Apparatus and method for limiting sound transmission

Abstract

In general, a device (1) for limiting sound transmission from an acoustic emitter (2) is provided, the device comprising a container (4) arranged to at least partially surround the acoustic emitter, the container containing a liquid wherein the liquid comprises at least 2% dissolved oxygen, and wherein the device further comprises an agitator (6) configured to agitate the liquid so as to form bubbles (8) in the liquid.

Description

Technical Field

[0001] The present invention relates to an apparatus and an associated method for restricting sound transmission in a liquid. Background Art

[0002] Noise pollution, especially that caused by heavy machinery, can be a serious problem, affecting not only wildlife but also humans' ability to enjoy the environment. Many governments have placed restrictions on the amount of noise that can be generated in certain areas, including underwater environments, both in terms of the absolute peak intensity of the noise that can be generated and the noise that can be generated over a specific period (such as a month or a year).

[0003] However, in some cases, it is necessary to operate machines that generate such noise, and thus it is necessary to restrict the transmission of such noise. Currently available devices for restricting noise transmission are large, expensive, require a large amount of energy to operate, and typically only work over a relatively narrow frequency band.

[0004] The present disclosure is made in this context. Summary of the Invention

[0005] A first aspect of the present invention provides an apparatus configured to restrict sound transmission (e.g., through a liquid) from a sound emitter. The apparatus includes a container arranged to at least partially surround (e.g., the) sound emitter, the container containing a liquid, wherein the liquid includes at least 2% (optionally at least 10%) by volume of dissolved oxygen, and wherein the apparatus further includes an agitator configured to agitate (e.g., at least a portion of) the liquid (within the container) such that gas (e.g., oxygen) bubbles are formed in the liquid (within the container).

[0006] The inventors have found that the formation of gas (e.g., oxygen) bubbles in a liquid restricts the transmission of sound in the liquid over a wide frequency band (e.g., including but not limited to frequencies audible to humans and including ultrasonic frequencies). It has been found that agitating a liquid containing at least 2% (e.g., at least 10%) oxygen is a particularly effective way of causing bubble formation, as agitation causes some of the oxygen dissolved in the liquid to be released from the liquid, thus forming a large number of gas (oxygen) bubbles when the liquid is agitated. Thus, bubbles can be formed without using a compressor or similar device to force the bubbles through the liquid, and thus the apparatus is more efficient than in the case of using a compressor. In addition, a greater proportion (e.g., number) of bubbles can be generated more quickly compared to the case of using a compressor or a conventional bubble curtain generator to generate bubbles. At least a portion of the bubbles can be formed by nucleation. At least a portion of the bubbles can be formed by cavitation.

[0007] Without being bound by theory, the inventors believe that sound transmission is limited by bubbles in the liquid because when sound waves reach the bubbles, the sound waves encounter recurring liquid-gas interfaces and gas-liquid interfaces (e.g., when the sound waves enter and leave each bubble). Some scattering and absorption may occur at each such interface, resulting in the absorption of sound energy and sound attenuation. The reflection and absorption coefficients are considered to be functions of the acoustic impedances of the gas and the liquid. There may also be some resonant absorption when the sound waves have an appropriate frequency to cause the resonance of some bubbles. Since a large number of bubbles are generated and these bubbles have a wide range of different sizes, sounds of a correspondingly wide range of different wavelengths may be scattered and absorbed by the bubbles. In other words, the sound attenuation at a specific frequency is considered to be a function of the bubble size. It is also believed that since the liquid contains a large amount of gas in the form of bubbles, this reduces the speed of sound. Therefore, the spectrum of sound waves whose transmission is limited (e.g., the spectrum of sound waves that will be attenuated) is considered to be a wide spectrum and depends on the bubble size and the distribution of the bubble sizes.

[0008] The device may be a device configured to attenuate sound (e.g., through a liquid, such as the liquid in a container). The device may be a device configured to limit sound transmission (e.g., through a liquid, such as the liquid in a container).

[0009] The liquid may include at least 2% (e.g., at least 10%) by volume of dissolved oxygen. The liquid may include at least 25% by volume of dissolved oxygen, such as at least 50%, such as at least 75%, such as at least 80%. The liquid may include less than 100% by volume of dissolved oxygen, such as less than 99%, such as less than 90%. The liquid may have an oxygen saturation of at least 50%. The liquid may have an oxygen saturation of at least 80%. The liquid may have an oxygen saturation of at least 100%. The liquid may contain supersaturated oxygen, e.g., an oxygen saturation exceeding 100%. The liquid may have an oxygen saturation of at least 120%. The oxygen saturation of the liquid may be lower than 200%, such as lower than 150%. When the liquid is agitated, the saturated oxygen is more easily released from the liquid, thereby forming gas (oxygen) bubbles, and at this time the percentage of dissolved oxygen in the liquid is relatively high.

[0010] In some examples, the liquid may include at least 5 grams (dissolved) oxygen per kilogram of the liquid, such as at least 10 grams (dissolved) oxygen per kilogram of the liquid, such as at least 20 grams (dissolved) oxygen per kilogram of the liquid, such as at least 50 grams (dissolved) oxygen per kilogram of the liquid, such as at least 100 grams (dissolved) oxygen per kilogram of the liquid (i.e., the liquid in which oxygen is dissolved, optionally water). The liquid may include less than 1,000 grams (dissolved) oxygen per kilogram of the liquid, such as less than 750 grams (dissolved) oxygen per kilogram of the liquid, such as less than 500 grams (dissolved) oxygen per kilogram of the liquid (i.e., the liquid in which oxygen is dissolved, optionally water).

[0011] At least one opening may be defined in the container such that gas bubbles can leave the container through the opening. A plurality of openings may be defined in the container. The at least one opening may be an opening at the top of the container, such as at or above the liquid surface. The container may have an open top side, such as at or above the liquid surface. In use, gas (such as oxygen) bubbles may continuously form, rise under buoyancy (this may occur for very small bubbles after they fuse with other bubbles to form larger bubbles), and leave through the opening.

[0012] The opening may define an area of at least 1 cm 2 , such as at least 5 cm 2 , such as at least 10 cm 2 . The opening may define an area of less than 10 m 2 , such as less than 7 m 2 , such as less than 5 m 2 . The opening may span the entire upper surface of the container. The opening may define an area of at least 50% of the entire upper surface of the container, such as at least 80%. When a plurality of openings are provided, the total combined area of the openings may be at least 1 m 2 , such as at least 2 m 2 , such as at least 5 m 2 . When a plurality of openings are provided, the total combined area of the openings may be less than 50 m 2 , such as less than 40 m 2 , such as less than 30 m 2 .

[0013] Since gas (such as oxygen) bubbles tend to move upward under buoyancy (sometimes after fusing with other bubbles), it is necessary to continuously agitate the liquid to generate additional gas (such as oxygen) bubbles so that, for example, across the entire height of the container, a continuous flow of gas (such as oxygen) bubbles is distributed throughout the container. The provision of the opening allows gas (such as oxygen) bubbles to leave the container, and thus the pressure inside the container does not increase significantly. Thus, in use, as the liquid is continuously agitated, gas (such as oxygen) bubbles will continuously form, leave through the opening, and will be replaced by new gas (such as oxygen) bubbles.

[0014] The agitator may include (e.g., be) a stirrer. The agitator may include (e.g., be) a mixer. The agitator may include (e.g., be) an agitation pump, optionally an agitation pump fluidly connected to the interior of the container, e.g., via a pipe. The agitator may include (e.g., be) a flexible sheet (e.g., more flexible than the walls of the container). The agitator may include (e.g., be) a tarp, e.g., a tarp at least partially submerged in the liquid and moving under the action of waves in the liquid. The agitator may include (e.g., be) an actuator. The agitator may include (e.g., be) a transducer, e.g., a frequency generator (optionally, an additional sound emitter, typically a sound emitter other than the sound emitter that emits the sound to be restricted in transmission by the device). The agitator may include (e.g., be) a bubble curtain generator. The bubble curtain generator may be arranged (e.g., configured) to generate a bubble curtain that at least partially surrounds the sound emitter. The bubble curtain may be an annular bubble curtain. In other words, the bubble curtain may be in the form of a cylinder having an inner radius, an outer radius, and a height, where the cylinder is defined by (e.g., within the container) a liquid containing bubbles (i.e., between the inner radius and the outer radius and below the height), e.g., the number of bubbles within the bubble curtain may be at least twice (e.g., at least 3 times, e.g., at least 5 times, optionally less than 100,000 times) the number of bubbles outside the bubble curtain. The bubble curtain generator may include a compressor. Those skilled in the art will appreciate that the pressure and volume output of the compressor can be selected according to the volume of the container.

[0015] Using a bubble curtain generator to agitate (e.g., within the container) the liquid may generate an even greater number of bubbles in the liquid (i.e., some bubbles are generated due to agitation causing dissolved oxygen to be released from the liquid to form bubbles, while some bubbles come from the bubble curtain generator itself). The greater the number of bubbles, the more effective the sound attenuation and the more effectively the sound transmission is restricted.

[0016] The container may house the sound emitter. The container may enclose the sound emitter. The container may contain the sound emitter. The sound emitter may be submerged in (e.g., within the container) the liquid. When the sound emitter is housed within the container and / or submerged in the liquid, the restriction of sound transmission is more effective.

[0017] The container may be a first container including one or more first container walls. The device may include a second container, the second container including one or more second container walls. The second container may at least partially surround the sound emitter. The first container may at least partially surround the second container and be spaced apart from the second container. In other words, the first container may house the sound emitter, and the sound emitter may be housed within the second container such that the first container may also be considered to house the sound emitter.

[0018] The said or each first container wall in one or more first container walls may be (e.g., substantially) rigid and / or may include one or more (e.g., substantially) rigid portions. The said or each second container wall in one or more second container walls may be (e.g., substantially) rigid and / or may include one or more (e.g., substantially) rigid portions. For example, the said or each first container wall in one or more first container walls and / or the said or each second container wall in one or more second container walls may include (e.g., substantially) rigid plastic material (e.g., formed therefrom), or may include portions containing (e.g., substantially) rigid plastic material (e.g., formed therefrom). The said or each first container wall in one or more first container walls and / or the said or each second container wall in one or more second container walls may include (e.g., substantially) rigid metal (e.g., formed therefrom), or may include portions containing (e.g., substantially) rigid metal (e.g., formed therefrom). The said or each first container wall in one or more first container walls and / or the said or each second container wall in one or more second container walls may include (e.g., substantially) rigid glass or ceramic material (optionally fiberglass material) (e.g., formed therefrom), or may include portions containing (e.g., substantially) rigid glass or ceramic material (optionally fiberglass material) (e.g., formed therefrom). In an example, one or more first container walls and / or one or more second container walls may include a tube (e.g., formed therefrom), the tube including (e.g., substantially) rigid plastic material.

[0019] The said or each first container wall in one or more first container walls may be flexible (e.g., elastically deformable) and / or may include one or more flexible (e.g., elastically deformable) portions. The said or each second container wall in one or more second container walls may be flexible (e.g., elastically deformable) and / or may include one or more flexible (e.g., elastically deformable) portions. The said or each first container wall in one or more first container walls may include a tarp. The said or each second container wall in one or more second container walls may include a tarp. The said or each first container wall in one or more first container walls may be waterproof, e.g., impermeable. The said or each second container wall in one or more second container walls may be waterproof, e.g., impermeable.

[0020] The said or each first container wall of one or more first container walls and / or the said or each second container wall of one or more second container walls may comprise (e.g., be formed of) a waterproof material. The said or each first container wall of one or more first container walls and / or the said or each second container wall of one or more second container walls may comprise (e.g., be formed of) an ultraviolet-resistant material. The said or each first container wall of one or more first container walls and / or the said or each second container wall of one or more second container walls may comprise (e.g., be formed of) a hydrogen peroxide-resistant material. The said or each first container wall of one or more first container walls and / or the said or each second container wall of one or more second container walls may comprise a coating. The coating may be a saltwater-resistant coating. The coating may be an ultraviolet-resistant coating. The coating may be a hydrogen peroxide-resistant coating. The coating may be an anti-fouling coating. The said or each first container wall of one or more first container walls and / or the said or each second container wall of one or more second container walls may comprise (e.g., be formed of) a material strong enough to withstand tidal forces. The said or each first container wall of one or more first container walls and / or the said or each second container wall of one or more second container walls may comprise a reinforcing structure.

