Zeitschriftenartikel: „Low wind“

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Khaghaninia, S., S. Mohammadi, A. Srafrazi, K. Nejad und R. Zahiri. „Geometric Morphometric Study on Geographic Dimorphism of Coding Moth Cydia Pomonella (Lepidoptera, Tortricidae) from North West of Iran“. Vestnik Zoologii 45, Nr. 5 (01.01.2011): e-20-e-28. http://dx.doi.org/10.2478/v10058-011-0028-z.

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Geometric Morphometric Study on Geographic Dimorphism of Coding MothCydia Pomonella(Lepidoptera, Tortricidae) from North West of IranDuring years 2003-2004, nine geographical populations of codling moth Cydia pomonella (Linnaeus) from 4 north western provinces of Iran were collected. By preparing 575 images from fore wings and 564 from hind wings, a total of 15 and 11 landmarks were determined for fore and hind wings, respectively. With transforming of landmark's geometrical data into partial warp scores, 26 and 18 scores were obtained for fore and hind wings, respectively. Canonical correlation analysis (CCA) revealed significant correlation between environmental parameters and wing shape variables. Among environmental parameters, wind speed showed the highest correlation with wing shape variables whereas, the correlation between latitude, relative humidity as well as amount of precipitation and wing shape variables was low. Considering the effect of various environmental parameters on wing shape, wind speed was determined as important parameter affecting geographic dimorphism. Among the populations collected from different regions, two geographic population pairs; Meshkinshahr-Mahneshan and Zandjan-Khoramdareh were selected as representative of low and high windy regions, respectively. Relative warp analysis (RWA) of fore and hind wings shape variables in the areas with high and low wind showed shorter and wider fore wings as well as slender and narrower hind wings in populations from high windy regions compared with populations from low wind regions. Centroid size of fore and hind wings in high windy area populations were smaller compared with those from low windy ones as revealed by t-test. The results showed aerodynamic shape and small size of wings are as adapted traits for powerful flight and its control in high windy regions.

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Lawrence, W., D. Langridge und D. Johnston. „Low wind speed wind generation scheme“. Renewable Energy 4, Nr. 5 (Juli 1994): 489–94. http://dx.doi.org/10.1016/0960-1481(94)90211-9.

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Furevik, Birgitte Rugaard, Harald Schyberg, Gunnar Noer, Frank Tveter und Johannes Röhrs. „ASAR and ASCAT in Polar Low Situations“. Journal of Atmospheric and Oceanic Technology 32, Nr. 4 (April 2015): 783–92. http://dx.doi.org/10.1175/jtech-d-14-00154.1.

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AbstractForecasting and monitoring polar lows are, to a large degree, based on satellite observations from passive radiometers and from scatterometer winds in addition to synoptic observations and numerical models. Synthetic aperture radar (SAR) brings higher resolution compared to other remotely sensed sources of ocean wind, such as scatterometer data and passive microwave wind products. The added information in polar low situations from SAR and the increased-resolution scatterometer wind fields are investigated. Statistically, higher variability in the MetOp Advanced Scatterometer (ASCAT) wind is clearly found during polar low situations compared to all situations. Slightly more variability is also seen in the ASCAT 12.5-km wind product compared to the operational European Centre for Medium-Range Weather Forecasts (ECMWF) model surface winds. In two analyzed polar low cases, Environmental Satellite (Envisat) Advanced SAR (ASAR) images reveal numerous interesting features, such as the sharp fronts and the location and strength of the strongest wind field in the polar low. It is likely that if SAR images are available to operational weather forecasting, that it can in some cases lead to earlier detection of polar lows. However, a reliable wind field from SAR is still needed.

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Berkovic, Sigalit, und Pinhas Alpert. „A Synoptic Study of Low Troposphere Wind at the Israeli Coast“. Open Atmospheric Science Journal 12, Nr. 1 (13.08.2018): 80–106. http://dx.doi.org/10.2174/1874282301812010080.

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Objective:This research is dedicated to the study of the feasibility of surface wind downscaling from 925 or 850 hPa winds according to synoptic class, season and hour.Methods:Two aspects are examined: low tropospheric wind veering and wind speed correlation and verification of the ERA-Interim analysis wind by comparison to radiosonde data at Beit Dagan, a station on the Israeli coast.Results:Relatively small (< 60°) cross angles between the 1000 hPa wind vector and the 925 hPa or 850 hPa wind vector at 12Z and high correlation (0.6-0.8) between the wind speed at the two levels were found only under winter lows. Relatively small cross angles and small wind speed correlation were found under highs to the west and Persian troughs.The verification of ERA-Interim analysis in comparison with radiosonde data has shown good prediction of wind direction at 12Z at 1000, 925 and 850 hPa levels (RMSE 20°-60°) and lower prediction quality at 1000 hPa at 0Z (RMSE 60°-90°). The analysis under-predicts the wind speed, especially at 1000 hPa. The wind speed RMSE is 1-2 m/s, except for winter lows with 2-3 m/s RMSE at 0Z, 12Z at all levels.Conclusion:Inference of surface wind may be possible at 12Z from 925 or 825 hPa winds under winter lows. Inference of wind direction from 925 hPa winds may be possible under highs to the west and Persian troughs. Wind speed should be inferred by interpolation, according to historical data of measurements or high resolution model.

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Song, Hai Hui, Jian Jun Wang, Zhi Hua Hu und Jin Zhou. „Research on Low-Wind-Speed Wind Power“. Applied Mechanics and Materials 448-453 (Oktober 2013): 1811–14. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.1811.

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For high-wind-speed wind power development and problems, propose development and application of low-wind-speed wind power (LWSP). Analysis of the characteristics of LWSP , advantages and necessity of development and application of it. Research the key technologies of LWSP development. It ultimately lay the foundation for research, development and application of LWSP technologies.

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Nasrul, Muhammad, und Illa Rizianiza. „Shrouded wind turbine for low wind speed“. IOP Conference Series: Materials Science and Engineering 1034, Nr. 1 (01.02.2021): 012042. http://dx.doi.org/10.1088/1757-899x/1034/1/012042.

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Conley, Stephen A., Ian C. Faloona, Donald H. Lenschow, Anna Karion und Colm Sweeney. „A Low-Cost System for Measuring Horizontal Winds from Single-Engine Aircraft“. Journal of Atmospheric and Oceanic Technology 31, Nr. 6 (01.06.2014): 1312–20. http://dx.doi.org/10.1175/jtech-d-13-00143.1.

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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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Mohd Hafiz, Mohd Noh, Abdul Hamid Ahmad Hussein, Rashid Helmi, Wisnoe Wirachman und Syahmi Nasir Mohd. „Wind Tunnel Experiment for Low Wind Speed Wind Turbine Blade“. Applied Mechanics and Materials 110-116 (Oktober 2011): 1589–93. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.1589.

