The effect of wind speed averaging time on the calculation of sand drift potential: New scaling laws

2020 ◽  
Vol 544 ◽  
pp. 116373
Author(s):  
Hezi Yizhaq ◽  
Zhiwei Xu ◽  
Yosef Ashkenazy
Keyword(s):  
Wind Speed ◽  
Scaling Laws ◽  
Sand Drift ◽  
Drift Potential ◽  
Averaging Time

scholarly journals Monitoring Sand Drift Potential and Sand Dune Mobility over the Last Three Decades (Khartouran Erg, Sabzevar, NE Iran)

2021 ◽  
Vol 13 (16) ◽  
pp. 9050
Author(s):  
Mohammad Reza Rahdari ◽  
Andrés Rodríguez-Seijo
Keyword(s):  
Wind Speed ◽  
Sand Dune ◽  
Sand Dunes ◽  
Average Wind Speed ◽  
Wind Speeds ◽  
Average Wind ◽  
Sand Drift ◽  
Drift Potential ◽  
Long Time ◽  
Ne Iran

Aeolian sediments cover about 6% of the earth’s surface, of which 97% occur in arid regions, and these sediments cover about 20% of the world’s lands. Sand drifts can harm sensitive ecosystems; therefore, this research has aimed to study wind regimes and the monitoring of sand drift potential and dune mobility in the Khartouran Erg (NE Iran). The study investigated 30 years of wind speed and direction to better understand sand dune mobility processes using the Fryberger and Tsoar methods. The results of the wind regime study showed that the eastern (33.4%) and northeastern (14.3%) directions were more frequent, but the study of winds greater than the threshold (6 m/s) in winter, spring, and autumn indicated the dominance of eastern and northern wind directions. Findings of calm winds showed that winters (40.4%) had the highest frequency, and summers (15%) had the lowest frequency; the annual frequency was 30%. The average wind speed in summers was the highest (4.38 m/s), and, in the winters, it was the lowest (2.28 m/s); the annual average wind speed was 3.3 m/s. The annual drift potential (DP = 173 VU) showed that it was categorized as low class, and the winds carried sand to the southwest. The monitoring of drift potential showed that there was a sharp increase between 2003 and 2008, which could have been attributed to a change in wind speeds in the region. Unite directional index, the index of directional variability, has been alternating from 0.3 to 0.6 for 30 years. Furthermore, monitoring of sand mobility recorded a value from 0.1 to 0.4, and the lowest and highest values were registered from 0.08 to 0.9, with an average of 0.27. Finally, it can be concluded that sand dunes have been fixed for a long time, and the intensity of the mobility index is affected by climate changes.

scholarly journals Pointing Errors of Large Telescopes Due to Wind

1984 ◽  
Vol 79 ◽  
pp. 177-181
Author(s):  
Bobby L. Ulich
Keyword(s):  
Mechanical Properties ◽  
Wind Speed ◽  
Scaling Laws ◽  
Tracking Error ◽  
Structural Materials ◽  
Pointing Errors ◽  
Direct Measurements ◽  
Large Telescopes ◽  
Mirror Telescope

AbstractScaling laws are presented which show the dependence of the tracking error of large telescopes on structural materials, mechanical properties and dimensions of the mount, and wind speed. Based on direct measurements on the Multiple Mirror Telescope, predictions are made for future very large telescopes. It is shown that good tracking can be achieved most of the time even without a traditional dome to block the wind, and this may result in better images by eliminating “dome seeing”.

Fallacies of the Enthalpy Transfer Coefficient over the Ocean in High Winds

2011 ◽  
Vol 68 (7) ◽  
pp. 1435-1445 ◽  
Author(s):  
Edgar L Andreas
Keyword(s):  
Wind Speed ◽  
Latent Heat ◽  
Large Scale ◽  
Scaling Laws ◽  
Surface Fluxes ◽  
Neutral Stability ◽  
Transfer Coefficients ◽  
Wide Range ◽  
Interfacial Transfer ◽  
High Winds

