Tropical storm Jeanne. Wind Vel. and platform oscillation

the wind speed versus time for 17 hours starting at 14:30 AST 15sep04 (.ps)   (.pdf)
the tension in tiedown 12 versus hour of day for 15sep04 (.ps).   (.pdf)
the magnitude and frequency of the oscillations(.ps)   (.pdf)

   Tropical storm jeanne passed thru the observatory on 15sep04 around 17:00 hours. The wind speed was recorded using john hagen's wind monitor  on the platform. The vertical oscillation frequency of the platform was measured using the load cells on tiedown 12.

The wind speed:

• front panel output (14 volts = 140 mph) to a 4db attenuator, then to an opamp with times 2 voltage gain, and then into the radar interface which is a 50 ohm load.
• The data was sampled at 10 hz using the 12 bit a/d. It has a maximum input voltage of 2.5 volts.
• To calibrate the measurement I read the voltage off a dvm while the operator called out the wind speed. A linear fit of windspeed vs a/d count was done to 25 of these readings.

• The top plot is the wind speed versus hour of day. 24 Hours is the start of 16sep04. The data has been smoothed to 1 second. The wind meter peak hold showed a maximum value of 60 Mph so the calibration may have been off by 30% or the peak hold may have a longer time constant on it. The dropout at 16:15 to 17:00 was caused by someone removing the cable.
• The bottom plot shows the calibration data and the linear fit to the data. The fit coef's were vel=1.743+.0365*AtoDcounts.

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Platform vertical oscillations.

    The first plot shows the tension in tiedown 12 versus hour of day for 15sep04 (.ps)  (.pdf). The tension was slowly varying (from temperature) until 8 am. After 8am, the tension began to jump around. This jumping reached a maximum at 17:30. The deviations got up to 8 kips (in this 1 tiedown).

    To compute the oscillation strength, 1 hour at a time (3600 1 second samples) was transformed and then the magnitude was computed: osc=abs(fft(tiedownTensionFor1Hour)). The second set of plots shows the strength of the oscillations (.ps)  (.pdf).

• Fig 1 plots the oscillation strength versus frequency for 1 hour steps starting at 8:30 (bottom) and going to 23:30 (top). The frequencies .328, .354, and .450 Hz have been flagged for reference. Power in these frequencies start to increase at 8:30 am and continue until they hit a maxi ma at 18:30.
• Fig 2-4 plots the oscillation strength from 6:30 thru 23:30 . The scale on the left is kips (kilo pounds).  The frequency resolution is .2 millihz.

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