[0021] One or more first container walls may comprise one or more first container sidewalls extending from the bottom of the first container to the top of the first container. One or more second container walls may comprise one or more second container sidewalls extending from the bottom of the second container to the top of the second container. One or more first container sidewalls may extend above the surface of the liquid (i.e., the liquid within the first container, optionally, the liquid outside the first container). One or more second container sidewalls may extend above the surface of the liquid (i.e., the liquid within the first container, optionally, the liquid outside the first container). In an embodiment, the first container may comprise one or more first container sidewalls and may be open at the top and bottom. The container may comprise a weight to hold down one or more first container walls, optionally such that the one or more first container walls contact the ground or bottom (e.g., the seabed). The container wall may be configured to contact the ground or bottom (e.g., the seabed) in a watertight manner. There may be a seal between the container wall and the ground or bottom (e.g., the seabed).

[0022] The second container may be located within the first container and spaced apart from the first container. Thus, a space may be defined between the first container and the second container (e.g., between the walls of the first container and the second container). A liquid (optionally, a portion of the liquid) may be contained within the first container, in the space between the first container and the second container (e.g., between the walls of the first container and the second container). A liquid (optionally, a portion of the liquid) may be contained between the wall of the first container and the wall of the second container. A stirrer may be contained in the space between the first container and the second container (e.g., between the walls of the first container and the second container). Advantageously, the second container may be selected to contain an acoustic emitter but not require the containment of any liquid. This is particularly useful when the acoustic emitter is a device or machine that cannot operate when immersed in a liquid. In such cases, the stirrer may be used to agitate the liquid in the space between the first container and the second container (e.g., between the walls of the first container and the second container), and the resulting bubbles will limit the transmission of sound from the acoustic emitter to the space. The second container may contain a liquid (e.g., a portion of the liquid).

[0023] The first and / or second container walls may be impermeable, optionally impermeable to gases (e.g., oxygen). However, this is not necessary, and in some examples, the first and / or second container walls may be selectively permeable, e.g., permeable to water and impermeable to gases (e.g., oxygen). One or more of the first container walls may include a water-permeable portion. One or more of the second container walls may include a water-permeable portion.

[0024] The liquid may include (e.g., be) water. The liquid may include (e.g., be) an aqueous solution. Water resources are abundant and inexpensive. Water is also particularly useful when the acoustic emitter is a marine piling device, as in such cases, water already surrounds the acoustic emitter being used. The liquid may include (e.g., be) seawater, optionally an aqueous solution including seawater. The liquid may include (e.g., be) fresh water, optionally an aqueous solution including fresh water. The liquid may include (e.g., be) a salt solution, optionally an aqueous solution including a salt solution. The liquid may include (e.g., be) pure water, or an aqueous solution including pure water (e.g., water having a resistivity of about 10 MΩ·cm at 25 °C).

[0025] The liquid may include (e.g., contain) hydrogen peroxide (i.e., H 2 O 2 ). The liquid may include (e.g., be) an aqueous solution including hydrogen peroxide. Hydrogen peroxide readily decomposes to form water and oxygen according to the following equation:

[0026] 2H 2 O 2 →2H 2 O + O 2

[0027] Hydrogen peroxide is thermodynamically unstable and can spontaneously decompose to form oxygen and water. Thus, a liquid (or its aqueous solution) containing hydrogen peroxide provides both a source of dissolved oxygen and, in some cases, a source of gas (e.g., oxygen) bubbles.

[0028] The liquid may include an aqueous solution containing hydrogen peroxide, where the concentration of hydrogen peroxide is greater than or equal to 0.001 mg / L, or greater than or equal to 0.01 mg / L, or greater than or equal to 0.1 mg / L, or greater than or equal to 1 mg / L, or greater than or equal to 20 mg / L, or greater than or equal to 50 mg / L, or greater than or equal to 80 mg / L, or greater than or equal to 200 mg / L, or greater than or equal to 500 mg / L, or greater than or equal to 800 mg / L, or greater than or equal to 1,000 mg / L. The liquid may include an aqueous solution containing hydrogen peroxide, where the concentration of hydrogen peroxide is less than or equal to 2,500 mg / L, or less than or equal to 2,200 mg / L, or less than or equal to 1,500 mg / L. The liquid may include an aqueous solution containing hydrogen peroxide, where the concentration of hydrogen peroxide is from 20 mg / L to 2,500 mg / L (including the end values), or from 200 mg / L to 2,500 mg / L (including the end values), or from 20 mg / L to 2,200 mg / L (including the end values), or from 200 mg / L to 2,200 mg / L (including the end values). The liquid may include an aqueous solution containing hydrogen peroxide at a concentration of about 1,500 mg / L (e.g., a concentration from 1,300 mg / L to 1,700 mg / L, including the end values). The aqueous solution may include hydrogen peroxide at a concentration from 500 mg / L to 1,500 mg / L (including the end values).

[0029] In an example, hydrogen peroxide at a concentration of 1,500 mg / L can decompose to produce 0.609 liters of oxygen per liter, an amount that exceeds the amount needed to form sufficient bubbles to limit sound transmission.

[0030] Furthermore, if at least 10% of the container volume is composed of gas (e.g., oxygen) bubbles (e.g., bubbles released from dissolved oxygen in the liquid due to agitation of the liquid), this can reduce the speed of sound in the liquid and bubbles to approximately 30 m / s -1 . Assuming where λ is the wavelength of the sound wave, v is the speed of sound in the medium, and f is the frequency of the sound, this is particularly useful when the sound emitter is a marine piling, because the peak frequency of the sound emitted by a marine piling is about 100 Hz, and thus in normal seawater (where the speed of sound is about 1,500 m / s -1 ) its wavelength is about 15 meters. However, when the presence of bubbles reduces the speed of sound to 30 m / s -1At that time, this wavelength will drop to 0.3 meters. Therefore, a 1-meter-thick oxygen bubble curtain formed by the bubbles described in this article will be more effective than a traditional bubble curtain in attenuating the sound emitted by offshore piling equipment.

[0031] It is further considered that the absorption of sound by the liquid and bubbles (e.g., the limitation of sound transmission) is related to the total distance traveled by the sound wave through the bubbles (e.g., the path length) and the total distance traveled by the sound wave through the liquid (e.g., the path length), expressed as a multiple of the wavelength of the sound wave. Therefore, reducing the wavelength size of the sound wave at any frequency (e.g., by making the sound wave propagate in a medium with a lower speed of sound than that in air or water) will enhance the sound absorption at that frequency. Therefore, the limitation of sound transmission from the sound source will be improved. As described above, it is considered that the speed of sound in a liquid containing a high density of bubbles is less than the speed of sound in air and less than the speed of sound in the liquid. Therefore, a liquid including a high density of bubbles is more effective in limiting sound transmission than, for example, an air gap. In addition, the bubbles generated by the oxygen released from water containing a high proportion of dissolved oxygen are at least initially very small (e.g., microscopic, e.g., on the order of a few micrometers or less in diameter), and are therefore particularly effective in limiting the transmission of higher frequencies.

[0032] The liquid may comprise (e.g., contain) an enzyme for decomposing hydrogen peroxide. The enzyme may be peroxidase. The enzyme may be catalase, optionally a synthetic catalase (e.g., as opposed to a naturally occurring catalase). The aqueous solution may comprise (e.g., contain) an enzyme for decomposing hydrogen peroxide. The liquid (optionally, the aqueous solution) may comprise an enzyme for catalytically decomposing hydrogen peroxide at a concentration of 0.0001% w / w to 5% w / w in water or 0.001% w / w to 5% w / w or 0.05% w / w to 5% w / w or at a concentration of 0.1% w / w to 4% w / w or 0.5% w / w to 3% w / w in water. The aqueous solution may comprise an enzyme for catalytically decomposing hydrogen peroxide at a concentration of at least 0.0001% w / w or at least 0.001% w / w or at least 0.01% w / w or at least 0.03% w / w in water. The aqueous solution may comprise no more than 6% w / w of enzyme / water. The aqueous solution may comprise at least 0.001 mg / L or 0.005 mg / L or 0.05 mg / L or 0.075 mg / L or 0.75 mg / L or 1 mg / L or 1.5 mg / L of the enzyme per liter of water (e.g., per liter of seawater), and optionally no more than 20 mg / L or 15 mg / L or 10 mg / L or 1 mg / L or 0.1 mg / L or 0.01 mg / L. The weight ratio of hydrogen peroxide to the enzyme may be 100:1 to 1:1, or 50:1 to 1:1, or 30:1 to 1:1, or 10:1 to 2:1, or 5:1 to 3:1. The ratio of hydrogen peroxide to the enzyme described herein provides sufficient hydrogen peroxide reaction (e.g., >95% of hydrogen peroxide reacts) to form bubbles. The aqueous solution optionally comprises at least 10 mg / L, 50 mg / L, 200 mg / L, 300 mg / L, 400 mg / L or 500 mg / L of the enzyme (e.g., catalase).

[0033] The liquid (optionally, the aqueous solution) may comprise between 1 kU and 100 kU of the enzyme (e.g., catalase) per 1 liter of water. The liquid (optionally, the aqueous solution) may comprise at least 5 kU of the enzyme (e.g., catalase) per 1 liter of water, or at least 10 kU, or at least 20 kU. The liquid (optionally, the aqueous solution) may comprise no more than 150 kU of the enzyme (e.g., catalase) per 1 liter of water, or no more than 170 kU, or no more than 200 kU, or no more than 500 kU. It should be understood that 1 U (1 enzyme unit) of the enzyme (e.g., catalase) is the amount that decomposes 1 micromole of hydrogen peroxide per minute at pH 7.0 and 25 °C (e.g., when the hydrogen peroxide concentration drops from 10.3 mM to 9.2 mM), and 1 kU is 1,000 times this amount. Those skilled in the art may choose to use a larger amount of the enzyme (e.g., catalase) such that it may be present in excess.

[0034] Advantageously, using a liquid (or aqueous solution) comprising hydrogen peroxide and an enzyme to catalytically decompose hydrogen peroxide means that more hydrogen peroxide is decomposed into oxygen and water (and / or this decomposition occurs at an accelerated rate) compared to a situation where the liquid (or aqueous solution) comprises hydrogen peroxide but does not contain (or contains very little) such an enzyme. The total amount of oxygen produced depends on the concentration of hydrogen peroxide used (e.g., the amount of hydrogen peroxide). Using an enzyme means that a lower concentration of hydrogen peroxide can be used.

[0035] The device can be configured to (and / or can include a liquid, optionally an aqueous solution) such that the concentration of hydrogen peroxide decreases by at least 5% within one hour, e.g., decreases by at least 10% within one hour, optionally decreases by at least 25% within one hour, typically decreases by less than 80% within one hour, e.g., decreases by less than 70% within one hour, e.g., decreases by less than 60% within one hour (e.g., when an initial concentration of 750 mg / L of hydrogen peroxide is provided). Advantageously, decomposing hydrogen peroxide at these rates results in a stable supply of bubbles, rather than producing too few bubbles over too long a time, or producing too many bubbles and requiring a resupply of hydrogen peroxide to produce more bubbles. The device can be configured to allow for a resupply of hydrogen peroxide at predetermined intervals (e.g., once per hour, or once every 2 hours, or once every 3 hours).

[0036] The liquid can include (e.g., contain) a surfactant. The liquid can include an aqueous solution containing a surfactant. Advantageously, when a surfactant is provided, bubbles are less likely to leave the container at the liquid surface, and thus more gas can be retained (since, for example, due to the liquid flow caused by a pump, the bubbles can be urged back into the liquid). This means that it is not necessary to frequently replace the gas (e.g., oxygen) and / or gas bubbles (e.g., oxygen bubbles) in the liquid, and thus the energy required to agitate the liquid with a stirrer can be saved. In some cases, this also means that a smaller amount of chemicals (e.g., hydrogen peroxide and the enzyme for decomposing hydrogen peroxide) is required.

[0037] The surfactant may be a surfactant that has been evaluated as safe for use in a marine environment. The surfactant may be a surfactant that has been evaluated as safe for use in a freshwater environment. The surfactant may include soap berry. The surfactant may include yucca extract. The surfactant may include lecithin. The surfactant may include monoglyceride. The surfactant may include diglyceride. The surfactant may include fatty acid. The surfactant may include functionalized protein. The surfactant may include (e.g., be) a natural surfactant. The surfactant may include (e.g., be) a synthetic surfactant. The surfactant may include a Tween-type surfactant. The surfactant may include sodium stearoyl lactate. The surfactant may include calcium stearoyl lactate. The surfactant may include sucrose ester.

