EM 1110-2-1100 (Part II)
30 Apr 02
Example Problem II-8-1 (Continued)
Option 2: (use Equation II-8-3)
Equation II-8-3 can be applied to 3 or more complete years of data. Up to 14 years of data are available
in this example. Normally, all full years would be used together. For illustration, the following solution
treats four 3-year samples from the full record as well as the 14-year sample extending from March 1969
through February 1983. Means and standard deviations of maximum monthly wind speeds are given
in Table II-8-10.
Table II-8-10
Wind Speed Statistics
Um , m/s
σm , m/s
Years
1971-73
17.50
3.32
1974-76
16.08
4.58
1977-79
14.03
3.62
1980-82
14.03
4.02
Mar 69 - Feb 83
15.53
4.06
U25 is calculated from Equation II-8-3 for the years 1971-73 as
U25 ' Um % 0.78 σm [ ln(1225) & 0.577 ]
' Um % 4.00 σm ' 17.50 % 4.003.32 ' 30.8
m/s
Similarly, U50 is calculated from Equation II-8-3 for the years 1971-73 as
U50 ' Um % 0.78 σm [ ln(1250) & 0.577 ]
' Um % 4.54 σm ' 17.50 % 4.543.32 ' 32.6
m/s
The standard deviation of the sampling error in estimating Ur for the years 1971-73 may be calculated
from Equation II-8-4 as
σm
0.49 % 0.89 ln(12Um) % 0.67 [ln(12Um) & 0.577]2
σrm '
36
3.32
0.49 % 0.89 ln(1217.50) % 0.67 [ln(1217.50) & 0.577]2
'
36
3.32
0.49 % 0.895.347 % 0.67[5.347&0.577]2
' 20.49 0.553 ' 2.5 m/s
'
6
(Sheet 3 of 4)
Hydrodynamic Analysis and Design Conditions
II-8-23
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