal forcing leads to a combination of sea breeze with Mistral and weaker Mistral due to the enhanced friction while, during autumn, absence of convective turbulence leads to substantial acceleration as low-level jets are generated in the stably stratified planetary boundary layer. At the exit of the Rhône valley, the gap flow dynamics dominates, whereas at the lee of the Alps, the dynamics is driven by the relative contribution of "flow around" and "flow over" mechanisms, upstream of the Alps. This paper analyses vertical velocity and turbulence, i.e. turbulent dissipation rate, with data obtained by the same UHF wind profilers during the same Mistral events. In autumn, the motions are found to be globally and significantly subsident, which is coherent for a dry, cold and stable flow approaching the sea, and the turbulence is found to be of pure dynamical origin (wind shears and mountain/lee wave breaking), which is coherent with non-convective situations. In summer, due to the ground heating and to the interactions with thermal circulation, the vertical motions are less pronounced and no longer have systematic subsident charateristics. In addition, those vertical motions are found to be much less developed during the nighttimes because of the stabilization of the nocturnal planetary boundary layer due to a ground cooling. The enhanced turbulent dissipation-rate values found at lower levels during the afternoons of weak Mistral cases are consistent with the installation of the summer convective boundary layer and show that, as expected in weaker Mistral events, the convection is the preponderant factor for the turbulence generation. On the other hand, for stronger cases, such a convective boundary layer installation is perturbed by the Mistral.

Caccia, J.; Guénard, V.; Benech, B.; Campistron, B.; Drobinski, P.

2004-11-01

141

Flow past a thin wedge in a wind tunnel with partially perforated walls at high subsonic velocities  

Microsoft Academic Search

The problem of flow past a thin two-dimensional wedge at high subsonic velocity in a wind tunnel with partially perforated walls is considered for low suction flow rates. The solution of this model problem may be used in determining the optimal parameters of the suction system for which the aerodynamic characteristics in the tunnel are closest to those in an

E. G. Shifrin

1966-01-01

142

Reducing the background noise level in the test section of a wind tunnel for transonic flow velocities  

Microsoft Academic Search

The paper reports the results of an experimental study of the background noise in the test section of a wind tunnel with perforated walls. The principal sources of the noise at transonic flow velocities are identified. Some methods for reducing the level of the background noise are discussed, and their efficiency evaluated.

A. G. Ereza; V. G. Mikeladze; A. G. Munin; E. P. Stoliarov; R. D. Filippova; A. N. Shliagun

1990-01-01

143

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

144

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

NASA Astrophysics Data System (ADS)

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

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

2012-11-01

145

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

146

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

NASA Astrophysics Data System (ADS)

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

Ng, C. K.

2014-05-01

147

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

NASA Astrophysics Data System (ADS)

This is the first study to compare plasma depletion drifts with the ambient plasma drifts and neutral winds in the post sunset equatorial ionosphere using global-scale satellite observations. 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 operated on the IMAGE satellite during 10 March to 7 June 2002. These depletion drift velocities are compared with the simultaneously measured ion drift velocities and 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 18:00-20:00 magnetic local time, and after 21:00, the variations of these velocities are similar. The difference of the plasma depletion drift with the background is found to be smaller at lower latitudes. Furthermore, the zonal drift velocity of the depletion is found 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 those studies use models and they only compare the depletion drifts with the modeled neutral winds. This study provides a measure of the difference that has never been studied before by any study using global observations. It has been suggested that polarization electric fields inside the plasma depletion structure drive the plasma to drift westward and thus the depletion structure moves to the east. The latitudinal gradient of the depletion drift velocity seen here in this study could also be explained by the polarization electric fields. For the C-shaped (reversed C) depletion, the polarization electric fields inside the depletion drive a westward drift of plasma and this drift velocity changes with increasing latitude. Consequently, the depletion drift has a latitudinal gradient becoming significant at higher latitudes.

Liu, Guiping; England, Scott L.; Frey, Harald U.; Immel, Thomas J.; Lin, Chin S.; Pacheco, Edgardo E.; Häusler, Kathrin; Doornbos, Eelco

2013-11-01

148

Design of a control scheme for a maximum power extraction in low power wind turbine-generator system  

NASA Astrophysics Data System (ADS)

This document presents the modeling of a wind turbine-generator system and developing a control scheme for maximum power extraction. The system comprises a low-power variable speed wind rotor coupled to a squirrel cage induction generator through gearbox. The generator delivers electrical energy to a DC load through a PWM three phase rectifier which control variables are duty cycle and the fundamental frequency of the modulated signal. The control scheme maintains constant relationship voltage/frequency in the stator of the generator to operate the machine with constant air gap flow at its nominal value, thereby decreasing electrical losses in the circuit of the stator and rotor. The controller is based on MPPT algorithms for determining the operating point the system and achieve the proper mechanical speed shaft. The performance is evaluated through simulations in MatlabRTM/simulink. and presents this type of control as a good alternative for handling low-power wind turbine-generator systems effectively and efficiently

Henao Bravo, Elkin Edilberto

149

Three dimensional modeling with the changeable solar wind velocity and expected spatial distributions of the gradients and anisotropy of Galactic Cosmic Rays  

Microsoft Academic Search

We develop a three dimensional (3-D) model of the recurrent decreases (Forbush effect) of GCR including the changeable solar wind velocity. We found the solution of the equation divB = 0 of the Interplanetary Magnetic field (IMF) B for the azimuthally dependence of the radial component of the solar wind velocity. In this case there exist all three components -

Michael Alania; Renata Modzelewska; Anna Wawrzynczak-Szaban

2008-01-01

150

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

151

Calculation of area-averaged vertical profiles of the horizontal wind velocity from volume-imaging lidar data  

SciTech Connect

This work is part of the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), an international land-surface-atmosphere experiment aimed at improving the way climate models represent energy, water, heat, and carbon exchanges, and improving the utilization of satellite based remote sensing to monitor such parameters. Here the authors report on the use of volume imaging LIDAR to calculate horizontal wind velocities in different vertical profiles. The LIDAR observes backscatter from naturally occurring aerosols, and is capable of imaging a 50 to 70 km[sup 2] area every 3 to 4 minutes. Spatial averaging of the wind velocities has the advantage of averaging out convective scale velocities which are inherent in all measurements, and which can only be averaged out of fixed measurements by averaging for times long compared to the drift time for such convective structures to pass the measurement point, which is often of the order of hours. Data have been analyzed for two particular cases, one a convective light wind case, and the other a case with moderate to high wind speeds, and shear effects.

Schols, J.L.; Eloranta, E.W. (Univ. of Wisconsin, Madison (United States))

1992-11-30

152

Diode laser lidar wind velocity sensor using a liquid-crystal retarder for non-mechanical beam-steering.  

PubMed

We extend the functionality of a low-cost CW diode laser coherent lidar from radial wind speed (scalar) sensing to wind velocity (vector) measurements. Both speed and horizontal direction of the wind at ~80 m remote distance are derived from two successive radial speed estimates by alternately steering the lidar probe beam in two different lines-of-sight (LOS) with a 60° angular separation. Dual-LOS beam-steering is implemented optically with no moving parts by means of a controllable liquid-crystal retarder (LCR). The LCR switches the polarization between two orthogonal linear states of the lidar beam so it either transmits through or reflects off a polarization splitter. The room-temperature switching time between the two LOS is measured to be in the order of 100 ?s in one switch direction but 16 ms in the opposite transition. Radial wind speed measurement (at 33 Hz rate) while the lidar beam is repeatedly steered from one LOS to the other every half a second is experimentally demonstrated - resulting in 1 Hz rate estimates of wind velocity magnitude and direction at better than 0.1 m/s and 1° resolution, respectively. PMID:25401817

Rodrigo, Peter John; Iversen, Theis F Q; Hu, Qi; Pedersen, Christian

2014-11-01

153

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

154

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

155

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

156

Limits imposed by solenoid damage on the maximum velocity achieved by an electromagnetic coilgun: A computational study  

NASA Astrophysics Data System (ADS)

CAD has set up an electromagnetic acceleration and impact facility for studies of material fracture and deformation at high strain rates. The target is to reach projectile velocities of 200-500 m/s. The mechanical strength of the solenoid coil and potting material is an important factor affecting coil survival during experiments. We have performed a computational study, using the materials and coil and circuit parameters typically used in experiments, and found the operating limits up to which the coil can survive without breaking.

Madhavan, S.; Sijoy, C. D.; Pahari, S.; Chaturvedi, S.

2012-06-01

157

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

PubMed

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

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

2008-01-15

158

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

SciTech Connect

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

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

2013-03-15

159

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

NASA Astrophysics Data System (ADS)

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 Alfvén 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 relation can be extended to the more general core-halo-strahl feature in the solar wind. The temperature ratio between the core and hot components is nearly independent of the heliospheric distance to the Sun. We show that the core-halo relative drift previously reported is a relic of the fully saturated two-stream instability. Our theoretical results are consistent with the observations while new tests for this model are provided.

Che, H.; Goldstein, M. L.

2014-11-01

160

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

Microsoft Academic Search

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

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

1979-01-01

161

FlowCapt: a new acoustic sensor to measure snowdrift and wind velocity for avalanche forecasting  

Microsoft Academic Search

Wind can create even greater unstable accumulations of snow in mountainous areas than heavy snowfalls. But knowing wind conditions is not sufficient to predict these accumulations because their formations also depend on the snow quality of the snowpack surface upwind of the release zone. Consequently, assessment of snowdrift is required to improve avalanche forecasting. In accordance with this assumption, a

V Chritin; R Bolognesi; H Gubler

1999-01-01

162

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

NASA Astrophysics Data System (ADS)

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

Fenton, L. K.

2012-12-01

163

Plasma velocities in the Heliosheath and the influence of the interstellar wind  

E-print Network

A new coordinate system (Interstellar Heliospheric Coordinates, or IHC) is introduced to enable the detailed study of the influence of the interstellar wind on the heliosheath. Recent, in situ measurements of plasma ...

Chronopoulos, Chris

2009-01-01

164

Using pollution to determine the dimension of the atmosphere: "Does the wind have a velocity?" reads a subtitle of an eighty-year old paper by  

E-print Network

Using pollution to determine the dimension of the atmosphere: "Does the wind have a velocity of the concentrations of small particles pushed around by the wind ­ in our case pollution - is made possible the small scale supposedly 3-D turbulence which is thus reduced to a kind of background noise. But what

Lovejoy, Shaun

165

Assessing effect of wind tunnel sizes on air velocity and concentration boundary layers and on ammonia emission estimation using computational fluid dynamics (CFD)  

Microsoft Academic Search

The objective of this study was to investigate the effect of different geometric sizes of wind tunnels on aerial boundary layers above the emission surface and therefore their effect on ammonia emission using CFD tool. Five wind tunnels of different sizes were used for the CFD simulation. Detail experimental measurements on air velocity and concentration profiles above the emission surface

Chayan Kumer Saha; Wentao Wu; Guoqiang Zhang; Bjarne Bjerg

2011-01-01

166

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

NASA Astrophysics Data System (ADS)

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

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

2005-01-01

167

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

168

Vector Wind Velocity, Speed, and Mode Summaries for the Southeastern U. S.  

SciTech Connect

This report presents wind speed and direction summaries for a wide area of the Southeastern United States (including EPA Region 4) and portions of the Ohio and Mississippi River Valleys in a monthly time series format that is further broken down for eight hours of the day (01:00, 04:00, 07:00, 10:00, 13:00, 16:00, 19:00, 22:00 EST). The data used for these summaries were obtained from the International Station MeteorologicalClimate Summary (FCCA, 1996), a publicly available source of tabular data from weather stations around the world distributed through the National Climatic Data Center. The advantage of examining the data in the form presented in this report is that it is far easier to examine and understand regional and diurnal weather patterns than would be possible with the tabular data in its original format. The winds presented here can be viewed online in any of three formats through an Internet link. The first format is the traditional wind rose as used in our earlier reports f or 13 stations in the Southeast, c.f., Weber, Buckley, and Parker 2002 and Weber, Buckley, and Kurzeja 2003. The second format is the mode, or most frequent wind direction sector from the wind rose plots (i.e., the longest ''petal'' from the individual station roses). Finally, the third format depicted is the average wind vector. The average wind vector was determined by extracting the wind speed and direction for each of the 16 sectors from a station's wind record and then summing components of these vectors for the month and time of observation. Each station was then plotted on a sequence of maps for the Southeastern U.S. using ArcView software. These maps form a time series in 3-hour increments showing changes in vector wind speed and direction for each month of the year. The complete set of color figures are too numerous to be included in this report, but may be accessed by contacting one of the authors.

WEBER, ALLENH.

2004-08-18

169

Review and critical analysis of the research papers published till date on maximum power point tracking in wind energy conversion system  

Microsoft Academic Search

Maximum power point tracking (MPPT) is a very important necessity in a system of energy conversion from a renewable energy source. Every year a number of publications appear in various journals and conferences claiming to offer better and faster MPPT techniques for wind energy conversion system (WECS). This research paper provides a concise yet comprehensive critical analysis of these techniques

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

2010-01-01

170

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

171

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

Microsoft Academic Search

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

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

1982-01-01

172

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

173

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

174

Maximum Power Extraction from a Small Wind Turbine Emulator using a DC - DC Converter Controlled by a Microcontroller  

Microsoft Academic Search

An isolated small wind turbine emulator based on a separately excited DC motor is developed to emulate and evaluate the performance of a small wind turbine using different control strategies. The test rig consists of a 3HP separately excited DC motor coupled to a synchronous generator. A dump load is connected to the generator through a buck-boost converter controlled by

M. T. Iqbal; J. E. Quaicoe

2006-01-01

175

Wind motor applications for transportation  

SciTech Connect

Motion equation for a vehicle equipped with a wind motor allows, taking into account the drag coefficients, to determine the optimal wind drag velocity in the wind motor`s plane, and hence, obtain all the necessary data for the wind wheel blades geometrical parameters definition. This optimal drag velocity significantly differs from the flow drag velocity which determines the maximum wind motor power. Solution of the motion equation with low drag coefficients indicates that the vehicle speed against the wind may be twice as the wind speed. One of possible transportation wind motor applications is its use on various ships. A ship with such a wind motor may be substantially easier to steer, and if certain devices are available, may proceed in autonomous control mode. Besides, it is capable of moving within narrow fairways. The cruise speed of a sailing boat and wind-motored ship were compared provided that the wind velocity direction changes along a harmonic law with regard to the motion direction. Mean dimensionless speed of the wind-motored ship appears to be by 20--25% higher than that of a sailing boat. There was analyzed a possibility of using the wind motors on planet rovers in Mars or Venus atmospheric conditions. A Mars rover power and motor system has been assessed for the power level of 3 kW.

Lysenko, G.P.; Grigoriev, B.V.; Karpin, K.B. [Moscow Aviation Inst. (Russian Federation)

1996-12-31

176

Scale-dependent angle of alignment between velocity and magnetic field fluctuations in solar wind turbulence  

Microsoft Academic Search

Under certain conditions, freely decaying magnetohydrodynamic (MHD) turbulence evolves in such a way that velocity and magnetic field fluctuations ?v and ?B approach a state of alignment in which ?v$\\\\propto$?B. This process is called dynamic alignment. Boldyrev has suggested that a similar kind of alignment process occurs as energy cascades from large to small scales through the inertial range in

J. J. Podesta; B. D. G. Chandran; A. Bhattacharjee; D. A. Roberts; M. L. Goldstein

2009-01-01

177

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

SciTech Connect

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

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

1982-01-01

178

Differential velocity between solar wind protons and alpha particles in pressure balance structures  

Microsoft Academic Search

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

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

2004-01-01

179

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

180

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

181

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

182

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

PubMed

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

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

2004-01-01

183

Temporal and spatial rotational spectra of wind-velocity variations with periods 2-40 days in lower and middle atmospheres of the Earth  

Microsoft Academic Search

Current work is dedicated to the investigation of temporal and spatial energy spectra of wave processes in the field of lower and middle atmospheres (0-100 km) of the Earth. For analysis we used data of wind measurements at heights 80-100 km performed at meteor radar in Kazan (56N, 49E). Also we used data of BADC UK MO containing wind velocity

Dmitry V. Korotyshkin; Antonina N. Fahrutdinova; V. V. Guryanov

2004-01-01

184

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

185

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

186

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

187

Full field flow visualization and computer-aided velocity measurements in a bank of cylinders in a wind tunnel  

NASA Technical Reports Server (NTRS)

The full field flow tracking (FFFT) method that is presented in this paper uses a laser-generated, mechanically strobed planar sheet of light, a low luminosity TV camera coupled with a long distance microscope, and a computer-controlled video recorder to study nonintrusively and qualitatively the flow structures in a bank of cylinders that are placed in a wind tunnel. This setup simulates an upscale version of the geometry of internal cooling passageways characteristic of small air-cooled radial turbines. The qualitative images supplied by the FFFT system are processed by means of a computer-integrated image quantification (CIIQ) method into quantitative information, trajectories and velocities, that describe the flow upstream of and within the bank of cylinders. The tracking method is Lagrangian in concept, and permits identification and tracking of the same particle, thus facilitating construction of time dependent trajectories and the calculation of true velocities and accelerations. The error analysis evaluates the accuracy with which the seed particles follow the flow and the errors incurred during the quantitative processing of the raw data derived from the FFFT/CIIQ method.

Braun, M. J.; Canacci, V. A.; Russell, L. M.

1992-01-01

188

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

189

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

190

Wind-tunnel and Flight Investigations of the Use of Leading-Edge Area Suction for the Purpose of Increasing the Maximum Lift Coefficient of a 35 Degree Swept-Wing Airplane  

NASA Technical Reports Server (NTRS)

An investigation was undertaken to determine the increase in maximum lift coefficient that could be obtained by applying area suction near the leading edge of a wing. This investigation was performed first with a 35 degree swept-wing model in the wind tunnel, and then with an operational 35 degree swept-wing airplane which was modified in accord with the wind-tunnel results. The wind-tunnel and flight tests indicated that the maximum lift coefficient was increased more than 50 percent by the use of area suction. Good agreement was obtained in the comparison of the wind-tunnel results with those measured in flight.

