ASA 125th Meeting Ottawa 1993 May

5aSA9. Stop-band and passband behavior of ribbed cylinders.

Joseph A. Clark

Michael A. Sartori

Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000

As observed through an experimental analysis, the presence of ribs in a cylinder produces two types of stop-band and passband behavior. One type of stop-band and passband behavior concerns the passage of waves along the cylinder. Depending on frequency, energy from a vibrational source will either pass along a ribbed cylinder or be stopped by the ribs. A second type of stop-band and passband behavior involves the radiation of vibrational energy to the far field, which is also dependent upon frequency. These two types of behavior have been observed experimentally on an immersed cylinder 5 ft. in length, 1 ft. in diameter, and with 30 ribs. Exciting the cylinder in an n=0 circumferential mode with an internal array of shakers, the cylinder's radiation was measured at 180 positions along the cylinder's length with a hydrophone located in the cylinder's evanescent near field. Measurements of two cylinders (one with ribs and one without ribs) were made and were processed to obtain position---frequency and wave number---frequency plots. Using these plots, the stop-band and passband behavior that can be attributed to the ribs will be presented as features of wave propagation along the cylinder and as radiation effects in the far field. The experimental results will also be compared with a numerical analysis of an infinite cylinder with periodically spaced ribs. [Work supported by ONT.]