Abstract Mesoscale and large-scale atmospheric models use a bulk surface flux algorithm to compute the turbulent flux boundary conditions at the bottom of the atmosphere from modeled mean meteorological quantities such as wind speed, temperature, and humidity. This study, on the other hand, uses a state-of-the-art bulk air–sea flux algorithm in stand-alone mode to compute the surface fluxes of momentum, sensible and latent heat, and enthalpy for a wide range of typical (though randomly generated) meteorological conditions over the open ocean. The flux algorithm treats both interfacial transfer (controlled by molecular processes right at the air–sea interface) and transfer mediated by sea spray. Because these two transfer routes obey different scaling laws, neutral-stability, 10-m transfer coefficients for enthalpy CKN10, latent heat CEN10, and sensible heat CHN10 are quite varied when calculated from the artificial flux data under the assumption of only interfacial transfer—the assumption in almost all analyses of measured air–sea fluxes. That variability increases with wind speed because of increasing spray-mediated transfer and also depends on surface temperature and atmospheric stratification. The analysis thereby reveals as fallacious several assumptions that are common in air–sea interaction research—especially in high winds. For instance, CKN10, CEN10, and CHN10 are not constants; they are not even single-valued functions of wind speed, nor must they increase monotonically with wind speed if spray-mediated transfer is important. Moreover, the ratio CKN10/CDN10, where CDN10 is the neutral-stability, 10-m drag coefficient, does not need to be greater than 0.75 at all wind speeds, as many have inferred from Emanuel’s seminal paper in this journal. Data from the literature and from the Coupled Boundary Layers and Air–Sea Transfer (CBLAST) hurricane experiment tend to corroborate these results.

Frequency-Response Matching to Optimize Wind-Turbine Test Data Correlation

1986 ◽  
Vol 108 (3) ◽  
pp. 246-251
Author(s):  
A. C. Hansen ◽  
T. E. Hausfeld
Keyword(s):  
Wind Speed ◽  
Transfer Function ◽  
Wind Turbine ◽  
Test Data ◽  
Wind Turbines ◽  
Power Coefficient ◽  
Wide Range ◽  
Averaging Time ◽  
Measured Response ◽  
Selection Of

Pre-averaging is often applied to wind turbine test data to improve correlation between wind speed and power output data. In the past, trial and error or intuition have been used in the selection of pre-averaging time and researchers and institutions have differed widely in their pre-averaging practice. In this paper a standardized method is proposed for selection of the optimum pre-averaging time. The method selects an averaging time such that the test data are low-pass-filtered at the same frequency as the response frequency of the test wind turbine/anemometer system. A theoretial method is provided for estimation of the wind system transfer function as a function of the anemometer location, rotor moment of inertia, the stiffness of the connection between the rotor and the electrical grid, hub height, rotor speed and wind speed. The method is based in proven theory, repeatable, easy to use and applicable to a wide range of wind turbines and test conditions. Results of the transfer function predictions are compared with the measured response of two wind systems. Agreement between the predicted and measured response is completely adequate for the purposes of the method. Example results of calculated averaging times are presented for several wind turbines. In addition, a case study is used to demonstrate the dramatic effects of test design and data analysis methods on the results of a power coefficient measurement.

Evaluation of Roofing Systems in Malaysia Based on MS 1553 BS 6399, EC1-1-4 and IS 875 Wind Codes

2014 ◽  
Vol 567 ◽  
pp. 577-582
Author(s):  
Kang Seavhai ◽  
S.P. Narayanan
Keyword(s):  
Wind Speed ◽  
Limit State ◽  
Wind Pressure ◽  
Numerical Comparison ◽  
General Area ◽  
Static Test ◽  
Pressure Coefficients ◽  
Wind Climate ◽  
Wind Pressures ◽  
Averaging Time

This paper evaluates the performance of different roofing sheet systems for different roof types using four different codes namely MS 1553, EC1-1-4, IS 875 and BS 6399. The maximum roof pressures using different codes (MS 1553, EC1-1-4, IS 875 and BS 6399) on critical and general area of the different roof types considering buildings with non-dominant opening, dominant opening and canopies have been evaluated. The maximum recommended wind speed in MS 1553 namely 33.5 m/s has been used as the reference for the numerical comparison. The major differences in the codes include averaging time for wind speed, terrain, reference height, and pressure coefficients. The study examines the conservativeness or not of the codes if used in the Malaysian context, even though they have been developed for a different wind climate and region. Further, the results of static test on different steel roofing sheets used in Malaysia using AS 1562.1 available as the limit state wind pressure capacities in the technical brochures are compared with design wind pressures for critical and interior regions of the roof for different wind zones. The suitability of a particular roofing sheet system for a particular wind zone is then assessed.

