Efficacy of Averaging Interval for Nonstationary Winds
Publication: Journal of Engineering Mechanics
Volume 140, Issue 1
Abstract
In comparison with atmospheric boundary-layer winds, which are generally regarded as stationary, windstorms such as hurricanes and thunderstorms/downbursts have strong nonstationary features characterized by rapid changes in wind speed and direction. The averaging interval associated with turbulent wind characteristics in boundary-layer winds is typically varied between 10 min and 1 h. A fixed averaging interval (FAI), which uses a constant mean to isolate the fluctuating wind component, has been effective in characterizing boundary-layer winds; however, the question remains as to whether the user-defined interval is appropriate for nonstationary winds. To address this concern, a variable averaging interval (VAI) scheme is proposed. For better understanding of the characteristics of nonstationary winds, traditional FAI methods are compared with alternative FAI approaches that use time-varying means and the proposed VAI approaches. In addition, the definitions for gust factor, turbulence intensity, and turbulence integral length scale are revised to ensure compatibility with the proposed schemes. Nonstationary data measured during the passage of Hurricane Lili and transient data measured during a rear-flank downdraft obtained from the 2002 thunderstorm outflow field experiment are used to examine the efficacy of FAI and VAI schemes and the associated turbulent wind characteristics.
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Acknowledgments
The authors acknowledge the financial support in part by National Science Foundation (NSF) Grant No. CMMI 09-28282 and the Global Center of Excellence at Tokyo Polytechnic University (TPU), funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. The authors also thank the Department of Atmospheric Science at Texas Tech University for the rear-flank draft (RFD) data and the Florida Coastal Monitoring Program at the University of Florida for the Hurricane Lili data used in this research.
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Information & Authors
Information
Published In
Journal of Engineering Mechanics
Volume 140 • Issue 1 • January 2014
Pages: 1 - 19
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Nov 29, 2011
Accepted: Mar 22, 2013
Published online: Dec 16, 2013
Published in print: Jan 1, 2014
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