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Environment and green energy awareness are two main factors why this study has been carried out. This research is focused on aerodynamics study for airfoil structure modification based on NACA 0044 and NACA 0063 by using wind tunnel experiment. Aerodynamic characteristics such as lift coefficient, CL, drag coefficient, CD, lift to drag ratio and cell relative velocity has been investigated in this study. CFD simulation has been carried out at the early stage of the investigation (for NACA 0044 and NACA 0063), and a new airfoil profile had been created (0044-63) by modified the chord length and the location of maximum thickness of the airfoil by using the modified NACA Four-Digit Series. Wind tunnel experiment has been take place for three different wind speeds from 25m/s, 35m/s and 45m/s at various angles of attack from 0o to 40o with 5o incremental for the respective airfoil. The results show that the modified 0044-63 produced the better lift coefficient and this airfoil has been fabricated and tested in the wind tunnel experiment in order to validate the CFD result. This paper reports the result of aerodynamics characteristics for respective new airfoil and it shows that at angle of attack between 5 o to 15 o, this airfoil produced good lift to drag ratio value. Also, by modified the location of maximum thickness 30% to the trailing edge give the increment of lift to drag ratio produced approximately 15% and at the same time, give insignificant changes to the drag coefficient value.

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Bowen, Brent M. „Improved Wind and Turbulence Measurements Using a Low-Cost 3-D Sonic Anemometer at a Low-Wind Site“. Open Atmospheric Science Journal 2, Nr. 1 (09.07.2008): 131–38. http://dx.doi.org/10.2174/1874282300802010131.

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A year of data from sonic anemometer and mechanical wind sensors was analyzed and compared at a low-wind site. Results indicate that 15-minute average and peak 1-second wind speeds (u) from the sonic agree well with data derived from a co-located cup anemometer over a wide range of speeds. Wind direction data derived from the sonic also agree closely with those from a wind vane except for very low wind speeds. Values of standard deviation of longitudinal wind speed (σu) and wind direction fluctuations (σø) from the sonic and mechanical sensors agree well for times with u > 2 ms-1 but show significant differences with lower u values. The most significant differences are associated with the standard deviation of vertical wind fluctuations (σw): the co-located vertical propeller anemometer yields values increasingly less than those measured by the sonic anemometer as u decreases from 2.5 approaching 0 ms-1. The combination of u over-estimation and under-estimation of σw from the mechanical sensors at low wind speeds causes considerable underestimation of the standard deviation of vertical wind angle fluctuations (σø), an indicator of vertical dispersion. Calculations of σø from sonic anemometer measurements are typically 5° to 10° greater than from the mechanical sensors when the mechanical instruments indicate that σø < 5° or so. The errors with the propeller anemometer, cup anemometer and wind vane, caused by their inability to respond to higher frequency (smaller scale) turbulent fluctuations, can therefore lead to large (factors of 2 to 10 or more) errors in both the vertical and horizontal dispersion during stable conditions with light winds. The sonic anemometer clearly provides more accurate and reliable wind data than the mechanical wind sensor with u < 2.5 ms-1

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Chen, Sina, Ari Laor, Ehud Behar, Ranieri D. Baldi, Joseph D. Gelfand, Amy E. Kimball, Ian M. McHardy, Gabor Orosz und Zsolt Paragi. „Windy or Not: Radio Parsec-scale Evidence for a Broad-line Region Wind in Radio-quiet Quasars“. Astrophysical Journal 975, Nr. 1 (23.10.2024): 35. http://dx.doi.org/10.3847/1538-4357/ad74fc.

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Abstract Does a broad-line region (BLR) wind in radio-quiet (RQ) active galactic nuclei (AGN) extend to parsec scales and produce radio emission? We explore the correlations between a parsec-scale radio wind and the BLR wind in a sample of 19 RQ Palomar–Green quasars. The radio wind is defined based on the spectral slope and the compactness of the emission at 1.5–5 GHz, and the BLR wind is defined by the excess blue wing in the C iv emission line profile. The five objects with both radio and BLR wind indicators are found at high Eddington ratios, L/L Edd (≥0.66), and eight of the nine objects with neither radio nor BLR winds reside at low L/L Edd (≤0.28). This suggests that the BLR wind and the radio wind in RQ AGN are related to a radiation-pressure-driven wind. Evidence for free–free absorption by AGN photoionized gas, which flattens the spectral slope, is found in two objects. Radio outflows in three low-L/L Edd (0.05–0.12) objects are likely from a low-power jet, as suggested by additional evidence. The presence of a mild equatorial BLR wind in four intermediate-L/L Edd (0.2–0.4) objects can be tested with future spectropolarimetry.

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IIDA, Akiyoshi. „Low Noise Wind Tunnel“. Journal of the Society of Mechanical Engineers 108, Nr. 1042 (2005): 726–27. http://dx.doi.org/10.1299/jsmemag.108.1042_726.

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M. M. Takeyeldein, Tholudin Mat Lazim, Iskandar Shah Ishak, N. A. R. Nik Mohd und Essam Abubakr Ali. „Wind Lens Performance Investigation at Low Wind Speed“. Evergreen 7, Nr. 4 (Dezember 2020): 481–88. http://dx.doi.org/10.5109/4150467.

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M. M. Takeyeldein, Tholudin Mat Lazim, Iskandar Shah Ishak, N. A. R. Nik Mohd und Essam Abubakr Ali. „Wind Lens Performance Investigation at Low Wind Speed“. Evergreen 7, Nr. 4 (Dezember 2020): 481–88. http://dx.doi.org/10.5109/4150467.

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Chen, Sheng, Fangli Qiao, Chuan Jiang Huang und Biao Zhao. „Deviation of Wind Stress From Wind Direction Under Low Wind Conditions“. Journal of Geophysical Research: Oceans 123, Nr. 12 (Dezember 2018): 9357–68. http://dx.doi.org/10.1029/2018jc014137.

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Kalapureddy, M. C. R., D. N. Rao, A. R. Jain und Y. Ohno. „Wind profiler observations of a monsoon low-level jet over a tropical Indian station“. Annales Geophysicae 25, Nr. 10 (06.11.2007): 2125–37. http://dx.doi.org/10.5194/angeo-25-2125-2007.

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Abstract. Three-year high-resolution wind observations of the wind profiler have been utilized to characterize the diurnal and seasonal features of the monsoon Low-Level Jet (LLJ) over a tropical station, Gadanki (13.5° N, 79.2° E), with a focus on the diurnal variability of low-level winds. The Boreal summer monsoon winds show a conspicuously strong westerly LLJ with average wind speed exceeding 20 m s−1. The L-band wind profiler measurements have shown an advantage of better height and time resolutions over the conventional radiosonde method for diurnal wind measurements. An interesting diurnal oscillation of LLJ core has been observed. It is varying in the height range of 1.8±0.6 km with the maximum and minimum intensity noticed during the early morning and afternoon hours, respectively. The jet core (wind maxima) height is observed to coincide with the inversion height. Strong wind shears are normally located beneath the LLJ core. The sole wind profiler observations are capable of identifying the monsoon phases, such as onset, break and active spells, etc. The mutual influence between the LLJ and the boundary layer has been discussed. One notices that the observed LLJ diurnal structures depend on the local convective activity, wind shears and turbulence activity associated with boundary layer winds. The day-to-day change in the LLJ structure depends on the latitudinal position of the LLJ core.