Holzhauser, Curt A; Bray, Richard S

1956-01-01

191

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

192

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 whi...

Georgiev, L

2005-01-01

193

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

194

VELOCITY-SHEAR-INDUCED MODE COUPLING IN THE SOLAR ATMOSPHERE AND SOLAR WIND: IMPLICATIONS FOR PLASMA HEATING AND MHD TURBULENCE  

SciTech Connect

We analytically consider how velocity shear in the corona and solar wind can cause an initial Alfven wave to drive up other propagating signals. The process is similar to the familiar coupling into other modes induced by non-WKB refraction in an inhomogeneous plasma, except here the refraction is a consequence of velocity shear. We limit our discussion to a low-beta plasma, and ignore couplings into signals resembling the slow mode. If the initial Alfven wave is propagating nearly parallel to the background magnetic field, then the induced signals are mainly a forward-going (i.e., propagating in the same sense as the original Alfven wave) fast mode, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; both signals are compressive and subject to damping by the Landau resonance. For an initial Alfven wave propagating obliquely with respect to the magnetic field, the induced signals are mainly forward- and backward-going fast modes, and a driven signal propagating like a forward-going Alfven wave but polarized like the fast mode; these signals are all compressive and subject to damping by the Landau resonance. A backward-going Alfven wave, thought to be important in the development of MHD turbulence, is also produced, but it is very weak. However, we suggest that for oblique propagation of the initial Alfven wave the induced fast-polarized signal propagating like a forward-going Alfven wave may interact coherently with the initial Alfven wave and distort it at a strong-turbulence-like rate.

Hollweg, Joseph V.; Chandran, Benjamin D. G. [Space Science Center, Morse Hall, University of New Hampshire, Durham, NH 03824 (United States); Kaghashvili, Edisher Kh., E-mail: joe.hollweg@unh.edu, E-mail: ekaghash@aer.com, E-mail: benjamin.chandran@unh.edu [Atmospheric and Environmental Research, A Verisk Analytics Company, 131 Hartwell Avenue, Lexington, MA 02421 (United States)

2013-06-01

195

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

-derived dust emission in semi-arid regions needs to account for the in¯uence of the soil moisture on the wind moisture increases. When the soil moisture content is close to but smaller than the maximum amount as a function of soil moisture and w¢ is derived from retention curves. From this expression, a parametriza

Boyer, Edmond

196

Response of the radiation belt electron flux to the solar wind velocity: Parameterization by radial distance and energy  

NASA Astrophysics Data System (ADS)

The solar wind velocity is the primary driver of the electron flux variability in Earth's radiation belts. The response of the logarithmic flux ("log-flux") to this driver has been determined at the geosynchronous orbit and at a fixed energy [Baker, D.N., McPherron, R.L., Cayton, T.E., Klebesadel, R.W., 1990. Linear prediction filter analysis of relativistic electron properties at 6.6 RE. Journal of Geophysical Research 95(A9), 15,133-15,140) and as a function of L shell and fixed energy [Vassiliadis, D., Klimas, A.J., Kanekal, S.G., Baker, D.N., Weigel, R.S., 2002. Long-term average, solar-cycle, and seasonal response of magnetospheric energetic electrons to the solar wind speed. Journal of Geophysical Research 107, doi:10.1029/2001JA000506). In this paper we generalize the response model as a function of particle energy (0.8-6.4 MeV) using POLAR HIST measurements. All three response peaks identified earlier figure prominently in the high-altitude POLAR measurements. The positive response around the geosynchronous orbit is peak P1 ([tau]=2±1 d; L=5.8±0.5; E=0.8-6.4 MeV), associated with high-speed, low-density streams and the ULF wave activity they produce. Deeper in the magnetosphere, the response is dominated by a positive peak P0 (0±1 d; 2.9±0.5RE; 0.8-1.1 MeV), of a shorter duration and producing lower-energy electrons. The P0 response occurs during the passage of geoeffective structures containing high IMF and high-density parts, such as ICMEs and other mass ejecta. Finally, the negative peak V1 (0±0.5 d; 5.7±0.5RE; 0.8-6.4 MeV) is associated with the "Dst effect" or the quasiadiabatic transport produced by ring-current intensifications. As energies increase, the P1 and V1 peaks appear at lower L, while the Dst effect becomes more pronounced in the region L<3. The P0 effectively disappears for E>1.6 MeV because of low statistics, although it is evident in individual events. The continuity of the response across radial and energy scales supports the earlier hypothesis that each of the three modes corresponds to a qualitatively different type of large-scale electron acceleration and transport.

Vassiliadis, D.

2008-11-01

197

Dependence of solar wind velocity and interplanetary magnetic field on Pc4 magnetic pulsations at low latitudes in India  

NASA Astrophysics Data System (ADS)

Employing an array of three low latitude stations situated in India at Hanley (HAN) (L=1.178 R_{E}), Nagpur (NAG) (L=0.974 R_{E}) and Pondicherry (PON) (L=0.910 R_{E} ), a recent study has been carried out for Ultra Low Frequency (ULF) Magneto-hydrodynamic (MHD) waves in the 6.7 to 22.2 mHz frequency range, designated as Pc4 Magnetic Pulsations. These are observed mainly in the dayside (0400-2000 hrs LT) magnetosphere. The present research has been undertaken for describing the dependence of low latitude Pc4 occurrence (with time resolution of 1 minute) on the Solar Wind Velocity (V_{SW}) (hourly data) and the Interplanetary Magnetic Field (IMF) (hourly data) for the period range 01 January to 31 December, 2005. The mean measured frequency ranges of occurrence for HAN, NAG and PON were determined as 12.9 to 14.6 mHz, 12.7 to 14.2 mHz and 12.0 to 15.0 mHz respectively. The results for the whole year 2005 provided similar patterns of Pc4 occurrence for V_{SW} at all the three stations. Although Pc4 occurrence was reported for V_{SW} ranging from 250 to 1000 km/s, yet the major Pc4 events occurred for a V_{SW} range of 300-700 km/sec. Even though at all the three stations, the IMF magnitude spread up to 22 nT, yet the majority of Pc4 events occurred for a narrower range of 2-10 nT. However, it is important to note that the peak in the Pc4 occurrence was observed for IMF range of 3 to 6 nT. The implications of these results are reported in this study.

Ansari, I. A.; Nafees, K. A.; Sinha, A. K.; Pathan, B. M.

198

The Change in Cosmic Ray Intensity Variation with the Solar Wind Velocity (Using GRAPES3 muon narrow angle telescopes and Kiel neutron monitor)  

Microsoft Academic Search

GRAPES-3 experiment is situated at Ooty in South India 76.7 East 11.4 North. Effective observation area of our muon telescopes is 560 m2. They are the largest detector in the world of its kind. There were several reports that increase of the solar wind velocity suppresses the intensity of cosmic rays. But there are few which studied qualitatively. We have

H. Kojima; Y. Hayashi; K. Hayashi

2008-01-01

199

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

200

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

201

Maximum rates of sustained metabolic rate in cold-exposed Djungarian hamsters (Phodopus sungorus): the second wind.  

PubMed

Djungarian hamsters (Phodopus sungorus) tolerate short-term exposure to ambient temperatures (T(a)s) down to -70°C, but surprisingly, previously appeared to reach maximum sustainable metabolic rate (SusMR) when kept at T(a)s as high as ?-2°C. We hypothesized that SusMR in Djungarian hamsters may be affected by the degree of prior cold acclimation and temporal patterns of T(a) changes experienced by the animals, as average T(a) declines. After cold-acclimation at +5°C for 6 weeks, hamsters reached rates of SusMR that were 35% higher than previously determined and were able to maintain positive energy balances down to T(a) -9°C. SusMR was unaffected, however, by whether mean cold load was constant or caused by T(a)s cycling between +3°C and as low as -25°C, at hourly intervals. At mean T (a)s between +3 and -3°C hamsters significantly reduced body mass and energy expenditure, but were able to maintain stable body mass at lower T (a)s (-5 to -9°C). These results indicate that prior cold-acclimation profoundly affects SusMR in hamsters and that body mass regulation may play an integral part in maintaining positive energy balance during cold exposure. Because the degree of instantaneous cold load had no effect on SusMR, we hypothesize that limits to energy turnover in Djungarian hamsters are not determined by the capacity to withstand extreme temperatures (i.e., peripheral limits) but are due to central limitation of energy intake. PMID:20458591

Ruf, Thomas; Grafl, Beatrice

2010-10-01

202

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

NASA Technical Reports Server (NTRS)

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

Rothermel, Jeffry

1987-01-01

203

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

204

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

205

A novel control of a small wind turbine driven generator based on neural networks  

Microsoft Academic Search

This paper presents a novel control strategy of turbine directly driven permanent magnet synchronous generator (PMSG) for a small wind generation system. Compared to the traditional techniques, this new method has following advantages: 1) the proposed neural networks provides a fast and accurate estimation of actual wind velocity without anemometer; 2) the maximum mechanical power of small wind turbine can

K. L. Shi; H. Li

2004-01-01

206

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

207

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

208

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

NASA Technical Reports Server (NTRS)

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

Scudder, J. D.

1978-01-01

209

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

210

Strahl variations with the Solar Wind properties  

NASA Astrophysics Data System (ADS)

In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze the strahl component in the ambient solar wind since the launch of Cluster. The excursion of Cluster into the solar wind provides the opportunity to analyze this component of the electron velocity distribution function in a wide range of solar wind velocities and densities. The moment density and fluid velocity have been computed by spherical harmonic spectral model method. The analysis shows a correlation of the strahl density with the solar wind velocity and the time variation of the strahl density with solar cycle. This result agrees with the postulate that coronal holes are the source of this population. These preliminary results have been extended to include half solar cycle data (e.g., from 2001) to provide continuous results from solar maximum to minimum.

Nieves-Chinchilla, T.; F.-Viñas, A.; Goldstein, M. L.; Gurgiolo, C.

2009-04-01

211

The Nature of Magnetohydrodynamic Fluctuations in the Solar Wind as Determined from Four-Point Measurements of Magnetic Field and (Electron) Plasma Velocity on Cluster  

NASA Astrophysics Data System (ADS)

One of the goals of the Cluster mission is to use large spacecraft separations (? 10,000 km) to examine the three-dimensional structure of magnetohydrodynamic turbulence in the solar wind. Pioneering work using the magnetometer data has been done in recent years. Analyses have included use of k-filtering or wave telescope, and correlation techniques (e.g., see, Glassmeier et al., 2001; Sahraoui et al., 2003; Matthaeus et al., 2005). The plasma properties of these fluctuations have not been examined due primarily to the lack of four-point measurements of the plasma velocity. We have examined the possibility of using velocity moments computed from high-resolution three-dimensional distribution functions obtained during burst mode from the PEACE experiment on all four Cluster spacecraft. Preliminary analysis suggests that for fluctuations with periods below about 10 sec, spectra of Elsässer variables have spectral indices close to the Kolmogorov value of -5/3 seen in fluid turbulence and known to be characteristic of solar wind turbulence when proton velocities are used. The spectra using PEACE data compare well with spectra for the same time intervals computed using proton velocity moments from the CIS experiment on C1. For some intervals, the PEACE spectra show the presence of highly compressible waves in the Earth's foreshock with periods of ? 30 sec. We will report on progress using multi-spacecraft techniques (e.g., the wave telescope) to identify the wave modes present at times when the spacecraft are in the solar wind at separations as large as 10,000 km. Glassmeier, K. H. et al. (2001), Cluster as a wave telescope--first results from the fluxgate magnetometer, Ann. Geophys., 19, 1439-1447. Sahraoui, F. et al. (2003), Ulf wave identification in the magnetosheath: K-filtering technique applied to Cluster II data, J. Geophys. Res., 108, 1335. Matthaeus, W. H. et al. (2005), Spatial correlation of solar-wind turbulence from two-point measurements, Phys. Rev. Lett., 95.

Goldstein, M. L.; Fazakerley, A.; Narita, Y.; Parks, G.; Roberts, D. A.; Glassmeier, K.; Le, G.

2006-12-01

212

Growing Neural Gas (GNG) based Maximum Power Point Tracking for high performance VOC-FOC based wind generator system with an induction machine  

Microsoft Academic Search

This paper presents a MPPT technique for high performance wind generator with induction machine based on the Growing Neural Gas (GNG) network. Here a GNG network has been trained off-line to learn the turbine characteristic surface torque versus wind speed and machine speed, and implemented on-line so to perform the inversion of this function obtaining the wind free speed on

Maurizio Cirrincione; Marcello Pucci; Gianpaolo Vitale

2009-01-01

213

Effects of non-Maxwellian electron velocity distribution functions and nonspherical geometry on minor ions in the solar wind  

NASA Technical Reports Server (NTRS)

A previous model has shown that in order to account for the charge state distribution in the low-speed solar wind, a high coronal temperature is necessary and that this temperature peak goes together with a peak of nx/np in the corona. In the present paper, one of the assumptions made previously, i.e., that coronal electrons are Maxwellian, is relaxed, and a much cooler model is presented, which could account for the same oxygen charge states in the solar wind due to the inclusion of non-Maxwellian electrons. Also, due to a different choice of the coronal magnetic field geometry, this model would show no enhancement of the coronal nx/np. Results of the two models are then compared, and observational tests to distinguish between the two scenarios are proposed: comparison of directly measured coronal Te to charge state measurements in the solar wind, determination of the coronal nx/np measurement of ion speeds in the acceleration region of the solar wind, and measurement of the frozen-in silicon charge state distribution.

Burgi, A.

1987-01-01

214

Full field flow visualization and computer-aided velocity measurements in a bank of cylinders in a wind tunnel  

Microsoft Academic Search

The full field flow tracking (FFFT) method that is presented in this paper uses a laser-generated, mechanically strobed planar\\u000a sheet of light, a low luminosity TV camera coupled with a long distance microscope, and a computer-controlled videorecorder\\u000a to study non-intrusively and qualitatively the flow structures in a bank of cylinders that are placed in a wind tunnel. This\\u000a setup simulates

M. J. Braun; V. A. Canacci; L. M. Russell

1992-01-01

215

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

216

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

217

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.

218

Source localization corrections for airborne acoustic platforms based on a climatological assessment of temperature and wind velocity profiles  

NASA Astrophysics Data System (ADS)

Acoustic sensors are being employed on airborne platforms, such as Persistent Threat Detection System (PTDS) and Persistent Ground Surveillance System (PGSS), for source localization. Under certain atmospheric conditions, airborne sensors oer a distinct advantage over ground sensors. The performance of both ground and airborne sensors is aected by environmental factors, such as atmospheric turbulence and wind and temperature proles. For airborne sensors, the eects of refraction must be accounted for in order to determine the source coordinates. Such a method for ground-to-air applications has been developed and is further rened here. Ideally, knowledge of the exact atmospheric proles will allow for the most accurate mitigation of refractive eects. However, acoustic sensors deployed in theater are rarely supported by atmospheric sensing systems that retrieve real-time temperature and wind elds. Atmospheric conditions evolve through seasons, time of day, and are strongly location dependent. Therefore, the development of an atmospheric proles database based on a long time series climatological assessment will provide knowledge for use in physics-based bearing estimation algorithms, where otherwise no correction would have been performed. Long term atmospheric data sets from weather modeling systems are used for a climatological assessment of the refraction corrections and localization errors over selected sites.

Ostashev, Vladimir E.; Cheinet, Sylvain; Collier, Sandra L.; Reiff, Christian; Ligon, David A.; Wilson, D. Keith; Noble, John M.; Alberts, W. C. Kirkpatrick, II

2012-06-01

219

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

220

An Analysis of a Turbo-Fan Used to Improve the Velocity Distribution in a Low Speed Wind-Tunnel  

E-print Network

of the tangential and axial velocities relative to the blade at each blade station. Such a pitch distribution is commonly referred to as a perfect helical pitch distribution. Since the blade sections must produce either positive or negative lif t, they should... be symmetrical about the zero lif t chord line. The most significant result of Collar's investigation xs the equation expressing the variation of the desired. turbo-fan solxdity, bc. 8' U a, ~ cosP Where: b is the number of blades in the turbo-f'an. C...

Wells, Otis Dean

2012-06-07

221

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

222

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

NASA Technical Reports Server (NTRS)

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

Moore, M. T.

1980-01-01

223

Three-dimensional elastic lidar winds  

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 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.

1996-07-01

224

Microburst vertical wind estimation from horizontal wind measurements  

NASA Technical Reports Server (NTRS)

The vertical wind or downdraft component of a microburst-generated wind shear can significantly degrade airplane performance. Doppler radar and lidar are two sensor technologies being tested to provide flight crews with early warning of the presence of hazardous wind shear. An inherent limitation of Doppler-based sensors is the inability to measure velocities perpendicular to the line of sight, which results in an underestimate of the total wind shear hazard. One solution to the line-of-sight limitation is to use a vertical wind model to estimate the vertical component from the horizontal wind measurement. The objective of this study was to assess the ability of simple vertical wind models to improve the hazard prediction capability of an airborne Doppler sensor in a realistic microburst environment. Both simulation and flight test measurements were used to test the vertical wind models. The results indicate that in the altitude region of interest (at or below 300 m), the simple vertical wind models improved the hazard estimate. The radar simulation study showed that the magnitude of the performance improvement was altitude dependent. The altitude of maximum performance improvement occurred at about 300 m.

Vicroy, Dan D.