[0038] The agitation zone may surround the agitator. The agitator may be configured to optionally cause sufficient bubble formation, for example, after 60 seconds of agitator operation, such as after 2 minutes, such as after 5 minutes (optionally after less than 20 minutes, such as after less than 18 minutes, such as after less than 15 minutes), so that the combined volume of the bubbles is at least 1% of the total volume of the (e.g., the) agitation zone surrounding the agitator (e.g., where the agitator is located at the bottom of the agitation zone). For example, sufficient bubbles may be formed such that the combined volume of the bubbles is at least 2% (optionally, 10%) of the total volume of the agitation zone, such as at least 25% of the total volume of the agitation zone. The agitator may be configured to cause sufficient bubble formation such that the combined volume of the bubbles is less than 99% of the total volume of the agitation zone, such as less than 90%, such as less than 75%. The liquid and the bubbles may together form a foam, such as a fluid foam. The higher the proportion of bubbles in the liquid (e.g., the more the number of bubbles and / or the greater the total volume of the bubbles relative to the total volume of the liquid), the more effectively the transmission of sound from the sound emitter through the liquid can be restricted.

[0039] The device (such as a stirrer, optionally in combination with a fluid) can be configured to activate the stirrer for a period of (e.g., initial) activation, thereby causing sufficient bubble generation such that the bubbles will subsequently remain suspended in the fluid for a decay period that is longer than the (e.g., initial) activation period. For example, the device can be configured such that the stirrer is activated for an initial activation period of at least 1 minute (e.g., at least 2 minutes, e.g., at least 5 minutes, optionally less than 60 minutes, e.g., less than 30 minutes, e.g., less than 15 minutes), thereby producing a decay period of at least 30 minutes, e.g., at least 2 hours, e.g., at least 4 hours, typically less than 12 hours, e.g., less than 8 hours, e.g., less than 6 hours. Those skilled in the art will recognize that the appropriate initial activation period and subsequent decay period will depend on various factors, including the composition of the fluid, the temperature of the fluid, the size and configuration of the container, the peak sound pressure emitted by the sound emitter, etc. By selecting an activation period that will cause sufficient bubble generation such that the decay period is longer than the activation period (optionally taking into account the composition and / or temperature of the fluid, and / or the size and configuration of the container, and / or the peak sound pressure emitted by the sound emitter, etc.), a more efficient device can be provided as less energy is required to continuously activate the stirrer.

[0040] The stirrer can be configured to produce bubbles, where the average (e.g., mean) diameter of the bubbles is at least 0.5 microns, e.g., at least 1 micron, e.g., at least 0.01 cm, e.g., at least 0.05 cm, e.g., at least 0.1 cm. The stirrer can be configured to produce bubbles, where the average (e.g., mean) diameter of the bubbles is less than 1 cm, e.g., less than 0.5 cm, e.g., less than 0.2 cm. At least 50% of the bubbles produced have a diameter between 1 micron and 0.1 cm, e.g., at least 75% of the bubbles produced have a diameter between 1 micron and 0.1 cm, e.g., at least 85% of the bubbles produced have a diameter between 1 micron and 0.1 cm. In an example, the stirrer can be configured to produce bubbles, where the bubbles have an average (e.g., mean) diameter of 5 mm. Those skilled in the art will understand that the diameters described above can refer to the maximum diameter of the bubbles from their generation up to 3 seconds after generation, optionally up to 15 seconds after generation, optionally up to 1 minute after generation (and this can depend on the size of the container), and the size of the bubbles can vary over time (e.g., due to changes in pressure as the bubbles rise in the liquid, or due to fusion with other bubbles).

[0041] It has been found that the presence of hydrogen peroxide is particularly effective in generating smaller bubbles. When the liquid includes water, hydrogen peroxide, and an enzyme for decomposing hydrogen peroxide, agitating this liquid can form sufficient bubbles within 30 seconds to limit the transmission of sound. Accordingly, the device (e.g., a mixer, e.g., for combining liquids) can be configured to cause sufficient bubble formation within 30 seconds, e.g., within 20 seconds, e.g., within 10 seconds, e.g., within 5 seconds to limit the transmission of sound. The device (e.g., a mixer, e.g., for combining liquids) can be configured to cause sufficient bubble formation within 1 second, e.g., within 3 seconds to limit the transmission of sound (e.g., reducing the sound pressure by at least 20 decibels). For example, the agitator can be configured to agitate a sufficient amount of liquid within a sufficiently short period of time to cause sufficient bubble formation within 1 second, e.g., within 3 seconds, thereby limiting the transmission of sound (e.g., reducing the sound pressure by at least 20 decibels). When the liquid includes hydrogen peroxide and an enzyme for decomposing hydrogen peroxide, it has also been found that agitation of the liquid increases the rate of decomposition of hydrogen peroxide into water and oxygen. In addition, such liquids are more effective at limiting the transmission of sound than water containing air bubbles, take longer to dissipate when agitation stops, and reform more quickly when re-agitated.

[0042] The agitator can be configured such that when the agitator operates, it generates at least 1,000 bubbles per minute in a 1-liter volume, e.g., at least 10,000 bubbles per minute in a 1-liter volume, e.g., at least 100,000 bubbles per minute in a 1-liter volume. The agitator can be configured such that when the agitator operates, it generates at least 5,000,000 bubbles per minute in a 1-liter volume, e.g., at least 1,000,000 bubbles per minute in a 1-liter volume, e.g., at least 500,000 bubbles per minute in a 1-liter volume. Those skilled in the art will appreciate that the size and number of bubbles generated will depend on several factors, including but not limited to the temperature of the liquid, the pH value of the liquid, the pressure within the liquid, the oxygen saturation of the liquid, the rate at which the agitator agitates the liquid (e.g., the liquid flow rate induced by the agitator), the presence of any substances in the liquid, the type and concentration of any substances (e.g., hydrogen peroxide, enzyme, surfactant) in the liquid, etc.

[0043] The first container can define a volume of at least 0.5 m 3 , e.g., 1 m 3 , e.g., at least 5 m 3 , e.g., at least 10 m 3 , e.g., at least 15 m 3 (optionally including the volume of the second container when a second container is present). The first container can define a volume of less than 5,000 m 3 , e.g., less than 2,500 m 3 , e.g., less than 1,000 m 3(Optionally, including the volume of the second container when present). The second container may define a volume of at least 0.25 m 3 , such as at least 0.5 m 3 , such as at least 4 m 3 , such as at least 8 m 3 , such as at least 10 m 3 . The second container may define a volume less than 2,000 m 3 , such as less than 1,000 m 3 , such as less than 500 m 3 . The space between the first container and the second container (e.g., between the walls of the first container and the second container) may define a volume of at least 0.25 m 3 , such as at least 0.5 m 3 , such as at least 1 m 3 , such as at least 2 m 3 , such as at least 5 m 3 . The space between the first container and the second container (e.g., between the walls of the first container and the second container) may define a volume less than 3,000 m 3 , such as less than 1,500 m 3 , such as less than 500 m 3 . Those skilled in the art will understand that the device and thus the size of the container can be selected according to the size of the sound emitter. Such volumes are suitable (e.g., at least in part) for enclosing large sound emitters, such as heavy machinery, such as drilling equipment, offshore piling equipment, etc.

[0044] The container may include one or more barriers, where the or each barrier extends at least partially through the interior of the container, thereby forming a plurality of sub-containers. Each of the plurality of sub-containers may have a respective agitator provided therein. Each of the plurality of sub-containers may have a respective orifice defined therein, each respective orifice being arranged to allow bubbles to leave the respective sub-container (and optionally leave the container). The one or more barriers may extend in a horizontal direction. The one or more barriers may extend in a vertical direction. The one or more barriers may extend in a direction inclined relative to the horizontal direction. The one or more barriers may be planar. The one or more barriers may extend between one or more first container walls and one or more second container walls. The volume of each sub-container may be at least 5%, such as at least 10%, such as at least 20% of the total volume of the (e.g., first) container. The volume of each sub-container may be less than 80%, such as less than 60%, such as less than 50% of the total volume of the (e.g., first) container. Each sub-container may be the same size as each other sub-container, but this is not necessary. In an example, one or more (optionally each) of the plurality of sub-containers may have a (vertical) height of at least 5 meters, such as at least 20 meters, such as at least 40 meters. One or more (optionally) each of the plurality of sub-containers may have a (vertical) height of less than 100 meters, such as less than 75 meters, such as less than 60 meters. The or each barrier may include a material (e.g., formed therefrom) having a relatively low acoustic impedance. The or each barrier may include a sound-absorbing material (e.g., formed therefrom). The sub-containers may be stacked vertically (e.g., a first sub-container is located above a second sub-container, etc.). The agitators may be stacked vertically.

[0045] When the sound emitter is particularly large, it is helpful to provide a particularly large container to (e.g., at least partially) surround the sound emitter. However, it takes some time for the bubbles to travel upward under the action of buoyancy (especially in the case of very small bubbles, this upward travel may only occur after fusing with other bubbles to form larger bubbles), or move in other directions as the fluid flows within the container. Therefore, if an agitator is provided only at one location within the large container, it takes a long time for there to be a sufficient number of bubbles throughout the liquid in the container to effectively limit the transmission of sound. By providing barriers within the container (thereby effectively dividing the container into a plurality of sub-containers) and an agitator within each sub-container, the time required to provide sufficient bubbles can be reduced. It should also be noted that both the bubble size and the speed of sound are related to pressure, and the pressure increases with increasing depth. Providing the sub-containers described herein can help control this situation.

[0046] The device may include a pump configured to cause liquid flow on the liquid surface. The pump may include a pump inlet located at the upper part of the container (e.g., at or near the liquid surface). The pump may include a pump outlet located at or near the bottom of the container. There may be a pipe extending between the pump inlet and the pump outlet. The pump may be configured to cause the liquid to flow in a downward direction. The device may include one or more pumps configured to cause liquid flow within the container. Each sub-container may include a corresponding pump configured to cause liquid flow, optionally at the top of the sub-container, e.g., in a downward direction.

[0047] The advantage of providing a pump configured to cause liquid flow on the liquid surface is that it allows bubbles that float to the surface to be pushed back down into the container (e.g., by causing the fluid to flow in a downward direction). This means that fewer bubbles need to be replaced, and the agitator can operate less continuously, or at a lower rate, or require a lower percentage of dissolved oxygen, or require a lower concentration of hydrogen peroxide, or require a smaller amount of the enzyme for decomposing hydrogen peroxide. In short, using such pumps can make the device more efficient.

[0048] The pump(s) may be configured to have a displacement of at least 1 L per minute, e.g., at least 500 L per minute, e.g., at least 1000 L per minute (optionally, in combination). The pump(s) may be configured to have a displacement of up to 50,000 L per minute, e.g., up to 25,000 L per minute, e.g., up to 10,000 L per minute (optionally, in combination). Those skilled in the art will understand that the type and capacity of the pump can be selected according to the size of the container. For example, the pump may be configured to discharge 100% of the capacity of the container at least once every 30 minutes, e.g., at least once every 15 minutes, e.g., at least once every 10 minutes. The pump may be configured to discharge 100% of the capacity of the container at least once every 3 minutes, e.g., at least once every 5 minutes.

[0049] The agitator can be configured to form sufficient bubbles such that in the agitation zone (such as the one) surrounding the agitator, the optical (such as light) intensity of (for example, visible) light (such as within the wavelength range of 300 nm to 800 nm, such as 350 nm to 780 nm, such as 380 nm to 750 nm) traveling through 10 cm of liquid is reduced by at least 10% (such as at least 50%, such as at least 80%, optionally up to 99%) compared to the intensity of the light before it travels through the liquid. The agitator can be configured to form sufficient bubbles such that in the agitation zone surrounding the agitator, the optical (such as light) intensity of (for example, visible) light (such as within the wavelength range of 300 nm to 800 nm, such as 350 nm to 780 nm, such as 380 nm to 750 nm) traveling through 10 cm of liquid is reduced by at least 10% (such as at least 50%, such as at least 80%, optionally up to 99%) compared to the intensity of the light traveling through 10 cm of liquid without any bubbles.

[0050] Those skilled in the art should understand that the optical (such as light) intensity of light can be calculated according to the following equation:

[0051]

[0052] where x is the distance through the liquid (including any bubbles in the liquid), I(x) is the intensity of light at distance x, I 0 is the initial intensity of light at distance x = 0, κ v is the opacity of the liquid, and ρ is the mass density of the liquid. Thus, in this context, the optical (such as, light) intensity should be understood as a function of the opacity of the medium through which the light travels. A liquid containing relatively high-density (such as relatively small) bubbles has a higher opacity than a liquid containing relatively low-density (such as relatively small) bubbles. It should also be understood that a liquid containing a higher proportion of dissolved oxygen may have a different opacity to light compared to a liquid containing a lower proportion of dissolved oxygen. Additionally, when brine (such as seawater) contains dissolved oxygen, its opacity to light can also be different from that of fresh water containing dissolved oxygen.