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SURESH, R. „An account of low level wind shear over Chennai airport - Part II : Turbulence and eddy dissipation“. MAUSAM 60, Nr. 3 (27.11.2021): 325–42. http://dx.doi.org/10.54302/mausam.v60i3.1104.

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In-flight reports on Low Level Wind Shear (LLWS) received from aircrafts are used to issue wind shear alerts for all subsequent landing aircrafts as per standing guidelines of International Civil Aviation Organisation (ICAO). In this paper, winds reported by aircrafts at 1000 and 1800 ft. are used to validate the wind estimated from DWR measured radial wind data employing standard algorithms. Turbulence indices and parameters have been computed independently using conventional (RS/RW) upper air data, aircraft measured winds and DWR estimated winds and compared these with wind shear induced turbulence reported by aircrews. Mean power law (wind escalation law) profiles in the boundary layer have been arrived at for unstable and stable atmospheric conditions. Three dimensional shear (3DS) upto 600 m a.g.l. has been worked out from DWR measured radial velocity data and compared with wind shear computed from RS/RW and aircraft measured winds and DWR estimated winds. It is found that 3DS values of more than 16 * 10-3 s-1 predict well the occurrence of moderate turbulence. Contrary to the general belief that wind shear is a short lived phenomenon which may last for a few minutes only, it has been observed that incidences of LLWS and induced moderate turbulence lasting more than 10 hrs are not at all uncommon over Chennai aircraft.

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Vidotto, A. A. „Incorporating magnetic field observations in wind models of low-mass stars“. ASTRA Proceedings 1 (06.06.2014): 19–22. http://dx.doi.org/10.5194/ap-1-19-2014.

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Abstract. Stellar winds of cool, main-sequence stars are very tenuous and difficult to observe. Despite carrying away only a small amount of the stellar mass, they are important for regulating the rotation of the star and, consequently, its activity and magnetism. As it permeates the interplanetary space, the stellar wind interacts with any exoplanet encountered on its way, until it reaches the interstellar medium (ISM). These interactions can result in complex physical processes that depend on the characteristics of the wind. To better constrain the wind characteristics, more realistic wind models that account for factors such as stellar rotation and the complex/diverse observationally-derived stellar magnetic field configurations of cool stars are required. In this paper, I present a three-dimensional model of the wind of cool stars, which adopt as boundary condition observationally-derived magnetic maps. I also discuss how these studies are relevant for, e.g., the characterisation of the interaction between stellar winds and planets/ISM, and the propagation of cosmic rays.

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Shi 施, Fangzheng 方正, Feng Yuan, Francesco Tombesi und Fu-guo Xie. „Comparing Observed Properties of Winds in Low-luminosity Active Galactic Nuclei with Theoretical Predictions“. Astrophysical Journal 985, Nr. 1 (15.05.2025): 88. https://doi.org/10.3847/1538-4357/adcc17.

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Abstract Theoretical and numerical simulations of black hole hot accretion flows have shown the ubiquitous existence of winds and predicted their properties, such as velocity and mass flux. In this paper, we have summarized from the literature the physical properties of winds launched from low-luminosity active galactic nuclei (LLAGN), which are believed to be powered by hot accretion flows, and compared them with theoretical predictions. We infer that for both ultrafast outflows and hot winds, the observed wind velocity as a function of their launching radius and the ratio between wind mass flux and black hole accretion rate show good consistency with theoretical predictions. For the prototype LLAGN M81* with abundant observational data, we have examined various observed properties of wind in detail, including velocity, mass flux of the wind, the power-law index of the radial profile of inflow rate, and the jet-to-wind power ratio. Good agreements are found with theoretical predictions, providing strong support to the theory of wind launched from hot accretion flows.

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Li, Gang, Juan Cui, Tingshan Liu, Yongqiu Zheng, Congcong Hao, Xiaojian Hao und Chenyang Xue. „Triboelectric-Electromagnetic Hybrid Wind-Energy Harvester with a Low Startup Wind Speed in Urban Self-Powered Sensing“. Micromachines 14, Nr. 2 (23.01.2023): 298. http://dx.doi.org/10.3390/mi14020298.

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Wind energy as a renewable energy source is easily available and widely distributed in cities. However, current wind-energy harvesters are inadequate at capturing energy from low-speed winds in urban areas, thereby limiting their application in distributed self-powered sensor networks. A triboelectric–electromagnetic hybrid harvester with a low startup wind speed (LSWS-TEH) is proposed that also provides output power within a wide range of wind speeds. An engineering-implementable propeller design method is developed to reduce the startup wind speed of the harvester. A mechanical analysis of the aerodynamics of the rotating propeller is performed, and optimal propeller parameter settings are found that greatly improved its aerodynamic torque. By combining the high-voltage output of the triboelectric nanogenerator under low-speed winds with the high-power output of the electromagnetic generator under high-speed winds, the harvester can maintain direct current output over a wide wind-speed range after rectification. Experiments show that the harvester activates at wind speeds as low as 1.2 m/s, powers a sensor with multiple integrated components in 1.7 m/s wind speeds, and drives a Bluetooth temperature and humidity sensor in 2.7 m/s wind speeds. The proposed small, effective, inexpensive hybrid energy harvester provides a promising way for self-powered requirements in smart city settings.

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Sukrurkdee, Nantasak, Punyawee Bumroongrads, Peerapol Sangsawat und Chawannat Jaroenkhasemmeesuk. „Designing and Developing of Savonius Wind Turbine for Efficiency Improvement in Low-Speed Wind Sources“. Journal of Clean Energy Technologies 7, Nr. 6 (November 2019): 77–80. http://dx.doi.org/10.18178/jocet.2019.7.6.513.

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Tollinger, Mathias, Rune Graversen und Harald Johnsen. „High-Resolution Polar Low Winds Obtained from Unsupervised SAR Wind Retrieval“. Remote Sensing 13, Nr. 22 (18.11.2021): 4655. http://dx.doi.org/10.3390/rs13224655.

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High-resolution sea surface observations by spaceborne synthetic aperture radar (SAR) instruments are sorely neglected resources for meteorological applications in polar regions. Such radar observations provide information about wind speed and direction based on wind-induced roughness of the sea surface. The increasing coverage of SAR observations in polar regions calls for the development of SAR-specific applications that make use of the full information content of this valuable resource. Here we provide examples of the potential of SAR observations to provide details of the complex, mesoscale wind structure during polar low events, and examine the performance of two current wind retrieval methods. Furthermore, we suggest a new approach towards accurate wind vector retrieval of complex wind fields from SAR observations that does not require a priori wind direction input that the most common retrieval methods are dependent on. This approach has the potential to be particularly beneficial for numerical forecasting of weather systems with strong wind gradients, such as polar lows.

