SONIC
Suppression Of underwater Noise Induced by Cavitation
With the steady growth of shipping activities over the last decades, underwater noise is
increasing. It may be hindering sea mammals, or may even be harmful to them. Underwater
noise is a European concern and is identified as a qualitative descriptor for determining
the Good Environmental Status under the Marine Strategy Framework Directive. The main
sources of noise are the ships' propellers, especially if the flow around the propellers is
cavitating. Most propellers are cavitating when the ship is sailing at its designed speed.
The surge for more fuel-efficient propellers is increasing cavitation. Therefore the dilemma
is the following: less CO2 emissions into the air yields more noise emissions under water. |
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The first goal of the project is to enhance the
understanding of radiated noise from ships.
From earlier studies, it is known that the kind
of noise generated far away from the ship can
vary according to the form of cavitation. Based
on this knowledge, the project aims to improve
computational and measurement techniques
used in the design of a ship. Numerical tools
are extended and tuned to correctly predict the
noise level; measurement techniques in model
basins and cavitation tunnels are calibrated to
correct noise measurement for the reflection | of noise from the walls of the facilities. Both
the numerical and experimental tools need to
be validated for the frequency ranges that are
most harmful to sea mammals. Once a ship
is designed, it is critical to establish the actual
noise level with a trial. Such trials are usually
conducted at ballast conditions, for which cavitation
is absent. Noise measurements, therefore,
need to be performed during service of
the ship with the minimum possible hindrance
to the economical operation of the ship. New
techniques will be tested to measure the noise |
generated by the propeller on-board the ship.
Another technique is to measure the noise offboard
with buoys or sound arrays. Both techniques
will be compared in order to obtain
a reliable and cheap measurement procedure.
With data available on the noise level of ships, it
becomes possible to estimate underwater noise
given the actual shipping activity. Using AIS
(Automatic Identification System) data, the project
will develop a technique for mapping underwater
noise in the North Sea. This map can be
used by authorities to manage shipping or to
study the influence of mitigation measures. |
The project will use model basins to study the
noise emission from ships in design stage. Fullscale
measurements at sea will be performed to
establish accurately the noise of several ships,
but also to determine long-term noise profiles
of seas. All measurements will be fed into
a database which will be made available to ship
designers outside the project. The project will
finally use computational tools to predict the
noise in a given sea for a longer period, showing
the hinder to sea mammals in a noise map.
SONIC will closely cooperate with the AQUO
project, which will adopt a complementary
approach to study cavitation noise. |
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