UNDERWAY VIBRATION SURVEY OF NS SAVANNAH.
DAVID TAYLOR MODEL BASIN WASHINGTON D C ACOUSTICS AND VIBRATION LAB
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Vertical natural hull frequencies for NS SAVANNAH as determined by spectral analysis of vibratory displacements recorded during anchor drop tests compared favorably with those calculated and measured during vibration generator tests. Vertical, athwartship, and torsional vibration amplitudes of the stern, and longitudinal displacement amplitudes of the thrust-bearing housing were measured at blade frequency throughout the speed range. Mode shapes of the hull were measured at resonant conditions. The effect of hull fouling on hull vibratory levels was found to be negligible. The alternating thrust calculated from wake data was in good agreement with shaft strain measurements. Comparison of the forced vibration amplitudes measured at the stern during vibration generator tests with stern amplitudes measured during underway trials gave at 102 rpm an estimated net blade frequency exciting force acting at Frame 219 of plus or minus 21,000 and plus or minus 9,000 lb single amplitude for the vertical and athwartship directions, respectively. The vertical force acting on the hull due to the alternating pressure field at 102 rpm at blade frequency was estimated at plus or minus 19,000 lb single amplitude. Author
- Marine Engineering
- Nuclear Propulsion