Estimation of Hydro-acoustic Signatures Originated from Ship's Hull Vibration

Abstract

The origin of shipboard hull vibrations is dominantly determined by vessels propulsion system, main machinery, auxiliary systems, pumps, breaking of the waves at the ship hull, etc. All of these peripherals and systems origin the static and dynamic induction of underwater sound in water environment. As a source of underwater sound, individual vessel has displayed unique characteristics of directivity and diversity of hydro-acoustic spectrum. Many researches had been completed on identification and quantified estimation of the noise or the multiple vibrations resulted from ship and machinery. The paper is focussed on to study the hull transferred vibration of the vessel's structure to sea and are analysed using vibration spectra using onboard measurements of a naval vessel. Sea trials at following conditions had been carried out. Sea State : 1-2, 2-3; Loading Condition : Full Load, Half Load; Wind Condition : Moderate < 15 knots; Sea Direction : Ahead, Astern The measuring of the radiated hydro-acoustic noise was done simultaneously with multi channel measurements of the vessels vibrations at few characteristic positions of the vessel. The hydro-acoustic signals that are transferred through water column is to be analyzed using spectra and higher order spectral analysis bispectra with under water transducers / hydrophones was not performed due to financial constraints and limitations of underwater measuring technology in Sri Lanka. Numerical relationship was established using similar study outcomes performed by Poland Navy.