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Kume, Kenichi, Hiroki Ohba, Hideo Orihara e Shuji Mizokami. "Wind Velocity Profile and Representative Wind Velocity for Wind Resistance Measurement of Ship Models". Journal of the Japan Society of Naval Architects and Ocean Engineers 30 (2019): 1–13. http://dx.doi.org/10.2534/jjasnaoe.30.1.
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Conley, Stephen A., Ian C. Faloona, Donald H. Lenschow, Anna Karion e Colm Sweeney. "A Low-Cost System for Measuring Horizontal Winds from Single-Engine Aircraft". Journal of Atmospheric and Oceanic Technology 31, n. 6 (1 giugno 2014): 1312–20. http://dx.doi.org/10.1175/jtech-d-13-00143.1.
Testo completoAbstract (sommario):
Abstract The implementation and accuracy of a low-rate (~1 Hz) horizontal wind measurement system is described for a fixed-wing aircraft without modification to the airframe. The system is based on a global positioning system (GPS) compass that provides aircraft heading and a ground-referenced velocity, which, when subtracted from the standard true airspeed, provides estimates of the horizontal wind velocity. A series of tests was performed flying “L”-shaped patterns above the boundary layer, where the winds were assumed to be horizontally homogeneous over the area bounded by the flight (approximately 25 km2). Four headings were flown at each altitude at a constant airspeed. Scaling corrections for both heading and airspeed were found by minimizing the variance in the 1-s wind measurements; an upper limit to the error was then computed by calculating the variance of the corrected wind measurements on each of the four headings. A typical uncertainty found in this manner tends to be less than 0.2 m s−1. The measurement system described herein is inexpensive and relatively easy to implement on single-engine aircraft.
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Wang, Tian, Yunbo Shi, Xiaoyu Yu, Guangdong Lan e Congning Liu. "Novel strategy for wide-range wind vector measurement using the hybrid CP/CTD heating mode and sequential measuring and correcting". PLOS ONE 16, n. 7 (8 luglio 2021): e0254256. http://dx.doi.org/10.1371/journal.pone.0254256.
Testo completoAbstract (sommario):
To improve the performance of wind sensors in the high velocity range, this paper proposes a wind measurement strategy for thermal wind velocity sensors that combines the constant power and constant temperature difference driving modes of the heating element. Based on the airflow distribution characteristics from fluid dynamics, sequential measurement and correction is proposed as a method of measuring wind direction. In addition, a wind velocity and direction measurement instrument was developed using the above-mentioned approaches. The test results showed that the proposed instrument can obtain large dynamic wind velocity measurements from 0 to 60 m/s. The wind velocity measurement accuracy was ±0.5 m/s in the common velocity range of 0–20 m/s and ±1 m/s in the high velocity range of 20–60 m/s. The wind direction accuracy was ±3° throughout the 360° range. The proposed approaches and instrument are not only practical but also capable of meeting the requirements of wide-range and large dynamic wind vector measurement applications.
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González-Rocha, Javier, Stephan F. J. De Wekker, Shane D. Ross e Craig A. Woolsey. "Wind Profiling in the Lower Atmosphere from Wind-Induced Perturbations to Multirotor UAS". Sensors 20, n. 5 (29 febbraio 2020): 1341. http://dx.doi.org/10.3390/s20051341.
Testo completoAbstract (sommario):
We present a model-based approach to estimate the vertical profile of horizontal wind velocity components using motion perturbations of a multirotor unmanned aircraft system (UAS) in both hovering and steady ascending flight. The state estimation framework employed for wind estimation was adapted to a set of closed-loop rigid body models identified for an off-the-shelf quadrotor. The quadrotor models used for wind estimation were characterized for hovering and steady ascending flight conditions ranging between 0 and 2 m/s. The closed-loop models were obtained using system identification algorithms to determine model structures and estimate model parameters. The wind measurement method was validated experimentally above the Virginia Tech Kentland Experimental Aircraft Systems Laboratory by comparing quadrotor and independent sensor measurements from a sonic anemometer and two SoDAR instruments. Comparison results demonstrated quadrotor wind estimation in close agreement with the independent wind velocity measurements. However, horizontal wind velocity profiles were difficult to validate using time-synchronized SoDAR measurements. Analysis of the noise intensity and signal-to-noise ratio of the SoDARs proved that close-proximity quadrotor operations can corrupt wind measurement from SoDARs, which has not previously been reported.
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Garman, K. E., K. A. Hill, P. Wyss, M. Carlsen, J. R. Zimmerman, B. H. Stirm, T. Q. Carney, R. Santini e P. B. Shepson. "An Airborne and Wind Tunnel Evaluation of a Wind Turbulence Measurement System for Aircraft-Based Flux Measurements*". Journal of Atmospheric and Oceanic Technology 23, n. 12 (1 dicembre 2006): 1696–708. http://dx.doi.org/10.1175/jtech1940.1.
Testo completoAbstract (sommario):
Abstract Although the ability to measure vertical eddy fluxes of gases from aircraft platforms represents an important capability to obtain spatially resolved data, accurate and reliable determination of the turbulent vertical velocity presents a great challenge. A nine-hole hemispherical probe known as the “Best Air Turbulence Probe” (often abbreviated as the “BAT Probe”) is frequently used in aircraft-based flux studies to sense the airflow angles and velocity relative to the aircraft. Instruments such as inertial navigation and global positioning systems allow the measured airflow to be converted into the three-dimensional wind velocity relative to the earth’s surface by taking into account the aircraft’s velocity and orientation. Calibration of the aircraft system has previously been performed primarily through in-flight experiments, where calibration coefficients were determined by performing various flight maneuvers. However, a rigorous test of the BAT Probe in a wind tunnel has not been previously undertaken. The authors summarize the results of a complement of low-speed wind tunnel tests and in-flight calibrations for the aircraft–BAT Probe combination. Two key factors are addressed in this paper: The first is the correction of systematic error arising from airflow measurements with a noncalibrated BAT Probe. The second is the instrumental precision in measuring the vertical component of wind from the integrated aircraft-based wind measurement system. The wind tunnel calibration allows one to ascertain the extent to which the BAT Probe airflow measurements depart from a commonly used theoretical potential flow model and to correct for systematic errors that would be present if only the potential flow model were used. The precision in the determined vertical winds was estimated by propagating the precision of the BAT Probe data (determined from the wind tunnel study) and the inertial measurement precision (determined from in-flight tests). The precision of the vertical wind measurement for spatial scales larger than approximately 2 m is independent of aircraft flight speed over the range of airspeeds studied, and the 1σ precision is approximately 0.03 m s−1.
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Medvedev, Andrey V., Konstantin G. Ratovsky, Maxim V. Tolstikov, Roman V. Vasilyev e Maxim F. Artamonov. "Method for Determining Neutral Wind Velocity Vectors Using Measurements of Internal Gravity Wave Group and Phase Velocities". Atmosphere 10, n. 9 (13 settembre 2019): 546. http://dx.doi.org/10.3390/atmos10090546.
Testo completoAbstract (sommario):
This study presents a new method for determining a neutral wind velocity vector. The basis of the method is measurement of the group velocities of internal gravity waves. Using the case of the Boussinesq dispersion relation, we demonstrated the ability to measure a neutral wind velocity vector using the group velocity and wave vector data. An algorithm for obtaining the group velocity vector from the wave vector spectrum is proposed. The new method was tested by comparing the obtained winter wind pattern with wind data from other sources. Testing the new method showed that it is in quantitative agreement with the Fabry–Pérot interferometer wind measurements for zonal and vertical wind velocities. The differences in meridional wind velocities are also discussed here. Of particular interest were the results related to the measurement of vertical wind velocities. We demonstrated that two independent methods gave the presence of vertical wind velocities with amplitude of ~20 m/s. Estimation of vertical wind contribution to plasma drift velocity indicated the importance of vertical wind measurements and the need to take them into account in physical and empirical models of the ionosphere and thermosphere.
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Park, Soojin, Sang-Woo Kim, Moon-Soo Park e Chang-Keun Song. "Measurement of Planetary Boundary Layer Winds with Scanning Doppler Lidar". Remote Sensing 10, n. 8 (10 agosto 2018): 1261. http://dx.doi.org/10.3390/rs10081261.