Spray Drift from Dicamba and Glyphosate Applications in a Wind Tunnel

2017 ◽  
Vol 31 (3) ◽  
pp. 387-395 ◽  
Author(s):  
Guilherme Sousa Alves ◽  
Greg R. Kruger ◽  
João Paulo A. R. da Cunha ◽  
Bruno C. Vieira ◽  
Ryan S. Henry ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Laser Diffraction ◽  
Spray Drift ◽  
Downwind Distance ◽  
Fluorescent Tracer ◽  
Drift Potential ◽  
Herbicide Treatments ◽  
Low Speed Wind Tunnel ◽  
Nozzle Type

With the recent introductions of glyphosate- and dicamba-tolerant crops, such as soybean and cotton, there will be an increase in POST-applied tank-mixtures of these two herbicides. However, few studies have been conducted to evaluate drift from dicamba applications. This study aimed to evaluate the effects of dicamba with and without glyphosate sprayed through standard and air induction flat-fan nozzles on droplet spectrum and drift potential in a low-speed wind tunnel. Two standard (XR and TT) and two air induction (AIXR and TTI) 110015 nozzles were used. The applications were made at 276 kPa pressure in a 2.2 ms−1 wind speed. Herbicide treatments evaluated included dicamba alone at 560 gaeha−1 and dicamba+glyphosate at 560+1,260 gaeha−1. The droplet spectrum was measured using a laser diffraction system. Artificial targets were used as drift collectors, positioned in a wind tunnel from 2 to 12 m downwind from the nozzle. Drift potential was determined using a fluorescent tracer added to solutions, quantified by fluorimetry. Dicamba droplet spectrum and drift depended on the association between herbicide solution and nozzle type. Dicamba alone produced coarser droplets than dicamba+glyphosate when sprayed through air induction nozzles. Drift decreased exponentially as downwind distance increased and it was reduced using air induction nozzles for both herbicide solutions.

scholarly journals Drift Evaluation of a Quadrotor Unmanned Aerial Vehicle (UAV) Sprayer: Effect of Liquid Pressure and Wind Speed on Drift Potential Based on Wind Tunnel Test

2021 ◽  
Vol 11 (16) ◽  
pp. 7258
Author(s):  
Qi Liu ◽  
Shengde Chen ◽  
Guobin Wang ◽  
Yubin Lan
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
High Efficiency ◽  
Plant Protection ◽  
Spray Drift ◽  
Liquid Pressure ◽  
Agricultural Plant ◽  
Wind Speeds ◽  
Drift Potential ◽  
Test Platform

Background: Unmanned Aerial Vehicles (UAVs) applied to agricultural plant protection is widely used, and the field of operation is expanding due to their high efficiency and pesticide application reduction. However, the work on pesticide drift lags behind the development of the UAV spraying device. Methods: We compared the spray drift potential at four liquid pressures of 2, 3, 4, and 5 bar ejected from the hydraulic nozzles mounted on a UAV test platform exposed to different wind speeds of 2, 4, and 6 m/s produced by a wind tunnel. The combination of the wind tunnel and the UAV test platform was used to obtain strict test conditions. The droplet size distribution under spray drift pressures was measured by a laser diffraction instrument. Results: Increasing the pressure leads to smaller droplet volume diameters and produced fine droplets of less than 100 µm. The deposition in the drift area was elevated at most of the sampling locations by setting higher pressure and faster wind speed. The deposition ratios were all higher than the flow ratios under three wind speeds after the adjustment of pressures. For most samples within a short drift distance (2–8 m), the drift with the rotor motor off was more than an order of magnitude higher than that with the rotor motor on at a pressure of 3 bar. Conclusions: In this study, the wind speed and liquid pressure all had a significant effect on the UAV spray drift, and the rotor wind significantly inhibited a large number of droplets from drifting further.

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