ASTM_D_5741_-_96_2011.pdf

Designation:D574196(Reapproved 2011)Standard Practice forCharacterizing Surface Wind Using a Wind Vane andRotating Anemometer1This standard is issued under the fixed designation D5741;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers a method for characterizing surfacewind speed,wind direction,peak one-minute speeds,peakthree-second and peak one-minute speeds,and standard devia-tions of fluctuation about the means of speed and direction.1.2 This practice may be used with other kinds of sensors ifthe response characteristics of the sensors,including theirsignal conditioners,are equivalent or faster and the measure-ment uncertainty of the system is equivalent or better thanthose specified below.1.3 The characterization prescribed in this practice willprovide information on wind acceptable for a wide variety ofapplications.NOTE1This practice builds on a consensus reached by the attendeesat a workshop sponsored by the Office of the Federal Coordinator forMeteorological Services and Supporting Research in Rockville,MD onOct.2930,1992.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2D1356 Terminology Relating to Sampling and Analysis ofAtmospheresD5096 Test Method for Determining the Performance of aCup Anemometer or Propeller AnemometerD5366 Test Method for Determining the Dynamic Perfor-mance of a Wind Vane3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 aerodynamic roughness length(z0,m)a character-istic length representing the height above the surface whereextrapolation of wind speed measurements,below the limit ofprofile validity,would predict the wind speed would becomezero(1).3It can be estimated for direction sectors from alandscape description.3.1.2 damped natural wavelength(d,m)a characteristicof a wind vane empirically related to the delay distance and thedamping ratio.See Test Method D5366 for test methods todetermine the delay distance and equations to estimate thedamped natural wavelength.3.1.3 damping ratio(,dimensionless)the ratio of theactual damping,related to the inertial-driven overshoot of windvanes to direction changes,to the critical damping,the fastestresponse where no overshoot occurs.See Test Method D5366for test methods and equations to determine the damping ratioof a wind vane.3.1.4 distance constant(L,m)the distance the air flowspast a rotating anemometer during the time it takes the cupwheel or propeller to reach(1 1 e)or 63%of the equilib-rium speed after a step change in wind speed.See Test MethodD5096.3.1.5 maximum operating speed(um,m/s)as related toanemometer,the highest speed as which the sensor will survivethe force of the wind and perform within the accuracyspecification.3.1.6 maximum operating speed(um,m/s)as related towind vane,the highest speed at which the sensor will survivethe force of the wind and perform within the accuracyspecification.3.1.7 standard deviation of wind direction(,degrees)the unbiased estimate of the standard deviation of winddirection samples about the mean horizontal wind direction.The circular scale of wind direction with a discontinuity atnorth may bias the calculation when the direction oscillates1This practice is under the jurisdiction ofASTM Committee D22 on Air Qualityand is the direct responsibility of Subcommittee D22.11 on Meteorology.Current edition approved Oct.1,2011.Published October 2011.Originallyapproved in 1996.Last previous edition approved in 2007 as D5741-96(2007).DOI:10.1520/D5741-96R11.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refers to the list of references at the endof this standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 about north.Estimates of the standard deviation such assuggested by(2,3)are acceptable.3.1.8 standard deviation of wind speed(u,m/s)the esti-mate of the standard deviation of wind speed samples about themean wind speed.3.1.9 startingthreshold(u0,m/s)asrelatedtoanemometer,the lowest speed at which the sensor begins toturn and continues to turn and produces a measurable signalwhen mounted in its normal position(see Test Method D5096).3.1.10 starting threshold(u0,m/s)as related to system,theindicated wind speed when the anemometer is at rest.3.1.11 starting