Environmental Wind Engineering And Design Of Wind Energy Structures

~ SpringerWienNewYork CISM COURSES AND LECTURES Series Editors: The Rectors Friedrich Pfe f iffe f r - Munich Franz G. Rammerstorfer f - Wien Jean Salençon - Palaiseau The Secretary General Executive Editor The series presents lecture notes, monographs, edited works and and Applied Mathematics. ! and technical community results obtained in some of the activities " #$ % % & %'( )'*(%+'*/ '() 0+) 1*'% */ % ' + ) *'2 / ( ) ' & 345 '6%)+' '(*/ 7%'2 '8%' )%'8 *'2 2 %8' +0 7%'2 ' )89 () ( ) 2%( 2 9 1*)*/* + & *'%+(+ + /+ *)% (+(/ '%6 ) %(9 +0 (1 */+'%;% 8) /* 2%+ +))% '%6 ) %(9 +0 0/+) ' 0%) ' 5 m/s is less than 20% of the time (Pendwarden and Wise 1975). Recognizing the importance of frequency of occurrence along with the magnitude of wind speeds, Figures 6, 7, and 8 provide threshold mean wind speeds for various types of activity as functions of theaverage annual number of storm occurrences. Naturally the mean wind speed threshold level drops significantly as the yearly average number of occurrences increases. Utilization of mean wind speeds as comfort criteria for pedestrian-level winds has been questioned by the wind engineering community. In fact, the most prevailing opinion seeks an effective wind speed, which is related to the gustiness of the wind, to be used for that purpose. Such effective speeds can be derived from the following equation expressing their outcome in terms of the mean and a number (ranging from 1 to 3) of standard deviations of the wind speed: V e V (1 v' 2 1/ 2 V ) (1) 1/ 2 where ' 2 is the rms of longitudinal velocity fluctuations and is a constantequal to 1~3. Figure 6. Wind tunnel exposure of people at 10-15 km/h winds. C. andC.Design Baniotopoulos of Wind Energy et al (eds), Structures Environmental Wind Engineering and Design of Win © CISM, Udine 2011 5O T. Stathopoulos Figure 7. Wind tunnel exposure of people at 20 (left) and 40 (right) km/h winds. Figure 8. Wind tunnel exposure of people at 70 km/h winds. Wind tunnel experiments and observations of pedestrian performance suggest that = 3 is the most appropriate value. Figure 9 shows acceptance criteria for wind speeds for various annual frequencies of occurrence proposed by Isyumov and Davenport (1975). Note that these criteria are different from previous criteria in that, instead of specifying a wind speed for various activities, frequencies of occurrence are specified for different wind speeds. Murakami et al. (1986) produced the wind comfort criteria described in Table 2. C. andC.Design Baniotopoulos of Wind Energy et al (eds), Structures Environmental Wind Engineering and Design of Win © CISM, Udine 2011 % X * $ 54 Figure 9. Acceptance criteria for wind speeds for various annual frequencies of occurrence, after Isyumov and Davenport (1975). Table 2. Wind environment criteria of Murakami