1994-01-01

225

Large-scale variability of wind erosion mass flux rates at Owens Lake. 2. Role of roughness change, particle limitation, change of threshold friction velocity, and the Owen effect  

NASA Astrophysics Data System (ADS)

Variability in airborne particles larger than sand flux for distance scales larger than 200 m was observed during wind erosion episodes on the northeast side of a dry lake bed (Owens Lake). Measurements were made during erosion episodes on a ˜3-km line of wind measuring and sand flux collecting instruments. Data were selected for winds that (1) aligned with the instrument line and (2) had mean speeds cubed at 4-m heights at the beginning, middle, and end of the line that differed by less than 5% (i.e., mean wind speeds differed by less than 1.7%). Four mechanisms were determined to cause the large-scale differences in the mass flux profiles. In order of their importance, the mechanisms are as follows: (1) change of the drag coefficient (or the ratio u*/U, where u* is wind friction velocity and U is mean wind speed from place to place), this is a measure of variability in roughness height; (2) particle limitation (depletion of the loose "available" erodible material on the surface); (3) variation of the threshold friction velocity; and (4) the Owen effect (the increase of u*/U with U).

Gillette, Dale A.; Hardebeck, Ellen; Parker, Jim

1997-11-01

226

Wind Engineering  

NASA Technical Reports Server (NTRS)

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

1983-01-01

227

Saturation wind power potential and its implications for wind energy  

E-print Network

Saturation wind power potential and its implications for wind energy Mark Z. Jacobsona,1 to determine the maximum theo- retical wind power potential on Earth, based on the concept of "saturation". The saturation wind power potential (SWPP) is the maximum wind power that can be extracted upon increasing

228

Full-scale-wind-tunnel Tests of a 35 Degree Sweptback Wing Airplane with High-velocity Blowing over the Training-edge Flaps  

NASA Technical Reports Server (NTRS)

A wind-tunnel investigation was made to determine the effects of ejecting high-velocity air near the leading edge of plain trailing-edge flaps on a 35 degree sweptback wing. The tests were made with flap deflections from 45 degrees to 85 degrees and with pressure ratios across the flap nozzles from sub-critical up to 2.9. A limited study of the effects of nozzle location and configuration on the efficiency of the flap was made. Measurements of the lift, drag, and pitching moment were made for Reynolds numbers from 5.8 to 10.1x10(6). Measurements were also made of the weight rate of flow, pressure, and temperature of the air supplied to the flap nozzles.The results show that blowing on the deflected flap produced large flap lift increments. The amount of air required to prevent flow separation on the flap was significantly less than that estimated from published two-dimensional data. When the amount of air ejected over the flap was just sufficient to prevent flow separation, the lift increment obtained agreed well with linear inviscid fluid theory up to flap deflections of 60 degrees. The flap lift increment at 85 degrees flap deflection was about 80 percent of that predicted theoretically.With larger amounts of air blown over the flap, these lift increments could be significantly increased. It was found that the performance of the flap was relatively insensitive to the location of the flap nozzle, to spacers in the nozzle, and to flow disturbances such as those caused by leading-edge slats or discontinuities on the wing or flap surfaces. Analysis of the results indicated that installation of this system on an F-86 airplane is feasible.

Kelley, Mark W; Tolhurst, William H JR

1955-01-01

229

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

230

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 ÃÂStop #ÃÂ drop down menu sets the number of samples taken, the ÃÂUpdate #ÃÂ 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

2009-07-20

231

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

232

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

233

Pigeon flight in a wind tunnel  

Microsoft Academic Search

1.An 8 part 9 m long wind tunnel, built of wooden frames and chipboards supported by an iron tube base, specially suited for bird flight investigation, is described (Fig. 1, 2). The working section measures 1×1×1.4 m and consists of smoothly fitting interchangeable walls of glass, wood or metal. Maximum velocity is 24 m s-1 (86 km h-1). In the

H.-J. Rothe; W. Nachtigall

1987-01-01

234

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

235

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

236

Describing Velocity  

NSDL National Science Digital Library

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

Consortium, The C.

2012-02-07

237

Numerical simulations of flow fields through conventionally controlled wind turbines & wind farms  

NASA Astrophysics Data System (ADS)

In the current study, an Actuator-Line Model (ALM) is implemented in our in-house pseudo-spectral LES solver SP-WIND, including a turbine controller. Below rated wind speed, turbines are controlled by a standard-torque-controller aiming at maximum power extraction from the wind. Above rated wind speed, the extracted power is limited by a blade pitch controller which is based on a proportional-integral type control algorithm. This model is used to perform a series of single turbine and wind farm simulations using the NREL 5MW turbine. First of all, we focus on below-rated wind speed, and investigate the effect of the farm layout on the controller calibration curves. These calibration curves are expressed in terms of nondimensional torque and rotational speed, using the mean turbine-disk velocity as reference. We show that this normalization leads to calibration curves that are independent of wind speed, but the calibration curves do depend on the farm layout, in particular for tightly spaced farms. Compared to turbines in a lone-standing set-up, turbines in a farm experience a different wind distribution over the rotor due to the farm boundary-layer interaction. We demonstrate this for fully developed wind-farm boundary layers with aligned turbine arrangements at different spacings (5D, 7D, 9D). Further we also compare calibration curves obtained from full farm simulations with calibration curves that can be obtained at a much lower cost using a minimal flow unit.

Emre Yilmaz, Ali; Meyers, Johan

2014-06-01

238

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

239

Design criteria for small wind turbines. Part 2: Wind characterizing  

Microsoft Academic Search

A calculation model to determine turbulent wind velocity and Wind Direction Fluctuations (WDFs) on a rotating wind turbine rotor was developed to draw up simply applicable and rotor type differentiated design criteria. Using statistical methods, fatiguing and extreme wind gusts as well as turbulent WDFs were constructed and determined as dependent upon criteria chosen (exceed chances). Interstationary (mesoscale) WDFs expected

G. L. H. Beugeling; P. E. J. Vermeulen

1985-01-01

240

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

241

33 CFR 156.320 - Maximum operating conditions.  

Code of Federal Regulations, 2013 CFR

...wind velocity is 56 km/hr (30 knots) or more; or (2) The wave height is 3 meters (10 feet) or more. (b) Cargo transfer...The wind velocity exceeds 82 km/hr (44 knots); or (2) Wave heights exceed 5 meters (16...

2013-07-01

242

33 CFR 156.320 - Maximum operating conditions.  

...wind velocity is 56 km/hr (30 knots) or more; or (2) The wave height is 3 meters (10 feet) or more. (b) Cargo transfer...The wind velocity exceeds 82 km/hr (44 knots); or (2) Wave heights exceed 5 meters (16...

2014-07-01

243

Estimation of systematic errors of onboard measurement of angle of attack and sliding angle based on integration of data of satellite navigation system and identification of wind velocity  

Microsoft Academic Search

A method for estimation of systematic errors of onboard measurement of angle of attack and sliding angle of an aircraft in\\u000a the course of flight tests using high precision velocity measurements performed by a satellite navigation system is proposed.\\u000a The main specific feature of the proposed method is that for providing compatibility of measurements of angle of attack and\\u000a sliding

O. N. Korsun; B. K. Poplavskii

2011-01-01

244

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

245

Velocity determination from velocity spectra  

E-print Network

VELOCITY DETERMINATION FRON VELOCITY SPECTRA A Thesis by SUNG JIN YANG Submutted to the Graduate C:lleEe of Texas ASM University in partial fulfill sent of requirement for the degree of EASTER GF SCIENCE December 1973 Naj or Subject...: Ccophysics VELOCITY DETEPddINATION FROM VELOCITY SPECTRA A Thesis by SUNG JIN YANG Approved as to style and content by: ( Chai~ of C a0nitte ) (Read oi: Doper ent-IL irber) ( Meraber ) (i~ &r) Decen'bex' 1973 487460 ABSTRACT Velocity Determinati...

Yang, Sung Jin

2012-06-07

246

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

247

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

NASA Astrophysics Data System (ADS)

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


Wilson, John D.

2004-08-01

248

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

249

Wind turbines in simulated gusts  

NASA Astrophysics Data System (ADS)

The results of trials in the T4 wind tunnel to simulate the effects of gusts on wind turbines are reported. Three-bladed NACA 0012 and 0018 profile and a six bladed 0012 profile machines were examined in gusts of 10 sec duration. The mean free stream velocity was 7-8 m/sec and the gusts generated had an amplitude of 30-40 pct. An aeroelastic analysis was carried out from high speed photographic images taken at 400-4000 images/sec of the blades in steady and gusting flows. The power output was measured by using a variable resistance alternator in the wind turbine, and comparisons were made between the power extracted from a steady flow to flows marked by gusts. It was found that increasing the pitch angle of the blades lowered power coefficient, as predicted, and a maximum power coefficient of 0.42 was obtained, which was higher than predicted for the 0012 blades. An absence of significant vibration effects was noted, although permanent deformations did appear in the 0012 blades. Finally, gusting winds caused power fluctuations on the order of 74 pct, while the presence of gusts augmented the average power produced by up to 16 pct.

Egozcue, C.; Leblanc, R.; Goethals, R.

1982-11-01

250

High velocity blue-shifted FeII absorption in the dwarf star-forming galaxy PHL293B: Evidence for a wind driven supershell?  

E-print Network

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

Terlevich, R; Bosch, G; Diaz, A I; Hagele, G; Cardaci, M; Firpo, V

2014-01-01

251

Velocity diagrams  

NASA Technical Reports Server (NTRS)

The selection and design of velocity diagrams for axial flow turbines are considered. Application is treated in two parts which includes: (1) mean-section diagrams, and (2) radial variation of diagrams. In the first part, the velocity diagrams occurring at the mean section are assumed to represent the average conditions encountered by the turbine. The different types of diagrams, their relation to stage efficiency, and their selection when staging is required are discussed. In the second part, it is shown that in certain cases the mean-section diagrams may or may not represent the average flow conditions for the entire blade span. In the case of relatively low hub- to tip-radius ratios, substantial variations in the velocity diagrams are encountered. The radial variations in flow conditions and their effect on the velocity diagrams are considered.

Whitney, W. J.; Stewart, W. L.

1972-01-01

252

Relative Velocity  

NSDL National Science Digital Library

This applet simulates a boat crossing a river. The user can set the speed at which the river flows, and the magnitude and direction of the boat's velocity. The applet then displays the path taken by the boat. It also calculates the velocity of the boat with respect to the river and the shore, as well as the time it takes for the boat to cross the river.

Duffy, Andrew

2008-07-31

253

Field Study of the Space Uniformity of Meteorological and Wave Parameters in the Coastal Zone. On the Problem of Calibration of a Side-Looking Radar on the Sich-1M Satellite as an Instrument for Measuring Wind Velocity over the Sea  

Microsoft Academic Search

We study the problem of subsatellite calibration of a side-looking radar (SLR) of the Sich-1M satellite regarded as an instrument for the evaluation of the velocity of surface wind and discuss the possibility of application of the meteorological and wave parameters measured from the stationary oceanographic platform of the Experimental Department of the Marine Hydrophysical Institute (Ukrainian Academy of Sciences)

V. A. Dulov; A. N. Bol'shakov; V. E. Smolov; M. V. Ivanchik

2005-01-01

254

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

255

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

256

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

257

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

258

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

259

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

260

On the extraordinary katabatic winds of Adélie Land  

NASA Astrophysics Data System (ADS)

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

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

261

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

262

Solar wind driving of magnetospheric ultra-low frequency pulsations  

Microsoft Academic Search

Two solar wind parameters in particular are thought to be responsible for the majority of solar wind-driven ULF waves. These two parameters, solar wind dynamic pressure and solar wind velocity, are studied in this work through the use of global magnetohydrodynamic (MHD) simulations of the solar wind- magnetosphere interaction. We drive the global MHD simulations with idealized solar wind input

Seth G. Claudepierre

2008-01-01

263

Quantum Gravity and Maximum Attainable Velocities in the Standard Model  

SciTech Connect

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

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

2007-06-19

264

Velocity and velocity bounds in static spherically symmetric metrics  

E-print Network

We find simple expressions for velocity of massless particles in dependence of the distance $r$ in Schwarzschild coordinates. For massive particles these expressions put an upper bound for the velocity. Our results apply to static spherically symmetric metrics. We use these results to calculate the velocity for different cases: Schwarzschild, Schwarzschild-de Sitter and Reissner-Nordstr\\"om with and without the cosmological constant. We emphasize the differences between the behavior of the velocity in the different metrics and find that in cases with naked singularity there exists always a region where the massless particle moves with a velocity bigger than the velocity of light in vacuum. In the case of Reissner-Nordstr\\"om-de Sitter we completely characterize the radial velocity and the metric in an algebraic way. We contrast the case of classical naked singularities with naked singularities emerging from metric inspired by noncommutative geometry where the radial velocity never exceeds one. Furthermore, we solve the Einstein equations for a constant and polytropic density profile and calculate the radial velocity of a photon moving in spaces with interior metric. The polytropic case of radial velocity displays an unexpected variation bounded by a local minimum and maximum.

I. Arraut; D. Batic; M. Nowakowski

2010-05-06

265

14 CFR Appendix A to Part 440 - Information Requirements for Obtaining a Maximum Probable Loss Determination for Licensed or...  

Code of Federal Regulations, 2010 CFR

...tumble turn data with zeta angles and velocity magnitudes stated. A separate table...to: Variation in orbital position and velocity at the reentry initiation time; variation...ballistic coefficient; position and velocity variation due to winds; and...

2010-01-01

266

14 CFR Appendix A to Part 440 - Information Requirements for Obtaining a Maximum Probable Loss Determination for Licensed or...  

Code of Federal Regulations, 2013 CFR

...tumble turn data with zeta angles and velocity magnitudes stated. A separate table...to: Variation in orbital position and velocity at the reentry initiation time; variation...ballistic coefficient; position and velocity variation due to winds; and...

2013-01-01

267

14 CFR Appendix A to Part 440 - Information Requirements for Obtaining a Maximum Probable Loss Determination for Licensed or...  

Code of Federal Regulations, 2011 CFR

...tumble turn data with zeta angles and velocity magnitudes stated. A separate table...to: Variation in orbital position and velocity at the reentry initiation time; variation...ballistic coefficient; position and velocity variation due to winds; and...

2011-01-01

268

14 CFR Appendix A to Part 440 - Information Requirements for Obtaining a Maximum Probable Loss Determination for Licensed or...  

Code of Federal Regulations, 2012 CFR

...tumble turn data with zeta angles and velocity magnitudes stated. A separate table...to: Variation in orbital position and velocity at the reentry initiation time; variation...ballistic coefficient; position and velocity variation due to winds; and...

2012-01-01

269

14 CFR Appendix A to Part 440 - Information Requirements for Obtaining a Maximum Probable Loss Determination for Licensed or...  

...tumble turn data with zeta angles and velocity magnitudes stated. A separate table...to: Variation in orbital position and velocity at the reentry initiation time; variation...ballistic coefficient; position and velocity variation due to winds; and...

2014-01-01

270

Comparison of wind-stress algorithms and their influence on wind-stress curl using buoy measurements over the shelf off Bodega Bay, California  

NASA Astrophysics Data System (ADS)

The main objectives of this study were to compare three wind-stress algorithms of varying intricacy and estimate the extent to which each method altered computed wind-stress curl. The algorithms included (1) a simple bulk formula for neutral conditions that is dependent only on wind velocity components; (2) a formula that in addition to dependence on wind components includes a simplified effect of thermal stability through differences in air and sea temperatures; and (3) an algorithm that includes full treatment of dynamics and atmospheric stability. Data for the analysis were from a field program that used a special buoy network off Bodega Bay during 28 June-4 August 2001. A diamond-shaped setup of five closely separated buoys in Bodega Bay allowed for one of the first attempts to compute wind-stress curl over the ocean using buoy measurements. Based on an analysis of the available dataset, the marine layer over Bodega Bay is characterized by positive wind-stress curl with a median value around 0.2 Pa (100 km) -1 and maximum values reaching 2.5 Pa (100 km) -1. Positive wind-stress curl was observed for all wind speed conditions, whereas negative wind-stress curl episodes were associated mostly with low-wind conditions. Comparison of wind-stress curl computed using the three algorithms showed that differences among them can be significant. The first and third algorithms indicated similar stress curl (difference around 10%), but the differences between these two and the second algorithm were much higher (approximately 40%). The reason for the difference is the stability correction, which in the third algorithm strongly decreases with an increase in wind speeds, but stays at a similar level for all wind speeds in the second algorithm. Consequently, for higher wind speeds the variability of wind stress calculated using the second algorithm is greater than for the other two algorithms, causing significant differences in computed wind-stress curl (root mean-square error equal to 0.19 Pa (100 km) -1). Despite the apparent biases in computed wind stress and wind-stress curl among the algorithms, all of them show a significant trend of decreasing sea-surface temperature (SST) with increasing wind-stress curl. The bootstrapping analysis has revealed that both the along-shore wind stress and wind-stress curl have noticeable correlation with the changes in the sea-surface temperature as an indirect indication of the upwelling. An additional analysis, based on the low-pass filtered data, showed also significant agreement between the measured divergence in the cross-shore surface transport and the wind-stress curl computed for all three algorithms.

Kochanski, Adam; Kora?in, Darko; Dorman, Clive E.

2006-12-01

271

On optimal velocity during cycling.  