Testo completoAbstract (sommario):
The accurate measurement of wind profiles in the planetary boundary layer (PBL) is important not only for numerical weather prediction, but also for air quality modeling. Two wind retrieval methods using scanning Doppler light detection and ranging (lidar) measurements were compared and validated with simultaneous radiosonde soundings. A comparison with 17 radiosonde sounding profiles showed that the sine-fitting method was able to retrieve a larger number of data points, but the singular value decomposition method showed significantly smaller bias (0.57 m s−1) and root-mean-square error (1.75 m s−1) with radiosonde soundings. Increasing the averaging time interval of radial velocity for obtaining velocity azimuth display scans to 15 min resulted in better agreement with radiosonde soundings due to the signal averaging effect on noise. Simultaneous measurements from collocated wind Doppler lidar and aerosol Mie-scattering lidar revealed the temporal evolution of PBL winds and the vertical distribution of aerosols within the PBL.
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Ogasawara, Toshinori, e Takashi Yasuda. "Mass Flux and Vertical Distribution of Currents Caused by Strong Winds in a Wave Tank". Journal of Physical Oceanography 34, n. 12 (1 dicembre 2004): 2712–20. http://dx.doi.org/10.1175/jpo2659.1.
Testo completoAbstract (sommario):
Abstract The velocity fields of wind-driven currents under strong winds were measured in a wind-wave tank with a double bottom. The tank has the characteristics to satisfy partially the continuity of the mass flux and to reduce return-flow effects on the currents. The lower part of the double-bottom tank functions as a duct to circulate the currents, allowing the measurement of the return-flow velocity. The velocity measurements were made on the currents just below the mean water level by using a high-resolution particle image velocimetry (PIV) system and tracking floats and on the currents inside of the duct by using a normal PIV system. Thus, accurate data of the vertical distribution and mass flux of the currents driven by strong winds were obtained from the PIV data. As a result, it is found that the flux in the surface layer with the thickness of 2 times the significant wave height amounts to about 30% of the total mass flux of the currents driven by strong winds with a reference wind speed of 12.0 m s−1.
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Wilhelm, Paul, Michael Eggert, Julia Hornig e Stefan Oertel. "High Spatial and Temporal Resolution Bistatic Wind Lidar". Applied Sciences 11, n. 16 (19 agosto 2021): 7602. http://dx.doi.org/10.3390/app11167602.
Testo completoAbstract (sommario):
The high-resolution bistatic lidar developed at the Physikalisch-Technische Bundesanstalt (PTB) aims to overcome the limitations of conventional monostatic lidar technology, which is widely used for wind velocity measurements in wind energy and meteorology applications. Due to the large measurement volume of a combined optical transmitter and receiver tilting in multiple directions, monostatic lidar generally has poor spatial and temporal resolution. It also exhibits large measurement uncertainty when operated in inhomogeneous flow; for instance, over complex terrain. In contrast, PTB’s bistatic lidar uses three dedicated receivers arranged around a central transmitter, resulting in an exceptionally small measurement volume. The coherent detection and modulation schemes used allow the detection of backscattered, Doppler shifted light down to the scale of single aerosols, realising the simultaneous measurement of all three wind velocity components. This paper outlines the design details and theory of operation of PTB’s bistatic lidar and provides an overview of selected comparative measurements. The results of these measurements show that the measurement uncertainty of PTB’s bistatic lidar is well within the measurement uncertainty of traditional cup anemometers while being fully independent of its site and traceable to the SI units. This allows its use as a transfer standard for the calibration of other remote sensing devices. Overall, PTB’s bistatic lidar shows great potential to improve the capability and accuracy of wind velocity measurements, such as for the investigation of highly dynamic flow processes upstream and in the wake of wind turbines.
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Gordienko, Vyacheslav M., e Yu Ya Putivskii. "Coherent Doppler TEA CO2lidar for wind velocity measurement". Quantum Electronics 24, n. 3 (31 marzo 1994): 266–72. http://dx.doi.org/10.1070/qe1994v024n03abeh000068.
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Zu, Gongbo, e Kit Ming Lam. "Simultaneous measurement of wind velocity field and wind forces on a square tall building". Advances in Structural Engineering 21, n. 15 (7 maggio 2018): 2241–58. http://dx.doi.org/10.1177/1369433218770822.
Testo completoAbstract (sommario):
Vortex shedding from a tall building is known to be responsible for the quasi-periodic across-wind force exerted on the building. This article unveils the exact relationship between the vortex shedding pattern and the fluctuating across-wind force. Simultaneous particle-image velocimetry and pressure measurements are carried out on a square-plan tall building model in the wind tunnel toward an understanding of the velocity–pressure–force relation for across-wind force generation on the building. A collection of instantaneous wind flow patterns and synchronized wind pressure distributions suggests the existence of full periods of vortex shedding from the building. The results are further analyzed using the conditional sampling method by which the roles of development and shedding of large-scale vortices in the building wake on the generation of peak across-wind forces are evidently found. Furthermore, quasi-periodicity of across-wind excitation is clearly confirmed with Hilbert transform of the across-wind force signal. The phase averaging technique is applied to the particle-image velocimetry flow fields and distinct vortex shedding patterns from the building are observed for most of the measurement time, together with an evident phase relationship with the across-wind forces.
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Olasek, Krzysztof, Maciej Karczewski, Michal Lipian, Piotr Wiklak e Krzysztof Józwik. "Wind tunnel experimental investigations of a diffuser augmented wind turbine model". International Journal of Numerical Methods for Heat & Fluid Flow 26, n. 7 (5 settembre 2016): 2033–47. http://dx.doi.org/10.1108/hff-06-2015-0246.
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Purpose A solution to increase the energy production rate of the wind turbine is proposed by forcing more air to move through the turbine working section. This can be achieved by equipping the rotor with a diffusing channel ended with a brim (diffuser augmented wind turbine – DAWT). The purpose of this paper is to design an experimental stand and perform the measurements of velocity vector fields through the diffuser and power characteristic of the wind turbine. Design/methodology/approach The experiments were carried out in a small subsonic wind tunnel at the Institute of Turbomachinery, Lodz University of Technology. An experimental stand design process as well as measurement results are presented. Model size sensitivity study was performed at the beginning. The experimental campaign consisted of velocity measurements by means of particle image velocimetry (PIV) and pneumatic pitot probe as well as torque and rotational velocity measurements. Findings Characteristics (power coefficient vs tip speed ratio) of the bare and shrouded wind turbine were obtained. The results show an increase in the wind turbine power up to 70-75 per cent by shrouding the rotor with a diffuser. The mechanisms responsible for such a power increase were well explained by the PIV and pneumatic measurement results revealing the nature of the flow through the diffuser. Research limitations/implications Experimental stand for wind turbine rotor testing is of a preliminary character. Most optimal methodology for obtaining power characteristic should be determined now. Presented results can serve as good input for choice of stable and reliable control system of wind turbine operational parameters. Practical implications A 3 kW DAWT is being developed at the Institute of Turbomachinery, Lodz University of Technology. Aim of the study is to design a compact and smart wind turbine optimised for low wind speed conditions. Developed wind turbine has a potential to be used as an effective element within a net of distributed generation, e.g. for domestic use. Originality/value Research carried out is the continuation of theoretical study began in 1970s. It was also inspired by practical solutions proposed by Japanese researchers few years ago. Presented paper is the summary of work devoted to optimisation of the DAWT for wind conditions in the region. Original solution has been applied, e.g. for experimental stand design (3D printing application).
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Wu, Jian Jun, e Li Hong He. "Experimental Measurement of Wind Velocity Fluctuation and its Influences on Sand Particle Trajectory". Applied Mechanics and Materials 39 (novembre 2010): 271–76. http://dx.doi.org/10.4028/www.scientific.net/amm.39.271.
