Prediction of Low Frequency Vibrational Frequencies of Submerged Structures

Abstract

Practical numerical techniques are described for calculating the low frequency vibrational resonances of general submerged structures. Both finite element and boundary element approaches for calculating fully-coupled added mass matrices are presented and illustrated. The finite element approach is implemented using existing structural analysis capability in NASTRAN. The boundary element approach uses the NASHUA structural acoustics program in combination with NASTRAN to compute the added mass matrix. The two procedures are compared in application to a submerged cylindrical shell with flat end closures. Both procedures proved capable of computing accurate submerged resonances; the more elegant boundary element procedure is easier to use but may be more expensive computationally.