PubMed

This paper focuses on the solution of two problems related to cycling. One is to determine the velocity as a function of distance which minimizes the cyclist's energy expenditure in covering a given distance in a set time. The other is to determine the velocity as a function of the distance which minimizes time for fixed energy expenditure. To solve these problems, an equation of motion for the cyclist riding over arbitrary terrain is written using Newton's second law. This equation is used to evaluate either energy expenditure or time, and the minimization problems are solved using an optimal control formulation in conjunction with the method of Miele [Optimization Techniques with Applications to Aerospace Systems, pp. 69-98 (1962) Academic Press, New York]. Solutions to both optimal control problems are the same. The solutions are illustrated through two examples. In one example where the relative wind velocity is zero, the optimal cruising velocity is constant regardless of terrain. In the second, where the relative wind velocity fluctuates, the optimal cruising velocity varies. PMID:8132689

Maro?ski, R

1994-02-01

272

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

273

Thermospheric wind measurements in the polar region  

NASA Technical Reports Server (NTRS)

In order to study the coupling of neutral atmospheric motions with solar wind induced effects, the neutral wind and ion flow velocities were simultaneously measured at an altitude of 225 km in the polar cap F-region by releasing barium and strontium tracers from sounding rockets launched on 22 and 24 August 1971, and 10 December 1972. Ion and neutral cloud trajectories for 22 and 24 August experiments were plotted, and in both cases an anti-solar flow was deduced from the ion tracks. During the December experiment a southern and northern cloud were observed, and the magnitude of the pressure force deduced from the southern cloud motion was found in agreement with OGO-6 measurements. This confirmed that a local temperature maximum is located in the winter polar thermosphere.

Kelley, M. C.; Jorgensen, T. S.; Mikkelsen, I. S.

1977-01-01

274

New Sensors For Flow Velocity And Acoustics  

NASA Technical Reports Server (NTRS)

Paper describes two sensor-development programs at Fluid Mechanics Laboratory at NASA Ames Research Center. One program for digital image velocimetry (DIV) sensors, and other program, for advanced acoustic sensors for wind tunnels. DIV measures, in real time, instantaneous velocity fields of time-varying flow or of collection of objects moving with varying velocities. Advanced acoustic sensors for wind tunnels being developed to reduce effects of interference from wind noise, noise from interactions between flows and sensors, flow-induced vibrations of sensors, deflections of accoustic waves by boundary layers induced by sensors, and reflections from walls and sensor supports.

Cho, Y. C.

1991-01-01

275

Wind Speed Estimation Based Sensorless Output Maximization Control for a Wind Turbine Driving a DFIG  

Microsoft Academic Search

This paper proposes a wind speed estimation based sensorless maximum wind power tracking control for variable-speed wind turbine generators (WTGs). A specific design of the proposed control algorithm for a wind turbine equipped with a doubly fed induction generator (DFIG) is presented. The aerodynamic characteristics of the wind turbine are approximated by a Gaussian radial basis function network based nonlinear

Wei Qiao; Wei Zhou; JosÉ M. Aller; Ronald G. Harley

2008-01-01

276

Coronal Holes and Solar Wind High-Speed Streams: I. Forecasting the Solar Wind Parameters  

NASA Astrophysics Data System (ADS)

We analyze the relationship between the coronal hole (CH) area/position and physical characteristics of the associated corotating high-speed stream (HSS) in the solar wind at 1 AU. For the analysis we utilize the data in the period DOY 25 125 of 2005, characterized by a very low coronal mass ejection (CME) activity. Distinct correlations between the daily averaged CH parameters and the solar wind characteristics are found, which allows us to forecast the solar wind velocity v, proton temperature T, proton density n, and magnetic field strength B, several days in advance in periods of low CME activity. The forecast is based on monitoring fractional areas A, covered by CHs in the meridional slices embracing the central meridian distance ranges [-40°,-20°], [-10°,10°], and [20°,40°]. On average, the peaks in the daily values of n, B, T, and v appear delayed by 1, 2, 3, and 4 days, respectively, after the area A attains its maximum in the central-meridian slice. The peak values of the solar wind parameters are correlated to the peak values of A, which provides also forecasting of the peak values of n, B, T, and v. The most accurate prediction can be obtained for the solar wind velocity, for which the average relative difference between the calculated and the observed peak values amounts to overline{\\vert?\\vert}?10 %. The forecast reliability is somewhat lower in the case of T, B, and n ( overline{\\vert?\\vert}?20 , 30, and 40%, respectively). The space weather implications are discussed, including the perspectives for advancing the real-time calculation of the Sun Earth transit times of coronal mass ejections and interplanetary shocks, by including more realistic real-time estimates of the solar wind characteristics.

Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid M.

2007-02-01

277

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

278

Stellar disks Maximum disk  

E-print Network

& Stellar Systems 5, ch.21 (1965) 7 P.C. van der Kruit & K.C. Freeman, K.C., Ap.J. 303, 556 (1986) Piet vanOutline Stellar disks Maximum disk Truncations Conclusions STRUCTURE, MASS AND STABILITY Stellar disks Maximum disk Truncations Conclusions Outline Stellar disks Vertical stellar dynamics Stellar

Kruit, Piet van der

279

Prediction of solar energetic particle event histories using real-time particle and solar wind measurements  

NASA Technical Reports Server (NTRS)

The comparatively well-ordered magnetic structure in the solar corona during the decline of Solar Cycle 20 revealed a characteristic dependence of solar energetic particle injection upon heliographic longitude. When analyzed using solar wind mapping of the large scale interplanetary magnetic field line connection from the corona to the Earth, particle fluxes display an approximately exponential dependence on heliographic longitude. Since variations in the solar wind velocity (and hence the coronal connection longitude) can severely distort the simple coronal injection profile, the use of real-time solar wind velocity measurements can be of great aid in predicting the decay of solar particle events. Although such exponential injection profiles are commonplace during 1973-1975, they have also been identified earlier in Solar Cycle 20, and hence this structure may be present during the rise and maximum of the cycle, but somewhat obscured by greater temporal variations in particle injection.

Roelof, E. C.; Gold, R. E.

1978-01-01

280

Supplement Regarding Pressure-Velocity-Velocity Statistics.  

National Technical Information Service (NTIS)

The sensitivity to compressibility of a fluid of the relationship between pressure-velocity-velocity (PVV) statistics and velocity structure functions is quantified. For the first time, correct and complete incompressibility conditions on fourth-order vel...

R. J. Hill

1996-01-01

281

An examination of wake effects and power production for a group of large wind turbines  

SciTech Connect

Data from a group of three MOD-2 wind turbines and two meteorological towers at Goodnoe Hills were analyzed to evaluate turbine power output and wake effects (losses in power production due to operation of upwind turbines), and atmospheric factors influencing them. The influences of variations in the ambient wind speed, wind direction, and turbulence intensity were the primary factors evaluated. Meteorological and turbine data collected at the Goodnoe Hills site from April 1 to October 17, 1985, were examined to select the data sets for these analyses. Wind data from the two meteorological towers were evaluated to estimate the effect of a wake from an upwind turbine on the wind flow measured at the downwind tower. Maximum velocity deficits were about 25% and 12% at downwind distances of 5.8 and 8.3 rotor diameters (D), respectively. However, the maximum deficits at 5.8 D were about 14/degree/ off the centerline orientation between the turbine and the tower, indicating significant wake curvature. Velocity deficits were found to depend on the ambient wind speed, ranging from 27% at lower speeds (15 to 25 mph) to 20% at higher speeds (30 to 35 mph). Turbulence intensity increases dramatically in the wake by factors of about 2.3 and 1.5 over ambient conditions at 5.8 D and 8.3 D, respectively. An analysis of the ambient (non-wake) power production for all three turbines showed that the MOD-2 power output depends, not only on wind speed, but also on the turbulence intensity. At wind speeds below rated, there was a dramatic difference in turbine power output between low and high turbulence intensities for the same wind speed. One of the turbines had vortex generators on the blades. This turbine produced from 10% to 13% more power than the other two turbines when speeds were from 24 to 31 mph. 11 refs., 21 figs., 2 tabs.

Elliott, D.L.; Buck, J.W.; Barnard, J.C.

1988-04-01

282

Response of a Vertical Axis Wind Turbine to Time Varying Wind Conditions found within the Urban  

E-print Network

Response of a Vertical Axis Wind Turbine to Time Varying Wind Conditions found within the Urban, 2010 PP 389­401 389 ABSTRACT Experimental testing of a vertical axis wind turbine within the urban of the turbine. Temporal variation of the wind with respect to the direction and velocity fluctuations

Tullis, Stephen

283

Industry guidelines for the calibration of maximum anemometers  

SciTech Connect

The purpose of this paper is to report on a framework of guidelines for the calibration of the Maximum Type 40 anemometer. This anemometer model is the wind speed sensor of choice in the majority of wind resource assessment programs in the U.S. These guidelines were established by the Utility Wind Resource Assessment Program. In addition to providing guidelines for anemometers, the appropriate use of non-calibrated anemometers is also discussed. 14 refs., 1 tab.

Bailey, B.H. [AWS Scientific, Inc., Albany, NY (United States)

1996-12-31

284

Utilization of Wind Energy at High Altitude  

Microsoft Academic Search

Ground based, wind energy extraction systems have reached their maximum capability. The limitations of current designs are: wind instability, high cost of installations, and small power output of a single unit. The wind energy industry needs of revolutionary ideas to increase the capabilities of wind installations. This article suggests a revolutionary innovation which produces a dramatic increase in power per

Alexander Bolonkin

2007-01-01

285

Maximum thrust mode evaluation  

NASA Technical Reports Server (NTRS)

Measured reductions in acceleration times which resulted from the application of the F-15 performance seeking control (PSC) maximum thrust mode during the dual-engine test phase is presented as a function of power setting and flight condition. Data were collected at altitudes of 30,000 and 45,000 feet at military and maximum afterburning power settings. The time savings for the supersonic acceleration is less than at subsonic Mach numbers because of the increased modeling and control complexity. In addition, the propulsion system was designed to be optimized at the mid supersonic Mach number range. Recall that even though the engine is at maximum afterburner, PSC does not trim the afterburner for the maximum thrust mode. Subsonically at military power, time to accelerate from Mach 0.6 to 0.95 was cut by between 6 and 8 percent with a single engine application of PSC, and over 14 percent when both engines were optimized. At maximum afterburner, the level of thrust increases were similar in magnitude to the military power results, but because of higher thrust levels at maximum afterburner and higher aircraft drag at supersonic Mach numbers the percentage thrust increase and time to accelerate was less than for the supersonic accelerations. Savings in time to accelerate supersonically at maximum afterburner ranged from 4 to 7 percent. In general, the maximum thrust mode has performed well, demonstrating significant thrust increases at military and maximum afterburner power. Increases of up to 15 percent at typical combat-type flight conditions were identified. Thrust increases of this magnitude could be useful in a combat situation.

Orme, John S.; Nobbs, Steven G.

1995-01-01

286

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

287

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

288

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

289

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 (??//), peak precipitating electron energy (peak Ee), and precipitating electron energy flux (?) as functions of solar wind (SW) and interplanetary magnetic field (IMF) are investigated with DMSP 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 08 - 16 MLT suggest that R1 at these local times are frequently open while R1 at 06 - 08 and 17 - 18 MLTs are frequently closed. R2 is located mostly on closed field lines. In the afternoon open R1 at 12 - 16 MLTs, an increase in nsw increases J//, decreases maximum peak Ee (proxy for ??//), but has little effect on maximum ?. In the same R1 region, an increase in Vsw increases J//, maximum peak Ee, and maximum ?. The dependencies of J//, maximum peak Ee, and maximum ? are consistent with the Knight relation and the voltage generator at the magnetopause boundary in the afternoon open R1. Near noon, the response of J// to Vsw is higher for southward than 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 appear to be more sensitive to merging rate than to SW dynamic pressure.

Wing, S.; Ohtani, S.; Johnson, J.; Newell, P. T.; Higuchi, T.; Echim, M.; Wilson, G. R.

2011-12-01

290

Maximum ratio transmission  

Microsoft Academic Search

This paper presents the concept, principles, and analysis of maximum ratio transmission for wireless communications, where multiple antennas are used for both transmission and reception. The principles and analysis are applicable to general cases, including maximum-ratio combining. Simulation results agree with the analysis. The analysis shows that the average overall signal-to-mise ratio (SNR) is proportional to the cross correlation between

Titus K. Y. Lo

1999-01-01

291

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

292

Maximum Parsimony and Maximum Likelihood Methods Comparisons and Bootstrap Tests  

E-print Network

Maximum Parsimony and Maximum Likelihood Methods Comparisons and Bootstrap Tests Character Likelihood Methods Comparisons and Bootstrap Tests Character Reconstruction PHYLIP and T-REX Exercises Outline 1 Maximum Parsimony and Maximum Likelihood 2 Methods Comparisons and Bootstrap Tests 3 Character

Qiu, Weigang

293

Determination of the Brunt-Vaisala frequency from vertical velocity spectra  

NASA Technical Reports Server (NTRS)

Recent work on the spectra of vertical velocity oscillations due to gravity waves in the troposphere, stratosphere and the mesosphere has revealed a typical feature which we call the Brunt-Vaisala cutoff. Several observers noticed a spectral peak near the Brunt-Vaisala frequency. This peak often is characterized by a very steep slope at the high frequency part, but a fairly shallow slope towards lower frequencies. Some example spectra of stratosphere observations are given. This distinct spectral shape (most clear at the upper height 22.5 km) can be explained by the fact that the vertical velocity amplitudes of atmospheric gravity waves increase with frequency up to their natural cutoff at the Brunt-Vaisala frequency. The measurement of the frequency of the peak in a vertical velocity spectrum was found to yield most directly the Brunt-Vaisala-frequency profile. Knowing the Brunt-Vaisala frequency profile, one can deduce the potential temperature profile, if one has a calibration temperature at one height. However, even the uncalibrated profile will be quite useful, e.g., to determine fronts (defined by temperature inversions) and the tropopause height. This method fails for superadiabatic lapse rates when the Brunt-Viasala frequency is imaginary. The application of this method will also be difficult when the wind velocity is too high, causing the Doppler effect to smear out the total spectrum and blur the Brunt-Vaisala cutoff. A similar deficiency will also appear if the gravity-wave distribution has a maximum in wind direction.

Rottger, J.

1986-01-01

294

A Quasar Wind Model  

E-print Network

A quasar wind model is proposed to describe the spatial and velocity structure of the broad line region. This model requires detailed photoionization and magnetohydrodynamic simulation, as the broad line region it too small for direct spatial resolution. The emission lines are Doppler broadened, since the gas is moving at high velocity. The high velocity is attained by the gas from a combination of radiative and magnetic driving forces. Once this model is complete, the model predictions will be tested against recent microlensing data in conjunction with diverse existing observations.

Andrea Ruff

2008-09-16

295

Quality, precision and accuracy of the maximum No. 40 anemometer  

SciTech Connect

This paper synthesizes available calibration data for the Maximum No. 40 anemometer. Despite its long history in the wind industry, controversy surrounds the choice of transfer function for this anemometer. Many users are unaware that recent changes in default transfer functions in data loggers are producing output wind speed differences as large as 7.6%. Comparison of two calibration methods used for large samples of Maximum No. 40 anemometers shows a consistent difference of 4.6% in output speeds. This difference is significantly larger than estimated uncertainty levels. Testing, initially performed to investigate related issues, reveals that Gill and Maximum cup anemometers change their calibration transfer functions significantly when calibrated in the open atmosphere compared with calibration in a laminar wind tunnel. This indicates that atmospheric turbulence changes the calibration transfer function of cup anemometers. These results call into question the suitability of standard wind tunnel calibration testing for cup anemometers. 6 refs., 10 figs., 4 tabs.

Obermeir, J. [Otech Engineering, Davis, CA (United States); Blittersdorf, D. [NRG Systems Inc., Hinesburg, VT (United States)

1996-12-31

296

Observations of mesoscale vertical velocities around frontal zones  

NASA Technical Reports Server (NTRS)

Vertical velocity and reflectivity data obtained with a VHF Doppler radar over a 15-day period in October and November of 1981 are analyzed. Standard radiosonde data and surface observations were used to locate two occluded fronts, two warm fronts, and a cold front that passed the radar site. These fronts are also evident in the radar reflectivity data. Most studies of the vertical circulation patterns associated with mososcale systems have used precipitation and cloud formations as tracers. Unlike other observational techniques, the VHF radar permits the continuous measurement of the three-dimensional air velocity vector in time and height from a fixed location. With the beam in a vertically pointing position, signals are scattered from turbulent variations in the refractive index with half the scale of the radar wavelength and by regions with sudden changes in the refractive index associated with horizontally stratified layers. Generally, the strongest echoes occur at the maximum in the vertical gradient of refractivity, usually at the base of a temperature inversion, such as the tropopause. VHF radars can also be used to locate atmospheric fronts, which are characterized by static stability, large horizontal temperature gradients, large vorticities, and vertical wind shears. These radars can provide the velocity field data needed to study wave motions associated with fronts and compare the actual vertical circulation to theoretical predictions.

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

1986-01-01

297

Robust Multi-loop Airborne SLAM in Unknown Wind Environments  

E-print Network

Robust Multi-loop Airborne SLAM in Unknown Wind Environments Jonghyuk Kim Department of Engineering presents a robust multi-loop airborne SLAM structure which also augments wind information. The air velocity. This can be tackled by augmenting the unknown wind velocity into the state vector of SLAM, simultaneously

Kim, Jonghyuk "Jon"

298

Stability Simulation of Wind Turbine Systems  

Microsoft Academic Search

A simulation and digital computer modeling effort is described in which a wind turbine-generator system is adapted for stability evaluation using a large scale transient stability computer program. Component models of the MOD-2 wind generator system are described and their digital model equations are provided. A versatile wind velocity model is described, which provides the capability of simulating a wide

P. M. Anderson; Anjan Bose

1983-01-01

299

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

300

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

301

Wind-speed measurements with a scanning elastic-backscatter lidar  

SciTech Connect

During the 1992 Summer Olympics, the Los Alamos National Laboratory (LANL) lidar team participated in the Barcelona Air Quality Initiative (BAQI). One of the main objectives of this experiment was the remote measurement of wind speeds around the city to verify wind speeds and directions predicted by the Nonhydrostatic Mesoscale Model (MEMO). Remote determination of wind velocities in the mixing layer is important for the verification and determination of critical input parameters of urban-pollution transport models. Most present elastic-backscatter-lidar wind-speed-measurement methods rely on data acquired over time periods between 5 to 10 minutes (Matsui, 1990) and 30 minutes to 1 hour (Schols, et al. 1992). Lidar can measure the spatial properties of the wind field over large volumes of space. This capability is an improvement over present methods, which rely on instruments attached to balloons that measure only those winds along the path the balloon travels. The material that follows describes the principles implicit in the measurement of winds with an elastic-backscatter lidar, as well as the maximum cross-correlation algorithm used to extract wind speeds from lidar data acquired during the Summer Olympics at Barcelona, Spain, in July 1992.