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The wind flow, the main driving force of sand movement, has already been known for its random fluctuation characteristics especially in the boundary layer. An experimental test for the wind velocity fluctuation is conducted for naturally mixed sands with a wind profiler in a field wind tunnel. On the basis of the experimental data, a fitting form of an empirical formula for the wind velocity fluctuation in the horizontal direction is obtained. After that, the influences of the wind velocity fluctuation are simulated on the particle trajectories, which demonstrate that the fluctuating velocity of the wind has greater influences on the trajectories of the particles with smaller diameter. The trajectory forms of the smaller sand particles, computed from the instantaneous velocity, might be in continuous saltation or even suspension besides smoothing parabola forms, which are obviously different from those computed only from the average velocity of the wind. For the particles with larger diameter, all the trajectories are almost the same in smoothing parabola forms under both fluctuating velocity and average velocity of the wind.
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Oertel, Stefan, Michael Eggert, Christian Gutsmuths, Paul Wilhelm, Harald Müller e Helmut Többen. "Validation of three-component wind lidar sensor for traceable highly resolved wind vector measurements". Journal of Sensors and Sensor Systems 8, n. 1 (8 gennaio 2019): 9–17. http://dx.doi.org/10.5194/jsss-8-9-2019.
Testo completoAbstract (sommario):
Abstract. Conventional monostatic wind lidar (light detection and ranging) systems are well-established wind speed remote sensing devices in the field of wind energy that provide reliable measurement results for flat terrain and homogeneous wind fields. These conventional wind lidar systems use a common transmitting and receiving unit and become unacceptably inaccurate as the wind fields become increasingly inhomogeneous due to their spatial and temporal averaging procedure (large measurement volume) that is inherent to the monostatic measurement principle. The new three-component fiber laser-based wind lidar sensor developed by the Physikalisch-Technische Bundesanstalt (PTB) uses one transmitting unit (fiber laser) and three receiving units to measure the velocity vector of single aerosols in a spatially highly resolved measurement volume (with diameter d and length l) in heights from 5 m (d=300 µm, l=2 mm) to 250 m (d=14 mm, l=4 m) with a resolution of about 0.1 m s−1. Detailed comparison measurements with a 135 m high wind met mast and a conventional lidar system have proven that the high spatial and temporal resolution of the new, so-called bistatic lidar leads to a reduced measurement uncertainty compared to conventional lidar systems. Furthermore, the comparison demonstrates that the deviation between the bistatic lidar and the wind met mast lies well within the measurement uncertainty of the cup anemometers of the wind met mast for both homogeneous and inhomogeneous wind fields. At PTB, the aim is to use the bistatic wind lidar as a traceable reference standard to calibrate other remote sensing devices, necessitating an in-depth validation of the bistatic lidar system and its measurement uncertainty. To this end, a new, specially designed wind tunnel with a laser Doppler anemometer (LDA) as flow velocity reference has been erected on a platform at a height of 8 m; this allows the new wind lidar to be positioned below the wind tunnel test section to be validated for wind vector measurements that are traceable to the SI units. A first validation measurement within the wind tunnel test section is presented, showing a deviation between the bistatic lidar system and the LDA clearly below 0.1 %.
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Wang, Xu, Huaqiang Li, Zengshun Chen, Yuanhao Qian, Yanru Wang e Xinlai Peng. "Field measurement of near-surface typhoon characteristics using a smart monitoring system on a long-span arch bridge site". Advances in Structural Engineering 22, n. 8 (19 febbraio 2019): 1977–87. http://dx.doi.org/10.1177/1369433219830510.
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During landfall of Typhoon Haikui in Eastern China in 2012, ground level wind data were recorded using a smart monitoring system installed on JiuBao Bridge in Hangzhou, China. This article documents the mean flow and turbulence characteristics from data recorded during the storm. The results show that both turbulence intensity and gust factor decrease with the increase in the mean wind velocity. However, as the mean wind velocity increases, this trend gradually attenuates. The peak factor distribution with gust averaging time duration derived with the Typhoon Haikui data agrees well with the Durst curve. However, the longitudinal gust factor derived from the typhoon wind-speed record in this study is higher compared with the curves proposed by Durst and Krayer-Marshall. Analyses of the gust factor distribution with the turbulence intensity during the passage of the storm reveal a similarity to the empirical curves of Ishizaki and Choi. Results show that the relationship between lateral turbulence and gust factors can be well represented by a quadratic polynomial. Turbulence scale increased with mean wind velocity. The values of autocorrelation coefficients in longitudinal direction are larger than those in lateral direction. There has no obvious dependency of cross-correlation coefficients with mean wind velocity. In general, the wind characteristics in this study are shown to be very similar to those of winds under normal circumstance.
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Plant, William J., William C. Keller e Kenneth Hayes. "Simultaneous Measurement of Ocean Winds and Waves with an Airborne Coherent Real Aperture Radar". Journal of Atmospheric and Oceanic Technology 22, n. 7 (1 luglio 2005): 832–46. http://dx.doi.org/10.1175/jtech1724.1.
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Abstract A coherent, X-band airborne radar has been developed to measure wind speed and direction simultaneously with directional wave spectra on the ocean. The coherent real aperture radar (CORAR) measures received power, mean Doppler shifts, and mean Doppler bandwidths from small-resolution cells on the ocean surface and converts them into measurements of winds and waves. The system operates with two sets of antennas, one rotating and one looking to the side of the airplane. The rotating antennas yield neutral wind vectors at a height of 10 m above the ocean surface using a scatterometer model function to relate measured cross sections to wind speed and direction. The side-looking antennas produce maps of normalized radar cross section and line-of-sight velocity from which directional ocean wave spectra may be obtained. Capabilities of CORAR for wind and wave measurement are illustrated using data taken during the Shoaling Waves Experiment (SHOWEX) sponsored by the Office of Naval Research. Wind vectors measured by CORAR agree well with those measured by nearby buoys. Directional wave spectra obtained by CORAR also agree with buoy measurements and illustrate that offshore winds can produce dominant waves at an angle to the wind vector that are in good agreement with the measurements. The best agreement is produced using the Joint North Sea Wave Project (JONSWAP) parameterizations of the development of wave height and period with fetch.
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Duncan, James B., Brian D. Hirth e John L. Schroeder. "Doppler Radar Measurements of Spatial Turbulence Intensity in the Atmospheric Boundary Layer". Journal of Applied Meteorology and Climatology 58, n. 7 (luglio 2019): 1535–55. http://dx.doi.org/10.1175/jamc-d-18-0151.1.
Testo completoAbstract (sommario):
AbstractRemote sensing instruments that scan have the ability to provide high-resolution spatial measurements of atmospheric boundary layer winds across a region. However, the time required to collect the volume of measurements used to produce this spatial representation of atmospheric winds typically limits the extraction of atmospheric turbulence information using traditional temporal analysis techniques. To overcome this constraint, a spatial turbulence intensity (STI) metric was developed to quantify atmospheric turbulence intensity (TI) through analysis of spatial wind field variability. The methods used to determine STI can be applied throughout the measurement domain to transform the spatially distributed velocity fields to analogous measurement maps of STI. This method enables a comprehensive spatial characterization of atmospheric TI. STI efficacy was examined across a range of wind speeds and atmospheric stability regimes using both single- and dual-Doppler measurements. STI demonstrated the ability to capture rapid fluctuations in TI and was able to discern large-scale TI trends consistent with the early evening transition. The ability to spatially depict atmospheric TI could benefit a variety of research disciplines such as the wind energy industry, where an understanding of wind plant complex flow spatiotemporal variability is limited.
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Sathe, A., J. Mann, J. Gottschall e M. S. Courtney. "Can Wind Lidars Measure Turbulence?" Journal of Atmospheric and Oceanic Technology 28, n. 7 (1 luglio 2011): 853–68. http://dx.doi.org/10.1175/jtech-d-10-05004.1.
