Showing papers on "Wind profile power law published in 1983"

Normal Monthly Wind Stress Over the World Ocean with Error Estimates

Abstract: Over 35 million surface observations covering the world ocean from 1870–1976 have been processed for the purpose of calculating monthly normals and standard errors of the eastward and northward components of the wind stress and work done by the winds in the lower 10 m of the atmosphere. The fields are intended to serve as boundary conditions for models of the ocean circulation. Wind and air-minus-sea temperatures are calculated in a form suitable for determining stress by any bulk aerodynamics model in which the drag coefficient can be represented by six or less coefficients of a second-degree polynomial in wind speed and stability. The particular case of the wind speed and stability dependent drag coefficient discussed by Bunker is selected for analysis. January and July charts of wind stress, curl of the wind stress, mass transport stream-function, divergence of the Ekman transport and the rate of mechanical energy transfer are illustrated and discussed.

Experiments with a Diffuser-Augmented Model Wind Turbine

Abstract: The initial stages of the experimental development of the diffuser-augmented wind turbine (DAWT) employed various screen meshes to simulate the energy extraction mechanisms of a wind turbine. In this investigation in a 2 × 3 m wind tunnel, a three-bladed constant chord, untwisted turbine model was incorporated into a DAWT model. The objectives were to add real turbine characteristics such as swirl, and centerbodies effects, to the flow. Although this turbine model was not well matched to the diffuser, the model DAWT system increased the power output by more than four times that of the model turbine operating as a conventional wind energy conversion system; more than 3.4 times the power potential of an ideal wind turbine was measured.

On the Theory of the Horizontal-Axis Wind Turbine

Abstract: The extraction of energy from the wind is an old idea, one used by sailing ships and windmills for many centuries. The development of ancient windmills was based on empiricism and engineering skill. The develop­ ment of the fluid mechanics, or more specifically the aerodynamics, of windmills (wind turbines in modern· usage) is more recent. The study of the aerodynamics of wind turbines was begun after W orId War I by Betz ( 1926) and Glauert ( l935a) and got a new impulse after the \"energy crisis\" of 1973-74. Nowadays, it is a worldwide field of research, stimulated and guided by national research programs in the US, Sweden, Denmark, The Netherlands, Great Britain, and many other countries.

Estimation of Low-Frequency Wind Stress Fluctuations over the Open Ocean

Abstract: A simple, approximate formula for mean wind stress is given in terms of the mean and variance of the wind fluctuations over the averaging period. The formula is nonlinear with respect to the mean wind speed. The formula is tested using 3 h wind observations from eight North Atlantic Ocean Weather Ships. Mean wind stress is calculated 1) by vector averaging the 3 h wind stresses and 2) by applying the approximate formula. For an averaging period of 4 months the two methods agree to within ±0.025 Pa, 95% of the time. For an averaging period of 1 month the approximate formula slightly overestimates the stress. This is due to skewness in the probability density function of the observed 3 h wind fluctuations. An expression for the modification of the mean stress due to skewness is given. A straightforward method is described for the estimation of vector mean wind and variance fields, and thus mean stress fields, over the open ocean. To cheek the method, the long-term stress field of the North Atlantic...

The effects of Coulomb collisions on solar wind ion velocity distributions

Abstract: The effects of coulomb collisions on solar wind ion velocity distributions are investigated by using Helios data obtained between 0.3 and 1 AU. The mean free path of ions moving at thermal speed (in the solar wind frame) varies by three orders of magnitude in dependence on the plasma parameters. The number of collisions (roughly defined as collision frequency times the solar wind expansion time) can easily exceed one in low-speed wind near the heliospheric current sheet. In these regions, almost Maxwellian distributions are observed. In solar wind with intermediate speeds (ranging from 400--600 km/s) one usually finds distributions with a nearly isotropic core which again can be understood by the action of coulomb collisions. On the other hand, the major part of high-speed solar wind ion distributions can by good reason, be called collisionless on local scales.

