Estimating Ship Underwater Radiated Noise from Onboard Vibrations

The acoustic signature of an Orca-class training vessel (Patrol Craft Training, PCT) Moose from the Royal Canadian Navy (RCN) was measured at the RCN’s Patricia Bay acoustic range on Vancouver Island, British Columbia, Canada. The acoustic range trials included accelerometer measurements on the ship hull and in the engine room and hydrophone measurements at approximately 100 m from the ship. The trials were carried out at the ship speed range of 3 to 20 knots. The test data from all the trial runs was used to derive, evaluate and validate the method of estimating ship underwater radiated noise from onboard vibrations. In the investigation, the runs were split into two sets: a training set and a testing set. A least squares approximation, AQV (average quadratic velocity) SL (source level) correlation, was then applied to the training set data to formulate a transfer function to estimate the underwater radiated noise from onboard vibrations. The AQV is calculated from accelerometer measurements (vibration levels) and SL is obtained from the hydrophone measurements. The third octave frequency band (from 10 Hz to 10 kHz) SL estimations of the testing set runs (using the transfer function and AQV) are within 1 to 3 dB of SL from the hydrophone measurements. This study demonstrates a capability of monitoring underwater radiated noise from ships using only onboard vibration levels which may be of interest for future projects relating to the reduction of shipping noise against a threshold in acoustically sensitive environments.