Testo completoAbstract (sommario):
Abstract Modeling of the systematic errors in the second-order moments of wind speeds measured by continuous-wave (ZephIR) and pulsed (WindCube) lidars is presented. These lidars use the conical scanning technique to measure the velocity field. The model captures the effect of volume illumination and conical scanning. The predictions are compared with the measurements from the ZephIR, WindCube, and sonic anemometers at a flat terrain test site under different atmospheric stability conditions. The sonic measurements are used at several heights on a meteorological mast in combination with lidars that are placed on the ground. Results show that the systematic errors are up to 90% for the vertical velocity variance, whereas they are up to 70% for the horizontal velocity variance. For the ZephIR, the systematic errors increase with height, whereas for the WindCube, they decrease with height. The systematic errors also vary with atmospheric stability and are low for unstable conditions. In general, for both lidars, the model agrees well with the measurements at all heights and under different atmospheric stability conditions. For the ZephIR, the model results are improved when an additional low-pass filter for the 3-s scan is also modeled. It is concluded that with the current measurement configuration, these lidars cannot be used to measure turbulence precisely.
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You, Ki-Pyo, e Young-Moon Kim. "Wind Velocity Decreasing Effects of Windbreak Fence for Snowfall Measurement". Advances in Meteorology 2014 (2014): 1–20. http://dx.doi.org/10.1155/2014/791256.
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Meteorological observatories use measuring boards on even ground in open areas to measure the amount of snowfall. In order to measure the amount of snowfall, areas unaffected by wind should be found. This study tried to determine the internal wind flow inside a windbreak fence, identifying an area unaffected by wind in order to measure the snowfall. We performed a computational fluid dynamics analysis and wind tunnel test, conducted field measurements of the type and height of the windbreak fence, and analyzed the wind flow inside the fence. The results showed that a double windbreak fence was better than a single windbreak fence for decreasing wind velocity. The double fence (width 4 m, height 60 cm, and fixed on the bottom) has the greatest wind velocity decrease rate at the central part of octagonal windbreak.
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Shust, Michael R., e James C. Rogers. "Reduction of microphone wind noise using local wind velocity measurements." Journal of the Acoustical Society of America 99, n. 4 (aprile 1996): 2488–500. http://dx.doi.org/10.1121/1.415606.
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Lundquist, J. K., M. J. Churchfield, S. Lee e A. Clifton. "Quantifying error of lidar and sodar Doppler beam swinging measurements of wind turbine wakes using computational fluid dynamics". Atmospheric Measurement Techniques 8, n. 2 (23 febbraio 2015): 907–20. http://dx.doi.org/10.5194/amt-8-907-2015.
Testo completoAbstract (sommario):
Abstract. Wind-profiling lidars are now regularly used in boundary-layer meteorology and in applications such as wind energy and air quality. Lidar wind profilers exploit the Doppler shift of laser light backscattered from particulates carried by the wind to measure a line-of-sight (LOS) velocity. The Doppler beam swinging (DBS) technique, used by many commercial systems, considers measurements of this LOS velocity in multiple radial directions in order to estimate horizontal and vertical winds. The method relies on the assumption of homogeneous flow across the region sampled by the beams. Using such a system in inhomogeneous flow, such as wind turbine wakes or complex terrain, will result in errors. To quantify the errors expected from such violation of the assumption of horizontal homogeneity, we simulate inhomogeneous flow in the atmospheric boundary layer, notably stably stratified flow past a wind turbine, with a mean wind speed of 6.5 m s−1 at the turbine hub-height of 80 m. This slightly stable case results in 15° of wind direction change across the turbine rotor disk. The resulting flow field is sampled in the same fashion that a lidar samples the atmosphere with the DBS approach, including the lidar range weighting function, enabling quantification of the error in the DBS observations. The observations from the instruments located upwind have small errors, which are ameliorated with time averaging. However, the downwind observations, particularly within the first two rotor diameters downwind from the wind turbine, suffer from errors due to the heterogeneity of the wind turbine wake. Errors in the stream-wise component of the flow approach 30% of the hub-height inflow wind speed close to the rotor disk. Errors in the cross-stream and vertical velocity components are also significant: cross-stream component errors are on the order of 15% of the hub-height inflow wind speed (1.0 m s−1) and errors in the vertical velocity measurement exceed the actual vertical velocity. By three rotor diameters downwind, DBS-based assessments of wake wind speed deficits based on the stream-wise velocity can be relied on even within the near wake within 1.0 m s−1 (or 15% of the hub-height inflow wind speed), and the cross-stream velocity error is reduced to 8% while vertical velocity estimates are compromised. Measurements of inhomogeneous flow such as wind turbine wakes are susceptible to these errors, and interpretations of field observations should account for this uncertainty.
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Iungo, G. V., e F. Porté-Agel. "Measurement procedures for characterization of wind turbine wakes with scanning Doppler wind LiDARs". Advances in Science and Research 10, n. 1 (30 maggio 2013): 71–75. http://dx.doi.org/10.5194/asr-10-71-2013.
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Abstract. The wake flow produced from an Enercon E-70 wind turbine is investigated through three scanning Doppler wind LiDARs. One LiDAR is deployed upwind to characterize the incoming wind, while the other two LiDARs are located downstream to carry out wake measurements. The main challenge in performing measurements of wind turbine wakes is represented by the varying wind conditions, and by the consequent adjustments of the turbine yaw angle needed to maximize power production. Consequently, taking into account possible variations of the relative position between the LiDAR measurement volume and wake location, different measuring techniques were carried out in order to perform 2-D and 3-D characterizations of the mean wake velocity field. However, larger measurement volumes and higher spatial resolution require longer sampling periods; thus, to investigate wake turbulence tests were also performed by staring the LiDAR laser beam over fixed directions and with the maximum sampling frequency. The characterization of the wake recovery along the downwind direction is performed. Moreover, wake turbulence peaks are detected at turbine top-tip height, which can represent increased fatigue loads for downstream wind turbines within a wind farm.
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Kelberlau, Felix, e Jakob Mann. "Cross-contamination effect on turbulence spectra from Doppler beam swinging wind lidar". Wind Energy Science 5, n. 2 (30 aprile 2020): 519–41. http://dx.doi.org/10.5194/wes-5-519-2020.
Testo completoAbstract (sommario):
Abstract. Turbulence velocity spectra are of high importance for the estimation of loads on wind turbines and other built structures, as well as for fitting measured turbulence values to turbulence models. Spectra generated from reconstructed wind vectors of Doppler beam swinging (DBS) wind lidars differ from spectra based on one-point measurements. Profiling wind lidars have several characteristics that cause these deviations, namely cross-contamination between the three velocity components, averaging along the lines of sight and the limited sampling frequency. This study focuses on analyzing the cross-contamination effect. We sample wind data in a computer-generated turbulence box to predict lidar-derived turbulence spectra for three wind directions and four measurement heights. The data are then processed with the conventional method and with the method of squeezing that reduces the longitudinal separation distances between the measurement locations of the different lidar beams by introducing a time lag into the data processing. The results are analyzed and compared to turbulence velocity spectra from field measurements with a Windcube V2 wind lidar and ultrasonic anemometers as reference. We successfully predict lidar-derived spectra for all test cases and found that their shape is dependent on the angle between the wind direction and the lidar beams. With conventional processing, cross-contamination affects all spectra of the horizontal wind velocity components. The method of squeezing improves the spectra to an acceptable level only for the case of the longitudinal wind velocity component and when the wind blows parallel to one of the lines of sight. The analysis of the simulated spectra described here improves our understanding of the limitations of turbulence measurements with DBS profiling wind lidar.
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Iwai, Hironori, Shoken Ishii, Ryoko Oda, Kohei Mizutani, Shinya Sekizawa e Yasuhiro Murayama. "Performance and Technique of Coherent 2-μm Differential Absorption and Wind Lidar for Wind Measurement". Journal of Atmospheric and Oceanic Technology 30, n. 3 (1 marzo 2013): 429–49. http://dx.doi.org/10.1175/jtech-d-12-00111.1.
