Underwater noise can be an important pollutor of marine ecosystems. Noise radiated by ships is estimated to increase the natural background noise level by 20 to 30 dB in the frequency range from 10 to 300 Hz. The frequency band between 63 and 125 Hz is especially sensitive since it coincides with important frequencies many marine mammals and fish use for communication or perception and and is therefore potentially harmful to the conservation of these populations. Propeller cavitation is one of the main sources of radiated noise in this frequency range. Noise in this and other frequency ranges can have a negative effect on humans as well. On-board measurements on merchant ships have frequently recorded the highest noise levels in the above mentioned lower-frequency bands that are mainly attributed to propeller cavitation. This form of noise is posing a health hazard for crew under long-term exposure as well as decreasing comfort for passengers.

Notwithstanding the importance of other sources in the overall picture of ship induced noise, the propeller cavitation noise is herefore identified as the dominating noise source, and it needs to be adressed in the development of noise mitigation measures regarding both the radiated and on-board noise levels. This requires reliable tools that can predict propeller noise accurately.

Objectives

The overall objective of the present project is to improve the numerical and experimental methods for the prediction of noise and vibration induced by a propeller operating behind ship hull in full scale conditions, and to elaborate practical recommendations for the reduction of noise and vibration levels for specific design applications.

Approach

The overall objective is split into different tasks that are addressed successively:

• Development of more reliable methods to increase the accuracy of experimental predictions in low frequency range, accounting for the influence of facility size and test procedures, sound reflection on walls and/or free surface, and filtering of facility background noise
• Collection of reliable and accurate experimental data for the validation of CFD models and design tools for noise predictions, in model and full scale conditions
• Improvement of numerical methods for the simulation of multiscale flow turbulence, induced vorticity, cavitation dynamics and acoustic propagation
• Extension of the applicability of the numerical tools to accommodate the effects of hull and appendages, and to improve the accuracy of predictions in higher frequency range
• Filling gaps in understanding of fundamental physical mechanisms underlying propeller noise emission related to turbulence, cavitation and bubble dynamics
• Evaluation and enhancement of previously outlined noise mitigation measures in application to specific types of ships and propulsion systems

Funding

The joint project is funded within the MarTERA consortium by the partners Research Council of Norway (RCN), German Federal Ministry of Economic Affairs and Energy (BMWi) and Italian Ministry of Education, Universities and Research (MIUR) and co-funded by the European Union.

Links

For more information visit http://www.pronovi.eu/