A traditional noise control approach is to place some type of barrier around the noise source. To be effective at low frequencies, the barrier would have to be significantly larger than the noise source itself and more dense than the water, making it impractical in most cases.
In underwater noise abatement, curtains of small freely rising bubbles are often used in an attempt to reduce the noise; however, these bubbles are often ineffective at the low frequencies at which the loudest components of the noise occur. We developed a new type of underwater air-filled acoustic resonator that is very effective at attenuating underwater noise at low frequencies. The resonators consist of underwater inverted air-filled cavities with combinations of rigid and elastic wall members.
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They are intended to be fastened to a framework to form a stationary array surrounding an underwater noise source, such as the ones previously mentioned, or to protect a receiving area from outside noise. The key idea behind our approach is that our air-filled resonator in water behaves like a mass on a spring, and hence it vibrates in response to an excitation. A good example of this occurring in the real world is when you blow over the top of an empty bottle and it makes a tone.
The specific tone it makes is related to three things: In this case, a passing acoustic wave excites the resonator into a volumetric oscillation.
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The air inside the resonator acts as a spring and the water the air displaces when it is resonating acts as a mass. Like a mass on a spring, a resonator in water has a resonance frequency of oscillation, which is inversely proportional to its size and proportional to its depth in the water. At its resonance frequency, energy is removed from the passing sound wave and converted into heat through compression of the air inside the resonator, causing attenuation of the acoustic wave. A portion of the acoustic energy incident upon an array of resonators is also reflected back toward the sound source, which reduces the level of the acoustic wave that continues past the resonator array.
The resonators are designed to reduce noise at a predetermined range of frequencies that is coincident with the loudest noise generated by any specific noise source. Underwater photograph of a panel array of air-filled resonators attached to a framework. The individual resonators are about 8 cm across, 15 cm tall, and open on the bottom. The entire framework is about cm wide and about cm tall. We investigated the acoustic properties of the resonators in a set of laboratory and field experiments. Lab measurements were made to determine the properties of individual resonators, such as their resonance frequencies and their effectiveness in damping out sound.
These lab measurements were used to iterate the design of the resonators so they would have optimal acoustic performance at the desired noise frequencies. Initially, we targeted a resonance frequency of Hz—the loudest components of the noise from activities like marine pile driving for offshore wind farm construction are between Hz and Hz. We then constructed a large number of resonators so we could make arrays like the panel shown in the photograph.
Loughborough University Research Publications
Three or four such panels could be used to surround a noise source like an offshore wind turbine foundation or to protect an ecologically sensitive area. Fluvial Remote Sensing for Science and Management. Deepwater Foundations and Pipeline Geomechanics. Listening in the Ocean. Animal Communication and Noise. Fish Population Dynamics, Monitoring, and Management. Coral Reef Remote Sensing. Seafloor Mapping along Continental Shelves. The Ecology and Biology of Nephrops Norvegicus. Biological Sampling in the Deep Sea. Hurricanes and Climate Change.
Advances in Marine Biology. Understanding Sea-level Rise and Variability. Indo-Pacific Climate Variability and Predictability. Wind Energy and Wildlife Interactions. Principles of Marine Bioacoustics. Submarine Mass Movements and their Consequences. Introduction to Volcanic Seismology. Four Laws of Psychophysics.
» 3aPA8 – Using arrays of air-filled resonators to reduce underwater man-made noise – Kevin M. Lee
Arctic Sea Ice Decline. Virginia Woolf and Neuropsychiatry. The Pacific Arctic Region. Synaptic Mechanisms in the Auditory System. Perspectives on Auditory Research.
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- Identifying Modeled Ship Noise Hotspots for Marine Mammals of Canada's Pacific Region.
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Antarctic Subglacial Aquatic Environments. The Mammalian Auditory Pathways. Insights from Comparative Hearing Research. The behavior and sensory biology of elasmobranch fishes: The Human Auditory Cortex. Ecological Connectivity among Tropical Coastal Ecosystems. Underwater Acoustic Modeling and Simulation. Basic Aspects of Hearing.
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The Auditory System at the Cocktail Party. Reef Fish Spawning Aggregations: Biology, Research and Management. Yvonne Sadovy de Mitcheson. The Monsoons and Climate Change. Vertebrate Sound Production and Acoustic Communication. Oxygen Homeostasis and Its Dynamics.
Remote Sensing of the African Seas. Microglia in Health and Disease.