Testo completoAbstract (sommario):
Abstract A coherent 2-μm differential absorption and wind lidar (Co2DiaWiL) has been built with a high-power Q-switched Tm,Hm:YLF laser to measure CO2 concentration and radial wind speed. The performance of the Co2DiaWiL is described and analyzed, with a view to demonstrating system capabilities for remote measurements of wind velocities in the atmospheric boundary layer and free troposphere. Bias in the velocity measurements was estimated at −0.0069 m s−1 using measurements from a stationary hard target. The Co2DiaWiL achieved a velocity precision of 0.12 m s−1, derived from the magnitude of random error in radial wind velocity measurements. These measurements were made for ranges out to 20–25 km by using a horizontally fixed beam mode for average times of 1 min. Quantitative intercomparisons of 1-min averages between the Co2DiaWiL and a sonic anemometer revealed a correlation coefficient of 0.99. This study demonstrated measurements of horizontal wind profiles, by making radial wind velocity measurements with the Co2DiaWiL using conical scanning. Profile differences at higher levels could be attributed to probable large horizontal separations of the radiosondes and the low signal-to-noise ratio of the Co2DiaWiL. A pseudo-dual-Doppler technique was developed to retrieve horizontal wind components with a single-Doppler lidar and a steering mirror. Intercomparisons of the 1-min-averaged u and υ components from the pseudo-dual-Doppler lidar measurements with those from the sonic anemometer revealed correlation coefficients of 0.84 and 0.83, respectively.
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Newsom, Rob K., W. Alan Brewer, James M. Wilczak, Daniel E. Wolfe, Steven P. Oncley e Julie K. Lundquist. "Validating precision estimates in horizontal wind measurements from a Doppler lidar". Atmospheric Measurement Techniques 10, n. 3 (30 marzo 2017): 1229–40. http://dx.doi.org/10.5194/amt-10-1229-2017.
Testo completoAbstract (sommario):
Abstract. Results from a recent field campaign are used to assess the accuracy of wind speed and direction precision estimates produced by a Doppler lidar wind retrieval algorithm. The algorithm, which is based on the traditional velocity-azimuth-display (VAD) technique, estimates the wind speed and direction measurement precision using standard error propagation techniques, assuming the input data (i.e., radial velocities) to be contaminated by random, zero-mean, errors. For this study, the lidar was configured to execute an 8-beam plan-position-indicator (PPI) scan once every 12 min during the 6-week deployment period. Several wind retrieval trials were conducted using different schemes for estimating the precision in the radial velocity measurements. The resulting wind speed and direction precision estimates were compared to differences in wind speed and direction between the VAD algorithm and sonic anemometer measurements taken on a nearby 300 m tower.All trials produced qualitatively similar wind fields with negligible bias but substantially different wind speed and direction precision fields. The most accurate wind speed and direction precisions were obtained when the radial velocity precision was determined by direct calculation of radial velocity standard deviation along each pointing direction and range gate of the PPI scan. By contrast, when the instrumental measurement precision is assumed to be the only contribution to the radial velocity precision, the retrievals resulted in wind speed and direction precisions that were biased far too low and were poor indicators of data quality.
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VIDELER, JOHN, e ALEX GROENEWOLD. "Field Measurements of Hanging Flight Aerodynamics in the Kestrel Falco Tinnunculus". Journal of Experimental Biology 155, n. 1 (1 gennaio 1991): 519–30. http://dx.doi.org/10.1242/jeb.155.1.519.
Testo completoAbstract (sommario):
Hunting kestrels were observed to hang, almost without wing-flapping, in fixed positions over a sea dike. The height and position with respect to the dike profile, the wind direction and velocity and the percentage of hunting time without wing beating were recorded in 429 cases. The vertical wind angle, θ, the wind speed and its horizontal direction were measured at 13 heights up to 8.8m above the windward slope, the top and the leeward slope of the dike under various wind conditions in 225 cases. These wind profile measurements were used to estimate 6 and wind speed near the hanging birds. Kestrels hanging more than 90% of the hunting time preferred a position 6.5±1.5m (S.D.) over the windward slope with sea winds blowing at 8.7±1.5ms−1 (S.D.) perpendicular (±30°) to the longitudinal dike axis. For these birds angle θ was approximately 6–7°. These angles are larger than expected from aerodynamic models and windtunnel measurements. The minimum gliding angle for a kestrel under steady conditions is estimated to be 5°. Hanging kestrels save two-thirds of the energy used during normal windhovering but have to spend 1.6 times more time to catch the same number of voles.
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Wildmann, Norman, Nikola Vasiljevic e Thomas Gerz. "Wind turbine wake measurements with automatically adjusting scanning trajectories in a multi-Doppler lidar setup". Atmospheric Measurement Techniques 11, n. 6 (28 giugno 2018): 3801–14. http://dx.doi.org/10.5194/amt-11-3801-2018.
Testo completoAbstract (sommario):
Abstract. In the context of the Perdigão 2017 experiment, the German Aerospace Center (DLR) deployed three long-range scanning Doppler lidars with the dedicated purpose of investigating the wake of a single wind turbine at the experimental site. A novel method was tested for the first time to investigate wake properties with ground-based lidars over a wide range of wind directions. For this method, the three lidars, which were space- and time-synchronized using the WindScanner software, were programmed to measure with crossing beams at individual points up to 10 rotor diameters downstream of the wind turbine. Every half hour, the measurement points were adapted to the current wind direction to obtain a high availability of wake measurements in changing wind conditions. The linearly independent radial velocities where the lidar beams intersect allow the calculation of the wind vector at those points. Two approaches to estimating the prevailing wind direction were tested throughout the campaign. In the first approach, velocity azimuth display (VAD) scans of one of the lidars were used to calculate a 5 min average of wind speed and wind direction every half hour, whereas later in the experiment 5 min averages of sonic anemometer measurements of a meteorological mast close to the wind turbine became available in real time and were used for the scanning adjustment. Results of wind speed deficit measurements are presented for two measurement days with varying northwesterly winds, and it is evaluated how well the lidar beam intersection points match the actual wake location. The new method allowed wake measurements to be obtained over the whole measurement period, whereas a static scanning setup would only have captured short periods of wake occurrences.
28
Spychała, Jarosław, Paweł Majewski e Mariusz Żokowski. "A Laboratory System to Testing Characteristics Wind Turbine at Low Speeds of Wind". Solid State Phenomena 251 (luglio 2016): 55–60. http://dx.doi.org/10.4028/www.scientific.net/ssp.251.55.
Testo completoAbstract (sommario):
The article presents design solutions air generator systems, measurement of air velocity and software of acquisition and control. It also provides the results obtained during the calibration of the test tunnel developed at Air Force Institute of Technology.
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van Dooren, Marijn Floris, Filippo Campagnolo, Mikael Sjöholm, Nikolas Angelou, Torben Mikkelsen e Martin Kühn. "Demonstration and uncertainty analysis of synchronised scanning lidar measurements of 2-D velocity fields in a boundary-layer wind tunnel". Wind Energy Science 2, n. 1 (20 giugno 2017): 329–41. http://dx.doi.org/10.5194/wes-2-329-2017.
Testo completoAbstract (sommario):
Abstract. This paper combines the research methodologies of scaled wind turbine model experiments in wind tunnels with short-range WindScanner lidar measurement technology. The wind tunnel at the Politecnico di Milano was equipped with three wind turbine models and two short-range WindScanner lidars to demonstrate the benefits of synchronised scanning lidars in such experimental surroundings for the first time. The dual-lidar system can provide fully synchronised trajectory scans with sampling timescales ranging from seconds to minutes. First, staring mode measurements were compared to hot-wire probe measurements commonly used in wind tunnels. This yielded goodness of fit coefficients of 0.969 and 0.902 for the 1 Hz averaged u and v components of the wind speed, respectively, validating the 2-D measurement capability of the lidar scanners. Subsequently, the measurement of wake profiles on a line as well as wake area scans were executed to illustrate the applicability of lidar scanning to the measurement of small-scale wind flow effects. An extensive uncertainty analysis was executed to assess the accuracy of the method. The downsides of lidar with respect to the hot-wire probes are the larger measurement probe volume, which compromises the ability to measure turbulence, and the possible loss of a small part of the measurements due to hard target beam reflection. In contrast, the benefits are the high flexibility in conducting both point measurements and area scanning and the fact that remote sensing techniques do not disturb the flow during measuring. The research campaign revealed a high potential for using short-range synchronised scanning lidars to measure the flow around wind turbines in a wind tunnel and increased the knowledge about the corresponding uncertainties.
30
Baker, R. W., S. N. Walker e P. C. Katen. "Wake Measurements Around Operating Wind Turbines". Journal of Solar Energy Engineering 107, n. 2 (1 maggio 1985): 183–85. http://dx.doi.org/10.1115/1.3267674.