[0053] When sufficient bubbles are generated such that the optical (such as, light) intensity of (visible) light is reduced as described above, the inventors have found that the transmission of sound is also effectively limited.

[0054] However, it should also be understood that bubbles with a small enough diameter may not (e.g., visibly) change the opacity of the liquid while still being effective in attenuating sound waves. Surprisingly, it has been found that bubbles with a diameter less than 1 mm and that do not significantly change the opacity of 10 cm of water in number still have an attenuation effect. The device (e.g., agitator) can be configured to produce bubbles with a diameter less than 1 mm (typically greater than 1 μm). The device (e.g., agitator) can be configured to form sufficient bubbles such that in the (e.g., said) agitation zone surrounding the agitator, the optical (e.g., light) intensity of (e.g., visible) light traveling through 10 cm of liquid (e.g., in the wavelength range from 300 nm to 800 nm, e.g., from 350 nm to 780 nm, e.g., from 380 nm to 750 nm) is reduced by less than 10% (e.g., less than 5%, e.g., less than 2%) compared to the intensity of the light before it travels through the liquid.

[0055] The device can include an (e.g., visible) light detector configured to output an indication of the light intensity of the liquid that has traveled a certain distance. The device can include an (e.g., visible) light emitter configured to emit light (e.g., that can then be detected by the light detector). The distance can be at least 5 cm, e.g., at least 10 cm, e.g., at least 20 cm. The distance can be a distance within the agitation zone. The device can include a sound detector configured to output an indication of the sound intensity transmitted outside the (e.g., first) container. Providing such light and / or sound detectors provides an indication of whether sufficient bubbles have been produced to effectively limit sound transmission. Providing a sound detector provides an indication of sound transmission. Both detectors can assist in the monitoring of the operation of the device, especially by a user located away from the device.

[0056] The device may include a controller. The controller may be configured to receive an indication (e.g., from a light detector) of the (e.g., visible) light intensity of the liquid that has traveled a certain (e.g., the) distance; and in response to the received indication, adjust the amount of agitation caused by the agitator so as to maintain a target light intensity. The target light intensity may be within a certain light intensity range. The light intensity range may be between 90% and 10% of the (e.g., visible) light intensity of the liquid that has not traveled the distance, optionally between 80% and 20%, e.g., between 60% and 40%. The target light intensity may be lower than a threshold light intensity. The threshold light intensity may be 30% of the (e.g., visible) light intensity of the liquid that has not traveled the distance, or may be 20% of the (e.g., visible) light intensity of the liquid that has not traveled the distance, or may be 10% of the (e.g., visible) light intensity of the liquid that has not traveled the distance. The light detector may be configured to compare the light intensity of the liquid that has traveled a certain (e.g., the) distance with the light intensity of a reference beam, where the reference beam is a beam that has not traveled through the liquid, optionally where the reference beam is a beam from the same light source as the light source of the light that has traveled through the liquid.

[0057] When there are enough bubbles, the light intensity when light passes through the liquid decreases, which also indicates that the transmission of sound in the liquid is restricted. The agitation of the liquid by the agitator causes bubbles to form, and when the agitation stops, the bubbles stably leave the liquid (e.g., under the action of buoyancy, e.g., through an opening in the container). Thus, by providing the controller described herein, a feedback system can be arranged, where when the light intensity increases above or outside the threshold (since this indicates fewer bubbles present and thus more sound can be transmitted), the agitator is operated, and when the light intensity is below the threshold or within the range (since this indicates more bubbles present and thus less sound can be transmitted), the agitator is not operated. This means that the agitator does not need to be continuously operated, thus making the device more efficient.

[0058] Gas (e.g., oxygen) bubbles can form a gas (e.g., oxygen) bubble curtain. The gas (e.g., oxygen) bubble curtain can include gas (e.g., oxygen) bubbles formed due to the agitation of the fluid by an agitator. The gas (e.g., oxygen) bubbles can form a gas (e.g., oxygen) bubble curtain that at least partially surrounds the sound emitter. The gas (e.g., oxygen) bubble curtain can be an annular gas (e.g., oxygen) bubble curtain. For example, a relatively higher gas (e.g., oxygen) bubble density can be found inside the annular space (gas (e.g., oxygen) bubble curtain) in the container than outside the annular space. The number of bubbles present in the gas (e.g., oxygen) bubble curtain can be at least twice (e.g., at least three times, e.g., at least five times, optionally less than 100,000 times) the number of bubbles present outside the gas (e.g., oxygen) bubble curtain. The annular space can have an inner circumference, an outer circumference, and a height, and the sound emitter can be surrounded by the inner circumference. The thickness of the annular space (e.g., between the inner circumference and the outer circumference) can be at least 5 cm, e.g., at least 10 cm, e.g., at least 50 cm. The thickness of the annular space can be less than 10 m, e.g., less than 5 m, e.g., less than 1 m. However, those skilled in the art should understand that the oxygen bubble curtain can be formed into substantially any shape (e.g., by the positioning of the agitator and / or the positioning and use of pumps), and can be configured to partially or fully surround the sound emitter. For example, the oxygen bubble curtain can be generally cuboid in shape, having a length parallel to the bottom of the container, a height parallel to the height dimension of the container, and a width perpendicular to its height. The width of the oxygen bubble curtain (e.g., between the inner circumference and the outer circumference) can be at least 5 cm, e.g., at least 10 cm, e.g., at least 50 cm. The width of the oxygen bubble curtain can be less than 10 m, e.g., less than 5 m, e.g., less than 1 m. The inventors unexpectedly found that even if the bubble curtain has a relatively small thickness or width (e.g., less than 50 cm), the bubbles in the bubble curtain can effectively limit the transmission of sound.

[0059] The device can be configured to generate sufficient bubbles to reduce sound transmission such that the sound pressure of the sound emitted by the sound emitter after passing through the bubbles is at least 20 dB lower, e.g., at least 40 dB lower, e.g., at least 60 dB lower, e.g., at least 100 dB lower than the sound pressure of the sound emitted by the sound emitter before passing through the bubbles. The device can be configured to generate sufficient bubbles to prevent at least 60% by amplitude, e.g., at least 80% by amplitude, e.g., at least 90% by amplitude of the sound from the sound emitter from transmitting outside the bubbles. The device can be configured to generate sufficient bubbles to reduce the peak frequency of the sound wave from the sound emitter by at least 60% so as not to transmit outside the bubbles, e.g., reduce by at least 80%, e.g., reduce by at least 90% by amplitude. The device can be configured to generate sufficient bubbles such that substantially no sound is transmitted from the sound emitter outside the bubbles.

[0060] The controller can be configured to receive an indication (e.g., a first indication) of the sound intensity outside a (e.g., the) container; and in response to the received indication of the sound intensity, adjust the amount of agitation caused by the agitator so as to maintain a target sound intensity. The target sound intensity can be within a certain sound intensity range. The sound intensity range can be between 0 and 500 decibels, such as between 1 and 300 decibels, such as between 5 and 100 decibels. The target sound intensity can be lower than a threshold sound intensity. The threshold sound intensity can be less than 150 decibels, such as less than 80 decibels, such as less than 50 decibels, such as less than 20 decibels.

[0061] The device can include a temperature sensor configured to output an indication of the liquid temperature. The device can include a heater configured to heat the liquid. The device can include a thermal regulator (e.g., including a heat exchanger) configured to adjust the liquid temperature. The thermal regulator (e.g., the heat exchanger) can transfer heat from the liquid inside the container to the liquid outside the container and vice versa. The device can include a cooler configured to cool the liquid. The controller can be configured to: receive an indication (e.g., the indication) of the liquid temperature; and in response to the received indication of the liquid temperature, adjust the amount of agitation caused by the agitator. This is helpful because the amount and size of the bubbles generated by the operation of the agitator can be related to the temperature. The controller can be configured to, for example, adjust the temperature of the liquid in response to the received indication of the liquid temperature so as to optionally maintain a target temperature. The target temperature can be within a certain temperature range. The temperature range can be from 5 °C to 50 °C (including the end values), such as from 10 °C to 30 °C (including the end values), such as from 18 °C to 22 °C (including the end values).

[0062] The device can include a pH sensor configured to output an indication of the pH value of the liquid. The pH sensor can be calibrated for the salinity of the liquid in the container. The controller can be configured to: receive an indication (e.g., the indication) of the pH value of the liquid; and in response to the received indication of the liquid pH value, adjust the amount of agitation caused by the agitator. This is helpful because the amount and size of the bubbles generated by the operation of the agitator can be related to the pH value.

[0063] The device can include a pressure sensor configured to output an indication of the pressure of the liquid, such as in the agitation zone. The controller can be configured to: receive an indication (e.g., the indication) of the pressure of the liquid; and in response to the received indication of the liquid pressure, adjust the amount of agitation caused by the agitator. This is helpful because the amount and size of the bubbles generated by the operation of the agitator can be related to the pressure.

[0064] The device may include an oxygen detector configured to output an indication of the percentage of oxygen saturation in the liquid. The controller may be configured to: receive an indication (such as the aforementioned) of the percentage of oxygen saturation in the liquid; and in response to the received indication of the percentage of oxygen saturation in the liquid, adjust the amount of agitation caused by the agitator. This is helpful because the amount and size of the bubbles generated by the operation of the agitator may depend on the amount of dissolved oxygen in the liquid.

[0065] The sound emitter may include mechanical means, such as a mechanical actuator. The sound emitter may include a mechanical machine. The sound emitter may include a marine piling device. The sound emitted by a marine piling device is particularly loud, and it is particularly challenging to limit the sound transmission of marine piling equipment. However, limiting the sound transmission of such equipment has significant benefits for marine life. In particular, marine mammals and some cetaceans can hear frequencies much higher than those within the frequency range audible to humans, including some frequencies generated by marine piling (beyond the frequencies within the audible frequency range of humans). As described herein, the sound emitter may emit sound waves with peak frequencies in the range of 50 Hz to 200 kHz (including the end values), optionally 10 Hz to 300 kHz (including the end values), optionally 5 Hz to 500 kHz (including the end values). The device may be configured to limit the transmission of sound waves with peak frequencies in the range of 50 Hz to 200 kHz (including the end values), optionally 10 Hz to 300 kHz (including the end values), optionally 5 Hz to 500 kHz (including the end values).

[0066] The sound emitter may include a valve, such as a control valve. For example, the sound emitter may include a valve (such as a control valve) of a gas distribution pipe. The gas distribution pipe may contain very large valves (such as control valves) that function to manage the energy flow and emit a great deal of noise during normal steady-state operation.

[0067] The sound emitter may (for example, be configured to) emit sound within the audible frequency range of humans. The sound emitter may (for example, be configured to) emit ultrasonic waves. The sound emitter may (for example, be configured to) emit sound with a frequency lower than the audible frequency range of humans. For example, the sound emitter may (for example, be configured to) emit sound waves with a peak frequency of at least 1 Hz, such as at least 20 Hz, such as at least 50 Hz. The sound emitter may (for example, be configured to) emit sound waves with a peak frequency less than 500 kHz, such as less than 200 kHz, such as less than 100 kHz. The sound emitter may (for example, be configured to) emit sound waves with a peak frequency between 50 Hz and 100 kHz (including the end values), such as between 1 kHz and 50 kHz (including the end values), such as between 10 kHz and 50 kHz (including the end values). In an example, the sound emitter may (for example, be configured to) emit sound waves with a frequency range of 13 Hz to 3 kHz.

[0068] In some examples, the diameter of the bubbles at a relatively deep depth (e.g., on average, such as the mean value) may be relatively small, and thus may more effectively limit the transmission of relatively high-frequency sounds, while the diameter of the bubbles at a relatively shallow depth (e.g., on average, such as the mean value) may be relatively large, and thus may more effectively limit the transmission of relatively low-frequency sounds. The device may be configured to limit the transmission of sound waves within a first frequency range at a first depth and limit the transmission of sound waves within a second frequency range (different from the first frequency range) at a second depth (different from the first depth). The first depth may be greater than the second depth. The first frequency range may be a higher frequency range than the second frequency range.

[0069] In some example embodiments, the container may include one or more barriers, thereby forming a plurality of sub-containers as described herein. The plurality of sub-containers may include one or more deep sub-containers located at a relatively large depth and one or more shallow sub-containers located at a relatively small (e.g., shallower) depth. Advantageously, this allows for bubble equilibration at higher pressures (e.g., in the deep sub-containers), and thus smaller bubbles, thereby maintaining the absorption frequency range. The higher the pressure at depth, the smaller the bubbles, and thus the higher the frequency absorption rate.