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Ham, Yoo-Geun, Jong-Seong Kug und Mi-Jung Lim. „Rectification Feedback of High-Frequency Atmospheric Variability into Low-Frequency Zonal Flows in the Tropical Pacific“. Journal of Climate 25, Nr. 14 (15.07.2012): 5088–101. http://dx.doi.org/10.1175/jcli-d-11-00303.1.

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Abstract In this study, the rectification process of high-frequency (HF) zonal-wind variability on the low-frequency (LF) zonal wind is investigated through an idealized experiment using an atmospheric general circulation model (AGCM). Through an idealized AGCM experiment with a fixed SST boundary forcing, it is shown that there is positive (negative) correlation between HF (2–90-day period) zonal-wind variance and LF (3-month average) zonal wind where the HF zonal-wind variance is positively (negatively) skewed because the stronger HF westerly (easterly) wind events than HF easterly (westerly) wind events induce a residual westerly (easterly), and it results in an additional rectified LF westerly (easterly) anomaly. This means that, over regions with positively skewed HF zonal winds, LF westerly anomalies are generated due to the residuals of the HF zonal winds. It implies that the LF zonal wind can be generated through internal processes of the atmosphere without external forcing and the interaction between LF and HF is not a one-way process from LF to HF but, rather, a two-way interaction process.

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Quint, Daphne, Julie K. Lundquist und David Rosencrans. „Simulations suggest offshore wind farms modify low-level jets“. Wind Energy Science 10, Nr. 1 (14.01.2025): 117–42. https://doi.org/10.5194/wes-10-117-2025.

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Abstract. Offshore wind farms are scheduled to be constructed along the East Coast of the US in the coming years. Low-level jets (LLJs) – layers of relatively fast winds at low altitudes – also occur frequently in this region. Because LLJs provide considerable wind resources, it is important to understand how LLJs might change with turbine construction. LLJs also influence moisture and pollution transport; thus, the effects of wind farms on LLJs could also affect the region’s meteorology. In the absence of observations or significant wind farm construction as yet, we compare 1 year of simulations from the Weather Research and Forecasting (WRF) model with and without wind farms incorporated, focusing on locations chosen by their proximity to future wind development areas. We develop and present an algorithm to detect LLJs at each hour of the year at each of these locations. We validate the algorithm to the extent possible by comparing LLJs identified by lidar, constrained to the lowest 200 m, to WRF simulations of these very low LLJs (vLLJs). In the NOW-WAKES simulation data set, we find offshore LLJs in this region occur about 25 % of the time, most frequently at night, in the spring and summer months, in stably stratified conditions, and when a southwesterly wind is blowing. LLJ wind speed maxima range from 10 m s−1 to over 40 m s−1. The altitude of maximum wind speed, or the jet “nose”, is typically 300 m above the surface, above the height of most profiling lidars, although several hours of vLLJs occur in each month in the data set. The diurnal cycle for vLLJs is less pronounced than for all LLJs. Wind farms erode LLJs, as LLJs occur less frequently (19 %–20 % of hours) in the wind farm simulations than in the no-wind-farm (NWF) simulation (25 % of hours). When LLJs do occur in the simulation with wind farms, their noses are higher than in the NWF simulation: the LLJ nose has a mean altitude near 300 m for the NWF jets, but that nose height moves higher in the presence of wind farms, to a mean altitude near 400 m. Rotor region (30–250 m) wind veer is reduced across almost all months of the year in the wind farm simulations, while rotor region wind shear is similar in both simulations.

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Kamiakito, Noboru, Masayuki Shimura, Toshikazu Osafune, Takashi Nomura, Hiroshi Hasebe, Hiroshi Iwabuki und Kimikazu Ikeya. „Wind Noise Estimation Method in Low-Frequency Sound Measurement in Windy Outdoor Environment“. INTER-NOISE and NOISE-CON Congress and Conference Proceedings 268, Nr. 4 (30.11.2023): 4671–82. http://dx.doi.org/10.3397/in_2023_0664.

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It is generally known that low-frequency sound is affected by natural winds when measured on-site. In this paper, the estimation method of wind noise by wind tunnel and outdoor natural wind has been examined step by step. Firstly, wind tunnel experiments were conducted to confirm the relationship between wind velocity time average values and turbulence intensity, and to create the estimation fornula. Secondary, the field experiment was conducted using a low-frequency sound generator as a sound source, and the different results between the wind tunnel experiment and outdoor experiment were discovered. Then, we accumulated the field data in different roughness divisions and tried to create the wind noise estimation fornula at each point. As a result, we considered the different results according to the roughness division and obtained the results that it is possible to estimate the wind noise by using the proposed estimation fornula.

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Syed, Abdul Haseeb, und Jakob Mann. „Simulating low-frequency wind fluctuations“. Wind Energy Science 9, Nr. 6 (25.06.2024): 1381–91. http://dx.doi.org/10.5194/wes-9-1381-2024.

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Abstract. Large-scale flow structures are vital in influencing the dynamic response of floating wind turbines and wake meandering behind large offshore wind turbines. It is imperative that we develop an inflow wind turbulence model capable of replicating the large-scale and low-frequency wind fluctuations occurring in the marine atmosphere since the current turbulence models do not account well for this phenomenon. Here, we present a method to simulate low-frequency wind fluctuations. This method employs the two-dimensional (2D) spectral tensor for low-frequency, anisotropic wind fluctuations presented by Syed and Mann (2024) to generate stochastic wind fields. The simulation method generates large-scale 2D spatial wind fields for the longitudinal u and lateral v wind components, which can be converted into a frequency domain using Taylor's frozen turbulence hypothesis. The low-frequency wind turbulence is assumed to be independent of the high-frequency turbulence; thus, a broad spectral representation can be obtained just by superposing the two turbulent wind fields. The method is tested by comparing the simulated and theoretical spectra and co-coherences of the combined low- and high-frequency fluctuations. Furthermore, the low-frequency wind fluctuations can also be subjected to anisotropy. The resulting wind fields from this method can be used to analyze the impact of low-frequency wind fluctuations on wind turbine loads and dynamic response and to study the wake meandering behind large offshore wind farms.

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Valiev, M., R. Stepanov, V. Pakhov, M. Salakhov, V. Zherekhov und G. N. Barakos. „Analytical and experimental study of the integral aerodynamic characteristics of low-speed wind turbines“. Aeronautical Journal 118, Nr. 1209 (November 2014): 1229–44. http://dx.doi.org/10.1017/s0001924000009957.