Testo completoAbstract (sommario):
Researchers at Oregon State University have conducted wind measurement programs to describe the wake behind large horizontal axis turbines at Goodnoe Hills, Washington, (MOD-2), and behind the FloWind vertical axis wind turbine near Ellenburg, Washington. Wake measurements were taken using portable kite anemometers as well as fixed place anemometers under several atmospheric stability conditions and turbine operating conditions. Centerline hub height (midrotor) measurements were taken downwind and crosswind from 3–9 diameters. These wake programs are discussed and the velocity deficits measured are compared to the estimated deficits calculated from wake models.
31
Godin, Oleg A., Vladimir G. Irisov e Mikhail I. Charnotskii. "Wind velocity measurements with acoustic daylight." Journal of the Acoustical Society of America 127, n. 3 (marzo 2010): 2037. http://dx.doi.org/10.1121/1.3385357.
Testo completo
32
Takagaki, Naohisa, Naoya Suzuki, Yuliya Troitskaya, Chiaki Tanaka, Alexander Kandaurov e Maxim Vdovin. "Effects of current on wind waves in strong winds". Ocean Science 16, n. 5 (10 settembre 2020): 1033–45. http://dx.doi.org/10.5194/os-16-1033-2020.
Testo completoAbstract (sommario):
Abstract. It is important to investigate the effects of current on wind waves, called the Doppler shift, at both normal and extremely high wind speeds. Three different types of wind-wave tanks along with a fan and pump are used to demonstrate wind waves and currents in laboratories at Kyoto University, Japan, Kindai University, Japan, and the Institute of Applied Physics, Russian Academy of Sciences, Russia. Profiles of the wind and current velocities and the water-level fluctuation are measured. The wave frequency, wavelength, and phase velocity of the significant waves are calculated, and the water velocities at the water surface and in the bulk of the water are also estimated by the current distribution. The study investigated 27 cases with measurements of winds, waves, and currents at wind speeds ranging from 7 to 67 m s−1. At normal wind speeds under 30 m s−1, wave frequency, wavelength, and phase velocity depend on wind speed and fetch. The effect of the Doppler shift is confirmed at normal wind speeds; i.e., the significant waves are accelerated by the surface current. The phase velocity can be represented as the sum of the surface current and artificial phase velocity, which is estimated by the dispersion relation of the deepwater waves. At extremely high wind speeds over 30 m s−1, a similar Doppler shift is observed as under the conditions of normal wind speeds. This suggests that the Doppler shift is an adequate model for representing the acceleration of wind waves by current, not only for wind waves at normal wind speeds but also for those with intensive breaking at extremely high wind speeds. A weakly nonlinear model of surface waves at a shear flow is developed. It is shown that it describes dispersion properties well not only for small-amplitude waves but also strongly nonlinear and even breaking waves, which are typical for extreme wind conditions (over 30 m s−1).
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Kelberlau, Felix, e Jakob Mann. "Better turbulence spectra from velocity–azimuth display scanning wind lidar". Atmospheric Measurement Techniques 12, n. 3 (21 marzo 2019): 1871–88. http://dx.doi.org/10.5194/amt-12-1871-2019.
Testo completoAbstract (sommario):
Abstract. Turbulent velocity spectra derived from velocity–azimuth display (VAD) scanning wind lidars deviate from spectra derived from one-point measurements due to averaging effects and cross-contamination among the velocity components. This work presents two novel methods for minimizing these effects through advanced raw data processing. The squeezing method is based on the assumption of frozen turbulence and introduces a time delay into the raw data processing in order to reduce cross-contamination. The two-beam method uses only certain laser beams in the reconstruction of wind vector components to overcome averaging along the measurement circle. Models are developed for conventional VAD scanning and for both new data processing methods to predict the spectra and identify systematic differences between the methods. Numerical modeling and comparison with measurement data were both used to assess the performance of the methods. We found that the squeezing method reduces cross-contamination by eliminating the resonance effect caused by the longitudinal separation of measurement points and also considerably reduces the averaging along the measurement circle. The two-beam method eliminates this averaging effect completely. The combined use of the squeezing and two-beam methods substantially improves the ability of VAD scanning wind lidars to measure in-wind (u) and vertical (w) fluctuations.
34
Adachi, Ahoro, Takahisa Kobayashi, Kenneth S. Gage, David A. Carter, Leslie M. Hartten, Wallace L. Clark e Masato Fukuda. "Evaluation of Three-Beam and Four-Beam Profiler Wind Measurement Techniques Using a Five-Beam Wind Profiler and Collocated Meteorological Tower". Journal of Atmospheric and Oceanic Technology 22, n. 8 (1 agosto 2005): 1167–80. http://dx.doi.org/10.1175/jtech1777.1.
Testo completoAbstract (sommario):
Abstract In this paper a five-beam wind profiler and a collocated meteorological tower are used to estimate the accuracy of four-beam and three-beam wind profiler techniques in measuring horizontal components of the wind. In the traditional three-beam technique, the horizontal components of wind are derived from two orthogonal oblique beams and the vertical beam. In the less used four-beam method, the horizontal winds are found from the radial velocities measured with two orthogonal sets of opposing coplanar beams. In this paper the observations derived from the two wind profiler techniques are compared with the tower measurements using data averaged over 30 min. Results show that, while the winds measured using both methods are in overall agreement with the tower measurements, some of the horizontal components of the three-beam-derived winds are clearly spurious when compared with the tower-measured winds or the winds derived from the four oblique beams. These outliers are partially responsible for a larger 30-min, three-beam standard deviation of the profiler/tower wind speed differences (2.2 m s−1), as opposed to that from the four-beam method (1.2 m s−1). It was also found that many of these outliers were associated with periods of transition between clear air and rain, suggesting that the three-beam technique is more sensitive to small-scale variability in the vertical Doppler velocity because of its reliance on the point measurement from the vertical beam, while the four-beam method is surprisingly robust. Even after the removal of the rain data, the standard deviation of the wind speed error from the three-beam method (1.5 m s−1) is still much larger than that from the four-beam method. Taken together, these results suggest that the spatial variability of the vertical airflow in nonrainy periods or hydrometeor fall velocities in rainy periods makes the vertical beam velocities significantly less representative over the area across the three beams, and decreases the precision of the three-beam method. It is concluded that profilers utilizing the four-beam wind profiler technique have better reliability than wind profilers that rely on the three-beam wind profiler technique.
35
Plagge, Amanda M., Douglas Vandemark e Bertrand Chapron. "Examining the Impact of Surface Currents on Satellite Scatterometer and Altimeter Ocean Winds". Journal of Atmospheric and Oceanic Technology 29, n. 12 (1 dicembre 2012): 1776–93. http://dx.doi.org/10.1175/jtech-d-12-00017.1.
Testo completoAbstract (sommario):
Abstract A 5-yr dataset collected over two surface current and meteorological moorings allows rigorous evaluation of questions surrounding wave–current interaction and the scatterometer. Results demonstrate that scatterometer winds represent winds relative to the moving sea surface, affirming previous observational efforts that inferred the phenomenon using climatological approaches over larger time and space scales in equatorial and western boundary currents. Comparisons of wind residuals between Ku-band Quick Scatterometer (QuikSCAT) and buoy measurements show nearly one-to-one correlations with ocean surface velocity for 5-, 12.5-, and 25-km resolution wind speed products, especially under conditions of moderate wind speed and near-neutral atmospheric stability. Scatterometer and buoy wind direction differences due to currents were observed to be negligible for the range of surface velocities encountered and the length scales observed by QuikSCAT. Similar analyses are applied to C-band Advanced Scatterometer (ASCAT) satellite wind measurements at the same sites, as well as to satellite altimeter winds, and overall confirm the results seen with QuikSCAT; differences are likely the combined result of sampling, satellite wind algorithms, and geophysical wind–wave coupling in the presence of currents. On the whole, this study affirms that at length scales of 10 km and longer the scatterometer wind can be considered to be current relative. Observed differences between earth-relative and current-relative winds of order 10%–20% of the wind velocity are not uncommon in this and other ocean regions and this study more fully validates that microwave remote sensing winds appear to respond to wind stress even in the presence of larger-scale currents.