[0070] A liquid (e.g., water, such as an aqueous solution) including at least 2% (e.g., at least 10%) by volume of dissolved oxygen can be formed by combining water and hydrogen peroxide and allowing the hydrogen peroxide to decompose into water and oxygen (e.g., naturally). A liquid (e.g., water, such as an aqueous solution) including at least 2% (e.g., at least 10%) by volume of dissolved oxygen can be formed by combining water, hydrogen peroxide, and an enzyme (e.g., catalase) for decomposing hydrogen peroxide and causing the hydrogen peroxide to decompose into water and oxygen under the action of the enzyme. A liquid (e.g., water, such as an aqueous solution) including at least 2% (e.g., at least 10%) by volume of dissolved oxygen can be formed by pressing oxygen (optionally oxygen bubbles) into the liquid (e.g., water, such as an aqueous solution), optionally by using a mechanical system. A water including at least 2% (e.g., at least 10%) by volume of dissolved oxygen can be formed by using an oxygenation system, such as by injecting oxygen with a membrane diffusion (e.g., oxygenation) system. The device may include a membrane diffusion (e.g., oxygenation) system. When the device includes a membrane diffusion (e.g., oxygenation) system, the bubbles may include oxygen bubbles, and / or nitrogen bubbles and / or air bubbles. A water including at least 2% (e.g., at least 10%) by volume of dissolved oxygen can be formed by a micro-bubbling system. The device may include a micro-bubbling system. A water including at least 2% (e.g., at least 10%) by volume of dissolved oxygen can be formed by using a venturi system. The device may include a venturi system.

[0071] The device may include a gas (e.g., oxygen) tank. The device may include one or more gas supply pipes extending between the gas (e.g., oxygen) tank and a membrane diffusion (e.g., oxygenation) system, each pipe including at least one valve configured to fluidly connect and disconnect the gas (e.g., oxygen) tank from the membrane diffusion (e.g., oxygenation) system. The device may include one or more gas supply pipes extending between the gas (e.g., oxygen) tank and a micro-bubbling system, each pipe including at least one valve configured to fluidly connect and disconnect the gas (e.g., oxygen) tank from the micro-bubbling system. The device may include one or more gas supply pipes extending between the gas (e.g., oxygen) tank and a Venturi system, each pipe including at least one valve configured to fluidly connect or disconnect the gas (e.g., oxygen) tank from the Venturi system.

[0072] The container may, for example, surround the sound emitter in all directions, except for the opening, (e.g., completely). For example, the second container wall may be configured to surround the sound emitter in all directions except where the first opening is provided, and the first container wall may be configured to surround the second container wall in all directions except where the second opening is provided, and the first opening and the second opening may be offset from each other. The first container wall may, for example, surround the sound emitter in all directions, except where the opening is provided, (e.g., completely). The second container wall may, for example, surround the sound emitter in all directions, except where the opening is provided, (e.g., completely). The container may include a closable opening. The container may include a door configured to open and close the opening.

[0073] However, it should be understood that a container arranged to at least partially surround the sound emitter need not restrict sound transmission in all directions. For example, the container may be an open-topped cylinder, so that sound transmission from the sound emitter is restricted in the downward and lateral directions but not (or less restricted) in the upward direction. Similarly, a container arranged to at least partially surround the sound emitter may restrict sound transmission in one direction, or restrict transmission within a certain angular range outward from the sound emitter. It is useful to provide a container in the form of a barrier, where the container restricts sound transmission from the sound emitter to a particular space. The container may be provided in the form of a barrier. The device (e.g., container) may be configured to restrict sound transmission from the sound emitter to a particular space.

[0074] Accordingly, another aspect of the present invention provides an apparatus for restricting sound transmission from a sound emitter, the apparatus comprising: a sound insulation barrier including a container containing a liquid, wherein the liquid comprises at least 2% (e.g., at least 10%) by volume of dissolved oxygen; and an agitator configured to agitate the liquid so as to form gas (e.g., oxygen) bubbles in the liquid. Advantageously, when there is a space near the sound emitter and it is preferably to restrict sound from entering the space, the sound insulation barrier can be placed between the sound emitter and the space. The liquid and the bubbles will then restrict sound transmission into the space.

[0075] Another aspect of the present invention provides a method for restricting sound transmission from a sound emitter (e.g., in a liquid), the sound emitter being at least partially surrounded by a container (optionally, a first container) containing a liquid comprising at least 2% (e.g., at least 10%) by volume of dissolved oxygen, and the method comprising: causing agitation (e.g., agitating) of (e.g., at least a portion of) the liquid in the container so as to form gas (e.g., oxygen) bubbles in the liquid. Causing the formation of gas (e.g., oxygen) bubbles may include releasing oxygen from the liquid to form bubbles.

[0076] It has been found that agitating a liquid comprising at least 2% (e.g., at least 10%) by volume of dissolved oxygen is a particularly effective method for forming sufficient bubbles to restrict sound transmission in (e.g., through) the liquid.

[0077] The method may optionally include receiving an indication of the (e.g., visible) light intensity of light passing through a certain distance of the liquid from a light detector. The method may include adjusting the amount of agitation caused in response to the received indication so as to maintain a target light intensity. The target light intensity may be within a certain light intensity range. The light intensity range may be between 90% and 10% of the (e.g., visible) light intensity of the liquid not passing through the distance, optionally between 95% and 5%, optionally between 80% and 20%, e.g., between 60% and 40%. The target light intensity may be lower than a threshold light intensity. The threshold light intensity may be 30% of the (e.g., visible) light intensity of the liquid not passing through the distance, or may be 20% of the (e.g., visible) light intensity of the liquid not passing through the distance, or may be 10% of the (e.g., visible) light intensity of the liquid not passing through the distance. The method may include comparing the light intensity of the liquid that has passed through a certain (e.g., the) distance with the light intensity of a reference beam, wherein the reference beam is a beam of light that has not passed through the liquid, optionally wherein the reference beam is from the same source as the source of the light of the liquid that has passed through the distance.

[0078] The method may include receiving an indication of the sound intensity outside the container (optionally outside the first container), and adjusting the amount of agitation induced in response to the received sound intensity indication so as to maintain a target sound intensity. The target sound intensity may be within a certain sound intensity range. The sound intensity range may be between 0 and 100 decibels, such as between 1 and 80 decibels, such as between 5 and 40 decibels. The target sound intensity may be lower than a threshold sound intensity. The threshold sound intensity may be less than 100 decibels, such as less than 50 decibels, such as less than 20 decibels.

[0079] Those skilled in the art will appreciate that the size and number of bubbles generated will depend on several factors, including but not limited to the temperature of the liquid, the pH value of the liquid, the pressure within the liquid, the oxygen saturation of the liquid, the rate at which the agitator agitates the liquid (e.g., the liquid flow rate induced by the agitator), whether any substances are present in the liquid, the type and concentration of any substances (e.g., hydrogen peroxide, enzymes, surfactants) in the liquid, etc.

[0080] Accordingly, the method may include receiving an indication of the liquid temperature. The method may include adjusting the temperature of the liquid (e.g., in response to the received liquid temperature indication) so as to maintain a target temperature. The target temperature may be within a certain temperature range. The temperature range may be from 5°C to 50°C (including the end values), such as from 10°C to 30°C (including the end values), such as from 18°C to 22°C (including the end values). The method may include adjusting the amount of agitation induced in response to the received liquid temperature indication.

[0081] The method may include receiving an indication of the pH value of the liquid. The method may include adjusting the amount of agitation induced in response to the received pH value indication of the liquid.

[0082] The method may include receiving an indication of the pressure of the liquid, such as in the agitation zone. The method may include adjusting the amount of agitation induced in response to the received liquid pressure indication.

[0083] The method may include receiving an indication of the volume of liquid within the container. The method may include supplying additional liquid to the container. The method may include feeding additional liquid into the container. The method may include causing excess liquid to leave the container. The method may include removing excess liquid.

[0084] Another aspect of the present invention provides a method of forming a liquid comprising water and at least 2% (e.g., at least 10%) by volume of dissolved oxygen, as described above, the method comprising: causing a mixture of water, hydrogen peroxide, and a catalyst for decomposing hydrogen peroxide (e.g., mixing them).

[0085] It is easier to form oxygen bubbles in water containing at least 2% (e.g., at least 10%) by volume of dissolved oxygen by agitating the water than in water containing a lower percentage of dissolved oxygen.

[0086] The liquid may contain at least 2% (e.g., at least 10%) by volume of dissolved oxygen. The liquid may contain at least 25% by volume of dissolved oxygen, e.g., at least 50%, e.g., at least 75%, e.g., at least 80%. The liquid may contain less than 100% of dissolved oxygen, e.g., less than 99%, e.g., less than 90%. The liquid may have an oxygen saturation of at least 50%. The liquid may have an oxygen saturation of at least 80%. The liquid may have an oxygen saturation of at least 100%. The liquid may contain supersaturated oxygen, e.g., an oxygen saturation exceeding 100%. The liquid may have an oxygen saturation of at least 120%. The oxygen saturation of the liquid may be less than 200%, e.g., less than 150%. When the liquid is agitated, oxygen is more likely to be released from the liquid to form oxygen bubbles in the presence of a higher percentage of dissolved oxygen in the liquid (e.g., especially when the liquid contains at least 10% by volume of dissolved oxygen, but some effects are also observed when the liquid contains at least 2% by volume of dissolved oxygen).

[0087] The controller may include one or more processors and a computer-readable memory (e.g., a non-transitory computer-readable storage medium) storing instructions that, when executed by the one or more processors, cause the controller to perform actions for which the controller is configured.

[0088] The acoustic emitter can be an acoustic emitter in a body of water (such as an ocean, sea, lake, bay, reservoir, pond, etc.) having a water surface and a bottom (such as an ocean floor, seabed, lake bottom, etc.). The device can be positioned in the body of water. The method can include installing the device in the body of water. The liquid surface inside the container can be higher than the water surface outside the container (such as due to the water pressure acting on the container walls). Gas (such as oxygen) bubbles formed due to liquid agitation and then reaching the liquid surface may cause some liquid to be removed from the container (such as due to bubble ejection). In some examples, the acoustic emitter can emit sound at a high enough sound pressure such that the sound waves cause (for example, at least a portion of) the bubbles in the liquid to burst. The method can include supplying additional liquid and / or forming additional bubbles to replace the burst bubbles. The device can include a liquid supply pipe configured to supply additional liquid into the container (such as to replace the liquid that leaves the container when the bubbles reach the liquid surface and / or the liquid that leaves the container due to a leak in the container). The device can include a liquid supply pump configured to supply additional liquid into the container, for example, through the liquid supply pipe. The method can include optionally causing additional liquid to be supplied into the container through the liquid supply pipe. The method can include optionally supplying additional liquid into the container through the liquid supply pipe.

[0089] The device can include a liquid volume detector configured to output an indication of the volume of liquid inside the container. The device can include an excess liquid outlet. The opening can include (such as be) (such as the) excess liquid outlet. The controller can be configured to: receive the (such as the) indication of the volume of liquid inside the container; and in response to receiving an indication of the volume of liquid inside the container that has dropped below a low liquid threshold, cause additional liquid to be supplied into the container (such as through the liquid supply pipe, optionally by activating the liquid supply pump). The low liquid threshold can be 95% of the container capacity, optionally 90% of the container capacity, optionally 85% of the container capacity. The controller can be configured to receive the (such as the) indication of the volume of liquid inside the container; and in response to receiving an indication of the volume of liquid inside the container that has risen above a high liquid threshold, cause excess liquid to leave the container (such as through the excess liquid outlet). The high liquid threshold can be higher than 95% of the container capacity, such as higher than 98% of the container capacity, such as higher than 99% of the container capacity.

