Abstract
The dominant underwater noise source of a ship is known to be propeller cavitation. Recently, attempts have been made to quantify the source strength using on-board pressure sensors near the propeller, as this has advantages over conventional noise measurement. In this study, a beamforming method was used to estimate the source strength of a cavitating propeller. The method was validated against a model-scale measurement in a cavitation tunnel, which showed good agreement between the measured and estimated source levels. The method was also applied to a full-scale measurement, in which the source level was measured using an external hydrophone array. The estimated source level using the hull pressure sensors showed good agreement with the measured one above 400 Hz, which shows potential for noise monitoring using on-board sensors. A parametric study was carried out to check the practicality of the method. From the results, it was shown that a sufficient recording time is required to obtain a consistent level at high frequencies. Changing the frequency resolution had little effect on the result, as long as enough data were provided for the one-third octave band conversion. The number of sensors affected the mid- to low-frequency data.
Highlights
The increase in commercial shipping has led to the development of ships with higher speeds and higher capacities, and the ambient noise of the sea has increased as a result [1,2].the noise pollution from commercial ships is considered to be one of the major issues in the ocean environment [3,4], and the International Maritime Organization (IMO) has set guidelines to mitigate it
Using the simple beamforming method, the source level was estimated for each run, and the results were averaged
A simple beamforming method for propeller noise monitoring was validated in a model-scale measurement
Summary
The increase in commercial shipping has led to the development of ships with higher speeds and higher capacities, and the ambient noise of the sea has increased as a result [1,2].the noise pollution from commercial ships is considered to be one of the major issues in the ocean environment [3,4], and the International Maritime Organization (IMO) has set guidelines to mitigate it. It is well known that the dominant underwater noise source of commercial ships is propeller cavitation. The radiated noise can be measured by a procedure based on ISO 17208-1 [5], which exploits an external noise measurement system located away from the target vessel [6,7,8]. This has several disadvantages in cost and time, and the measured noise is affected by the sea state
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