36
Li, Qiang, Markus Rapp, Gunter Stober e Ralph Latteck. "High-resolution vertical velocities and their power spectrum observed with the MAARSY radar – Part 1: frequency spectrum". Annales Geophysicae 36, n. 2 (3 aprile 2018): 577–86. http://dx.doi.org/10.5194/angeo-36-577-2018.
Testo completoAbstract (sommario):
Abstract. The Middle Atmosphere Alomar Radar System (MAARSY) installed at the island of Andøya has been run for continuous probing of atmospheric winds in the upper troposphere and lower stratosphere (UTLS) region. In the current study, we present high-resolution wind measurements during the period between 2010 and 2013 with MAARSY. The spectral analysis applying the Lomb–Scargle periodogram method has been carried out to determine the frequency spectra of vertical wind velocity. From a total of 522 days of observations, the statistics of the spectral slope have been derived and show a dependence on the background wind conditions. It is a general feature that the observed spectra of vertical velocity during active periods (with wind velocity > 10 m s−1) are much steeper than during quiet periods (with wind velocity < 10 m s−1). The distribution of spectral slopes is roughly symmetric with a maximum at −5/3 during active periods, whereas a very asymmetric distribution with a maximum at around −1 is observed during quiet periods. The slope profiles along altitudes reveal a significant height dependence for both conditions, i.e., the spectra become shallower with increasing altitudes in the upper troposphere and maintain roughly a constant slope in the lower stratosphere. With both wind conditions considered together the general spectra are obtained and their slopes are compared with the background horizontal winds. The comparisons show that the observed spectra become steeper with increasing wind velocities under quiet conditions, approach a spectral slope of −5/3 at a wind velocity of 10 m s−1 and then roughly maintain this slope (−5/3) for even stronger winds. Our findings show an overall agreement with previous studies; furthermore, they provide a more complete climatology of frequency spectra of vertical wind velocities under different wind conditions. Keywords. Meteorology and atmospheric dynamics (turbulence; waves and tides)
37
Shannak, B., K. Träumner, A. Wieser, U. Corsmeier e Ch Kottmeier. "Flow characteristics above a forest using light detection and ranging measurement data". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, n. 4 (14 settembre 2011): 921–39. http://dx.doi.org/10.1177/0954406211417944.
Testo completoAbstract (sommario):
New wind velocity measurement method using a light detection and ranging instrument was conducted. Based on the presented experimental data, the airflow characteristics above a forest were investigated: wind velocity distribution, friction (shear) wind velocity, roughness length, stream lines, drag force, and depth of the boundary layer. The results demonstrated that windward the forest, the boundary layer is shifted and sloped above the forest. Thereby, the fluid streamlines cannot abruptly change direction, as a consequence flat wind velocity profiles, wavy inflected wind velocity profiles, eddies, and flow recirculation were developed; hence, flow separation at a forest ratio x/ h of 2, flow contraction at x/ h of 12, and flow expansion at x/ h of 22 appeared. The shear wind velocity was about 1/10 of the mean wind velocity and the roughness length 1/15 of the forest height. Within a boundary layer depth of about 130 m, the drag force of the forest was 1300 times greater than that of the grass. Behind the forest, the air flow expands and eddies were developed at x/ h of about 7. Passing through the agriculture area and the forest, the physical parameters (turbulent kinetic energy, friction wind velocity, drag force, and depth of the boundary layer) are increasing at the point of roughness increase. To decrease such parameters and to avoid energy and friction losses and damage to trees due to divergence, convergence, separation, and recirculation of airflow, the sharp edge of the forest should be rounded in the range x/ h up to 2. A curved cutting of the front area of the forest may allow to decrease the slope of the boundary layer and the streamlines before, above, and behind the forest and hence lead to a quasi-steady and stable flow with less turbulence, momentum, heat, and mass transfer between the canopy and the atmosphere.
38
Wang, H., R. J. Barthelmie, P. Doubrawa e S. C. Pryor. "Errors in radial velocity variance from Doppler wind lidar". Atmospheric Measurement Techniques 9, n. 8 (29 agosto 2016): 4123–39. http://dx.doi.org/10.5194/amt-9-4123-2016.
Testo completoAbstract (sommario):
Abstract. A high-fidelity lidar turbulence measurement technique relies on accurate estimates of radial velocity variance that are subject to both systematic and random errors determined by the autocorrelation function of radial velocity, the sampling rate, and the sampling duration. Using both statistically simulated and observed data, this paper quantifies the effect of the volumetric averaging in lidar radial velocity measurements on the autocorrelation function and the dependence of the systematic and random errors on the sampling duration. For current-generation scanning lidars and sampling durations of about 30 min and longer, during which the stationarity assumption is valid for atmospheric flows, the systematic error is negligible but the random error exceeds about 10 %.
39
Wang, H., R. J. Barthelmie, A. Clifton e S. C. Pryor. "Wind Measurements from Arc Scans with Doppler Wind Lidar". Journal of Atmospheric and Oceanic Technology 32, n. 11 (novembre 2015): 2024–40. http://dx.doi.org/10.1175/jtech-d-14-00059.1.
Testo completoAbstract (sommario):
AbstractDefining optimal scanning geometries for scanning lidars for wind energy applications remains an active field of research. This paper evaluates uncertainties associated with arc scan geometries and presents recommendations regarding optimal configurations in the atmospheric boundary layer. The analysis is based on arc scan data from a Doppler wind lidar with one elevation angle and seven azimuth angles spanning 30° and focuses on an estimation of 10-min mean wind speed and direction. When flow is horizontally uniform, this approach can provide accurate wind measurements required for wind resource assessments in part because of its high resampling rate. Retrieved wind velocities at a single range gate exhibit good correlation to data from a sonic anemometer on a nearby meteorological tower, and vertical profiles of horizontal wind speed, though derived from range gates located on a conical surface, match those measured by mast-mounted cup anemometers. Uncertainties in the retrieved wind velocity are related to high turbulent wind fluctuation and an inhomogeneous horizontal wind field. The radial velocity variance is found to be a robust measure of the uncertainty of the retrieved wind speed because of its relationship to turbulence properties. It is further shown that the standard error of wind speed estimates can be minimized by increasing the azimuthal range beyond 30° and using five to seven azimuth angles.
40
Baidar, S., S. C. Tucker, M. Beaubien e R. M. Hardesty. "The Optical Autocovariance Wind Lidar. Part II: Green OAWL (GrOAWL) Airborne Performance and Validation". Journal of Atmospheric and Oceanic Technology 35, n. 10 (ottobre 2018): 2099–116. http://dx.doi.org/10.1175/jtech-d-18-0025.1.
Testo completoAbstract (sommario):
AbstractA two-look airborne Doppler wind lidar operating at the 532-nm laser wavelength, the Green Optical Autocovariance Wind Lidar (GrOAWL), was built and flown aboard the NASA WB-57 research aircraft. Flight campaign goals were to validate the instrument wind measurements and to demonstrate the two-look measurement concept proposed for spaceborne mission concepts such as the Atmospheric Transport, Hurricanes, and Extratropical Numerical Weather Prediction with the Optical Autocovariance Wind Lidar (ATHENA-OAWL) mission. The GrOAWL-measured winds were compared with collocated dropsonde measurements. Line-of-sight velocity (LOSV) measurements for the individual GrOAWL looks showed excellent agreement with dropsondes (R2 > 0.9). The LOSV biases were very small and not statistically different from 0 m s−1 at the 95% confidence interval (−0.07 ± 0.07 m s−1 and 0.01 ± 0.07 m s−1 for look 1 and look 2, respectively). The wind speed and direction profiles retrieved by combining the two GrOAWL looks were also in very good agreement (R2 > 0.85). An instrument performance model indicated the instrument wind measurement precision was likely lowered (uncertainty was increased) by a factor of ~3.3 during the flights relative to predicted “as built” instrument performance. The reduced performance was not observed during ground-based atmospheric testing and thus has been attributed to impacts of the harsh operating conditions of the WB-57 aircraft (high vibration, thermal gradients, and high humidity). The exercise of scaling the GrOAWL instrument performance and grid scale to space showed space-based OAWL wind measurements would yield products with precision at least as good as the GrOAWL instrument.