Buttler, W.T.; Eichinger, W.E.

1994-01-01

302

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

303

Velocity measurement of the interplanetary hydrogen  

NASA Astrophysics Data System (ADS)

We are proposing to use HST/STIS over a single orbit to make Lyman-alpha observations of the interplanetary hydrogen during the March-April period of this year {2012}. This special request is driven by a recent reanalysis of HST data {Vincent et al. 2011, published after the last call for proposals}.The heliospheric interface results from the interaction of the solar wind and the interstellar medium {ISM}. Within the heliosphere, the interplanetary hydrogen {IPH} flows at an average speed of about 23 km/sec, carrying the signature of the ISM and the heliospheric interface. The IPH has been observed for decades through the backscattering of solar Lyman-alpha photons and solar cycle 23 provided the first partial temporal map of the IPH velocity. It is now well established that the IPH velocity depends on solar activity. Moreover some analyses suggested that it may be also affected by the obliquity of the interstellar magnetic field, yielding a change of 1-2 km/sec.However a combination of the uncertainty of some measurements {e.g. GHRS} and the clustering of others near points on the cycle make it difficult to identify an unambiguous trend. Only one limited set is able to show a cycle dependence, but these represent an annual average and do not match the existing models. The best approach to address these issues is a new set of yearly spectroscopic measurements for at least a half solar cycle. Since we are currently just leaving a solar maximum, it is essential to start immediately in order to have an adequate baseline for temporal measurements.

Vincent, Frederic

2011-10-01

304

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

305

High-Resolution Optical Spectroscopy of the R Coronae Borealis Star V532 Ophiuchi at Maximum Light  

NASA Astrophysics Data System (ADS)

High-resolution optical spectra of the R Coronae Borealis (RCB) star V532 Oph at light maximum are discussed. The absolute visual magnitude MV of the star is found to be -4.9 ± 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 C2 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.

Kameswara Rao, N.; Lambert, David L.; Woolf, Vincent M.; Hema, B. P.

2014-11-01

306

Velocity and Residual Velocity Fields of Spiral Galaxies  

NASA Astrophysics Data System (ADS)

Imaging Fabry-Perot data has been acquired for a sample of spiral galaxies from which two-dimensional velocity fields have been constructed. These velocity fields are then examined for evidence of noncircular motions. Individual spectra are extracted and the resultant line profiles are fit with Voigt, Gaussian, and Lorentzian functions. Gaussians are shown to be a better model for simultaneously fitting a large number of line profiles, successfully fitting a higher fraction. The kinematic disk (i.e. tilted ring) modeling procedure is studied in detail and is shown to accurately recover the underlying rotational structure of galactic disks. The process of obtaining rotation curves from full 2-dimensional velocity data is examined. Small scale 'bumps and wiggles' on the rotation curves are shown to be due to the inclusion of noncircular motions. Use of the rotation curve estimate returned by the modeling procedure rather than deprojection of the velocity field is recommended to avoid their inclusion. Investigation of the symmetry of the major and minor axis rotation curves reveal strong evidence of nonconcentric gas orbits with the maximum center shift of 300 pc. Minor axis rotation curves show little evidence for large scale streaming motions or motions perpendicular to the plane of the disk. The kinematic disk models are used to find the residual velocity fields, and typical residuals are found to be 10-15 km s-1 over regions 0.5-1.5 kpc in diameter. Correlations are shown to exist between the residual velocity fields and both the H? intensity and the velocity dispersion images. The residual velocity fields are examined for signs of noncircular orbits by looking for azimuthal angular harmonics. Assuming constant ellipticity between galaxies, the ellipticity of the gas orbits is found to be ~<0.08.

Beauvais, Charles S.

307

Winding for the wind  

Microsoft Academic Search

The mechanical properties and construction of epoxy-impregnated fiber-glass blades for wind turbines are discussed, along with descriptions of blades for the Mod 0A and Mod 5A WECS and design goals for a 4 kW WECS. Multicell structure combined with transverse filament tape winding reduces labor and material costs, while placing a high percentage of 0 deg fibers spanwise in the

O. Weingart

1981-01-01

308

Coronal temperatures, heating, and energy flow in a polar region of the sun at solar maximum  

NASA Technical Reports Server (NTRS)

The profiles of resonantly scattered Lyman-alpha coronal radiation have been used to determine the hydrogen kinetic temperature from 1.5 to 4 solar radius from the center of the polar region of the corona observed in 1980 at solar maximum. Hydrogen temperatures derived from the line profiles were found to decrease with height from 1.2 million K at r = 1.5 solar radii to 600,000 K at r = 4 solar radius. Comparison of the measured kinetic temperatures with predictions from a semiempirical two-fluid model showed evidence of a small amount of heating or a nonthermal contribution to the motions of coronal protons between 1.5 and 4 solar radius. The widths of the profiles confirmed an upper limit of 110 + or - 15 km/s on the rms magnitude of the line-of-sight component of velocities between 1.5 and 4 solar radius. Density measurements obtained in situ in the solar wind in the ecliptic were used to locate the sources of low speed and high-speed winds in the polar region. An eclipse photograph of the corona at solar maximum is provided.

Withbroe, G. L.; Kohl, J. L.; Weiser, H.; Munro, R. H.

1985-01-01

309

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

310

Field Tests of Wind Turbine Unit with Tandem Wind Rotors and Double Rotational Armatures  

NASA Astrophysics Data System (ADS)

This paper discusses the field tests of the wind turbine unit, in which the front and the rear wind rotors drive the inner and the outer armatures of the synchronous generator. The wind rotors were designed conveniently by the traditional procedure for the single wind rotor, where the diameters of the front and the rear wind rotors are 2 m and 1.33 m. The tests were done on a pick-up type truck driven straightly at constant speed. The rotational torque of the unit is directly proportional to the induced electric current irrespective of the rotational speeds of the wind rotors, while the induced voltage is proportional to the relative rotational speed. The performance of the unit is significantly affected not only by the wind velocity, but also by the blade setting angles of both wind rotors and the applied load especially at lower wind velocity.

Galal, Ahmed Mohamed; Kanemoto, Toshiaki

311

Application of power laws for wind energy assessment  

Microsoft Academic Search

Variations in the exponent in the power law relating height to wind velocity are investigated for a series of measurements of nocturnal low-level winds in northern Illinois in order to determine the applicability of power laws in estimates of attainable wind power. Hourly, seasonal and annual frequency distributions of power law exponents representing the best fit to wind profiles obtained

D. L. Sisterson; B. B. Hicks

1979-01-01

312

A twisted flow wind tunnel for testing yacht sails  

Microsoft Academic Search

The paper outlines the requirements for wind tunnel testing model yachts for sail aerodynamics investigations. It is shown that the apparent wind onto a yacht is “twisted” over the mast height, due to the vector addition of the yacht and wind velocities. The design features of a special wind tunnel built in New Zealand which can produce twisted flow in

Richard G. J. Flay

1996-01-01

313

Altimeter Estimation of Sea Surface Wind Stress for Light to Moderate Winds  

NASA Technical Reports Server (NTRS)

Aircraft altimeter and in situ measurements are used to examine relationships between altimeter backscatter and the magnitude of near-surface wind and friction velocities. Comparison of altimeter radar cross section with wind speed is made through the modified Chelton-Wentz algorithm. Improved agreement is found after correcting 10-m winds for both surface current and atmospheric stability. An altimeter friction velocity algorithm is derived based on the wind speed model and an open-ocean drag coefficient. Close agreement between altimeter- and in situ-derived friction velocities is found. For this dataset, quality of the altimeter inversion to surface friction velocity is comparable to that for adjusted winds and clearly better than the inversion to true 10-m wind speed.

Vandemark, Douglas; Edson, James B.; Chapron, Bertrand

1997-01-01

314

Wind and turbine characteristics needed for integration of wind turbine arrays into a utility system  

NASA Technical Reports Server (NTRS)

Wind data and wind turbine generator (WTG) performance characteristics are often available in a form inconvenient for use by utility planners and engineers. The steps used by utility planners are summarized and the type of wind and WTG data needed for integration of WTG arrays suggested. These included long term yearly velocity averages for preliminary site feasibility, hourly velocities on a 'wind season' basis for more detailed economic analysis and for reliability studies, worst-case velocity profiles for gusts, and various minute-to-hourly velocity profiles for estimating the effect of longer-term wind fluctuations on utility operations. wind turbine data needed includes electrical properties of the generator, startup and shutdown characteristics, protection characteristics, pitch control response and control strategy, and electro-mechanical model for stability analysis.

Park, G. L.

1982-01-01

315

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

316

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

317

Evaluation of coherent Doppler lidar velocity estimators in nonstationary regimes.  

PubMed

We evaluate the mean velocity estimator performance for coherent Doppler lidar measurements of wind fields with wind shear and nonuniform system response as a function of target range. Performance of the velocity estimates is characterized by the bias and standard deviation that are determined by computer simulations. Results are for solid-state lasers with a Gaussian transmitted pulse. We consider data with high signal energy that produces negligible random outliers. PMID:18264319

Lottman, B T; Frehlich, R G

1997-10-20

318

Solar wind interaction with the earth's magnetic field. IV - Preshock perturbation of the solar wind  

Microsoft Academic Search

Heos-1 plasma and magnetic field data are used to study the interaction of solar wind protons with protons reflected at the bow shock. The shape of this preshock perturbation region of the solar wind, created by the reflected protons, depends on the magnetic field direction along which the protons move with a velocity twice that of the solar wind. The

V. Formisano; E. Amata

1976-01-01

319

The Solar Maximum observatory  

NASA Technical Reports Server (NTRS)

The successful retrieval and repair of the Solar Maximum Mission (SMM) satellite by Shuttle astronauts in April 1984 permitted continuance of solar flare observations that began in 1980. The SMM carries a soft X ray polychromator, gamma ray, UV and hard X ray imaging spectrometers, a coronagraph/polarimeter and particle counters. The data gathered thus far indicated that electrical potentials of 25 MeV develop in flares within 2 sec of onset. X ray data show that flares are composed of compressed magnetic loops that have come too close together. Other data have been taken on mass ejection, impacts of electron beams and conduction fronts with the chromosphere and changes in the solar radiant flux due to sunspots.

Rust, D. M.

1984-01-01

320

WIND VARIABILITY IN BZ CAMELOPARDALIS  

SciTech Connect

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 and 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{alpha} line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald and Naylor reported common occurrences of redshifted H{alpha} emission components in their BZ Cam spectra. We have attributed these emission components in H{alpha} 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 {lambda}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. [Astronomy Department, Indiana University, Swain Hall West, Bloomington, IN 47405 (United States); Kafka, S. [Department of Terrestrial Magnetism, Carnegie Institute of Washington, 5241 Broad Branch Road NW, Washington, DC 2001 (United States); Robertson, J. W., E-mail: honey@astro.indiana.edu, E-mail: skafka@dtm.ciw.edu, E-mail: jrobertson@atu.edu [Department of Physical Sciences, Arkansas Tech University, 1701 North Boulder Avenue, Russellville, AR 72801-2222 (United States)

2013-02-01

321

Rotating, magnetic, radiation-driven wind model for Wolf-Rayet stars  

SciTech Connect

A radiation-driven wind model that incorporates the effects of rotation and an open magnetic field is applied to WR stars in order to address the wind momentum problem. The dependence of the mass-loss rate and terminal velocity on the rotation rate and surface magnetic field is studied for the flow in the equatorial region. The transition from a purely radiatively driven wind to a rotationally and magnetically driven wind is investigated for the case in which the stellar luminosity is consistent with Maeder's mass-luminosity relation. An alternative picture for WR winds is developed in which there is a slower but denser equatorial flow and a fast radiation-driven wind at higher latitudes. Wind models for several stars are presented that are consistent with interior theory. If the stars have field of about 1500 G and rotate at rates greater than about 85 percent maximum, they can satisfy the radio and UV observations and explain the momentum problem, and also overcome the spindown problem. 52 references.

Poe, C.H.; Friend, D.B.; Cassinelli, J.P.

1989-02-01

322

Vertical wind estimation from horizontal wind measurements  

NASA Technical Reports Server (NTRS)

The objective of this study was to assess the ability of simple vertical wind models to improve the hazard prediction capability of an airborne Doppler sensor in a realistic microburst environment. The results indicate that in the altitude region of interest (at or below 300 meters), both the linear and empirical vertical wind models improved the hazard estimate. The radar simulation study showed that the magnitude of the performance improvement was altitude dependent. The altitude of maximum performance improvement occurred at about 300 meters. At the lower altitudes the percent improvement was minimized by the diminished contribution of the vertical wind. The vertical hazard estimate errors from flight tests were less than those of the radar simulation study.

Vicroy, Dan D.

1994-01-01

323

Meteorology (Wind)  

Wind speed at 50 m (m/s) The average and percent difference minimum and ... are given.   Percent of time for ranges of wind speed at 50 m (percent) Percentage [frequency] of time that wind ... 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

324

State of the Art in Condition Monitoring in Wind Turbines Based on Embedded FBG Sensors  

Microsoft Academic Search

Wind energy is one of renewable energy sources, which is copiously available without any limitation. Wind turbines are used to tap the potential of wind energy. Thus, stability and reliability of wind turbine is critical to extract this maximum amount of energy from the wind. To keep the wind turbine in operation, implementation of condition monitoring is paramount. This paper,

Huang Xue-feng; Luo Dan; Wang Guan-qing; Ding Ning; Xu Jiang-rong; Liu Yan; Fan Hao

2010-01-01

325

Concepts of relative velocity  

E-print Network

The central concept of the theory of relativity is the relativity of velocity. The velocity of a material body is not an intrinsic property of the body; it depends on a free choice of reference system. Relative velocity is thus reference-dependent, it is not an absolute concept. We stress that even zero-velocity must be relative. Every reference system possesses its own zero-velocity relative only to that particular reference system. Does the theory of relativity formulated in terms of relative velocities, with many zero-velocities, imply the Lorentz isometry group? We discuss the many relative spaces of Galileo and Poincare, as quotient spaces.

Zbigniew Oziewicz; William S. Page

2011-03-30

326

Winding for the wind  

NASA Astrophysics Data System (ADS)

The mechanical properties and construction of epoxy-impregnated fiber-glass blades for wind turbines are discussed, along with descriptions of blades for the Mod 0A and Mod 5A WECS and design goals for a 4 kW WECS. Multicell structure combined with transverse filament tape winding reduces labor and material costs, while placing a high percentage of 0 deg fibers spanwise in the blades yields improved strength and elastic properties. The longitudinal, transverse, and shear modulus are shown to resist stresses exceeding the 50 lb/sq ft requirements, with constant stress resistance expected until fatigue failure is approached. Regression analysis indicates a fatigue life of 400 million operating cycles. The small WECS under prototype development features composite blades, nacelle, and tower. Rated at 5.7 kW in a 15 mph wind, the machine operates over a speed range of 9-53.9 mph and is expected to produce 16,200 kWh annually in a 10 mph average wind measured at 30 ft.

Weingart, O.

327

Winding for the wind  

NASA Technical Reports Server (NTRS)

The mechanical properties and construction of epoxy-impregnated fiber-glass blades for wind turbines are discussed, along with descriptions of blades for the Mod 0A and Mod 5A WECS and design goals for a 4 kW WECS. Multicell structure combined with transverse filament tape winding reduces labor and material costs, while placing a high percentage of 0 deg fibers spanwise in the blades yields improved strength and elastic properties. The longitudinal, transverse, and shear modulus are shown to resist stresses exceeding the 50 lb/sq ft requirements, with constant stress resistance expected until fatigue failure is approached. Regression analysis indicates a fatigue life of 400 million operating cycles. The small WECS under prototype development features composite blades, nacelle, and tower. Rated at 5.7 kW in a 15 mph wind, the machine operates over a speed range of 9-53.9 mph and is expected to produce 16,200 kWh annually in a 10 mph average wind measured at 30 ft.

Weingart, O.

1981-01-01

328

Workshop report: Velocity coupling  

NASA Technical Reports Server (NTRS)

Velocity coupled combustion instability and related combustion instability topics were considered. The knowledge of velocity coupled combustion instability was assessed; the state of the art of velocity coupled measurement techniques was determined; and particularly laboratory devices or T burner related devices; recommendations were made on how to improve the state of knowledge on velocity coupled combustion instability. Test conditions for a round robin of velocity coupled response measurement techniques were established.

Beckstead, M. W.

1980-01-01

329

Generalized Maximum Entropy  

NASA Technical Reports Server (NTRS)

A long standing mystery in using Maximum Entropy (MaxEnt) is how to deal with constraints whose values are uncertain. This situation arises when constraint values are estimated from data, because of finite sample sizes. One approach to this problem, advocated by E.T. Jaynes [1], is to ignore this uncertainty, and treat the empirically observed values as exact. We refer to this as the classic MaxEnt approach. Classic MaxEnt gives point probabilities (subject to the given constraints), rather than probability densities. We develop an alternative approach that assumes that the uncertain constraint values are represented by a probability density {e.g: a Gaussian), and this uncertainty yields a MaxEnt posterior probability density. That is, the classic MaxEnt point probabilities are regarded as a multidimensional function of the given constraint values, and uncertainty on these values is transmitted through the MaxEnt function to give uncertainty over the MaXEnt probabilities. We illustrate this approach by explicitly calculating the generalized MaxEnt density for a simple but common case, then show how this can be extended numerically to the general case. This paper expands the generalized MaxEnt concept introduced in a previous paper [3].

