Structural-Acoustic Measurements of a Submerged Cylindrical Shell

This paper describes how a steel cylindrical shell with end caps was structurally and acoustically tested in air and in water. The shell has one hemispherical end cap and one flat circular end cap and was fabricated from schedule 40S stainless steel pipe with a nominal outer diameter of 0.457 m (18 in.) and wall thickness of 9.53 x 10-3 m (3/8 in.). The interior wall of the shell and the outside edge of each of the end caps were threaded to allow both end caps to be removed and replaced. Because of practical complications in the fabrication process, the shell cross section could not be made exactly circular, nor could the shell thickness be made completely uniform. These asymmetries will lead to non-ideal structural-acoustic properties of the shell. The shell has a theoretical in vacuo ring frequency of about 3.65 kHz. Here the ring frequency is the frequency at which one structural longitudinal wavelength is equal to the circumference of the shell. The critical frequency, found by equating structural bending wave speed to the acoustic wave speed of water, is about 25 kHz. The shell has an axial length of 1.22 m (48 in.), not including the end caps. The vibro-acoustic behavior of the shell is characterized in terms of its natural frequencies, mode shapes, and modal loss factors in air and in water, along with its acoustic radiation in water. Estimates of the modal density and radiation efficiency computed using empirical formula, derived for use in Statistical Energy Analysis (SEA) simulations, is compared to the measurements.

Language

  • English

Media Info

  • Media Type: CD-ROM
  • Features: Figures; Photos; References;
  • Pagination: pp 183-192
  • Monograph Title: Noise-Con 04. The 2004 National Conference on Noise Control Engineering

Subject/Index Terms

Filing Info

  • Accession Number: 01054161
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Jul 16 2007 2:18PM