41
van den Kroonenberg, Aline, Tim Martin, Marco Buschmann, Jens Bange e Peter Vörsmann. "Measuring the Wind Vector Using the Autonomous Mini Aerial Vehicle M2AV". Journal of Atmospheric and Oceanic Technology 25, n. 11 (1 novembre 2008): 1969–82. http://dx.doi.org/10.1175/2008jtecha1114.1.
Testo completoAbstract (sommario):
Abstract The meteorological mini unmanned aerial vehicle (M2AV) was used for measuring the meteorological wind. The wind is the vector difference between the aircraft speed relative to the earth (inertial velocity) and relative to the airflow (true airspeed). The latter was computed from five-hole-probe pressure measurements in combination with calibration–coefficient polynomials obtained during wind tunnel calibration. The aircraft inertial velocity, position, and attitude were calculated using a Kalman filter that combined data from a global positioning system (GPS) and an inertial navigation system (INS). The temporal (and spatial) resolution of the M2AV wind measurement is remarkably fine. An inertial subrange of locally isotropic turbulence can be measured up to 40 Hz (or 0.55 m at 22 m s−1 airspeed). The first M2AV wind estimation showed some systematic deviations compared to the expected values (like a constant mean wind in every flight direction). Therefore, an in-flight wind calibration technique was developed that corrects for the inaccuracy of the true heading, the constant offset of the pitch angle, and the underestimation of the true airspeed. The final adjusted wind measurements were verified during a field experiment at the measurement field of the German Meteorological Service, southeast of Berlin. The mean horizontal and vertical wind measured by the M2AV agreed well with simultaneous sodar and tower measurements.
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Belu, Radian, e Darko Koračin. "Regional analysis of wind velocity patterns in complex terrain". Geofizika 36, n. 2 (31 gennaio 2020): 111–30. http://dx.doi.org/10.15233/gfz.2019.36.6.
Testo completoAbstract (sommario):
Wind energy is a weather and climate-dependent energy resource with natural spatio-temporal variabilities at time scales ranging from fraction of seconds to seasons and years, while at spatial scales it is strongly affected by the terrain and vegetation. To optimize wind energy systems and maximize the energy extraction, wind measurements on various time scales as well as wind energy forecasts are required and needed. This study focuses on spatio-temporal characteristics of the wind velocity in complex terrain, relevant to wind energy assessment, operation, and grid integration, using data collected at 11 towers ranging from 40 to 80 m tall over a 12-year period in complex terrain of western-central and northern Nevada, USA. The autocorrelation analysis, Detrended Fluctuation Analysis (DFA) and Detrended Cross-Correlation Analysis (DCCA) showed strong coherence between the wind speed and direction with slowly decreasing amplitude of the multi-day periodicity with increasing lag periods. Besides pronounced diurnal periodicity at all locations, statistical analysis and DFA also showed significant seasonal and annual periodicities, long-memory persistence with similar characteristics at all sites and towers with a relatively narrow range of the Weibull parameters. The DCCA indicates similar wind patterns at each tower, and strong correlations between measurement sites in spite of separations of about 300 km across the towers’ setup. The northern Nevada area exhibits higher wind resource potential and higher wind persis-tence compared to the western-central region. Overall, the DFA and DCCA results suggest higher degree of complementarity among wind data at measure-ment sites compared to previous standard statistical analysis.
43
Al-Ghussain, Loiy, e Sean C. C. Bailey. "An approach to minimize aircraft motion bias in multi-hole probe wind measurements made by small unmanned aerial systems". Atmospheric Measurement Techniques 14, n. 1 (11 gennaio 2021): 173–84. http://dx.doi.org/10.5194/amt-14-173-2021.
Testo completoAbstract (sommario):
Abstract. A multi-hole probe mounted on an aircraft provides the air velocity vector relative to the aircraft, requiring knowledge of the aircraft spatial orientation (e.g., Euler angles), translational velocity and angular velocity to translate this information to an Earth-based reference frame and determine the wind vector. As the relative velocity of the aircraft is typically an order of magnitude higher than the wind velocity, the extracted wind velocity is very sensitive to multiple sources of error including misalignment of the probe and aircraft coordinate system axes, sensor error and misalignment in time of the probe and aircraft orientation measurements in addition to aerodynamic distortion of the velocity field by the aircraft. Here, we present an approach which can be applied after a flight to identify and correct biases which may be introduced into the final wind measurement. The approach was validated using a ground reference, different aircraft and the same aircraft at different times. The results indicate a significant reduction in wind velocity variance at frequencies which correspond to aircraft motion.
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Iungo, Giacomo Valerio, Yu-Ting Wu e Fernando Porté-Agel. "Field Measurements of Wind Turbine Wakes with Lidars". Journal of Atmospheric and Oceanic Technology 30, n. 2 (1 febbraio 2013): 274–87. http://dx.doi.org/10.1175/jtech-d-12-00051.1.
Testo completoAbstract (sommario):
AbstractField measurements of the wake flow produced from a 2-MW Enercon E-70 wind turbine were performed using three scanning Doppler wind lidars. A GPS-based technique was used to determine the position of the wind turbine and the wind lidar locations, as well as the direction of the laser beams. The lidars used in this study are characterized by a high spatial resolution of 18 m, which allows the detailed characterization of the wind turbine wake. Two-dimensional measurements of wind speed were carried out by scanning a single lidar over the vertical symmetry plane of the wake. The mean axial velocity field was then retrieved by averaging 2D scans performed consecutively. To investigate wake turbulence, single lidar measurements were performed by staring the laser beam at fixed directions and using the maximum sampling frequency. From these tests, peaks in the velocity variance are detected within the wake in correspondence of the turbine top tip height; this enhanced turbulence could represent a source of dangerous fatigue loads for downstream turbines. The spectral density of the measured velocity fluctuations shows a clear inertial-range scaling behavior. Then, simultaneous measurements with two lidars were performed in order to characterize both the axial and the vertical velocity components. For this setup, the two velocity components were retrieved only for measurement points for which the two laser beams crossed nearly at a right angle. Statistics were computed over the sample set for both velocity components, and they showed strong flow fluctuations in the near-wake region at turbine top tip height, with a turbulence intensity of about 30%.
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Kim, Young-Moon, Ki-Pyo You e Jang-Youl You. "Characteristics of Wind Velocity and Temperature Change Near an Escarpment-Shaped Road Embankment". Scientific World Journal 2014 (2014): 1–13. http://dx.doi.org/10.1155/2014/695629.
Testo completoAbstract (sommario):
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.
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SPIES, PETER-JOST, IAN K. McEWAN e GRAEME R. BUTTERFIELD. "On wind velocity profile measurements taken in wind tunnels with saltating grains". Sedimentology 42, n. 3 (giugno 1995): 515–21. http://dx.doi.org/10.1111/j.1365-3091.1995.tb00387.x.
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Werner, C. "Computer simulation of coherent Doppler lidar measurement of wind velocity and retrieval of turbulent wind statistics". Optical Engineering 44, n. 7 (1 luglio 2005): 071205. http://dx.doi.org/10.1117/1.1955167.
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Garcia-Magariño, Adelaida, Suthyvann Sor, Rafael Bardera e Javier Muñoz. "Mars 2020 Wind Velocity Measurement Interferences at High Reynolds Numbers". Journal of Spacecraft and Rockets 57, n. 2 (marzo 2020): 354–63. http://dx.doi.org/10.2514/1.a34591.
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Watanabe, Jun-Ichi. "Measurement of the solar wind velocity with cometary tail rays". Solar Physics 132, n. 2 (aprile 1991): 395–407. http://dx.doi.org/10.1007/bf00152295.
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M., McWilliam, e Johnson D.A. "Velocity Measurement of Flow Around Model Vertical Axis Wind Turbines". International Journal of Green Energy 5, n. 1-2 (15 febbraio 2008): 55–68. http://dx.doi.org/10.1080/15435070701845691.
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