Absorption of Sound in Seawater

Neighbors, Thomas H.

doi:10.1016/b978-0-12-811240-3.00004-7

Cited by 5 publications

(4 citation statements)

References 48 publications

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“…Actually, our design considers only a 70 mm distance from the transmitter to receiver, yet, significant drops are found in SPL, APF and receiver displacements. Hence, higher energy density will be required for a longer distance (>100 m) underwater [16,17]. This reason supports the KHz range frequencies for underwater wireless power transfer [18].…”

Section: Acoustic Pressure Fieldmentioning

confidence: 58%

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

Awal

Yahya

Afrizal

et al. 2021

CFDL

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Acoustic propagation in seawater is an important aspect of scientific investigation. However, the impact of the THz scale frequencies for acoustic propagation is not included in the studies. Thus, a finite element analysis of such propagation in a seawater medium is presented in this paper applying THz frequencies. A transmitter (circular with a diameter of 14 mm, a thickness of 3 mm) and a rectangular receiver (20×10×0.5 mm3) are designed to trace the variations in the propagation mediums. A propagation medium of seawater (70×40×60 mm3) with ice and softwood is modelled. A scale of frequencies (1 kHz to 1 THz) is applied to trace the impact on the propagation pattern. It is found that THz range frequencies provide a very small wavelength. As a result, the potential propagation distance is very small. As such, the sound pressure level, displacements of the receiver and pressure field shows very rapid drops in the magnitude. This work considers only 70 mm as propagation distance, yet the sharp decrement of performance parameters suggests that it is rather inconvenient to achieve useful efficiency using THz frequencies for acoustic propagation.

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Section: Acoustic Pressure Fieldmentioning

confidence: 58%

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

Awal

Yahya

Afrizal

et al. 2021

CFDL

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“…В работе Neighbors (2017) [45] обсуждается поглощение звука в зависимости от таких факторов как соленость, температура, водородный показатель и давление. Обсуждаются экспериментальные результаты, полученные за несколько десятилетий.…”

Section: основные этапы исследований поглощения звукаunclassified

Sound Attenuation in the Marine Environment (Review)

YAROCHENKO,

DEGTYAR

2023

EBRC BSEC

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Одним из факторов, влияющих на дальность распространения звука в морской среде, является поглощение звука. Многие исследователи внесли свой вклад в современное знание о затухании звука в морской воде. В статье представлен краткий исторический обзор работ, посвященных исследованию поглощению звука в морской воде. Приведен ряд эмпирических формул для расчета коэффициента поглощения звука в морской среде. Рассматривается современное состояние проблемы. Поглощение звука зависит от температуры, давления, солености, кислотности (водородного показателя pH ) и частоты. Для высоких частот поглощение звука намного выше, чем для низких. При увеличении гидростатического давления снижается поглощение. Повышение температуры, солености и водородного показателя увеличивает поглощение. Поглощение звука в морской воде обусловлено наличием растворенных в ней солей магния, бора и брома. В морской воде происходит большое количество процессов, но только на две релаксации приходится большая часть поглощения. Это релаксация сульфата магния MgSO4 (частота релаксации fr ∼ 100 кГц) и борной кислоты В(ОН)3 (fr ∼ 1 кГц). Выявлена еще третья релаксация с участием карбоната магния MgCO3 (fr ∼ 10 кГц). На частотах от 0,2 до 10 кГц основной вклад в поглощение вносит борная кислота В(ОН)3. На частотах ниже 1 кГц коэффициент поглощения в океане зависит от pH. Зависимость от pH связывают с релаксацией видов: В(ОН)3 -борной кислоты и MgСO3 -карбоната магния. В диапазоне частот от 10 до 1000 кГц основной вклад в затухание вносит сульфат магния MgSO4. На высоких частотах (> 1000 кГц) поглощение зависит от вязкости. На частотах ниже 200 Гц наблюдается разброс экспериментальных данных. Этот разброс связывают с региональной зависимостью.

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“…The high frequency sonars traditionally used by AUVs can be within the hearing thresholds of cetaceans categorised in the HF / VHF hearing groups by Southall et al (2019). These high frequency sonars are unlikely to cause as widespread ensonification of the water column as MFAS due to the comparatively fast absorption rates of high frequency sounds in water (Neighbors, 2017). This absorption causes more significant propagation loss than for less readily absorbed lower frequency sounds.…”

Section: Sonar Risk Assessmentmentioning

confidence: 99%

Development of Environmental Mitigation Measures for the Sound Sources of Autonomous Underwater Vehicles (AUVs)

Byford¹,

Rushton²

2022

Preprint

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Autonomous Underwater Vehicles (AUVs) will be vital to support future Marine Research and enhance Defence capabilities. As these new technologies emerge it is important to ensure all possible environmental impacts have been assessed and appropriately mitigated. Unmanned Underwater Vehicles (UUVs) and Autonomous Underwater Vehicles can comprise of a wide variety of acoustic sensors as can the accompanying survey ship. National and European legislation is in place to protect habitats and species from harm which includes the disturbance to marine mammals (The Conservation of Offshore Marine Habitats and Species Regulations, 2017; The Habitats Directive, 1992). Emission of impulsive sound from acoustic sensors have the potential to adversely impact marine mammals (Finneran, 2015;Harris, et al., 2016). These impacts can range from general disturbance to hearing damage when certain thresholds of the received sounds are breached. In the most severe cases, permanent shifts to hearing thresholds can occur (Southall, et al., 2019). Understanding the environmental impact and developing appropriate mitigation measures for UUVs and AUVs will therefore ensure these new Defence capabilities are minimising the impact to marine mammals whilst ensuring Defence operations are not at risk. A first screening and scoping study determined the environmental aspects and impacts related to the sensors onboard AUVs procured in Defence. Further analysis is being conducted to inform the extent of the impact and to determine if any existing mitigation strategies could be adopted and integrated into the Standard Operating Procedures for planned AUV use and exercises e.g. running bespoke Sonar Risk Assessments ahead of deployments together with temporal (seasonal) and/or spatial planning of operations. This paper explores the environmental management techniques adopted to understand the environmental impact and introduce mitigation measures for future challenges related to the deployment of AUVs such as the cumulative effects of multiple AUVs functioning together and the deconfliction of other anthropogenic sound sources.

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Absorption of Sound in Seawater

Cited by 5 publications

References 48 publications

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

Impact of THz Frequency on Underwater Acoustic Wave Propagation for Short Range Wireless Applications

Sound Attenuation in the Marine Environment (Review)

Development of Environmental Mitigation Measures for the Sound Sources of Autonomous Underwater Vehicles (AUVs)

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