[0090] The device may include one or more container supply conduits configured to (e.g., selectively) supply one or more substances (such as hydrogen peroxide, optionally, enzymes, etc.) to a container. The controller may be configured to receive an indication (such as the aforementioned) of the liquid temperature and, in response thereto, optionally via the liquid supply conduit, optionally using a liquid supply pump, regulate the liquid supply into the container. The controller may be configured to receive an indication (such as the aforementioned) of the pH value of the liquid and, in response thereto (optionally via one or more supply conduits, such as the liquid supply conduit, optionally using a liquid supply pump), regulate the supply of substances (such as liquid, salt, hydrogen peroxide, buffer, acid, base, surfactant, enzyme, etc.) into the container. The controller may be configured to receive an indication (such as the aforementioned) of the percentage of oxygen saturation of the liquid and, in response thereto (optionally via the liquid supply conduit, optionally using a liquid supply pump), regulate the supply of the liquid (such as the liquid including hydrogen peroxide) into the container. The controller may be configured to optionally regulate the supply of hydrogen peroxide into the container according to a predetermined decomposition rate, for example, to replace the decomposed hydrogen peroxide. The decomposition rate may depend on many factors, including but not limited to the peak sound pressure of the sound emitted from the sound emitter.

[0091] The device may include a wired communication link. The device may include a wireless communication link. The device may include a computer-readable storage medium. The device may be configured to transmit and / or receive data (such as information) via the wired communication link. The method may include transmitting and / or receiving data (such as information) via the wired communication link. The device may be configured to transmit and / or receive data (such as information) via the wireless communication link. The method may include transmitting and / or receiving data (such as information) via the wireless communication link. The device may be configured to transmit and / or receive data (such as information) via Wi-Fi(TM). The method may include transmitting and / or receiving data (such as information) via Wi-Fi(TM). Wi-Fi(TM) is a series of wireless network protocols based on the IEEE 802.11 series of standards.

[0092] It should be understood that the liquid can be water, optionally water containing one or more other substances (such as salts, hydrogen peroxide, enzymes, buffers, surfactants, etc.). It should be understood that the bubbles can be oxygen bubbles or air bubbles, for example, may include nitrogen. It should be understood that when referring to light, this refers to light within the visible spectrum. In addition, when referring to sound or noise, this includes sounds within the audible range of humans, but is not limited to sounds within the audible range of humans, for example, may extend to ultrasonic waves. The sound emitter can emit sound, and the sound includes sound waves with peak frequencies in the range of 50 Hz to 200 kHz (including the end values), optionally in the range of 10 Hz to 300 kHz (including the end values), optionally in the range of 5 Hz to 500 kHz (including the end values). The device can be configured to limit the sound transmission of sound waves including peak frequencies in the range of 50 Hz to 200 kHz (including the end values), optionally in the range of 10 Hz to 300 kHz (including the end values), optionally in the range of 5 Hz to 500 kHz (including the end values).

[0093] Offshore piling devices may output sound in the form of "impact pulses" (usually caused by impacts and containing sounds of almost all frequencies). Since traditional bubble curtains usually only produce bubbles of one size, the effect of traditional bubble curtains is not as good as that of the bubble curtain provided by the present disclosure, because the bubble curtain provided by the present disclosure contains bubbles with a wide range of sizes and can therefore limit the sound transmission of a wide range of frequencies (for example, attenuate sound). The vertical rise of the sound pressure level of the "impact pulse" generated by the offshore piling device may cause bubble rupture. Therefore, it may take some time to cause more bubbles to form in the liquid (for example, due to the agitator agitating the liquid) so that the sound transmission of subsequent impact pulses can be limited (for example, attenuated) subsequently.

[0094] Therefore, the device may include an impact pulse detector configured to output an indication of impact pulse detection. The device can be configured to receive an indication of the occurrence of an impact pulse, for example, from an offshore piling device when a piling impact is performed. The controller can be configured to: receive the (for example, the above-mentioned) indication of impact pulse detection (optionally, occurrence); and send a signal to the offshore piling device (optionally, its user) to pause for a waiting time before performing (for example, subsequent) piling impacts. The waiting time can depend on one or more of the following: the (for example, visible) light intensity passing through a certain distance of the liquid being lower than a threshold (for example, the above-mentioned) indication; the sound intensity outside the container being lower than a threshold (for example, the above-mentioned) indication; the (for example, the above-mentioned) indication of the liquid pressure; the (for example, the above-mentioned) indication of the liquid temperature; the (for example, the above-mentioned) indication of the liquid pH value. The waiting time can be at least 5 seconds, for example, at least 10 seconds, for example, at least 30 seconds, for example, at least 1 minute, optionally less than 60 minutes, for example, less than 30 minutes, for example, less than 15 minutes.

[0095] The method may include receiving an indication of a shock pulse detection (optionally, occurrence). The method may include causing a signal to be sent to an offshore piling device (optionally, its user) to pause for a waiting period before performing (e.g., a subsequent) piling impact. The method may include sending a signal to an offshore piling device (optionally, its user) to pause for a waiting period before performing (e.g., a subsequent) piling impact.

[0096] Compared to the proportion of dissolved oxygen present in water when the device (or the method) is not used, the device may be configured to increase (or the method may include increasing) the proportion of dissolved oxygen by at least 2% by volume (e.g., at least 10%, e.g., at least 25%, e.g., at least 50%, e.g., at least 75%, e.g., at least 80%).

[0097] In some applications, the container may be omitted. While this may result in faster dissipation of dissolved oxygen and bubbles, in certain usage cases, this may be acceptable. For example, such rapid dissipation problems may be addressed by providing additional oxygen to the liquid or providing additional liquid including at least 2% (optionally at least 10%) by volume of dissolved oxygen (e.g., near a stirrer). The device may be configured to allow additional oxygen to be provided to the liquid and / or allow the provision of additional liquid including at least 2% (optionally at least 10%) by volume of dissolved oxygen. For example, the device may include a pipe configured to receive a fluid and supply the fluid to a stirrer. The method may include providing additional oxygen to the liquid, and / or providing additional liquid including at least 2% (optionally at least 10%) by volume of dissolved oxygen. For example, the method may include optionally supplying a fluid to a stirrer through a pipe.

[0098] This is considered to be inventive in itself. Accordingly, another aspect of the present invention provides a device configured to limit sound transmission from an acoustic emitter (e.g., through a liquid), the device including a liquid, wherein the liquid includes at least 2% (optionally at least 10%) by volume of dissolved oxygen, and wherein the device further includes a stirrer disposed in the liquid, the stirrer being configured to stir (e.g., at least a portion of) the liquid proximal to the stirrer, thereby causing gas (e.g., oxygen) bubbles to form in the liquid. Optional features of the other aspects described above may also be optional features of this other aspect.

[0099] Another aspect of the present invention provides a method of limiting sound transmission from an acoustic emitter, the acoustic emitter being at least partially surrounded by a liquid including at least 2% by volume of dissolved oxygen, and the method including: stirring the liquid, thereby causing bubbles to form in the liquid. Optional features of the other aspects described above may also be optional features of this other aspect.

[0100] It should be understood that, except for those methods that are inherently incompatible, the steps of the methods described above with reference to any particular method can be combined with any other method described herein in substantially any combination. It should also be understood that the method steps can be executed in an order different from the described order and, in some cases, simultaneously, unless it is essentially impossible. The features of any one aspect can be optional features of any other aspect. Description of the Drawings

[0101] Exemplary embodiments of the present invention will now be described with reference to the following drawings, in which:

[0102] Figure 1 is a side elevation cross-sectional view of a first exemplary embodiment of the apparatus according to the present invention;

[0103] Figure 2 is a second side elevation cross-sectional view of a first exemplary embodiment of the apparatus according to the present invention;

[0104] Figure 3 is a side elevation cross-sectional view of a second exemplary embodiment of the apparatus according to the present invention;

[0105] Figure 4 is a side elevation cross-sectional view of a third exemplary embodiment of the apparatus according to the present invention;

[0106] Figure 5 is a plan elevation view of another exemplary embodiment of the apparatus according to the present invention;

[0107] Figure 6 is a flow chart of the steps in a method according to an exemplary embodiment of the present invention;

[0108] Figure 7 is a schematic diagram of an apparatus according to an exemplary embodiment of the present invention; and

[0109] Figure 8 is a plotted graph of the speed of sound through a fluid. Detailed Description of the Invention

[0110] Those skilled in the art should understand that any dimensions and relative orientations mentioned in this specification, such as lower and higher, upper and lower, etc., and directions such as vertical, horizontal, upper, lower, longitudinal, axial, radial, lateral, circumferential, etc., refer to the art and the described apparatus and methods, and are all within the expected structural tolerances and limits, and should be interpreted in consideration of this point.

[0111] Figure 1This is a side elevation view of a first exemplary embodiment of the device 1 according to the present invention. Here, the sound emitter 2 is an offshore pile, which is part of the offshore piling equipment group 10. The container 4 is arranged to surround the offshore pile 2, and the container 4 is filled with a liquid, which is seawater including 50% by volume of dissolved oxygen in this example. At the lower part of the container 4, an agitator in the form of a mixer 6 is provided, which agitates the fluid during use, so that oxygen is released from the water and forms bubbles 8. A pump 22 is provided at the top of the container 4, and the pump is configured to make the liquid near the top of the container and near the liquid surface 18 flow in a downward direction, as shown by the arrow 24. In Figure 1 In this case, the mixer 6 only operates for a few seconds, so the number of bubbles generated is relatively small.

[0112] The offshore pile 2 is partially immersed in the liquid in the container, and about 85% of the offshore pile 2 is located below the liquid surface 18. The container 4 is in turn partially surrounded by the sea and thus surrounded by seawater. The container 4 extends from above the sea surface 20 to the seabed 26. The container 4 has a cylindrical outer wall 30, but its bottom and top are open. Heavy weights (not shown) are provided on the cylindrical outer wall 30 to press the wall down to make it in sealing contact with the seabed 26. Therefore, in this case, the seabed 26 can be considered to provide the bottom of the container 4. The open top provides an opening in the container 4 through which the bubbles 8 can leave the container, for example when they rise through the liquid under the action of buoyancy. The outer cylindrical wall 30 of the container 4 extends both above the liquid surface 18 and above the sea surface 20. In this case, the liquid surface 18 is slightly higher than the sea surface 20 because the density of the fluid is slightly less than that of seawater, so the hydrostatic pressure acts on the container 4 (which is slightly flexible), thereby slightly compressing the container and causing a hydrostatic pressure head in the container 4.

[0113] Figure 2 This is a second side elevation view of a first exemplary embodiment of the device 1. Here, the mixer 6 has been operating for a longer time (about 60 minutes), so a large number of bubbles 8 are formed. Since the mixer 6 agitates the fluid, bubbles 8 are continuously formed. The bubbles 8 tend to float upward in the fluid under the action of buoyancy. When the bubbles 8 approach the fluid surface 18, the flow caused by the pump 22 tends to make a part of the bubbles 8 move back downward through the fluid, rather than allowing all the bubbles 8 to leave the fluid when they reach the fluid surface 18. Thus, an annular bubble curtain 32 is formed, which partially surrounds the offshore pile (that is, the part of the pile located below the liquid surface 18 is radially surrounded by the bubble curtain 32).

[0114] Figure 3 This is a side elevation cross-sectional view of a second exemplary embodiment of the device 101 according to the present invention. Compared with Figure 1 and 2As in the embodiment, the device 101 includes a container arranged to surround the sound emitter (also in the form of the offshore piling equipment 110), and the container is filled with liquid. In this case, the container has two horizontal barriers 114a, 114b, each barrier being in the form of a flat disc and having central holes 116a, 116b. The horizontal barriers 114a, 114b each extend from the inner side of the cylindrical wall towards the central part of the container through a part of the interior of the container, where the holes 116a, 116b surround the marine pile such that there is a space between each barrier 114a, 114b and the pile. Thus, the container can be understood to be composed of three sub - containers 104a, 104b, 104c. Each sub - container 104a, 104b, 104c is provided with two mixers 106a, 106b, 106c, 106d, 106e, 106f, which, when in use, agitate the fluid in the corresponding sub - container 104a, 104b, 104c, thereby releasing oxygen from the water and forming bubbles 108.

[0115] The barrier 114b forms the top of the lowermost container 104c, and since the barrier 114b has a hole 116b that surrounds the pile and is arranged to provide a space between the pile and the barrier 114b, the bubbles 108 that reach the top of the sub - container 104c can leave the sub - container 104c and move through the hole 116b into the intermediate sub - container 104b. Similarly, the barrier 114a forms the top of the intermediate sub - container 104b, and since the barrier 114a has a hole 116a that surrounds the pile and is arranged to provide a space between the pile and the barrier 114a, the bubbles 108 that reach the top of the sub - container 104b can leave the sub - container 104b and enter the uppermost sub - container 104a through the hole 116a. The top surface of the uppermost sub - container 104a is open, so the bubbles 108 that reach the top of the uppermost sub - container 104a can leave the liquid surface 118. Pumps (not shown) are provided at the top of each sub - container 104a, 104b, 104c, which are configured to cause the liquid near the top of each corresponding sub - container 104a, 104b, 104c and near the liquid surface 118 to flow in the downward direction. In Figure 3 this case, each mixer 106a, 106b, 106c, 106d, 106e, 106f operates for only a few seconds, so each mixer 106a, 106b, 106c, 106d, 106e, 106f generates a relatively small number of bubbles. However, since each sub - container 104a, 104b, 104c is smaller than Figure 1 and 2 the container 4, and each sub - container is provided with two mixers 106a, 106b, 106c, 106d, 106e, 106f, a large number of bubbles can be generated per liter of liquid in a relatively short time.

