A numerical model calibrated by in-situ measurement for predicting the underwater radiated noise of an azimuth thruster structure of a passenger ship

In a global context of limiting the impact of noise pollution on the behavior of marine fauna, the understanding of acoustic radiation phenomena from underwater sound sources of a passenger ship is of primary importance. Although diesel engines and propellers are considered to be ones of the main sources of ship noise, our observations have shown that immersed motors contribute significantly to the noise radiated into the water by passenger ships at low speeds. This contribution summarizes a semi-empirical method for estimating the noise radiated into the water from an azimuth thruster-type structure. An analysis of the vibroacoustic behavior in water of the structure excited by an internal acoustic source is detailed. Beyond the complexity of performing full-scale measurements in a noisy environment, the analysis of the measurements allows to estimate the vibration modes of the immersed structure. A numerical model of the dedicated structure, calibrated on the basis of an experimental modal analysis, is used to estimate the pressure field radiated by the structure into the water. As a result of these analyses, a simplified model of radiated noise in the water is developed for use in nominal thruster operation.