Cheeseman, Peter; Stutz, John

2005-01-01

330

A Windmill's Theoretical Maximum Extraction of Power from the Wind.  

ERIC Educational Resources Information Center

Explains that the efficiency and the useful power available from a windmill turbine, of a laminar-flow model, will vary due to rotational kinetic energy of the downwind stream and turbulent mixing from outside the boundaries of the idealized stream. (GA)

Inglis, David Rittenhouse

1979-01-01

331

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

332

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

333

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

334

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

335

Wind turbines in simulated gusts  

Microsoft Academic Search

The results of trials in the T4 wind tunnel to simulate the effects of gusts on wind turbines are reported. Three-bladed NACA 0012 and 0018 profile and a six bladed 0012 profile machines were examined in gusts of 10 sec duration. The mean free stream velocity was 7-8 m\\/sec and the gusts generated had an amplitude of 30-40 pct. An

C. Egozcue; R. Leblanc; R. Goethals

1982-01-01

336

Isthmus of Tehuantepec Wind Climatology and ENSO Signal  

Microsoft Academic Search

The statistical characteristics of the winds at the Isthmus of Tehuantepec and their seasonal and interannual variability are studied through the analysis of several datasets and a reconstruction of the winds for a 31-yr period. Observations show that the long-term monthly mean wind speeds and frequency of occurrence of northerly winds have a strong seasonal signal, with maximum values during

Rosario Romero-Centeno; Jorge Zavala-Hidalgo; Artemio Gallegos; James J. O'Brien

2003-01-01

337

Superstatistical distributions from a maximum entropy principle.  

PubMed

We deal with a generalized statistical description of nonequilibrium complex systems based on least biased distributions given some prior information. A maximum entropy principle is introduced that allows for the determination of the distribution of the fluctuating intensive parameter beta of a superstatistical system, given certain constraints on the complex system under consideration. We apply the theory to three examples: the superstatistical quantum-mechanical harmonic oscillator, the superstatistical classical ideal gas, and velocity time series as measured in a turbulent Taylor-Couette flow. PMID:19113089

Van der Straeten, Erik; Beck, Christian

2008-11-01

338

Minimum maximum temperature gradient coil design.  

PubMed

Ohmic heating is a serious problem in gradient coil operation. A method is presented for redesigning cylindrical gradient coils to operate at minimum peak temperature, while maintaining field homogeneity and coil performance. To generate these minimaxT coil windings, an existing analytic method for simulating the spatial temperature distribution of single layer gradient coils is combined with a minimax optimization routine based on sequential quadratic programming. Simulations are provided for symmetric and asymmetric gradient coils that show considerable improvements in reducing maximum temperature over existing methods. The winding patterns of the minimaxT coils were found to be heavily dependent on the assumed thermal material properties and generally display an interesting "fish-eye" spreading of windings in the dense regions of the coil. Small prototype coils were constructed and tested for experimental validation and these demonstrate that with a reasonable estimate of material properties, thermal performance can be improved considerably with negligible change to the field error or standard figures of merit. PMID:23042696

While, Peter T; Poole, Michael S; Forbes, Larry K; Crozier, Stuart

2013-08-01

339

Analysis of CASES-99 Lidar and Turbulence Data in Support of Wind Turbine Effects: April 1, 2001 to Januay 31, 2003  

SciTech Connect

The nocturnal low-level jet (LLJ) of the Great Plains of the central United States has been identified as a promising source of high-momentum wind flow for wind energy. The acceleration of the winds after sunset above the surface produces a jet profile in the wind velocity, with maximum speeds that often exceed 10 m s-1 or more at heights near 100 m or more. These high wind speeds are advantageous for wind energy generation. The high speeds aloft, however, also produce a region of high shear between the LLJ and the earth's surface, where the nocturnal flow is often calm or nearly so. This shear zone below the LLJ generates atmospheric waves and turbulence that can cause strong vibration in the turbine rotors. It has been suggested that these vibrations contribute to premature failures in large wind turbines, which, of course, would be a considerable disadvantage for wind energy applications. In October 1999, a field project called the Cooperative Atmosphere-Surface Exchange Study 1999 campaign, or CASES-99, was conducted in southeastern Kansas to study the nocturnal stable boundary layer. One of the instruments deployed during CASES-99 was the High-Resolution Doppler Lidar, a new scanning, remote-sensing, wind-mapping instrument.

Banta, R. M.

2003-06-01

340

Analysis of maximum pressure attainable by water jet impact  

SciTech Connect

The maximum pressure attainable in an impacting jet has been addressed by researchers for jet-cutting technology, notably in rock-drilling operations and the minimization of turbine-blade erosion. The authors have analyzed the maximum pressure attainable in a liquid jet when it impinges on a rigid surface. The CALE hydrodynamics code has been used for this purpose. The calculated maximum pressure for a given jet velocity is higher than the so-called water-hammer value, {rho}{sub 0}C{sub 0}V where the term {rho} denotes the liquid density, C the sound speed, V the flow velocity, and the subscript o the undisturbed (upstream) region in the jet. However, the calculated results agree well with experimental data and with a well-known generalized water hammer pressure expression for high (as well as low) jet velocities.

Reitter, T.A.; Kang, S.W.

1993-05-01

341

Analysis of maximum pressure attainable by water jet impact  

SciTech Connect

The maximum pressure attainable in an impacting jet has been addressed by researchers for jet-cutting technology, notably in rock-drilling operations and the minimization of turbine-blade erosion. The authors have analyzed the maximum pressure attainable in a liquid jet when it impinges on a rigid surface. The CALE hydrodynamics code has been used for this purpose. The calculated maximum pressure for a given jet velocity is higher than the so-called water-hammer value, [rho][sub 0]C[sub 0]V where the term [rho] denotes the liquid density, C the sound speed, V the flow velocity, and the subscript o the undisturbed (upstream) region in the jet. However, the calculated results agree well with experimental data and with a well-known generalized water hammer pressure expression for high (as well as low) jet velocities.

Reitter, T.A.; Kang, S.W.

1993-05-01

342

Last Glacial Maximum  

NSDL National Science Digital Library

Short lecture on CLIMAP project (see PowerPoint) 20 minutes Powerpoint (PowerPoint 444kB Nov7 10) Group activity - Reading for CLIMAP study assumptions, 20 minutes to read, 20 minutes for discussion Student Handout (Microsoft Word 50kB Nov7 10) Students break into groups (4 per group is good division of work) with 2 students per paper. Split the assumptions between students. Each group skims the CLIMAP papers for the assumptions (modern and/or LGM) used in the CLIMAP model-based reconstruction of the LGM. In the groups, students compare the assumptions between papers. Resources: CLIMAP (1976), The surface of the ice-age earth, Science, 191(4232), 1131-1137 and CLIMAP (1984), The last interglacial ocean, Quaternary Research, 21(2), 123. Class Discussion - Summarize assumptions used in CLIMAP studies. Group activity Exploring CLIMAP LGM Reconstructions, 40 minutes for model data, 20 minutes for discussion (Could be modified with as a "jigsaw" activity with a larger class). Learn more about the jigsaw teaching method. Students work on this activity in pairs; one person will create LGM maps, the other modern. Students should sit together with their computer monitors close together to compare. The students will use the IRI/LDEO Climate Data Library to access the CLIMAP reconstruction and produce maps using the tools available on this web site. In a web browser, go to http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/ This is the main page for the CLIMAP Model output for the LGM 18,000 BP. In the middle of the page is the label "Datasets and variables" with two data sets below http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/.LGM/ and http://iridl.ldeo.columbia.edu/SOURCES/.CLIMAP/.MOD/. Each student clicks on the link they are assigned to. There are several data sets listed for each period and the students will examine each data set and compare the LGM and Modern. As a class, go through each data set allowing pairs to compare the maps then summarize the results as a class. The worksheet has a table for the students and the PowerPoint has table for summarizing. Class Discussion - Summarize differences between modern and LGM in the CLIMAP model output. Discuss how the assumptions of the CLIMAP model studies may have influenced the results. Extra activities The students can explore the data further using the data selection and filters in the IRI/LDEO Climate Data Library. For the two SST data sets, click on "Data Selection" and narrow the data to the just the tropics (23.5º N-S). Click on "Filters" then select XY next to "Average over." The next window gives you the average over the tropics close to the top of the page. In the next class, the students repeat the Readings exercise by reading the COHMAP and MARGO papers to see how the scientific knowledge has progressed since the original CLIMAP studies. COHMAP Members, (1988), Climatic Changes of the Last 18,000 Years: Observations and Model Simulations, Science, 241(4869), 1043-1052. MARGO (2009), Constraints on the magnitude and patterns of ocean cooling at the Last Glacial Maximum, Nature Geoscience, 2(2), 127-132.

Delong, Kristine

343

Maximum likelihood estimation of turbulence spectrum parameters  

NASA Technical Reports Server (NTRS)

Estimation of the integral scale and intensity of a generic turbulence record is treated as a statistical problem of parameter estimation. Properties of parameter estimators and the method of maximum likelihood are reviewed. Likelihood equations are derived for estimation of the integral scale and intensity applicable to a general class of turbulence spectra that includes the von Karman and Dryden transverse and longitudinal spectra as special cases. The method is extended to include the Bullen transverse and longitudinal spectra. Coefficients of variation are given for maximum likelihood estimates of the integral scale and intensity of the von Karman spectra. Application of the method is illustrated by estimating the integral scale and intensity of an atmospheric turbulence vertical velocity record assumed to be governed by the von Karman transverse spectrum.

Mark, W. D.

1984-01-01

344

Design Method of a High Field HTS Magnet Consisting of Pancake Windings Having Different Current in Each Pancake Winding  

Microsoft Academic Search

HTS pancake windings have been commonly used for the insert coil of high field magnets. All pancake windings have been connected in series and excited by a single power source. In that case, currents of the whole pancake windings were limited by the minimum current of the top and the bottom pancake windings where maximum perpendicular magnetic field was applied.

Myunghun Kang; Kwangyoun Lee; Gueesoo Cha; Heejoon Lee

2008-01-01

345

Internal velocity factors  

NASA Technical Reports Server (NTRS)

Computer program analyzes the entries and planetary trajectories of space vehicles. It obtains the equivalence of altitude and flight path angle, respectively, to acceleration load factor with respect to velocity for a given inertial velocity.

Cathcart, J. R.; Frank, A. J.; Massaglia, J. L.

1968-01-01

346

Prediction of fragment velocities and trajectories  

NASA Technical Reports Server (NTRS)

Analytical techniques are described which predict: (1) the velocities of two unequal fragments from bursting cylindrical pressure vessels; (2) the velocity and range of portions of vessels containing a fluid which, when the vessel ruptures, causes the fragment to accelerate as the fluid changes from the liquid to the gaseous phase; and (3) the ranges of fragments subjected to drag and lift forces during flight. Numerous computer runs were made with various initial conditions in an effort to generalize the results for maximum range in plots of dimensionless range versus dimensionless velocity.

Kulesz, J. J.; Vargas, L. M.; Moseley, P. K.

1979-01-01

347

Stellar winds driven by Alfven waves  

NASA Technical Reports Server (NTRS)

Models of stellar winds were considered in which the dynamic expansion of a corona is driven by Alfven waves propagating outward along radial magnetic field lines. In the presence of Alfven waves, a coronal expansion can exist for a broad range of reference conditions which would, in the absence of waves, lead to static configurations. Wind models in which the acceleration mechanism is due to Alfven waves alone and exhibit lower mass fluxes and higher energies per particle are compared to wind models in which the acceleration is due to thermal processes. For example, winds driven by Alfven waves exhibit streaming velocities at infinity which may vary between the escape velocity at the coronal base and the geometrical mean of the escape velocity and the speed of light. Upper and lower limits were derived for the allowed energy fluxes and mass fluxes associated with these winds.

Belcher, J. W.; Olbert, S.

1973-01-01

348

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

349

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

350

The Average Velocity in a Queue  

ERIC Educational Resources Information Center

A number of cars drive along a narrow road that does not allow overtaking. Each driver has a certain maximum speed at which he or she will drive if alone on the road. As a result of slower cars ahead, many cars are forced to drive at speeds lower than their maximum ones. The average velocity in the queue offers a non-trivial example of a mean…

Frette, Vidar

2009-01-01

351

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 ...

352

Observational consequences of Martian wind regimes.  

NASA Technical Reports Server (NTRS)

The connection with past and future observations of Mars of the high velocity relief winds deduced by Gierasch and Sagan (1971) is examined with the assistance of a large topographic map of Mars. A unimodal hypsometric curve is derived. Seasons and locales of wind velocities at the half surface pressure level below 80 m/sec, sufficient to lift dust at the surface, are identified. A number of suggestions are made that can be checked by observations with the Mariner Mars 1971 orbiters.

Sagan, C.; Veverka, J.; Gierasch, P.

1971-01-01

353

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

354

Wind Whispers  

NSDL National Science Digital Library

The Advanced Technology Environmental and Energy Center (ATEEC) provides this presentation on the career and technical aspects of wind energy. In addition to discussing careers in wind, the presentation covers the siting of wind turbines and some electricity basics. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item.

2011-03-09

355

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

356

What is a Hurricane? Tropical system with maximum sustained  

E-print Network

· Abnormal rise in sea level accompanying a hurricane. #12;Storm Surge Flooding-Katrina #12;HurricaneHurricane 101 #12;What is a Hurricane? · Tropical system with maximum sustained surface wind of 74 mph or greater. A hurricane is the worst and the strongest of all tropical systems. · Also known

Meyers, Steven D.

357

Principal wind turbines for a conditional portfolio approach to wind farms  

E-print Network

We introduce a measure for estimating the best risk-return relation of power production in wind farms within a given time-lag, conditioned to the velocity field. The velocity field is represented by a scalar that weighs the influence of the velocity at each wind turbine at present and previous time-steps for the present "state" of the wind field. The scalar measure introduced is a linear combination of the few turbines, that most influence the overall power production. This quantity is then used as the condition for computing a conditional expected return and corresponding risk associated to the future total power output.

Lopes, Vitor V; Raischel, Frank; Lind, Pedro G

2014-01-01

358

Principal wind turbines for a conditional portfolio approach to wind farms  

NASA Astrophysics Data System (ADS)

We introduce a measure for estimating the best risk-return relation of power production in wind farms within a given time-lag, conditioned to the velocity field. The velocity field is represented by a scalar that weighs the influence of the velocity at each wind turbine at present and previous time-steps for the present "state" of the wind field. The scalar measure introduced is a linear combination of the few turbines, that most influence the overall power production. This quantity is then used as the condition for computing a conditional expected return and corresponding risk associated to the future total power output.

Lopes, Vitor V.; Scholz, Teresa; Raischel, Frank; Lind, Pedro G.

2014-06-01

359

The Local Velocity Field  

E-print Network

We only see a small fraction of the matter in the universe, but the rest gives itself away by the impact of its gravity. The distortions from pure Hubble flow (or peculiar velocities) that this matter creates have the potential to be a powerful cosmological tool, but are also a nuisance for extragalactic astronomers who wish to use redshifts to estimate distances to local galaxies. We provide a quick overview of work on the local peculiar velocity field, discussing both simple spherical infall models, non-parametric modeling using redshifts surveys, and full velocity and density field reconstruction from peculiar velocities. We discuss results from a multiattractor model fit to data from the SFI++ sample of peculiar velocities - the best peculiar velocity data currently available. We also talk about the future of samples for the study of the local velocity field, especially the 2MASS Tully-Fisher (2MTF) survey.

Karen L. Masters

2008-03-27

360

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

361

Measuring Venus’ winds using the Absolute Astronomical Accelerometer: Solid super-rotation model of Venus’ clouds  

NASA Astrophysics Data System (ADS)

We present a new method of measuring the Venus winds by Doppler velocimetry on the full visible spectrum of solar light scattered by the clouds. In January 2003, we carried out observations to measure the winds of Venus, using the EMILIE high-resolution, cross-dispersed spectrograph and its associated calibrating instrument the Absolute Astronomical Accelerometer (AAA), at Observatoire de Haute-Provence, France. The motivation of this type of measurements is that it measures the actual velocity of cloud particles, while the other method (track of cloud features) may be sensitive to the deformation of the clouds. During observations, Venus was near maximum western elongation, at a phase angle near 90°. The EMILIE-AAA system allows us to measure accurately the Doppler shift induced in the reflected solar spectrum by the radial component of the motion of the clouds of Venus. We present the measurements and compare them with a forward simulation of a solid super-rotation of the atmosphere of Venus. Taking into account the Doppler shift relative to the Sun and that relative to the Earth, the theoretical total Doppler shift induced in the solar spectra is easily computed as a function of the velocity of the reflecting target. A first forward simulation is computed, with a wind model considering a purely horizontal and zonal wind. The magnitude of the wind is assumed to depend on cos(latitude), as for a solid-body rotation. The comparison with the measurements at various points on the illuminated semi-disc allowed us to determine an equatorial velocity of 66, 75, 91 and 85 m/s on 4 consecutive mornings, consistent with previous ultraviolet cloud tracking wind measurements, showing that wave propagation is not a major factor in the apparent motion of the cloud marks. Further, we discuss the effect of the finite angular size of the Sun and its rapid equatorial rotation (that we call the Young effect). It mainly affects measurements taken near the terminator, where the largest discrepancies are found. These discrepancies are alleviated when the Young effect is taken into account in the model but then the retrieved Venus equatorial velocity is reduced to only 48±3 m/s. This is well below classical ultraviolet markings velocities, but the altitude at which the visible photons are scattered (66 km) that we use is 5 km below the UV markings, confirming the vertical gradient of the horizontal winds shown by previous in-situ measurements.

