Tropical storm Jeanne. Wind Vel. and platform oscillation

15sep04

plots:

the wind speed versus time for 17 hours starting at 14:30 AST 15sep04 (.ps)   (.pdf)
the tenstion in tiedown 12 versus hour of day for 15sep04 (.ps).   (.pdf)
the strength 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:

    Jon hagen's wind speed monitor was running during the storm. The program that normally monitors the data was not writing to disk. I took the front panel output and sampled it using the radar interface. The setup was : The plots show the wind speed versus time for 17 hours starting at 14:30 AST 15sep04 (.ps) (.pdf) (extending till 7:45 16sep04).


Platform vertical oscillations.

    The tiedowns have loadcells connected to each cable (2 cables per tiedown). This data is read at a 1 hz rate by the computer. The tiedowns had been released to 3 inches to lower the tension on the platform in preparation for the storm.On 15sep04 at 14:00 tiedown 4 and tiedown 8 went off line when the breakers on tiedown 4 tripped. I used the tension readings from tiedown 12 since they were available for the entire day.
The azimuth arm was locked in an east-west position for the storm. Td 12 is perpendicular to this in the north corner of the triangle.

    The first plot shows the tenstion 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).

When hurricane george passed in 1998, the oscillation frequencies were measured with all of the tiedowns, and with the tilt sensors in the dome (they sampled at 5 hz). The tiedowns measured a .35 hz oscillation while the tilt sensors found a .57 hz  oscillation. The .450 oscillation on 15sep04 is actually .55 hz aliased down to .45 hz.
 
date of measurement measured frequency
sep98 georges .35,.57 hz
sep04 jeanne .354, .55 
after undoing alias.
 
processing: x101/040916/doit.pro, td.pro, doit.pro
 home_~phil