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Abstract This paper proposes a new wind turbine concept suitable for low-speed winds. The design is studied using a combination of wind-tunnel experimentation and aerodynamic theory. After processing the experimental results, and after comparison with theory, the optimal conditions for the operation of the turbine are identified. Experimental and theoretical results suggest that the design offers a realistic alternative to conventional horizontal axis wind turbines. In addition, the proposed turbine has good power efficiency at low wind speeds, and is suitable for deployment in areas not yet favoured by wind farm developers.

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Xue, Lin, Ying Li und Sen Yao. „A Statistical Analysis of Tropical Cyclone-Induced Low-Level Winds near Taiwan Island“. Atmosphere 14, Nr. 4 (14.04.2023): 715. http://dx.doi.org/10.3390/atmos14040715.

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Using ERA5 reanalysis data and the tropical cyclone (TC) best track datasets from the China Meteorological Administration and Joint Typhoon Warning Center (from 1979 to 2021), TC-induced low-level winds near Taiwan Island are statistically analyzed. This study mainly concerns TC activity, low-level wind fields around Taiwan Island under TCs, and the detailed characteristics of TC wind structure. Results show that on average, 8.3 TCs enter the study region near Taiwan Island every year mainly from May to November, with more frequent and stronger TCs on the eastern and southern sides of Taiwan Island. For TC centers located at different positions around Taiwan Island, positive and negative vertical vorticity belts alternate between Taiwan Island and the TC center. Moreover, stronger and more frequent TC-induced winds mainly occur on the eastern side of Taiwan Island and the north of Taiwan Strait. TCs to the east of Taiwan Island have stronger maximum sustained wind than those on the western side of the island. Radii of the maximum wind (RMW) for TCs around Taiwan Island range from 5 to 90 nautical mile (nm, 9.3 to 116.7 km) with a mean value of 24.7 nm (44.4 km). Moreover, the RMWs of TCs are the largest (smallest) when the TC centers are located to the southwest (east) of the island. In addition, the outer sizes of TC winds vary from 52 to 360 nm (17.2 to 666.7 km) in the study region, with 187.4 nm (347.1 km) on average, and smaller values for TCs on the western side of the island. The average radii of severe winds, including R34, R50, and R64, are largest in the northeast quadrant and smallest in the southwest quadrant of the TC. The higher the specific wind speed is, the smaller the TC radius and the more symmetric its wind circle. These statistical results may provide references for TC gale forecasting and wind-resistant design for offshore engineering to mitigate TC-induced wind hazards.

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Ishida, Yasuyuki, Akihito Yoshida, Shuhei Kamata, Yuta Yamane und Akashi Mochida. „Wind Tunnel Experiments on Interference Effects of a High-Rise Building on the Surrounding Low-Rise Buildings in an Urban Block“. Wind 3, Nr. 1 (21.02.2023): 97–114. http://dx.doi.org/10.3390/wind3010007.

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High-rise buildings cause accelerated winds around them. However, the interference effects of high-rise buildings on the surrounding low-rise buildings in urban blocks have not been evaluated. This study investigated the wind pressure coefficients on the roofs and walls of low-rise buildings surrounding a high-rise building through wind tunnel experiments. Seventy-two wind directions were considered from 0° to 355° in 5° increments, and the influence of the wind direction on the wind pressure coefficients of surrounding buildings was evaluated. At a 30° wind direction angle, the positive and negative peak wind pressure coefficients occurred in a low-rise building at the leeward side of the high-rise building. The positive peak pressure, approximately 1.4 times that without a nearby high-rise building, occurred at the windward corner on the front wall of a low-rise building. The negative peak value, approximately three times that without a nearby high-rise building, was observed at the windward edge on the roof of a low-rise building. Thus, accelerated winds caused by high-rise buildings may result in unexpected damage to the surrounding low-rise buildings.

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Hendriana, Dena, Eka Budiarto, Alexander Clements und Arko Djajadi. „Design comparison of wind turbines for low wind speed“. ICONIET PROCEEDING 2, Nr. 3 (13.02.2019): 222–29. http://dx.doi.org/10.33555/iconiet.v2i3.36.

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Wind energy is one of the potential renewable energy, but the applications have to beadjusted to the available wind characteristic in the area. In Indonesia, the wind speed is inaverage not very high, only around 4 m/s. Therefore the wind turbine design have to be adjustedfor usage in Indonesia. In this research, two wind turbine designs are compared. One design isof the form Horizontal-Axis Wind Turbine (HAWT) and the other is of the form Vertical-AxisWind Turbine (VAWT). Both designs are optimized for wind speed of 4 m/s. The comparisonsare done using computer simulation software OpenFOAM. The result shows VAWT design canproduce similar power with smaller turbine dimension than the HAWT design.

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Maryon, R. H. „Determining cross-wind variance for low frequency wind Meander“. Atmospheric Environment 32, Nr. 2 (Januar 1998): 115–21. http://dx.doi.org/10.1016/s1352-2310(97)00325-7.

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Mortarini, Luca, Michel Stefanello, Gervasio Degrazia, Debora Roberti, Silvia Trini Castelli und Domenico Anfossi. „Characterization of Wind Meandering in Low-Wind-Speed Conditions“. Boundary-Layer Meteorology 161, Nr. 1 (02.06.2016): 165–82. http://dx.doi.org/10.1007/s10546-016-0165-6.

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Alizadeh Choobari, O., P. Zawar-Reza und A. Sturman. „Low level jet intensification by mineral dust aerosols“. Annales Geophysicae 31, Nr. 4 (05.04.2013): 625–32. http://dx.doi.org/10.5194/angeo-31-625-2013.

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Abstract. Modification of the intensity of a low level jet (LLJ) and near-surface wind speed by mineral dust is important as it has implications for dust emission and its long-range transport. Using the Weather Research and Forecasting with Chemistry (WRF/Chem) regional model, it is shown that direct radiative forcing by mineral dust reduces temperature in the lower atmosphere, but increases it in the layers aloft. The surface cooling is shown to be associated with a reduction of turbulent kinetic energy (TKE) and hence vertical mixing of horizontal momentum. Changes in the vertical profile of temperature over the regions that are under the influence of a LLJ are shown to result in an intensification of the LLJ and near-surface wind speed, but a decrease of winds aloft. These changes in the wind speed profile differ from results of previous research which suggested a decrease of wind speed in the lower atmosphere and its increase in the upper boundary layer.

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Warrick, Douglas R., Tyson L. Hedrick, Andrew A. Biewener, Kristen E. Crandell und Bret W. Tobalske. „Foraging at the edge of the world: low-altitude, high-speed manoeuvering in barn swallows“. Philosophical Transactions of the Royal Society B: Biological Sciences 371, Nr. 1704 (26.09.2016): 20150391. http://dx.doi.org/10.1098/rstb.2015.0391.