Gabsi, Younes; Bertaux, Jean Loup; Hauchecorne, Alain; Schmitt, Jérôme; Guibert, Stéphane

2008-10-01

362

Estimates of solar wind heating inside 0.3 AU  

NASA Technical Reports Server (NTRS)

Helios 1 proton temperature data have been normalized in order to determine a base temperature-velocity curve at 0.3 AU and to provide quantitative estimates on the close-in heating at different solar wind velocities. The results suggest that the slope of the solar wind temperature gradients for high-speed streams inside 0.3 AU is about half of that found beyond it. The very-low-speed wind is shown to expand adiabatically all the way out. It is also found that intermediate speed winds have enhanced heating rates in proportion to their velocities.

Freeman, John W.

1988-01-01

363

Tiber winding pack design  

SciTech Connect

A preliminary winding pack design was performed with the goal of showing feasibility of producing 10-T maximum field with a pack current density of 40 A.mm/sup -2/ while accepting 2.7 kW per coil nuclear heating. A cable-in-conduit conductor design (CIC), reported at the 6th Topical Meeting on the Technology of Fusion Energy, was based on several key issues.

Miller, J.R.

1985-08-19

364

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

365

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 observed was 27 m/sec, or 0.5 percent of the impact velocity. The measured spall velocities were within the range predicted by the Melosh (1984) spallation model for the given experimental parameters. The compatability between the Melosh model for large planetary impacts and the results of these small scale experiments is considered in detail. The targets were also bisected to observe the internal fractures. A series of fractures were observed whose location coincided with the boundary of the theoretical near surface zone predicted by Melosh. Above this boundary the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.

Polanskey, Carol A.; Ahrens, Thomas J.

1986-01-01

366

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

367

Preliminary Investigations of Wind Potential at Marietta College  

NASA Astrophysics Data System (ADS)

Marietta College received a grant to build a wind turbine on campus for educational purposes, as a demonstration of alternative energy production, and to promote new energy systems minors. We report on an investigation of the potential wind energy profile on Marietta College's campus and preliminary wind tunnel studies of variations in shroud design for a shrouded horizontal axis wind turbine. Anemometers were placed in three locations on the campus and wind velocity data was logged for several months. The data provides average wind speeds as well as prevailing wind directions. A wind tunnel was constructed to test shrouded wind turbines. A shrouded wind turbine with a diffuser and flange can maximize the wind speed through a turbine, thus maximizing its power output. This paper sets the stage for future projects to further develop the turbine models' geometry that will maximize power output.

Vance, William; Kuhl, Dennis

2012-04-01

368

An assessment of wind energy as an alternative energy resource in Malaysia  

Microsoft Academic Search

The paper investigates the prospect of wind power in the East Coast of Peninsular Malaysia based on wind statistics from meteorological stations at Mersing, Kuantan, Kota Bharu and Kuala Trengganu. From these data, the frequency, wind direction and velocity over a prolonged period are determined. The velocity and power duration curves are drawn and the power outputs are estimated for

F. F. Ling; J. Seah; C. P. Tai

1981-01-01

369

Discrete time blade pitch control for wind turbine torque regulation with digitally simulated random turbulence excitation  

Microsoft Academic Search

A time domain simulation model that approximates the three-dimensional velocity fluctuations of wind turbulence was developed. This model is used in a discrete time control algorithm to regulate the output torque of a wind turbine by changing the pitch angle of the turbine blade. The wind model provides a velocity field that varies randomly with time and space and gives

Sharif-Razi

1986-01-01

370

Angular velocity discrimination  

NASA Technical Reports Server (NTRS)

Three experiments designed to investigate the ability of naive observers to discriminate rotational velocities of two simultaneously viewed objects are described. Rotations are constrained to occur about the x and y axes, resulting in linear two-dimensional image trajectories. The results indicate that observers can discriminate angular velocities with a competence near that for linear velocities. However, perceived angular rate is influenced by structural aspects of the stimuli.

Kaiser, Mary K.

1990-01-01

371

Solar Wind Forecasting with the SOLIS-VSM  

Microsoft Academic Search

A web based solar wind forecasting resource applying a simple empirical model with SOLIS-VSM (Vector Spectromagnetograph) data is presented here. The solar wind empirical model uses the locations of coronal holes on the observed solar disk to forecast an estimated solar wind velocity at Earth. The model coefficients are estimated minimizing the difference between 10+ years of coronal hole images

S. J. Robbins; C. J. Henney; J. W. Harvey

2005-01-01

372

Optimal storage scheduling for minimizing schedule deviations considering variability of generated wind power  

Microsoft Academic Search

Incorporation of energy storage units with wind farms is being considered critical for wind farms to address variability in wind power generation and meeting committed generation schedules. However, operational constraints such as limited energy of storage units, in addition to the inherent variability of wind power, limit the maximum generation commitment that can be met reliably by a wind farm

S. Dutta; T. J. Overbye

2011-01-01

373

How to hit home runs: Optimum baseball bat swing parameters for maximum range trajectories  

NASA Astrophysics Data System (ADS)

Improved models for the pitch, batting, and post-impact flight phases of a baseball are used in an optimal control context to find bat swing parameters that produce maximum range. The improved batted flight model incorporates experimental lift and drag profiles (including the drag crisis). An improved model for bat-ball impact includes the dependence of the coefficient of restitution on the approach relative velocity and the dependence of the incoming pitched ball angle on speed. The undercut distance and bat swing angle are chosen to maximize the range of the batted ball. The sensitivity of the maximum range is calculated for all model parameters including bat and ball speed, bat and ball spin, and wind speed. Post-impact conditions are found to be independent of the ball-bat coefficient of friction. The lift is enhanced by backspin produced by undercutting the ball during batting. An optimally hit curve ball will travel farther than an optimally hit fastball or knuckleball due to increased lift during flight.

Sawicki, Gregory S.; Hubbard, Mont; Stronge, William J.

2003-11-01

374

Optimal control of wind turbine using neural networks  

Microsoft Academic Search

Variable-speed, fixed-pitch wind turbines are required to optimize power output performance without the aerodynamic controls. In steady-state, a wind turbine generator system is operated such that the optimum points of wind rotor curve and electrical generator curve coincide. In order to obtain maximum power output of a wind turbine generator system, it is necessary to drive the wind turbine at

Mahinsasa Narayana; Ghanim Putrus

2010-01-01

375

The Local Velocity Anomaly  

E-print Network

There is a velocity discontinuity at about 7 Mpc between the galaxies of the Local Sheet that are moving together with low internal velocity dispersion and the adjacent structures. The Local Sheet bounds the Local Void. The Local Sheet is determined to have a peculiar velocity of 260 km/s away from the center of the void. In order for this large velocity to be generated by an absence of gravity, the Local Void must be at least 45 Mpc in diameter and be very empty.

R. Brent Tully

2007-08-17

376

Comment on "A statistical comparison of solar wind sources of moderate and intense geomagnetic storms at solar minimum and maximum" by Zhang, J.-C., M. W. Liemohn, J. U. Kozyra, M. F. Thomsen, H. A. Elliott, and J. M. Weygand, JGR, 2006  

E-print Network

Conditions in the solar wind resulting in magnetic storms on the Earth are a subject of long and intensive investigations. Recently Zhang et al. (2006), published a paper, where they used superposed epoch analyses method to study solar wind features during 549 geomagnetic storms. Unfortunately, the used methodical approach has not allowed to improve essentially understanding of relation of magnetic storms with conditions in the solar wind, and first of all for the following reasons: (1) they did not take into account of existance of storms generated by different types of solar wind, and (2) they took minimum Dst index time as epoch zero time rather than storm onset.

Yermolaev, Y I; Lodkina, I G; Yermolaev, Yu. I.

2006-01-01

377

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

378

Maximum entropy discrimination Tommi Jaakkola  

E-print Network

;) that maximizes the entropy H(P ) subject to the classi#12;cation constraints R P(#2;) [ y t L(X t j#2;) ] d#2Maximum entropy discrimination Tommi Jaakkola MIT AI Lab 545 Technology Sq. Cambridge, MA 02139 framework for discriminative estimation based on the maximum entropy principle and its extensions. All

Jaakkola, Tommi S.

379

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

380

The Dornier Wind Tunnel  

NASA Technical Reports Server (NTRS)

After completion of the required calibrations, the Dornier open-throat tunnel is now in operation. With an elliptic test section of 3 by 4 m (9.84 by 3.12 ft.), its length is 7 m (22.97 ft.), its maximum horsepower 800, and its maximum air speed 60 m/s (134.2 mph). As to local uniformity of velocity, static pressure as well as jet direction, and turbulence factor, this tunnel is on par with those of the good German and foreign research labs.

Schlichting, H

1938-01-01

381

Velocity Profile Spatial Profile  

E-print Network

by different colors. The black horizontal bar indicates the time window used for the ROC-analysis. (B *New York University, Center for Neural Science 3. ROC-ANALYSIS 5. RESULTS 4. TIME COURSE Visual0 0 0 Velocity Profile velocity time increment decrement no change Spatial Profile t t0 1 Averaged

382

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

383

Video Measurement of the Muzzle Velocity of a Potato Gun  

ERIC Educational Resources Information Center

Using first principles, a theoretical equation for the maximum and actual muzzle velocities for a pneumatic cannon was recently derived. For a fixed barrel length, this equation suggests that the muzzle velocity can be enhanced by maximizing the product of the initial pressure and the volume of the propellant gas and decreasing the projectile…

Jasperson, Christopher; Pollman, Anthony

2011-01-01

384

The superimposed photospheric and stellar wind variability of the O-type supergiant alpha Cam  

E-print Network

(Abridged) We provide empirical constraints on the different physical components that can act to yield temporal variability in predominantly or partially wind-formed optical lines of luminous OB stars, and thus potentially affect the reliable determination of fundamental parameters, including mass-loss rates via clumped winds. Using time-series spectroscopy from epochs spread over $\\sim$ 4 years, a case study of the O9.5 supergiant $\\alpha$ Cam is presented. We demonstrate that the He I 5876 (2$^3$P$^0$--3$^3$D) line is an important diagnostic for photospheric and wind variability in this star. The optical line profiles of $\\alpha$ Cam are affected by (i) deep-seated fluctuations close to, or at, the photosphere, (ii) atmospheric velocity gradients, and (iii) large-scale stellar wind structure. This study provides new empirical perspectives on accurate line-synthesis modelling of stellar wind signatures in massive luminous stars. Using a pure Halpha line-synthesis code we interpret maximum changes in the red-ward and peak emission of $\\alpha$ Cam in terms of mass-loss rate differences in the range $\\sim$ 5.1 $\\times$ 10$^{-6}$ to 6.5 $\\times$ 10$^{-6}$ M$_\\odot$ yr$^{-1}$. However, the models generally fail to reproduce the morphology of blueward (possibly absorptive) regions of the profiles.

R. K. Prinja; N. Markova; S. Scuderi; H. Markov

2006-06-29

385

Specific gust shapes leading to extreme response of pitch-regulated wind turbines  

NASA Astrophysics Data System (ADS)

Via so-called constrained stochastic simulation gusts can be generated which satisfy some specified constraint. Constrained stochastic simulation is based on conditional densities of normal random variables and it has previously been applied to generate maximum amplitude gusts and velocity jumps. In this paper it is used in order to generate specific wind gusts which will lead to local maxima in the response of (pitch-regulated) wind turbines. The method is demonstrated on basis of a linear model of a wind turbine, inclusive pitch control. The mean gust shape as well as the mean shape of the response, for some gust amplitude, is shown. By performing many simulations (for given gust amplitude) the conditional distribution of the response is obtained. By a weighted average of these conditional distributions over the probability of the gusts the overall distribution of the response can be obtained. Analytical expressions for the conditional distribution of the response (for given gust amplitude) as well as the overall distribution are specified. These form an ideal test case of tools (e.g. fitting to an extreme value distribution) to be used for non-linear wind turbine models. The application of the above method on a non-linear model of a wind turbine has still to be done.

Bierbooms, Wim

2007-07-01

386

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

387

Changes in the Wind Regime Over Northern Eurasia  

NASA Astrophysics Data System (ADS)

The wind regime of Russia varies a great deal due to the large size of the country's territory and variety of climate and terrain conditions. Changes in the regime of surface wind are of great practical importance. They can affect heat and water balance. Strong wind is one of the most hazardous meteorological event for various sectors of economy and for infrastructure. At meteorological stations wind speed and wind direction are measured at the height of 10-12 meters over the land surface with the help of wind meters or wind wanes. Due to the turbulent state of the atmosphere wind speed and wind direction in each moment of time fluctuate considerably about the average value. Therefore, the average wind speed over the period of either 2 or 10 minutes (depending on the technical capacity of the instrument used for measurements) is measured, the maximum value of wind speed (gust wind speed) in the same periods of time is determined as well as the average wind direction over the period of 2 minutes. Calculations were made on the basis of data for the period of 1980-2011. It allowed the massive scale disruption of homogeneity to be eliminated and sufficient period needed to obtain sustainable statistic characteristics to be retained. Data on average and maximum wind speed measured at 1457 stations of Russia were used. The analysis of changes in wind characteristics was made on the basis of point data and series of average characteristics obtained for 18 quasi-homogeneous climatic regions. Statistical characteristics (average and maximum values of wind speed, prevailing wind direction, values of the boundary of the 90%, 95% and 99%-confidence interval in the distribution of maximum wind speed) were obtained for all seasons and for the year as a whole. Values of boundaries of the 95% and 99%-confidence interval in the distribution of maximum wind speed were considered as indicators of extremeness of the wind regime. The trend of changes in average and maximum wind speed was assessed with a linear trend coefficient. A special attention was paid to wind changes in the Arctic where dramatic changes in surface air temperature and sea ice extent and density have been observed during the past decade. The analysis of the results allowed seasonal and regional features of changes in the wind regime on the territory of the northern part of Eurasia to be determined. The outcomes could help to provide specific recommendations to users of hydrometeorological information for making reasonable decisions to minimize losses caused by adverse wind-related weather conditions.

Bulygina, O.; Korshunova, N.; Razuvaev, V.

2012-12-01

388

Whistler Waves Driven by Anisotropic Strahl Velocity Distributions: Cluster Observations  

NASA Astrophysics Data System (ADS)

Observed properties of the strahl using high resolution 3D electron velocity distribution data obtained from the Cluster/PEACE experiment are used to investigate its linear stability. An automated method to isolate the strahl is used to allow its moments to be computed independent of the solar wind core+halo. Results show that the strahl can have a high temperature anisotropy (T?/T||>~2). This anisotropy is shown to be an important free energy source for the excitation of high frequency whistler waves. The analysis suggests that the resultant whistler waves are strong enough to regulate the electron velocity distributions in the solar wind through pitch-angle scattering.

F-Viñas, A.; Gurgiolo, C.; Nieves-Chinchilla, T.; Gary, S. P.; Goldstein, M. L.

2010-03-01

389

Tropospheric Wind Measurements From Space: The SPARCLE Mission And Beyond  

NASA Technical Reports Server (NTRS)

For over 20 years researchers have been investigating the feasibility of profiling tropospheric vector wind velocity from space with a pulsed Doppler lidar. Efforts have included theoretical development, system and mission studies, technology development, and ground-based and airborne measurements. Now NASA plans to take the next logical step towards enabling operational global tropospheric wind profiles by demonstrating horizontal wind measurements from the Space Shuttle in early 2001 using a coherent Doppler wind lidar system.

Kavaya, Michael J.; Emmitt, G. David

1998-01-01

390

Tropospheric Wind Measurements from Space: The SPARCLE Mission and Beyond  

NASA Technical Reports Server (NTRS)

For over 20 years researchers have been investigating the feasibility of profiling tropospheric vector wind velocity from space with a pulsed Doppler lidar. Efforts have included theoretical development, system and mission studies, technology development, and ground-based and airborne measurements. Now NASA plans to take the next logical step towards enabling operational global tropospheric wind profiles by demonstrating horizontal wind measurements from the Space Shuttle in early 2001 using a coherent Doppler wind lidar system.

Kavaya, Michael J.; Emmitt, G. David

1998-01-01

391

MHD Disk Winds in PNe and pPNe  

E-print Network

Winds from accretion disks have been proposed as the driving source for precessing jets and extreme bipolar morphologies in Planetary Nebulae (PNe) and proto-PNe (pPNe). Here we apply MHD disk wind models to PNe and pPNe by estimating separately the asymptotic MHD wind velocities and mass loss rates. We show that the resulting winds can recover the observed momentum and energy input rates for PNe and pPNe.

Adam Frank

2003-10-19

392

Wave-and Anemometer-Based Sea Surface Wind (WASWind) for Climate Change Analysis*  

E-print Network

Wave- and Anemometer-Based Sea Surface Wind (WASWind) for Climate Change Analysis* HIROKI TOKINAGA-based measurements of sea surface wind speed display a spurious upward trend due to increases in anemometer height (ICOADS). The Wave- and Anemometer-based Sea surface Wind (WASWind) dataset is available for wind velocity

Xie, Shang-Ping

393

Wind loading on solar collectors  

SciTech Connect

The present design methodology for the determination of wind loading on the various solar collectors has been reviewed and assessed. The total force coefficients of flat plates of aspect ratios 1.0 and 3.0, respectively, at various angles of attack obtained by using the guidelines of the ANSI A58.1-1982, have been compared with those obtained by using the methodology of the ASCE Task Committee, 1961, and the experimental results of the full-scale test of heliostats by Peglow. The turbulent energy spectra, currently employed in the building code, are compared with those of Kaimal et al., Lumley, and Ponofsky for wind velocities of 20.0 m/s and 40.24 m/s at an elevation of 9.15 m. The longitudinal spectra of the building code overestimates the Kaimal spectra in the frequency range of 0.007 Hz to 0.08 Hz and underestimates beyond the frequency of 0.08 Hz. The peak angles of attack, on the heliostat, stowed in horizontal position, due to turbulent vertical and lateral components of wind velocity, have been estimated by using Daniel's methodology for three wind velocities and compared with the value suggested by the code. The experimental results of a simple test in the laboratory indicate the feasibility of decreasing the drag forces of the flat plate by reducing the solidity ratio.