[0116] Compared withFigure 1 And 2 Similarly, the ocean pile is partially submerged in the liquid in the container, with approximately 85% of the ocean pile being below the liquid surface 18. The container is in turn partially surrounded by seawater, where the sub - containers 104b and 104c are surrounded by seawater, while the sub - container 104a is partially surrounded by seawater and partially extends above the sea surface 120. The container extends from above the sea surface 120 to the seabed. The container has a weighted cylindrical outer wall, but its bottom and top are open. Thus, in this case, the seabed can be considered to provide the bottom of the lowermost sub - container 104c. The open top provides an opening in the uppermost sub - container 104a through which bubbles 8 can leave the container, for example, as they rise through the liquid under buoyancy. The outer cylindrical wall of the container extends both above the liquid surface 118 and above the sea surface 120.

[0117] In use, the mixers 6, 106a, 106b, 106c, 106d, 106e, 106f are switched on and start agitating the fluid in the container 4 or the sub - containers 104a, 104b, 104c. When the fluid is agitated, the oxygen dissolved in the fluid is released therefrom, thereby forming bubbles 8, 108. The bubbles 8, 108 travel upward in the fluid and in the container 4 or the sub - containers 104a, 104b, 104c towards the liquid surface 18 or the tops of the sub - containers 104b, 104c. At the liquid surface 18, or at the tops of the sub - containers 104b, 104c, the flow caused by the pump 22 ( Figure 3 (not shown in the figure)) causes the liquid and a portion of the bubbles 8, 108 therein to travel in the downward direction shown by the arrow 24 ( Figure 3 (not shown in the figure)). Thereby, the bubbles 8, 108 circulate within the container 4 or the sub - containers 104a, 104b, 104c and form (or can form in each respective sub - container) a bubble curtain 32 surrounding the sound emitter 2.

[0118] After the bubble curtain 32 is formed, the sound emitter (here, the offshore pile) 2 can be activated. Sound travels outward from the sound emitter 2 and especially from the point where the offshore pile 2 contacts the seabed 26. The sound waves travel through the liquid until they encounter the bubble curtain 32. When the sound waves reach the bubble curtain 32, the sound waves repeatedly pass through and are scattered by multiple liquid-gas boundaries. Each bubble 8, 108 that the sound waves encounter represents two such boundaries (the first boundary occurs when the sound waves travel from the liquid into the gas of the bubble 8, 108, and the second boundary occurs when the sound waves travel from the gas of the bubble 8, 108 back into the liquid surrounding the bubble 8, 108). Without being bound by theory, the inventors believe that as a result of the scattering and absorption of the sound waves at each such interface, the sound energy is absorbed and the sound is attenuated after a large number of interactions with the bubbles 8, 108 in the bubble curtain 32, so that the sound transmission is limited. Therefore, hardly any sound can travel all the way through the bubble curtain 32 and escape from the container 4 (or the sub-containers 104a, 104b, 104c) into the sea.

[0119] Offshore piling can generate pressures of 180 decibels and above at a distance of 750 meters from the offshore pile. This is harmful to marine life. The bubbles 8, 108 generated by the operation of the devices 1, 101, 201 limit the sound transmission, such that the sound pressure on the side of the bubbles 8, 108 opposite to the sound emitter 2 is reduced by 40 decibels compared to the sound pressure on the same side of the bubbles 8, 108 as the sound emitter 2. Therefore, the application of the devices 1, 101, 201 is beneficial to marine life and can reduce the environmental sound coverage area.

[0120] When the offshore piling operation is completed (or paused), the mixers 6, 106a, 106b, 106c, 106d, 106e, 106f and the pump 22 stop. The bubbles 8, 108 rise to the fluid surface 18, 118 under the action of buoyancy and steadily leave the fluid and the container 4. If no further offshore piling is required, the devices 1, 101 can be removed and optionally moved to the next offshore pile 2.

[0121] Figure 4 is a side elevation cross-sectional view of a third exemplary embodiment of the device 201 according to the present invention. Similar to Figure 1 、 2 and the embodiments of 3, the device 201 includes a container 204 arranged to surround the sound emitter 202 (here, the generator), and the container 204 is filled with liquid. In this case, the container 204 is an annular outer container 204, and its internal space 212 is filled with air. The internal space 212 can be considered as an inner cylindrical container 212 that houses the sound emitter 202. The outer container 204 is provided with an agitator in the form of a mixer 206, which agitates the fluid in the outer container 204 during use, thereby releasing oxygen from the water and forming bubbles 208.

[0122] A pump 222 is provided at the top of the outer container 204, and the pump is configured to cause the liquid near the liquid surface 218 to flow in the downward direction indicated by the arrow 224. In Figure 4 this case, the mixer 206 is only operated for a few seconds, so the number of bubbles generated is relatively small.

[0123] In this exemplary embodiment, the sound source is located inside the inner container 212, and the inner container is in turn partially surrounded by the outer container 204, and thus is partially surrounded by the liquid in the outer container 204. The outer container 204 has an outer cylindrical wall 230, an inner cylindrical wall 236, and a bottom 238, but its top is open. The inner cylindrical wall 236 of the outer container 204 forms the cylindrical wall of the inner container 212. The inner container 212 also has a bottom 240 and an upper wall 242. The open top of the outer container 204 provides an opening in the outer container 204, and the bubbles 208 can leave the outer container 204 through the opening when, for example, they rise through the liquid under the action of buoyancy. The outer cylindrical wall 230 of the outer container 204 extends above the liquid surface 218.

[0124] The device 201 also has a light detector 215 (here a photoelectric detector) and a light source 217 (here in the form of an LED) located inside the outer container 204. The light detector 215 is configured to detect the light emitted by the LED 217 and output an indication of the detected light intensity. The distance between the light detector 215 and the LED 217 is 20 cm. The device 201 also has a controller (not shown), and the controller is configured to receive the indication of the detected light intensity and adjust the amount of agitation caused by the mixer 206 in response to the received indication, so as to maintain the target light intensity.

[0125] Since the mixer 206 agitates the fluid, bubbles 208 are continuously formed. The bubbles 208 tend to float upward in the fluid due to the action of buoyancy. When the bubbles 208 approach the liquid surface 218, the flow caused by the pump 222 tends to cause a part of the bubbles 208 to move downward back through the fluid, rather than allowing all the bubbles 208 to leave the fluid when they reach the fluid surface 218. As a result, an annular bubble curtain is formed in the outer container 204 ( Figure 4 not shown in the figure), and thus the sound emitter 202 is partially surrounded by the bubble curtain.

[0126] The sound wave travels from the sound emitter 202 through the air in the inner container 212 until it reaches the inner cylindrical wall 236. The sound wave passes through the inner cylindrical wall 236 and enters the fluid inside the outer container 204, and continues to travel through this fluid until it reaches the bubble curtain. Here, the sound wave is absorbed and scattered by the bubbles 208, similar to the situation described in Figure 1 、 2 and 3. The mixer 206 and the pump 224 can be operated continuously, or can be operated only when the sound emitter 202 emits sound.

[0127] Light travels from the LED 217 through the liquid in the outer container 204 and is scattered by the bubbles. Thus, when the mixer 206 is not operating (and thus there are relatively few bubbles present), there is less light scattering, and the light detector 215 will detect more light. Accordingly, the light detector 215 will output an indication of detecting a relatively high light intensity. Conversely, when the mixer 206 is operating (and thus there are relatively more bubbles present), more light scattering occurs, and thus the light detector 215 will output an indication of detecting a relatively low light intensity.

[0128] If there are no bubbles to scatter light, then there are also no bubbles to scatter sound. Thus, when the controller receives an indication that the light intensity received by the light detector 215 is below a threshold, the controller causes the degree of agitation caused by the mixer 206 to increase (e.g., by increasing the speed of the mixer 206). When the controller receives an indication that the light intensity received by the light detector 215 is above a threshold, the controller causes the degree of agitation caused by the mixer 206 to decrease (e.g., by decreasing the speed of the mixer 206) or stop. In this way, the device 201 can be operated more efficiently because it is not necessary to continuously operate the mixer 206. In an example, it has been found that the mixing of the mixer 206 can be paused for 20 seconds before an increase in light intensity is detected, and when an increase in light intensity is detected, the mixer can mix the fluid until a decrease in light intensity is again detected.

[0129] Figure 5 is a plan elevation view of another exemplary embodiment of the device 301 according to the present invention. Similar to Figures 1 to 4 the embodiment of, the device 301 includes a container 304 arranged to surround a sound emitter 302, and the container 304 is filled with a liquid. In this case, the container is an open-topped rectangular cuboid having four vertical side walls 330a, 330b, 330c, 330d and a bottom (not shown). The container 304 is provided with an agitator in the form of a mixer 306 that agitates the fluid in the container 304 during use, thereby releasing oxygen from the water and forming bubbles ( Figure 5 not shown in). At the top of the container 304, a pump ( Figure 5 not shown in) is provided that is configured to cause the liquid near the liquid surface to flow in a downward direction.

[0130] In this case, the sound emitter 302 is a control valve 302 of a gas distribution pipe 311. The container has an orifice that allows for the inlet and outlet of the pipe 311. The container 304 is sealed around the pipe 311 at the orifice such that no liquid can leave the container through the orifice.

[0131] As mixer 306 agitates the fluid, bubbles are continuously formed. Due to the buoyancy force, the bubbles tend to float upward in the fluid. When the bubbles approach the top of the container 306, the flow induced by the pump tends to move a portion of the bubbles back down through the fluid rather than allowing all the bubbles to leave the fluid when they reach the fluid surface. As a result, a bubble curtain is formed in container 304 ( Figure 5 not shown in), and thus the acoustic emitter 302 is partially surrounded by the bubble curtain. The sound waves travel from the acoustic emitter 302 through the fluid within the container 304 and continue to travel through this fluid until they reach the bubble curtain. Here, the sound waves are absorbed and scattered by the bubbles, similar to the situation described with respect to Figure 1 、 2 and 4. This is particularly useful for restricting the sound transmission from the control valve 302 to the air that would otherwise surround the control valve. Without the device 301, the control valve 302 would by default be surrounded by air, which would result in Helmholtz resonance.

[0132] When considering the maximum sizes that the bubbles 8, 108, 208 will have from the moment they are generated until 3 seconds after generation, the average diameter of the bubbles 8, 108, 208 is 0.05 cm. Thereafter, the sizes of the bubbles 8, 108, 208 will generally change, especially when the bubbles move upward in the liquid. Where the bubble curtain 32 is located, the bubble curtain 32 contains at least 1,000 bubbles per 1 liter volume. However, those skilled in the art will understand that a relatively large number of the bubbles 8, 108, 208 will generally be present near the mixers 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306, and over time, the bubbles 8, 108, 208 will become somewhat dispersed such that fewer of the bubbles 8, 108, 208 will be present further away from the mixers 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306.

[0133] The walls of the containers 4, 104, 204 are formed of a waterproof cloth with a reinforcing mesh layer. The wall of the container 304 is formed of high-density polyethylene (HDPE). The said or each mixer 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306 is a paddle mixer having two steel blades that can be rotated about an axis by an electric motor at a speed of 100 rpm. The pumps 22, 222 are positive displacement pumps configured to have a displacement of 1000 L per minute (but those skilled in the art should understand that the selection of the pump will depend on the size of the container). The barriers 114a, 114b (if present) are formed of HDPE discs.

[0134] The liquid in containers 4, 104, 204, 304 is water that includes 50% by volume of dissolved oxygen. The water also contains 20 mg / L of hydrogen peroxide and 5 kU of catalase per 1 liter of water. Catalase decomposes hydrogen peroxide into water and oxygen. Some of the oxygen immediately forms additional bubbles, while some of the oxygen dissolves into the water and can form additional bubbles when the liquid is agitated by mixers 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306. Catalase increases the rate of decomposition of hydrogen peroxide. Mixers 6, 106a, 106b, 106c, 106d, 106e, 106f, 206, 306 prevent the catalase from precipitating at the bottom of the container and keep it in suspension, thereby enhancing the efficiency of the catalase acting on hydrogen peroxide.

