Specifications

Section 11. Programming Resource Library
11-29
11.5.2.1 Measured Raw Data
S
i
= horizontal wind speed
Θ
i
= horizontal wind direction
Ue
i
= east-west component of wind
Un
i
= north-south component of wind
N = number of samples
11.5.2.2 Calculations
FIGURE 11.5-1. Input Sample Vectors
In FIGURE 11.5-1, the short,
head-to-tail vectors are the input sample vectors
described by
i
s and
i
Θ
, the sample speed and direction, or by Ue
i
and Un
i
, the
east and north components of the sample vector. At the end of data storage
interval T, the sum of the sample vectors is described by a vector of magnitude
U and direction Θu. If the input sample interval is t, the number of samples in
data storage interval
T
is
t/TN
=
. The mean vector magnitude is
N/UU =
.
Scalar mean horizontal wind speed, S:
S=(Σs
i
)/N
where in the case of orthogonal sensors:
S
i
=(Ue
i
2
+Un
i
2
)
1/2
Unit vector mean wind direction, Θ1:
Θ1=Arctan (Ux/Uy)
where
Ux=(Σsin Θ
i
)/N
Uy=(Σcos Θ
i
)/N
s
n
Θ
u
s
2
North
East
U
s
1
s
3
s
4