Underwater ship-noise characterization

Ship noise affects the underwater environment, requiring acoustic assessment. Since Japan has no large-scale underwater ranging capability, JRC Tokki invested in a portable sound-intensity system from Brüel & Kjær. This static ranging system uses hydrophones mounted on a floating raft to make underwater Noise Source Identification (NSI) measurements on large vessels.

Challenge

In order to get a complete characterization for the whole of the underwater structure of a ship, a portable system was needed that would enable field measurements. As the curvature of a ship’s stern and bow often varies, JRC Tokki needed a solution that could account for this by following the hull closely, at a uniform distance.

Solution

Underwater sound intensity measurements are made using phase-matched hydrophones mounted in a custom measurement jig suspended from a movable floating platform. Type 8104 Hydrophones are used at lower frequencies; the high frequency band is measured using the miniature Type 8103.

Results

JRC Tokki can now create a complete characterization of the underwater structure using many individual measurements – a virtual “mesh” the covers the entire underwater surface of a ship. Using these measurements, contour maps can be made that give a 3D picture of the sound intensity performance of the ship’s hull.

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