[0135] Advantageously, the formation of oxygen bubbles 8, 108, 208 in the liquid limits the transmission of sound through the liquid. It has been found that agitating a liquid that includes at least 50% by volume of dissolved oxygen is a particularly effective way to form bubbles 8, 108, 208 because when the liquid is agitated, some of the oxygen dissolved in the liquid is released from the liquid, thereby forming a large number of oxygen bubbles 8, 108, 208. Thus, bubbles 8, 108, 208 can be formed without using a compressor or similar device to force the bubbles through the liquid, and thus, devices 1, 101, 201, 301 are also more efficient than in the case of using a compressor.

[0136] Figure 6 It is a flowchart of the steps in a method according to an exemplary embodiment of the present invention. The steps here include providing 50 sound emitters in a container and agitating 52 the liquid in the container.

[0137] Figure 7 It is a schematic diagram of a device 1 according to an exemplary embodiment of the present invention. Device 1 has at least one mixer 6 and a controller 40. Controller 40 is configured to send a signal 42 to mixer 6. Controller 40 is generally also configured to transmit data elsewhere through a wireless data connection, such as to other components of device 1, and / or to a device external to device 1. Signal 42 includes a signal generated by controller 40 based on data received by controller 40, for example, from user input and / or from a light detector 215. In this example, controller 40 is implemented by one or more processors 44 and a computer-readable memory 46. Memory 46 stores instructions that, when executed by one or more processors 44, cause device 1 to operate as described herein. Although controller 40 is shown as part of device 1, it should be understood that one or more components of controller 40, or even the entire controller 40, can be provided separately from device 1. For example, the controller can be remote from device 1 and can exchange signals with mixer 6 through wireless communication.

[0138] Figure 8 is a plot of the speed of sound through a fluid, where the speed of sound varies with the ratio of water to air in the fluid. As can be seen from this figure, the speed of sound is relatively high in 100% water and also relatively high in 100% air. However, when the fluid is a combination of water and air, the speed of sound is relatively low. The reduction in the speed of sound results in a correspondingly shorter wavelength for a given frequency of sound in a fluid containing a water and air mixture compared to the wavelengths possible in a fluid consisting of only water or only air. This in turn changes the way sound can be attenuated, either by individual bubbles or by a bubble curtain (e.g., a bubble curtain created by mixing a liquid containing a high proportion of dissolved oxygen to form bubbles, as described herein).

[0139] Although in the above example, the agitators 6, 106, 206, 306 are provided in the form of mixers, this is not necessary and other means can be used to agitate the liquid. For example, in some embodiments, the agitator can be a bubble curtain generator in the form of a compressor connected to a perforated pipe to force bubbles through the liquid. The compressor can be a single compressor or can consist of a group of compressors (e.g., at 7 bar) with a combined output of 10,000 L / min. The compressor can be arranged to form a bubble curtain around the lower outer perimeter of the container. Using a bubble curtain generator to agitate the liquid can create an even greater number of bubbles in the liquid (i.e., some bubbles are created due to agitation causing dissolved oxygen to be released from the liquid to form bubbles, while some bubbles come from the bubble curtain generator itself). The greater the number of bubbles, the more effective the sound attenuation and the more effectively sound transmission is limited.

[0140] Summary of Experimental Tests

[0141] The inventors have tested examples of the devices and methods described herein. The following summary of this test provides a non - limiting example of how the devices and methods can be used.

[0142] A 3 m container is formed with a tarpaulin container wall, and this container is filled with an aqueous solution, in this case seawater. 30 L of hydrogen peroxide is added to the container along with 100 ml of catalase (which promotes the decomposition of hydrogen peroxide). The mixer (in this case an air mixer) is operated for 2 minutes to create a large number of buoyant bubbles, with an average (mean) diameter of approximately 5 mm. The resulting fluid is transparent. 3 An acoustic emitter in the form of a frequency generator is activated and a 10 ms acoustic pulse is applied at a frequency of approximately 190 dB. The pulse starts at approximately 2 kHz and increases in steps of approximately 500 Hz to approximately 13 kHz, with a 100 ms interval between each pulse.

[0143] ​

[0144] A hydrophone was used to record the sound passing through an aqueous solution at depths of 1 m and 2 m at distances of 0.5 m, 1 m, and 2 m from the sound emitter. After the mixer was activated for 2 minutes, the hydrophone could not measure the sound level for more than 2 hours. However, it was found that the sound was distinguishable through amplified playback. By this method, it was confirmed that the attenuation increases with the increase in distance (i.e., the distance the sound wave travels through the fluid).

[0145] It was also found that the hydrogen peroxide concentration decreased by approximately 27% over a 2-hour period. In this test, it was also noted that the attenuation effect was greatest at shallower depths, and the deeper hydrophone detected the sound faster than the shallower hydrophone. It should be noted that the speed of sound is a function of pressure (and the greater the depth, the greater the pressure), and the bubble size is also a function of pressure (where higher pressure causes smaller bubbles). It was further observed that, at least in some cases, the attenuation effect was observed at shallower depths and then at deeper depths (corresponding to the effect ending faster at greater depths). Therefore, those skilled in the art should understand that depth and buoyancy are just two of several parameters to be considered when seeking to implement the present invention. It should also be understood that the rate of generation of dissolved gas is considered (e.g., at least) to depend on the hydrogen peroxide concentration, the amount of enzyme present (e.g., catalase), and the presence or absence (and quantity) of any biomass (e.g., fish).

[0146] It is worth noting that the waves acting on the tarp cause gentle movement of the fluid, and this provides further mixing during the test, thus likely contributing to a relatively long effective time for sound attenuation.

[0147] Further tests with frequent mixing also obtained similar attenuation, but preliminary results indicate that some mixing methods may lead to less stable fluid conditions (e.g., larger variations in the number of bubbles, etc.). That is, in this sense, changing the concentrations of hydrogen peroxide and catalase also seems to affect the stability of the fluid (i.e., in addition to mixing).

[0148] The attenuation effect seems to be most obvious for smaller bubbles compared to larger bubbles. It has been found that the achieved attenuation is better than previous noise mitigation strategies (e.g., a simple bubble curtain). Surprisingly, it was found that overmixing may reduce the effect of sound attenuation in some cases. Without reducing the effect, the optimal mixing rate to promote the decomposition of hydrogen peroxide (thus generating bubbles and dissolved oxygen) will depend on the conditions within the liquid.

[0149] In the description and claims of this specification, the words "comprising" and "including" and their variants mean "including but not limited to", and these words are not intended to nor do they exclude other components, wholes or steps. Throughout the description and claims of this specification, the singular includes the plural unless the context otherwise requires. In particular, when using the indefinite article, this specification should be understood to contemplate both the plural and the singular unless the context otherwise requires.

[0150] Features, wholes, characteristics or groups described in connection with specific aspects, embodiments or examples of the present invention should be understood to be applicable to any other aspect, embodiment or example described herein, unless incompatible therewith. All features disclosed in this specification (including any appended claims, abstract and drawings) and / or all steps of any method or process so disclosed may be combined in any combination, unless at least some of the features and / or steps are mutually exclusive combinations. The present invention is not limited to the details of any of the foregoing embodiments. The present invention encompasses any novel feature or any novel combination of features disclosed in this specification (including any appended claims, abstract and drawings), or any novel feature or any novel combination of steps of any method or process disclosed.

[0151] Generally speaking, there is provided a device (1) for restricting sound transmission from a sound emitter (2), the device comprising a container (4) arranged to at least partially surround the sound emitter, the container containing a liquid, wherein the liquid comprises at least 2% dissolved oxygen, and wherein the device further comprises an agitator (6) configured to agitate the liquid so as to form bubbles (8) in the liquid.

Claims

1. An apparatus for restricting sound transmission from a sound emitter, the apparatus comprising a container arranged to at least partially surround the sound emitter, the container containing a liquid, wherein the liquid comprises at least 2% by volume of dissolved oxygen, and wherein the apparatus further comprises an agitator configured to agitate the liquid so as to form bubbles in the liquid.

2. The apparatus according to claim 1, wherein at least one opening is defined in the container such that the bubbles can leave the container through the opening.

3. The apparatus according to claim 1 or claim 2, wherein the agitator comprises a bubble curtain generator optionally arranged to produce a bubble curtain at least partially surrounding the sound emitter.

4. The apparatus according to any one of the preceding claims, wherein the container houses the sound emitter and wherein the sound emitter is immersed in the liquid.

5. The apparatus according to any one of the preceding claims, wherein the container is a first container comprising one or more first container walls, wherein the apparatus comprises a second container, the second container comprising one or more second container walls, the second container at least partially surrounding the sound emitter, and wherein the first container at least partially surrounds the second container and is spaced apart from the second container.

6. The apparatus according to claim 5, wherein the liquid is contained between the first container wall and the second container wall.

7. The apparatus according to any one of the preceding claims, wherein the liquid comprises water.

8. The apparatus according to any one of the preceding claims, wherein the liquid comprises hydrogen peroxide.

9. The apparatus according to claim 8, wherein the liquid comprises an enzyme for decomposing hydrogen peroxide.

10. The apparatus according to any one of the preceding claims, wherein the liquid comprises a surfactant.

11. The apparatus according to any one of the preceding claims, wherein the liquid comprises at least 10% by volume of dissolved oxygen.

12. The apparatus according to any one of the preceding claims, wherein an agitation zone surrounds the agitator and wherein the agitator is configured to form sufficient bubbles such that the combined volume of the bubbles is at least 1% of the total volume of the agitation zone.

13. The device according to any one of the preceding claims, wherein the first container defines a volume of at least 0.5 m 3 .

14. The apparatus according to any one of the preceding claims, wherein the container comprises one or more barriers, each of the or each barrier extending through the interior of the container so as to form a plurality of sub - containers, optionally, wherein each of the plurality of sub - containers is provided with a respective agitator.

15. The apparatus according to any one of the preceding claims, which comprises a pump configured to cause the liquid to flow on the liquid surface, optionally in a downward direction.

16. The apparatus according to any one of the preceding claims, wherein an agitation zone surrounds the agitator and wherein the agitator is configured to cause sufficient bubble formation such that in the agitation zone, the light intensity of light traveling through 10 cm of the liquid is reduced by at least 10% compared to the intensity of the light before traveling through the liquid.

17. The apparatus according to any one of the preceding claims, comprising a light detector configured to output an indication of the light intensity through a certain distance of the liquid.

18. The apparatus according to claim 17, comprising a controller configured to: receive the indication of the light intensity through the distance of the liquid; and adjust the amount of agitation caused by the agitator in response to the received indication so as to maintain a target light intensity.

19. The apparatus according to any one of the preceding claims, wherein the sound emitter comprises a marine piling device.

20. An apparatus for restricting sound transmission from a sound emitter, the apparatus comprising: a sound insulation barrier comprising a container containing a liquid, wherein the liquid comprises at least 2% by volume of dissolved oxygen; and, an agitator configured to agitate the liquid so as to form bubbles in the liquid.

21. The apparatus according to any one of the preceding claims, wherein the apparatus is configured to activate the agitator for an activation period so as to generate sufficient bubbles such that the bubbles will subsequently remain suspended in the fluid for a decay period longer than the activation period.

22. A method of restricting sound transmission from a sound emitter, the sound emitter being at least partially surrounded by a container containing a liquid comprising at least 2% by volume of dissolved oxygen, and the method comprising: agitating the liquid in the container so as to form bubbles in the liquid.

23. The method according to claim 22, wherein causing the formation of bubbles comprises releasing oxygen from the liquid so as to form bubbles.

24. The method according to claim 22 or claim 23, the method comprising: receiving an indication of the light intensity through a certain distance of the liquid; and adjusting the amount of agitation caused in response to the received indication so as to maintain a target light intensity.

25. A method of forming a liquid comprising water and at least 2% by volume of dissolved oxygen as claimed in claim 1, claim 20 or claim 22, the method comprising: mixing water, hydrogen peroxide and a catalyst for decomposing hydrogen peroxide.

26. An apparatus configured to restrict sound transmission from a sound emitter, the apparatus comprising a liquid, wherein the liquid comprises at least 2% by volume of dissolved oxygen, and wherein the apparatus further comprises an agitator disposed in the liquid and configured to agitate the liquid proximal to the agitator so as to form bubbles in the liquid.

27. A method of restricting sound transmission from a sound emitter, the sound emitter being at least partially surrounded by a liquid comprising at least 2% by volume of dissolved oxygen, and the method comprising: agitating the liquid so as to form bubbles in the liquid.

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