THE SIGNIFICANCE OF SHELL-LIKE VIBRATION OF NS SAVANNAH AT LOW FREQUENCIES

摘要

The report examines the significance of shell-like behavior of NS SAVANNAH at low frequencies as measured during underway vibration trials and as estimated by an analog study. In the vicinity of Bulkhead 80, out-of-phase motions were measured which cannot be predicted in any nonuniform bar approach to the analysis of a ship hull, but which might be predicted by treating the hull as a shell. However, examination of the maximum vertical vibration levels at filtered frequencies at this bulkhead showed that these motions were not significant. Vibration levels at blade frequencies indicated the presence of natural frequencies in which the largest amplitude occurred in the vertical direction and in which relatively large athwart ship motion occurred, and vice versa. The significant frequencies obtained from vertically oriented transducers at Bulkhead 80 below 9 cps corresponded to hull flexural frequencies.