Bhaduri, S.; Murphy, L.M.

1985-06-01

394

Development of a Wind Turbine Test Rig and Rotor for Trailing Edge Flap Investigation: Static Flap Angles Case  

NASA Astrophysics Data System (ADS)

One of the strategies used to improve performance and increase the life-span of wind turbines is active flow control. It involves the modification of the aerodynamic characteristics of a wind turbine blade by means of moveable aerodynamic control surfaces. Trailing edge flaps are relatively small moveable control surfaces placed at the trailing edge of a blade's airfoil that modify the lift of a blade or airfoil section. An instrumented wind turbine test rig and rotor were specifically developed to enable a wide-range of experiments to investigate the potential of trailing edge flaps as an active control technique. A modular blade based on the S833 airfoil was designed to allow accurate instrumentation and customizable settings. The blade is 1.7 meters long, had a constant 178mm chord and a 6° pitch. The modular aerodynamic parts were 3D printed using plastic PC-ABS material. The blade design point was within the range of wind velocities in the available large test facility. The wind facility is a large open jet wind tunnel with a maximum velocity of 11m/s in the test area. The capability of the developed system was demonstrated through an initial study of the effect of stationary trailing edge flaps on blade load and performance. The investigation focused on measuring the changes in flapwise bending moment and power production for different trailing edge flap spanwise locations and deflection angles. The relationship between the load reduction and deflection angle was linear as expected from theory and the highest reduction was caused by the flap furthest from the rotor center. Overall, the experimental setup proved to be effective in measuring small changes in flapwise bending moment within the wind turbine blade and will provide insight when (active) flap control is targeted.

Abdelrahman, Ahmed; Johnson, David A.

2014-06-01

395

Radial velocity moments of dark matter haloes  

E-print Network

Using cosmological N-body simulations we study the radial velocity distribution in dark matter haloes focusing on the lowest-order even moments, dispersion and kurtosis. We determine the properties of ten massive haloes in the simulation box approximating their density distribution by the NFW formula characterized by the virial mass and concentration. We also calculate the velocity anisotropy parameter of the haloes and find it mildly radial and increasing with distance from the halo centre. The radial velocity dispersion of the haloes shows a characteristic profile with a maximum, while the radial kurtosis profile decreases with distance starting from a value close to Gaussian near the centre. We therefore confirm that dark matter haloes possess intrinsically non-Gaussian, flat-topped velocity distributions. We find that the radial velocity moments of the simulated haloes are quite well reproduced by the solutions of the Jeans equations obtained for the halo parameters with the anisotropy measured in the simulations. We also study the radial velocity moments for a composite cluster made of ten haloes out to ten virial radii. In this region the velocity dispersion decreases systematically to reach the value of the background, while kurtosis increases from below to above the Gaussian value of 3 signifying a transition from a flat-topped to a strongly peaked velocity distribution with respect to the Gaussian, which can be interpreted as the dominance of ordered flow with a small dispersion. We illustrate the transition by showing explicitly the velocity distribution of the composite cluster in a few radial bins.

Radoslaw Wojtak; Ewa L. Lokas; Stefan Gottloeber; Gary A. Mamon

2005-03-17

396

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasises the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters, but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M (dot) q(sub i)) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in terms of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, D.; Oliversen, R. (Technical Monitor)

2002-01-01

397

The Winds of B Supergiants  

NASA Technical Reports Server (NTRS)

We present the most suitable data sets available in the International Ultraviolet Explorer (IUE) archive for the study of time-dependent stellar winds in early B supergiants. The UV line profile variability in 11 B0 to B3 stars is analyzed, compared and discussed, based on 16 separate data sets comprising over 600 homogeneously reduced high-resolution spectrograms. The targets include 'normal' stars with moderate rotation rates and examples of rapid rotators. A gallery of grey-scale images (dynamic spectra) is presented, which demonstrates the richness and range of wind variability and highlights different structures in the winds of these stars. This work emphasizes the suitability of B supergiants for wind studies, under-pinned by the fact that they exhibit unsaturated wind lines for a wide range of ionization. The wind activity of B supergiants is substantial and has highly varied characteristics. The variability evident in individual stars is classified and described in terms of discrete absorption components, spontaneous absorption, bowed structures, recurrence, and ionization variability and stratification. Similar structures can occur in stars of different fundamental parameters but also different structures may occur in the same star at a given epoch. We discuss the physical phenomena that may be associated with the spectral signatures, and highlight the challenges that these phenomena present to theoretical studies of time-dependent outflows in massive stars. In addition, SEI line-synthesis modelling of the UV wind lines is used to provide further information about the state of the winds in our program stars. Typically the range, implied by the line profile variability, in the product of mass-loss rate and ion fraction (M qi) is a factor of approximately 1.5, when integrated between 0.2 and 0.9 v infinity; it it can however be several times larger over localized velocity regions. At a given effective temperature the mean relative ion ratios can differ by a factor of 5. The general excess in predicted (forward-scattered) emission in the low velocity regime is discussed in turns of structured outflows. Mean ion fractions are estimated over the B0 to B1 spectral classes, and trends in the ionic ratios as a function of wind velocity are described. The low values obtained for the ion fractions of UV resonance lines may reflect the role of clumping in the wind.

Massa, Derck; West, D. (Technical Monitor)

2002-01-01

398

Application of correlation lidar data to modeling and prediction of wind components.  

PubMed

Statistical estimation of the quality of lidar wind velocity measurements by the correlation method and the results of their application to the study of local and regional climates as well as to the reconstruction and ultrashort-range prediction (for forecasting periods wind velocity components are presented. Wind velocity measurents with a three-path correlation lidar can be used successfully for climatic-ecological monitoring of local territories. PMID:18250882

Zuev, V E; Komarov, V S; Kreminskii, A V

1997-03-20

399

Wind Energy Leasing Handbook  

E-print Network

Wind Energy Leasing Handbook Wind Energy Leasing Handbook E-1033 Oklahoma Cooperative Extension?..................................................................................................................... 31 What do wind developers consider in locating wind energy projects?............................................................................................ 37 How do companies and individuals invest in wind energy projects?....................................................................

Balasundaram, Balabhaskar "Baski"

400

Relativistic Radiation Hydrodynamical Accretion Disk Winds  

E-print Network

Accretion disk winds browing off perpendicular to a luminous disk are examined in the framework of fully special relativistic radiation hydrodynamics. The wind is assumed to be steady, vertical, and isothermal. %and the gravitational fields is approximated by a pseudo-Newtonian potential. Using a velocity-dependent variable Eddington factor, we can solve the rigorous equations of relativistic radiative hydrodynamics, and can obtain radiatively driven winds accelerated up to the {\\it relativistic} speed. For less luminous cases, disk winds are transonic types passing through saddle type critical points, and the final speed of winds increases as the disk flux and/or the isothermal sound speed increase. For luminous cases, on the other hand, disk winds are always supersonic, since critical points disappear due to the characteristic nature of the disk gravitational fields. The boundary between the transonic and supersonic types is located at around $\\hat{F}_{\\rm c} \\sim 0.1 (\\epsilon+p)/(\\rho c^2)/\\gamma_{\\rm c}$, where $\\hat{F}_{\\rm c}$ is the radiative flux at the critical point normalized by the local Eddington luminosity, $(\\epsilon+p)/(\\rho c^2)$ is the enthalpy of the gas divided by the rest mass energy, and $\\gamma_{\\rm c}$ is the Lorentz factor of the wind velocity at the critical point. In the transonic winds, the final speed becomes 0.4--0.8$c$ for typical parameters, while it can reach $\\sim c$ in the supersonic winds.

Jun Fukue; Chizuru Akizuki

2007-11-09

401

Variations of Strahl Properties With Fast and Slow Solar Wind  

NASA Astrophysics Data System (ADS)

The interplanetary solar wind electron velocity distribution function generally shows three different populations. Two of the components, the core and halo, have been the most intensively analyzed and modeled populations using different theoretical models. The third component, the strahl, is usually seen at higher energies, is confined in pitch-angle, is highly field-aligned and skew. This population has been more difficult to identify and to model in the solar wind. In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze this component in the ambient solar wind during high and slow speed solar wind. The moment density and fluid velocity have been computed by a semi-numerical integration method. The variations of solar wind density and drift velocity with the general bulk solar wind speed could provide some insight into the source, origin, and evolution of the strahl.

Nieves-Chinchilla, T.; Viñas, A. F.; Goldstein, M. L.; Gurgiolo, C.

2008-12-01

402

Variations of Strahl Properties with Fast and Slow Solar Wind  

NASA Technical Reports Server (NTRS)

The interplanetary solar wind electron velocity distribution function generally shows three different populations. Two of the components, the core and halo, have been the most intensively analyzed and modeled populations using different theoretical models. The third component, the strahl, is usually seen at higher energies, is confined in pitch-angle, is highly field-aligned and skew. This population has been more difficult to identify and to model in the solar wind. In this work we make use of the high angular, energy and time resolution and three-dimensional data of the Cluster/PEACE electron spectrometer to identify and analyze this component in the ambient solar wind during high and slow speed solar wind. The moment density and fluid velocity have been computed by a semi-numerical integration method. The variations of solar wind density and drift velocity with the general build solar wind speed could provide some insight into the source, origin, and evolution of the strahl.

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

2008-01-01

403

Maximum Diameter of Impacting Liquid Droplets  

NASA Astrophysics Data System (ADS)

The maximum diameter a droplet that impacts on a surface will attain is the subject of controversy, notably for high-velocity impacts of low-viscosity liquids such as water or blood. We study the impact of droplets of simple liquids of different viscosities, and a shear-thinning complex fluid (blood), for a wide range of surfaces, impact speeds, and impact angles. We show that the spreading behavior cannot simply be predicted by equating the inertial to either capillary or viscous forces, since, for most situations of practical interest, all three forces are important. We determine the correct scaling behaviors for the viscous and capillary regimes and, by interpolating between the two, allow for a universal rescaling. The results for different impact angles can be rescaled on this universal curve also, by doing a simple geometrical correction for the impact angle. For blood, we show that the shear-thinning properties do not affect the maximum diameter and only the high-shear rate viscosity is relevant. With our study, we solve a long-standing problem within the fluid-dynamics community: We attest that the spreading behavior of droplets is governed by the conversion of kinetic energy into surface energy or dissipated heat. Energy transfer into internal flows marginally hinders droplet spreading upon impact.

Laan, Nick; de Bruin, Karla G.; Bartolo, Denis; Josserand, Christophe; Bonn, Daniel

2014-10-01

404

Transverse spectral velocity estimation.  

PubMed

A transverse oscillation (TO)-based method for calculating the velocity spectrum for fully transverse flow is described. Current methods yield the mean velocity at one position, whereas the new method reveals the transverse velocity spectrum as a function of time at one spatial location. A convex array probe is used along with two different estimators based on the correlation of the received signal. They can estimate the velocity spectrum as a function of time as for ordinary spectrograms, but they also work at a beam-to-flow angle of 90°. The approach is validated using simulations of pulsatile flow using the Womersly-Evans flow model. The relative bias of the mean estimated frequency is 13.6% and the mean relative standard deviation is 14.3% at 90°, where a traditional estimator yields zero velocity. Measurements have been conducted with an experimental scanner and a convex array transducer. A pump generated artificial femoral and carotid artery flow in the phantom. The estimated spectra degrade when the angle is different from 90°, but are usable down to 60° to 70°. Below this angle the traditional spectrum is best and should be used. The conventional approach can automatically be corrected for angles from 0° to 70° to give fully quantitative velocity spectra without operator intervention. PMID:25389160

Jensen, Jørgen

2014-11-01

405

Quadraphonic Wind  

NSDL National Science Digital Library

In this activity, learners discover how the extent of various wind speeds changes in each of the four quadrants around a hurricane. Learners use data from the 'present' location of Hurricane Bill (2009) to plot the distance of various wind speeds that extend from the center of the storm. This resource includes brief background information about hurricanes and forecasting as well as an explanation of the Hurricane Bill data used in this activity and how small increases in wind speed can cause increased potential for damage.

Service, National W.

2012-12-18

406

Wind Tunnel  

NSDL National Science Digital Library

Scientists use enormous wind tunnels to test the design of planes, helicopters, even the Space Shuttle. In this simulation activity, learners create a miniature wind tunnel test by blowing air with a fan or blow dryer through a large tube, then flying paper airplanes, helicopters and other folded paper models in the "wind." Unless the source of the air is a fan that stands on its own, for example, more than one person will be needed to do the activity.This activity can be combined with the Helicopter Twirl, Parachute Drop and Boomerang activities, also found on the Lawrence Hall of Science Kids Site.

Science, Lawrence H.

2009-01-01

407

Global Winds  

NSDL National Science Digital Library

On this worksheet, students examine a diagram of global winds and learn the position of the prevailing westerlies, the polar easterlies, the trade winds, the horse latitudes and the doldrums, and that together, the uneven heating of the planet by the Sun and the Coriolis Effect are responsible for the global wind belts. The resource is part of the teacher's guide accompanying the video, NASA Why Files: The Case of the Mysterious Red Light. Lesson objectives supported by the video, additional resources, teaching tips and an answer sheet are included in the teacher's guide.

408

Stellar Winds  

NASA Astrophysics Data System (ADS)

A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ? evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ˜ ?? 1. 4M ?. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various dynamical driving processes and what they imply for key wind parameters like the wind flow speed and mass loss rate.

Owocki, Stan

409

Application of laser Doppler velocimetry to measurement of the velocity field close to regularly arrayed rough surfaces  

Microsoft Academic Search

Most pollution releases in urban areas occur at or near ground level and therefore well within the building canopy. In order to study the dispersion of these emissions, it is necessary to know the wind velocity profile inside the canopy of large groups of buildings or obstacles. An ultra-low-speed small wind tunnel was set up to investigate the velocity field

Mansen Wang

2006-01-01

410

Assessment of fatigue life for small composite wind turbine blades  

Microsoft Academic Search

The present design and assessment of fatigue life for the small composite wind turbine blades (SCWTBs) can be certified by IEC 61400-2 “Wind Turbines - Part2: Design requirements of small wind turbines”. The paper will establish an analytical method on the fatigue life analysis of SCWTBs. Using the Microsoft Office EXCEL to calculate the maximum stress, minimum stress and stress

Jia-Hroung Wu

2010-01-01

411

Probabilistic capacity of a grid connected wind farm  

Microsoft Academic Search

This paper proposes a method to find the maximum acceptable wind power injection regarding the thermal limits, steady state stability limits and voltage limits of the grid system. The probabilistic wind power is introduced based on the probability distribution of wind speed. Based on power transfer distribution factor (PTDF) and voltage sensitivities, a predictor-corrector method is suggested to calculate the

Menghua Zhao; Zhe Chen; Frede Blaabjorg

2005-01-01

412

Wind turbine availability analysis based on statistical data  

Microsoft Academic Search

Availability is an important performance index for wind turbines. To predict wind turbine availability, failure rate and repair rate have to be known. There are some sources of wind turbine failure data that can be used to estimate parameters of the failure rate function and the repair rate. With repair rate assumed to be constant, this paper first presents maximum

Haitao Guo; Xianhui Yang; Jianping Xiang; Simon Watson

2009-01-01

413

An assessment of wind energy as an alternative energy resource in Malaysia  

NASA Astrophysics Data System (ADS)

The paper investigates the prospect of wind power in the East Coast of Peninsular Malaysia based on wind statistics from meteorological stations at Mersing, Kuantan, Kota Bharu and Kuala Trengganu. From these data, the frequency, wind direction and velocity over a prolonged period are determined. The velocity and power duration curves are drawn and the power outputs are estimated for a 3.66m (12 ft) diameter wind propeller.

Ling, F. F.; Seah, J.; Tai, C. P.

1981-04-01

414

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 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. These models are scheduled to be updated to operate using the most current Environmental Systems Research Institute ArcGIS Geographic Information System platform, and have several improvements implemented to wave calculations, data processing, and functions of the toolbox.

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

2012-01-01

415

The collision velocity of the bullet cluster in conventional and modified dynamics  

E-print Network

We consider the orbit of the bullet cluster 1E 0657-56 in both CDM and MOND using accurate mass models appropriate to each case in order to ascertain the maximum plausible collision velocity. Impact velocities consistent with the shock velocity (~ 4700km/s) occur naturally in MOND. CDM can generate collision velocities of at most ~ 3800km/s, and is only consistent with the data provided that the shock velocity has been substantially enhanced by hydrodynamical effects.

Garry W. Angus; Stacy S. McGaugh

2007-04-03

416

Wind Surge  

NSDL National Science Digital Library

This site features an interactive applet from the University of Delaware. The applet illustrates the way water can pile up against the downwind side (of a basin) due to stresses exerted on the surface by strong wind.

Dalrymple, Robert A.; Delaware, University O.

417

Filament winding  

NASA Astrophysics Data System (ADS)

The major aspects of filament winding are discussed, emphasizing basic reinforcement and matrix materials, winding procedures, process controls, and cured composite properties. Fiberglass (E-glass and S-glass strengths are 500,000 and 665,000 psi respectively) and polyester resins are the principal reinforcement constituent materials. Graphite and aramid reinforcements are being used more frequently, primarily for the more critical pressure vessels. Matrix systems are most commonly based on epoxy as it has superior mechanical properties, fatigue behavior, and heat resistance as compard with polyesters. A fiberglass overwrap of PVC pipe is an anticipated development in on-site winding and combination winding, and the compression molding of filament wound lay-ups will be investigated. The fabrication of weight-sensitive structural components may be achieved by using such moldings.

Shibley, A. M.

418

Winds and Accretion in Young Stars  

E-print Network

Establishing the origin of accretion powered winds from forming stars is critical for understanding angular momentum evolution in the star-disk interaction region.