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While prior studies of swallow manoeuvering have focused on slow-speed flight and obstacle avoidance in still air, swallows survive by foraging at high speeds in windy environments. Recent advances in field-portable, high-speed video systems, coupled with precise anemometry, permit measures of high-speed aerial performance of birds in a natural state. We undertook the present study to test: (i) the manner in which barn swallows ( Hirundo rustica ) may exploit wind dynamics and ground effect while foraging and (ii) the relative importance of flapping versus gliding for accomplishing high-speed manoeuvers. Using multi-camera videography synchronized with wind-velocity measurements, we tracked coursing manoeuvers in pursuit of prey. Wind speed averaged 1.3–2.0 m s −1 across the atmospheric boundary layer, exhibiting a shear gradient greater than expected, with instantaneous speeds of 0.02–6.1 m s −1 . While barn swallows tended to flap throughout turns, they exhibited reduced wingbeat frequency, relying on glides and partial bounds during maximal manoeuvers. Further, the birds capitalized on the near-earth wind speed gradient to gain kinetic and potential energy during both flapping and gliding turns; providing evidence that such behaviour is not limited to large, fixed-wing soaring seabirds and that exploitation of wind gradients by small aerial insectivores may be a significant aspect of their aeroecology. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight'.

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Tanasheva, N. K. „INVESTIGATION OF THE AERODYNAMIC FORCES OF A TRIANGULAR WIND TURBINE BLADE FOR THE LOW WIND SPEEDS“. Eurasian Physical Technical Journal 18, Nr. 4 (38) (21.12.2021): 59–64. http://dx.doi.org/10.31489/2021no4/59-64.

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This article investigates the aerodynamic characteristics and finds the critical angle of attack of a triangular sail blade of a wind turbine for low wind speeds. For this purpose, a triangular sail blade of various parameters has been developed. The prototype is made of metal frame rods, the material of the triangular sail blade consists of a light and durable material (silk), one end of which is fixed to the top of the frame with a strong thread and support rods and bearing with an inner diameter of 8 mm. A sail blade differs from other blades in that the sails are made with the ability to change the angle of attack using a movable thread. To determine the critical angle of attack, the aerodynamic forces of the sail blade were investigated at different angles of attack 00 ; 150 ; 300 ; 450 , 600 ; 750 ; 900 . From the data analysis, it was found that the critical angle of attack is 150 , at which the value of the lift is maximum. Furthermore, at the critical angle of attack, the dependences of the lift and drag force on the air flow velocity were established, the value of which varied from 4 to 12 m/s.

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Clarizia, Maria Paola, und Christopher S. Ruf. „Bayesian Wind Speed Estimation Conditioned on Significant Wave Height for GNSS-R Ocean Observations“. Journal of Atmospheric and Oceanic Technology 34, Nr. 6 (Juni 2017): 1193–202. http://dx.doi.org/10.1175/jtech-d-16-0196.1.

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AbstractSpaceborne Global Navigation Satellite System reflectometry observations of the ocean surface are found to respond to components of roughness forced by local winds and to a longer wave swell that is only partially correlated with the local wind. This dual sensitivity is largest at low wind speeds. If left uncorrected, the error in wind speeds retrieved from the observations is strongly correlated with the significant wave height (SWH) of the ocean. A Bayesian wind speed estimator is developed to correct for the long-wave sensitivity at low wind speeds. The approach requires a characterization of the joint probability of occurrence of wind speed and SWH, which is derived from archival reanalysis sea-state records. The Bayesian estimator is applied to spaceborne data collected by the Technology Demonstration Satellite-1 (TechDemoSat-1) and is found to provide significant improvement in wind speed retrieval at low winds, relative to a conventional retrieval that does not account for SWH. At higher wind speeds, the wind speed and SWH are more highly correlated and there is much less need for the correction.

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Shtanko, Oleksandr, Maryna Litvinova, Iryna Zorina, Svitlana Karpova und Roman Avdiunin. „Improving the oscillating wind turbine model“. Eastern-European Journal of Enterprise Technologies 3, Nr. 8 (123) (30.06.2023): 46–53. http://dx.doi.org/10.15587/1729-4061.2023.281228.

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Disadvantages in the structure of the most common rotary wind generators limit their use. This motivates the development of alternative types of wind turbines, the most promising of which are oscillating wind generators. The object of the study is the structure of an oscillating type wind generator, which provides self-oscillating movement of the blade-wing. The design of the wind generator uses a modified wing shape to provide maximum lift. For this purpose, added elements are the tip and flap, which affect the shape of the wing, its angle of attack, and regulate the direction of the lifting force. The principle of attaching the tip and flap to the wing using spiral springs has been developed. The structure also includes locking magnets that affect the movement of the wing during a turn. The mechanism that drives the self-oscillating mode of operation of the wind turbine was described. This mode occurs under the action of the inertial force of the movement of the wing, the force of elasticity, the repulsive force of the magnets, and the pressure force of the air flow. A computer simulation of the wind generator was carried out using the Ansys CFX software package. The model of the flow around an absolutely rigid body at small values of the Reynolds number was applied. The resulting dynamics of the horizontal movement of the wing of the wind turbine make it possible to use it for energy generation already at a wind speed of 2 m/s. The low cost of the wing and the automatic regulation of its movement make it possible to install many wings to increase the power of the wind generator. Thus, the improved wind turbine is low-cost, harmless to birds, has self-regulation of wing movement and can use the low-speed component of the wind, which significantly expands the geography of its operation. It is possible to transfer the proposed technological solutions for the construction of hydroelectric generators

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Kudritzki, Rolf-Peter. „Line driven winds, ionizing fluxes and UV-spectra of hot stars at extremely low metalIicity“. Symposium - International Astronomical Union 212 (2003): 325–33. http://dx.doi.org/10.1017/s0074180900212394.

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Wind models of very massive stars with metallicities in a range from 10–4-1.0 Z⊙ are presented using a new treatment of radiation driven winds with depth dependent radiative force multipliers and a comprehensive list of more than two million of spectral lines in non-LTE. The models yield mass-loss rates, wind velocities, wind momenta and wind energies as a function of metallicity and can be used to discuss the influence of stellar winds on the evolution of very massive stars in the early universe and on the interstellar medium in the early phases of galaxy formation. It is shown that the normal scaling laws, which predict stellar mass-loss rates and wind momenta to decrease as a power law with metal abundance break down at a certain threshold. The new wind models are applied to calculate ionizing fluxes and observable UV-spectra of very massive stars as a function of metallicity using the wm-basic code developed by Pauldrach et al. (2001), and the efffects of metallicity are discussed.

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Yohana, Eflita, MSK Tony Suryo U, Binawan Luhung, Mohamad Julian Reza und M. Badruz Zaman. „Experimental Study of Wind Booster Addition for Savonius Vertical Wind Turbine of Two Blades Variations Using Low Wind Speed“. E3S Web of Conferences 125 (2019): 14003. http://dx.doi.org/10.1051/e3sconf/201912514003.

