Experimental and Computational Determination of Global Resonances in Ship Structures
Abstract
How machinery vibrations are transmitted through a foundation, into a hull and ultimately into the water is of great concern to ship designers. Global modes result from strong coupling between the vibration modes of a machine's foundation and the ship's hull, and can cause peaks in the radiated sound power spectrum. In simple structures the global modes can be identified and altered by making drive point mobility measurements and adding mass to the structure. Radiated sound power is altered because the added mass shifts the modal frequencies and modifies the coupling. In a more realistic structure with a higher impedance foundation there is more interaction with the hull and a greater density of modes making global mode identification harder, so additional methods are needed for identification. A finite element method is used to determine the vibration modes of a fluid loaded model foundation and hull. The forced response of the hull model is calculated and used in a boundary element method to predict the radiated sound power of the structure in water. The results are compared to experimental measurements from the actual model in a reverberant sound tank. Numerical methods are shown to be very useful in classifying the modes of a structure and predicting frequency shifts resulting in modal coupling to form global modes.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 1991
- Accession Number
- ADA245259
Entities
People
- Matthew E. Barber
Organizations
- Massachusetts Institute of Technology