Mathematical Model for the Analysis of Wind-Turbine Wakes

Abstract: The concept of wind farms with clustered wind turbines at a given site seems to offer an attractive means for extracting wind power on a large scale. Techniques for minimizing the effect of upstream wind-turbine wakes on downstream wind turbines are needed to optimize overall performance of the wind-turbine array. A numerical model for prediction of the interaction of the wind turbine with the prevailing wind flow is described. The model is based on a numerical solution of the three-dimensional Navier-Stokes equations for the planetary boundary layer with the hydrostatic approximation. Three different hypothetical wind-turbine configurations are analyzed to demonstrate the utility of this model. Model predictions from the present study compare favorably with the basic characteristics of measured wind-turbine wakes. Nomenclature a = axial interference factor D = turbine blade diameter / = Coriolis parameter k = von Karman constant KM = turbulent diffusion coefficient KM - dKM/dz, gradient of turbulent diffusion coefficient L = Monin-Obukov length P = atmospheric pressure t =time U = characteristic wind speed u = velocity component in x direction ur = velocity at reference height zr u* = friction velocity v = velocity component in y direction w = velocity component in z direction x,y,z = orthogonal Cartesian coordinates Z0 = aerodynamic surface roughness Z = height of the inversion base A = incremental change p = atmospheric density 6,\I/ = dimensionless functions Subscripts

Characteristics of air flow above and within soybean canopies

Abstract: Air flow was observed above and within canopies of a number of kinds of soybeans. The Clark cultivar and two isolines of the Harosoy cultivar were studied in 1979 and 1980, respectively. Wind speed above the canopy was measured with cup anemometers. Heated thermistor anemometers were used to measure air flow within the canopy. Above-canopy air flow was characterized in terms of the zero-plane displacement (d), roughness parameter (z o) and drag coefficient (C d). d and z o were dependent on canopy height but were independent of friction velocity in the range 0.55 to 0.75 m s−1 · C d for the various canopies ranged from 0.027 to 0.035. Greater C d values were measured over an erectophile canopy than over a planophile canopy. C d was not measurably affected by differences in leaf pubescence. Within-canopy wind profiles were measured at two locations: within and between rows. The wind profile was characterized by a region of great wind shear in the upper canopy and by a region of relatively weak wind shear in the middle canopy. Considerable spatial variability in wind speed was evident, however. This result has significant implications for canopy flow modeling efforts aimed at evaluating transport in the canopy. In the lower canopy, wind speed within a row increased with depth whereas wind speed between two rows decreased with depth. The wind speeds at the two locations tended to converge to a common value at a height near 0.10 m. The attenuation of within-canopy air flow was stronger in canopies with greater foliage density. Canopy flow attenuation seemed to decrease with increasing wind speed, suggesting that high winds distorted the shape of the canopy in such a manner that the penetration of wind into the canopy increased.

Sea surface winds from sun glitter observations

Abstract: Solar light reflected by the surface of the sea depends strongly on the sea state which is driven by the wind. The relationship between the reflected light and wind speed is described by the well-known model of Cox and Munk. Using their model, a method is derived for the retrieval of the synoptic field of wind magnitude from measurements of the glitter pattern from space. This method is applied to data obtained by the TIROS-N satellite series. Comparison of the wind estimated in this way and the wind derived from isobaric charts shows very close agreement. The method is simple and has application over broad geographical areas.

Fifteen‐day observation of mesospheric and lower thermospheric motions with the aid of the Arecibo UHF radar

Abstract: An attempt was made to have a continuous observation of the zonal wind component in the tropical mesosphere and lower thermosphere for 15 days of August 1–15, 1980, with the aid of the UHF radar at Arecibo (18°N). By using the wind data, together with additional data obtained from meteorological rockets, meteor radar, and Tiros-N satellite, analyses were made of the time-mean zonal wind profile, tides, long-period waves, and short-period gravity-type waves, respectively. There appears a remarkable day-to-day variation of the zonal wind throughout the region between 70 and 95 km with a characteristic time scale of about 5 days, indicating the passage of traveling planetary-scale waves in the summertime tropical middle atmosphere. It was also found that the short-period oscillation with a time scale of a few 10 min appears intermittently in association with the strong vertical shear of the background flow. This oscillation is considered to be the manifestation of the Kelvin-Helmholtz type instability in the lower thermosphere.

The sensitivity of upper ocean structure to time varying wind direction

Abstract: Observations and models show that sudden changes in the magnitude of the wind stress which occur within a time interval of one-half inertial period are most effective in increasing surface current speeds and mixing the upper layers of the ocean. The purpose of the present study is to quantify the effects of concurrent time dependent wind direction. The Mellor-Yamada level 2 1/2 turbulence closure model is used. A series of model runs was executed in order to determine the relative sensitivity of mixed layer depth and sea surface temperature to wind speed as compared with the rate of change of wind direction. The results indicate that the accuracy and time resolution of wind direction should be given special consideration in the design and interpretation of field experiments which will be used for testing prognostic mixed layer models.

