WP2: Noise Sources

Leader: University of Genoa

Contact person: Prof. Enrico Rizzuto, University of Genoa, (enrico.rizzuto@unige.it)

Main objectives

• To characterise the underwater noise emissions of the ship, providing input data for the noise footprint model
• To validate and/or improve models and methods to predict noise underwater noise radiated from propeller, including cavitation effects, and interactions with the ship hull (wake, vibro-acoustic response).

Task 2.1 Derivation of ship URN patterns

For different types of vessels, an underwater radiated noise pattern is defined by a representation of spectral noise vs. frequency. The novelty of the approach proposed here is to split the global radiated noise into several components, one for machinery noise, the other for propeller without cavitation, and the last one to account for cavitation. For each component a semi-empirical formula was introduced to account for ship size and speed.

Task 2.2 Predictive theoretical models for propeller URN

Wave pattern prediction

                        

Cavitation prediction

              

In this task the characterisation of the propeller as a source for underwater radiated noise will be considered from a theoretical viewpoint. Predictive methods are implemented and validated with experimental surveys.                             

Task 2.3 Experimental investigations in model scale

Screenshot of propeller cavitation                            Cavitation tunnel setup                                               Propeller model scale radiated noise results

Results are analysed in order to provide feed-back and validation to the prediction models developed in the various steps of task 2.2; further validations come from full scale surveys (WP3). Two complete hull models are built for towing tank tests (CEHIPAR, SSPA) and cavitation tunnel (SSPA). Three propeller models are tested in cavitation tunnels. In the large cavitation tunnel (SSPA), the propeller are tested behind a complete ship model. In the medium sized cavitation tunnels (CEHIPAR, UNIGE), the propellers are tested behind wire mesh screens (or dummys).

Task 2.4 Propeller-hull vibro-acoustic interaction

Main objective of the task is to determine how much vibro-acoustic response of ship structure amplifies the direct radiated noise from the propeller. Two main phenomena are involved:

• propeller-induced  hull vibrations;
• direct vibro-acoustic excitation of the hull located near the propeller through the fluid, in the form of fluctuant hydrodynamic loads and impinging acoustic pressure field.

For modelling interaction between ships structure and the surrounding fluid, structural models are required of a considerable part of the aft ship where the mass elastic behaviour represents the propeller generated underwater noise.

Task 2.5 - Synthesis: impact of propeller noise on global URN

In this task, the noise contributions from the cavitating and/or non-cavitating propeller are compared with other noise sources (in particular machinery). A synthesis of all contribution into a total ship radiated noise pattern is sought. The effect of running at different propeller loads and ship speeds is also studied.

WP2 Partners: