WIND ENERGY SYSTEMS - Cd3wd

Chapter 3—Wind Measurements 3–35
2. The distance constant for the Climet Instruments Model WS- 011 anemometer is 1.5 m.
Equilibrium has been reached at a wind speed of 4 m/s when the wind speed suddenly
increases to 7 m/s. How long does it take for the indicated wind speed to reach 6.9 m/s?
3. The distance constant for the Climatronics Model WM-III anemometer is 2.5 m. Equilibrium
has been reached at 5 m/s when the wind speed suddenly increases to 9 m/s,
remains there for one second, and then decreases suddenly to 6 m/s, as shown in Fig. 21.
Assume that the indicated wind speed after one second, u ′ o, is the new equilibrium speed
for the time period denoted by t ′ . Assume that the anemometer has the voltage output
of Fig. 4, and that the A/D converter of Problem 1 is connected to the anemometer
and is sampling the voltage every 0.2 s starting at t = 0. Make a table of the expected
digital output of the A/D converter (in decimal form) from time t =0tot =2s. Sketch
the indicated wind speed for this time range. Does this sampling rate appear adequate
to detect and represent gusts of this height and duration? Discuss.
Figure 21: Applied wind speed u and indicated wind speed u i for Problem 3.
4. The U.S. Corps of Engineers has recorded a considerable amount of wind speed data
using a 1/15 mile contact anemometer and a summation period of 5 minutes. What is
the average wind speed in m/s during a 5 minute period for which the count was 18?
5. A pressure plate anemometer has a plate 0.1 m on a side. The constant c may be taken
as unity and the atmosphere is at standard conditions (0 o C and 101.325 kPa).
(a) What is the force on the plate at wind speeds of 2, 5, 10, 20, and 40 m/s? If the
output signal is proportional to force, comment on the difficulty of building a meter
which will accept all speeds up to 40 m/s and still read accurately in the 2 - 6 m/s
range.
Wind Energy Systems by Dr. Gary L. Johnson November 12, 2001