Distribution and Correlation of Dynamic Wind Loads

Abstract: Types of aeroelastic and elastic wind tunnel models available for measuring fluctuating wind loads on tall buildings are described together with some of their advantages and limitations. A new technique for using numerous pressure transducers to directly measure these fluctuating wind loads is presented. In this technique, analog circuits are used to sum individual pressure measurements in obtaining records which represent loads over segements of the model or over the entire model. Recent tests using the technique are described and sample results are shown. Forces measured with the transducers on a fixed model are used to predict the response of an aeroelastic model of similar shape, for which response measurements have been published in the literature. It is shown that the predicted and measured response agree within the bounds of expected errors up to values of reduced gradient velocity of approximately 15. At reduced gradient velocities in excess of 15, the fixed model predictions underestimate the aeroelastic model results and the slope of the response curve is quite different because motion of the aeroelastic model alters the aerodynamics.

Wind Tunnel Measurements of the Power Imparted to a Model of a Vibrating Conductor

Abstract: Predicting the severity of aeolian vibration of overhead conductors requires knowledge of the damping in the span and of the power that the wind can supply to it. There is considerable dispersion in the published data on wind power input. New measurements were made, using a novel test arrangement, in an effort to develop more reliable information. The tests covered a broad range of wind speeds, above and below that at which power input is greatest, to lay a basis for development of methods for dealing with the effects of turbulence in natural winds. Correlation of the new results with previous data is reviewed in depth.

Response to Wind Action of 265‐M Mount Isa Stack

Abstract: Measurements were made of the response to wind action of the 265‐m high, reinforced concrete stack at Mount Isa Mines in Queensland, Australia. Data were reduced from accelerometer, strain gage and pressure transducer records from four wind storms. Particular attention was paid to determining reference freestream wind speeds at stack height and wind structure, which involved using records from a number of anemometer sites and for which position errors were determined from topographical model studies in a boundary layer wind tunnel. In this paper, the full scale data are reduced and presented such that they can readily be used to compare with results from physical and mathematical model studies of stack response to wind action. Mean, standard deviation and peak tip displacements, and base overturning moment coefficients are given, along with estimates of structural damping, peak factors and dominant wake frequencies, at Reynolds numbers up to 2×107.

On the Evaluation of Wind Power from Short Wind Records.

Abstract: A method to estimate the meteorological mean wind power of a given site and year based upon data of only three months is presented. It is based on the minimization of the rms errors between observations and a representation by means of empirical orthogonal functions. These functions are calculated from a matrix formed by annual series of wind speed data from stations belonging to the same region. A numerical experiment has been performed using wind series of 20 stations in the U.S. Midwest and East. The method allowed the recovery of both the mean wind speed value and its variance with a small error. The meteorological mean wind power of the year was calculated using the Weibull-II and Rayleigh probability distributions. Using the Weibull-II distribution, the method outlined above, and only 13-week observations, estimations of the true meteorological wind power were obtained with a 6% average relative error when only 11 central stations were computed. The experiment showed that the method is also...

Wind turbine with gale protection

Abstract: A wind turbine with a single rotor blade drives an alternator whose output is connected to an a-c network to supply same with power when the alternator acts as a generator under the driving force of the wind. The network establishes a synchronous speed for the alternator which corresponds to a rotor speed so chosen that a certain laminar flow along the blade will be maintained even at high wind velocities. Changing the pitch of the blade allows a wide range of wind velocities to be accommodated.

Wind dependence of underwater ambient noise

Abstract: Sound generated underwater by wind waves displays two sensitivities to wind speed depending on whether the waves are breaking. A historical review is presented of several experimental studies over the years, as well as new results obtained at a relatively quiet, deep equatorial Pacific site. The duration of the experiment, the multiple high frequency bands as well as the desirable acoustic attributes of the site are useful in establishing the wind sensitivity, and its variability. The results are compared to a recent theoretical model of sound generation by oscillating bubbles in breaking waves.

VHF Radar Observations of a Kelvin-Helmholtz Instability in a Subtropical Jet Stream

Abstract: In connection with the large dish at the Arccibo Observatory (Puerto Rico), the mobile SOUSY VHF Radar has been used to carry out velocity measurements in the troposphere with height and time resolutions of a few hundreds of meters and some tens of seconds, respectively. During the passage of a strong subtropical jet stream, vertical velocity oscillations have been observed at heights of maximum wind shear. The height and time variations of the velocity and the background wind profile deduced from radiosonde data indicate that a Kelvin-Helmholtz instability (KHI), with a period of 340s, a wavelength of 12 km and a velocity amplitude of about 1 ms−1 was the source of the oscillations. Model calculations show good agreement with the observed quantities.