VIBRATION MEASUREMENTS OF THE HULL, TRIPOD MAST, PROPULSION SYSTEM, AND RUDDER SYSTEM OF USS AUSTIN (LPD-4).
Research and development rept.,
NAVAL SHIP RESEARCH AND DEVELOPMENT CENTER WASHINGTON D C ACOUSTICS AND VIBRATION LAB
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Natural hull frequencies in vertical and athwartship direction and in rotation were identified. Vibration amplitudes did not exceed 2.5 mils during steady-speed runs and were below 12 mils during maneuvers. Vibration levels for all test conditions are not considered excessive. Natural frequencies of the tripod mast were measured, and amplitudes at the highest radar platform were found to be below 36 mils during steady-speed runs and below 44 mils during maneuvers. Critical speeds of the propulsion system for longitudinal vibration occurred at 132 and 174 rpm for the starboard and port shafts, respectively. When the ship was on a steady course, the levels of longitudinal vibration, alternating thrust, and alternating torque in the propulsion system were low even at critical speeds. The alternating thrust increased considerably when the ship was in a hard left turn at or near 174 rpm or in a hard right turn at or near 132 rpm. Variable torque in the propulsion system was satisfactorily low--less than 2 percent of the mean torque. A torsional shaft critical at 2.3 Hz was excited by blade frequency only at very low power. Motor current surges in the steering gear system exceeded the design limit at high speeds. Surges at the port motor were higher than at the starboard motor. Pressures in the hydraulic ram cylinders were below design pressure. Author
- Marine Engineering