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The Wind turbine is a tool used in Wind Energy Conversion System (WECS). The wind turbine produces electricity by converting wind energy into kinetic energy and spinning to produce electricity. Vertical Axis Wind Turbine (VAWT) is designed to produce electricity from winds at low speeds. Vertical wind turbines have 2 types, they are wind turbine Savonius and Darrieus. This research is to know the effect of addition wind booster to Savonius vertical wind turbine with the variation 2 blades and 3 blades. Calculation the power generated by wind turbine using energy analysis method using the concept of the first law of thermodynamics. The result obtained is the highest value of blade power in Savonius wind turbine without wind booster (16.5 ± 1.9) W at wind speed 7 m/s with a tip speed ratio of 1.00 ± 0.01. While wind turbine Savonius with wind booster has the highest power (26.3 ± 1.6) W when the wind speed of 7 m/s with a tip speed ratio of 1.26 ± 0.01. The average value of vertical wind turbine power increases Savonius after wind booster use of 56%.

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Hughes, Christopher P., und Dana E. Veron. „Characterization of Low-Level Winds of Southern and Coastal Delaware“. Journal of Applied Meteorology and Climatology 54, Nr. 1 (Januar 2015): 77–93. http://dx.doi.org/10.1175/jamc-d-14-0011.1.

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AbstractWinds across the Delaware Peninsula transport pollutants, modify the temperature, and play a critical role within the state’s agricultural and tourism industries. The low-level winds inland and near Delaware’s coastline are characterized using observations from eight meteorological stations operated by the Delaware Environmental Observing System and the National Data Buoy Center from 2005 through 2012. The low-level winds have pronounced dominant directions during the summer (southwest/southeast) and winter (northwest) seasons, with the greatest spatial and temporal variability occurring in the summer. This inhomogeneity was further investigated with a set of simulations of the low-level winds over the Delaware Bay and surrounding landmass using the Weather Research and Forecasting Model for a subset of days from 2006 through 2012. The model was run with three nests, with the inner nest having a 2-km horizontal resolution. The randomly selected days were organized by synoptic type and season. Mesoscale wind events such as the sea-breeze circulation introduce significant variability in the local wind field of coastal Delaware—an effect that is seen in both observed and modeled data. Southerly winds off Delaware’s coast frequently shift counterclockwise up the Delaware Bay in alignment with the bay coastline. Long-term data from station B44009 (1984–2012) indicate a May decrease (0.03 m s−1 yr−1; significance p = 0.026) and an October increase (0.04 m s−1 yr−1; p = 0.006) of the mean wind speed. Results suggest that the local wind regime is multifaceted and contains significant seasonal, diurnal, and spatial variations.

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HOSOMI, Masao, und Kazuyoshi KOBA. „The Low Speed Wind Tunne“. Wind Engineers, JAWE 1993, Nr. 54 (1993): 19–22. http://dx.doi.org/10.5359/jawe.1993.19.

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Greenblatt, David. „Unsteady Low-Speed Wind Tunnels“. AIAA Journal 54, Nr. 6 (Juni 2016): 1817–30. http://dx.doi.org/10.2514/1.j054590.

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42

Tomaru, Ryota, Chris Done, Ken Ohsuga, Mariko Nomura und Tadayuki Takahashi. „The thermal-radiative wind in low-mass X-ray binary H1743−322: radiation hydrodynamic simulations“. Monthly Notices of the Royal Astronomical Society 490, Nr. 3 (03.10.2019): 3098–111. http://dx.doi.org/10.1093/mnras/stz2738.

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Abstract Blueshifted absorption lines are seen in high inclination black hole binary systems in their disc-dominated states, showing these power an equatorial disc wind. While some contribution from magnetic winds remain a possibility, thermal and thermal-radiative winds are expected to be present. We show results from radiation hydrodynamic simulations that show that the additional radiation force from atomic features (bound–free and lines) is important along with electron scattering. Together, these increase the wind velocity at high inclinations, so that they quantitatively match the observations in H1743−322, unlike purely thermal winds that are too slow. We highlight the role played by shadowing of the outer disc from the (subgrid) inner disc Compton heated layer, and show that the increase in shadow from the higher Compton temperature after the spectral transition to the hard state leads to strong suppression of the wind. Thermal-radiative winds explain all of the spectral features (and their disappearance) in this simplest wind system and magnetic winds play only a minor role. We speculate that thermal-radiative winds can explain all the spectral features seen in the more complex (larger disc size) binaries, GRO J1655−40 and GRS 1915+105, without requiring magnetic winds.

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Kim, YC, Y. Tamura, A. Yoshida, T. Ito, W. Shan und Q. Yang. „Experimental investigation of aerodynamic vibrations of solar wing system“. Advances in Structural Engineering 21, Nr. 15 (07.05.2018): 2217–26. http://dx.doi.org/10.1177/1369433218770799.

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The general characteristics of aerodynamic vibrations of a solar wing system were investigated through wind tunnel tests using an aeroelastic model under four oncoming flows. In total, 12 solar panels were suspended by cables and orientated horizontally. Distances between panels were set constant. Tests showed that the fluctuating displacement increases proportionally to the square of the mean wind speed for all wind directions in boundary-layer flows. Larger fluctuating displacements were found for boundary-layer flows with larger power-law indices. Under low-turbulence flow, the fluctuating displacement increased proportionally to the square of the mean wind speed for wind directions between 0° and 30°, but an instability vibration was observed at high mean wind speed for wind directions larger than 40°. And when the wind direction was larger than 60°, a limited vibration was observed at low mean wind speed and the instability vibration was also observed at high mean wind speed. Fluctuating displacements under grid-generated flow showed a similar trend to that of the boundary-layer flows, although the values became much smaller.

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Caton Harrison, Thomas, Stavroula Biri, Thomas J. Bracegirdle, John C. King, Elizabeth C. Kent, Étienne Vignon und John Turner. „Reanalysis representation of low-level winds in the Antarctic near-coastal region“. Weather and Climate Dynamics 3, Nr. 4 (02.12.2022): 1415–37. http://dx.doi.org/10.5194/wcd-3-1415-2022.

