Study On Typhoon Gust Factor Based On Field Measurements

Typhoon strikes southeast China and causes great damages every year,asking for a higher requirement on safety of wind resistenec design. Gust factor,which is a key parameter to measure the strength of turbulence, plays animportant role in wind resistence design. This dissertation will focus on thedetermination of gust factor and its corresponding influence factors based onfield measured data in typhoon field; mainly includes the following three parts.A movable observing network for near surface typhoon field is established.This network is made up by8observing towers and has the merit of flexible andefficient. With the help of it, a simultaneous multi-point observation of typhooncould be done. Field measurement of natural wind was carried out and the windproperties like turbulence integral scale, wind spectrum, correlation coefficientand coherence function were analysised with the obtained dataA method to determine gust factor considering mean wind speed andstructure dimension effect is put forward. First the determination principle ofgust duration is achieved through the equivalence between running average filterand aerodynamic admittance (AA). Five common AAs are investigated and acomprehensive formula is got. Then, a theoretical formula of gust factor fornon-Gaussian process(harden and soften) is deduced to consider thenon-Gaussian property of natural wind, and the validity of the formula is checked.At last, data from three typhoons during2006-2008are used and the theoreticalformula revised gust factor curve for terrain A and B are presented at the end.Thus, a reasonable determination approach for gust factor has been set up.To explore the rationality and forming mechanism of some large gust factorin typhoon field,8anomalous gust factor samples and an added extreme one areselected from375field measured samples in typhoon. At first, influence factorslike positions in typhoon field, non-Gaussian and non-stationary property areinvestigated. Then a detailed research on coherent structure is carried out withwavelet transform. The changes of multi scale energy distribution, non-Gaussian,non-stationary property and gust factor values before and after the extraction ofcoherent structure are compared, showing that, turbulence intermittency causedby multi-scale coherent structure, is the root of anomalous gust factor, whilenon-Gaussian and non-stationary property of the time series are the direct causes.