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Abstract. Low-level easterly winds encircling Antarctica help drive coastal currents which modify transport of circumpolar deep water to ice shelves, and the formation and distribution of sea ice. Reanalysis datasets are especially important at high southern latitudes where observations are few. Here, we investigate the representation of the mean state and short-term variability of coastal easterlies in three recent reanalyses, ERA5, MERRA-2 and JRA-55. Reanalysed winds are compared with summertime marine near-surface wind observations from the Advanced Scatterometer (ASCAT) and surface and upper air measurements from coastal stations. Reanalysis coastal easterlies correlate highly with ASCAT (r= 0.91, 0.89 and 0.85 for ERA5, MERRA-2 and JRA-55, respectively) but notable wind speed biases are found close to the coastal margins, especially near complex orography and at high wind speeds. To characterise short-term variability, 12-hourly reanalysis and coastal station winds are composited using self-organising maps (SOMs), which cluster timesteps under similar synoptic and mesoscale influences. Reanalysis performance is sensitive to the flow configuration at stations near steep coastal slopes, where they fail to capture the magnitude of near-surface wind speed variability when synoptic forcing is weak and conditions favour katabatic forcing. ERA5 exhibits the best overall performance, has more realistic orography, and a more realistic jet structure and temperature profile. These results demonstrate the regime behaviour of Antarctica's coastal winds and indicate important features of the coastal winds which are not well characterised by reanalysis datasets.

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Singh, Raj Kumar, Sajal Garg und Lohit Gudivada. „Design and Experimental Analysis of a 200W Micro Wind Turbine“. International Journal of Advance Research and Innovation 4, Nr. 2 (2016): 100–104. http://dx.doi.org/10.51976/ijari.421616.

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Majority of the regions in India are characterized by moderate and low wind regimes. These regions have variable and gusty winds. Our low-wind energy turbine addresses this problem and is capable of providing power to millions of people not connected to the grid in low wind conditions. Our objective is to design a suitable wind turbine applicable in low speed regions extracting maximum power output. Our team aims to take on the challenge of improving wind turbine efficiencies, at low to medium wind speeds, to reduce environmental impact and encourage adoption of wind energy at domestic and commercial building rooftops and small distributed systems. Blade Element Momentum theory was adopted to find the suitable parameters at the required wind speeds. Tools like Q-Blade and X-foil were used to optimize the CAD model of the blade. A customized Wind tunnel was fabricated by the team to validate the practical results against the theoretical ones. Rapid Prototyping technique of 3-D printing was used to manufacture the blades. Final results establish a close relationship between the theoretical and experimental values.

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Pierini, Stefano. „Low-Frequency Variability, Coherence Resonance, and Phase Selection in a Low-Order Model of the Wind-Driven Ocean Circulation“. Journal of Physical Oceanography 41, Nr. 9 (01.09.2011): 1585–604. http://dx.doi.org/10.1175/jpo-d-10-05018.1.

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Abstract In this paper, a low-order spectral quasigeostrophic (QG) model of the wind-driven ocean circulation is derived and used to analyze the low-order character of the intrinsic low-frequency variability of the midlatitude double-gyre ocean circulation and of the related coherence resonance and phase selection phenomena. The model includes an exponential in the basis functions that allows for westward intensification, retains only four modes in the Galerkin projection, is defined in a rectangular domain, and is forced by deterministic and stochastic winds, thus extending previous low-order QG ocean models. The solution under steady forcing is first obtained, and the results are also analyzed in terms of dynamical systems theory. A homoclinic bifurcation (with the wind amplitude chosen as the control parameter) leads to intrinsic decadal relaxation oscillations (ROs) similar in several respects to those obtained with primitive equation models. The system is then forced with an additional red noise wind, and, in a parameter range preceding the global bifurcation, a coherence resonance scenario very similar to the one found with a primitive equation model of the Kuroshio Extension is obtained: this suggests that such a phenomenon is of low-order character. To study the RO excitation mechanism, a method denoted as phase selection is proposed. The system is forced with additional fictitious periodic winds that produce an emergence of ROs yielding strong phase dependence with the periodic forcing. The subsequent analysis reveals the character of the wind forcing that is most likely to excite a RO. All the results are discussed within the general framework of climate dynamics.

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Shitzer, Avraham, und Richard de Dear. „Inconsistencies in the “New” Windchill Chart at Low Wind Speeds“. Journal of Applied Meteorology and Climatology 45, Nr. 5 (01.05.2006): 787–90. http://dx.doi.org/10.1175/jam2373.1.

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Abstract An apparent error was detected in the calculation of windchill equivalent temperatures (WCETs) in the “new” chart and corresponding equation that were adopted in 2001 by the weather services in the United States and Canada. The problem is caused by significant discontinuities in WCETs at the assumed “calm” wind speed condition of 1.34 m s−1. As a result, published WCETs are not equal to, as they should be by definition, but are lower than air temperatures at the assumed calm wind speed condition. This inconsistency further propagates to higher wind speeds beyond the assumed calm condition. In this paper, a straightforward correction is proposed to circumvent these inconsistencies of the new windchill. The proposed correction makes this transition gradual rather than abrupt by applying it to the expression used for estimating the effects of wind on the convective heat exchange coefficient between humans and their cold and windy environment.

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Kalaga, Sriram, Pranava C. Jayanti und Aruna Kalyanaraman. „Wind and Ice Loads on Transmission Structures: A State of the Art Review“. European Journal of Theoretical and Applied Sciences 2, Nr. 6 (01.11.2024): 630–42. https://doi.org/10.59324/ejtas.2024.2(6).56.

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Climactic loads imposed on transmission conductors include ice, wind and ice concurrent with wind. Structural reliability under these loads depends on the statistical variation of applied loads and associated resistances. Analytical treatment for combined wind and ice effects is difficult given the different probability distribution functions of ice thickness and wind speeds. Existing design codes and guidelines are somewhat inconsistent in defining what actually applies for low and extreme winds. This paper reviews the present state of the art in research on wind speed and ice thickness distributions, associated risks, forecasting models, MRIs (recurrence intervals), field-based weather records and databases. The main inference from this study is that low to moderate winds should be modeled with a probability distribution different from that of extreme or hurricane winds. Reasonable reliability design procedures for combined ice and wind loads can be developed for utility structures with proper statistical assumptions.

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Bandyopadhyay, G. „Low speed aerodynamics of canard configurations“. Aeronautical Journal 93, Nr. 921 (Januar 1989): 22–28. http://dx.doi.org/10.1017/s0001924000016651.

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SummaryNumerical methods have been developed for the prediction of aerodynamic characteristics of canard wing configurations by considering both attached and separated flow over the canard surface; the flow over the main wing surface is always assumed to be attached. Experimental tests have been conducted in a low speed wind tunnel to compare the theoretical results predicted by the numerical methods. The comparison shows good agreement up to approximately 16° incidence.

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King, J. C. „Low-level wind profiles at an Antarctic coastal station“. Antarctic Science 1, Nr. 2 (Juni 1989): 169–78. http://dx.doi.org/10.1017/s095410208900026x.

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Wind and temperature profiles in the lowest 2000 m of the atmosphere at Halley (75°35′S, 26°50′W) have been analysed. Surface winds blow most frequently from the sector 090° ± 45° but the 2000 m wind direction is much more evenly distributed and appears to be determined by synoptic-scale pressure gradients. A simple one-dimensional boundary layer model, which includes the effects of stably-stratified air overlying a sloping surface, is able to reproduce some of the features of the observed profiles.

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